TY - JOUR T1 - Pheophorbide A: Fluorescent Bcrp substrate to measure oral drug-drug interactions in real time in vivo JF - Drug Metabolism and Disposition JO - Drug Metab Dispos DO - 10.1124/dmd.118.083584 SP - dmd.118.083584 AU - Kazuto Yasuda AU - Samit Ganguly AU - Erin G Schuetz Y1 - 2018/01/01 UR - http://dmd.aspetjournals.org/content/early/2018/08/15/dmd.118.083584.abstract N2 - We investigated whether pheophorbide A (PhA) could serve as a selective BCRP substrate (victim) to screen in vivo using fluorescent live animal imaging for transporter-mediated interactions with orally administered inhibitors (perpetrators), and whether that could be coupled with serum sampling to measure PhA's systemic concentration with a fast-throughput in vitro fluorescent assay. PhA is a breakdown product of chlorophyll and is highly fluorescent in the near infrared (NIR) spectrum. Whole body NIR fluorescence was greater in the Bcrp KO compared to WT mice fed a regular diet containing chlorophyll and PhA, with fluorescence in WT mice confined to the intestine. PhA intestinal enterocyte fluorescence, after removing lumen contents, was greater in Bcrp KO vs. WT mice due to PhA enterocyte absorption and lack of PhA efflux by Bcrp. This difference was eliminated by maintaining the mice on an alfalfa (chlorophyll/PhA) free diet. The AUCFL 0-6h of orally administrated PhA was 3.5-times greater in the Bcrp KO compared to WT mice, and the PhA serum concentration was 50-fold higher in KO mice. Pre-treatment with known BCRP inhibitors lapatinib, curcumin, elacridar, pantoprazole, and sorafenib, at clinically relevant doses, significantly increased PhA AUCFL 0-6h by 2.4-, 2.3-, 2.2-, 1.5- and 1.4-fold, respectively, while PhA serum AUCSerum 0-6h increased by 13.8-, 7.8-, 5.2-, 2.02-, and 1.45-fold, respectively, and corresponded to their hierarchy as in vitro BCRP inhibitors. Our results demonstrate that live animal imaging utilizing PhA can be used to identify BCRP inhibitors and to assess the potential for BCRP mediated clinical drug-drug interactions. ER -