Inhibition of store-operated calcium entry contributes to the anti-proliferative effect of non-steroidal anti-inflammatory drugs in human colon cancer cells

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit proliferation and angiogenesis in colorectal cancer. We examined a possible involvement of store-operated calcium (SOC) entry in human colon carcinoma cells (HRT-18), which require calcium for proliferation. Acetyl-salicylic-acid (ASA), mefenamic acid (MEF) and sulindac sulfide (SUS) inhibited cell proliferation with the following order of potency: SUS > MEF > ASA. SUS but not MEF and ASA induced apoptosis following low-dose treatment. Furthermore, SUS and MEF significantly altered the cell cycle distribution. The ability of NSAIDs to inhibit SOC entry was assessed by measuring the intracellular calcium concentration ([Ca2+]i) in response to calcium store depletion using the endoplasmic calcium ATPase inhibitor thapsigargin. SUS and MEF, but not ASA significantly inhibited SOC entry. A causal link between SOC entry inhibition and anti-proliferative activity was tested using the inorganic SOC entry inhibitor La3+ and the specific organic inhibitor N-1-n-octyl-3,5-bis-(4-pyridyl)triazole (DPT). Both La3+ and DPT inhibited cell proliferation and SOC entry. Analogous to MEF, the anti-proliferative effect of DPT was mediated by cell cycle arrest and not by induction of apoptosis. These data indicate a role of SOC entry for cell proliferation in cancer cells and suggest a novel anti-proliferative NSAID mechanism in addition to its known influence on lipid metabolism.