Development and preclinical evaluation of a decoy DLL4-encoding oncolytic HSV-1 for high-grade glioma.

Preclinical and clinical investigation of oncolytic HSV-1 (oHSV) treatment for cancer has indicated increased Notch signaling in tumors after treatment. Since Notch activation often heralds cancer cell stemness, angiogenesis, and invasion, the induction of this pathway after oHSV virotherapy can support tumor growth and limit response to virotherapy. Here, we evaluated the impact of blocking DLL4, a Notch ligand, on virotherapy. Matched tumor biopsies pre- and post-oHSV (CAN-3110, NCT03152318) treatment revealed an induction of DLL4 post-therapy. We observed that expression of a recombinant soluble decoy DLL4 (sDLL4) could block Notch activation in tumor cells. Thus, we engineered an oHSV vector designed to encode soluble DLL4 (OVsDLL4) to block ligand-mediated Notch signaling. RNA sequencing and gene set enrichment analysis revealed that, relative to control oHSV, OVsDLL4 blocked Notch and sprouting angiogenesis pathways after treatment. Despite slower virus replication in vitro, OVsDLL4 cytotoxicity remained effective against tumor cells. Transcriptome profiling also indicated a significant dysregulation of metabolic pathways related to oxidative phosphorylation and glutathione metabolism, in accordance with increased oxygen consumption observed by Seahorse analysis in cells expressing sDLL4. OVsDLL4-treated cells further showed increased reactive oxygen species relative to control oHSV-treated cells. Co-culture of infected tumor cells with immune cells revealed that OVsDLL4 treatment polarized them toward an inflammatory phenotype. In vivo, the therapeutic efficacy of OVsDLL4 was underscored, as treatment of glioma-bearing mice resulted in reduced tumor burden and prolonged survival.