Abstract LB-243: Targeting the PI3K-mTOR signaling with metformin for the prevention of HPV-associated malignancies in HIV- and HIV+ individuals

Abstract

Abstract The majority of head and neck squamous cell carcinoma (HNSCC) lesions exhibit persistent activation of the PI3K-mTOR pathway, including cases associated with traditional risk factors or human papillomavirus (HPV) infection. This overreliance on the PI3K-mTOR signaling circuitry for tumor growth can potentially be exploited for therapeutic purposes. Indeed, we have shown that mTOR inhibitors are highly effective in decreasing tumor burden and metastasis in multiple in vitro and in vivo models. However, currently available PI3K and mTOR inhibitors may raise safety concerns regarding their long term use in patients diagnosed with potential premalignant oral lesions. We have recently shown that the first-line, oral antidiabetic drug metformin prevents HNSCC development in chemically-induced experimental oral premalignant lesions by reducing mTOR activity through stimulation of the AMP-activated protein kinase (AMPK) signaling pathway. Noteworthy, metformin is safely used by more than two million Americans on a daily basis. We have optimized the oral delivery of metformin to achieve clinically relevant blood levels, and explored its preclinical activity in representative HNSCC tumor xenograft models. HNSCC cells harboring PIK3CA mutations or HPV oncogenes were very sensitive to the growth inhibitory activity of metformin in vitro, concomitant with AMPK activation and mTOR inhibition. These effects were dependent on the expression of organic cation transporter 3 (OCT3), a metformin uptake transporter that is highly expressed in dysplastic oral squamous epithelium and HNSCC. Furthermore, metformin administration in vivo caused a dramatic, OCT3-dependent reduction in tumor growth of PIK3CA and HPV+ HNSCC cells transplanted into immunocompromised mice. In this regard, the incidence of HPV-related malignancies, including HNSCC, is increasing among HIV-infected individuals, irrespective of the restoration of their immune function by the use of highly active antiretroviral therapy. This prompted us to examine mTOR activation and OCT3 expression as surrogate biomarkers for metformin sensitivity, in a large panel of HNSCC lesions from HIV- and HIV-infected (HIV+) individuals. We found that in HIV- patients (n=490), 21% of the HNSCC lesions were HPV+, whereas 35% of the HNSCC in HIV+ patients were HPV+ (n=164, p<0.001). The majority of these lesions, as well as perianal and cervical SCCs arising in HIV+ patients, exhibit increased mTOR activity and high OCT3 expression. We can conclude that activation of the PI3K-mTOR pathway is a widespread event in SCCs, including HPV- and HPV+ lesions arising in HIV+ patients, all of which express OCT3. These observations may provide a rationale for the clinical evaluation of metformin to halt SCC development from precancerous lesions, including in HIV-infected individuals that are at high risk of developing HPV-associated cancers. Citation Format: Dmitriy Madera, Lynn Vitale-Cross, Daniel Martin, Abraham Schneider, Alfredo Molinolo, J. Silvio Gutkind. Targeting the PI3K-mTOR signaling with metformin for the prevention of HPV-associated malignancies in HIV- and HIV+ individuals. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-243. doi:10.1158/1538-7445.AM2014-LB-243