Selective CCK-A but not CCK-B receptor antagonists inhibit HT-29 cell proliferation:: synergism with pharmacological levels of melatonin

Some data suggest that cholecystokinin (CCK) receptor agonists stimulate the growth of colon cancer. Melatonin, an endogenous indoleamine with strong antioxidant properties, displays antiproliferative and proapoptotic properties both in vivo or in vitro in several types of tumors. We used HT-29 human colon cancer cells, expressing CCK receptors, to test the antiproliferative effects of several antagonists of CCK-A and/or CCK-B and their possible synergism with melatonin. HT-29 cells were cultured in RPMI 1640 medium supplemented with fetal bovine serum at 37 degrees C. Cell proliferation was assessed by the incorporation of [H-3]-thymidine into DNA. Annexin V-FITC plus propidium iodine were used for flow cytometry apoptosis/necrosis evaluation. The following drugs were tested: gastrin (CCK-B agonist); CCK-8s (CCK-A agonist); proglumide (CCK-A plus CCK-B antagonist); lorglumide (CCK-A antagonist); PD 135,158 (CCK-B antagonist and weak CCK-A agonist); devazepide or L 364,718 (CCK-A antagonist); L 365,260 (CCK-B antagonist), and melatonin. The results shown a lack of effects of gastrin on HT-29 cell proliferation, whereas CCK-8s induced proliferation at high doses. The order of the antiproliferative effect of the other drugs was devazepide > lorglumide > proglumide. These drugs produce cell death mainly inducing apoptosis. Melatonin showed strong antiproliferative effect at millimolar concentrations, and it induced apoptotic cell death. Melatonin generally enhanced the antiproliferative effects of devazepide, lorglumide and proglumide and increased the proglumide-induced apoptosis. These results suggest that melatonin and CCK-A antagonists are useful for controlling human colon cancer cell growth in culture and in combined therapy significantly increases their efficiency.