This project is focused on identifying and developing novel dithiolethiones for the prevention of urinary bladder cancer. Many lines of evidence show that carcinogen-detoxifying Phase 2 enzymes play a major role in bladder cancer prevention. We have recently found that 5,6-dihydrocyclopenta[c]-1,2-dithiole-3(4H)-thione (CPDT) is an extremely efficacious inducer of Phase 2 enzymes in rodent bladders in vivo and hypothesize that CPDT or a more potent analog would be a highly effective protector against bladder cancer.
Aim 1 of the project is to further characterize the Phase 2 enzyme-inducing property of CPDT, to examine the toxicity and pharmacokinetic behavior of CPDT, and to test CPDT analogs for identification of more potent inducers of Phase 2 enzymes. These studies will be performed in rats; the impact of the test compound on three important Phase 2 enzymes (GST, NQO1 and UGT) will be measured; CPDT analogs will be synthesized; various parameters of toxicity and pharmacokinetics of CPDT will be measured.
Aim 2 is to determine which GST and UGT isoforms are induced by CPDT and its more potent analogs (identified in Aim 1), whether such induction is species specific, and if CPDT is metabolized in cells to a new inducer form. The response of the isoforms of GST and UGT which were shown to play important roles in bladder cancer prevention will be examined using bladder epithelial cells from humans and rodents. CPDT metabolism will be investigated using radiolabeled CPDT and LC/MS/MS.
Aim 3 is to elucidate the molecular mechanism responsible for the induction of Phase 2 enzymes by CPDT and its analogs. We hypothesize that Nrf2 (a transcriptional factor) plays a major role in mediating such an induction.
Aim 4 is to assess the protective effects of CPDT or a more promising analog against the genotoxicities of bladder carcinogens in bladder cells both in vitro and in vivo, as measured by DMA damage and cell/tissue proliferation, and to investigate the role of the Nrf2 signaling pathway in mediating such an effect, using cultured bladder epithelial cells and mice with and without Nrf2 function. Studies carried out in Aim 4 will also serve to identify the appropriate dose levels of the dithiolethione for further experimentation in Aim 5.
Aim 5 is to determine the inhibitory effect of the dithiolethione examined in Aim 4 on bladder tumorigenesis induced by a chemical carcinogen in vivo and the role of Nrf2 signaling in mediating such an effect, using wild type and Nrf2 knockout mice. ? ? ?
