Micromolar Zn2+ potentiates the cytotoxic action of submicromolar econazole in rat thymocytes: Possible disturbance of intracellular Ca2+ and Zn2+ homeostasis

Econazole, one of imidazole antifungals, has been reported to exhibit an inhibitory action on Mycobacterium tuberculosis and its multidrug-resistant strains under in vitro and ex vivo conditions. There is a chemotherapeutic potential of econazole against tuberculosis. We have revealed that Zn2+ at micromolar concentrations potentiates the cytotoxicity of imidazole antifungals by increasing membrane Zn2+ permeability. It is reminiscent of a possibility that econazole exhibits harmful action on human in the presence of Zn2+ at a physiological range when the agent is systemically administered. Because it is necessary to characterize the cytotoxic action of econazole in the presence of Zn2+, we have cytometrically examined the effects of econazole, ZnCl2, and their combination on rat thymocytes. ZnCl2 at concentrations ranging from 1 μM to 30 μM significantly increased the lethality induced by 10 μM econazole in a concentration-dependent manner. Econazole at a sublethal concentration of 1 μM significantly augmented the intensity of side scatter in the presence of micromolar ZnCl2, suggesting the change in an intracellular circumstance by the combination of econazole and ZnCl2. Econazole at 0.3 μM or more in the presence of ZnCl2 increased the intensity of Fluo-3 fluorescence, an indicator for intracellular Ca2+. Furthermore, the intensity of FluoZin-3 fluorescence, an indicator for intracellular Zn2+, was also augmented by econazole at 0.1 μM or more in the presence of ZnCl2. Results suggest that the combination of submicromolar econazole with micromolar ZnCl2 may increase the intracellular concentration of Ca2+ and Zn2+, leading to disturbance of intracellular Ca2+ and Zn2+ homeostasis that triggers cytotoxic action.