G-quadruplex ligand RHPS4 compromises cellular radio-resistance by blocking the increase in mitochondrial mass and activity induced by ionising irradiation.

A major challenge in radiotherapy is to enhance tumor cell sensitivity to radiation while minimizing damage to healthy tissues. Ionising radiation (IR) induces mitochondrial DNA (mtDNA) alterations that can impair mitochondrial function and cell survival. Since mitochondria play a key role in tumor cell proliferation, they represent a promising therapeutic target for cancer treatment. In this study, we characterized the impact of different IR sources on mitochondrial function in radioresistant cancer cells. Our findings revealed several adaptive responses that may contribute to radioresistance, including increased mtDNA content, mitochondrial mass, enhanced activity, and hyperfusion of the mitochondrial network. Notably, the use of mitochondrial-targeted G-quadruplex (G4) ligands, which block mtDNA replication and transcription, disrupted these responses, reducing cancer cell survival in an mtDNA-dependent manner. These results demonstrate that mitochondrial adaptations contribute to radioresistance and highlight mitochondria as a novel target for the radiosensitizing effects of G4-ligands, extending their potential beyond telomere destabilization.