clostridium-perfringens-delta-toxin and Urinary-Bladder-Neoplasms

NF-E2-related factor 2 (Nrf2) is a major cytoprotective gene and is a key chemopreventive target against cancer and other diseases. Here we show that Nrf2 faces a dilemma in defense against 4-aminobiphenyl (ABP), a major human bladder carcinogen from tobacco smoke and other environmental sources. Although Nrf2 protected mouse liver against ABP (which is metabolically activated in liver), the bladder level of N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-ABP), the predominant ABP-DNA adduct formed in bladder cells and tissues, was markedly higher in Nrf2(+/+) mice than in Nrf2(-/-) mice after ABP exposure. Notably, Nrf2 protected bladder cells against ABP in vitro. Mechanistic investigations showed that the dichotomous effects of Nrf2 could be explained at least partly by upregulation of UDP-glucuronosyltransferase (UGT). Nrf2 promoted conjugation of ABP with glucuronic acid in the liver, increasing urinary excretion of the conjugate. Although glucuronidation of ABP and its metabolites is a detoxification process, these conjugates, which are excreted in urine, are known to be unstable in acidic urine, leading to delivery of the parent compounds to bladder. Hence, although higher liver UGT activity may protect the liver against ABP, it increases bladder exposure to ABP. These findings raise concerns of potential bladder toxicity when Nrf2-activating chemopreventive agents are used in humans exposed to ABP, especially in smokers. We further show that 5,6-dihydrocyclopenta[c][1,2]-dithiole-3(4H)-thione (CPDT) significantly inhibits dG-C8-ABP formation in bladder cells and tissues but does not seem to significantly modulate ABP-catalyzing UGT in liver. Thus, CPDT exemplifies a counteracting solution to the dilemma posed by Nrf2.

Topics: Aminobiphenyl Compounds; Animals; Carcinogens; Cell Line, Tumor; Chemoprevention; Cytoprotection; DNA Adducts; DNA Damage; Glucuronosyltransferase; Humans; Liver; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; NF-E2-Related Factor 2; Sulfhydryl Compounds; Thiones; Tumor Cells, Cultured; Urinary Bladder; Urinary Bladder Neoplasms

Dithiolethiones are a family of promising cancer chemopreventive agents, and induction of phase 2 enzymes is key to their chemopreventive activities. Two dithiolethiones have been evaluated in humans for cancer prevention. While some chemopreventive activities were detected in several human studies, potential side effects are a concern. Herein, we report structure-activity relationships of 25 dithiolethiones. Several compounds show exceedingly potent and bladder specific activity in phase 2 enzyme induction. Structural features responsible for such activity, as well as those inhibiting the activity, are discussed. Moreover, the compounds activate and depend on Nrf2 for their inductive activities. Nrf2 is a major transcriptional stimulator of cytoprotective genes and is critical for cancer prevention. Thus, several new dithiolethiones that are highly promising for bladder cancer prevention have been identified. Because the compounds act specifically in the bladder, the likelihood of potential systemic toxicity may be low.

Topics: Animals; Anticarcinogenic Agents; Cell Line, Tumor; Enzyme Induction; Female; Gene Knockdown Techniques; Glutathione Transferase; NAD(P)H Dehydrogenase (Quinone); NF-E2-Related Factor 2; Organ Specificity; Rats; Rats, Sprague-Dawley; Structure-Activity Relationship; Thiones; Thiophenes; Urinary Bladder; Urinary Bladder Neoplasms

It has been widely recognized that induction of Phase 2 enzymes is an effective and sufficient strategy for achieving protection against carcinogenesis. Nrf2 is the unifying master regulator of these enzymes and its activation in various tissues, including the urinary bladder, is associated with inhibition of carcinogenesis. 5,6-Dihydrocyclopenta[c][1,2]-dithiole-3(4H)-thione (CPDT) is a highly potent inducer of Phase 2 enzymes and an activator of Nrf2. In vivo, it is particularly effective in the bladder, showing significant effects in this tissue when dosed to rats at levels as low as 0.98 micromol/(kgday) (0.17 mg/(kg day)). The activities of key Phase 2 enzymes, including glutathione S-transferase, NAD(P)H:quinone:oxidoreductase 1 and glutamate cysteine synthetase, and levels of glutathione were elevated by CPDT in rat bladder in vivo and in cultured bladder cells in vitro. In the bladder, enzyme induction and Nrf2 activation appear to occur exclusively in the epithelium. This is highly significant, since almost all bladder cancers develop from the epithelium. Studies in cultured bladder cells using siRNA to knock down Nrf2 or in cells with total Nrf2 knockout showed that the ability of CPDT to induce Phase 2 enzymes depends completely on Nrf2. In conclusion, CPDT potently and preferentially induces Phase 2 enzymes in the bladder epithelium and Nrf2 is its key mediator.

Topics: Animals; Antineoplastic Agents; Blotting, Western; Cell Line, Tumor; Cells, Cultured; Dose-Response Relationship, Drug; Enzyme Activation; Female; Glutathione; Immunohistochemistry; NF-E2-Related Factor 2; Rats; Rats, Sprague-Dawley; Sulfhydryl Compounds; Thiones; Time Factors; Urinary Bladder Neoplasms