Characterization of organic anion transporting polypeptide 1B1 and 1B3 humanized rat as a translational model to study the pharmacokinetics of OATP1B substrate drugs

Organic anion transporting polypeptide (OATP)1B1 and OATP1B3 (OATP1B) are clinically important transporters that mediate active hepatic uptake for a broad range of drugs and endogenous compounds and play a pivotal role in hepatic disposition and drug-drug interactions (DDIs) of substrate drugs. Efforts have been made on developing humanized transgenic OATP1B rodent models to mechanistically understand the role of OATP1B in drug disposition and DDIs. However, the lack of robust OATP1B functional activities limits their utility. We therefore developed humanized OATP1B1 and OATP1B3 and double-humanized OATP1B1/1B3 rat models in an Oatp1a1/1a4/1b2 knockout rat background. The knockout of rat Oatp1a1/1a4/1b2 and humanized transgenic overexpression of OATP1B1 and OATP1B3 in rat liver did not cause profound compensatory changes in gene expression of other transporters and metabolizing enzymes. The protein expression of OATP1B1 and OATP1B3 in humanized OATP1B rat liver was 4.7-fold and 22.3-fold higher than those reported in human liver tissues, respectively, and higher than those reported in humanized OATP1B mice. This has subsequently led to a robust in vitro and in vivo functional activity for a range of OATP1B substrate drugs. A translational analysis indicated a good correlation between in vitro hepatic uptake clearance measured in these models and human hepatocytes after correcting for OATP1B protein expression. Furthermore, these humanized OATP1B rats predicted the relative contribution of OATP1B in hepatic uptake of several OATP1B substrate drugs. Overall, these data suggest that our humanized OATP1B rat model is a promising tool to study OATP1B-mediated drug disposition in humans, advancing preclinical to clinical translation. SIGNIFICANCE STATEMENT: Humanized OATP1B1 and OATP1B3 and double-humanized OATP1B1/1B3 rat models were successfully generated and characterized in an Oatp1a1/1a4/1b2 knockout rat background. These novel humanized OATP1B models demonstrate greater functional activity than the existing humanized OATP1B rodent models, enabling evaluation of human OATP1B activity in vitro and in vivo in a preclinical setting. This study showed that these models are promising tools to improve the prediction of OATP1B-mediated hepatic uptake and DDIs in humans.