Mapping of cytochrome P-450 distribution and function with monoclonal antibodies and cDNA expression.

A large number of cytochrome P-450 forms are responsible for the metabolism and detoxification as well as the mutagenic and carcinogenic activation of numerous classes of xenobiotics. These include drugs and carcinogens and other environmental chemicals. The cytochrome P-450 enzymes are also responsible for the metabolism of endogenous substrates including fatty acids, prostaglandins and all classes of steroids. In order to fully understand the role of each P-450 in a specific metabolic reaction, it is necessary to know both the substrate and product specificity of each P-450 as well as the contribution of the individual P-450 to the total metabolism catalyzed in a tissue containing many P-450 forms. Our laboratory has cloned and expressed, with various vectors, a number of rodent and human P-450s. This technique has enabled us to determine the specificity of individual forms of P-450 for certain substrate utilization and product formation, as well as for the metabolic activation of promutagens to their mutagenic forms. The latter has been measured with the Ames mutagen detection system coupled to mutagen activation by vaccinia expressed single P-450s. Mutagenesis and DNA binding have also been measured with a human cell line stably expressing a single P-450. The former approach determines the specificity of single P-450s in cell lysates and the latter determines P-450 specificity in the living cell. In a complementary approach, we have prepared, characterized and utilized inhibitory monoclonal antibodies to six epitope specific classes of P-450. The inhibitory antibodies block the enzymatic activities of specific P-450s in tissue preparations and thus define the contribution of the single P-450 to the total reaction. This approach can be used to measure many P-450 functions, e.g., substrate utilization, product formation, stereochemical metabolism, mutagen activation, drug toxicity, and DNA binding. The two complementary techniques of cDNA expression and immunoinhibition have been used to examine a number of different classes of compounds with respect to their metabolism and mutagen activation. These approaches may eventually yield an atlas of individual P-450 function and their contribution to the total metabolism of xenobiotics and endobiotics.