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 a simple quantitative fluorescent assay method for determining the activity of transport proteins, more specifically multi-drug resistance associated proteins (MRPs). The method of the invention is performed on a well sealed culture of polarized cells expressing a transport protein of interest grown to confluency on a permeable support, said confluent cell culture forming well separated apical and basolateral compartments. The cells are contacted with a cell permeable non-fluorescent derivative of a fluorescent compound (e.g. calcein AM) in one compartment and, after a certain period of incubation, the fluorescence intensity detected in a sample taken from the opposite compartment is indicative of the activity of the transport protein of interest expressed in the cells.

Abstract: Disclosed herein are methods and reagent kits for the quantitative in vitro determination of the functional determination of multi-drug resistance in cells, as well as for the clinical screening of potential modulators of multi-drug resistant transport activity in cells

Abstract: The invention generally features a rapid, quantitative method of diagnosing multi-drug resistance in a patient. The method involves (a) exposing cells of a biological specimen to a calcein compound, the calcein compound becoming fluorescent in the cell; and (b) measuring calcein compound accumulating in the specimen cells relative to control cells, reduced calcein accumulation in specimen cells relative to control cells indicating the presence of multi-drug resistance in the biological specimen. The method is useful for diagnosing multi-drug resistance in patients undergoing drug therapy, e.g., chemotherapeutic or antibiotic therapy.