Drug Metabolism and Pharmacokinetic Evaluation of a Novel RNase H2 Inhibitor for the Treatment of Triple-Negative Breast Cancer

Objectives: A thorough understanding of pharmacokinetics and metabolism is critical during early drug development. This study investigates the absorption, distribution, metabolism, and excretion (ADME) profile of R14, a novel compound, using a combination of in vitro and in vivo approaches. Methods: In vitro studies included Caco-2 permeability assays, metabolic stability evaluations in liver microsomes and hepatocytes, and identification of CYP isoforms responsible for R14 metabolism. In vivo pharmacokinetic and metabolic profiling was conducted in rats following oral administration. R14 was quantified using UHPLC-MS/MS. Metabolites were identified using high-resolution UHPLC- QTOF MS/MS, and relative exposure was estimated using peak area-derived AUCs. Results: R14 exhibited low oral bioavailability (13.4%) and high systemic clearance (2.63 L/h/kg), indicating high hepatic extraction. A total of 21 plasma and 38 urine metabolites were identified. Major metabolic pathways included initial hydroxylation and hydrogenation, followed by sequential methylation and Phase II conjugations (glucuronidation and sulfation). Key metabolites (M3, M4, M22, M38) accounted for the majority of systemic exposure. Less than 1% of the unchanged drug was excreted in urine, confirming extensive metabolism. Notably, discrepancies between in vitro and in vivo metabolite profiles suggested rapid further transformation of initial metabolites in vivo, which were not fully captured in vitro. Conclusions: This study demonstrates an efficient and integrated strategy for early-phase ADME characterization. The combined use of in vitro assays and in vivo studies, guided by advanced analytical techniques, provides a robust framework for understanding drug metabolism. These findings can inform drug optimization and help minimize risks in later stages of development.