AMPHOTERIC LIPOSOME FORMULATIONS
An amphoteric liposome composed of a mixture of lipids, said mixture comprising a cationic amphiphile, an anionic amphiphile and optionally one or more neutral amphiphiles, at least one of said cationic and anionic amphiphiles being chargeable and the respective amounts of said cationic and anionic amphiphiles being selected such there is a stoichiometric excess of positively charged cationic amphiphile at a first lower pH, a stoichiometric excess of negatively charged anionic amphiphile at a second higher pH and said mixture has an isoelectric point intermediate said first and second pHs; characterised in that said positively charged cationic and negatively charged anionic amphiphiles are adapted to form a lipid salt with one another at said isoelectric point. Also disclosed are methods of predicting the fusogenicity of an amphoteric liposome at a given pH, formulating an amphoteric liposome and loading an amphoteric liposome with a cargo moiety.
This application is a continuation-in-part of U.S. patent application Ser. No. 11/581,054, filed on Oct. 13, 2006 and European Patent Application No: 06255277.3, also filed on Oct. 13, 2006.
Each of the applications and patents cited in this text, as well as each document or reference cited in each of the applications and patents (including during the prosecution of each issued patent; “application cited documents”), and each of the U.S. and foreign applications or patents corresponding to and/or claiming priority from any of these applications and patents, and each of the documents cited or referenced in each of the application cited documents, are hereby expressly incorporated herein by reference. More generally, documents or references are cited in this text, either in a Reference List before the claims, or in the text itself; and, each of these documents or references (“herein-cited references”), as well as each document or reference cited in each of the herein-cited references (including any manufacturer's specifications, instructions, etc.), is hereby expressly incorporated herein by reference. Documents incorporated by reference into this text may be employed in the practice of the invention.
FIELD OF THE INVENTIONThe present invention relates to improvements in or relating to amphoteric liposomes. In particular, the present invention provides a novel method for formulating such liposomes and a method for loading them, as well as liposomes produced by such methods.
BACKGROUND OF THE INVENTIONAmphoteric liposomes have been found to exhibit excellent biodistribution and to be well tolerated in animals. They can encapsulate active agents, including nucleic acid molecules, with high efficiency.
In contrast to zwitterionic structures, amphoteric liposomes advantageously have an isoelectric point and are negatively charged at higher pH values and positively charged at lower pH values. Amphoteric liposomes belong to the larger group of pH-sensitive liposomes that were introduced by Straubinger, et al. (FEBS Lett., 1985, 179(1), 148-154). Typical pH-responsive elements in pH-sensitive liposomes are cholesterol hemisuccinate (CHEMS), palmitoylhomocysteine, dioleoylglycerol hemisuccinate (DOG-Succ) and the like. CHEMS can stabilise dioleoylphosphatidylethanolamine (DOPE), a lipid which preferentially adopts the inverted hexagonal phase at temperatures above 10° C., into the lamellar phase at pH 7.4. Lamellar CHEMS/DOPE systems can be prepared at neutral or slightly alkaline pH but these systems become unstable and fuse at acidic pH (Hafez and Cullis, Biochim. Biophys. Acta, 2000, 1463, 107-114).
Fusogenic liposomes are very useful in pharmaceutical applications, especially for the intracellular delivery of drugs, e.g., nucleic acids, such, for example, as plasmids and oligonucleotides. After the uptake of a liposome into a cell by endocytosis the release of the drug from the endosome is a crucial step for the delivery of a drug into the cytosol of cells. The pH within an endosome is slightly acidic and therefore pH sensitive liposomes can fuse with the endosomal membrane and thereby allowing the release of the drug from the endosome. This means that destabilisation of the lipid phase, e.g., by enhanced fusogenicity, facilitates endosome escape and intracellular delivery. Also other environments of low pH can trigger the fusion of such liposomes, e.g., the low pH found in tumors or sites of inflammation.
Hafez, et al. (Biophys. J. 2000, 79(3), 1438-1446) were unsatisfied with the limited control over the pH at which such fusion occurs and demonstrated a rational approach to fine-tune the fusion point by adding cationic lipids. Such mixtures have true amphoteric properties in that they exist in a cationic state at low pH and as anionic particles at higher pH, typically at physiological pH. According to Hafez, et al. fusion starts at pH values where the net charge of the particles is zero (their isoelectric point), and once such point is crossed (the pH is lower to any extent) fusion is a continuous process. This view is shared by Li and Schick (Biophys. J., 2001, 80, 1703-1711) who analysed the fusion tendency for amphoteric lipid mixtures using a mathematical model.
Israelachvili and Mitchell in 1975 (Biochim. Biophys. Acta, 1975, 389, 13-19) introduced the molecular shape concept which assumes that the overall form of lipid molecules determines the structure of the hydrated lipid membrane. This means that the lipid geometry and more specifically the size ratio between the polar head-group and the hydrophobic membrane anchor is the key parameter determining the lipid phase (Israelachvili, et al. Biochim Biophys Acta. 1977 17; 470(2):185-201). The original theory however did not consider counterions being a steric part of the polar head-group, but this was contributed by Li and Schick (Biophys. J., 2001, 80, 1703-1711). In their description of the DODAC/CHEMS system, the sodium ion enlarges the head-group of CHEMS at neutral pH, but dissociates as the pH drops, thus minimising the head-group volume and promoting a hexagonal phase; DODAC as a strong cation is assumed to be in constant association with its respective counterion, irrespective of the pH. The model predicts fusion at some pH and below.
Lipid phases according to the molecular shape concept (Israelachvili et al., 1980, Q. Rev. Biophys., 13(2), 121-200):
The addition of neutral lipids to amphoteric lipid mixtures has been found to have little impact on the isoelectric point of amphoteric liposomes. WO 02/066012 (Panzner, et al.) discloses certain amphoteric liposomes comprising neutral lipids with a stable size at both low and neutral pHs. WO 02/066012 also describes a method of loading such particles with nucleic acids starting from a low pH.
Amphoteric liposomes are complex structures and comprise at least a complementary pair of charged lipids. The inclusion of one or more such neutral lipids significantly adds to the complexity of the mixture, especially since the individual amounts of the components may vary. Hafez, et al. (Biophys. J. 2000, 79(3), 1438-1446) and WO 02/066012 provide some guidance as to how to select lipid mixtures with truly amphoteric properties and more specifically how to determine their isoelectric point and onset of fusion. Nevertheless, the very high number of possible combinations of lipids represents a practical hurdle towards a more rapid optimisation of amphoteric liposomes, and there remains a need in the art for a method of predicting or analysing which mixtures of lipids form satisfactorily stable lamellar phases at high and low pH, whilst forming a fusogenic, hexagonal phase at an intermediate pH.
It is an object of the present invention therefore to provide improved methods for formulating such fusogenic amphoteric liposomes. Amphoteric liposomes that form a stable lipid phase at neutral pH and a fusogenic phase at low pH represent another object of the invention. Yet another object of the invention is the provision of amphoteric liposomes that form stable lipid phases both at low pH and at neutral pH, but undergo fusion at an intermediate pH. The inventors have recognised that it would be desirable to control the pH at which an amphoteric liposome is fusogenic, so as to enable the liposome to be better targeted in some applications to the endosomal environment where its cargo is desired to be released. Yet another object of the invention therefore is to provide a way of controlling the pH at which fusion of such amphoteric liposomes occurs.
SUMMARY OF THE INVENTIONAccording to one aspect of the present invention therefore there is provided a method of formulating amphoteric liposomes comprising:
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- (i) selecting an anionic amphiphile, a cationic amphiphile, each of said anionic and cationic amphiphiles having respective polar head and apolar tail-groups, cationic and anionic counterions for said anionic and cationic amphiphiles respectively, and optionally one or more neutral amphiphiles, at least one of said anionic and cationic amphiphiles being chargeable;
- (ii) calculating the κ values for each of said anionic and cationic amphiphiles, when uncharged and when charged and associated respectively with said cationic and anionic counterions, and said one or more optional neutral amphiphiles and the κsalt value for a lipid salt comprising said anionic and cationic amphiphiles in charged form, κ being the ratio of the molecular volume of the polar head-group Vhead to the molecular volume of the apolar tail-group Vapolar of the respective species, the molecular volumes of the polar head-groups of the charged anionic and cationic amphiphiles including the respective counterions, κsalt being defined as:
wherein Vhead(cat) is the molecular volume of the polar head-group of the cationic amphiphile without the respective counter-anion, Vhead(an) is the molecular volume of the polar head-group of the anionic amphiphile without the respective counter-cation, Vapolar (cat) is the molecular volume of the apolar tail-group of the cationic amphiphile and Vapolar(an) is the molecular volume of the apolar tail-group of the anionic amphiphile;
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- (iii) modelling the function κtotal(pH) for a lipid mixture of said anionic and cationic amphiphiles and said one or more optional neutral amphiphiles, assuming said cationic and anionic amphiphiles form said lipid salt when charged, the respective amounts of said amphiphiles in said lipid mixture being chosen such that said mixture of lipids has an isoelectric point between a first lower pH and a second higher pH and has a stoichiometric excess of positively charged cationic amphiphile at said first pH and a stoichiometric excess of negatively charged anionic amphiphile at said second pH, κtotal (pH) being defined as:
κtotal (pH)=κan·can (pH)+κcat·ccat (pH)+κan−·can−(pH)+κcat++·ccat+(pH)+κsalt·csalt (pH)+Σκn·cn
wherein can (pH), ccat (pH), can− (pH), ccat+ (pH) and csalt (pH) are the respective concentrations in the lipid mixture of the uncharged anionic, uncharged cationic, charged anionic and charged cationic amphiphiles and said lipid salt as a function of pH, cn is the concentration in the lipid mixture of the or each optional neutral amphiphile, and κan, κcat, κan−, κcat+, κsalt and κn are the respective κ values for the uncharged anionic, uncharged cationic, charged anionic and charged cationic amphiphiles, said lipid salt and the or each optional neutral amphiphile;
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- (iv) determining that κtotal(pH) exhibits a minimum at said isoelectric point;
- (v) making liposomes composed of said lipid mixture and empirically confirming that said mixture exhibits a stable lamellar phases at said second pH and, optionally, at said first pH and a fusogenic, hexagonal phase at or around said isoelectric point; and thereafter
- (vi) manufacturing an amphoteric liposome composed of said lipid mixture.
Suitably said molecular volumes may be calculated by molecular modelling.
Said mixture may have an isoelectric point in the range pH 4 to pH 8, preferably in the range pH 5 to pH 7.
Suitably, said first pH may be in the range pH 4 to pH 5 or in the range pH 2 to pH 4. Said second pH may be in the range pH 7 to pH 8. Advantageously, said second pH is about physiological pH (about pH 7.4).
According to another aspect of the present invention there is provided an amphoteric liposome composed of a mixture of lipids, said mixture comprising a cationic amphiphile, an anionic amphiphile and optionally one or more neutral amphiphiles, at least one of said cationic and anionic amphiphiles being chargeable and the respective amounts of said cationic and anionic amphiphiles being selected such there is a stoichiometric excess of positively charged cationic amphiphile at a first lower pH, a stoichiometric excess of negatively charged anionic amphiphile at a second higher pH, and said mixture has an isoelectric point intermediate said first and second pHs; characterised in that said positively charged cationic and negatively charged anionic amphiphiles are adapted to form a lipid salt with one another at said isoelectric point.
Anionic and cationic amphiphiles have respective polar head and apolar tail-groups. In accordance with the invention, the polar head and apolar tail-groups of the anionic and cationic amphiphiles and said counterions may be selected such that κtotal(pH) for the mixture exhibits a minimum at said isoelectric point, whereby said mixture exhibits stable lamellar phases at said second pH and, optionally, at said first pH and a fusogenic, hexagonal phase at or around said isoelectric point.
Suitably, therefore, κtotal (pH) (as defined above) for the amphoteric liposome according to the invention exhibits a minimum at said isoelectric point.
It has been found therefore that the combination of the following assumptions allows a proper description of lipid phase behaviour:
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- 1) shape theory as a basis for the description;
- 2) for polar head-groups in the charged state, counterions become part of the head-group volume; and
- 3) lipid-lipid salt formation occurs in the membrane
The method of the present invention therefore facilitates the identification of fusogenic amphoteric liposomes, the description of their fusion behaviour with respect to the relationship between lipid composition and fusion pH and the impact of counterions on the stability and fusion behaviour of amphoteric liposomes.
The amphoteric liposomes of the present invention comprise a lipid pair that is capable of forming a lipid-lipid salt within a bilayer. In some embodiments the capacity of the lipid pair to form a lipid-lipid salt may render the liposome bistable. Alternatively, the liposome may be stable only at said second pH and fusogenic at or around said isoelectric point.
In some embodiments, said amphoteric liposome of the invention may comprise a lipid mixture comprising a chargeable anionic amphiphile and a chargeable cationic amphiphile that are adapted to form a lipid salt with one another, wherein κsalt<0.34.
Said anionic amphiphile may be selected from Chems, DMGS, DMGM, DMGG, DMGA, DMAS, DMAM, DMAG, DMAA, DOGS, DOGM, DOGG, DOGA, DOAS, DOAM, DOAG, DOAA, DMS, DMM, DMG, DMA, DOS, DOM, DOG, DOA, Chol-C3, Chol-C5 and Chol-C6. Said cationic amphiphile may be cholesterol-based or based on diacylglycerols, and may be selected from MoChol, Chim, HisChol and Desh4.
Alternatively, said amphoteric liposome may comprise a chargeable anionic amphiphile and a chargeable cationic amphiphile that are adapted to form a lipid salt with one another, wherein κsalt<0.45; and wherein said chargeable cationic amphiphile is selected from DmC4Mo2, DmC3Mo2, C4Mo4, C3Mo3, C3Mo2, C5Mo2, C6Mo2 and C8Mo2; and said chargeable anionic amphiphile is selected from Chems, DMGS, DMGM, DMGG, DMGA, DMAS, DMAM, DMAG, DMAA, DOGS, DOGM, DOGG, DOGA, DOAS, DOAM, DOAG, DOAA, DMS, DMM, DMG, DMA, DOS, DOM, DOG, DOA, Chol-C3, Chol-C5 and Chol-C6.
In yet another alternative, said amphoteric liposome may comprise a chargeable anionic amphiphile and a stable cationic amphiphile that are adapted to form a lipid salt with one another, said chargeable anionic amphiphile being in excess; wherein κsalt≧0.34 and the difference between κtotal(pH 8) for C/A=0.5 and κsalt>0.08.
In such case, said chargeable anionic amphiphile may be selected from Chems, DMGS, DMGM, DMGG, DMGA, DMAS, DMAM, DMAG, DMAA, DOGS, DOGM, DOGG, DOGA, DOAS, DOAM, DOAG, DOAA, DMS, DMM, DMG, DMA, DOS, DOM, DOG, DOA, Chol-C3, Chol-C5 or Chol-C6 and fatty acids.
In yet another alternative, said amphoteric liposome may comprise a chargeable anionic amphiphile and a stable cationic amphiphile that are adapted to form a lipid salt with one another, said lipid mixture comprising an excess of said chargeable anionic amphiphile and κsalt being <0.34; wherein said stable cationic amphiphile is selected from DDAB, DC-Chol, DAC-Chol, TC-Chol, DODAP, N-methyl-PipChol, DOTAP, DOEPC and CTAB, and said chargeable anionic lipid is selected from DMGS, DMGM, DMGG, DMGA, DMAS, DMAM, DMAG, DMAA, DOGS, DOGM, DOGG, DOGA, DOAS, DOAM, DOAG, DOAA, DMS, DMM, DMG, DMA, DOS, DOM, DOG, DOA, Chol-C3, Chol-C5 and Chol-C6.
In still yet another alternative, said amphoteric liposome may comprise a lipid mixture comprising an excess of a chargeable cationic amphiphile and a stable anionic amphiphile, wherein said cationic lipid is selected from MoChol, Chim, HisChol or Desh4, DmC4Mo2, DmC3Mo2, C4Mo4, C3Mo3, C3Mo2, C5Mo2, C6Mo2 and C8Mo2, DOIM and DPIM.
Suitably, said amphoteric liposome may comprise one or more neutral or zwitterionic amphiphiles. In some embodiments, said neutral amphiphile may be cholesterol. The cholesterol can be present in the amphoteric liposomes as essentially the only neutral lipid, and can comprise more than 80 mol % of the total neutral lipids present in the liposomes. In other embodiments, cholesterol is the only neutral lipid present in the amphoteric liposomes of the invention. Alternatively, said neutral or zwitterionic lipid may be selected from phosphatidylcholines, sphingomyelins, ceramides, phosphatidylethanolamines, cholesterol and mixtures thereof.
In some embodiments, said neutral or zwitterionic lipids may be phosphatidylcholines, sphingomyelins or ceramides and may be present in the lipid mix in an amount of less than 40 mol %.
Alternatively, said neutral or zwitterionic lipids may be DOPE or cholesterol or a mixture thereof and maybe present in the lipid mix in an amount of less than 65 mol %.
In a further alternative, said neutral or zwitterionic lipids may comprise a mix of phosphatidylcholines (PC), sphingomyelins or ceramides and phosphatidylethanolamines (PE) or a mix of phosphatidylcholines (PC), sphingomyelins or ceramides and cholesterol (Choi); wherein said mix of neutral lipids is present in the lipid mix in an amount of not more than 80 mol %.
In another aspect of the invention the liposome may comprise a lipid salt other than those of the following specific combinations of amphiphiles DODAC/CHEMS; DDAB/CHEMS; DOTAP/DOGS; DOTAP/DMGS; DOTAP/DPGS; DOTAP/CHEMS; CHIM/CHEMS; CHIM/DMGS; CHIM/DOGS; HisChol/CHEMS; HisChol/DMGS; HisChol/DPGS; HisChol/DOGS; HisChol/DPPS; MoChol/CHEMS; MoChol/DMGS; MoChol/DPGS; MoChol/DOGS; MoChol/Cetyl-P; MoChol/DMPS; MoChol/DPPS; DC-CHOL/DOPA; DOTAP+CHIM/CHEMS; DC-Chol/Chems; DOIM/DMGS; DOIM/DOGS; DOTAP/oleic acid.
There are a number of amphoteric lipid combinations that show little or no fusion and might not form a lipid salt. Such lipid combinations are:
MoCHOL/POPG; MoCHOL/DPPG; HisCHOL/POPG; HisChol/DPPG.In another aspect of the invention, the liposome may comprise a lipid mixture other than one having one of the following specific combinations of amphiphiles:
In yet another aspect of the invention, the liposome may comprise a lipid mixture other than one having one of the following specific combinations of amphiphiles
In yet another aspect of the invention, the liposome may comprise a lipid mixture other than one having one of the following specific combinations of amphiphiles:
According to yet another aspect of the present invention there is provided a method of loading amphoteric liposomes according to the present invention with a negatively charged cargo moiety, said method comprising generating said liposomes in the presence of said negatively charged cargo moiety at said first pH using a first solvent comprising anionic counterions, and thereafter exposing said liposome to said second pH using a second solvent comprising cationic counterions.
Preferably such liposomes are bistable, exhibiting a stable lamellar phase at said first pH as well as at said second pH.
Suitably, said solvent changes are performed by the one-step admixture of the respective second solvent, such that said liposome is rapidly brought to the desired pH. Said first pH may be about pH 2-5, preferably pH 2-4. Said second pH may be about pH 7.4. In order to stabilise the liposome at said first pH, said counter-anions may preferably have a molecular volume of at least 50 A3. Thus, said counter-anions may be selected from citrate, pyrophosphate, barbituric acid and methyl sulphate.
In order to stabilise the liposome at said second pH, said counter-cations may preferably have a molecular volume of at least 50 A3.
In accordance with another aspect of the present invention, the liposome may encapsulate at least one active agent. In some embodiments, said active agent may comprise a nucleic acid. In particular, said active agent may comprise an oligonucleotide.
Without being limited to such use, the amphoteric liposomes according to the present invention are well suited for use as a carrier for nucleic acid-based drugs such, for example, as oligonucleotides and DNA plasmids. These drugs are classified into nucleic acids that encode one or more specific sequences for proteins, polypeptides or RNAs and into oligonucleotides that can specifically regulate protein expression levels or affect the protein structure through inter alia interference with splicing and artificial truncation.
In some embodiments of the present invention, therefore, the nucleic acid-based therapeutic may comprise a nucleic acid that is capable of being transcribed in a vertebrate cell into one or more RNAs, which RNAs may be mRNAs, shRNAs, miRNAs or ribozymes, wherein such mRNAs code for one or more proteins or polypeptides. Such nucleic acid therapeutics may be circular DNA plasmids, linear DNA constructs, like MIDGE vectors (Minimalistic Immunogenically Defined Gene Expression) as disclosed in WO 98/21322 or DE 19753182, or mRNAs ready for translation (e.g., EP 1392341).
In another embodiment of the invention, oligonucleotides may be used that can target existing intracellular nucleic acids or proteins. Said nucleic acids may code for a specific gene, such that said oligonucleotide is adapted to attenuate or modulate transcription, modify the processing of the transcript or otherwise interfere with the expression of the protein. The term “target nucleic acid” encompasses DNA encoding a specific gene, as well as all RNAs derived from such DNA, being pre-mRNA or mRNA. A specific hybridisation between the target nucleic acid and one or more oligonucleotides directed against such sequences may result in an inhibition or modulation of protein expression. To achieve such specific targeting, the oligonucleotide should suitably comprise a continuous stretch of nucleotides that is substantially complementary to the sequence of the target nucleic acid.
Oligonucleotides fulfilling the abovementioned criteria may be built with a number of different chemistries and topologies. Oligonucleotides may be single stranded or double stranded.
Oligonucleotides are polyanionic structures having 8-60 charges. Oligonucleotides are therefore well adapted for use as negatively charged cargo in the loading method of the present invention. In most cases these structures are polymers comprising nucleotides. The present invention is not limited to a particular mechanism of action of the oligonucleotides and an understanding of the mechanism is not necessary to practice the present invention.
The mechanisms of action of oligonucleotides may vary and might comprise effects on inter alia splicing, transcription, nuclear-cytoplasmic transport and translation.
In a preferred embodiment of the invention single stranded oligonucleotides may be used, including, but not limited to, DNA-based oligonucleotides, locked nucleic acids, 2′-modified oligonucleotides and others, commonly known as antisense oligonucleotides. Backbone or base or sugar modifications may include, but are not limited to, Phosphothioate DNA (PTO), 2′O-methyl RNA (2′Ome), 2′Fluoro RNA (2′F), 2′O-methoxyethyl-RNA (2′MOE), peptide nucleic acids (PNA), N3′-P5′ phosphoamidates (NP), 2′fluoroarabino nucleic acids (FANA), locked nucleic acids (LNA), Morpholine phosphoamidate (Morpholino), Cyclohexene nucleic acid (CeNA), tricyclo-DNA (tcDNA) and others. Moreover, mixed chemistries are known in the art, being constructed from more than a single nucleotide species as copolymers, block-copolymers or gapmers or in other arrangements. In addition to the aforementioned oligonucleotides, protein expression can also be inhibited using double stranded RNA molecules containing the complementary sequence motifs. Such RNA molecules are known as siRNA molecules in the art (e.g., WO 99/32619 or WO 02/055693). Other siRNAs comprise single stranded siRNAs or double stranded siRNAs having one non-continuous strand. Again, various chemistries were adapted to this class of oligonucleotides. Also, DNA/RNA hybrid systems are known in the art.
In another embodiment of the present invention, decoy oligonucleotides can be used. These double stranded DNA molecules and chemical modifications thereof do not target nucleic acids but transcription factors. This means that decoy oligonucleotides bind sequence-specific DNA-binding proteins and interfere with the transcription (e.g., Cho-Chung, et al. in Curr. Opin. Mol. Ther., 1999).
In a further embodiment of the invention, oligonucleotides that may influence transcription by hybridizing under physiological conditions to the promoter region of a gene may be used. Again various chemistries may adapt to this class of oligonucleotides.
In a still further alternative of the invention, DNAzymes may be used. DNAzymes are single-stranded oligonucleotides and chemical modifications thereof with enzymatic activity. Typical DNAzymes, known as the “10-23” model, are capable of cleaving single-stranded RNA at specific sites under physiological conditions. The 10-23 model of DNAzymes has a catalytic domain of 15 highly conserved deoxyribonucleotides, flanked by 2 substrate-recognition domains complementary to a target sequence on the RNA. Cleavage of the target mRNAs may result in their destruction and the DNAzymes recycle and cleave multiple substrates.
In yet another embodiment of the invention, ribozymes can be used. Ribozymes are single-stranded oligoribonucleotides and chemical modifications thereof with enzymatic activity. They can be operationally divided into two components, a conserved stem-loop structure forming the catalytic core and flanking sequences which are reverse complementary to sequences surrounding the target site in a given RNA transcript. Flanking sequences may confer specificity and may generally constitute 14-16 nt in total, extending on both sides of the target site selected.
In a still further embodiment of the invention, aptamers may be used to target proteins. Aptamers are macromolecules composed of nucleic acids, such as RNA or DNA, and chemical modifications thereof that bind tightly to a specific molecular target and are typically 15-60 nt long. The chain of nucleotides may form intramolecular interactions that fold the molecule into a complex three-dimensional shape. The shape of the aptamer allows it to bind tightly against the surface of its target molecule including but not limited to acidic proteins, basic proteins, membrane proteins, transcription factors and enzymes. Binding of aptamer molecules may influence the function of a target molecule.
All of the above-mentioned oligonucleotides may vary in length between as little as 10, preferably 15 and even more preferably 18, and 50, preferably 30 and more preferably 25, nucleotides. The fit between the oligonucleotide and the target sequence is preferably perfect with each base of the oligonucleotide forming a base pair with its complementary base on the target nucleic acid over a continuous stretch of the abovementioned number of oligonucleotides. The pair of sequences may contain one or more mismatches within the said continuous stretch of base pairs, although this is less preferred. In general, the type and chemical composition of such nucleic acids is of little impact for the performance of the inventive liposomes as vehicles be it in vivo or in vitro, and the skilled artisan may find other types of oligonucleotides or nucleic acids suitable for combination with the inventive liposomes.
According to yet another aspect of the present invention there is provided a pharmaceutical composition comprising an active-agent loaded amphoteric liposome according to the invention and pharmaceutically acceptable vehicle therefor.
Other features and advantages of the invention will be apparent from the following detailed description and claims.
The following Detailed Description, given by way of example, but not intended to limit the invention to specific embodiments described, may be understood in conjunction with the accompanying Figures, incorporated herein by reference, in which:
By “chargeable” is meant that the amphiphile has a pK in the range pH 4 to pH 8. A chargeable amphiphile may therefore be a weak acid or base. A “stable” amphiphile is a strong acid or base, having a substantially stable charge on the range pH 4 to pH 8.
By “amphoteric” herein is meant a substance, a mixture of substances or a supra-molecular complex (e.g., a liposome) comprising charged groups of both anionic and cationic character wherein:
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- 1) at least one, and optionally both, of the cation and anionic amphiphiles is chargeable, having at least one charged group with a pK between 4 and 8,
- 2) the cationic charge prevails at pH 4, and
- 3) the anionic charge prevails at pH 8.
As a result the substance or mixture of substances has an isoelectric point of neutral net charge between pH 4 and pH 8. Amphoteric character is by this definition different from zwitterionic character, as zwitterions do not have a pK in the range mentioned above. In consequence, zwitterions are essentially neutrally charged over a range of pH values; phosphatidylcholines and phosphatidylethanolamines are neutral lipids with zwitterionic character.
By “C/A” or “C/A ratio” or “C/A molar ratio” herein is meant the molar ratio of cationic amphiphiles to anionic amphiphiles in a mixture of amphiphiles.
By “κ(min)” herein is meant the minimum of the function κtotal (pH)
The following abbreviations for lipids are used herein, the majority of which abbreviations are in standard use in the literature:
- PC Phosphatidylcholine (unspecified membrane anchor)
- PE Phosphatidylethanolamine (unspecified membrane anchor)
- SM Sphingomyelin
- DMPC Dimyristoylphosphatidylcholine
- DPPC Dipalmitoylphosphatidylcholine
- DSPC Distearoylphosphatidylcholine
- POPC Palmitoyl-oleoylphosphatidylcholine
- DOPC Dioleoylphosphatidylcholine
- DOPE Dioleoylphosphatidylethanolamine
- DMPE Dimyristoylphosphatidylethanolamine
- DPPE Dipalmitoylphosphatidylethanolamine
- CHEMS Cholesterolhemisuccinate
- Chol-C3 Cholesterolhemimalonate
- Chol-C5 Cholesterolhemiglutarate
- Chol-C6 Cholesterolhemiadipate
- DGS or DG-Succ Diacylglycerolhemisuccinate (unspecified membrane anchor)
- DOGS or DOG-Succ Dioleoylglycerolhemisuccinate
- DMGS or DMG-Succ Dimyristoylglycerolhemisuccinate
- DPGS or DPG-Succ Dipalmitoylglycerolhemisuccinate
- DSGS or DSG-Succ Distearoylglycerolhemisuccinate
- POGS or POG-Succ Palmitoyloleoylglycerolhemisuccinate
- DOGM Dioleoylglycerolhemimalonate
- DOGG Dioleoylglycerolhemiglutarate
- DOGA Dioleoylglycerolhemiadipate
- DMGM Dimyristoylglycerolhemimalonate
- DMGG Dimyristoylglycerolhemiglutarate
- DMGA Dimyristoylglycerolhemiadipate
- DOAS 4-{(1,2-Dioleoyl-ethyl)amino}-4-oxobutanoic acid
- DOAM 4-{(1,2-Dioleoyl-ethyl)amino}-4-oxopropanoic acid
- DOAG 4-{(1,2-Dioleoyl-ethyl)amino}-4-oxopentanoic acid
- DOAA 4-{(1,2-Dioleoyl-ethyl)amino}-4-oxohexanoic acid
- DMAS 4-{(1,2-Dimyristoyl-ethyl)amino}-4-oxobutanoic acid
- DMAM 4-{(1,2-Dimyristoyl-ethyl)amino}-4-oxopropanoic acid
- DMAG 4-{(1,2-Dimyristoyl-ethyl)amino}-4-oxopentanoic acid
- DMAA 4-{(1,2-Dimyristoyl-ethyl)amino}-4-oxohexanoic acid
- DOS 5,6-Dioleoyl-hexanoic acid
- DOM 4,5-Dioleoyl-pentanoic acid
- DOG 6,7-Dioleoyl-heptanoic acid
- DOA 7,8-Dioleoyl-octanoic acid
- DMS 5,6-Dimyristoyl-hexanoic acid
- DMM 4,5-Dimyristoyl-pentanoic acid
- DMG 6,7-Dimyristoyl-heptanoic acid
- DMA 7,8-Dioleoyl-octanoic acid
- DOPS Dioleoylphosphatidylserine
- DPPS Dipalmitoylphosphatidylserine
- DOPG Dioleoylphosphatidylglycerol
- DPPG Dipalmitoylphosphatidylglycerol
- Chol-SO4 Cholesterol sulphate
- DOPA Dioleoylphosphatidic acid
- SDS Sodium dodecyl sulphate
- CHIM Cholesterol-(3-imidazol-1-yl propyl)carbamate
- DDRB Dimethyldioctadecylammonium bromide
- DOTAP, DMTAP, DPTAP, DSTAP:
- DODAP, DMDAP, DPDAP, DSDAP:
- DOEPC, DMEPC, DPEPC, DSEPC:
- DOTMA N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethyl ammonium chloride
- DOTIM 1-[2-(oleoyloxy)ethyl]-2-oleyl-3-(2-hydroxyethyl)imidazolinium chloride
- TMAG N-(a-trimethylammonioacetyl)-didodecyl-D-glutamate chloride
- BCAT O-(2R-1,2-di-O-(19Z,99Z-octadecadienyl)-glycerol)-N-(bis-2-aminoethyl)carbamate
- DODAC Dioleyldimethylammonium chloride
- DORIE 1,2-dioleoyl-3-dimethyl-hydroxyethyl ammonium bromide
- DMRIE 1,2-dimyristoyl-3-dimethyl-hydroxyethyl ammonium bromide
- DOSC 1,2-dioleoyl-3-succinyl-sn-glycerol choline ester
- DORI 1,2-dioleoyloxypropyl-3-dimethylhydroxyethylammonium chloride
- DHMHAC N,N-di-n-hexadecyl-N,Ndihydroxyethylammoniumbromide
- DHDEAB N,N-di-n-hexadecyl-N-methyl,N-(2-hydroxyethyl)ammonium chloride
- DMHMAC N,N-myristyl-N-(1-hydroxyprop-2-yl)-N-methylammoniumchloride
- DOTB 1,2-dioleoyl-3-(4′-trimethylammonio)butanoyl-sn-glycerol
- SAINT lipids Synthetic Amphiphiles INTerdisciplinary
- DPIM, DOIM 4,(2,3-bis-acyloxy-propyl)-1-methyl-1H-imidazole (unspecified membrane anchor)
- DPAPy 2,3-bis-palmitoyl-propyl-pyridin-4-yl-amine
- DC-Chol 3b-[N—(N9,N9-dimethylaminoethane)carbamoyl]cholesterol
- TC-Chol 3b-[N—(N9,N9-trimethylaminoethane)carbamoyl]cholesterol
- DAC-Chol 3b(N—(N,N′-Dimethylaminoethan)-carbamoyl)cholesterol
- PipC2Chol 4{N-2-ethylamino[(3′-cholesteryl)carbamoyl]}piperazine
- MoC2Chol {N-2-ethylamino[(3′-cholesteryl)carbamoyl]}morpholine
- MoC3Chol {N-2-propylamino[(3′-cholesteryl)carbamoyl]}morpholine
- N-methyl-PipChol N-methyl {4-N-amino[(3′-cholesteryl)carbamoyl]}piperazine
- PyrroC2Chol {N-2-ethylamino[(3′-cholesteryl)carbamoyl]}pyrrolidine
- PipeC2Chol {N-2-ethylamino[(3′-cholesteryl)carbamoyl]}piperidine
- ImC3Chol {N-2-propylamino[(3′-cholesteryl)carbamoyl]}imidazole
- PyC2Chol {N-2-ethylamino[(3′-cholesteryl)carbamoyl]}pyridine
- CTAB Cetyltrimethylammonium bromide
- NeoPhectin™ cationic cardiolipins (e.g. [1,3-Bis-(1,2-bis-tetradecyloxy-propyl-3-dimethylethoxyammoniumbromide)-propane-2-ol]
- HistChol N-Histidinyl-Cholesterol-hemisuccinate
- MoChol 4-(2-Aminoethyl)-Morpholino-Cholesterolhemisuccinate:
- HisChol Histaminyl-Cholesterolhemisuccinate:
- DmC4Mo2 4-(2-Aminoethyl)-Morpholino-Cholesterol-2,3-dimethylhemisuccinate
- DmC3Mo2 4-(2-Aminoethyl)-Morpholino-Cholesterol-2,2-dimethylhemimalonate
- C3Mo2 4-(2-Aminoethyl)-Morpholino-Cholesterol-hemimalonate
- C3Mo3 4-(2-Aminopropyl)-Morpholino-Cholesterol-hemimalonate
- C4Mo4 4-(2-Aminobutyl)-Morpholino-Cholesterol-hemisuccinate
- C5Mo2 4-(2-Aminoethyl)-Morpholino-Cholesterol-hemiglutarate
- C6Mo2 4-(2-Aminoethyl)-Morpholino-Cholesterol-hemiadipate
- C8Mo2 4-(2-Aminoethyl)-Morpholino-Cholesterol-hemiadipate
Lipid shape theory is built on a shape balance between the hydrophobic part and the polar head-group of a given amphiphile rather than on absolute values for the two molecular portions. In accordance with the present invention, κ is the volume ratio between the polar and apolar section of a lipid.
κ=molecular volume(head)/molecular volume(tail)
Various different ways are available to those skilled in the art to calculate molecular volumes and alternative methods and sources are discussed for example in Connolly, M. J. Am. Chem. Soc. (1985) 107, 1118-1124 and the references therein or are given at: http://www.ccl.net/cca/documents/molecular-modeling/node5.html
Molecular volume is commonly calculated by assigning a value called a van der Waals radius, rivdW, to each atom type in such a way that the sum of these quantities for a given atom pair, i and j, is equal to their closest possible distance (dij):
rivdW+rivdWdij
Many different tables of “best” van der Waals radii exist, even though the values for corresponding atoms coming from different authors are similar. In geometric terms, the van der Waals radius may be imagined as a spherical “shield” surrounding the atom, and the closest distance between two non-bonded atoms is when their respective shields touch. However, the shields of covalently bonded atoms intersect since bond lengths are shorter than the sum of the van der Waals radii partaking atoms. A molecular van der Waals surface, also called a van der Waals envelope, is composed of the spheres for individual atoms with their intersecting sections removed.
For a single molecule (i.e., molecule for which there is a path between any two atoms along covalent bonds), the van der Waals envelope is a closed surface, and hence, it contains volume.
This volume is called the molecular volume, or van der Waals volume and is usually given in Å3. The straightforward way of calculating molecular volume on a computer is by numerical integration.
In some embodiments, molecular volumes for lipid molecules and the respective head and tail fragments may be calculated using DS Viewer Pro 5.0 (Accelrys Inc., San Diego, Calif.) and volumes within the respective van der Waals radii were calculated.
Typical membrane fragments are 1,2-diacyl-ethyleneglycols that represent the hydrophobic section for common phospholipids, leaving the 3′ carbon atom of the original glycerol with the phosphocholine head-group. The same fragment is also found in the common cationic lipid DOTAP and its derivatives but also in diacylglycerols with other polar head-groups such as dimyristoylglycerol hemisuccinate and the like.
For the cholesterol derivatives, the entire sterol, but not the 3′ oxygene, is defined as the hydrophobic section and the head-group being complementary to that.
Likewise, for cationic or anionic alkyl derivatives the polar head-group is defined as the polar fragment involving the C1 carbon of the alkyl chain. Consequently, the residual chain with n−1 carbon atoms represents the hydrophobic apolar part.
Molecular volumes depend on the constants used for the calculations and may be affected by the conformation of the molecule. Typical values obtained for the hydrophobic apolar fragments are and were used for further calculations:
Molecular volumes for most counter-anions were derived the same way, but for Na+ or K+ the strongly bound hydration sphere is taken into account. The following values were used for further calculations:
The charged polar head-groups have different representations and the molecular volumes are given below for some individual members of this group. These values were used for further calculations:
It is possible to use other methods to determine molecular volumes for the lipids. Also, some parameters such as the exact split-point between membrane tail and polar head; number of water molecules in the hydration cage or the van der Waals radii can be varied without affecting the general applicability of the model. With the same understanding more subtle changes in the molecular volumes may be disregarded, in particular those arising from the dissociation of protons or from conformational changes. In some embodiments the molecular volumes recited in Tables 2 and 3 above may be used in the methods of the present invention.
The counterions fall into the same category of sizes than the actual polar head-groups. As such, it has been found that the addition or withdrawal of counterions from lipid polar regions has a substantial effect on the total head-group size and in consequence on the head/tail balance κ. As an example, the CHEMS sodium salt has a head-group size of 141 A3 which is reduced to 76 A3 in the undissociated form at pH 4. κ varies between 0.42 and 0.23, respectively. CHEMS does form a lamellar phase at pH 7.5 and higher but adopts a hexagonal phase at low pH.
Other lipids with known phase behaviour can be used to select κ values for discrimination between the lamellar and hexagonal phase; an example is given in Table 4 below. PE head-groups can form an intramolecular ring structure with hydrogen bonding between the terminal amino group and the oxygen in the phosphoester group (betaine structure)(e.g. Pohle et al., J. Mol. Struct., 408/409, (1997), 273-277). PC head-groups are sterically hindered and instead recruit counterions to their respective charged groups.
In a first model, in contradistinction to the present invention no lipid salt formation occurs between charged anionic and cationic lipids. This reflects the assumptions of Li and Schick (Biophys. J., 2001, 80, 1703-1711) and might be the case for lipids that are sterically hindered to form lipid salts (independent ion model).
The lipid species in the membrane comprise undissociated anions and cations as well as the dissociated anions and cations, the latter being complexed with their respective counterions. The κ value for such a mixture is assumed to be the weighted sum of its components:
κ=κ(anion0)*c(anion0)+κ(cation0)*c(cation0)+κ(anion−)*c(anion31)+κ(cation+)*c(cation+); (1)
-
- wherein anion0 or cation0 denotes the uncharged species and anion− or cation+ denotes the respective charged species; and wherein c herein denotes concentration.
The amounts of the individual species present under such assumption can be calculated from known equilibrium constants K for the acid or base dissociation:
c(anion−)=c(aniontot)/(cH+/K+1) (2)
c(anion0)=c(aniontot)−c(anion−) (3)
c(cation+)=c(cationtot)/(K/cH++1) (4)
c(cation0)=c(cationtot)−c(cation+) (5)
wherein anion0 is the undissociated anion, anion− the negatively charged molecule and aniontot the total concentration of the respective anion. Cations follow the same nomenclature and cH+ and K describe the proton concentration and the equilibrium constant for the acid or base, respectively.
However, taking possible interaction between a cationic and anionic amphiphile into account in accordance with the invention, the lipid salt occurs as a fifth species in the mixture:
κ=κ(anion0)*c(anion0)+κ(cation0)*c(cation0)+κ(anion−)*c(anion−)+κ(cation+)*c(cation+)+κ(salt)*c(salt) (6)
In a lipid salt, the cationic amphiphile serves as a counterion to the anionic amphiphile and vice versa thus displacing the small counterions like sodium or phosphate from the head-group. The lipid salt is net uncharged and its geometry has to be assumed to be the sum of both parts without the small counterions. Therefore:
κ(salt)=(vhead(cation)+vhead(anion))/(vapolar(cation)+vapolar(anion)) (7)
Salt formation is limited by the charged amphiphile that is present in the lowest concentration:
c(salt)=MIN(c(cation+);c(anion−)) (8)
Salt formation between the two charged amphiphiles is assumed to be complete within this model, but of course, an incomplete salt formation may be assumed. The following calculations further reflect the fact that the salt comprises two lipid molecules. It is of course possible to assume further some membrane contraction upon lipid salt formation and to put a different weight on the contribution of k(salt).
Model CalculationsTo achieve amphoteric character of a lipid mix, at least one of the lipid ions needs to be a pH-sensitive, weak acid or base (“chargeable”). A detailed disclosure is found in WO 02/066012 the contents of which are incorporated herein by reference. Being different in character, three basic systems are possible and are analysed here:
“Amphoter I” strong cation and weak anion,
“Amphoter II” weak cation and weak anion,
“Amphoter III” weak cation and strong anion.
Amphoter I systems need an excess of the pH-sensitive anion to achieve amphoteric character. At pH 7 to 8 the anionic lipid is fully charged and salt formation occurs until all cationic lipids are consumed. In an example with 70 mol. % anionic lipid and 30 mol. % cationic lipid, all cationic lipid and a corresponding 30 mol. % of the anionic lipid would exist as lipid salt while 40 mol. % of the anionic lipid is unbound and recruits its counterion to the head-group.
Starting from neutral conditions, a reduction of the pH discharges the anionic lipid, the κ value becomes smaller owing to loss of the counterion and reaches a minimum when the portion of still-charged anionic lipid is equal to the amount of cationic lipid. Therefore, κ is minimal at the isoelectric point of the amphoteric lipid mixture. If the pH is further lowered, an increasingly smaller portion of the anionic lipid remains charged. This means dissociation of the lipid salt and recruitment of counterions, now to the cationic lipid liberated from the lipid salt.
The left panel in
Amphoter I mixtures with less than 50 mol. % anionic lipid are no longer amphoteric since the anion can modulate, but not overcompensate, the charge on the cationic lipid. These mixtures might undergo a pH-dependent fusion, but do not provide a second stable phase at low pH. A 1:1 complex adopts a lamellar phase only at low pH and undergoes fusion at neutrality.
The parameters used for the calculations illustrated in
Amphoter II systems have the distinct advantage to be amphoteric over the entire range of anion:cation ratios and no charge overcompensation for the strong ion is needed as in Amphoter I or Amphoter III systems. A calculation for a model system is shown in
The parameters used for the calculation are given in Table 6 below; all volumes in Å3.
Again, the lipid salt model predicts stable states at neutral to slightly alkaline pH but also at slightly acidic pH and a pronounced valley of instability or fusogenicity in between.
In contrast to amphoter I systems, fusogenic states can be reached across a wide range of different lipid ratios between the anionic and cationic components. That is, the valley of fusogenicity extends across a wider range of anion/cation ratios, allowing a greater degree of control over the pH at which a given system is fusogenic.
Amphoter III MixturesAmphoter III mixtures comprising a stable anion and a pH-sensitive cation cannot form lipid salts at neutral pH, since little to no charged cationic lipid exists at this pH. It needs ongoing acidification to first create the cation which then may undergo salt formation. Calculation for a model system is shown in
The parameters used for the calculation are given in Table 7 below; all volumes in Å3.
As can be seen from
Experimental evidence for the fusion valley is given in the Examples 1 to 4 and provides confirmation for the central hypothesis of lipid salt formation in amphoteric liposomes. The examples also provide two closely related amphoter III systems (MoChol/POPG and MoChol/DOPA) where fusion is only observed in one of the two, namely MoChol/DOPA. This may be due to steric hindrance, as the protonated tertiary nitrogen in MoChol is situated at the lower end of the morpholino ring and is therefore not easily accessible. In addition, the phosphate in POPG sits right at the lipid/water interface and is protected with a glycerol towards the water phase. In contrast, the phosphate group in DOPA is easily accessible. The model described above can be used to describe both situations, if lipid salt formation is optionally removed from the model building assumptions (equations (1) to (5) above only). A comparison between the two scenarios is shown in
Whereas the lipid salt model predicts fusion with lower pH, a deletion of salt formation leads to a system where an increase of κ is observed when the cationic lipid becomes protonated. If at all, such situation leads to an even more lamellar and eventually to a micellar state of the membrane. However, the limit for micelle formation has not been determined within the context of this model.
The monoanionic state of DOPA (pKa 1=3, pKa 2=8) was used for the model since DOPA exists as a mono-anion when MoChol becomes ionised (pKa=6.5). The model predicts little or no fusogenicity at 33 mol. % anion, valley type fusion behaviour at 50 mol. % anion and monophasic fusion behaviour at 66 mol. % and more of the anion. The entire complexity of the model is reflected in the practical behaviour of the membrane as illustrated in Example 4 below.
The algorithm according to the present invention allows prediction of fusion behaviour of a wide range of amphoteric lipid mixtures. The prediction rules are derived from a simple geometrical description of the interacting lipids and are independent from the actual chemical representation of the molecules. As such, existing and novel lipid combinations can be easily tested by those skilled in the art, and the intended fusion behaviour can be predicted in a rational way. The following key parameters may illustrate such selection process, but other priorities might be set dependent on the respective goals of the application.
1. κ of the Lipid Saltκ of the lipid salt is calculated in equation (7) above and may suitably be lower than 0.34 or 0.35 to predict reasonably a fusogenic hexagonal phase. In some embodiments κ may be lower than 0.3; preferably lower than 0.25. κ(salt) is low when the combined polar head-groups are small and the combined hydrophobic portions are large. The preferred sum of head-group volumes is about 300 Å3 or smaller; in a more preferred embodiment this volume is smaller than 220 Å3, and an even more preferred value is smaller than 170 Å3. According to the selection made above, preferred sums for the tail group volumes are larger than 650 Å3 and may be as large as about 1000 Å3, wherein combinations of proper head and tail groups are governed by the preferred k(salt) values.
2. Amplitude of Change (d(κ)/d(pH))
In a preferred embodiment of the present invention, a lipid salt with a low value for κ is stabilised below or above its isoelectric point by recruitment of counterions. In a preferred embodiment of the invention larger counterions are used to stabilise either the cationic or the anionic state of the amphoteric lipid mixture.
It becomes apparent from the right panel of
In some embodiments of the present invention larger counter-cations are used to stabilise the amphoteric liposomes at neutral conditions. In a preferred embodiment such counter-cations have a molecular volume of 50 Å3 or more, in a more preferred embodiment this volume exceeds 75 Å3 and said neutral pH is between pH 7 and pH 8, more preferred about the physiological pH of 7.4.
If amphoteric liposomes are produced for pharmaceutical purposes, compatibility of the used ions with the application route needs to be obeyed. Suitable counter-cations can be selected from Table 2 above describing the ion sizes. Preferred counter-cations for pharmaceutical compositions are sodium or the respective ionized forms of tris(hydroxymethyl)aminomethane, tris-hydroxyethylaminomethane, triethylamine, arginine, in particular L-arginine and the like.
In an embodiment of the invention the amphoteric liposomes may be manufactured at a low pH in their cationic state. Under these conditions, the liposomes can bind polyanions such as proteins, peptides or nucleic acids, whether as large plasmids or smaller oligonucleotides. Such binding is useful for improvement of the encapsulation efficacy of said materials into the amphoteric liposomes.
It is advantageous to use a lipid phase with a low κ at acidic pH. Selection of large counter-anions facilitates stabilisation of said lipid phase, e.g., for the production of such liposomes and the encapsulation of cargo under these conditions.
Suitable large counter-anions have a molecular volume larger than 50 Å3, preferred large counterions have a molecular volume larger than 75 Å3. Suitable counter-anions can be selected from Table 2 above. Preferred counter-anions are citrate, pyrophosphate, barbiturate, methyl sulphate and the like.
After having contacted the lipid phase with the cargo to be encapsulated under acidic conditions, the liposomes are than neutralized and non-encapsulated cargo can optionally be removed. Typically, non-encapsulated cargo detaches from the lipid membrane since both carry the same charge under neutral conditions. The amphoteric liposomes are negatively charged above their isoelectric point, e.g., at a pH between 7 and 8 and the cargo molecules exist as polyanions at such a pH. This is in particular the case with nucleic acids that carry one negative charge per nucleobase. Such liposomes can undergo effective destabilisation when exposed to the low pH in combination with a smaller counter-anion. This is for example the case after systemic administration and cellular uptake and endocytosis of such liposomes. Chloride or phosphate are the most common counter-anions in the body fluids of animals, be it any animal, a mammal or humans. Phosphate, but even more so chloride, are small counterions with little or no hydration shell and molecular volumes <60 A3.
A mathematical description for the isoelectric point of amphoteric liposomes is been given in the WO 02/066012. In accordance with the present invention, the isoelectric point of the amphoteric liposomes can be adjusted to a wide range of conditions, and there is sufficient chemical representation for individual lipids with different pK dissociation constants that allows the skilled artisan to select useful components and combinations for the making of amphoteric liposomes. In addition, the isoelectric point for a given amphoteric lipid composition can be easily tuned through the molar ratio between the anionic and the cationic lipid as presented in Hafez et al., Biophys. J., 79, (2000), 1438-1446.
4. Relationship Between κ(Lipid Salt) and CounterionsPreferred values for κ and counterion size have been given above. In addition to these criteria, the absolute molecular volume of a lipid molecule is of importance. For large absolute volumes the relative impact of the counterion binding becomes smaller. This is illustrated in
In a preferred embodiment of the present invention the absolute molecular volumes for the lipids are small, e.g., <1000 Å3 for the combined volumes of an anionic and cationic lipid. More preferred are lipid pairs with about 700 Å3 molecular volume.
As was the case for counterions of different volumes, asymmetric stability of a cationic and anionic lipid phase can also be achieved by selection of lipids with different absolute molecular volumes, even if said lipids have equal κ values. The example in
The algorithm presented above according to the invention therefore provides structure-activity relationships between lipid chemistry and stability of the resulting membrane, in particular in response to the pH of the environment. Experimental data further illustrate the invention and justify the model predictions. There is clear evidence for the following:
- 1. Amphoteric liposomes form stable bilayers at neutral pH, but are fusogenic at intermediate pH. Some amphoteric liposomes form bistable liposomes that exist in a stable phase at low and neutral pHs, but undergo fusion at intermediate pHs. Examples 2, 3, 5 and 6 and corresponding
FIGS. 10, 11, 12 and 13 show this for different amphoteric systems and lipid geometries, e.g., lipids with dialkyl- or cholesterol- or monoalkyl membrane anchors. - 2. The intensity of fusion may be augmented or diminished through the use of counterions of different size, as shown in Examples 8 and 9 and the corresponding
FIGS. 16 and 17 . - 3. κ(salt) correlates inversely with the fusion intensity of different amphoteric systems. This means that systems with a lower κ(salt) show enhanced fusion. Experimental evidence is given in Examples 12 and 13.
FIGS. 19 a and 19b show an inverse correlation between fusion intensity (expressed as ΣFRET) and κ(salt) for a large number of amphoter II systems, said systems being formed from cholesterol based pH sensitive cationic lipids and pH sensitive anionic lipids.FIG. 19c illustrates such a plot for the cationic lipid DmC4Mo2 in combination with different anionic pH sensitive lipids. Likewise,FIG. 20 shows such an inverse correlation for amphoter I systems comprising DOTAP or DODAP and various pH sensitive anions. A clear correlation between the value of κ(salt) and the fusogenicity of the amphoteric systems becomes apparent from these experiments. - 4. The model also applies to amphoteric lipid mixtures further comprising neutral lipids and the quantitative impact of such admixtures is shown in Examples 15 and corresponding
FIGS. 21 to 24 . A relation between κ(neutral lipid admixture) and κ(min) is implicit in the model predictions and further described below. In brief, the inclusion of neutral lipids may decrease the fusion intensity of a given amphoteric system whenever κ(neutral) is higher than κ(min).FIGS. 21a,b and 24a,b demonstrate this experimentally. The opposite case can also be found, as demonstrated in theFIGS. 23a,b . Eventually, some systems are less affected by the introduction of neutral lipids, as shown inFIGS. 22a,b . Since experimental optimisation of systems with a higher number of components becomes increasingly difficult and laborious, numerical predictability according to the invention becomes even more important and allows rapid and efficacious prediction. - 5. The model predicts fusion around the isoelectric point of the lipid mixture. Such correlation can be demonstrated in the experiment and is analyzed in
FIG. 26 .
The data provided above show a high degree of predictability from model calculations. The algorithm, starting from molecular volume considerations and rather long range interactions of electrical charges, does not reflect steric fit or misfit of the components; it also does not take phase transition temperatures and the associated molecular movements into account which might occur in isolated cases. In some cases impaired fusion behaviour (e.g. between MoChol and POPG, but not MoChol and DOPA as described above) or enhanced fusion behaviour can be observed (e.g. DmC4Mo2 and various anionic lipids). In cases for which an enhanced fusion behaviour is observed k(salt) of the lipid salt may be higher than 0.35, but less than 0.45.
Following is an assessment of liposomal fusion for a wide range of amphoteric systems and selected preferred systems for further practical use.
The quantitative structure-activity relationships taught by this invention facilitate in silico screening and support rational selection and optimization. Such screening may be used on its own or in combination with empirical verification, e.g., by the inclusion of selected data points within a series of lipid homologues. The following sections comprise:
Section I: In silico screening of amphoteric systems
Section II: In silico screening of amphoteric systems, further comprising neutral lipids
Section III: Experimental screening of amphoteric systems
Section IV: Experimental screening of amphoteric systems, further comprising neutral lipids.
The present invention enables the selection of amphoteric liposomes for a number of technical purposes. A more detailed analysis is given below of the use of such amphoteric liposomes in pharmaceutical applications. Amongst such pharmaceutical applications, parenteral administration and direct administration into the blood stream of a human or non-human animal, preferably a mammal, is of particular importance. Amphoteric liposomes have specific applicability inter alia in the intracellular delivery of cargo molecules. As described above, during uptake into the cells, liposomes are exposed to an acidic environment in the endosome or lysosome of cells. Destabilisation of the lipid phase, e.g., by enhanced fusogenicity is known to facilitate endosome escape and intracellular delivery. It is possible that other environments of low pH will also trigger said fusion, e.g., the low pH conditions found in tumors or at sites of inflammation.
Amphoteric liposomes according to the present invention with a preferred low value of κ(salt) have been found to respond advantageously to acidification by destabilisation or formation of a fusogenic phase as intended.
To be stable under storage conditions or while in the blood stream, a certain difference between κ(total) at neutral pH and κ(salt) is necessary. In preferred embodiments, such difference, referred to herein as dκ(pH8), may be greater than or to equal 0.08. As noted above, κ(salt) is the dominant predictor for fusogenicity, whereas dκ(pH8)>=0.08 is a necessary, but not sufficient condition. A scoring of selected systems was done using 1/κ(salt) as a metric. High values indicate systems with good fusion and sufficient stability amplitude.
The difference between κ(salt) and κ(total) for acidic conditions is of less importance, since an unstable lipid phase under acidic conditions does not interfere with cellular uptake.
In addition, methods to stabilise such lipid phase for production have been described above.
The analysis is sensitive to counter-cation size and the proportion of anionic lipid in the mixture. As mentioned above, larger counter-cations make the selection less stringent, since this parameter directly improves the dκ(pH8) which means that systems with a low amplitude become more functional. It also means that systems with a low κ(salt) can be stabilized sufficiently to yield a stable phase at neutral pH. Although resulting in a more or less stringent selection, the counter-cation size does not change the observed overall pattern of selected systems. This fact effectively compensates the variability of counter-cation sizes that can be found in the literature.
Amphoteric lipid systems with lipid head-group sizes between 40 and 190 A3 and lipid hydrophobic tail sizes of 340, 410 or 500 A3 have been analyzed in the presence of a counter-cation, specifically sodium (65 A3). The counter-anion is of less relevance for the presented screen, since the ion (1) does not participate in the lipid salt and (2) does essentially not bind to the membrane at pH8.
The following in silico screens of amphoter I and amphoter II and III systems provide a more general and experimentally unbiased selection of fusogenic amphoteric liposomes. The calculations allow one skilled in the art to deduce amphiphiles with preferred head and tail sizes and subsequently to identify improved amphoteric lipid mixtures.
The following selections were made according to κ(salt)<0.34 and dκ(pH 8)<=0.08 and identified limits for preferred lipid systems. Other limits for selection can be used, allowing a broader or narrower search for amphoteric lipid systems as desired.
Amphoter I SystemsFor amphoter I systems, full dissociation of the anionic amphiphile was assumed at pH 8. A library of 324 amphoter I lipid systems having a C/A=0.5 was constructed and preferred lipid systems having κ(salt)<0.34 and dκ(pH 8)<=0.08 were selected from the entire population.
The table shows the positively screened systems and further reveals consistent patterns for such systems within specific combinations of lipid tail groups.
The effect of the lipid anion content in amphoter I systems is somewhat more complex. First of all, a lower presence of lipid anion (e.g. C/A 0.666 or 60 mol %) results in a more stringent selection, this is due to the smaller amplitude of such systems. Accordingly, the presence of higher amounts of lipid anion results in a less stringent selection. Results for the respective calculations are presented below.
The presence of lower amounts of the anionic lipids results in selection pressure towards sterol based lipid anions with large head groups in combination with cationic lipids of any tail size, provided that these lipids have a minimal head group with a molecular volume between 40 and 70 A3.
Presence of higher amounts of the anionic lipid lifts said selection pressure and makes the composition more promiscuous in general. It also shifts the optimum size for the lipid anion head group towards moderate values between 100 and 130 A3 as shown in the table below.
Preferred amphoter I systems may rapidly be identified with the procedures described above, said systems being characterized by
-
- κ(salt) being smaller than 0.34
- dκ(pH8) being greater than 0.08 More preferred systems have
- smaller lipid anion tail groups with a molecular volume smaller than 420 A3, selected from the group of sterols or dimyristoylethylenglycols, most preferred this group is a sterol
In another embodiment, the more preferred systems have
-
- anionic head groups with a molecular volume between 70 A3 and 190 A3, said groups are selected from but not limited to hemimalonates, hemisuccinates, hemiglutarates, hemiadipates, cyclohexanoic diacids, glucuronic acids and homologues thereof.
- cationic head groups with small molecular volume between 40 and 100 A3, most preferred between 40 and 70 A3, said groups being selected from but not limited to methylamine, dimethylamine, trimethylamines, tetramethylammonium salts, N-methylpyridinium salts, trimethyl-hydroxyethylammonium salts, N-a trimethylammoniumacetyl salts, dimethylaminoethylcarbamates, N-Methyl-mono(hydroxymethyl)aminomethane, N-Methyl-bis(hydroxymethyl)aminomethane and homologues thereof.
The most preferred amphoter I systems have low κ(salt) and high dκ(pH8) values in the presence of higher amounts of the lipid cation, thus facilitating better binding and encapsulation of polyanionic cargo molecules such as oligonucleotides. These systems have
-
- a sterol based lipid anion with a polar head group that is larger than 130 A3, most preferred about 160 to 190 A3
- a dioleoylglycerol based lipid cation with polar head group that is smaller than 100 A3, most preferred smaller than 70 A3.
For amphoter II systems, full dissociation of the anionic amphiphile was assumed at pH 8 and essentially no dissociation of the cationic amphiphile was assumed at this pH. Such selections also apply to amphoter III systems, as long as they contain 50% or less of the anionic amphiphile.
First, a library of 324 amphoter II lipid systems having a C/A=3 was constructed and preferred lipid systems having κ(salt)<0.34 and dκ(pH 8)<=0.08 were selected from this population.
Preferred cation-rich amphoter II (or amphoter III) systems can rapidly be identified with the procedures described above, said systems being characterized by
-
- k(salt) being smaller than 0.34
- dk(pH8) being greater than 0.08
- lipid cation tail groups with a molecular volume smaller than 420 A3, selected from the group of sterols or dimyristoylethylenglycols, most preferred this group is a sterol
- lipid anion tail groups with a molecular volume larger than 400 A3, selected from the groups of diacylethylenglycols, most preferred dipalmitoyl-distearoyl-palmitoyloleoyl- or dioleoylethylenglycols.
In another embodiment, the more preferred systems have
-
- cationic head groups with a molecular volume between 70 A3 and 160 A3, selected from but not limited to morpholines, propylimidazols, 3-imidazol-1-yl-propyl carbamates, piperazine 4-N-aminoethyl carbamoyls, 2-(4-Imidazolyl)ethylamine hemisuccinates, 1-[2-carboxyethyl]2-methyl-3-(2-hydroxyethyl)imidazolinium salts, ethylphosphocholines, N-Morpholino ethylamine hemisuccinates, 1-Methyl-4-choline-succinic acid diesters and homologues of said compounds.
- anionic head groups with small molecular volume between 40 and 100 A3, most preferred between 40 and 70 A3, said groups being selected from but not limited to hemimalonates, hemisuccinates, hemiglutarates and homologues thereof.
Amphoter II systems with about equimolar C/A have more complex selection patterns, but include the aforementioned cation-rich systems. Said systems therefore facilitate tuning of the isoelectric point without loosing functionality. Table 17 below presents systems that were selected in accordance with the criteria presented above:
In addition to the selection criteria used for cation-rich amphoter II system, the amphoter II (C/A=1) systems display a preference for
-
- lipid anion tail groups with a molecular volume smaller than 420 A3, selected from the group of sterols or dimyristoylethylenglycols, most preferred this group is a sterol
The anion-rich amphoter II systems are the least demanding ones, as far as structural constraints are concerned. However, this structural freedom comes at the cost of limited encapsulation efficiency for important cargo types, such polyanions, in particular oligonucleotides. The selection screen was applied to amphoter II system with C/A=0.5 and results in the following pattern:
Amphoter II systems with anion excess have a preference for
-
- cation head groups with a molecular volume of less than 130 A3, preferred less than 100 A3, being selected from but not limited to imidazols, methylimidazols, ethylimidazols, morpholins, methylmorpholins, ethylmorphlins, N-Methyl-tris(hydroxymethyl)aminomethanes, 3-imidazol-1-yl-propyl carbamates, piperazine 4-N-aminoethyl carbamoyls, N-Methyl-mono(hydroxymethyl)aminomethanes, N-Methyl-bis(hydroxymethyl)aminomethanes and homologues thereof.
- anionic head groups with a molecular volume of less than 130 A3, preferred about 70 A3 or less, being selected from but not limited to hemimalonates, hemisuccinates, hemiglutarates, hemiadipates, cyclohexanoic diacids and homologues thereof
- cation head groups with a molecular volume of less than 130 A3, preferred less than 100 A3, being selected from but not limited to imidazols, methylimidazols, ethylimidazols, morpholins, methylmorpholins, ethylmorphlins, N-Methyl-tris(hydroxymethyl)aminomethanes, 3-imidazol-1-yl-propyl carbamates, piperazine 4-N-aminoethyl carbamoyls, N-Methyl-mono(hydroxymethyl)aminomethanes, N-Methyl-bis(hydroxymethyl)aminomethanes and homologues thereof.
With more lipid anions in the mixture, the pattern of positively selected candidates resembles this of the amphoter I systems.
However, the latter ones are somewhat compromised in their dk(pH8) values as the constant formation of the lipid salt reduces this amplitude.
Section II: In Silico Screening of Amphoteric Systems, Further Comprising Neutral LipidsThe algorithm taught by this invention also facilitates quantitative predictions to be made on the effect of neutral lipid admixtures to amphoteric lipid systems. Such admixtures may result in improved stability of the liposome; they might further result in better resistance against serum proteins or enhanced uptake into cells. Optimization of amphoteric systems is a challenging task on its own, owing to the large number of useful components. This task becomes even more complicated with the addition of further components and rational approaches are urgently needed.
The methodology developed in the previous sections above was therefore applied to more complex systems including neutral lipid components. With respect to the main parameters k(salt) and dk(pH8), the addition of neutral lipids may result in
-
- an increase of k(min) if k(neutral) is higher than k(salt) and vice versa, said increase being proportional to the amount of neutral lipid added.
- a compression of the system amplitude dk(pH8) by addition of any neutral lipid, since these lipids do not change their geometry upon changes in the pH.
Still, even the more complex systems need a certain k(min) to achieve fusion and a certain dk(pH8) to maintain stability. The corresponding values from section 1 have been used for the analysis presented here, which are k(min) being the functional equivalent to k(salt), said k(min)<0.34 and dk(pH8)>0.08.
Amphoter I Systems Further Comprising Neutral LipidsLibraries of amphoter I systems (C/A=0.333) were constructed as described previously and highly functional systems were selected using k(min)<0.34 and dk(pH8)>0.08 as criteria. Fitness of the selected systems is presented as 1/k(min) in the table below for the addition of 30% cholesterol to the library.
In comparison with the data presented for the corresponding amphoter I library from section I, the addition of cholesterol results in a somewhat different selection that is more biased towards anionic lipids with large headgroups, while maintaining other features like the preference of amphoter I for cholesterol or dimyristoylglycol as tail regions for the anionic lipids.
Addition of a strongly lamellar lipid such as POPC or DOPC results in more stringent selection without qualitative impact on the selection rules presented before.
Amphoter II Systems Further Comprising Neutral LipidsLibraries of cation-rich amphoter II systems (C/A=3) were constructed as described previously and highly functional systems were selected using k(min)<0.34 and dk(pH8)>0.08 as criteria. Fitness of the selected systems is presented as 1/k(min) in Table 20 below for the addition of 30% cholesterol to the library.
In comparison with the data presented for the corresponding cation-rich amphoter II library from section I, the addition of cholesterol results in a somewhat different selection that is substantially biased towards cationic lipids with large headgroups, while maintaining other features like the preference of amphoter I for large tails regions such as dimyristoylglycol or dioleoylglycol for the anionic lipids.
Addition of a lamellar lipid such as POPC or DOPC results in more stringent selection without qualitative impact on the selection rules presented before.
Libraries of equilibrated amphoter II systems (C/A=1) were also constructed and introduced into the selection scheme in the presence of 30% cholesterol in this the library.
While the corresponding amphoter II library (C/A=1) from section I had numerous positive systems, the addition of 30% cholesterol resulted in a very stringent selection. This is counterintuitive to the addition of a lipid that promotes fusion and illustrates the impact of dk(pH8) as a selection criterium. A close group can be identified comprising:
-
- sterol based lipid anions with head group volumes greater than 100 A3
- diacylgylcol based cations with head group volumes smaller than 160 A3, more preferred smaller than 70 A3
In this group, the addition of a lamellar lipid such as POPC or DOPC had similar impact than the addition of cholesterol.
Libraries of anion-rich amphoter II systems (C/A=0.33) were also constructed and introduced into the selection scheme in the presence of 30% cholesterol in this the library.
Here, some bias of the positive candidates towards larger anion head groups can be observed. However, this needs to be interpreted carefully since the fusion activity is always improving in the presence of small anionic headgroups.
Addition of lamellar lipids such as POPC or DOPC imply more stringent selection criteria in comparison to the systems in section I, but do not qualitatively change the pattern of positive candidates.
Section III: Experimental Screen of Amphoteric Lipid SystemsThe fusogenicity of different amphoteric liposome mixtures comprising charged amphiphiles can be investigated using lipid fusion assays, particle growth or other methods known in the art, thereby allowing the identification of preferred mixtures. Lipid mixing can be tested with fluorescence resonance energy transfer (FRET), and experimental details are described in Example 11 wherein the fusion of amphoteric lipid mixtures was monitored within a pH range of between pH 2.5 and pH 7.5.
Amphoter I Systems Comprising Charged Amphiphiles OnlyAmphoter I systems are characterized by a stable cation in combination with an excess of a chargeable anion. Preferred amphoter I systems solely comprising charged amphiphiles form stable lamellar phases at pH 7 to pH 8 and fuse between pH 3 to pH 6, preferably between pH 4 to pH 6. Within a given amphoter I system fusion was monitored for different ratios of cationic to anionic lipid (C/A ratio, always <1).
Amphoter I systems that are stable at pH 7 to pH 8 and fuse between pH 3 to pH 6, preferably between pH 4 to pH 6 may be formed from mixtures of one or more cationic amphiphiles selected from DOTAP, DMTAP, DPTAP, DSTAP, POTAP, DDAB, DODAC, DOEPC, DMEPC, DPEPC, DSEPC, POEPC, DC-Chol, TC-Chol, DAC-Chol, DODAP, DMTAP, DPDAP, DSDAP, PODAP, N-methyl-PipChol, CTAB, DOTMA with one or more anionic amphiphile selected from diacylglycerol succinates, e.g. DOGS, DMGS, POGS; diacylglycerolmalonates, e.g. DOGM or DMGM; diacylglycerolglutarates, e.g. DOGG, DMGG; diacyiglyceroladipates, e.g. DOGA, DMGA; 4-{(1,2-Diacyl-ethyl)amino}-4-oxo acids, e.g. DOAS, DOAM, DOAG, DOAA, DMAS, DMAM, DMAG, DMAA; Diacyl-alkanoic acids, e.g. DOS, DOM, DOG, DOA, DMS, DMM, DMG, DMA; Chems and derivatives thereof, e.g. Chol-C3, Chol-C5 or Chol-C6; fatty acids.
In one embodiment of the invention, the cationic amphiphiles are selected from DODAP, DOTAP, N-methyl-PipChol, DDAB, DOEPC, DC-Chol, DAC-Chol or TC-Chol and combined with anionic amphiphiles selected from Chems, DMGS, DMGM, DMGG, DMGA, DMAS, DMAM, DMAG, DMAA, DOGS, DOGM, DOGG, DOGA, DOAS, DOAM, DOAG, DOAA, DMS, DMM, DMG, DMA, DOS, DOM, DOG, DOA, Chol-C3, Chol-C5 or Chol-C6.
In some embodiments of the invention the following amphoter I mixtures are preferred which comprise charged amphiphiles only, are stable at pH 7 to pH 8 and fuse between pH 3 to pH 6, preferably between pH 4 to pH 6 (Table 23):
Less preferred are amphoter I systems that are not stable at pH 7 to pH 8, for example the amphoter I systems DOTAP/stearic acid or DOTAP/oleic acid at C/A>0.33.
More versatile amphoter I systems of Table 23 are those that are fusogenic over a wide range of C/A ratios, thus allowing adjustment of the fusion pH without changing the chemistry of the system. Some versatile systems are fusogenic over C/A ratios that differ by ≧0.4, more versatile systems retain fusogenicity for C/A ratios that differ by >0.6 and some system are fusogenic over the entire range of C/A ratios. For example, the amphoter I system DDAB/DMGS shows fusion from C/A>0 to C/A=0.5. The range of C/A ratios for which this system is fusogenic is about 0.5.
Preferred amphoteric mixtures of Table 23 are fusogenic at higher C/A ratios, preferably at C/A≧0.4, and more preferably at C/A ratios≧0.5, thus facilitating the encapsulation of higher amounts of polyanionic cargoes, such as nucleic acids.
In another embodiment of the invention, the amphoter I systems may form a second stable phase at an acidic pH of between pH 2 to pH 4 in addition to the aforementioned stable lamellar phase at pH 7 to pH 8. However, as described before a stable lamellar phase at low pH is not mandatory and, e.g., for the production of amphoteric liposomes and the encapsulation of cargo under acidic conditions large counter-anions may stabilize the lipid phase at this pH range.
Preferred fusogenic amphoter I systems comprising charged amphiphiles only and having stable lamellar phases at pH 7 to pH 8 and at pH 2 to pH 4 and fusing between pH 3 and pH 6, preferably between pH 4 and pH 6 may comprise the following specific mixtures (Table 24):
Versatile amphoter I systems of Table 14 are fusogenic over a wide range of C/A ratios, preferably over a range of C/A ratios of ≧0.4, and more preferably over a range of C/A ratios of ≧0.6.
Furthermore, preferred are the amphoteric mixtures of Table 24 above that are fusogenic at higher C/A ratios, preferably at C/A≧0.4, and more preferably at C/A ratios≧0.5.
Amphoter II Systems Comprising Charged Amphiphiles OnlyAmphoter II systems comprise chargeable anions and chargeable cations and have therefore the advantage of being amphoteric over the entire range of anion:cation ratios. No charge overcompensation for the strong ion is needed as in Amphoter I or Amphoter III systems.
Amphoter II systems that are stable at pH 7 to pH 8 and fuse between pH 3 to pH 6, preferably between pH 4 to pH 6 may include mixtures of one or more cationic amphiphiles selected from MoChol, HisChol, Chim, MoC3Chol, DmC4Mo2, DmC3Mo2, C3Mo2, C5Mo2, C6Mo2, C8Mo2, C4Mo4, DOIM or DPIM with one or more anionic amphiphile selected from diacylglycerol succinates, like DOGS, DMGS, POGS; diacylglycerolmalonates, like DOGM or DMGM; diacylglycerolglutarates, e.g. DOGG, DMGG; diacylglyceroladipates, e.g. DOGA, DMGA; 4-{(1,2-Diacyl-ethyl)amino}-4-oxo acids, e.g. DOAS, DOAM, DOAG, DOAA, DMAS, DMAM, DMAG, DMAA; Diacyl-alkanoic acids, like DOS, DOM, DOG, Chems and derivatives thereof, e.g. Chol-C3, Chol-C5 or Chol-C6; fatty acids.
In one embodiment of the invention, the cationic amphiphiles are selected from MoChol, HisChol, Chim, MoC3Chol, DmC4Mo2, DmC3Mo2, C3Mo2, C5Mo2, C6Mo2, C8Mo2, C4Mo4, DOIM or DPIM and combined with anionic amphiphiles selected from Chems, DMGS, DMGM, DMGG, DMGA, DMAS, DMAM, DMAG, DMAA, DOGS, DOGM, DOGG, DOGA, DOAS, DOAM, DOAG, DOAA, DMS, DMM, DMG, DMA, DOS, DOM, DOG, DOA, Chol-C3, Chol-C5 or Chol-C6.
In some embodiments of the invention, amphoter II systems comprising charged amphiphiles only that are stable at pH 7 to pH 8 and fuse between pH 3 to pH 6, preferably between pH 4 to pH 6, are preferred (Table 25):
More versatile amphoter II systems of Table 25 are those that are fusogenic over a wide range of C/A ratios, thus allowing adjustment of the fusion pH without changing the chemistry of the system. Some versatile systems are fusogenic over C/A ratios that differ by ≧0.7, more versatile systems retain fusogenicity for C/A ratios that differ by ≧1 and some systems are fusogenic over the entire range of C/A ratios. For example, the amphoter I system DDAB/DMGS shows fusion from C/A>0 to C/A=0.5. The range of C/A ratios for which this system is fusogenic is about 0.5. For example, the mixture Chim/Chems may fuse between C/A>0 and C/A=1.5, resulting in a range of C/A ratios of >1.
Preferred amphoter II mixtures of Table 25 are fusogenic at higher C/A ratios, preferably at C/A≧0.7, and more preferably at C/A ratios≧1, thus facilitating the encapsulation of higher amounts of polyanionic cargoes such as nucleic acids.
In another embodiment of the invention, amphoter II systems may form a second stable phase at an acidic pH of between pH 2 and pH 4 in addition to the aforementioned stable lamellar phase at pH 7 to pH 8. However, as described before, a stable lamellar phase at low pH is not mandatory and, e.g., for the production of amphoteric liposomes and the encapsulation of cargo under acidic conditions, large counter-anions may stabilize the lipid phase at this pH range.
Further preferred are the following fusogenic amphoter II systems comprising charged amphiphiles only and having both a stable lamellar phase at pH 7 to pH 8 and at pH 2 to pH 4 and fusing between pH 3 and pH 6, preferably between pH 4 and pH 6 (Table 26):
Versatile amphoter II systems of Table 26 are fusogenic over a wide range of C/A ratios, preferably over a range of C/A ratios of ≧0.7, more preferably over a range C/A ratios of ≧1.
Furthermore, preferred are the amphoteric mixtures of Table 26 that are fusogenic at higher C/A ratios, preferably at C/A≧0.4, and more preferably at C/A ratios≧0.5.
Amphoter III Systems of Solely Charged AmphiphilesAmphoter III systems are characterized by a stable anion and a pH-sensitive cation. Thus amphoter III systems cannot form lipid salts at neutral pH, since little to no charged cationic lipid exists at this pH. Ongoing acidification is needed first to create the cation which then may undergo salt formation.
Amphoter III systems that are stable at pH 7 to pH 8 and fuse between pH 3 to pH 6, preferably between pH 4 to pH 6 may include mixtures of one or more cationic amphiphiles selected from MoChol, HisChol, Chim, MoC3Chol, DmC4Mo2, DmC3Mo2, C3Mo2, C5Mo2, C6Mo2, C8Mo2, C4Mo4, DOIM or DPIM with one or more anionic amphiphile selected from DOPA, DMPA, DPPA, POPA, DSPA, Chol-SO4, DOPG, DMPG, DPPG, POPG, DSPG or DOPS, DMPS, DPPS, POPS and DSPS.
Less preferred are amphoter III systems which do not show fusion owing to steric hindrance. One example that has been described above is the amphoter III system MoChol/POPG.
Preferred amphoter III systems comprising charged amphiphiles only that are stable at pH 7 to pH 8 and fuse between pH 3 and pH 6, preferably between pH 4 and pH 6 include the following specific mixtures (Table 27):
Among these amphoter III mixtures further preferred are the following mixtures having stable lamellar phase at pH 7 to pH 8 as well as stable phase at an acidic pH of between pH 2 and pH 4 (Table 28):
Neutral lipids comprise structures such as phosphatidylcholine, phosphatidyl ethanolamine, sphingolipids or cholesterol and the like. As these lipids do not have pH responsive elements that would react between pH 3 and 8, no changes in the molecular geometry occur in this range. Depending on the individual κ values of the neutral lipids, dilution of the bistable behaviour of the amphoteric lipid pair occurs and the steepness of d(κ)/d(pH) becomes smaller, as shown in
Thus, in some embodiments of the invention, 65 mol. % or less neutral lipids may be added to the salt forming charged lipids. More preferred are additions of 50 mol. % or less and even more preferred are additions of 35 mol. % or less neutral lipid. The addition of neutral lipids may stabilise further the lipid bilayer, and preferred lipids for such purpose have higher κ values, e.g., κ>0.4 or even about 0.5. Typical examples of such lipids are the phosphatidylcholines with C14 to C18 alkyl chains in the hydrophobic region. As with most polar regions of lipids, the head-groups of phosphatidylcholines recruit counterions.
The addition of neutral lipids may also extend the zone of fusogenic behaviour and to this end neutral lipids with low values of κ may be employed. Such preferred lipids have κ values of 0.3 or less; more preferred lipids have κ values of about 0.2. Typical examples of such lipids are phosphatidylethanolamines. Phosphatidylethanolamines are assumed to form internal salt bridges (betaine structures) between the terminal amino group and the phosphate; therefore no counterions are recruited to the head-groups.
Phosphatidylethanolamines with C14 to C18 alkyl chains are preferred lipids to modulated the fusogenicity of the amphoteric liposomes.
Cholesterol is another example of a lipid having low κ and might therefore extend the fusogenic behaviour of an amphoteric lipid system.
It is of course possible to use mixtures of different neutral lipids to optimize the balance between fusogenicity and stability of such systems.
In practical terms, the presence of neutral lipids in the membrane of amphoteric liposomes has an effect on the fusogenicity of the liposomes and may, as predicted by the presented algorithm of the present invention, improve or impair the fusion of the liposomes. It is apparent from the algorithm, that the nature of such effect is largely dictated by the relation between k(salt) of the amphoteric system and k(neutral), the membrane constant of the neutral lipid or a mixture of neutral lipids. If, for example k(salt), is higher than k(neutral), then the addition of such neutral lipids may stimulate fusion or expand the width of the fusion zone. Of course, k(total) has to reach a certain minimum for this. In some embodiments, such minimum is smaller than 0.34 or 0.35, more preferred smaller than 0.3 and even more preferred such minimum is smaller than 0.25.
Experimental evidence is given in Example 15 and
Neutral lipids may also have impact on other characteristics of amphoteric liposomes, such as colloidal stability or stability in body fluids. For example, the use of amphoteric liposomes in pharmaceutical applications requires stability of the liposomes during storage and travelling through the bloodstream.
It becomes apparent that the presence of phosphatidylcholines as single neutral lipid in the membrane of amphoteric lipid mixtures lowers the fusability of amphoteric lipid mixtures. Phosphatidylcholines are zwitterionic lipids having high k values of >0.4.
In one embodiment of the invention less than 40 mol %, preferably less than 30 mol % and more preferably less than 20 mol % of neutral or zwitterionic lipids with k>0.4 as single neutral component are present in the amphoteric lipid mix. Such neutral or zwitterionic lipids include, but are not limited to, phosphatidylcholines, sphingomyelins or ceramides.
Cholesterol as neutral lipid has either no effect on the fusogenicity of amphoteric lipid systems or may even lead to an improvement in fusability. Similar behaviour was observed for the lipid DOPE. Cholesterol and phosphatidylethanolamines are neutral or zwitterionic lipids that have k values below 0.3 and adopt hexagonal phases.
In a further embodiment of the invention, cholesterol or phosphatidylethanolamines or a mix of both lipids may be present in the amphoteric lipid mix as single neutral or zwitterionic lipids. Preferably not more than 65 mol %, more preferably not more than 50 mol %, of these lipids is used as single neutral or zwitterionic lipids in the amphoteric liposomes. In other embodiments of the present invention, where cholesterol is essentially the only neutral lipid, cholesterol may comprise more than 80 mol % of the total neutral lipids of the amphoteric liposomes described herein. In another embodiment, cholesterol is the only neutral lipid in the amphoteric liposomes.
For optimising the balance between fusogenicity and stability it may be advantageous to use a mix of neutral or zwitterionic lipids as neutral component in the amphoteric liposomes.
In a still further embodiment of the invention a mixture of neutral lipids, such as phosphatidylcholines (PC), sphingomyelins or ceramides and phosphatidylethanolamines (PE) or a mixture of phosphatidylcholines (PC), sphingomyelins or ceramides and cholesterol (Chol) may be used as neutral components in the amphoteric liposomes. Preferably the ratio of PC/PE or PC/Chol is between 4 and 0.25, more preferably between 3 and 0.33. These neutral lipid mixes may be added to the salt-forming charged lipids in the amount 80 mol % or less, preferably 65 mol % or less. Most preferred are additions of 50 mol % or less.
It has also been found that neutral lipids may extend fusability to further C/A ratios as compared to mixture solely of charged amphiphiles. For example, the addition of 40 mol % POPC/DOPE=0.33 to a HisChol/DOGS mixture leads to an extension of the range of fusogenicity from C/A=>0-0.7 to C/A=>0-1. Similarly, the addition of 40 mol % cholesterol expands the C/A ratio of DOTAP/Chems for fusion to occur from C/A=>0-0.4 to C/A=>0-0.67.
In summary, the algorithm disclosed herein is suitable to describe phase transitions in amphoteric liposomes. Essential elements of the algorithm are (i) the lipid shape theory, (ii) the notion that counterions form part of the head-group volume and (iii) that lipid salt formation may occur in bilayers, leading to dissociation of the counterions. The simplicity of the algorithm makes it easy for the person skilled in the art to reproduce the calculations and adopt the system to the individual goals. It is possible to use other tools well-known to those skilled in the art than indicated to calculate molecular volumes. The qualitative prediction would not even change if molecular cross-sections were used instead of the volumes. Of course, one would have to re-calibrate the results in such a case.
As mentioned above, steric hindrance may interfere with salt formation in isolated cases. In such cases, the phase behaviour may differ substantially from what has been hereinbefore described. Most importantly, no dual stability at low and neutral pH is observed. Instead, a saddle of stability is observed for an intermediate pH with zones of instability to one or either side, depending on the type of amphoter system. Typical examples are included into the examples below.
The molecular volume calculations disclosed herein are silent on chain saturation in the hydrophobic parts. Use of unsaturated lipids may have specific advantages, since lipid membranes comprising such lipids have higher fluidity at ambient temperature which may improve fusion behaviour. It is also known that unsaturated lipids exert lateral pressure in the membrane, thus a correction factor can be inserted to reflect the apparent volume of these components. Such correction factor is higher than 1.
The algorithm of the present invention assumes the formation of lipid salts with a 1:1 stoichiometry between the two charged partners. It is possible to extend this concept to more complex situations, e.g., binding of multiple, monocharged lipids to a single other lipid with a plurality of charged groups. Binding of CHEMS, DOGS or oleic acid to amphiphilic derivatives of spermin may provide an example of this, but many other combinations exist. In another embodiment, the charged groups on the lipids might be more complex and comprise different charged groups, e.g., as in HistChol.
In such a case, 1:1 complexes might be formed with either other lipid anions or cations. Applying the concept of this invention to this example, counterion displacement can occur between the imidazolium cation and a separate lipid anion, e.g., CHEMS, DOGS or oleic acid anions; in addition, parallel counterion dissociation from the carboxyl of the histidine moiety may further support the formation of a hexagonal phase.
It will be apparent to those skilled in the art that such more complex arrangements of lipids put an extra burden on the steric compatibility of the interaction partners which may lead to lack of experimental success or mixed forms of possible interactions where not every possible binding site is engaged in salt formation.
The methods disclosed herein substantially reduce the number of variables involved with the optimisation of the system.
The present invention has been exemplified with various calculations in the detailed description. Further experimental work is described in the following examples. Examples are given with the understanding of further detailing certain aspects of practising the current invention. The examples by no means limit the scope of this disclosure.
EXAMPLES Example 1 Preparation of Liposomes and pH-Dependent Fusion ExperimentBuffer System 100 mM sodium citrate and 200 mM sodium hydrogen phosphate were prepared as stock solutions and variable amounts of both solutions were mixed to adjust for the pH needed. CiP 7.0 as an example specifies a buffer from that series having a pH of 7.0 and is made from citrate and phosphate.
Liposome ProductionLiposomes were formed from a dried lipid film. In brief, 20 μmol of the respective lipid composition was dissolved in 1 mL chloroform/methanol 3:1 and dried in vacuum using a rotary evaporator. The resulting film was hydrated for 45 min in 1 mL of CiP 8.0 with gentle agitation. The resulting liposome suspension was frozen, sonicated after thawing and eventually extruded through 200 nm polycarbonate filters.
pH-Jump Experiment
10 μl liposomes in CiP 8.0 were placed into a glass tube and mixed rapidly with 1 mL of CiP buffer of the pH needed. Samples were allowed to stand for 1 h at room temperature and 3 mL of 200 mM sodium hydrogen phosphate were rapidly mixed with the sample. Liposomes were analyzed for size using a MALVERN Zetasizer 3000HS and sizes were recorded as Z-average.
Example 2 Fusion of Amphoter I Lipid MixturesLiposomes were prepared from DOTAP and CHEMS in sodium citrate/sodium phosphate pH 8.0 (CiP 8.0) and small amounts were injected into a CiP buffer with a lower pH (see Example 1 for details). Any larger structures observed at the lower pH might be either due to aggregate formations and generation of multicentric honeycomb structures or such structures might result from genuine fusion. To separate between these two outcomes we readjusted the pH to neutrality using 200 mM sodium hydrogen phosphate. Electrostatic repulsion dissociates multicentric vesicles but not fusion products. The results are illustrated in
As predicted in the mathematical salt bridge model, a valley of instability exists at slightly acidic conditions and fusion to larger particles was observed starting from pH 6.5. However, fast addition of the liposomes into low pH resulted in stabilisation of the particles as long as some DOTAP was present in the mixture. Liposomes from 100 mol. % CHEMS enter a fusogenic state below pH 4.5 and do not get stabilised at the lower pH.
Noteworthy, a 1:1 mixture of DOTAP/CHEMS cannot form liposomes in CiP 8.0 which is in good agreement with the mathematical model that predicts a non-lamellar phase for these parameters.
Example 3 Fusion of Amphoter II SystemsLiposomes were prepared from MoChol and CHEMS in sodium citrate/sodium phosphate pH 8.0 (CiP 8.0) and small amounts were injected into a CiP buffer with a lower pH (see Example 1 for details). Any larger structures observed at the lower pH might be either due to aggregate formations and generation of multicentric honeycomb structures or such structures might result from genuine fusion. To separate between these two outcomes we readjusted the pH to neutrality using 200 mM sodium hydrogen phosphate. Electrostatic repulsion dissociates multicentric vesicles but not fusion products.
Experimental evidence supports the salt bridge model. (See
The parameters used for the calculation are given in Table 30 below; CHEMS and MoChol in Na/H2PO4 were used as model compounds; all volumes in Å3.
Liposomes were prepared from POPG and MoChol in sodium citrate/sodium phosphate pH 8.0 (CiP 8.0) and small amounts were injected into a CiP buffer with a lower pH (see Example 1 for details). Any larger structures observed at the lower pH might be either due to aggregate formations and generation of multicentric honeycomb structures or such structures might result from genuine fusion. To separate between these two outcomes we readjusted the pH to neutrality using 200 mM sodium hydrogen phosphate. Electrostatic repulsion dissociates multicentric vesicles but not fusion products.
Experimental evidence supports only a situation where no salt bridge formation occurs. A mixture between MoChol and POPG does not undergo fusion in the pH-jump experiment (data not shown). This is quite possibly due to steric hindrance, as the protonated nitrogen in Mo-Chol is situated at the lower end of the morpholino ring and is therefore not easily accessible. In addition, the phosphate in POPG sits right at the lipid/water interface and is protected with a glycerol towards the water phase.
Example 5 Fusion in Amphoter III Systems, No Steric HindranceAmphoter III systems from POPG/MoChol do not undergo fusion (see Example 4 above). It was therefore questioned whether the removal of the protecting glycerol and exchange of POPG with DOPA would avoid such steric hindrance. In fact, such system undergoes fusion, as illustrated in the
Details as per Example 1 above. The parameters used for the calculation are given in Table 31 below; DOPA and MoChol in Na/H2PO4 were used as model compounds, and volumes are expressed as Å3.
The model calculation reflects the full complexity of the experimental fusion behaviour: no fusion for mixtures with less than 50% MoCHol, strong fusion for MoChol=DOPA and ongoing fusion with no stable phase under acidic conditions for mixtures with excess DOPA.
Example 6 Lipid Salt Formation with Monoalkyl LipidsOleic acid was chosen as a known and popular pH-sensitive membrane component. As the lipid tail is relatively small in volume, any change in the head-group has more pronounced consequences for the membrane stability. As shown in
DOTAP and CHEMS were chosen as an amphoter I charged lipid pair and POPC (κ ˜0.5) was added as a neutral lipid. As expected, the pure mixture of the charged components undergoes aggregation or fusion at and below the isoelectric point. However, as shown in
As shown in
In order to investigate the impact of different cations on the fusion behaviour of an amphoter I system, lipid films were prepared from 20 mol % DOTAP and 80 mol % CHEMS. A set of buffers was created starting from 20 mM citric acid and 40 mM phosphoric acid which were neutralized using KOH, NaOH, LiOH, Tris-(hydroxymethyl)aminomethane (TRIS, free base) or L-Arginine (free base).
The lipid films were hydrated at pH 8.0 and small amounts were injected into corresponding buffers with a lower pH (see Example 1 for details). After one hour incubation, the pH was readjusted to neutrality using the corresponding bases. The results are illustrated in
As predicted in the model, fusion of liposomes from 20 mol % DOTAP and 80 mol % CHEMS can be observed around pH 4 to 5 as long as rather small countercations like potassium or sodium are used. Larger countercations like L-arginine or TRIS effectively stabilize the formulation and reduce or completely suppress fusion of the liposomes.
Example 9 Large Countercations can Reduce Fusion in Amphoter II SystemsIn order to investigate the impact of different cations on the fusion behaviour of amphoter II systems, lipid films were prepared from 20 mol % MoCHOL and 80 mol % CHEMS. A set of buffers was created starting from 20 mM citric acid and 40 mM phosphoric acid which were neutralized using KOH, NaOH, LiOH, Tris-(hydroxymethyl)aminomethan (TRIS, free base) or L-Arginine (free base).
The lipid films were hydrated at pH 8.0 and small amounts were injected into corresponding buffers with a lower pH (see Example 1 for details). After one hour incubation, the pH was readjusted to neutrality using the corresponding bases. The results are illustrated in
As predicted in the model, fusion of liposomes from 20 mol % MoChol and 80 mol % CHEMS can be observed between pH 3.5 to 4.5 as long as rather small countercations like potassium or sodium are used. Larger countercations like L-arginine or TRIS effectively stabilize the formulation and reduce or completely suppress fusion of the liposomes.
Example 10 Countercations have Little or No Effect on Fusion in Amphoter III SystemsIn order to investigate the impact of different cations on the fusion behaviour of amphoter III systems, lipid films were prepared from 50 mol % MoCHOL and 50 mol % DOPA. A set of buffers was created starting from 20 mM citric acid and 40 mM phosphoric acid which were neutralized using KOH, NaOH, LiOH, Tris-(hydroxymethyl)aminomethan (TRIS, free base) or L-Arginine (free base).
The lipid films were hydrated at pH 8.0 and small amounts were injected into corresponding buffers with a lower pH (see Example 1 for details). After one hour incubation, the pH was readjusted to neutrality using the corresponding bases. The results are illustrated in
As predicted in the model, fusion of liposomes from 50 mol % MoChol and 50 mol % DOPA can be observed between pH 3.5 to 5 and there is little impact of the various cations on an amphoter III system. This is expected from the model, since MoCHOL and DOPA form a lipid salt at low pH conditions, thereby excluding countercations from the membrane. Consequently, once excluded from the lipid membrane, the countercations cannot contribute to membrane stability or instability.
Example 11 Fusion Assay Based on Fluorescence Resonance Energy Transfer (FRET)To investigate the fusability of different amphoteric lipid mixtures a lipid mixing assay, based on FRET was used. Liposomes, single labelled with 0.6 mol % NBD-PE (N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-1,2-dihexadecanoyl-sn-glycero-3-phosphoethanol-amine, triethylammonium salt) or Rhodamine-PE (Lissamine™ rhodamine B 1,2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine, triethylammonium salt), respectively, were prepared to monitor lipid fusion through the appearance of a FRET signal.
Lipids were dissolved in isopropanol (final lipid concentration 16 mM) and mixed. Liposomes were produced by adding buffer (acetic acid 10 mM, phosphoric acid 10 mM, NaOH, pH 7.5) to the alcoholic lipid mix, resulting in a final lipid concentration of 1.95 mM and a final isopropanol concentration of 12.2%. For the preparation of the liposomes a liquid handling robot (Perkin Elmer, Multiprobe II Ex) was used. The NBD-labelled and Rh-labelled amphoteric liposomes were combined in a ratio 1:1 and subsequent diluted 1:1 with the buffer mentioned above. Finally small aliquots of this mixed sample were brought to decreasing specific pH (HAc 50 mM, Phosphoric acid 50 mM, NaOH, pH 7.5-2.5) and incubated at 37° C. for 2 h. Liposomes were diluted again 1:1 in this step.
Samples were measured for fluorescence using two sets of filters: NBD/Rhodamine: 460/590 nm and NBD/NBD: 460/530 nm. FRET as a signal for membrane fusion was expressed as the ratio of emission (590 nm)/emission (530 nm). A background of 0.4 indicates background fluorescence and was therefore subtracted from the FRET signals.
To discriminate between fusion and mere aggregation the suspension was neutralized to pH 7.5 and FRET signals were measured again. A possible interference of the remaining alcohol content of 3% on the fusion of the liposomes was excluded by pre-experiments.
Example 12 Fusion Assay of Amphoter I Lipid Mixtures Comprising Solely Charged AmphiphilesFusion assays were performed as described in Example 8. Lipid pairs as indicated in Table 33 were tested for fusion in cation/anion molar ratios (C/A ratio) of 0.17, 0.33, 0.40, 0.50, 0.67, 0.75 and pure anionic liposomes were prepared as controls.
Table 33 shows the lipid pairs tested in the experiment. For each lipid pair, the ranges of C/A ratios for which stability at pH 7 to pH 8 and fusion between pH 4 to pH 6 was observed are included in the table. In addition, for each lipid pair, the ranges of C/A ratios having a stable lamellar phase both at pH 7 to pH 8 and at pH 2 to pH 4 and fusion between pH 4 to pH 6 are shown.
The fusion can be expressed as Σ FRET, the sum of all measured FRET signals of the complete matrix C/A=0.17-0.75 vs. pH.
The following Tables 34 a-d show the fusion profiles for tour selected amphoter I systems as matrix C/A vs. pH. In addition the fusion of liposomes of pure anionic lipid is shown (C/A=0). For example, it is known that liposomes of 100% Chems fuse at a pH of about 4.2 (Hafez et al, Biophys. J., 79, (2000), 1438-1446). This is confirmed by the present experiment. In addition the fusion profiles show the amphoter I mixtures having a stable lamellar phase both at pH 7 to pH 8 and at pH 2 to pH 4 and fuse between pH 4 to pH 6.
A fusion assay was performed as described in Example 8. Lipid pairs as indicated in Table 35 were tested for fusion in cation/anion molar ratios (C/A ratio) of 0.33, 0.5, 0.67, 1, 1.5, 2, 3 and pure anionic liposomes were prepared as controls.
Table 35 shows the lipid pairs tested in the experiment. For each lipid pair the ranges of C/A ratios for which stability at pH 7 to pH 8 and fusion between pH 4 to pH 6 was observed are included in the table. In addition, for each lipid pair the ranges of C/A ratios having a stable lamellar phase both at pH 7 to pH 8 and at pH 2 to pH 4 and fuse between pH 4 to pH 6 are shown.
The fusion can be expressed as Σ FRET, the sum of all measured FRET signals in the matrix C/A=0.33-3 vs. pH.
The following Tables 36 a-d show exemplary the matrix of the fusion profile for four selected amphoter II systems. In addition the fusion of liposomes of pure anionic lipid is shown (C/A=0). The fusion profiles indicate the amphoter II mixtures having a stable lamellar phase both at pH 7 to pH 8 and at pH 2 to pH 4 and fuse between pH 4 to pH 6.
Fusion assays were performed as described in Example 8. Lipid pairs as indicated in Table 37 were tested for fusion in cation/anion molar ratios (C/A ratio) of 1.5, 2, 3.
Table 37 shows the lipid pairs tested in the experiment. For each lipid pair the ranges of C/A ratios for which stability at pH 7 to pH 8 and fusion between pH 4 to pH 6 was observed are included in the table. In addition for each lipid pair the ranges of C/A ratios having a stable lamellar phase both at pH 7 to pH 8 and at pH 2 to pH 4 and fuse between pH 4 to pH 6 are shown.
The following Tables 37 a-d show by way of example the matrix of the fusion profile for the four tested amphoter III systems. In addition the fusion of liposomes of pure anionic lipid is shown (C/A=0). The fusion profiles indicate the amphoter III mixtures having a stable lamellar phase both at pH 7 to pH 8 and at pH 2 to pH 4 and fuse between pH 4 to pH 6. As described in Example 4 a mixture between MoChol and POPG does not undergo fusion owing to steric hindrance. This can be observed in the present FRET experiment as well. The same might be the case for the lipid pair MoChol/CholSO4.
Amphoteric liposomes with increasing amounts of neutral or zwitterionic lipids were prepared as described in Example 8.
Initially, an amphoter I system (DOTAP/DMGS) and an amphoter II (MoChol/DOGS) were prepared with the addition of 10-50% different neutral or zwitterionic lipids or mixtures thereof. Fusion was measured for a series of liposomes having different C/A ratios. Systems can be characterized using the sum of all such measurements in the entire matrix. The effect of the neutral or zwitterionic lipids was then analyzed using this global parameter (Σ FRET).
In a further experiment the effect of different neutral or zwitterionic lipid systems (POPC, cholesterol or POPC/DOPE=0.33) on the fusogenicity of other amphoteric lipid systems were determined. Tables 38 and 39 summarize these data and confirm the results of the first part of the experiment. Tables 38 and 39 show the Σ Fret and range of C/A ratios for which the amphoteric liposomes are stable at pH 7 to pH 8 and fuse between pH 3 to pH 6, preferably between pH 4 to pH 6.
It becomes apparent that amphoteric lipid systems having low fusogenicity can be clearly improved by the addition of neutral or zwitterionic lipids. Furthermore the results indicate that neutral or zwitterionic lipids may have also an impact on the range of fusogenicity. This means that the range of C/A ratios can be broadened or narrowed depending on the neutral or zwitterionic lipid used in the mixtures.
A. Synthesis of 2,3-Dimethylsuccinic-anhydride
2,3-Dimethyl succinic anhydride was prepared as described in Sutton, et al. OPPI 24 (1992) 39. Briefly, 7.1 g 2,3-dimethyl succinic acid and 6.9 ml acetanhydride were slowly heated up to 50° C. for 3 hours. Then acetanhydride was removed by distillation. The product was recrystallized from ethanol abs. and characterized by the melting point.
B. Synthesis of 2,3-Dimethylsuccinicacid-monocholesterylester
2,3-Dimethylsuccinic acid-monocholesterylester was prepared according to the Chems synthesis in J. T. Kley et al., Monatshefte Chem 129 (1998) 319. 2.9 g 2,3-dimethylsuccinic-anhydride, 6.3 ml triethylamine, 0.06 g dimethylaminopyridine and 50 ml chloroform were combined in a round-bottomed flask and refluxed. 7.8 g cholesterol was added to the mixture in two steps during 45 min. The mixture was refluxed for 6 days. Finally the solvent was evaporated and 100 ml toluol and 1.8 g pyridine were added. The mixture was refluxed again for 1.5 days. The solvent was removed at a rotovap and the crude product was first purified by column chromatography on silica gel (eluent: dichloromethane/methanol 96:4) followed by a recrystallization from ether and a second column chromatography on silica gel (eluent: acetic acid ethyl ester:petrol ether 1:1). Purity of the product was judged by thin layer chromatography.
Synthesis of DmC4Mo25.9 g 2,3-Dimethylsuccinic acid-monocholesterylester and 300 ml tetrahydrofurane were stirred under N2 atmosphere and cooled down to −10° C. 1.9 ml N-methylmorpholine was added to the mixture. Then 1.6 ml isobutylchloroformiate was added dropwise to the mixture. After on hour the mixture was brought to 0° C. and about 2 hours later to room temperature. Then the mixture was again cooled down to −10° C., 1.5 ml 4-(2-Aminoethyl)morpholine was added dropwise and the reaction was allowed to stir overnight at room temperature. The mixture was filtered, then the solvent was evaporated and the product was purified by column chromatography on silica gel (eluent: dichloromethane/methanol 96:4) and recrystallization from hexane. The product was characterized by thin layer chromatography, 1H-NMR and HPLC.
Synthesis of DmC3Mo2A. Synthesis of 2,2-Dimethyl-malonic acid monoethyl ester
25 g 2,2-Dimethyl-malonic acid diethyl ester, 7.8 g potassium hydroxide and 500 ml ethanol were mixed in a round-bottomed flask and refluxed for 3 hours. Then again 2.2 g potassium hydroxide were added and the mixture was refluxed overnight. The solvent was removed on a rotovap, 250 ml H2O were added and the mixture was washed with ether. The aqueous phase was acidified with HCl to pH 3-4 followed by two extractions with dichloromethane. The organic solvent was dried and evaporated and the resulting product was characterized by 1H-NMR.
B. Synthesis of 2,2-Dimethyl-N-(2-morpholin-4-yl-ethyl)-malonamic acid ethyl ester
19 g 2,2-Dimethyl-malonic acid monoethyl ester were weighed into a round-bottomed flask and under N2 atmosphere and room temperature, 200 ml tetrahydrofurane, 15.6 ml 4-(2-Aminoethyl)-morpholine and 32.6 ml N-Methylmorpholine were added. The reaction was stirred and cooled down to 5° C. Then, 43.8 g TBTU were added and the mixture was allowed to stir for another 1.5 hours. Finally the solvent was removed and the residue dissolved in 400 ml dichloromethane. This organic phase was washed two times with 500 ml NaHCO3 solution. The dichloromethane phase was dried then the solvent was evaporated. Purity of the product was judged by gas chromatography.
C. Synthesis of 2,2-Dimethyl-N-(2-morpholin-4-yl-ethyl)-malonamic acid (HCl salt)
34.1 g 2,2-Dimethyl-N-(2-morpholin-4-yl-ethyl)-malonamic acid ethyl ester, 8.4 g potassium hydroxide, 200 ml ethanol and 4.5 ml H2O were stirred at 80° C. for 6 hours. Then most of the solvent was removed and the pH was adjusted to pH 3-4 with about 100 ml 2N HCl. The solvent was evaporated and toluol was added and then removed. To the final residue methanol was added and the suspension was filtered to remove salts. The solvent was removed and the residue was dissolved in H2O and lyophilized. The product was characterized by 1H-NMR.
C. Synthesis of DmC3Mo2
10.7 g 2,2-Dimethyl-N-(2-morpholin-4-yl-ethyl)-malonamic acid (HCl salt) and 50 ml toluol were combined in a round-bottomed flask under N2 atmosphere. Then 13.9 ml thionyl chloride were added and the solution was refluxed for 3 hours. The solvent was evaporated and 150 ml chloroform were added to the residue. After the addition of 14.7 g cholesterol and 0.023 g 4-Dimethylaminopyridine the mixture was stirred at room temperature and 15 min later 10.7 ml triethylamine were added. The reaction was allowed to stir at room temperature for 1.5 days. Then the solvent was removed at a rotovap and the crude product was dissolved in 100 ml acetic acid ethyl ester and subsequent purified by column chromatography on silica gel (eluent: acetic acid ethyl ester/methanol 9:1) and recrystallization from ether. The final product was characterized by 1H-NMR and HPLC.
Synthesis of C3Mo3A. Synthesis of Malonic Acid Monochloride
Malonic acid monochloride was synthesized as described in Wilson, et al., J. Org. Chem 39 (1974) 3170. Briefly, 150 g malonic acid and 600 ml ether were added under N2 atmosphere in a round bottom flask. The mixture was stirred and 150.2 ml thionyl chloride were added dropwise. The suspension was refluxed for 5 hours before the solvent was removed at a rotovap. The residue was treated three times under sonication and 40° C. with 500 ml chloroform:hexane 1:2. The three extracts were combined and kept at −15° C. over night. The mother liquor was decanted and the yellow crystals were washed with hexane and dried. The mother liquor was concentrated and again kept at −15° C. resulting in further product.
B. Synthesis of Malonic Acid Mono Cholesteryl Ester
26 g cholesterol and 12.4 g malonic acid monochloride were weighed into a round bottom flask under N2 atmosphere. First 300 ml benzene were added and subsequent 11 ml pyridine dropwise. The mixture was stirred at room temperature and after one hour 100 ml chloroform were added. 3 hours later the mixture was sonicated for 40 min and subsequent again 100 ml chloroform were added and the mixture was further stirred for 0.5 days at room temperature. Then 250 ml H2O and 100 ml chloroform were added to the mixture. The organic phase was dried and the solvent was removed at a rotovap. The crude product was dissolved in 100 ml dichloromethane/methanol 9:1 and subsequent purified by column chromatography on silica gel (eluent: dichloromethane/methanol 9:1) and recrystallization from ether and petrol ether. The final product was characterized by 1H-NMR.
C. Synthesis of C3Mo3
6 g Malonic acid mono cholesteryl ester was weighed into a round bottom flask and under N2 atmosphere and at room temperature, 200 ml tetrahydrofurane, 2.2 ml 4-(2-Aminopropyl)-morpholine and 2.8 ml N-Methylmorpholine were added. The mixture was stirred and cooled down to 0° C. Then, 8.2 g TBTU were added stepwise and the reaction was allowed to stir at room temperature for 1 day. The suspension was pre-purified by filtering the mixture through a frit filled with silica gel (eluent: acetic acid ethyl ester/methanol 1:1). Finally the crude product was purified by column chromatography on silica gel (eluent: chloroform/methanol 9:1) and the resulting product was characterized by 1H-NMR and LC-MS.
Synthesis of C3Mo26 g Malonic acid mono cholesteryl ester was weighed into a round bottom flask and under N2 atmosphere and at room temperature, 200 ml Tetrahydrofuran, 2.0 ml 4-(2-Aminoethyl)-morpholine and 2.8 ml N-Methylmorpholine were added. The mixture was stirred and cooled down to 0° C. Then, 8.2 g TBTU were added stepwise and the reaction was allowed to stir at room temperature for 2 days. The suspension was pre-purified by filtering the mixture through a frit filled with silica gel (eluent: acetic acid ethyl ester/methanol 1:1). Finally the crude product was purified by chromatography on silica gel (1. chromatography→eluent: chloroform/methanol 9:1; 2. chromatography→eluent: chloroform/0-3% methanol). The resulting product was characterized by 1H-NMR and LC-MS.
Synthesis of C4Mo4A. Synthesis of 4-Morpholin-4-yl-butyronitrile
196.9 ml morpholine, 500 ml toluol and 100 ml chloroform were stirred in a round-bottomed flask under N2 atmosphere and at 80° C. After one hour 100 g 4-chlorobutyronitrile was added dropwise within one hour. The reaction was stirred one day at 80° C. and another day at room temperature. The mixture was fritted and the residue was washed two times with ether. The filtrate was concentrated and finally distilled under vacuum. The product fractions were collected at 95-100° C. and 1.2-0.89 Torr. The purity of the colourless oil was judged by gas chromatography and 1H-NMR.
B. Synthesis of 4-Morpholin-4-yl-butylamine
14.8 g lithium aluminium hydride were weighed under N2 atmosphere into a round-bottomed flask. The substance was cooled down to −55° C. and 150 ml ether was added dropwise. The suspension was allowed to stir; then 30 g 4-Morpholin-4-yl-butyronitrile were dissolved in 200 ml ether and the solution was added dropwise to the reaction mixture. Again 200 ml ether were added to the mixture and the reaction was stirred at room temperature overnight. At the next day the mixture was cooled down to less than 10° C. and 35 ml H2O were added carefully. After five hours the mixture was fritted and the residue was washed with 300 ml ether. The filtrate was dried, concentrated and finally distilled under vacuum. The product fractions were collected at 74-78° C. and 2.1-1.6 Torr. The purity of the colourless oil was judged by gas chromatography, GC-MS and 1H-NMR.
C. Synthesis of C4Mo4
9.7 g cholesterol hemisuccinate were dissolved in 100 ml tetrahydrofurane and stirred under N2 atmosphere and at −15° C. Then 3.3 ml N-Methylmorpholine were added dropwise within 10 min followed by the slow addition of 2.9 ml isobutyl chloroformate. Then 3.2 g 4-Morpholin-4-yl-butylamine were added dropwise. The temperature was raised to room temperature and the reaction was allowed to stir for 2.5 hours. The mixture was fritted and the residue was washed with 20 ml tetrahydrofurane. The solvent of the filtrate was evaporated and to the residue 100 ml boiling acetic acid ethyl ester was added. After a further filtration the mixture was kept at room temperature for 2.5 days. The solvent was again removed and the crude product was purified by column chromatography on silica gel (eluent: dichloromethane/methanol 96:4 and 83:17). The product was characterized by thin layer chromatography and 1H-NMR.
Synthesis of C5Mo2A. Synthesis of Pentanedioic Acid Mono Cholesteryl Ester
35 g cholesterol and 15.5 g glutaric anhydride were weighed into a round-bottomed flask. Under N, atmosphere 500 ml chloroform, 25.4 ml triethylamine and 0.22 g 4-dimethylamino pyridine were added. The reaction was refluxed for 5 days. Then 250 ml H2O were added and the pH was adjusted under stirring to pH 4-5 with 2N HCl. The organic phase was dried and finally evaporated. To the residue again 31 g glutaric anhydride were added together with 250 ml toluol, 22.1 ml pyridine and 0.22 g 4-dimethylamino pyridine. The mixture was allowed to reflux for 1 day. Then the solvent was evaporated and the residue was dissolved in dichloromethane/acetic acid ethylester (96:4) and purified by a frit on silica gel (eluent: dichloromethane/methanol 94:4). After further purification by column chromatography on silica gel (eluent: product was characterized by 1H-NMR and thin layer chromatography.
B. Synthesis of C5Mo2
Under N2 atmosphere 6 g pentanedioic acid mono cholesteryl ester were dissolved in 250 ml tetrahydrofurane. 2.8 ml 4-(2-Aminoethyl)morpholin and 2.6 ml N-Methylmorpholin were added and the mixture was cooled down to 10° C. Finally 7.7 g TBTU were added stepwise and the reaction was allowed to stir at room temperature for one day followed by an incubation at 4° C. for 3 days. Then the solvent was evaporated and the crude product was purified by column chromatography on silica gel and characterized by 1H-NMR.
Synthesis of C6Mo2A. Synthesis of Oxepane-2,7-dione
100 g adipinic acid and 100 ml acetanhydride were refluxed for 5 hours. The solvent was removed at a rotovap and 100 ml acetonitrile were added to the residue and the mixture was kept in a freezer over night. Then the mixture was fritted and the resulting residue was washed with 50 ml acetonitrile and dried.
B. Synthesis of Hexanedioic Acid Mono Cholesteryl Ester
65 g cholesterol and 33 g oxepane-2,7-dione were weighed into a round-bottomed flask. Under N2 atmosphere 300 ml toluol, 21.2 ml pyridine and 0.21 g 4-dimethylamino pyridine were added. The reaction was refluxed for 2 days. Then the solvent was evaporated and the residue was dissolved in dichloromethane/acetic acid ethylester (96:4) and purified by a frit on silica gel (eluent: dichloromethane/acetic acid ethyl ester (96:4). The product was characterized by 1H-NMR and thin layer chromatography.
C. Synthesis of C6Mo2
Under N2 atmosphere 10 g hexanedioic acid mono cholesteryl ester were dissolved in 250 ml tetrahydrofurane. 3.1 ml 4-(2-Aminoethyl)morpholin and 3.2 ml N-Methylmorpholin were added and the mixture was cooled down to 10° C. After the addition of further 100 ml tetrahydrofurane 9.4 g TBTU were added stepwise and the reaction was allowed to stir at room temperature overnight. Then the solvent was evaporated and the crude product was purified by column chromatography on silica gel (eluent: chloroform/0-5% methanol) and characterized by 1H-NMR, thin layer chromatography and LC-MS.
Example 17 Amphoteric Liposomes Encapsulating siRNAsiRNA-loaded amphoteric liposomes were manufactured using non-targeting scrambled siRNA. The lipid mixtures A (DC-Chol:DMGS:Chol, 26:39:35 mol %) or B (DC-Chol:DMGS:Chol, 20:40:40 mol %) were dissolved at a concentration of 30 mM or 60 mM (final lipid concentration) for both mixtures in ethanol. Appropriate volumes of siRNA stock were diluted in 20 mM NaAc, 300 mM Sucrose/NaOH pH 4.0. The organic and the aqueous solution were mixed in a 3:7 ratio and the liposomal suspension was immediately shifted to pH>7.5 with 136 mM Na2HPO4, 100 mM NaCl.
The amount of unencapsulated siRNA was determined by using ultrafiltration with Centrisart (Molecular Weight Cut off 300 kD (Sartorius, Göttingen, Germany)). The siRNA concentration of the filtrate was measured spectroscopically (OD260 nm). The amount of encapsulated oligonucleotide was determined by subtraction of unencapsulated amount of siRNA from the total amount of siRNA.
Particle characteristics after manufacturing:
It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.
Claims
1. An amphoteric liposome formulation comprising a cationic amphiphile, an anionic amphiphile, and one or more neutral amphiphiles.
2. The amphoteric liposome formulation of claim 1, wherein the cationic amphiphile is selected from the group consisting of 4-(2-aminoethyl)-morpholino-cholesterol-2,3-dimethylhemisuccinate (DmC4Mo2), 4-(2-aminoethyl)-morpholino-cholesterol-2,3-dimethylhemimalonate (DmC3Mo2), 4-(2-aminobutyl)-morpholino-cholesterol-hemisuccinate (C4Mo4), 4-(2-aminopropyl)-morpholino-cholesterol-hemimalonate (C3Mo3), 4-(2-aminoethyl)-morpholino-cholesterol-hemimalonate (C3Mo2), 4-(2-aminoethyl)-morpholino-cholesterol-hemiglutarate (C5Mo2), 4-(2-aminoethyl)-morpholino-cholesterol-hemiadipate (C6Mo2), 4-(2-aminoethyl)-morpholino-cholesterol-hemiadipate (C8Mo2), 4-(2-Aminoethyl)-Morpholino-Cholesterolhemisuccinate (MoChol), Cholesterol-(3-imidazol-1-yl propyl)carbamate (CHIM), and Histaminyl-Cholesterolhemisuccinate (HisChol).
3. The amphoteric liposome formulation of claim 1, wherein the anionic amphiphile is selected from the group consisting of cholesterol hemisuccinate CHEMS, Dimyristoylglycerolhemisuccinate DMGS, Dimyristoylglycerolhemimalonate DMGM, Dimyristoylglycerolhemiglutarate DMGG, Dimyristoylglycerolhemiadipate DMGA, 4-((1,2-Dimyristoyl-ethyl)amino)-4-oxobutanoic acid DMAS, 4-((1,2-Dimyristoyl-ethyl)amino)-4-oxopropanoic acid DMAM, 4-((1,2-Dimyristoyl-ethyl)amino)-4-oxopentanoic acid DMAG, 4-((1,2-Dimyristoyl-ethyl)amino)-4-oxohexanoic acid DMAA, Dioleoylglycerolhemisuccinate DOGS, Dioleoylglycerolhemimalonate DOGM, Dioleoylglycerolhemiglutarate DOGG, Dioleoylglycerolhemiadipate DOGA, 4-((1,2-Dioleoyl-ethyl)amino)-4-oxobutanoic acid DOAS, 4-((1,2-Dioleoyl-ethyl)amino)-4-oxopropanoic acid DOAM, 4-((1,2-Dioleoyl-ethyl)amino)-4-oxopentanoic acid DOAG, 4-((1,2-Dioleoyl-ethyl)amino)-4-oxohexanoic acid DOAA, 5,6-Dimyristoyl-hexanoic acid DMS, 4,5-Dimyristoyl-pentanoic acid DMM, 6,7-Dimyristoyl-heptanoic acid DMG, 7,8-Dioleoyl-octanoic acid DMA, 5,6-Dioleoyl-hexanoic acid DOS, 4,5-Dioleoyl-pentanoic acid DOM, 6,7-Dioleoyl-heptanoic acid DOG, 7,8-Dioleoyl-octanoic acid DOA, Cholesterolhemimalonate Chol-C3, Cholesterolhemiglutarate Chol-C5, and Cholesterolhemiadipate Chol-C6.
4. The amphoteric liposome formulation of claim 1, wherein the neutral amphiphiles are selected from the group consisting of phosphatidylcholines, sphingomyelins, ceramides, phosphatidylethanolamines, cholesterol, and mixtures thereof.
5. The amphoteric liposome formulation of claim 1, wherein the neutral amphiphiles are selected from phosphatidylcholines and phosphatidylethanolamines.
6. The amphoteric liposome formulation of claim 1, wherein the neutral amphiphiles are selected from POPC and DOPE.
7. The amphoteric liposome formulation of claim 1, wherein the formulation has an isoelectric point of from pH 4 to pH 8.
8. The amphoteric liposome formulation of claim 1, wherein the neutral amphiphiles are less than 50 mol % of the composition and the composition has an isoelectric point of from pH 4 to pH 8.
9. The amphoteric liposome formulation of claim 1, wherein the formulation comprises an amphoteric liposome.
10. The amphoteric liposome formulation of claim 1, wherein the formulation has an isoelectric point of from pH 5 to pH 7.
11. The amphoteric liposome formulation of claim 1, wherein the formulation has a stable lamellar phase at pH 7 to pH 8.
12. The amphoteric liposome formulation of claim 1, wherein the molar ratio of the cationic amphiphile to the anionic amphiphile is greater than or equal to 1.
13. The amphoteric liposome formulation of claim 1, wherein the neutral amphiphiles are less than 40 mol % of the formulation.
14. The amphoteric liposome formulation of claim 1, wherein the formulation comprises liposomes that encapsulate at least one active agent.
15. The amphoteric liposome formulation of claim 14, wherein the at least one active agent is a nucleic acid.
16. The amphoteric liposome formulation of claim 14, wherein the at least one active agent is an oligonucleotide.
17. The amphoteric liposome formulation of claim 14, wherein the at least one active agent is a biologically active agent.
18. An amphoteric liposome-nucleic acid particle, comprising a cationic amphiphile, an anionic amphiphile, one or more neutral amphiphiles, and a nucleic acid.
19. The amphoteric liposome-nucleic acid particle of claim 18, wherein the cationic amphiphile is selected from the group consisting of 4-(2-aminoethyl)-morpholino-cholesterol-2,3-dimethylhemisuccinate (DmC4Mo2), 4-(2-aminoethyl)-morpholino-cholesterol-2,3-dimethylhemimalonate (DmC3Mo2), 4-(2-aminobutyl)-morpholino-cholesterol-hemisuccinate (C4Mo4), 4-(2-aminopropyl)-morpholino-cholesterol-hemimalonate (C3Mo3), 4-(2-aminoethyl)-morpholino-cholesterol-hemimalonate (C3Mo2), 4-(2-aminoethyl)-morpholino-cholesterol-hemiglutarate (C5Mo2), 4-(2-aminoethyl)-morpholino-cholesterol-hemiadipate (C6Mo2), 4-(2-aminoethyl)-morpholino-cholesterol-hemiadipate (C8Mo2), 4-(2-Aminoethyl)-Morpholino-Cholesterolhemisuccinate (MoChol), Cholesterol-(3-imidazol-1-yl propyl)carbamate (CHIM), and Histaminyl-Cholesterolhemisuccinate (HisChol), the anionic amphiphile is selected from the group consisting of cholesterol hemisuccinate CHEMS, Dimyristoylglycerolhemisuccinate DMGS, Dimyristoylglycerolhemimalonate DMGM, Dimyristoylglycerolhemiglutarate DMGG, Dimyristoylglycerolhemiadipate DMGA, 4-((1,2-Dimyristoyl-ethyl)amino)-4-oxobutanoic acid DMAS, 4-((1,2-Dimyristoyl-ethyl)amino)-4-oxopropanoic acid DMAM, 4-((1,2-Dimyristoyl-ethyl)amino)-4-oxopentanoic acid DMAG, 4-((1,2-Dimyristoyl-ethyl)amino)-4-oxohexanoic acid DMAA, Dioleoylglycerolhemisuccinate DOGS, Dioleoylglycerolhemimalonate DOGM, Dioleoylglycerolhemiglutarate DOGG, Dioleoylglycerolhemiadipate DOGA, 4-((1,2-Dioleoyl-ethyl)amino)-4-oxobutanoic acid DOAS, 4-((1,2-Dioleoyl-ethyl)amino)-4-oxopropanoic acid DOAM, 4-((1,2-Dioleoyl-ethyl)amino)-4-oxopentanoic acid DOAG, 4-((1,2-Dioleoyl-ethyl)amino)-4-oxohexanoic acid DOAA, 5,6-Dimyristoyl-hexanoic acid DMS, 4,5-Dimyristoyl-pentanoic acid DMM, 6,7-Dimyristoyl-heptanoic acid DMG, 7,8-Dioleoyl-octanoic acid DMA, 5,6-Dioleoyl-hexanoic acid DOS, 4,5-Dioleoyl-pentanoic acid DOM, 6,7-Dioleoyl-heptanoic acid DOG, 7,8-Dioleoyl-octanoic acid DOA, Cholesterolhemimalonate Chol-C3, Cholesterolhemiglutarate Chol-C5, and Cholesterolhemiadipate Chol-C6, and the neutral amphiphiles are selected from the group consisting of phosphatidylcholines, sphingomyelins, ceramides, phosphatidylethanolamines, cholesterol, and mixtures thereof.
20. The amphoteric liposome-nucleic acid particle of claim 19, wherein the nucleic acid is a plasmid, a linear DNA construct, an oligonucleotide, a mRNA, a shRNA, a miRNA, a ribozyme, an aptamer, or an RNA that can specifically regulate a protein expression level.
Type: Application
Filed: Jan 31, 2016
Publication Date: Jun 2, 2016
Inventors: Steffen Panzner (Halle), Silke Lutz (Halle), Evgenios Siepi (Leipzig), Claudia Muller (Nerchau)
Application Number: 15/011,576
