In vitro inhibition of organic anion transporting polypeptide 2B1 (OATP2B1) is common among marketed drugs

Organic anion transporting polypeptide 2B1 (OATP2B1) is a cell membrane influx transporter that may have a role in drug absorption and disposition. Inhibition of intestinal OATP2B1 has been suggested to decrease the oral bioavailability of some OATP2B1 substrate drugs potentially impairing their efficacy. This study aimed to identify uncharacterized OATP2B1 inhibitors among 228 commonly used drugs. For inhibition studies, OATP2B1 influx assays were performed with human embryonic kidney (HEK) 293 cells transduced with BacMam baculovirus containing the gene for SLCO2B1 (encoding OATP2B1) or enhanced yellow fluorescence protein (negative control). The drug library was screened at 50 µM at pH 6.0 with fluorescent 5-carboxyfluorescein as the OATP2B1 substrate. Out of the 228 drugs, 52 reduced the relative transport activity of OATP2B1 to less than 25 % of the control and were classified as strong in vitro inhibitors. Eleven selected strong inhibitors were advanced for dose-response studies to determine the concentration required for 50 % inhibition (IC₅₀). The determined IC₅₀ values ranged between 0.075-31 µM, with the most potent inhibitors being telmisartan (0.075 µM), dabrafenib (0.40 µM), and dabigatran etexilate (0.72 µM). Comparison of the predicted maximal intestinal concentrations of the drugs and the IC₅₀ values showed ratios of >1000 for dabigatran etexilate, dabrafenib, pazopanib, sorafenib and telmisartan, suggesting that the risk of clinically significant drug-drug interactions cannot be excluded. Pharmacokinetic studies with victim drugs sensitive to OATP2B1 inhibition are warranted to investigate whether the found inhibitors inhibit OATP2B1 in vivo and cause drug-drug interactions in humans.