Towards an armed oncolytic virus approach to glioblastoma treatment.

Glioblastoma (GBM) is among the most aggressive and lethal human tumors. The current standard of care, surgical resection followed by chemotherapy, offers limited efficacy, as recurrence remains frequent and severe, underscoring the urgent need for novel therapeutic strategies. Photodynamic therapy (PDT) and oncolytic virotherapy have emerged as promising alternatives. PDT utilizes light-sensitive molecules to generate reactive oxygen species (ROS), selectively inducing tumor cell death, while oncolytic virotherapy employs viruses to lyse tumor cells and activate anti-tumor immune responses. Notably, talimogene laherparepvec (T-VEC), an HSV-1-based oncolytic virus (oHSV1), is already approved for treating unresectable melanoma. To explore a combinatorial approach for GBM, we engineered highly neuroattenuated oHSV1 variants with a genetic background similar to T-VEC, expressing KillerRed (KR) a photosensitizing protein alone or in combination with immunotherapeutic factors. Our results demonstrate potent cytolytic effects of these recombinant viruses in multiple murine and human GBM cell lines, as well as in primary tumor cells. In a syngeneic C57BL/6J mouse model, oHSV1 administration induced extensive tumor necrosis, accompanied by infiltration of CD3+ immune cells. Additionally, we confirmed the feasibility of monocyte mediated systemic delivery of oHSV1, further supporting its therapeutic potential for GBM.