Pharmacokinetics and Metabolism of Streptochlorin and Its Synthetic Derivative, 5-Hydroxy-2′-isobutyl Streptochlorin, in Mice

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The purpose of this study was to investigate the pharmacokinetics and metabolism of streptochlorin and its derivative 5-hydroxy-2′-isobutyl streptochlorin (HIS) in mice. Plasma concentration of streptochlorin declined rapidly resulting in a high sustemic plasma clearance (CL_p) (5.8±1.7 L/h/kg), a large volume of distribution (V_ss) (1.4±0.9 L/kg) and a short half-life (t_1/2) (0.4±0.1 h) after a single intravenous administration (5 mg/kg). Oral bioavailability (F) was 10.3±3.4% after a single oral administration (10 mg/kg). HIS also showed a rapid plasma decline with a high CL_p (11.3±8.8 L/h/kg), a high V_ss (0.8±1.0 L/kg) and a short t_1/2 (0.070±0.004 h) following intravenous administration. It was not detected in plasma after oral administration. Metabolic stability studies using mouse liver microsomes and S9 fractions predicted a high hepatic clearance for both compounds, consistent with the in vivo data. Metabolite identification studies revealed three metabolic pathways for streptochlorin: monooxygenation, glucuronidation of the indole moiety and oxidative opening of the 4-chlorooxazole ring. HIS was metabolized via monooxygenation of the isobutyl chain and glucuronidation of the indole ring. These results may aid in structural optimization to mitigate the metabolic liability of streptochlorin.