Abstract 1505: The effect of Cyr61 on oncolytic HSV-1 therapy for glioblastoma multiforme

Gliomas are the most prevalent primary brain tumor and categorized by WHO into four grades. Glioblastoma multiforme (GBM), the grade IV gliomas, have the worst prognosis, wherein despite standard radiation and chemotherapy, patients have a median survival of less than fifteen months. Hence there is a need for radical therapeutic options such as oncolytic viruses (OVs). OVs are viruses that are either natural occurring or genetically modified to selectively replicate and kill cancer cells. Clinical trials have shown the safety of OV therapy, however evidence of significant efficacy remains to be established. We have recently reported a significant induction of the secreted Cyr61 protein in glioma cells infected with an oncolytic HSV-1 (oHSV). Cyr61 is a secreted heparin-binding protein encoded by a growth factor immediate early gene. It has been associated with accelerated tumor growth, invasion, and vascularization in athymic nude mice. Cyr61 is known to promote cell proliferation, adhesion, and migration of various cell lines by its interaction with integrin receptors and heparan sulfate proteoglycans (HSPGs). To confirm the role of Cyr61 in gliomagenesis we performed a meta analysis of gene expression in all the studies available on Oncomine database on Cyr61 gene expression in normal brain to GBM. Our results showed a significant increase in Cyr61 expression in GBM compared to normal brain expression in each study. Additionally we have observed a negative correlation between levels of endogenous Cyr61 in a panel of glioma cell lines and their ability to be infected. Thus, we hypothesized that apart from its pro-angiogenic function, increased levels of Cyr61 inhibits oHSV entry into the cell and may contribute to glioma onco-resistance. We have found that transient transfection of two different glioma cells (Gli36, U251) with a plasmid expressing Cyr61 showed a reduction in viral presence following oHSV infection (fold=1.67, p=0.0118 for gli36 cells; fold=15.19, p=0.0043. for U251T2 cells). To confirm this result we have created tetracycline (tet) inducible glioma cells which express Cyr61 under a tet promotor. Western blot analysis confirmed rapid and dose-dependent induction of secreted Cyr61 in these cells. Furthermore, overexpression of Cyr61 inhibited OV infection/replication at 6 and 24 hours after infection (fold=1.47, p=0.0032; fold=3.79, p=0.0399). Consistent with this, a statistically significant reduction in viral propagation as measured by viral titration was also found in cells overexpressing Cyr61 (fold=3.74;p=0.0202). Thus we have found that Cyr61 has a negative impact on OV therapy. The results from this study will lead to a better understanding of the impact of the tumor microenvironment on OV therapy. Ultimately we hope to use the knowledge gained from these studies to create a more efficient OV, improving this therapeutic modality. 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 1505.