3-[1-(p-chlorobenzyl)-5-(isopropyl)-3-tert-butylthioindol-2-yl]-2, 2-dimethylpropanoic acid (MK-886) is widely used for inhibition of leucotriene synthesis in in vitro studies, however, many of its other effects have been reported. The present study investigated the effect of MK-886 on cytosolic-free Ca2+ concentrations ([Ca2+]i) and viability in human PC3 prostate cancer cells. [Ca2+]i in suspended cells was measured by using fura-2. MK-886 at concentrations of 1 µM and above increased [Ca2+]i in a concentration-dependent manner with an EC50 value of 20 µM. The Ca2+ signal was reduced partly by removing extracellular Ca2+. MK-886 evoked Mn2+ quenching of fura-2 fluorescence, implicating Ca2+ entry. MK-886-induced Ca2+ influx was inhibited by store-operated Ca2+ entry inhibitors nifedipine, econazole and SKF96365. In Ca2+-free medium, after pre-treatment with 10 µM MK-886, 1 µM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor)-induced [Ca2+]i rises were abolished; and conversely, thapsigargin pre-treatment abolished MK-886-induced [Ca2+]i rises. Inhibition of phospholipase C with U73122 did not alter MK-886-induced [Ca2+]i rises. MK-886 at concentrations of 1-100 µM concentration-dependently decreased cell viability with an IC50 value of 60 µM. The cytotoxic effect of MK-886 was not inhibited by pre-chelating cytosolic Ca2+ with BAPTA/AM. Together, in PC3 cells, MK-886 induced [Ca2+]i rises by causing phospholipase C-independent Ca2+ release from the endoplasmic reticulum; and Ca2+ influx via store-operated Ca2+ channels. Independently, MK-886 was cytotoxic to cells in a Ca2+-independent manner.