Fendiline-evoked [Ca2+]i rises and non-Ca2+-triggered cell death in human oral cancer cells

The effect of fendiline on cytosolic free Ca²⁺ concentrations ([Ca²⁺]_i) and proliferation has not been explored in human oral cancer cells. This study examined whether fendiline altered Ca ²⁺ levels and caused cell death in OC2 human oral cancer cells. [Ca²⁺]_i and cell viability were measured using the fluorescent dyes fura-2 and WST-1, respectively. Fendiline at concentrations above 10μM increased [Ca²⁺]_i in a concentration- dependent manner. The Ca²⁺ signal was reduced partly by removing extracellular Ca²⁺. The fendiline-induced Ca²⁺ influx was sensitive to blockade of L-type Ca²⁺ channel blockers. In Ca ²⁺-free medium, after pretreatment with 50μM fendiline, 1μM thapsigargin (an endoplasmic reticulum Ca²⁺ pump inhibitor)-induced [Ca²⁺]_i rises were inhibited; and conversely, thapsigargin pretreatment nearly abolished fendiline-induced [Ca²⁺]_i rises. Inhibition of phospholipase C with 2μM U73122 did not change fendiline-induced [Ca²⁺]_i rises. At concentrations between 5 and 25μM, fendiline killed cells in a concentration-dependent manner. The cytotoxic effect of 15μM fendiline was not reversed by prechelating cytosolic Ca²⁺ with BAPTA/AM. Collectively, in OC2 cells, fendiline induced [Ca²⁺]_i rises by causing Ca²⁺ release from the endoplasmic reticulum and Ca²⁺ influx from L-type Ca²⁺ channels. Furthermore, fendiline-caused cytotoxicity was not via a preceding [Ca²⁺]_i rise.