Abstract 4627: Role of intratumoral cell heterogeneity on therapeutic efficacy in glioblastoma.

Abstract

Abstract Glioblastoma (GBM), the most common and lethal malignancy of the brain, is typified by high degrees of histologic and molecular heterogeneity. The majority of GBM harbor amplification and/or mutations of receptor tyrosine kinases (RTKs), most frequently EGFR (40-50%) or PDGFRA (∼15%). We recently documented that a subset of glioblastoma harbors independent focal amplification of two or more RTKs, most commonly PDGFRA and EGFR. This phenomenon lends genetic evidence to support that co-expression of more than one RTK in the same cell serves a functional purpose in conferring selective growth advantage to GBM. In this study we demonstrate that EGF stimulates endogenous interaction between activated EGFR and PDGFRA, assessed using reciprocal coimmunoprecipitation and proximity ligation assays in patient-derived GBM tumor-sphere lines of multiple genotypes. EGF leads to phosphorylation of PDGFRA Y720. This transactivation and subsequent activation of Shp2 are abolished by EGFR inhibitors gefitinib or lapatinib at low concentrations. Evidence of EGFR-PDGFRA interaction was found in the majority of GBM tumorsphere lines where both receptors were expressed. We used multichannel phospho-FACS in a panel of tumorsphere lines to characterize the cell-to-cell heterogeneity of EGFR and PDGFRA expression levels and how these levels affect p-Akt and p-ERK baseline activity, response to ligands and response to targeted receptor inhibition. Indeed, high expression of both EGFR and PDGFRA identifies tumor cells with elevated MAPK and PI3K pathway activity. Notably, these tumor cells have high downstream pathway activation in the absence of explicit stimulation by ligand and appear to be refractory to dual RTK inhibition. Taken together, these data underscore the role of tumor cell RTK heterogeneity in therapeutic resistance to RTK inhibitors in GBM. This study also highlights a possible mechanism that heterotypic RTKs in the same cell may utilize to achieve growth advantage. Citation Format: Debyani Chakravarty, Alicia Pedraza, Angela H. Liu, Jesse Cotari, Grégoire Altan-Bonnet, Cameron W. Brennan. Role of intratumoral cell heterogeneity on therapeutic efficacy in glioblastoma. [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 4627. doi:10.1158/1538-7445.AM2013-4627