MP83-13 ONCOLYTIC VACCINIA VIRUS HAS SIGNIFICANT ACTIVITY AND INDUCES ANTI-TUMOR IMMUNITY IN BLADDER CANCER

Abstract

INTRODUCTION AND OBJECTIVES: Most Bladder Cancers (BCs) are diagnosed as non-muscle invasive, however with a recurrence rate of up to 80%, many patients require multiple treatment strategies that often fail. In particular, Bacillus Calmette-Guerin (BCG) carries the risk of infection and can be dangerous for immunocompromised (IC) patients. 30% of patients fail BCG therapy and cystectomy remains the standard treatment in these cases. Oncolytic viruses preferentially replicate in and lyse cancer cells while sparing normal cells. Virus replication requires an abundant supply of dNTPs, but because cellular enzymes that synthesize dNTPs are degraded at the end of S-phase, vaccinia virus (VAC) expresses its own biosynthetic enzymes including both I4L (large, R1) and F4L (small, R2) subunits of the heterodimeric ribonucleotide reductase. We have shown that deleting the F4L gene inhibits virus replication in normal cells and reduces virulence while retaining replication proficiency in cancer cells. METHODS: We developed preclinical and clinical grade VACs with deletions in F4L, J2R (viral thymidine kinase) or both. Oncolytic activities of these VACs were evaluated in a panel of human and rodent BC or normal cell lines in vitro. Two BC models were used to assess the VACs in vivo: Syngeneic AY-27 in immunocompetent rats and human RT112-luc xenografts in IC mice. RESULTS: Cytotoxicity assays showed a high degree of cell killing in infections with VACs. Highly efficient VAC replication was seen in BC cells with significantly less replication seen in normal cells (p<0.01). VACs selectively replicated in both AY-27 immunocompetent and RT112-luc IC BC models causing significant tumor regression (p<0.001) or complete ablation with no toxicity. Rats treated with the VACs developed a protective CD8+ T-cell mediated anti-tumor immunity, evident by tumor rejection upon challenge and in vitro assays. Finally, VAC replicated in BC cell lines made BCGrefractory. CONCLUSIONS: Our data indicate that DF4L VACs retain their replication proficiency and cytotoxicity in BC cells despite deletion of these critical viral genes required in non-transformed cells. Significant replication in BC cells that are resistant to the uptake of BCG was observed. Treatment with DF4L VACs in vivo is selective for BC cells, elicits an anti-tumor immunity, and shows no signs of toxicity. Further mechanistic investigations are being conducted on the antitumor effects of DF4L VACs in a BCG-resistant animal model. If successful VAC could provide an essential line of therapy for patients, particularly those refractory to BCG treatment.