Novel in Vitro Method Reveals Drugs That Inhibit Organic Solute Transporter Alpha/Beta (OSTα/ß).

Drug interactions with the organic solute transporter alpha/beta (OSTα/ß) are understudied even though OSTα/ß is an important transporter that is expressed in multiple human tissues including the intestine, kidneys, and liver. In this study, an in vitro method to identify novel OSTα/ß inhibitors was first developed using OSTα/ß-overexpressing Flp-In 293 cells. Incubation conditions were optimized using previously reported OSTα/ß inhibitors. A method including a 10 min preincubation step with the test compound was used to screen for OSTα/ß inhibition by 77 structurally diverse compounds and fixed-dose combinations. Seven compounds and one fixed-dose combination (100 µM final concentration) inhibited OSTα/ß-mediated dehydroepiandrosterone sulfate (DHEAS) uptake by >25%. Concentration-dependent OSTα/ß inhibition was evaluated for all putative inhibitors (atorvastatin, ethinylestradiol, fidaxomicin, glycochenodeoxycholate, norgestimate, troglitazone, and troglitazone sulfate). Ethinylestradiol, fidaxomicin, and troglitazone sulfate yielded a clear concentration-inhibition response with IC50 values <200 µM. Among all tested compounds, there was no clear association between physicochemical properties, the severity of hepatotoxicity, and the degree of OSTα/ß inhibition. This study utilized a novel in vitro method to identify OSTα/ß inhibitors and, for the first time, provided IC50 values for OSTα/ß inhibition. These data provide evidence that several drugs, some of which are associated with cholestatic drug-induced liver injury, may impair the function of the OSTα/ß transporter.