Autophagy-dependent sensitization effects of PARP inhibitors on recurrent nasopharyngeal carcinoma treated with carbon ion and photon irradiation

Tumor radioresistance and severe toxicity make reirradiation for recurrent nasopharyngeal carcinoma (NPC) a significant clinical challenge. This study aims to investigate the ability of the poly(ADP-ribose) polymerase (PARP) inhibitor olaparib to sensitize recurrent NPC cells irradiated with photon or carbon ion (C-ion), and to explore the underlying mechanism of the synergistic promotion of cell death by olaparib and ionizing radiation. The results show that olaparib has significant X-ray and C-ion radiosensitization effects on recurrent NPC cells and the associated HK-RR photon-resistant model. Radiation, particularly C-ion exposure, induces a homologous recombination (HR)-deficient gene signature in HR-proficient NPC cells, potentially increasing their sensitivity to PARP inhibition. C-ion and X-ray irradiation induces similar modes of cell death, and multiple cell death pathways [including apoptosis, necrosis, ferroptosis, senescence, and autophagic cell death (ACD)] contribute to the cytotoxic effects of radiation combined with olaparib, with ACD being the dominant pathway. Both the pharmacological and genetic inhibition of autophagy significantly attenuate the radiosensitization effect of olaparib. In conclusion, olaparib effectively sensitizes recurrent NPC cells to both X-ray irradiation and C-ion irradiation, with autophagy playing a central role in mediating this effect.