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

Carcinogenesis. 2016 Oct;37(10):1014-25. doi: 10.1093/carcin/bgw086. Epub 2016 Aug 18.

Abstract

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.

MeSH terms

  • 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
  • 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

Substances

  • Carcinogens
  • E6 protein, Human papillomavirus type 16
  • Oncogene Proteins, Viral
  • Papillomavirus E7 Proteins
  • Phorbol Esters
  • Repressor Proteins
  • oncogene protein E7, Human papillomavirus type 16
  • 9,10-Dimethyl-1,2-benzanthracene
  • 12-O-undecadienoylphorbol-13-acetate
  • TOR Serine-Threonine Kinases
  • mTOR protein, mouse
  • Sirolimus