DNA Demethylating Agents Synergize with Oncolytic HSV1 against Malignant Gliomas

Abstract

Purpose Oncolytic viruses (OV) based on herpes simplex virus type 1 (HSV1) are being utilized in clinical trials for a variety of cancers. The OV, rQNestin34.5, utilizes a nestin promoter/enhancer to selectively drive robust viral replication in malignant glioma cells. We have discovered that this promoter becomes extensively methylated in infected glioma cells, reducing OV efficacy. Experimental Design We utilized demethylating drugs (5-azacytidine), Decitabine or Valproic Acid (VPA) in both in vitro and in vivo malignant glioma models to determine if they improved the efficacy of rQNestin34.5 therapy. Results Utilization of demethylating agents, such as 5-azacytidine (5-Aza), improved OV replication and tumor cell lysis in vitro and, in fact, synergized pharmacologically by Chou-Talalay analysis. In vivo the combination of the demethylating agents, 5-Aza or Decitabine, with rQNestin34.5 significantly prolonged the survivorship of athymic mice harboring intracranial human glioma xenografts over single agent alone. Conclusion These results thus provide further justification for the exploration of demethylating agents when combined with the OV, rQNestin34.5, in preclinical therapeutics and possibly clinical trials for malignant glioma.

Enhanced efficacy with azacytidine and oncolytic BHV-1 in a tolerized cotton rat model of breast adenocarcinoma

“…Studies combining OVs with epigenetic modifiers such as 5-Aza have shown synergistic or additive effects that enhance tumor cell death. 23–25 To ensure that 5-Aza was functional in LCRT cells, the expression of Dnmt1 was evaluated as a control. When incorporated into DNA, 5-Aza forms a covalent bond with DNMT such as Dnmt1.…”

“… 35 Epigenetic modifiers enhance OV replication and cytotoxicity by modifying viral gene expression and antiviral immune responses. 23–25 In addition to upregulating genes associated with innate and adaptive immunity, 5-Aza increases the sensitivity of tumor cells to T cell mediated cytotoxicity by increasing expression of TAAs. 36 , 37 Enhanced immune activation following 5-Aza treatment may serve to break central and peripheral tolerance to TAAs.…”

“… 47 , 48 Recent studies have described using epigenetic modifiers such as 5-Aza in combination with OVs to improve antitumor responses. 23 It is plausible that epigenetic reprogramming by 5-Aza may synergize with that induced by BHV-1 to alter susceptibility of tumor cells to BHV-1 infection and modulate immune mediated antitumor effects. Further studies are required to unravel the relationship between BHV-1 and 5-Aza.…”

“… 3 , 21 , 22 Therefore, combining 5-Aza with agents that increase tumor cell death by counteracting the pro-survival effects of oncogenes may be efficacious. 20 , 23 …”

Oncolytic viruses against cancer stem cells: A promising approach for gastrointestinal cancer

“…Kambara et al[ 51 ] developed an oncolytic HSV-1 mutant rQNestin34.5 which expresses ICP-34.5 under control of a synthetic nestin promoter. Nestin is expressed in embryonic neuroglial cells and has been used as a CSC marker in several cancers including brain tumors, and rQNestin34.5 showed significantly more potent inhibition of tumor growth compared with control virus in vivo [ 52 ]. Further studies found that rQNestin34.5 can infect and kill neuroblastoma CSCs[ 9 ], implying that OncoHSV efficiently targets CSCs from gastrointestinal cancer.…”