Abstract 5315: Hydroxychloroquine inhibits proliferation and S6 phosphorylation in human renal carcinoma cells

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA mTOR inhibitors are used to treat metastatic renal cell cancer (RCC), but most patients eventually become resistant. One possible mechanism for resistance is upregulation of autophagy, a pathway which helps recycle intracellular proteins and promotes cell survival. Hydroxychloroquine (HCQ), a potent autophagy inhibitor used to treat malaria and autoimmune disorders, is currently being studied in the context of cancer treatment. Here, we have investigated the effects of HCQ on three different renal carcinoma derived cell lines. We found that HCQ treatment inhibits RCC cell growth, promotes apoptosis, inhibits mitochondrial oxygen consumption, and increases glycolysis rates. To understand the molecular mechanism behind these effects, we examined various nodes in the mTOR pathway and compared the effects of HCQ with the effects of the mTOR inhibitor RAD001. A key downstream readout of the pathway, phospho-S6 protein, was inhibited by both HCQ and RAD001. However, the upstream kinase, P70S6K, was only inhibited by RAD001 and not HCQ, suggesting that the block by HCQ was downstream of the p70S6K. Treatment with the proteasome inhibitor bortezomib, restored phospho-S6 levels, suggesting that the reduction of phospho S6 is caused by increased degradation of phospho, but not total S6. Surprisingly, depletion of the key autophagy regulator Atg7 did not mimic the effects of HCQ, indicating that HCQ regulates S6 phosphorylation by ATG7-independent mechanism. Our finding suggests that HCQ may be useful in the treatment of renal cell carcinoma. Citation Format: Hyung-Ok Lee, Aladdin Mustafa, Gary R. Hudes, Warren D. Kruger. Hydroxychloroquine inhibits proliferation and S6 phosphorylation in human renal carcinoma cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5315. doi:10.1158/1538-7445.AM2015-5315