302. Anti-Angiogenic Treatment Enhances Anti- Tumor Effects of an Oncolytic Virus in an Experimental Rat Glioma Model
Authors: Kazuhiko Kurozumi, Jennifer Cutter, William Carson, Ming Yang, Gregory Christoforidis, Antonio E. Chiocca, Balveen Kaur
Journal: Molecular Therapy (2006)

Oncolytic viruses (OVs) are viruses with selective ability to replicate & lyse in tumors. Recent results from clinical trials have established their safety yet efficacy remains elusive. We are examining stromal responses elicited upon treatment of intracerebral brain tumor by hrR3 (type 1 Herpes simplex virus (HSV-1) derived OV). Effect of OV treatment on host tumor vasculature. 7 days post intracerebral tumor implantation (D74HveC rat glioma cells), rats were treated with intratumoral injection of hrR3 or PBS. Effect of OV on tumor vasculature was evaluated by i.v injection of FITC- dextran 3 days post OV infection. Our results have uncovered a significant increase in vascular permeability in response to OV treatment of tumors. Quantification of the leaked fluorescent dye in tissue revealed that vascular leakage in OV treated groups was 4 fold higher than in control PBS injected animals (35.7 ± 6 (OV) Vs (8.9 ± 0.3) (PBS). This observation was confirmed on ultra high field, high resolution MRI performed at 8.0-Tesla using ultrasmall particle of iron oxide (USPIO) enhanced gradient echo sequence. Additionally this OV induced vascular leakage was not evident in Cyclophosphamide (CPA) treated immune suppressed rats. These results indicate that increased vessel permeability was a result of endothelial cell activation in response to OV infection. This increased permeability allows for host immune cell infiltration into the tumor which is deleterious to the presence of OV. Effect of OV treatment on angiogenesis. The host immune system uses the OV induced breach in Blood Brain Barrier (BBB) to infiltrate tumor tissue with macrophages resulting in destruction of therapeutic OV. Activated macrophages can secrete VEGF and initiate an angiogenic response. Tumor bearing rats treated with OV or PBS, were sacrificed prior to death and vessel density was evaluated in size matched tumors. The number of vessels/view field, was quantified by RECA-1 and CD31 immunostaining for endothelial cells. Neovascularization was significantly greater in tumors treated with OV compared to control (OV: 101 ± 21.6; versus PBS : 19.8 ± 10) (P = 0.0037). Effect of pretreatment with an anti-angiogenic agent on OV mediated therapy. Based on the above findings we hypothesized that a reduction in tumor blood vessels prior to OV infection would result in reduced tumor infiltration of host inflammatory cells leading to enhancement of OV efficacy. We tested this hypothesis by using Cilengitide (cRGD), a known anti-angiogenic agent & antagonist of integrin αvβ3. Pretreatment of rats with a single dose of cRGD prior to OV injection significantly increased survival of rats compared to rats treated with a single agent (median survival: PBS: d12; cRGD: d13; OV: d18; cRGD + OV: d22) (P < 0.05 between OV and cRGD + OV). Conclusions: Anti-angiogenic treatment prior to OV infection of brain tumors results in enhanced therapeutic efficacy.