CYP2C8-Mediated Formation of a Human Disproportionate Metabolite of the Selective Na_V1.7 Inhibitor DS-1971a, a Mixed Cytochrome P450 and Aldehyde Oxidase Substrate

Abstract

Predicting human disproportionate metabolites is difficult, especially when drugs undergo species-specific metabolism mediated by cytochrome P450s (P450s) and/or non-P450 enzymes. This study assessed human metabolites of DS-1971a, a potent Na v 1.7-selective blocker, by performing human mass balance studies and characterizing DS-1971a metabolites, in accordance with the Metabolites in Safety Testing (MIST) guidance. In addition, we investigated the mechanism by which the major human disproportionate metabolite (M1) was formed. After oral administration of radiolabeled DS-1971a, the major metabolites in human plasma were P450-mediated monoxidized metabolites M1 and M2 with area under the curve ratios of 27% and 10% of total drug-related exposure, respectively; the minor metabolites were dioxidized metabolites produced by aldehyde oxidase and P450s. By comparing exposure levels of M1 and M2 between humans and safety assessment animals, M1 but not M2 was found to be a human disproportionate metabolite, requiring further characterization under the MIST guidance. Incubation studies with human liver microsomes indicated that CYP2C8 was responsible for the formation of M1. Docking simulation indicated that, in the formation of M1 and M2, there would be hydrogen bonding and/or electrostatic interactions between the pyrimidine and sulfonamide moieties of DS-1971a and amino acid residues Ser100, Ile102, Ile106, Thr107, and Asn217 in CYP2C8, and that the cyclohexane ring of DS-1971a would be located near the heme iron of CYP2C8. These results clearly indicate that M1 is the predominant metabolite in humans and a human disproportionate metabolite due to species-specific differences in metabolism.

Physiologically Based Pharmacokinetic Modeling for Quantitative Prediction of Exposure to a Human Disproportionate Metabolite of the Selective NaV1.7 Inhibitor DS-1971a, a Mixed Substrate of Cytochrome P450 and Aldehyde Oxidase, Using Chimeric Mice With Humanized Liver

“…PK parameters were calculated by non-compartmental analysis of the simulated plasma PK profiles of DS-1971a and M1 in PXB-mice and humans using WinNonlin 6.3. The values of fum, fup, Qh, and Vh are cited from previous reports (Davies andMorris, 1993, Sinozuka et al, 2020;Asano et al, 2022) Based on this evidence and the fact that no metabolism of DS-1971a with human intestinal microsomes and S9 was observed (data not shown), both fraction absorbed (Fa) and intestinal availability (Fg) were assumed to be 1.0. These assumptions were also applicable to Fa and Fg values in PXB-mice both because Fh,p in PXB-mice can be calculated to be 0.59 by eq.…”

“…Here, oral dose in humans is 400 mg and human BW represents body weight of 70 kg for humans (Davies and Morris, 1993). Oral dose (3−10 mg/kg) and observed AUC in ICR mice, monkeys, rats, and dogs are cited from Asano et al (2021Asano et al ( , 2022, and those in SCID mice and PXB-mice are described in this manuscript.…”

“…Note that hepatic metabolism of M1 is not included in equation (eq.) ( 19) because M1 was reported to be metabolically stable against human liver microsomes and S9 (Asano et al, 2022), indicating that the only elimination pathways of M1 are its biliary and urinary excretion in its unchanged form.…”

“…A human mass balance study of radiolabeled DS-1971a in the fed condition demonstrated that more than 70% of the dose was absorbed and the predominant metabolite was M1 in human plasma, urine, and feces (Asano et al, 2022). The exposure level of M1 in human plasma was 1.5-fold higher than that of the parent compound (DS-1971a) and M1 exposure in animals used for safety assessments (mice and monkeys) was much smaller than that in humans, so M1 was found to be a human disproportionate metabolite.…”

“…The exposure level of M1 in human plasma was 1.5-fold higher than that of the parent compound (DS-1971a) and M1 exposure in animals used for safety assessments (mice and monkeys) was much smaller than that in humans, so M1 was found to be a human disproportionate metabolite. In addition, incubation studies with human liver microsomes (HLMs) pretreated with P450-specific inhibitors and with recombinant P450 have indicated that CYP2C8 plays a key role in M1 formation (Asano et al, 2022).…”