Humanization of SLCO2B1 in rats increases rCYP3A1 protein expression but not the metabolism of erlotinib to OSI-420 .

The organic anion transporting polypeptide (OATP) 2B1 (gene name SLCO2B1 ) is an uptake transporter that facilitates cellular accumulation of its substrates. In order to assess the in vivo relevance of the transporter, we applied SLCO2B1 +/+ knock-in and Slco2b1 -/- knock-out rats. A first pharmacological phenotyping with the OATP2B1 substrate-drug atorvastatin revealed reduced hepatic content and increased expression of rCYP3A1 in the humanized animals. It was the aim of this study to determine whether changes in metabolic activity affect the in vivo handling of the OATP2B1 and CYP3A1 substrate erlotinib, which is metabolized to OSI-420. Western blot analysis of rat liver lysates and microsomes confirmed higher rCYP3A1 protein expression in untreated SLCO2B1 +/+ compared to Slco2b1 -/ - rats. One hour after a single dose of erlotinib, the knock-in rats exhibited significantly lower serum levels, but no change was observed in metabolite concentration or the OSI-420/erlotinib-ratio. Similar results were obtained for liver tissue levels comparing SLCO2B1 +/+ and Slco2b1 -/- rats. Microsomes isolated from the treated animals were characterized for CYP3A activity using testosterone, showing higher activity in the knock-in rats. The contrary was observed, when microsomes isolated from treatment naive animals were assessed for the OSI-420 formation after erlotinib exposure. In summary, rats humanized for OATP2B1 showed higher expression of CYP3A1 in liver, reduced serum levels of erlotinib, but no change in the OSI-420/erlotinib-ratio despite a lower formation in isolated liver microsomes. Studies with CYP3A-specific substrates are warranted to evaluate whether there is a change in metabolic activity in vivo Significance Statement Prior studies showed increased expression of CYP3A1 in the liver of SLCO2B1 +/+ rats. SLCO2B1 encodes for the uptake transporter OATP2B1 and CYP3A1 is the rat isoform of CYP3A4. Our study further supports a link between the human transporter and the enzyme's expression and activity in rat liver. However, using the OATP2B1/CYP3A substrate erlotinib to investigate the interplay we observed lower erlotinib serum and liver concentrations, but no impact on the levels of its metabolite (OSI-420).