OATP1A/1B Transporters Affect Irinotecan and SN-38 Pharmacokinetics and Carboxylesterase Expression in Knockout and Humanized Transgenic Mice

Abstract

Organic anion-transporting polypeptides (OATP) mediate the hepatic uptake of many drugs, thus codetermining their clearance. Impaired hepatic clearance due to low-activity polymorphisms in human OATP1B1 may increase systemic exposure to SN-38, the active and toxic metabolite of the anticancer prodrug irinotecan. We investigated the pharmacokinetics and toxicity of irinotecan and SN-38 in Oatp1a/1b-null mice: Plasma exposure of irinotecan and SN-38 was increased 2 to 3-fold after irinotecan dosing (10 mg/kg, i.v.) compared with wildtype mice. Also, liver-to-plasma ratios were significantly reduced, suggesting impaired hepatic uptake of both compounds. After 6 daily doses of irinotecan, Oatp1a/1b-null mice suffered from increased toxicity. However, Oatp1a/1b-null mice had increased levels of carboxylesterase (Ces) enzymes, which caused higher conversion of irinotecan to SN-38 in plasma, potentially complicating pharmacokinetic analyses. Ces inhibitors blocked this increased conversion. Interestingly, liver-specific humanized OATP1B1 and OATP1B3 transgenic mice had normalized hepatic expression of Ces1 genes. While irinotecan liver-to-plasma ratios in these humanized mice were similar to those in Oatp1a/1b-null mice, SN-38 liver-to-plasma ratios returned to wild-type levels, suggesting that human OATP1B proteins mediate SN-38, but not irinotecan uptake in vivo. Upon direct administration of SN-38 (1 mg/kg, i.v.), Oatp1a/1b-null mice had increased SN-38 plasma levels, lower liver concentrations, and decreased cumulative biliary excretion of SN-38. Mouse Oatp1a/1b transporters have a role in the plasma clearance of irinotecan and SN-38, whereas human OATP1B transporters may only affect SN-38 disposition. Oatp1a/1b-null mice have increased expression and activity of Ces1 enzymes, whereas humanized mice provide a rescue of this phenotype. Mol Cancer Ther; 13(2); 492-503. Ó2013 AACR.

Evaluation of Organic Anion Transporting Polypeptide 1B1 and 1B3 Humanized Mice as a Translational Model to Study the Pharmacokinetics of Statins

“…The strongest reduction in Ces gene expression was observed in hOATP1B1 followed by hOATP1B3 mice. Interestingly, Oatp1a/1b KO mice showed increased levels of hepatic Ces1 expression in the study by Iusuf et al (2014), which were normalized in hOATP1B1 and hOATP1B3 mice, whereas we found unchanged or slightly decreased Ces1 levels in Oatp1a/1b KO mice in our analysis and a more pronounced repression in the humanized mice ( Fig. 1; Supplemental Table 1).…”

“…Future studies will need to assess if the changes in mRNA levels do result in alterations at both protein and activity levels. Nevertheless, studies in transgenic mice should be undertaken cautiously for compounds containing an ester functional group, since the changes in the expression of carboxylesterases can be a confounding factor, as was recently described for the Ces-dependent conversion of irinotecan to its active and toxic metabolite SN-38 (Iusuf et al, 2014). When translating the data from humanized OATP1B mice to the human situation, it is important to compare the amount of hepatic OATP1B protein in the humanized mice relative to human liver.…”

Role of Organic Anion-Transporting Polypeptides (OATPs) in Cancer Therapy

“…Similarly, transgenic humanized OATP1A/1B mouse models were generated with liverspecific expression of OATP1B1, OATP1B3, and OATP1A2 in an Oatp1a/1b knockout background. This model was utilized to show that paclitaxel, methotrexate, SN-38, docetaxel, and doxorubicin are transported by OATP1A/1B in vivo (19,20,57,58).…”

Evaluation of Rosuvastatin as an Organic Anion Transporting Polypeptide (OATP) Probe Substrate: In Vitro Transport and In Vivo Disposition in Cynomolgus Monkeys

“…For example, it is possible to delete the murine Oatp1b2 gene Zaher et al, 2008;Chang et al, 2014), introduce human OATP genes (van de Steeg et al, 2009), and develop combinations of OATP knockout and knock-in mice (Higgins et al, 2014;Salphati et al, 2014). However, the interpretation of data obtained with such models can be difficult in some cases when compensatory mechanisms are suspected Iusuf et al, 2014;Salphati et al, 2014). In addition, quantitative translation of data obtained with knockout and/or knock-in animals can be challenging.…”