A novel NRF2/ARE inhibitor gossypol induces cytotoxicity and sensitizes chemotherapy responses in chemo-refractory cancer cells   全文下載

A novel NRF2/ARE inhibitor gossypol induces cytotoxicity and sensitizes chemotherapy responses in chemo-refractory cancer cells

"NRF2/ARE signaling pathway is a principal regulator of cellular redox homoeostasis. The stress-induced transcriptionfactor, NRF2, can shield cells from the oxidative damages via binding to the consensus antioxidant-responsive element(ARE) and driving several cyto-protective genes expression. Increasing evidence indicated that aberrant activation ofNRF2 in malignant cells may support their survival through various pathways to detoxify chemotherapy drugs, attenuatedrug-induced oxidative stress, or induce drug efflux, all of which are crucial in developing drug resistance. Accordingly,NRF2 is a potential drug target for improving the effectiveness of chemotherapy and to reverse drug resistance in cancercells. A stable ARE-driven reporter human head and neck squamous cell carcinoma (HNSCC) cell line, HSC3-ARE9, wasestablished and utilized to screen novel NRF2 inhibitors from a compound library. The cotton plant derived phenolicaldehyde-gossypol was selected for further analyses. The effects of gossypol in cancer cells were determined by westernblotting, RT-qPCR, clonogenic assay, and cell viability assays. The gossypol-responsive gene expression levels wereassessed in the Oncomine database. The effects of gossypol on conferring chemo-sensitization were evaluated in etoposide-resistant and cisplatin-resistant cancer cells. Our study is the first to identify that gossypol is effective to reduceboth basal and NRF2 activator tert-butylhydroquinone (t-BHQ)-induced ARE-luciferase activity. Gossypol diminishesNRF2 protein stability and thereby leads to the suppression of NRF2/ARE pathway, which resulted in decreasing theexpression levels of NRF2 downstream genes in both time- and dose-dependent manners. Inhibition of NRF2 bygossypol significantly decreases cell viabilities in human cancer cells. In addition, we find that gossypol re-sensitizestopoisomerase II poison treatment in etoposide-resistant cancer cells via suppression of NRF2/ABCC1 axis. Moreover,gossypol suppresses NRF2-mediated G6PD expression thereby leads to induce synthetic lethality with cisplatin not onlyin parental cancer cells but also in cisplatin-resistant cancer cells. These findings suggest that gossypol is a novel NRF2/ARE inhibitor, and can be a potential adjuvant chemotherapeutic agent for treatment of chemo-refractory tumor."