Antitumor activity of oncolytic herpes symplex virus type 1 and photodynamic therapy in in vitro preclinical models of glioblastoma

Background Glioblastoma (GBM) remains the most aggressive primary brain tumor in adults, with limited therapeutic options and inevitable recurrence despite maximal standard-of-care treatment. Photodynamic therapy (PDT) and oncolytic virotherapy have independently shown promise as alternative approaches, yet their combined potential in GBM remains incompletely explored. Methods We engineered a highly neuroattenuated herpes simplex virus type 1–based oncolytic virus (oHSV1), genetically related to talimogene laherparepvec (T-VEC), to express the photosensitizer KillerRed (KR) targeted to the cell plasma membrane (memKR). The cytolytic activity of this recombinant virus was evaluated in multiple human and murine GBM cell lines, patient-derived GBM cells, and three-dimensional (3D) spheroid models. We further assessed whether photoactivation of virus-encoded memKR or of the chemical photosensitizer phthalocyanine could enhance oHSV1-mediated cytotoxicity, including in spheroids infected via monocyte-based viral delivery. Results The recombinant memKR-encoding virus (oHSV1-KR) efficiently infected and killed GBM cells across 2D and 3D culture systems. Photoactivation of memKR significantly enhanced virus-mediated cytotoxicity in patient-derived GBM spheroids, particularly at lower viral doses. Similarly, phthalocyanine photoactivation augmented oHSV1-induced cell death, accelerating loss of viability in both monolayer cultures and spheroids. Monocyte-mediated delivery of oHSV1-KR resulted in effective viral transfer to GBM spheroids and retained responsiveness to photodynamic activation. Conclusions These findings demonstrate that combiningoHSV1–based virotherapy with photodynamic activation enhances cytotoxic efficacy in advanced preclinical models of GBM. While limited to in vitro and ex vivo systems, this work establishes a modular and controllable therapeutic platform and provides a foundation for future in vivo and immunological studies aimed at translational development.