KCa3.1 mediates radioresistance of silver nanoparticles in human glioblastoma cells

Abstract Silver nanoparticles (AgNPs) have emerged as a promising therapeutic tool for managing glioblastoma (GB), particularly in radiosensitisation. However, their mechanisms of action are not yet fully understood. Since ion channel activity is implicated in various aspects of radioresistance, we investigated the electrophysiological effects of AgNPs on GB cells. In the U251 human GB cell line, the acute application of AgNPs induced the activation of a cationic nonselective current in a dose-dependent manner, which was not affected by ACA (TRPM2 blocker). In addition, AgNPs increased intracellular calcium concentration, caused depolarisation of the mitochondrial inner membrane, and promoted membrane blebbing. The investigation revealed that calcium influx is a critical step in the AgNPs-induced effects. Thiol reagents such as cysteine are known silver chelating agents and their application prevented the activation of cationic currents, intracellular calcium increases, and membrane blebbing formation induced by AgNPs. This finding suggested Ag + are the active species responsible for these effects, acting through IAg current previously characterized in our laboratory. Intracellular calcium influx induced by AgNPs activated intermediate-conductance calcium-activated potassium currents. This activation was accordingly blocked by TRAM-34, a selective inhibitor of KCa3.1 channels. Finally, AgNPs were found to reduce U251-GB cell viability in a dose-dependent manner and to increase G2/M phase accumulation following sublethal irradiation. In the presence of TRAM-34 the G2/M phase accumulation induced by the combined treatment with AgNPs and irradiation was reduced, suggesting the involvement of radioresistance-associated KCa3.1 currents. These results provide new insights into optimizing the use of AgNPs as radiosensitizing agents in GB therapy.