The cyclo-oxygenase-2 inhibitor celecoxib perturbs intracellular calcium by inhibiting endoplasmic reticulum Ca2+-ATPases: a plausible link with its anti-tumour effect and cardiovascular risks

Substantial evidence indicates that the cyclo-oxygenase-2 (COX-2) inhibitor celecoxib, a widely prescribed anti-inflammatory agent, displays anti-tumour effect by sensitizing cancercells to apoptosis. As part of our effort to understand the mechanism by which celecoxib mediates apoptosis in androgen-independent prostate cancercells, we investigated its effect on intracellular calcium concentration ([Ca²⁺]_i). Digital ratiometric imaging analysis indicates that exposure of PC-3cells to celecoxib stimulates an immediate [Ca²⁺]_i rise in a dose- and time-dependent manner. Kinetic data show that this Ca²⁺ signal arises from internal Ca²⁺ release in conjunction with external Ca²⁺ influx. Examinations of the biochemical mechanism responsible for this Ca²⁺ mobilization indicate that celecoxib blocks endoplasmic reticulum (ER) Ca²⁺-ATPases. Consequently, inhibition of this Ca²⁺ reuptake mechanism results in Ca²⁺ mobilization from ER stores followed by capacitative calcium entry, leading to [Ca²⁺]_i elevation. In view of the important role of Ca²⁺ in apoptosis regulation, this Ca²⁺ perturbation may represent part of the signalling mechanism that celecoxib uses to trigger rapid apoptotic death in cancercells. This Ca²⁺-ATPase inhibitory activity is highly specific for celecoxib, and is not noted with other COX inhibitors tested, including aspirin, ibuprofen, naproxen, rofecoxib (Vioxx^®), DuP697 and NS398. Moreover, it is noteworthy that this activity is also observed in many other cell lines examined, including A7r5 smooth musclecells, NIH 3T3 fibroblastcells and Jurkat Tcells. Consequently, this Ca²⁺-perturbing effect may provide a plausible link with the reported toxicities of celecoxib such as increased cardiovascular risks in long-term anti-inflammatory therapy.