Riluzole as a Dual-Targeted Radiosensitizer for Osteosarcoma: Targeting Tumor Cells and Angiogenic Vasculature to Enhance Single High Dose Radiotherapy Efficacy

Osteosarcoma is a highly aggressive bone malignancy primarily affecting children and young adults. It presents significant treatment challenges due to its inherent resistance to conventional fractionated radiotherapy (CFRT). Single high dose radiation therapy (SDRT) has promise for the treatment of radioresistant sarcomas, especially those characterized with extensive vascularity. However, its clinical application is severely constrained by toxicity to adjacent critical tissues. Radiosensitizers can enhance tumor cell susceptibility to radiation-induced DNA damage, improving therapeutic efficacy and potentially reducing collateral toxicity. Monotherapies targeting tumor vasculature alone in solid tumors have shown limited success as radiosensitizers in clinical settings. This highlights the importance of compounds that can simultaneously target both tumor cells and its associated microvasculature to maximize the therapeutic outcome to SDRT. Riluzole, the FDA-approved drug for Amyotrophic Lateral Sclerosis, is currently under investigation as a therapeutic agent for osteosarcoma. Riluzole acts to inhibit glutamate release, reduce glutathione levels in cancer cells, and mitigate tumor angiogenesis, positioning it as a potent radiosensitizing agent for the treatment of osteosarcoma. We hypothesize that Riluzole enhances osteosarcoma radiosensitivity to SDRT by simultaneously targeting intrinsic tumor radioresistance and pro-angiogenic signaling. Our findings demonstrate that Riluzole radiosensitizes osteosarcoma cells in vitro by reducing clonogenic survival and enhancing apoptosis. Mechanistically, Riluzole potentiates irradiation-induced reactive oxygen species (ROS) production, induces G2/M phase cell cycle arrest, inhibits DNA repair, and thereby amplifies radiation-induced DNA damage. Additionally, Riluzole suppresses radiation-induced Vascular Endothelial growth factor A (VEGFA) expression indicating its ability to overcome endothelial cell mediated radioresistance. Collectively, these results establish Riluzole as a promising radiosensitizer for osteosarcoma, with the potential to improve SDRT efficacy by overcoming both tumor-intrinsic and microvasculature-mediated radioresistance. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=102 SRC="FIGDIR/small/681036v1_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@1839ca2org.highwire.dtl.DTLVardef@1a05dcaorg.highwire.dtl.DTLVardef@16da8cborg.highwire.dtl.DTLVardef@64ce1d_HPS_FORMAT_FIGEXP M_FIG C_FIG This schematic illustrates the proposed mechanism by which Riluzole enhances SDRT efficacy in osteosarcoma by targeting both tumor cells and VEGFA-mediated pro-survival signaling in endothelial cells. Riluzole increases radiation-induced ROS levels, induces G2/M cell cycle arrest, and inhibits DNA repair in osteosarcoma cells, thereby overcoming intrinsic tumor radioresistance. It also suppresses tumor cell VEGFA expression, which may contribute to reduced pro-survival signaling in the angiogenic endothelial cells within the tumor microenvironment. Together, these effects sensitize osteosarcoma tumors to SDRT, improving therapeutic outcomes (Illustration created using BioRender (BioRender.com, 2025)).