Effect of MK-886 on Ca²⁺ level and viability in PC3 human prostate cancer cells

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 1M and above increased [Ca²⁺]_i in a concentration-dependent manner with an EC₅₀ value of 20M. 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 Ca ²⁺ entry inhibitors nifedipine, econazole and SKF96365. In Ca ²⁺-free medium, after pre-treatment with 10M MK-886, 1M thapsigargin (an endoplasmic reticulum Ca²⁺ pump inhibitor)-induced [Ca ²⁺]_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 [Ca ²⁺]_i rises. MK-886 at concentrations of 1-100 M concentration-dependently decreased cell viability with an IC₅₀ value of 60M. 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 endoplsmic reticulum; and Ca²⁺ influx via store-operated Ca²⁺ channels. Independently, MK-886 was cytotoxic to cells in a Ca²⁺-independent manner.