Cytostatic and cytotoxic effects of cyclooxygenase inhibitors and their synergy with docosahexaenoic acid on the growth of human skin melanoma A-375 cells.

Recent studies have suggested the inhibition of cyclooxygenase-2 (COX-2) as strategy to prevent colorectal cancer. In this study, the cytostatic and cytotoxic effects of different non-steroidal anti-inflammatory drugs (NSAIDs), all of them are reported COX inhibitors, were investigated in human skin melanoma A-375 cells. Using BrdU-cell proliferation assay, we showed that 50 and 100 microM of celecoxib (CEL) reduced proliferation of the melanoma cells at 72-h incubations by 34.0% and 82.7%, respectively. As determined by Toxilight-cytotoxicity assay, the drug was only toxic to the cancer cells at 100 microM. Indomethacin (IND) also inhibited the cell proliferation by about 40% at 240 and 480 pM and was only slightly toxic to the melanoma. Neither aspirin (ASP) nor piroxicam (PIR) exhibited cytostatic or cytotoxic effect on the cancer cells. Combinatory effects of the above NSAIDs with dietary docosahexaenoic acid (DHA) on inhibiting growth of the melanoma cells were further elucidated. Each of the NSAIDs, at doses 10-480 pM, was incubated simultaneously with the melanoma cells and 160 pM of DHA for 72 h. Results from MTT assay showed that both CEL and IND, starting from 20 microM. exhibited additive effects on the DHA-induced growth inhibition. ASP also enhanced the DHA-induced growth inhibition by 42.8% at 480 microM. To our surprise, although PRX did not suppress the melanoma growth, the drug at 40-240 microM enhanced the DHA-induced growth inhibition by 15.9-66.4%, respectively. Results from these studies suggest that the anticancer effects of NSAIDs may not be explained solely by their COX-inhibitory activities. Further studies are therefore required to understand their modes of action, before they could be used alone or in combinations with other agents for cancer chemoprevention.

Synergistic action of piroxicam on the eicosapentaenoic acid-induced apoptosis is associated with enhanced down-regulation of anti-apoptotic Bcl-2 expression but not promoted activation of pro-apoptotic Bid protein.

Eicosapentaenoic acid (EPA) is a dietary polyunsaturated fatty acid (PUFA) that is found abundantly in fish oils and induces apoptosis in human promyelocytic leukemia HL-60 cells. Cyclooxygenase (COX) converts EPA intracellularly into various inflammatory mediators that may affect the bioavailability of this fatty acid for inducing apoptosis in the cancer cells. In this study, effect of piroxicam (PRX), a COX inhibitor, on the EPA-induced apoptosis in HL-60 cells was investigated. EPA arrested cell cycle of the leukemic cells at G0/G1 phase after 8-h incubation and induced apoptosis after 24-h incubation. PRX induced neither cell-cycle arrest nor apoptosis significantly in HL-60 cells even after 48-h incubation. However, 24-h incubation with PRX followed by 24-h incubation with EPA significantly elevated both early-phase and late-phase apoptotic cells by 35% and 166% respectively, when compared to those induced by the fatty acid only. This synergistic action of PRX on the EPA-induced apoptosis was associated with enhanced down-regulation of anti-apoptotic Bcl-2 protein expression, but not promoted activation of pro-apoptotic Bid protein.