Rise of [Ca2+]i and Apoptosis Induced by M-3M3FBS in SCM1 Human Gastric Cancer Cells

M-3M3FBS (2,4,6-trimethyl-N-(meta-3-trifluoromethyl-phenyl)-benzenesulfonamide is a presumed phospholipase C activator which induced Ca2+ movement and apoptosis in different cell models. However, the effect of m-3M3FBS on cytosolic free Ca2+ concentrations ([Ca2+](i)) and apoptosis in SCM1 human gastric cancer cells is unclear. This study explored whether m-3M3FBS elevated basal [Ca2+](i) levels in suspended cells by using fura-2 as a Ca2+-sensitive fluorescent dye. M-3M3FBS at concentrations between 5-50 mu M increased [Ca2+](i) in a concentration-dependent manner. The Ca2+ signal was reduced by half by removing extracellular Ca2+. M-3M3FBS-induced Ca2+ influx was inhibited by nifedipine, econazole, SK&F96365, aristolochic acid, and GF109203X. In Ca2+-free medium, 50 mu M m-3M3FBS pretreatment inhibited the [Ca2+](i) rise induced by the endoplasmic reticulum Ca2+ pump inhibitor thapsigargin. Conversely, pretreatment with thapsigargin partly reduced m-3M3FBS-induced [Ca2+](i) rise. Suppression of inositol 1,4,5-trisphosphate production with U73122 did not change m-3M3FBS-induced [Ca2+](i) rise. At concentrations between 25 and 50 mu M m-3M3FBS killed cells in a concentration-dependent manner. The cytotoxic effect of m-3M3FBS was not reversed by prechelating cytosolic Ca2+ with acetoxy-methyl ester of bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA/AM). Annexin V/propidium iodide staining data suggest that m-3M3FBS induced apoptosis at 25 and 50 mu M. M-3M3FBS also increased levels of superoxide. Together, in human gastric cancer cells, m-3M3FBS induced a [Ca2+]; rise by inducing phospholipase C-independent Ca2+ release from the endoplasmic reticulum and Ca2+ entry via protein kinase C-sensitive store-operated Ca2+ channels. M-3M3FBS induced cell death that might involve apoptosis via reactive oxygen species production.