**William R. Arnold 1, Susan Zelasko 1, Daryl D. Meling 1, Kimberly Sam <sup>1</sup> and Aditi Das 1,2,3,4,\***


Received: 30 August 2019; Accepted: 13 September 2019; Published: 18 September 2019

**Abstract:** Cytochrome P450 2C8 (CYP2C8) epoxygenase is responsible for the metabolism of over 60 clinically relevant drugs, notably the anticancer drug Taxol (paclitaxel, PAC). Specifically, there are naturally occurring polymorphisms, CYP2C8\*2 and CYP2C8\*3, that display altered PAC hydroxylation rates despite these mutations not being located in the active site. Herein, we demonstrate that these polymorphisms result in a greater uncoupling of PAC metabolism by increasing the amount of hydrogen peroxide formed per PAC turnover. Anaerobic stopped-flow measurements determined that these polymorphisms have altered first electron transfer kinetics, compared to CYP2C8\*1 (wildtype), that suggest electron transfer from cytochrome P450 reductase (CPR) is disfavored. Therefore, these data demonstrate that these polymorphisms affect the catalytic cycle of CYP2C8 and suggest that redox interactions with CPR are disrupted.

**Keywords:** CYP2C8; polymorphisms; reactive oxygen species; paclitaxel; cytochrome P450 reductase; electron transfer
