Systemic administration of mutant vesicular stomatitis virus (VSV) completely eradicates nasopharyngeal carcinoma (NPC) models

Introduction: Nasopharyngeal carcinoma (NPC) is a malignancy of the head and neck region with unique clinical and demographic features. Standard therapy for NPC achieves only modest survival rates, underscoring a need to develop novel therapies. Our group has previously investigated multiple novel molecular therapeutics including adenoviral vectors, and antisense oligonucleotide approaches. None has succeeded in complete eradication of established xenograft tumours. Hence, we were interested in examining the therapeutic potential of vesicular stomatitis viruses (VSV), which preferentially replicate in malignant cells, presumably due to defects in their interferon (IFN) signaling. Materials and Methods: Two EBV-positive human NPC models were utilized: the C666-1, and the C17 tumours. The MTS assay was utilized to assess viability in vitro; apoptosis was measured using flow-based techniques including fraction of cells in the sub-G0/G1 phase, and caspase-3 activation. In vivo experiments were conducted using nu/nu mice, which are permissive to VSV infection. The VSV-delta51-GFP is a mutant VSV carrying the GFP reporter gene; control VSV was inactivated by UV radiation (30 min in laminar flow hood). Results: Our data demonstrated that VSV-delta51-GFP (MOI = 0.00001 to 10.0) was cytotoxic to C666-1 cells in a time and dose-dependent manner (75.4 to 87.2 killing at 72 hrs, respectively). Control VSV demonstrated no cytotoxicity. VSVdelta51 infection of C666-1 cells at MOI=1.0 induced apoptosis in > 6.2% of infected cells at 24 hrs and reached >10.8 % at 72 hrs. C666-1 cells (5x10^6) infected ex vivo with VSVdelta51-GFP (MOI=5.0) and then implanted into nu/nu mice demonstrated no tumour formation when injected subcutaneously, followed for 58 days, while C666-1 cells infected with UV-irradiated control virus formed tumors as early as day 27 post injection. Therapeutic efficacy of VSVdelta51-GFP was evaluated in both the C666-1 and C17 models. Four intravenous injections of VSVdelta51-GFP (5x1^8 pfu x 4) were able to completely eradicate established tumours followed for 31 days. No adverse effects were observed in mice treated with VSV; control VSV demonstrated no in vivo effect. Conclusion: These data demonstrate that VSV is a potentially promising novel oncolytic viral therapeutic modality for NPC. We are currently investigating the therapeutic benefit of combining VSV with RT and chemotherapy, and anticipate application to human patients in the near future if the combinatorial strategy demonstrates such impressive efficacy. Our finding may also be applicable to other human cancers.