Heat shock protein 72 mediates the synergistic anti‐cancer activity of hyperthermia and oncolytic herpes simplex viral therapy

NV1066, a replication‐competent herpes simplex virus type‐1 (HSV) mutant with deletion of gene coding for Infectious Cell Protein 0 (ICP0) preferentially replicate in and kill malignant cells. ICP 0, a key protein for productive infection, is necessary for the induction and nuclear translocation of heat shock protein HSP72, a molecular chaperone that facilitates viral protein synthesis and maturation. In this study, we have shown that hyperthermia potentiates NV1066 efficacy by recruiting HSP72, thereby promoting viral replication and enhancing cytotoxicity. Gastric cancer cell line, OCUM‐2MD3 were infected with NV1066 at multiplicities of infection (MOI; ratio of viral particles per tumor cell) 0.01 in vitro with or without hyperthermia for 2 hours. In vitro, combination therapy enhanced cell kill (lactate dehydrogenase assay) by 32% (p < 0.01), and viral replication (plaque assay) by 794‐fold (p < 0.01) compared to virus alone. In vivo, a significant reduction in tumor burden was demonstrated in an animal model of peritoneal carcinomatosis (p<0.001). Synergistic cytotoxicity correlated with HSP72 upregulation (qRT‐PCR and ELISA) (36 –fold, p < 0.001) and was eliminated following transfection with HSP72 siRNA. Chou‐Talalay analysis demonstrated significant dose reductions achievable with NV1066 when combined with hyperthermia. These data provide the cellular basis for the clinical investigation of combined use of hyperthermia with oncolytic HSV therapy in the treatment of advanced gastric cancer to achieve synergistic efficacy while minimizing dosage and toxicity. Research grant support by AACR Translational Research Fellowship (PSA), and NIH RO1 CA 76416 and RO1 CA/DK80982 (YF)