ACTIVATION OF CARCINOGENS BY UROTHELIUM IN VITRO

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The main objective of this project is to elucidate the biochemical mechanisms of 4-aminobiphenyl (ABP)-induced bladder carcinogenesis in humans. We hypothesize that enzymes present in the transitional epithelial cells of the bladder activate ABP and/or its proximate metabolites. Using human uroepithelial cells (UEC) and the human bladder carcinogen, ABP, as a model system, we will examine the biochemical steps and enzymes involved in the activation of ABP and its proximate metabolites, namely N-hydroxy-4-aminobiphenyl (N-OH-ABP), its N- glucuronide (N-Glu-OH-ABP), N-hydroxy-4-acetylaminobiphenyl (N-OH-AABP) and its O-glucuronide (N-OGlu-AABP). The proximate metabolites that are activated by human UEC will be determined by: 1) testing the cytosolic and microsomal fractions of human UEC for certain enzymatic activities such as acetylation, deacetylation, transacetylation, sulfonation, glucuronidation and peroxidation; ii) isolating and identifying the DNA-adducts; and iii) assaying for UEC-mediating mutagenicity. Our results with human UEC demonstrate that deacetylase may be involved in the activation of N-OH-AABP. The role of deacetylase(s) in susceptibility to bladder carcinogenesis induced by ABP and 4-acetylaminobiphenyl (AABP) will be assessed. Towards this aim, qualitative and quantitative comparative studies on the distribution of deacetylase(s) in the target UEC of refractory (rat) versus susceptible (human and dog) species will be conducted. The biological effects of the interactions of the electrophilic metabolites of ABP with urothelial cellular DNA will be examined by mutagenicity tests. For this purpose, we will first develop a human UEC-mutagenicity system selecting for mutants at the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) locus. Subsequently we will test the mutagenic effects of the different proximate metabolites of ABP directly on the target urothelial cells. These studies thus address the critical biochemical mechanisms involved in the initiation of bladder neoplasia in humans. The information gained from these studies will be useful in identifying the key metabolic factors that might be involved in susceptibility to arylamine-induced bladder carcinogenesis.