Abstract 1290: O6-methylguanine-methyltransferase modulates glioblastoma angiogenesis and invasion

Abstract

Abstract Background: Glioblastoma (GBM) is the most aggressive primary malignant brain tumor in adults. Approximately 50% of GBM patients are resistant to standard therapy with temozolomide (TMZ) because their tumors express the DNA repair protein O6-methylguanine methyltransferase (MGMT), which repairs tumoral DNA damage induced by TMZ. GBM, a highly vascularized tumor, consistently displays a locally invasive phenotype, which contributes to biological aggressiveness and clinical recurrence. Therefore, use of the anti-angiogenic and anti-invasive agent sunitinib malate could be a promising strategy for GBM treatment. We showed that sunitinib-based treatment significantly improved the response of MGMT-positive, but not MGMT-negative, cells and this differential effect was reversed upon MGMT depletion with O6-benzylguanine. In the present study, we investigated the relationship between the expression of MGMT and the angiogenic and invasive profile of GBM cell lines. Experimental Design: We performed microarray gene expression analysis and quantitative real-time RT-PCR and analyzed the differential expression of transcripts in GBM cell lines with differential expression levels of MGMT: U87 empty vector (MGMT-negative), its counterpart U87/MGMT (MGMT-positive) (stable transfection), and T98G (constitutively expressing MGMT). We also investigated the effect of MGMT expression on GBM angiogenesis by assessing vascular endothelial growth factor (VEGF) secretion and the ability of growth factors secreted in the GBM conditioned media to induce endothelial tube formation in vitro, and the effect of MGMT expression on GBM invasiveness by examining F-actin organization, and migration and invasion in vitro. Results: The gene chip microarray showed differential mRNA expression of transcripts involved in angiogenesis, invasion, and response to sunitinib in U87/MGMT cells compared to U87/EV cells. These results were confirmed for several transcripts by quantitative real-time RT-PCR or western blotting. Additionally, we also showed that MGMT-positive cells have reduced angiogenic and invasive potential compared to MGMT-negative cells based on decreased VEGF bioavailability, decreased endothelial tube formation, altered morphology, and decreased invasion and migration in vitro. Conclusion: Our study is the first to show a direct link between MGMT expression and decreased angiogenicity and invasiveness of GBM cells. This altered phenotype may account for the preferential in vitro efficacy of sunitinib malate in MGMT-positive GBM cell lines. Our data provide the rationale to further investigate the role of MGMT in the regulation of the angiogenic and invasive profile of GBM. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1290.