Econazole-induced Ca²⁺ fluxes and apoptosis in human oral cancer cells

The effect of econazole on cytosolic free Ca²⁺ concentrations ([Ca²⁺]_i) and viability was explored in human oral cancer cells (OC2), using the fluorescent dyes fura-2 and WST-1, respectively. Econazole at concentrations of >1 μM increased [Ca²⁺] _i in a concentration-dependent manner. The Ca²⁺ signal was reduced partly by removing extracellular Ca²⁺. The econazole-induced Ca²⁺ influx was sensitive to blockade of aristolochic acid (phospholipase A₂ inhibitor) and GF109203X (PKC inhibitor). In Ca²⁺-free medium, after treatment with 1 μM thapsigargin (an endoplasmic reticulum Ca²⁺ pump inhibitor), 30 μM econazole failed to induce a [Ca²⁺]_i rise. Inhibition of phospholipase C with 2 μM U73122 substantially suppressed econazole-induced [Ca ²⁺]_i rise. At concentrations of 5-70 μM econazole killed cells in a concentration-dependent manner. The cytotoxic effect of 50 μM econazole was enhanced by prechelating cytosolic Ca²⁺ with 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA). The ERK MAPK inhibitor, PD98059 (10 μM), also enhanced 20 μM econazole-induced cell death. Propidium iodide staining data suggest that econazole induced apoptosis between concentrations of 10-70 μM. Collectively, in OC2 cells, econazole induced [Ca²⁺]_i rises by causing Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ influx from phospholipase A₂/PKC-regulated Ca²⁺ channels. Furthermore, econazole caused cell death appeared to be regulated by ERK MAPK.