Dissertations, Theses, and Capstone Projects

Date of Degree

9-2026

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy

Program

Biochemistry

Advisor

Shahana S Mahajan

Committee Members

Adriana Haimovitz Friedman

Moira Sauane

Chad Euler

Eugenie Kleinerman

Subject Categories

Biochemistry | Molecular Biology

Keywords

Cancer, Osteosarcoma, Radiation therapy, Angiogenesis, Radioresistance

Abstract

Osteosarcoma (OS), the most common primary bone malignancy of children and young adults, is intrinsically radioresistant, and outcomes for patients with unresectable or metastatic disease have not improved in over four decades. Single-dose radiation therapy (SDRT) is a potent modality against radioresistant, highly vascularized sarcomas, but its application in OS is constrained by dose-dependent normal tissue toxicity. Radiosensitizers achieving tumor control at lower doses therefore offer a direct route to widening the therapeutic window. Critically, OS radioresistance is not tumor-cell-autonomous. It emerges from two coordinated compartments: aberrant DNA repair and antioxidant capacity intrinsic to the tumor cell, and a radioprotective, pro-angiogenic microvasculature. Antiangiogenic agents that target only the latter have nonetheless failed as radiosensitizers, as compensatory signaling and reciprocal crosstalk between surviving endothelial and tumor cells rapidly restore the resistant state. Overcoming SDRT resistance in OS thus requires agents that engage the tumor and vascular compartments simultaneously. We therefore hypothesized that riluzole, an FDA-approved glutamate modulator that inhibits both the cystine/glutamate antiporter xCT (SLC7A11) and tumor angiogenesis sensitizes OS tumors to SDRT by concurrently targeting radioresistance mechanisms in both the tumor and vascular compartments

xCT, which imports cystine for glutathione biosynthesis and sustains cellular antioxidant defense, was markedly overexpressed across OS cell lines relative to non-malignant osteoblasts. Riluzole suppressed radiation-induced xCT expression and depleted intracellular glutathione, sustaining the SDRT-generated reactive oxygen species (ROS) burst that tumor cells otherwise neutralize to survive irradiation-induced damage. Together, these effects significantly reduced clonogenic survival in riluzole-pretreated LM7 and OS482 cells relative to radiation alone, with a concomitant increase in apoptosis, demonstrating effective radiosensitization.

Within the vascular compartment, riluzole elevated endothelial ROS and inhibited VEGFA-driven endothelial proliferation and migration. Riluzole pretreatment further abrogated radiation-induced upregulation of vascular endothelial growth factor A expression in OS cells, disabling the compensatory paracrine loop underlying vasculature-mediated radioresistance. In vivo, these mechanisms converged therapeutically in LM7-ffLuc xenografts. Neither riluzole nor SDRT monotherapy controlled tumor progression, whereas combination therapy significantly reduced tumor growth relative to SDRT and all other control arms. Collectively, these findings establish riluzole as a dual-compartment radiosensitizer that simultaneously disables tumor-intrinsic and vascular-mediated radioresistance, offering a promising strategy to maximize the utility of ablative radiotherapy in OS.

Download

Share

COinS