Abstract 5389: Oncolytic herpes simplex virus expressing interleukin-12 for treating glioma stem cells
Authors: Cheema Tooba A. , Wakimoto Hiroaki , Rabkin Samuel , Martuza Robert L. 
Published: June 2012

Abstract
Glioblastoma multiforme (GBM) is an aggressive adult brain tumor that despite surgery, radiation and chemotherapy, inevitably recurs. This tumor recurrence is thought to be due to a subpopulation of cells with stem cell-like properties called glioma stem cells (GSCs), and specific targeting of these GSCs might improve GBM treatment. Oncolytic herpes simplex virus (oHSV) vectors are genetically engineered to selectively replicate in, and kill cancer cells, without harming normal tissue, and have been shown to be safe in glioma clinical trials. Our group has shown that oHSV G47delta (G47D) can kill human GSCs, yet its efficacy in vivo was insufficient. Moreover, it is not well understood if GSCs can be targeted effectively by an anti-tumor immune response, partly due to the lack of immune-competent mouse models of GSCs. In this study, we hypothesize that arming G47D with interleukin-12 (IL-12), a critical cytokine involved in adaptive and innate immune responses as well as anti-angiogenesis, will be more effective at targeting GSCs, and tested this using a new syngeneic mouse model of GSCs.
We characterized mouse 005 GSCs (obtained from I. Verma, UCSD) which constitutively express H-Ras and are p53-/+. They exhibit stem cells markers such as nestin and CD133, could be differentiated into neuronal and glial phenotype, and could form tumors in C57BL/6 mice with characteristic GBM necrosis, giant cells and CD31-positive vasculature. These 005 mGSCs expressed MHC/NK ligand markers, but lacked significant expression of co-stimulatory signaling molecules for T cells as observed by flow cytometry. In vitro, treatment of 005 GSCs with increasing concentrations of G47D-Empty (−E; without transgene) or G47D-IL12 resulted in increase in cytotoxicity with similar EC50 values (MOI∼0.1 at 4 days). G47D-IL12 also replicated well in 005 mGSCs leading to a significant release of IL-12 as measured by ELISA. Intracranial tumors established by implanting 005 mGSC in C57BL/6 mice were then treated with two intratumoral injections of either G47D-E or G47D-IL12 oHSV. This resulted in a significant inhibition in tumor growth with extension of survival with G47D-E (median survival 40.5 days; p&lt; 0.03) and G47D-IL12 (median survival 56 days; p&lt; 0.0001) compared with control saline-injected mice with a median survival of 37 days. Importantly, there was a significant increase in survival of mice treated with G47D-IL12 (p&lt; 0.0003) when compared with G47D-E. This increase in survival, potentially due to increased immune response and/or decrease in angiogenesis, is currently under investigation.
This is the first demonstration that GSC can be effectively targeted with oHSV-IL12 in a syngeneic GSC mouse model, showing its marked efficacy over G47D-E. This may be a promising strategy to eradicate glioma cell populations through direct oncolysis combined with enhancing anti-tumor immunity as well as altering the tumor vasculature microenvironment.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5389. doi:10.1158/1538-7445.AM2011-5389