TY - JOUR T1 - Application of Higher Throughput Screening (HTS) Inhibition Assays to Evaluate the Interaction of Antiparasitic Drugs with Cytochrome P450s JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 30 LP - 35 VL - 29 IS - 1 AU - Tashinga E. Bapiro AU - Ann-Charlotte Egnell AU - Julia A. Hasler AU - Collen M. Masimirembwa Y1 - 2001/01/01 UR - http://dmd.aspetjournals.org/content/29/1/30.abstract N2 - In this study we have evaluated the application and reliability of using fluorescence (FLUO)-based high throughput screening assays with recombinant CYPs (rCYP). This was accomplished by screening 29 clinically important antiparasitic drugs for inhibition of the five major drug-metabolizing CYPs (-1A2, -2C9, -2C19, -2D6, and -3A4). Data from FLUO/rCYP assays were compared with that obtained by conventional HPLC assays using human liver microsomes (HLM) and rCYPs. TheKi values showed good correlations: FLUO/rCYP and HPLC/rCYP (r2 = 0.81), HPLC/rCYP and HPLC/HLM (r2 = 0.82), and FLUO/rCYP and HPLC/HLM (r2 = 0.72). Niclosamide had substrate-dependent contrasting effects on CYP2C9 activity with an apparent activation (400%) of 7-methoxy-4-trifluoromethylcoumarin demethylase activity and potent inhibition (Ki = 6.00 μM) of diclofenac 4-hydroxylase activity. Potent inhibitors of CYP1A2 were artemisinin, dihydroartemisinin, thiabendazole, primaquine, and niclosamide (Ki = 0.43, 3.67, 1.54, 0.22, and 2.70 μM, respectively). Proguanil, cycloguanil, amodiaquine, and desethylamodiaquine inhibited CYP2D6 (Ki = 6.76, 5.97, 2.1, and 4.13 μM, respectively). Considering the Cmax of these drugs, artemisinin, thiabendazole, primaquine, amodiaquine, and desethylamodiaquine may cause clinically important interactions because they are predicted to inhibit 67 to 99% of the activities of the CYPs they interact with. In addition, our results suggest CYP1A2 inhibition as the mechanism behind the observed thiabendazole/theophylline and primaquine/antipyrine interactions in vivo. The American Society for Pharmacology and Experimental Therapeutics ER -