Abstract PR04: HER3 crosstalk with HPV16-E6E7 is a feedback resistance mechanism to PI3K-targeted therapies in head and neck cancer

Abstract

Abstract Human papillomavirus (HPV) 16 plays an etiologic role in a growing subset of head and neck squamous cell carcinoma (HNSCC), where viral expression of the E6 and E7 oncoproteins is necessary for tumor growth and maintenance. Although patients with HPV(+) tumors have a more favorable prognosis, there are currently no HPV-selective therapies. Accumulating evidence indicates that HPV oncoproteins can activate the Phosphoinositol-3-Kinase (PI3K) pathway, which contributes to transformation. Furthermore, PI3K is genomically activated by PIK3CA mutation or amplification in a disproportionately high number of HPV(+) tumors as compared to HPV(-) tumors. Based on this knowledge, we investigated the efficacy of PI3K-targeted therapies in preclinical models of HPV(+) HNSCC. Our results indicate that HPV(+) preclinical models were less sensitive to the PI3K inhibitors BYL719, BKM120, and BEZ235 as compared with HPV(-) models. Sensitivity of HPV(+) cell lines to PI3K inhibitors was increased upon knockdown of the E6 and E7 oncoproteins. Reciprocally, overexpression of E6 and E7 in HPV(-) cells rendered them resistant to PI3K-targeted therapies. Proteomic analyses indicated that treatment of HPV(+) cell lines and patient-derived xenografts (PDXs) with the PI3Kα inhibitor BYL719 induced expression of the receptor tyrosine kinase HER3, as well as E6 and E7. HER3 was found to regulate the abundance of E6 and E7 in the HPV(+) models. Targeting HER3 with siRNAs or the monoclonal antibody, KTN3379, blocked the increase in E6 and E7 protein levels following BYL719 treatment, and enhanced the efficacy of PI3K inhibitors in HPV(+) cell line and PDX models. Taken together, these results suggest that crosstalk between HER3 and HPV16-E6E7 can limit the efficacy of PI3K inhibitors, and that co-targeting HER3 and PI3K may be an effective therapeutic strategy in HPV(+) tumors. This abstract is also being presented as Poster 67. Citation Format: Toni M. Brand, Stefan Hartmann, Neil E. Bhola, Hua Li, Yan Zeng, Rachel O'Keefe, Max V. Ranall, Sourav Bandyopadhyay, Margaret Soucheray, Danielle L. Swaney, Nevan Krogan, Carolyn Kemp, Umamaheswar Duvvuri, Daniel E. Johnson, Michelle A. Ozbun, Julie E. Bauman, Jennifer R. Grandis. HER3 crosstalk with HPV16-E6E7 is a feedback resistance mechanism to PI3K-targeted therapies in head and neck cancer [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; April 23-25, 2017; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(23_Suppl):Abstract nr PR04.