Characterization of AST‐001 non‐clinical pharmacokinetics: A novel selective AKR1C3‐activated prodrug in mice, rats, and cynomolgus monkeys

Abstract AST‐001 is a chemically synthesized inactive nitrogen mustard prodrug that is selectively cleaved to a cytotoxic aziridine (AST‐2660) via aldo‐keto reductase family 1 member C3 (AKR1C3). The purpose of this study was to investigate the pharmacokinetics and tissue distribution of the prodrug, AST‐001, and its active metabolite, AST‐2660, in mice, rats, and monkeys. After single and once daily intravenous bolus doses of 1.5, 4.5, and 13.5 mg/kg AST‐001 to Sprague‐Dawley rats and once daily 1 h intravenous infusions of 0.5, 1.5, and 4.5 mg/kg AST‐001 to cynomolgus monkeys, AST‐001 exhibited dose‐dependent pharmacokinetics and reached peak plasma levels at the end of the infusion. No significant accumulation and gender differences were observed after 7 days of repeated dosing. In rats, the half‐life of AST‐001 was dose independent and ranged from 4.89 to 5.75 h. In cynomolgus monkeys, the half‐life of AST‐001 was from 1.66 to 5.56 h and increased with dose. In tissue distribution studies conducted in Sprague‐Dawley rats and in liver cancer PDX models in female athymic nude mice implanted with LI6643 or LI6280 HepG2‐GFP tumor fragments, AST‐001 was extensively distributed to selected tissues. Following a single intravenous dose, AST‐001 was not excreted primarily as the prodrug, AST‐001 or the metabolite AST‐2660 in the urine, feces, and bile. A comprehensive analysis of the preclinical data and inter‐species allometric scaling were used to estimate the pharmacokinetic parameters of AST‐001 in humans and led to the recommendation of a starting dose of 5 mg/m 2 in the first‐in‐human dose escalation study.