Abstract LB-7: HPV-associated HNSCC: Widespread mTOR pathway activity and preclinical evaluation of mTOR inhibitors rapamycin and RAD-001

Abstract

Abstract Traditional risk factors for head and neck squamous cell carcinomas (HNSCCs) include tobacco and alcohol consumption and betel nut chewing. Over the past three decades, the United States has experienced a considerable increase in the incidence of HNSCCs associated with human papillomavirus (HPV) infection. HPV is now recognized as an important etiologic agent in HNSCCs, particularly those originating in the oropharynx. To investigate the molecular mechanisms underlying HNSCC progression, we established the International HNSCC Tissue Array Initiative, which includes hundreds of HNSCC lesions from around the world. Using immunodetection of the p16INK4a protein (p16) as a surrogate marker for HPV-related HNSCC, we found that approximately 20% of the HNSCC cores could be classified as HPV+, irrespective of the country of origin. These results emphasize the emerging global impact of HPV-related HNSCCs. On the basis of the results from these tissue array analyses, we designed studies aimed at elucidating dysregulated signaling networks in HPV+ HNSCCs. Surprisingly, although HPV+ HNSCCs represent a distinct clinicopathological subset of HNSCC lesions, we observed frequent Akt-mTOR pathway activation in HPV+ HNSCC, aligned with our previous studies documenting the activation of this signaling route in non-HPV related HNSCCs. Thus, activation of the Akt-mTOR pathway represents a widespread event in HNSCC, irrespective of HPV status. These findings were confirmed in an independent cohort of 48 HNSCC cases of oral and oropharyngeal tumors, 28 of which were determined to be HPV+ as judged by HPV DNA detection and p16 expression levels. We observed elevated expression of markers for Akt and mTOR activity (pAktS473, pS6) in all 28 of the HPV+ cases when compared to normal controls. These observations prompted us to investigate whether specific allosteric inhibitors of mTOR (rapamycin and RAD001) represent a valid therapeutic approach for HPV+ HNSCC. Initially, we observed that a panel of HPV+ human derived HNSCC cell lines (n=5) exhibited elevated levels of pS6 by Western blot, which was blocked upon treatment with rapamycin and RAD001 (100 nM, 30 min). Two representative human HNSCC HPV+ cell lines were used to establish HPV+ HNSCC xenografts in the flanks of athymic (nu/nu) mice. Tumor bearing mice were treated with vehicle, rapamycin, or RAD001. Both treatment groups showed rapid tumor collapse and a significant decrease in tumor burden when compared to vehicle treated mice (p<0.0001). Successful inhibition of Akt-mTOR pathway activation was confirmed by pS6 and pAktS473 immunostaining of the xenograft tissue. We can conclude that activation of the Akt-mTOR pathway is a widespread event in HPV-associated HNSCC, and that mTOR inhibitors may represent attractive candidates for the treatment of HPV-positive squamous neoplastic lesions. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-7. doi:10.1158/1538-7445.AM2011-LB-7