Development of a TK6-derived cell line expressing four human cytochrome P450s for genotoxicity testing

Abstract

Metabolism is essential for in vitro genotoxicity testing. We previously developed a panel of TK6 cell lines, each expressing one of 14 human cytochrome P450 (CYP) enzymes, demonstrating their ability to effectively bioactivate indirect genotoxicants without relying on a rodent liver S9 fraction. In the present study, we extended this work by developing a TK6 cell line co-expressing four human CYP enzymes, including CYP2A6, CYP2E1, CYP2C19, and CYP3A4 (designated as TK6-4CYP), and subsequently assessed its capability to metabolize and activate pro-genotoxicants. Human lymphoblastoid TK6 cells were sequentially transduced with lentiviral vectors carrying CYP2A6/2E1 and CYP2C19/3A4, resulting in more than a 2¹⁰-fold increase in mRNA expression levels for each CYP compared to parental cells. RNA sequencing revealed selective upregulation of the four CYPs. Their protein expression and enzymatic activities were also confirmed. TK6-4CYP cells were subsequently tested with four CYP-metabolized pro-genotoxicants, including N-nitroso-diethylamine (NDEA) metabolized by CYP2A6, N-nitroso-dimethylamine (NDMA) by CYP2E1, N-nitroso-propranolol (NNP) by CYP2C19, and riddelliine by CYP3A4, in the micronucleus assay, cell cycle analysis, and comet assay. Significant increases were observed in the percentage (%) of micronuclei induction, G2/M phase arrest, and % DNA in tails with all compounds except riddelliine, which showed increases in % micronuclei induction and G2/M phase arrest but no positive response in the comet assay. This study establishes proof-of-concept for using a TK6 cell model co-expressing multiple drug-metabolizing enzymes for genotoxicity evaluation.