Hypoxia/anoxia is a well-characterized component of the solid tumor microenvironment and has profound consequences for patient outcome. In particular, clinical data indicate that patients with certain types of tumors treated with radiotherapy have a significantly better outcome if the tumors are less hypoxic. Therefore, we are interested in finding agents that can improve tumor oxygenation. In this study, we investigated the effects of two drugs on tumor oxygenation, NVP-BEZ235 (Novartis), a dual PI3K/mTOR inhibitor, and nelfinavir, an HIV protease inhibitor that inhibits PI3K signaling. Treatment of mice bearing SQ20B head and neck squamous cell carcinoma xenografts with either drug led to a decrease in tumor hypoxia as measured by binding of the 2-nitroimidazole EF3. In vitro O2 consumption measurements of cells grown in tissue culture using a Clark electrode showed that both drugs led to decreased O2 consumption. This result was confirmed using a XF Extracellular Flux Analyzer (Seahorse Bioscience). Using this technique, we found that incubation with NVP-BEZ235 caused a 30- 50% decrease in the oxygen consumption rate (OCR). O2 consumption was stimulated by addition of the uncoupling agent CCCP in both controls and NVP-BEZ235-treated cells, which indicates that they were not killed by NVP-BEZ235 treatment. Similar results were obtained with nelfinavir. In order to identify whether components of the PI3K/mTOR pathway could contribute to the decrease in O2 consumption, we used siRNA directed against either mTOR or the p110alpha subunit of PI3K. Knockdown of either protein led to a decrease in O2 consumption. Studies are ongoing to determine whether the mitochondria are a direct target of NVP-BEZ235 or nelfinavir and if so, which mitochondrial respiratory complex might be affected. In summary, we show that NVP-BEZ235 and nelfinavir, both of which inhibit PI3K signaling, decrease O2 consumption and ameliorate tumor hypoxia. We have found both of these agents to increase radiation response in vivo in animal models, and nelfinavir is currently being used in combination with radiotherapy in clinical trials. These findings offer insight as to how these agents act as radiation response modifiers.
Citation Format: George J. Cerniglia, Natalie Daurio, Shannon M. Gallagher-Colombo, Theresa M. Busch, Stephen W. Tuttle, Cameron J. Koch, Alexander Lin, Constantinos Koumenis, Amit Maity. Agents that target the PI3K/mTOR pathway decrease oxygen consumption, reduce tumor hypoxia and improve radiation response in solid tumors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1037. doi:10.1158/1538-7445.AM2013-1037