Histone deacetylase inhibitor boosts anticancer potential of fusogenic oncolytic vaccinia virus by enhancing cell–cell fusion

Abstract

AbstractOncolytic viruses have two anticancer functions: direct oncolysis and elicitation of antitumor immunity. We previously developed a novel fusogenic oncolytic vaccinia virus (FUVAC) from a non‐fusogenic vaccinia virus (VV) and, by remodeling the tumor immune microenvironment, we demonstrated that FUVAC induced stronger oncolysis and antitumor immune responses compared with non‐fusogenic VV. These functions depend strongly on cell–cell fusion induction. However, FUVAC tends to have decreased fusion activity in cells with low virus replication efficacy. Therefore, another combination strategy was required to increase cell–cell fusion in these cells. Histone deacetylase (HDAC) inhibitors suppress the host virus defense response and promote viral replication. Therefore, in this study, we selected an HDAC inhibitor, trichostatin A (TSA), as the combination agent for FUVAC to enhance its fusion‐based antitumor potential. TSA was added prior to FUVAC treatment of murine tumor B16‐F10 and CT26 cells. TSA increased the replication of both FUVAC and parental non‐fusogenic VV. Moreover, TSA enhanced cell–cell fusion and FUVAC cytotoxicity in these tumor cells in a dose‐dependent manner. Transcriptome analysis revealed that TSA‐treated tumors showed altered expression of cellular component‐related genes, which may affect fusion tolerance. In a bilateral tumor‐bearing mouse model, combination treatment of TSA and FUVAC significantly prolonged mouse survival compared with either treatment alone or in combination with non‐fusogenic VV. Our findings demonstrate that TSA is a potent enhancer of cell–cell fusion efficacy of FUVAC.