Effects of econazole on Ca²⁺ levels in and the growth of human prostate cancer PC3 cells

Econazole is used clinically as an antifungal drug with many different in vitro effects. However, the effects of econazole on prostate cancer cells are unknown. The effects of econazole on intracellular Ca²⁺ concentrations ([Ca²⁺]_i) in and the proliferation of human PC3 prostate cancer cells was explored in the present study using fura-2 and tetrazolium as fluorescent dyes. At a concentration of 0.1 μmol/L, econazole started to increase [Ca²⁺]_iin a concentration-dependent manner. The econazole-induced increase in [Ca²⁺]_i was reduced by 48% by removal of extracellular Ca²⁺, suggesting that the econazole-induced increase in [Ca²⁺]_i was composed of extracellular Ca²⁺ influx and intracellular Ca²⁺. This econazole-induced Ca²⁺ influx was via an L-type Ca²⁺ channel-like pathway. In Ca²⁺-free medium, 1 μmol/L thapsigargin, an inhibitor of the endoplasmic reticulum Ca²⁺-ATPase, caused a monophasic increase in [Ca²⁺]_i after which the effect of econazole to increase [Ca²⁺]_i was substantially inhibited. Conversely, pretreatment with 5 μmol/L econazole to deplete intracellular Ca²⁺ stores totally prevented thapsigargin from releasing more Ca²⁺. The phospholipase C (PLC) inhibitor U73122 (2 μmol/L) abolished the increase in [Ca²⁺]_i induced by 10 μmol/L ATP (a Ca²⁺ mobilizer that needs inositol 1,4,5-trisphosphate). Overnight incubation with 1-30 μmol/L econazole inhibited gargin proliferation of PC3 cells in a concentration-dependent manner. These findings suggest that, in PC3 cells, econazole increases [Ca²⁺]_i by stimulating Ca²⁺ influx into cells and Ca²⁺ release from the endoplasmic reticulum via a PLC-independent mechanism. Econazole is cytotoxic at submicromolar concentrations.