Production of metabolites of the anti-cancer drug noscapine using a P450BM3 mutant library

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Mutants of P450_BM3 can metabolise noscapine.

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Noscapine is N-demethylated with high selectivity.

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The metabolites produced are of interest for drug development.

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The profile of metabolites generated resembles that of mammalian CYP3A4.

Cytochrome P450 enzymes are a promising tool for the late-stage diversification of lead drug candidates and can provide an alternative route to structural modifications that are difficult to achieve with synthetic chemistry. In this study, a library of P450_BM3 mutants was produced using site-directed mutagenesis and the enzymes screened for metabolism of the opium poppy alkaloid noscapine, a drug with anticancer activity. Of the 18 enzyme mutants screened, 12 showed an ability to metabolise noscapine that was not present in the wild-type enzyme. Five noscapine metabolites were detected by LC-MS/MS, with the major metabolite for all mutants being N-demethylated noscapine. The highest observed regioselectivity for N-demethylation was 88%. Two hydroxylated metabolites, a catechol and two C-C cleavage products were also detected. P450-mediated production of hydroxylated and N-demethylated noscapine structures may be useful for the development of noscapine analogues with improved biological activity. The variation in substrate turnover, coupling efficiency and product distribution between the active mutants was considered alongside in silico docking experiments to gain insight into structural and functional effects of the introduced mutations. Selected mutants were identified as targets for further mutagenesis to improve activity and when coupled with an optimised process may provide a route for the preparative-scale production of noscapine metabolites.

Role of farnesoid X receptor in establishment of ontogeny of phase-I drug metabolizing enzyme genes in mouse liver

The expression of phase-I drug metabolizing enzymes in liver changes dramatically during postnatal liver maturation. Farnesoid X receptor (FXR) is critical for bile acid and lipid homeostasis in liver. However, the role of FXR in regulating ontogeny of phase-I drug metabolizing genes is not clear. Hence, we applied RNA-sequencing to quantify the developmental expression of phase-I genes in both Fxr-null and control (C57BL/6) mouse livers during development. Liver samples of male C57BL/6 and Fxr-null mice at 6 different ages from prenatal to adult were used. The Fxr-null showed an overall effect to diminish the “day-1 surge” of phase-I gene expression, including cytochrome P450s at neonatal ages. Among the 185 phase-I genes from 12 different families, 136 were expressed, and differential expression during development occurred in genes from all 12 phase-I families, including hydrolysis: carboxylesterase (Ces), paraoxonase (Pon), and epoxide hydrolase (Ephx); reduction: aldoketo reductase (Akr), quinone oxidoreductase (Nqo), and dihydropyrimidine dehydrogenase (Dpyd); and oxidation: alcohol dehydrogenase (Adh), aldehyde dehydrogenase (Aldh), flavin monooxygenases (Fmo), molybdenum hydroxylase (Aox and Xdh), cytochrome P450 (P450), and cytochrome P450 oxidoreductase (Por). The data also suggested new phase-I genes potentially targeted by FXR. These results revealed an important role of FXR in regulation of ontogeny of phase-I genes.

Isoniazid metabolism and hepatotoxicity

Isoniazid (INH) is highly effective for the management of tuberculosis. However, it can cause liver injury and even liver failure. INH metabolism has been thought to be associated with INH-induced liver injury. This review summarized the metabolic pathways of INH and discussed their associations with INH-induced liver injury.

Possible involvement of nuclear factor erythroid 2-related factor 2 in the gene expression of Cyp2b10 and Cyp2a5

Cytochrome P450 gene expression is altered by various chemical compounds. In this study, we used nuclear factor erythroid 2-related factor 2 (Nrf2)–deficient (Nrf2^−⧸−) mice to investigate the involvement of Nrf2 in Cyp2b10 and Cyp2a5 gene expression. Phorone, an Nrf2 activator, strongly increased Cyp2b10 and Cyp2a5 mRNA as well as Nrf2 target genes, including NAD(P)H-quinone oxidoreductase-1 and heme oxygenase-1, in wild-type mouse livers 8 h after treatment. The phorone-induced mRNA levels in Nrf2^−⧸− mouse livers were lower than that in wild-type mouse livers. Nrf2^−⧸− mice showed attenuated Cyp2b10 and Cyp2a5 induction by phenobarbital, a classical Cyp2b inducer. These findings suggest that the Nrf2 pathway is involved in Cyp2b10 and Cyp2a5 gene expression.

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Phorone, an α,β-unsaturated carbonyl compound, induced Cyp2b10 and Cyp2a5.

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Phorone suppressed the induction of Cyp2b10 and Cyp2a5 in Nrf2^−⧸− mouse livers.

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Nrf2^−⧸− mice showed suppressed phenobarbital-induced Cyp2b10 and Cyp2a5.