Lubiprostone Suppresses Growth of Colon Cancer Cells in vitro and in vivo

Purpose: Colon and other tumors show low levels of expression of 15-hydroxy-prostaglandin dehydrogenase [NAD+] (HPGD), also known as 15-PGDH, a prostone synthetase, which converts prostaglandins to their metabolites, prostones. 15-PGDH, a tumor suppressor, is low in HT-29 colon cancer cells. Deficiency in 15-PGDH results in high prostaglandin levels (and perhaps low prostone levels), which in turn may lead to stimulation of tumor growth. Lubiprostone is a prostone derivative that activates ClC-2 Cl- channels and is used for the treatment of chronic idiopathic constipation in adults and irritable bowel syndrome with constipation in adult women. Cellular effects of lubiprostone include activation of ion channels, subsequent membrane hyperpolarization, reduced intracellular free calcium ([Ca2+]i), and no effect on [cAMP]i. In contrast, PGE1 and PGE2 cause membrane depolarization and increased [Ca2+]i and [cAMP]i by binding to EP receptors (Prostaglandin and Other Lipid Mediators 86: 56-60, 2008). The effect of lubiprostone on tumor growth rate was investigated using wild-type, mock-transfected and 15-PGDH-transfected HT-29 colon cancer cells and HT-29-derived tumors orthotopically implanted on the cecum mucosa of nude mice. Methods: For in vitro studies, HT-29 cells were plated in 60-mm Petri dishes in triplicate and counted in a 1 mm2 area using a microscope grid in a randomly chosen field. Lubiprostone or vehicle (0.1% DMSO) was added after 48 h of plating and cells were then counted 24, 48, 72 and 96 h later. For the animal study, HT-29 tumors were surgically implanted on the cecum mucosa in nude mice and tumor sizes were measured once/week. Lubiprostone and vehicle were given daily orally at day 15 after tumor implantation and monitored at day 22 and day 29 after implantation. Results: Growth of HT-29 cells was significantly inhibited even at 24 h by 100 nM lubiprostone in vitro and inhibited up to about 73% by 72 h. Lubiprostone inhibition of HT-29 cell growth was dose dependent with IC50=1.8±0.3 nM. In PGDH-transfected-HT-29 cells, the inhibitory effect of lubiprostone was lost compared to mock-transfected or non-transfected cells. Lubiprostone (1, 3, 5 mg/kg) also significantly suppressed growth of HT-29 orthotopically implanted tumors by 40-50%. Conclusion: Lubiprostone suppresses growth of HT-29 colon cancer cells in vitro and HT-29 tumor growth in vivo. The mechanism might involve interference with the growth effects caused by high prostaglandin levels in tumor cells with low 15-PGDH (low prostone synthetase activity). These results suggest that lubiprostone might be useful for treatment and/or prevention of colon and potentially other cancers. Supported by Sucampo Pharmaceuticals, Inc. Disclosure: John Cuppoletti is a consultant to, holds stock options in, and has a research grant from Sucampo Pharmaceuticals Inc. Danuta H. Malinowska and Jayati Chakrabarti are supported by the grant from Sucampo Pharmaceuticals Inc. Takashi Sekida is an employee of Sucampo Pharmaceuticals, Inc. Ryuji Ueno is CEO and Chief Scientific Officer, Chairman of the Board and Founder of Sucampo Pharmaceuticals, Inc. This research was supported by an industry grant from Sucampo Pharmaceuticals Inc.