mTOR inhibition prevents rapid-onset of carcinogen-induced malignancies in a novel inducible HPV-16 E6/E7 mouse model

• Published in: Carcinogenesis (New York) 2016-10, Vol.37 (10), p.1014-1025
• Main Authors: Callejas-Valera, Juan Luis, Iglesias-Bartolome, Ramiro, Amornphimoltham, Panomwat, Palacios-Garcia, Julia, Martin, Daniel, Califano, Joseph A, Molinolo, Alfredo A, Gutkind, J Silvio
• Format: Article
• Language: English
• Subjects: 9,10-Dimethyl-1,2-benzanthracene - toxicity; Animals; Carcinogens - toxicity; Carcinoma, Squamous Cell - chemically induced; Carcinoma, Squamous Cell - drug therapy; Carcinoma, Squamous Cell - genetics; Carcinoma, Squamous Cell - virology; Cell Proliferation - drug effects; Gene Expression Regulation, Neoplastic; Human papillomavirus 16 - genetics; Human papillomavirus 16 - pathogenicity; Humans; Mice; Oncogene Proteins, Viral - genetics; Original Manuscript; Oropharyngeal Neoplasms - chemically induced; Oropharyngeal Neoplasms - drug therapy; Oropharyngeal Neoplasms - genetics; Oropharyngeal Neoplasms - virology; Papillomavirus E7 Proteins - genetics; Papillomavirus Infections - genetics; Papillomavirus Infections - pathology; Papillomavirus Infections - virology; Phorbol Esters - toxicity; Repressor Proteins - genetics; Sirolimus - administration & dosage; TOR Serine-Threonine Kinases - antagonists & inhibitors; TOR Serine-Threonine Kinases - biosynthesis; TOR Serine-Threonine Kinases - genetics
• ISSN: 0143-3334; 1460-2180
• DOI: 10.1093/carcin/bgw086

The rising incidence of human papillomavirus (HPV)-associated malignancies, especially for oropharyngeal cancers, has highlighted the urgent need to understand how the interplay between high-risk HPV oncogenes and carcinogenic exposure results in squamous cell carcinoma (SCC) development. Here, we describe an inducible mouse model expressing high risk HPV-16 E6/E7 oncoproteins in adults, bypassing the impact of these viral genes during development. HPV-16 E6/E7 genes were targeted to the basal squamous epithelia in transgenic mice using a doxycycline inducible cytokeratin 5 promoter (cK5-rtTA) system. After doxycycline induction, both E6 and E7 were highly expressed, resulting in rapid epidermal hyperplasia with a remarkable expansion of the proliferative cell compartment to the suprabasal layers. Surprisingly, in spite of the massive growth of epithelial cells and their stem cell progenitors, HPV-E6/E7 expression was not sufficient to trigger mTOR activation, a key oncogenic driver in HPV-associated malignancies, and malignant progression to SCC. However, 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, 12-O-tetradecanoylphorbol-13-acetate (TPA). Thus, only few oncogenic hits may be sufficient to induce cancer in E6/E7 expressing cells. All HPV-E6/E7 expressing SCC lesions exhibited increased mTOR activation. Remarkably, rapamycin, an mTOR inhibitor, abolished tumor development when administered to HPV-E6/E7 mice prior to DMBA exposure. Our findings revealed that mTOR inhibition protects HPV-E6/E7 expressing tissues form SCC development upon carcinogen exposure, thus supporting the potential clinical use of mTOR inhibitors as a molecular targeted approach for prevention of HPV-associated malignancies.