DMBA DERVIVATIVES AND CHEMICAL CARCINOGENESIS

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The unified hypothesis, for the carcinogenic properties of polycyclic aromatic hydrocarbons (PAH), predicts that the 7- hydroxymethyl sulfate ester, SMBA, plays a major role in the metabolic activation, DNA binding, and complete carcinogenicity of 7,12-dimethylbenz[a]a nth racene (DMBA). However, alternative hypotheses predict that other pathways may play a role in DMBA carcinogenesis. It is therefore a matter of considerable interest to identify clearly the ultimate electrophilic and carcinogenic forms. To test the validity and generality of the hypothesis for the carcinogenic properties of DMBA and model metabolites, we plan to carry out: 1) The preparation and characterization of selected DMBA derivatives, 2) The metabolism of DMBA and selected derivatives/metabolites in rat-liver homogenates, in vitro, and in liver and mammary gland, in vivo. The products of metabolism will be identified and compared using HPLC and GC/MS, with a number of reference model metabolites, 3) The identification of the most carcinogenic forms of DMBA and of the model metabolite 7-formyl-12-methyl benz[a]anthracene (7-FMBA) in a complete carcinogenesis model, 4) The formation and identification of DMBA and 7-FMBA related DNA adducts, in vitro and in vivo using the 32P-postlabeling method together with LC/MS/MS. Sulfation of the 7-hydroxymethyl derivative and other hydroxyalkyl derivatives of PAH, by 3'-phosphoadenosine-5'-phosphosulfate-dependent sulfotransferase activity, can metabolically activate primary and secondary benzylic alcohol derivatives to ultimate electrophilic mutagens and carcinogens. Since the aralkylating agents formed may be the most carcinogenic derivatives of PAH yet identified, electrophilic hydroxyalkyl sulfate ester formation appears to be a major pathway for the metabolic activation of proximate carcinogens to DNA damaging ultimate carcinogens. Work done by our group and by others has resulted in enough evidence to convince many researchers that electrophilic hydroxyalkyl sulfate esters, and closely related aralkylating agents, play a major role in causing DNA damage, mutagenesis, and carcinogenesis. Identification of the ultimate electrophilic and carcinogenic forms of DMBA and 7-FMBA may eventually lead to methods for the prevention of some of the human cancer that is currently considered to be caused by this class of chemical carcinogens.