Effects of MK‐886, a leukotriene synthesis inhibitor, on [Ca 2+ ] i and apoptosis in MG63 human osteosarcoma cells

The effect of MK‐886 (3‐[1‐( p ‐chlorobenzyl)‐5‐(isopropyl)‐3‐ tert ‐butylthioindol‐2‐yl]‐2, 2‐dimethylpropanoic acid), a compound widely used to inhibit leukotriene synthesis, on cytosolic free Ca 2+ concentrations ([Ca 2+ ] i ) in osteosarcoma cells has not been explored. This study examined whether MK‐886 altered [Ca 2+ ] i levels in suspended MG63 human osteosarcoma cells using fura‐2. MK‐886 at 0.1 μM and above increased [Ca 2+ ] i in a concentration‐dependent manner. The Ca 2+ signal was reduced partly by removing extracellular Ca 2+ . MK‐886 induced Mn 2+ quenching of fura‐2 fluorescence, implicating Ca 2+ entry. MK‐886‐induced Ca 2+ influx was inhibited by store‐operated Ca 2+ entry inhibitors, nifedipine, econazole, and SKF96365; and by the protein kinase C modulators, phorbol 12‐myristate 13‐acetate (PMA) and GF109203X. In Ca 2+ ‐free medium, after pretreatment with 5 μM MK‐886, 1 μM thapsigargin (an endoplasmic reticulum Ca 2+ pump inhibitor)‐induced [Ca 2+ ] i rises were abolished; conversely, thapsigargin pretreatment nearly abolished MK‐886‐induced [Ca 2+ ] i rises. Inhibition of phospholipase C with U73122 did not change MK‐886‐induced [Ca 2+ ] i rises. Collectively, in MG63 osteosarcoma cells, MK‐886 induced [Ca 2+ ] i rises by causing phospholipase C‐independent Ca 2+ release from the endoplasmic reticulum and Ca 2+ influx via protein kinase C‐regulated store‐operated Ca 2+ entry. Drug Dev Res 69: 49–57, 2008. © 2008 Wiley‐Liss, Inc.