Humanized Fruit Flies as a Novel Pre-Clinical Test Model for Membrane Drug Transporters.

Background: Membrane transport proteins are critical determinants of systemic and intracellular drug levels, thereby contributing substantially to drug response and/or adverse drug reactions. Therefore, the U.S. Food and Drug Administration and the European Medicines Agency, the regulatory authorities for drug approval in the U.S. and Europe, respectively, recommend pre-clinical testing of selected drug transporters during the drug development process to elucidate clinically relevant drug-drug interactions (DDIs). In the current proof-of-principle study, we describe the generation of fruit flies expressing human membrane drug transporters in their salivary glands to enable DDI studies in a time-saving manner and at low costs.

Methods: Using the Gal4/upstream activation sequence (UAS) expression system, we established fruit flies expressing human organic cation transporters (hOCTs) 1 and 2 and genetic variants thereof. Both transporters are key drug uptake transporters in humans and are recommended for pre-clinical DDI studies. After injecting fluorescent hOCT substrates, their accumulation in salivary gland cells was observed by confocal laser scanning microscopy.

Results: We demonstrate the feasibility of expressing hOCT1 and hOCT2 in the salivary glands of fruit fly embryos and subsequent alteration by clinically relevant genetic variants, corroborating results from mammalian cell experiments. Moreover, we show an OCT-dependent accumulation of the prototypic fluorescent OCT substrates ethidium (Et⁺) and 4-Di-1-ASP (4-(4-(dimethylamino)styryl)-N-methylpyridinium, ASP⁺) in the salivary gland cells and subsequent inhibition by clinically-used OCT drug inhibitors.

Conclusions: Based on the handling procedure and the lack of need for Animal Protection Act approval, we propose that the humanized Drosophila melanogaster fruit fly model opens a new avenue for pre-clinical functional transporter studies.