Induction of complementary function reductase enzymes in colon cancer cells by dithiole-3-thione versus sodium selenite

Potential Applications of NRF2 Modulators in Cancer Therapy

The nuclear factor erythroid 2-related factor 2 (NRF2)-Kelch-like ECH-associated protein 1 (KEAP1) regulatory pathway plays an essential role in protecting cells and tissues from oxidative, electrophilic, and xenobiotic stress. By controlling the transactivation of over 500 cytoprotective genes, the NRF2 transcription factor has been implicated in the physiopathology of several human diseases, including cancer. In this respect, accumulating evidence indicates that NRF2 can act as a double-edged sword, being able to mediate tumor suppressive or pro-oncogenic functions, depending on the specific biological context of its activation. Thus, a better understanding of the mechanisms that control NRF2 functions and the most appropriate context of its activation is a prerequisite for the development of effective therapeutic strategies based on NRF2 modulation. In line of principle, the controlled activation of NRF2 might reduce the risk of cancer initiation and development in normal cells by scavenging reactive-oxygen species (ROS) and by preventing genomic instability through decreased DNA damage. In contrast however, already transformed cells with constitutive or prolonged activation of NRF2 signaling might represent a major clinical hurdle and exhibit an aggressive phenotype characterized by therapy resistance and unfavorable prognosis, requiring the use of NRF2 inhibitors. In this review, we will focus on the dual roles of the NRF2-KEAP1 pathway in cancer promotion and inhibition, describing the mechanisms of its activation and potential therapeutic strategies based on the use of context-specific modulation of NRF2.

Ptgr1 expression is regulated by NRF2 in rat hepatocarcinogenesis and promotes cell proliferation and resistance to oxidative stress

Prostaglandin reductase-1 (Ptgr1) is an alkenal/one oxidoreductase that is involved in the catabolism of eicosanoids and lipid peroxidation such as 4-hydroxynonenal (4-HNE). Recently, we reported that Ptgr1 is overexpressed in human clinical and experimentally induced samples of hepatocellular carcinoma (HCC). However, how the expression of this gene is regulated and its role in carcinogenesis are not yet known. Here, we studied parameters associated with antioxidant responses and the mechanisms underlying the induction of Ptgr1 expression by the activation of Nuclear Factor (erythroid-derived-2)-like-2 (NRF2). For these experiments, we used two protocols of induced hepatocarcinogenesis in rats. Furthermore, we determined the effect of PTGR1 on cell proliferation and resistance to oxidative stress in cell cultures of the epithelial liver cell line, C9. Ptgr1 was overexpressed during the early phase in altered hepatocyte foci, and this high level of expression was maintained in persistent nodules until tumors developed. Ptgr1 expression was regulated by NRF2, which bound to an antioxidant response element at -653bp in the rat Ptgr1 gene. The activation of NRF2 induced the activation of an antioxidant response that included effects on proteins such as glutamate-cysteine ligase, catalytic subunit, NAD(P)H dehydrogenase quinone-1 (NQO1) and glutathione-S-transferase-P (GSTP1). These effects may have produced a reduced status that was associated with a high proliferation rate in experimental tumors. Indeed, when Ptgr1 was stably expressed, we observed a reduction in the time required for proliferation and a protective effect against hydrogen peroxide- and 4-HNE-induced cell death. These data were consistent with data showing colocalization between PTGR1 and 4-HNE protein adducts in liver nodules. These findings suggest that Ptgr1 and antioxidant responses act as a metabolic adaptation and could contribute to proliferation and cell-death evasion in liver tumor cells. Furthermore, these data indicate that Ptgr1 could be used to design early diagnostic tools or targeted therapies for HCC.

High Expression of PTGR1 Promotes NSCLC Cell Growth via Positive Regulation of Cyclin-Dependent Protein Kinase Complex

Lung cancer has been the most common cancer and the main cause of cancer-related deaths worldwide for several decades. PTGR1 (prostaglandin reductase 1), as a bifunctional enzyme, has been involved in the occurrence and progression of cancer. However, its impact on human lung cancer is rarely reported. In this study, we found that PTGR1 was overexpressed in lung cancer based on the analyses of Oncomine. Moreover, lentivirus-mediated shRNA knockdown of PTGR1 reduced cell viability in human lung carcinoma cells 95D and A549 by MTT and colony formation assay. PTGR1 depletion led to G2/M phase cell cycle arrest and increased the proportion of apoptotic cells in 95D cells by flow cytometry. Furthermore, silencing PTGR1 in 95D cells resulted in decreased levels of cyclin-dependent protein kinase complex (CDK1, CDK2, cyclin A2, and cyclin B1) by western blotting and then PTGR1 is positively correlated with cyclin-dependent protein by using the data mining of the Oncomine database. Therefore, our findings suggest that PTGR1 may play a role in lung carcinogenesis through regulating cell proliferation and is a potential new therapeutic strategy for lung cancer.

Sulforaphane Preconditioning Sensitizes Human Colon Cancer Cells towards the Bioreductive Anticancer Prodrug PR-104A

The chemoprotective properties of sulforaphane (SF), derived from cruciferous vegetables, are widely acknowledged to arise from its potent induction of xenobiotic-metabolizing and antioxidant enzymes. However, much less is known about the impact of SF on the efficacy of cancer therapy through the modulation of drug-metabolizing enzymes. To identify proteins modulated by a low concentration of SF, we treated HT29 colon cancer cells with 2.5 μM SF. Protein abundance changes were detected by stable isotope labeling of amino acids in cell culture. Among 18 proteins found to be significantly up-regulated, aldo-keto reductase 1C3 (AKR1C3), bioactivating the DNA cross-linking prodrug PR-104A, was further characterized. Preconditioning HT29 cells with SF reduced the EC50 of PR-104A 3.6-fold. The increase in PR-104A cytotoxicity was linked to AKR1C3 abundance and activity, both induced by SF in a dose-dependent manner. This effect was reproducible in a second colon cancer cell line, SW620, but not in other colon cancer cell lines where AKR1C3 abundance and activity were absent or barely detectable and could not be induced by SF. Interestingly, SF had no significant influence on PR-104A cytotoxicity in non-cancerous, immortalized human colonic epithelial cell lines expressing either low or high levels of AKR1C3. In conclusion, the enhanced response of PR-104A after preconditioning with SF was apparent only in cancer cells provided that AKR1C3 is expressed, while its expression in non-cancerous cells did not elicit such a response. Therefore, a subset of cancers may be susceptible to combined food-derived component and prodrug treatments with no harm to normal tissues.