ET-46 * ONCOLYTIC VIRAL THERAPY FOR MALIGNANT GLIOMAS USING MYXOMA VIRUS DELETED FOR ANTI-APOPTOTIC M11L GENE

Abstract

Brain Tumour Initiating Cells (BTICs) are stem-like cells hypothesized to mediate recurrence in high-grade gliomas. Myxoma virus (MyxV) is a promising oncolytic virus, which is highly effective in conventional long term resistant glioma cell lines and less effective in BTICs. We hypothesized that one possible factor limiting efficacy in BTICs is that cell death following infection with MyxV is inhibited by virally encoded anti-apoptotic proteins, such as the Bcl-2 structural homologue, M011L. To test this we evaluated and compared the efficacy of wtMYXV versus the viral construct MyxV-M011L-KO (in which the anti-apoptotic protein M11L has been deleted) in BTICs. We found that WT-MyxV does not induce significant level of apoptosis in infected BTICs, but that MyxV-M011L-KO induces dramatically more apoptosisas shown by caspase activation, PARP cleavage, and Cytochrome C release from the mitochondria M11L from the WT-MyxV localized to the mitochondrial membrane and prevented the association of Bax with the mitochondrial membrane. Finally, silencing of Bax using specific siRNAs significantly blocked the induction of apoptosis and cell death that occurs after infection with mutant MyxV-M011L-KO virus. Therefore MyxV-M011L-KO, which is has the anti-apoptotic virally derived gene M11L, dramatically improves the oncolytic efficacy in BTICs and this is dependent on the presence of the pro-apoptotic host protein, Bax. This is the first demonstration, that the MyxV mutant, genetically modified to promote apoptosis in tumor initiating cells, is significantly more efficacious than the wildtype virus. Strategies, such as this one, that promotes apoptosis in tumor initiating cells might be particularly effective.