Abstract B84: Activated c-Src enhances hypoxia in human glioblastoma multiforme and promotes tumor angiogenesis

Abstract

Abstract Exhibiting substantial vascularization and propensity to infiltrate surrounding brain tissue, glioblastoma multiforme (GBM) is the most aggressive primary brain tumor. Even with aggressive intervention afflicted individuals uniformly receive poor prognosis. Growth factor receptor tyrosine kinases (RTKs) are frequently amplified, overexpressed, and constitutively activated in malignant gliomas, and because targeting these molecules has produced promising results in the treatment of several human neoplasms, RTKs are emerging as increasingly viable targets in effective treatment of GBM. Functional ambiguity between normal and constitutively activated RTK signalling compounds the challenges of identifying suitable targets, however. Likewise, the functions of many reported downstream signalling molecules, namely Src family non-receptor tyrosine kinases (SFKs), remain cryptic. Our lab has previously developed a clinically relevant in vivo model that reliably maintains the genomic profiles of corresponding patient tumors, and employing this model, we are able to accurately investigate mechanisms of RTK signalling in human GBM. Ongoing studies suggest that tumor overexpression and activation of the epidermal growth factor receptor (EGFR) promotes the invasive phenotype in human GBM potentially via c-Src dependent signal transduction. In fact, we have observed SFK activation downstream of EGFR. To further investigate this, we implanted GBM patient tumor cells from two individuals with distinct EGFR protein expression, tumor phenotype, and c-Src activity into the brains of nude rats. Minimally expressing EGFR tumor cells from a patient displaying an angiogenic in vivo phenotype were transduced to stably overexpress activated c-Src. Likewise, EGFR-overexpressing tumor cells from a patient displaying an invasive, non angiogenic in vivo phenotype were transduced to stably overexpress kinase-inactive-dominant-negative c-Src. To our surprise, compared with corresponding xenograft control tumors, xenograft tumors overexpressing constitutively activated c-Src showed substantially increased contrast enhancement on MRI, enhanced histological features of angiogenesis, and revealed marked increases in molecular markers of tumor hypoxia and angiogenesis on western blot. Meanwhile, compared with corresponding xenograft control tumors, xenograft tumors overexpressing kinase-inactive-dominant-negative c-Src did not show increased contrast enhancement on MRI, showed no histological evidence of angiogenesis, and maintained a non-angiogenic molecular profile on western blot. We hereby report that activation of the SFK c-Src enhances tumor hypoxia, promotes the aggressive angiogenic tumor phenotype, and is subsequently not likely a primary downstream SFK substrate of overexpressed EGFR in human GBM. Overexpression of wild type EGFR may, instead, signal through a different SFK to promote the invasive phenotype. These results suggest that, more so than invasion, c-Src activation may be a valuable diagnostic and prognostic indicator of malignant progression. Furthermore, these results indicate that c-Src activation may be a strategic target in the therapeutic intervention of human malignant glioma. Citation Format: Eskil Eskilsson, Krishna M. Talasila, Gro V. Røsland, Lina Leiss, Narve Brekkå, Per Øystein Sakariassen, Per Øyvind Enger, Rolf Bjerkvig, Hrvoje Miletic. Activated c-Src enhances hypoxia in human glioblastoma multiforme and promotes tumor angiogenesis. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr B84.