Insights into drug metabolism by cytochromes P450 from modelling studies of CYP2D6-drug interactions.

The cytochromes P450 (CYPs) comprise a vast superfamily of enzymes found in virtually all life forms. In mammals, xenobiotic metabolizing CYPs provide crucial protection from the effects of exposure to a wide variety of chemicals, including environmental toxins and therapeutic drugs. Ideally, the information on the possible metabolism by CYPs required during drug development would be obtained from crystal structures of all the CYPs of interest. For some years only crystal structures of distantly related bacterial CYPs were available and homology modelling techniques were used to bridge the gap and produce structural models of human CYPs, and thereby obtain useful functional information. A significant step forward in the reliability of these models came seven years ago with the first crystal structure of a mammalian CYP, rabbit CYP2C5, followed by the structures of six human enzymes, CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2D6 and CYP3A4, and a second rabbit enzyme, CYP2B4. In this review we describe as a case study the evolution of a CYP2D6 model, leading to the validation of the model as an in silico tool for predicting binding and metabolism. This work has led directly to the successful design of CYP2D6 mutants with novel activity-including creating a testosterone hydroxylase, converting quinidine from inhibitor to substrate, creating a diclofenac hydroxylase and creating a dextromethorphan O-demethylase. Our modelling-derived hypothesis-driven integrated interdisciplinary studies have given key insight into the molecular determinants of CYP2D6 and other important drug metabolizing enzymes.

From "hemoabzymes" to "hemozymes": towards new biocatalysts for selective oxidations.

The design of artificial hemoproteins that could catalyze selective oxidations using clean oxidants such as O2 or H2O2 under ecocompatible conditions constitutes a real challenge for a wide range of industrial applications. In vivo, such reactions are performed by heme-thiolate proteins, cytochromes P450, which catalyze the oxidation of substrates by dioxygen in the presence of electrons delivered from NADPH by cytochrome P450 reductase. Several strategies were used to design new artificial hemoproteins that mimic these enzymes. The first one involved the non-covalent association of synthetic hemes with monoclonal antibodies raised against these cofactors. This led to the first generation of artificial hemoproteins or "hemoabzymes" that displayed a peroxidase activity, and in some cases catalyzed the regioselective nitration of phenols by H2O2/NO2 and the stereoselective oxidation of sulfides by H2O2. The second one involved the non-covalent association of easily affordable non-relevant proteins with metalloporphyrin derivatives, using either the "Trojan Horse strategy" or the "host-guest" strategy. This led to a second generation of artificial hemoproteins or "hemozymes", some of which were found able to catalyze the stereoselective oxidation of organic compounds such as sulfides and alkenes by H2O2 and KHSO5.