Abstract 4800: A next-gen animal model to Study PIK3CA-mTOR driven HPV-related oral malignancies
Authors: Juan Luis Callejas-Valera, Ramiro Iglesias-Bartolome, Panomwat Amornphimoltham, Julia Palacios-Garcia, Daniel Martin, Joseph A. Califano, Alfredo A. Molinolo, J.Silvio  Gutkind
Journal: Cancer Research (2017)

Abstract The rising incidence of HPV-associated malignancies, especially for head and neck squamous cell carcinoma (HNSCC), has highlighted the urgent need to understand the role of HPV-16 E6/E7 oncogenes in cancer initiation and progression. For that propose we decided to generate a doxycycline inducible E6/E7 transgenic mouse targeting E6/E7 onco-proteins to the basal epithelia layer, including the stem cell compartment, through a doxycycline inducible cytokeratin 5 promoter (cK5-rtTA). This system allows to turn on the expression of HPV genes after birth, minimizing the negative effect that viral E6/E7 expression may have during embryonic development, and mimicking the natural infection process that usually happens in adults after initiation of sexual activities. Interestingly, we found that after doxycycline induction, both E6 and E7 were highly expressed, resulting in a clear increase in the number of proliferative cells even in the suprabasal layers, which results in rapid epidermal hyperplasia. However, in our animal mouse model HPV-16 E6/E7 expression alone was not sufficient to induce spontaneous squamous carcinomas (SCC). Due that we decided to challenge the oncogenic role of HPV using a classical chemical carcinogenesis protocol (DMBA-TPA). These mice develop SCC rapidly after a single exposure to a skin carcinogen, DMBA, which was increased by the prolonged exposure to a tumor promoter, TPA. These data suggest that only few oncogenic hits may be sufficient to induce cancer in humans already infected with HPV-16 E6/E7. Then, we decided to elucidate whether or not a few genomic alterations in combination with HPV-16 expression may be sufficient to induce cancer. One of the most frequent mutations in HNSCC, including HPV-associated cancers, are those affecting the PI3K-mTOR pathway. Based on that, we engineered a genetically defined mouse model combining HPV-16 E6/E7 and PIk3CAH1047R expression under the control of a cytokeratin 14 promoter driven tamoxifen-regulated Cre recombinase (cK14-CreERTM). Surprisingly, we found that upon tamoxifen activation mice develop oral cancer in only few weeks. Furthermore, our HPV-related cancer mouse models exhibited a marker increase of mTOR activation which is a key oncogenic driver in malignant progression to SCC. Remarkably, rapamycin, an mTOR inhibitor, was able to block tumor development, supporting the potential clinical use of direct and indirect mTOR inhibitors as a molecular targeted approach for prevention of HPV-associated malignancies. Citation Format: Juan Luis Callejas-Valera, Ramiro Iglesias-Bartolome, Panomwat Amornphimoltham, Julia Palacios-Garcia, Daniel Martin, Joseph A. Califano, Alfredo A. Molinolo, J.Silvio Gutkind. A next-gen animal model to Study PIK3CA-mTOR driven HPV-related oral malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4800. doi:10.1158/1538-7445.AM2017-4800