A 3D spheroid system to evaluate inhibitors of the ABCG2 transporter in drug uptake and penetration

Abstract

None of the ABCG2 inhibitors are effective clinically against multidrug resistant tumors overexpressing ABCG2. New in vitro models are needed to characterize inhibitors and discover new ones. We report a 3D spheroid model and image-based method to quantify ABCG2 action. Nonadhesive micro-molds were used to self-assemble spheroids overexpressing ABCG2; these spheroids were then incubated with the transporter substrate Hoechst 33342. Time-lapse fluorescent microscopy was used to determine the transporter-dependent efflux of Hoechst 33342 and dose response of three inhibitors (Ko143, Iressa, Elacridar). This 3D microtissue model was also used to determine the time to maximal effect as well as duration of effect after inhibitor removal. All acted within one hour and Elacridar had a surprisingly long duration of effect, active 5 hours after removal. This model can be used with multiple cell types, provides new insight into the pharmacokinetics of inhibitors, and can be adapted to high throughput analyses.