TY - JOUR T1 - Enhanced and Persistent Inhibition of Organic Cation Transporter 1 (OCT1) Activity by Preincubation of Cyclosporine A JF - Drug Metabolism and Disposition JO - Drug Metab Dispos DO - 10.1124/dmd.119.087197 SP - dmd.119.087197 AU - Erika Panfen AU - Weiqi Chen AU - Yueping Zhang AU - Michael Sinz AU - Punit Marathe AU - Jinping Gan AU - Hong Shen Y1 - 2019/01/01 UR - http://dmd.aspetjournals.org/content/early/2019/08/19/dmd.119.087197.abstract N2 - Recent pharmacogenetic evidence indicates that hepatic organic cation transporter 1 (OCT1) can serve as the locus of drug-drug interactions (DDIs) with significant pharmacokinetic and pharmacodynamic consequences. We examined the impact of preincubation on the extent of OCT1 inhibition in transfected human embryonic kidney 293 (HEK293) cells. Following a 30 minute preincubation with an inhibitor, approximately 50-fold higher inhibition potency was observed for Cyclosporine (CsA) against OCT1-mediated uptake of metformin as compared to coincubation, with IC50 values of 0.43 ± 0.12 and 21.6 ± 4.5 μM, respectively. By comparison, only small shifts (≤ 2-fold) in preincubation IC50 versus coincubation were observed for quinidine, pyrimethamine, ritonavir, and trimethoprim. The shift in CsA OCT1 IC50 is substrate-dependent as it ranged from > 1.2 fold to 50.2-fold using different experimental substrates. The inhibition potential of CsA towards OCT1 is confirmed by fenoterol hepatocyte uptake experiment. Furthermore, no shift in CsA IC50 was observed with HEK293 cells transfected with OCT2 and organic anion transporter (OAT) 1 and OAT3. A short (30 min) exposure to 10 μM CsA produced long-lasting (at least 120 min) inhibition of the OCT1-mediated uptake of metformin in OCT1-HEK293 cells, which was likely attributable to the retention of CsA in the cells, as shown by the fact that inhibitory cellular concentrations of CsA are maintained long after the removal of the compound from incubation buffer. The potent and persistent inhibitory effect after exposure to CsA warrants careful consideration in the design and interpretation of clinical OCT1 DDI studies.SIGNIFICANCE STATEMENT Preincubation of OATP1B1 and OATP1B3 with their inhibitor may result in the enhancement of the inhibitory potency in a cell-based assay. However, limited data are available on potentiation of OCT1 inhibition by preincubation, which is a clinically relevant drug transporter. For the first time, we observed a 50-fold increase in CsA inhibitory potency against OCT1-mediated transport of metformin following a preincubation step. The CsA preincubation effect on OCT1 inhibition is substrate-dependent. Moreover, the inhibition potential of CsA towards OCT1 is confirmed by hepatocyte uptake experiment. This study delivers clear evidences about the potent and persistent inhibitory effect on OCT1 after exposure to CsA. Further studies are needed to assess the effect of CsA on OCT1 drug substrates in vivo. ER -