Tumor-associated macrophage-derived exosomes promote radio-resistance in nasopharyngeal carcinoma cells accompanied by suppression of the cGAS/STING pathway.

PURPOSE: Radiotherapy resistance remains a major obstacle in nasopharyngeal carcinoma (NPC), leading to poor prognosis. While tumor-associated macrophages (TAMs) are implicated in radio-resistance, their mechanistic role is unclear. This study investigates the pivotal function of TAM-derived exosomes (TAM-Exos) and their underlying molecular mechanisms in conferring radio-resistance to NPC cells.

MATERIALS AND METHODS: HK-1 cells were co-cultured with M0 macrophages derived from phorbol 12-myristate 13-acetate-induced THP-1 cells under conditions with or without ionizing radiation (IR). TAM-Exos were subsequently isolated by ultracentrifugation and characterized by transmission electron microscopy, nanoparticle tracking analysis, and western blot. HK-1 cells were treated with TAM-Exos prior to IR. The colony-forming ability and DNA damage repair were assessed by clonogenic assay and immunofluorescence staining with gamma histone 2AX foci. The protein levels of key components in the cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) pathway were assessed by western blot.

RESULTS: Co-culture with TAMs significantly enhanced the clonogenic survival and reduced DNA damage in HK-1 cells following IR, while these effects were reversed after treatment with GW4869, an inhibitor of neutral sphingomyelinase that suppresses exosome secretion, indicating that these effects are exosome-dependent. Consistently, TAM-Exos directly promoted clonogenic survival and enhanced DNA damage repair in HK-1 cells in a concentration-dependent manner, accompanied by repression of the cGAS/STING pathway. Notably, TAM-Exos had no effect in STING-knockdown HK-1 cells, suggesting that STING signaling may be involved in TAM-Exos-associated radioresistance.

CONCLUSION: TAM-Exos enhance DNA damage repair and cell survival in irradiated NPC cells, accompanied by suppression of the cGAS/STING pathway. These findings suggest that cGAS/STING signaling may be involved in TAM-Exos-associated radioresistance and support further investigation of pathway reactivation as a potential radiosensitizing strategy.