Human CYP2C9 Metabolism of Organophosphorus Pesticides and Nerve Agent Surrogates

Of the Cytochrome P450 enzymes, the CYP2C9 variant is very important in the metabolism of several human drugs, acting as a natural bioscavenger. Previously, CYP2C9 was shown to convert the thion (P=S) to the oxon (P=O) form for some organophosphorus (OP) pesticides, such as dimethoate, diazinon, and parathion. In this study, we tested the ability of CYP2C9 to degrade other OP compounds. We investigated the metabolism of OP compounds by CYP2C9 using LC-MS/MS as well as time-dependent inhibition using the previously developed pFluor50 fluorogenic assay. We found that CYP2C9 metabolizes thions preferentially over oxons, and that many OP compounds inhibit CYP2C9 activity in a time-dependent manner. Additionally, we performed molecular docking based on the crystal structure (1OG5) of the CYP2C9 receptor. We observed a positive, though moderate, correlation between the calculated binding energy and the CYP2C9 metabolism of various OP compounds (R = 0.59). These in vitro data, combined with further analysis and additional OP derivatives, could potentially be used to develop artificial intelligence (AI)/machine learning (ML) models to predict the metabolism of specific OP compounds by CYP2C9. This type of approach could be particularly relevant for the prediction of the metabolism of current and emerging chemical warfare agents.