Caroline J. Breitbach

Primary liver cancer (hepatocellular carcinoma; HCC) in patients not eligible for surgery or transplant is currently treated by locoregional therapeutic approaches, including trans-arterial chemoembolization and radiofrequency ablation. Sorafenib (Nexavar; Bayer/Onyx) is currently the only approved systemic therapy for patients having failed locoregional interventions. Oncolytic viruses are designed to selectively replicate within, and subsequently lyse, cancer cells by a unique mechanisms-of-action that is not cross-resistant with approved therapies (Kirn et al., Nat Med 7:781–787, 2001; Parato et al., Nat Rev Cancer 5:965–976, 2005; Chiocca, Nat Rev Cancer 2:938–950, 2002; Heise and Kern, J Clin Invest 105:847–851, 2000). Given that these therapeutics are self-amplifying in tumors, the impact of dose on patient outcome is unclear. Pexa-Vec (JX-594) is an oncolytic and immunotherapeutic vaccinia virus which was shown to be well tolerated by intratumoral injection and intravenous infusions in Phase 1 trials (Park et al., Lancet Oncol 9:533–542, 2008; Breitbach et al., Nature 477:99–102, 2011). We present the design of a randomized dose-finding trial of Pexa-Vec in patients with advanced HCC in which Pexa-Vec was delivered by intratumoral injection three times every 2 weeks at one of two dose levels (1 × 10⁸ plaque forming units (pfu) versus 1 × 10⁹ pfu).

Purpose: Nasopharyngeal carcinoma (NPC) is a malignancy of the head and neck region that is associated with EBV latency. Curative treatments for NPC achieve modest survival rates, underscoring a need to develop novel therapies. We evaluated the therapeutic potential of a mutant vesicular stomatitis virus (VSVΔ51) as single treatment modality or in combination with ionizing radiation (RT) in NPC. Experimental Design: MTS assay was used to assess cell viability in vitro; apoptosis was measured using propidium iodide staining and caspase activation. In vivo experiments were conducted using tumor-bearing nude mice with or without local RT (4 Gy). Apoptosis was assessed in excised tumor sections with terminal deoxynucleotidyl transferase–mediated dUTP nick end labeling staining. Results: Our data showed that NPC cells are exquisitely sensitive to VSVΔ51 oncolysis, which correlated with the presence of EBV. Efficacy of VSVΔ51 against NPC cells was further augmented when combined with RT. A single systemic injection of VSVΔ51 achieved 50% survival in treated mice, which increased to 83% when combined with local tumor RT. In addition to induction of apoptosis, an antiangiogenic effect of VSVΔ51 was observed in vivo, suggesting a novel tumoricidal mechanism for VSVΔ51. This virus also prevented growth of NPC sphere-forming cells in vitro, showing potential utility in targeting NPC-initiating cells. Conclusions: Our data represent the first report showing that EBV-positive NPC cells are exquisitely sensitive to VSVΔ51 oncolysis and documenting the successful utilization of this combinatorial regimen as a novel curative therapeutic strategy for NPC.

The field of oncolytic virus (OV) therapy is an innovative and evolving science, taking advantage of the ability of select viruses to preferentially infect and kill human tumor cells. However, the contribution of the tumor microenvironment, and especially the induced innate immune responses to both the tumor and the virus, has been demonstrated to be a major player in the success of OV therapies. Innate immunity and inflammation in particular can have opposing effects; these can augment OV therapy by enhancing tumor destruction, yet can also recognize and clear the invading virus to significantly hinder viral dissemination through the tumor tissues. This review considers how inflammation and innate immunity impinge on current OV candidates to either facilitate or hinder virotherapy. Novel approaches that modulate or harness the innate immune system to specifically enhance OV-mediated tumor destruction are also discussed.