Discovering and harnessing oxidative enzymes for chemoenzymatic synthesis and diversification of anticancer camptothecin analogues

Semi-synthetic derivatives of camptothecin, a quinoline alkaloid found in the Camptotheca acuminata tree, are potent anticancer agents. Here we discovered two C. acuminata cytochrome P450 monooxygenases that catalyze regio-specific 10- and 11-oxidations of camptothecin, and demonstrated combinatorial chemoenzymatic C-H functionalizations of the camptothecin scaffold using the new enzymes to produce a suite of anticancer drugs, including topotecan (Hycamtin®) and irinotecan (Camptosar®). This work sheds new light into camptothecin metabolism, and represents greener approaches for accessing clinically relevant camptothecin derivatives.

In Vitro Metabolism of E2, G2: Novel Bile Acid-Coupling Camptothecin Analogues, in Rat Liver Microsomes

Background: E2 (Camptothecin - 20 (S) - O- glycine - deoxycholic acid), and G2 (Camptothecin - 20 (S) - O - acetate - deoxycholic acid) are two novel bile acid-derived camptothecin analogues by introducing deoxycholic acid in 20-position of CPT(camptothecin) with greater anticancer activity and lower systematic toxicity in vivo. Objective: We aimed to investigate the metabolism of E2 and G2 by Rat Liver Microsomes (RLM). Methods: Phase Ⅰ and Phase Ⅱ metabolism of E2 and G2 in rat liver microsomes were performed respectively, and the mixed incubation of phase I and phase Ⅱ metabolism of E2 and G2 was also processed. Metabolites were identified by liquid chromatographic/mass spectrometry. Results: The results showed that phase I metabolism was the major biotransformation route for both E2 and G2. The isoenzyme involved in their metabolism had some difference. The intrinsic clearance of G2 was 174.7mL/min. mg protein, more than three times of that of E2 (51.3 mL/min . mg protein), indicating a greater metabolism stability of E2. 10 metabolites of E2 and 14 metabolites of G2 were detected, including phase I metabolites (mainly via hydroxylations and hydrolysis) and their further glucuronidation products. Conclusion: These findings suggested that E2 and G2 have similar biotransformation pathways except some difference in the hydrolysis ability of the ester bond and amino bond from the parent compounds, which may result in the diversity of their metabolism stability and responsible CYPs(Cytochrome P450 proteins).