In Vitro Interactions of Epacadostat and its Major Metabolites with Human Efflux and Uptake Transporters: Implications for Pharmacokinetics and Drug Interactions

Abstract

Epacadostat (EPAC) is a first-in-class, orally active inhibitor of the enzyme indoleamine 2,3-dioxygenase 1 and has demonstrated promising clinical activity. In humans, three major plasma metabolites have been identified: M9 (a glucuronide-conjugate), M11 (a gut microbiota metabolite), and M12 (a secondary metabolite formed from M11). It is proposed, based on the human pharmacokinetics of EPAC, that the biliary excretion of M9, the most abundant metabolite, leads to the enterohepatic circulation of EPAC. Using various in vitro systems, we evaluated in the present study the vitro interactions of EPAC and its major metabolites with major drug transporters involved in drug absorption and disposition. EPAC is a substrate for efflux transporters P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), but it is not a substrate for hepatic uptake transporters [organic anion transporting polypeptides OATP1B1 and OATP1B3]. The low permeability of M9 suggests an essential role for transporters in its disposition. M9 is likely excreted from hepatocytes into bile via multidrug resistance-associated protein 2 (MRP2) and BCRP, excreted into blood via MRP3, and transported from blood back into hepatocytes via OATP1B1 and OATP1B3. M11 and M12 are not substrates for P-gp, OATP1B1 or OATP1B3, and M11, but not M12, is a substrate for BCRP. With respect to inhibition of drug transporters, the potential of EPAC, M9, M11, and M12 to cause clinical drug-drug interactions via inhibition of P-gp, BCRP, OATP1B1, OATP1B3, OAT1, OAT3, or organic cation transporter 2 was estimated to be low. The current investigation underlines the importance of metabolite-transporter interactions in the disposition of clinically relevant metabolites, which may have implications for the pharmacokinetics and drug interactions of parent drugs.

Effects of Epacadostat on Brain Extracellular Fluid Concentrations of Serotonin—an Intracerebral Microdialysis Study in Sprague-Dawley Rats

“…These results support minimal brain penetration of EPAC in rats, which is in good agreement with a recent publication demonstrating the low brain penetration potential of EPAC in C57BL/6 mice following a 50 mg/kg oral dose with a correspondent plasma concentration close to 30 mM (Ladomersky et al, 2018). The restricted BBB penetration of EPAC may be due in part to efflux by both P-glycoprotein and/or breast cancer resistance protein (Zhang et al, 2017), two major efflux transporters expressed in the brain microvessel endothelial cells lining the BBB (Giacomini et al, 2010). The poor brain uptake for EPAC suggests that the potential for IDO1 inhibitory activity in the brain following EPAC oral dosing is limited.…”

Overview of Transporters in Pharmacokinetics and Drug Discovery

“…They can undergo differentiation, form tight junctions, and become polarized when grown on a membrane support that resembles the enterocytes lining the small intestine. These cells are widely used to determine permeability and evaluate the involvement of efflux transporters such as P‐gp and BCRP for NCEs and their metabolites (Hilgers, Conradi, & Burton, ; Q. Zhang et al., ). Throughput of compounds for permeability assessment in Caco‐2 cells can be enhanced when cells are grown in 96‐well format, especially when LC‐MS/MS methods are used to quantify drug concentrations.…”

“…For inhibitor determination, the accumulation of a probe substrate is measured with various concentrations of the compound of interest. The examination of the IDO1 inhibitor, epacadostat, and its three major metabolites in single transporter transfected cell lines to assess their role as substrates or inhibitors of transporters like BCRP, OATP1B1, and OATP1B3 showed no transporter‐mediated DDI liabilities with the drug candidate and its metabolites (Q. Zhang et al., ).…”

“…Therefore, the pharmacokinetics of EPAC and enterohepatic recirculation of M9 may be potentially influenced by the metabolite‐transporter interactions (Fig. ; Q. Zhang et al., ).…”

“…They can undergo differentiation, form tight junctions, and become polarized when grown on a membrane support that resembles the enterocytes lining the small intestine. These cells are widely used to determine permeability and evaluate the involvement of efflux transporters such as P-gp and BCRP for NCEs and their metabolites (Hilgers, Conradi, & Burton, 1990;Q. Zhang et al, 2017).…”