γ(1)34.5-Deleted HSV-1 Expressing Human Cytomegalovirus IRS1 Gene Kills Human Glioblastoma Cells as Efficiently as Wild-type HSV-1 in Normoxia or Hypoxia

Pathophysiological hypoxia, which fosters the glioma stem-like cell (GSC) phenotype, is present in high-grade gliomas and has been linked to tumor development, invasiveness, and resistance to chemotherapy and radiation. Oncolytic virotherapy with engineered herpes simplex virus-1 (HSV-1) is a promising therapy for glioblastoma; however efficacy of γ(1)34.5-deleted HSVs, which have been used in clinical trials, was diminished in hypoxia. We investigated the ability of a chimeric HCMV/HSV-1 virus, which expresses the human CMV PKR evasion gene IRS1 and is in preparation for clinical trials, to infect and kill adult and pediatric patient-derived glioblastoma xenografts in hypoxia and normoxia. Infectivity, cytotoxicity and viral recovery were significantly greater with the chimeric virus compared to the γ(1)34.5-deleted virus, regardless of oxygen tension. The chimeric virus infected and killed CD133+ GSCs similarly to wild-type HSV-1. Increased activation of mitogen-activated protein kinase (MAPK) p38 and its substrate heat shock protein 27 (Hsp27) was seen after viral infection in normoxia compared to hypoxia. Hsp27 knockdown or p38 inhibition reduced virus recovery indicating that the p38 pathway plays a role in the reduced efficacy of the γ(1)34.5-deleted virus in hypoxia. Together these findings demonstrate chimeric HCMV/HSV-1 efficiently targets both CD133+ GSCs and glioma cells in hypoxia.