Interactive effects of nrf2 genotype and oltipraz on benzo[a]pyrene-DNA adducts and tumor yield in mice

Abstract

The cancer chemopreventive actions of oltipraz (4-methyl-5-[2-pyrazinyl]-1,2-dithiole-3-thione) have been primarily associated with the induction of phase 2 detoxifying enzymes through transcriptional activation of the antioxidant response element (ARE) in the promoter regions of these genes. The transcription factor Nrf2 has been shown to bind to and activate AREs. Previously, we demonstrated that nrf2-deficient mice had low basal expression of phase 2 enzymes and were substantially more susceptible to benzo[a]pyrene (B[a]P)-induced neoplasia of the forestomach than wild-type. Moreover, loss of Nrf2 abrogated the chemopreventive action of oltipraz, when administered 48 h before B[a]P, an interval allowing maximal induction of many phase 2 enzymes. Oltipraz also inhibits some cytochrome P450s involved in the bioactivation of B[a]P. In the present study we observed that oltipraz had no protective effect on tumor burden in the forestomach of nrf2-deficient mice when administered 1 h before B[a]P, a timeline that selectively optimizes for possible inhibitory effects on cytochrome P450s. To evaluate the role of nrf2 genotype on B[a]P disposition, levels of B[a]P-DNA adducts were measured as tetrols released from DNA isolated from target (forestomach) and non-target tissues (liver) of wild-type and nrf2-deficient mice treated with either vehicle or oltipraz 1 or 48 h before B[a]P. Levels of B[a]P-DNA adducts in forestomach were significantly higher in nrf2-deficient compared with wild-type mice. Oltipraz treatment at 1 or 48 h before B[a]P had no protective effect on forestomach tetrol levels in nrf2-deficient mice, whereas a significant reduction was observed in wild-type mice treated with oltipraz 48 h, but not 1 h, before carcinogen. Combining all treatments and genotypes, there was a strong correlation (R(2) = 0.91) between levels of B[a]P-DNA adducts in forestomach and subsequent yield of tumors. In contrast to the results in forestomach, nrf2 genotype did not modify hepatic B[a]P-DNA adduct levels while both oltipraz treatments were protective, suggesting that Nrf2-independent mechanisms (e.g. P450 inhibition) for oltipraz can also occur in vivo in some tissues.

Increased colonic inflammatory injury and formation of aberrant crypt foci in Nrf2‐deficient mice upon dextran sulfate treatment

“…Previous studies have already confirmed the efficacy of small molecule activators of Nrf2 signaling in the prevention of electrophile-induced chemical carcinogenesis. 26,51,52 Given the strong influence of Nrf2 genotype on the progression of inflammationmediated tumorigenesis, modulation of the Nrf2 pathway by small molecules may be a useful chemopreventive strategy in this setting as well.…”

Protection from mitochondrial complex II inhibitionin vitroandin vivoby Nrf2-mediated transcription

“…These enzymes consequently increase levels of glutathione and NADPH, freeradical scavenging, and other protective pathways. Nrf2 Ϫ/Ϫ mice, lacking the ability to induce ARE-driven gene expression, are more susceptible to a variety of toxic insults in vivo (35,38,59,60). Furthermore, Nrf2 Ϫ/Ϫ mice are known to spontaneously develop hemolytic anemia and a lupus-like syndrome relatively late in life (52,61,62).…”

Kinetic, Thermodynamic, and Structural Characterizations of the Association between Nrf2-DLGex Degron and Keap1

“…Structural characteristics of Keap1-DC and DLG long-peptide interaction. We compared the previous Keap1-DLG crystal structure with a short DLG peptide, DLG 15 (9,41), with the current Keap1-DLGex crystal structure. We found that the main chain of DLGex shows nearly the same configuration as that of DLG 15 (Fig.…”

“…Nrf2-deficient mice are prone to both chemical toxicity and tumorigenesis (15)(16)(17)(18). Recently, somatic mutations of human KEAP1 and NRF2 have also been identified in various types of cancers.…”