Stimulation of electroporation-induced inward currents in glioblastoma cell lines by the heat shock protein inhibitor AUY922

Membrane electroporation (MEP) increases the electrical conductivity of the plasma membrane by addition of an external electrical field. Combining MEP-induced current (I_MEP) with antineoplastic agents has been increasingly considered as a new therapeutic manoeuvre, especially in the treatment of malignant gliomas. Thus, the aim of the present study was to evaluate the effect of AUY922 (AUY), a potent inhibitor of heat-shock protein 90 (HSP90), on I_MEP in glioblastoma cells. The I_MEP in glioblastoma cells (U373) was generated by repetitive hyperpolarization from -80 to -200 mV. The amplitude of I_MEP was increased by AUY in a concentration-dependent manner, with an EC₅₀ of 0.32 μmol/L. In addition AUY shortened the latency to I_MEP generation. Before depolarization to +50 mV, hyperpolarization to -200 mV for 50 msec produced Ca²⁺ influx and subsequently increased the amplitude of the Ca²⁺-activated K⁺ current (I_K(Ca)). The amplitude of I_K(Ca) and Ca²⁺ influx was further increased by AUY through its ability to activate I_MEP. Other HSP90 inhibitors, namely 17-(allylamino)-17-demethoxygeldanamycin (17-AAG; 1 μmol/L) and 6-chloro-9-[(4-methoxy-3,5-dimethylpyridin-2-yl)methyl]-9H-purin-2-amine (BIIB021; 1 μmol/L), only slightly (albeit significantly) increased the amplitude of I_MEP in glioblastoma cells. A 50 msec depolarizing step elevated Ca²⁺ influx and subsequently increased the amplitude of I_K(Ca) in the presence of these three inhibitors. These data indicate that the AUY-mediated stimulation of I_MEP and I_K(Ca) in glioblastoma cells is independent of HSP90 inhibition. Moreover, these results indicate that AUY-stimulated I_MEP and the subsequent activation of I_K(Ca) may create important signalling events in glioblastoma cells. Thus, AUY is a drug that could potentially be used to augment the effectiveness of electrochemotherapy.