Our objective is to elucidate the mechanism(s) by which naturally occurring organosulfur compounds (OSCs) inhibit benzo(a)pyrene (BP) induced neoplasia of lung and forestomach in mice. It is well known that BP induced neoplasia depends upon the activation/inactivation pathways of its metabolism. While cytochrome P450 dependent monooxygenases contribute to the generation of reactive metabolites including the ultimate carcinogenic species anti-BPDE, glutathione transferases (GST) and UDP- glucuronyl transferase (UDP-GT) play an important role in detoxification of BP metabolites. Thus, it is reasonable to hypothesize that OSCs may exert anti-neoplastic activity by modulating the activation and/or inactivation pathways of BP metabolism. Although OSC treatment is known to increase GST activity in certain mice tissues, their effect on other pathways of BP metabolism are not fully known. The role of BP activation pathways in chemoprevention by OSCs will be assessed by determining the effect of OSCs on (i) cellular levels as well as catalytic activities of the enzymes involved in bioactivation of BP, (ii) nature and persistence of BP-DNA adduction, and (iii) pattern of BP metabolism in female A/J mice liver, lung and forestomach. Effect of OSCs on inactivation pathways of BP metabolism will also be determined to evaluate their significance in the anti-neoplastic activity of these phytochemicals. To accomplish this, we propose to determine the effect of OSCs on the levels of individual GST isoenzymes and UDP-GT in mice tissues. Substrate specificity and kinetic constants of purified murine GSTs for the conjugation of anti-BPDE with GSH will also be determined. Finally, to establish the significance of GST induction in anti-neoplastic activity of OSCs, we propose to determine the effect of buthionine sulfoximine induced GSH depletion (which will interfere with the GST catalyzed inactivation of anti-BPDE) on BP induced neoplasia of lung and forestomach in control and OSC treated animals. Diallyl sulfide, diallyl disulfide and diallyl trisulfide will be utilized in these studies to uncover the reasons for the differential effectiveness and tissue selectivity of certain OSCs. Saturated analogues of diallyl sulfide and diallyl disulfide (dipropyl sulfide and dipropyl disulfide, respectively), which do not inhibit BP induced neoplasia, will be used as negative controls and may help in identifying the mechanism(s) involved in chemoprevention by OSCs. These studies, in the long term, may prove to be useful in developing strategies for chemoprevention.
