Abstract: The invention relates to methods for screening selective modulators of half transporter proteins of the ABCG family, more closely of ABCG1 and ABCG4. In particular the invention relates to methods for determining whether a substance is a selective activator, an inhibitor or a substrate of an ABCG1 or ABCG4 homodimer or of an ABCG1/ABCG4 heterodimer protein, methods for detection of ABCG1 protein in a biological sample, methods for modulating the function of said proteins, and methods for detecting the presence of and/or quantitating ABCG1/ABCG4 heterodimer activity in a biological sample. Moreover, the invention relates to isolated ABCG1/ABCG4 heterodimer proteins and antibodies selective for ABCG1 or ABCG4. The closely related human ABC half-transporters, ABCG1 and ABCG4, have been suggested to play an important role in cellular lipid/sterol regulation. ABCG1 and ABCG4 and mutants thereof have been expressed and studied by the present inventors in whole cells as well as isolated membrane preparations.

Abstract: The invention relates to an isolated nucleic acid comprising a sequence encoding a half transporter protein of the ABCG-family for use in gene therapy, to the use of the isolated nucleic acid for selecting somatic mammalian cells against at least one drug transportable by the transporter protein, to vectors, cells, pharmaceutical compositions and kits comprising the nucleic acid and methods for protecting and selecting cells against a cytotoxic drug transportable by said transporter protein and for gene therapy methods.

Abstract: The overexpression of an ABC half-transporter, ABCG2 (MXR/BCRP) transporter causes multidrug resistance in tumors. The present invention is based on the in vitro expression of the ABCG2 protein in insect cells as an expression system free of other, closely related, functional ABC transporters. In particular, the invention is related to a method for testing drugs for their effect on ABCG2 protein, method for the expression of active ABCG2, isolated ABCG2 homooligomers, preferably homodimers and uses thereof for testing drugs. The invention is further related to cell membrane preparations and cells, preferably insect cells comprising active ABCG2 and reagent kits for testing drugs for their effect on an ABCG2 half transporter protein. The invention is also related to a method for identifying ABCG2 activity in a biological sample, utilizing its substrate/inhibitor specificity.