Discovering Nrf2 inhibitors to enhance cancer chemotherapy and radiotherapy

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DESCRIPTION (provided by applicant): Nuclear factor erythroid-2-related factor 2 (Nrf2) is a redox-sensitive transcription factor that regulates the expression of electrophile and xenobiotic detoxification enzymes and efflux proteins, which confer cytoprotection against oxidative stress and apoptosis in normal cells. We and others have reported that loss of function mutations in the Nrf2 inhibitor, Kelch-like ECH-associated protein (Keap1), results in constitutive activation of Nrf2 function in non-small cell lung cancer, breast cancer, gall bladder cancer and more recently in prostate cancer. We recently showed that constitutive activation of Nrf2 in lung cancer and prostate cancer cells promotes tumorigenicity and contributes to chemoresistance by up-regulation of glutathione, thioredoxin, and the drug efflux pathways involved in detoxification of electrophiles and broad spectrum of drugs. RNAi-mediated reduction of Nrf2 expression suppressed growth of lung cancer and prostate cancer cells, and resulted in increased sensitivity to chemotherapeutic drug-induced cell death in vitro and in vivo. Inhibiting Nrf2 expression using naked siRNA duplexes in combination with carboplatin significantly inhibits tumor growth in a subcutaneous model of lung cancer. Thus we hypothesize that dysregulated Nrf2-Keap1 pathway is a novel determinant of chemoresistance/radioresistance and inhibition of Nrf2 signaling will enhance the efficacy of chemotherapeutic and radiotherapy. However, efficient delivery and sustained action of siRNA still remains a major challenge limiting its use in treatment of solid tumors and small molecule inhibitors of Nrf2 will overcome this hurdle and prove very beneficial in this scenario. Specific Aim: To develop small molecule inhibitors of Nrf2 for circumventing therapeutic resistance and enhancing the efficacy of chemotherapy and radiotherapy. A pilot screening of Sigma LOPAC library identified few putative inhibitors of Nrf2 with our optimized screening cell based assay but they were not very effective in inhibiting Nrf2 dependent signaling. We propose to screen MLSMR repository of small molecules, which contains more than 300,000 synthetic and natural compounds. Screening and identification of potent small molecule inhibitors of Nrf2 will provide novel opportunities to modulate Nrf2 activity in patients with tumors and increase the efficacy of cancer therapy. PUBLIC HEALTH RELEVANCE: The studies proposed in this project have potential for developing novel drugs which can be used as adjuvant to enhance the efficacy of chemotherapy and radiotherapy. Successful completion of this project will develop a new therapeutic strategy for cancer treatment.