Auranofin-mediated inhibition of PI3K/AKT/mTOR axis and anticancer activity in non-small cell lung cancer cells

Purpose: Krüppel-like factor 4 (KLF4) is a zinc-finger protein that plays important roles in stem cells and the development of gastric cancers. However, the role of KLF4 in primary lung cancer is unknown. The purpose of this study is to determine possible roles of KLF4 in lung cancer. Experimental Design: The KLF4 expression in primary lung cancer tissues and case-matched normal lung tissues were determined by protein and mRNA analyses. The effects of KLF4 on cell proliferation, clonogenic formation, and cell cycle progression were determined in cultured lung cancer cells or bronchial epithelial cells after enforced KLF4 overexpression or small interfering RNA knockdown. The in vivo antitumor activity of KLF4 was evaluated by using stably transfected lung cancer cells and by adenovector-mediated gene delivery. The effect of KLF4 in regulating p21 and cyclin D1 was also evaluated. Results: KLF4 protein and mRNA levels were dramatically decreased in most primary lung tumors compared with in case-matched normal lung tissues. Enforced expression of KLF4 resulted in marked inhibition of cell growth and clonogenic formation. The tumor-suppressive effect of KLF4 was associated with its role in up-regulating p21 and down-regulating cyclin D1, leading to cell cycle arrest at the G₁-S checkpoint. Knockdown of KLF4 promoted cell growth in immortalized human bronchial epithelial cells. The enforced expression of KLF4 gene to lung cancer cells by ex vivo transfection or adenovector-mediated gene transfer suppressed tumor growth in vivo. Conclusions: Our results suggest that KLF4 plays an important role in suppressing the growth of lung carcinoma. (Clin Cancer Res 2009;15(18):5688–95)

Ibrutinib, which irreversibly inhibits Bruton tyrosine kinase, was evaluated for antitumor activity in a panel of non–small cell lung cancer (NSCLC) cell lines and found to selectively inhibit growth of NSCLC cells carrying mutations in the epidermal growth factor receptor (EGFR) gene, including T790M mutant and erlotinib-resistant H1975 cells. Ibrutinib induced dose-dependent inhibition of phosphor-EGFR at both Y1068 and Y1173 sites, suggesting ibrutinib functions as an EGFR inhibitor. Survival was analyzed by Kaplan–Meier estimation and log-rank test. All statistical tests were two-sided. In vivo study showed that ibrutinib statistically significantly suppressed H1975 tumor growth and prolonged survival of the tumor bearing mice (n = 5 per group). The mean survival times for solvent- and erlotinib-treated mice were both 17.8 days (95% confidence interval [CI] = 14.3 to 21.3 days), while the mean survival time for ibrutinib-treated mice was 29.8 days (95% CI = 26.0 to 33.6 days, P = .008). Our results indicate that ibrutinib could be a candidate drug for treatment of EGFR-mutant NSCLC, including erlotinib-resistant tumors.

Glutathione (GSH)/GSH reductase (GSR) and thioredoxin/thioredoxin reductase (TXNRD) are two major compensating thiol-dependent antioxidant pathways that maintain protein dithiol/disulfide balance. We hypothesized that functional deficiency in one of these systems would render cells dependent on compensation by the other system for survival, providing a mechanism-based synthetic lethality approach for treatment of cancers. The human GSR gene is located on chromosome 8p12, a region frequently lost in human cancers. GSR deletion was detected in about 6% of lung adenocarcinomas in The Cancer Genome Atlas database. To test whether loss of GSR sensitizes cancer cells to TXNRD inhibition, we knocked out or knocked down the GSR gene in human lung cancer cells and evaluated their response to the TXNRD inhibitor auranofin. GSR deficiency sensitized lung cancer cells to this agent. Analysis of a panel of 129 non–small cell lung cancer (NSCLC) cell lines revealed that auranofin sensitivity correlated with the expression levels of the GSR, glutamate-cysteine ligase catalytic subunit (GCLC), and NAD(P)H quinone dehydrogenase 1 (NQO1) genes. In NSCLC patient-derived xenografts with reduced expression of GSR and/or GCLC, growth was significantly suppressed by treatment with auranofin. Together, these results provide a proof of concept that cancers with compromised expression of enzymes required for GSH homeostasis or with chromosome 8p deletions that include the GSR gene may be targeted by a synthetic lethality strategy with inhibitors of TXNRD. Significance: These findings demonstrate that lung cancers with compromised expression of enzymes required for glutathione homeostasis, including reduced GSR gene expression, may be targeted by thioredoxin/thioredoxin reductase inhibitors.