Abstract 5411: Inhibition of mTOR attenuates tumor lactate production & enhances cisplatin/radiation induced immune mediated clearance of HPV-positive head & neck squamous cell cancer.
Authors: Coppock Joseph D. 
Published: August 2014

Human papillomavirus type-16 (HPV-16) is the most identifiable cause of head and neck squamous cell cancer (HNSCC), for which inclusive median five year survival is only fifty percent. Incidence of oropharyngeal SCC is on the rise, nearly tripling in the past thirty years in accord with increasing oropharyngeal infection with HPV. Our lab has recently shown that an immune response is required for long-term cures in response to standard of care cisplatin/radiation therapy (CRT). Our preliminary data and others past work also show that tumor metabolism and production of lactate attenuate this immune response. Although not fully understood, HPV plays a role in conferring the metabolic phenotype of related HNSCC, including through E6 oncoprotein activation of mammalian target of rapamycin (mTOR). Thus, we investigated the mTOR inhibitor, rapamycin, as a concurrent agent to standard of care CRT. Our hypothesis is that inhibition of mTOR has the potential to attenuate tumor lactate production, thus enhancing CRT induced immune mediated clearance of this antigenic tumor type. A C57Bl/6 derived mouse tonsil epithelial (MTE) cell line retrovirally transduced with HPV-16 E6 & E7 was evaluated for its response to rapamycin in vitro with proliferation assays, Western blots, and lactate assays. Mouse cell line results were substantiated in human squamous cell carcinoma (SCC) lines. Clonogenic assays and a pre-clinical mouse model consisting of our model HPV-positive MTE cell line grafted into syngeneic mice were used to assess rapamycin as a concurrent agent to CRT. The potential of rapamycin to enhance immune response through lactate attenuation was assessed using quantitative tumor lactate bioluminescence and a cell-mediated immunity (CMI) assay using HPV-16 E6E7 vaccinated mouse splenocytes. Rapamycin inhibited cell proliferation and significantly decreased lactate production with associated decreases in mTOR signaling both in vitro and in vivo. Survival was prolonged by rapamycin in both immunocompetent and immunocompromised mice, but concurrent with CRT tumor-free survival increased in immunocompetent mice only. These findings suggest enhancement of immune mediated tumor clearance by rapamycin. This correlated with the fact that lactic acid was found to significantly inhibit CMI specific to our tumor model. The results may provide a rationale for the use of mTOR inhibitors concurrent with standard of care cisplatin/radiation therapy for treatment of HPV-positive head and neck squamous cell cancers.

Citation Format: Joseph D. Coppock. Inhibition of mTOR attenuates tumor lactate production & enhances cisplatin/radiation induced immune mediated clearance of HPV-positive head & neck squamous cell cancer. [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 5411. doi:10.1158/1538-7445.AM2013-5411