Abstract 4947: Inhibition of Rapamycin induced AKT activation elicits differential anti-tumor response in head and neck cancers.

Abstract

The PI3K/AKT/mTOR pathway is an important signaling axis that is perturbed in majority of cancers. Biomarkers such as pS6RP, GLUT1 and tumor FDG uptake are being evaluated in patient stratification for mTOR pathway inhibitors. In the absence of a clear understanding of the underlying mechanisms in tumor signaling, the biomarker strategy for patient stratification is of limited use. Here, we show that no discernible correlation exists between FDG uptake and the corresponding Ki67, GLUT1, pS6RP expression in tumor biopsies from Head and Neck Cancer (HNC) patients. Correlation between GLUT1 and pS6RP levels in tumors was observed but elevated pS6RP was noticed even in the absence of concomitant AKT activation, suggesting other downstream molecules of PI3K/AKT and/or other pathways upstream of mTOR, are active in these tumors. Using an ex-vivo platform, we identified putative responders to Rapamycin, an mTOR inhibitor in these tumors. However, Rapamycin did not induce anti-tumor effect in the majority of tumors with activated mTOR, potentially attributable to the observation that Rapamycin induces feedback activation of AKT. Accordingly, treatment of these tumors with an AKT inhibitor and Rapamycin uniformly resulted in abrogation of mTOR inhibition induced AKT activation in all tumors but failed to induce anti-tumor response in a subset. Phosphoproteomic profiling of tumors resistant to dual AKT/mTOR inhibitors revealed differential activation of multiple pathways involved in proliferation and survival. Collectively, our data suggest that in addition to biomarker based segregation, functional assessment of patient tumor prior to treatment with mTOR/AKT inhibitors might be useful for patient stratification. Citation Format: Padhma Radhakrishnan, Ulaganathan Baraneedharan, Muthu Dhandapani, Allen Thyakumar, Dency Pinto, Arun Prasath, Ayyappan Velu, A Kamal, Nilesh Brijwani, Rohini Nair, R Basavaraja, Misti Jain, Saravanan Thiyagarajan, Biswanath Majumder, Mallik Sundaram, Prasad Narayanan, Vikram D. Kekatpure, Pradip K. Majumder. Inhibition of Rapamycin induced AKT activation elicits differential anti-tumor response in head and neck cancers. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4947. doi:10.1158/1538-7445.AM2013-4947