Expression and activity of taxane-metabolizing enzymes in ovarian tumors

Current firstline chemotherapy for ovarian cancer consists of carboplatin combined with either paclitaxel or docetaxel. Disposition of carboplatin is determined by renal clearance, while the taxanes are metabolized by cytochrome P450 (CYP450) enzymes. Although the majority of taxane metabolism occurs in the liver, recent data have shown that some solid tumors express CYP450 enzymes in the tumors themselves. The objective of this study was to determine whether ovarian tumors express genes regulating cellular efflux and subsequent metabolism, and whether any clinico-pathologic features correlated with expression.

Gene expression of CYP2C8, CYP3A4/A5 and the ABC transporter ABCB1 was determined in 56 primary epithelial ovarian tumors. Cells were grown from seven different tumors and exposed ex vivo to paclitaxel (PAC) and docetaxel (DOC) for up to 24 h. PAC and DOC concentrations were measured in the media by an LC-MS assay.

Results from this analysis demonstrate that ovarian cancer cells do express functional taxane-metabolizing enzymes. Such expression appeared to enhance the ability of cancer cells to metabolize DOC. Specifically, the PK of DOC was correlated with the ratio of CYP4A5 to ABCB1 gene expression, thus representing a novel mechanism of chemotherapy resistance. There was no relationship between PAC PK parameters and gene expression.

Knowledge of inter-individual variation in CYP450 enzyme and ABC transporter tumor expression and activity may influence the individualization of chemotherapy, by avoiding agents that are rapidly metabolized and selecting agents that are not.