ABSTRACT:Recently, two new classes of reversible inhibitors, the benzbromarones (BZBRs) and the N-3 substituted phenobarbitals (PBs), were used to study the active site characteristics of CYP2C9 and 2C19, respectively. Since these ligands are some of the first CYP2C ligands to extend into the low nanomolar K i range (K i < 100 nM), they were subjected to three-dimensional quantitative structureactivity relationship (3D-QSAR) analysis. Given that BZBRs or the PB ligands bind very tightly, it can be assumed that these structures complement the binding pocket(s) for these enzymes. Thus, the resulting models should output a 3D arrangement of interaction sites predicted to be important for near optimal binding to the CYP2C9 and CYP2C19 enzymes. These predicted interaction regions may then improve the ability to predict drug-drug interactions. The resulting models generated from these new high affinity ligands are discussed, as are novel uses of 3D-QSAR and molecular modeling techniques that may be useful in the study of cytochromes P450 specifically.In ligand-based molecular modeling, knowledge accumulated from experimentation is used to build and test potential models for predicting ligand-protein interactions and hence drug-drug interactions, the sites of drug metabolism, toxicity, and other parameters. Recently, CYP2C9 and CYP2C19 inhibitors with 1 to 2 orders of magnitude lower K i values than previously characterized compounds have been reported (Suzuki et al., 2002;Locuson et al., 2003). These new inhibitors should help expand various models for CYP2C metabolism. Several groups have published 3D quantitative structure-activity relationship analysis (3D-QSAR) models for P450s, including multiple models for CYP2C9. Therefore, it is relevant to address how the newer, more potent inhibitors, which fit the same alignment rules used previously, have altered existing QSAR models for CYP2C9 and, in some cases, provided distinctions between the chemical properties that appear to define inhibitors of CYP2C9 and CYP2C19. Finally, new applications of 3D-QSAR modeling and how it may enhance P450 metabolism research is discussed.
What Can High Affinity Ligands of P450s Tell Us?The pursuit for, and study of, high affinity P450 ligands remains an important endeavor. High affinity ligands for each P450 enzyme can help define the enzyme in the form of a pharmacophore, improving the identification of drug leads with the highest potential for drugdrug interactions based on their structure. In practice, this is a lofty goal because determining drug interaction potential in any quantitative manner requires an accurate, universal binding model that can predict any compound's affinity for a given enzyme. Establishing such a model, however, can be difficult because: 1) models used for prediction can only be based on what is currently known, and 2) P450s display complex binding behavior and conformational flexibility. Investigators may have the ability to screen new drugs for their drug interaction potential with the use of selective su...