Abstract: ABC multidrug transporters are key players in cancer multidrug resistance and in general xenobiotic elimination, thus their functional assays provide important tools for research and diagnostic applications. It has been found that in cells expressing functional ABCG2, ABCB1, or ABCC1 transporters, cellular PG fluorescence is strongly reduced. The invention relates to methods and uses of fluorescein derivative ester compounds of formula Ia which are analogs of PG for assessing ABC transporter activity of ABC multidrug transporters. The present accumulation assay is a novel tool for the parallel determination of the function of the multidrug transporters, in particular ABCG2, ABCB1, and ABCC1. The assay is applicable for diagnostic purposes and also allows the selection, separation and culturing of selected cell populations expressing such transporters.

Abstract: The invention provides for a novel cholesterol loaded insect cell membrane preparation having an increased cholesterol level as compared to physiological cholesterol levels of insect cell membranes or to control insect cell membrane preparations without cholesterol loading, wherein said cholesterol loaded membrane preparation comprises an ABC transporter protein having an increased substrate transport activity due to increased cholesterol level of the membrane. The invention also relates to reagent kits comprising the preparations of the invention. The invention also relates to methods for manufacturing said preparations and methods for measuring any type of activity of the ABC transporters present in the cholesterol loaded membranes as well as studying or testing compounds and interaction of compounds and ABC transporters, in this assay systems. The invention also provides for a test system useful for testing whether ABC transporter proteins can be activated by cholesterol in an insect cell membrane.

Abstract: The invention provides for a novel cholesterol loaded insect cell membrane preparation having an increased cholesterol level as compared to physiological cholesterol levels of insect cell membranes or to control insect cell membrane preparations without cholesterol loading, wherein said cholesterol loaded membrane preparation comprises an ABC transporter protein having an increased substrate transport activity due to increased cholesterol level of the membrane. The invention also relates to reagent kits comprising the preparations of the invention. The invention also relates to methods for manufacturing said preparations and methods for measuring any type of activity of the ABC transporters present in the cholesterol loaded membranes as well as studying or testing compounds and interaction of compounds and ABC transporters, in this assay systems. The invention also provides for a test system useful for testing whether ABC transporter proteins can be activated by cholesterol in an insect cell membrane.