Amiloride inhibits the growth of human colon cancer cells in vitro

Cytoplasmic alkalinization induced by activation of the Na⁺ H⁺ antiport plays an essential role in the initiation of cell proliferation. In the present study we examined the effects of amiloride, a specific and reversible inhibitor of Na⁺ H⁺ antiporter, on the growth of human colon cancer cells (HT-29). Amiloride (50-800 μm) inhibited the growth of HT-29 cells in a dose-dependent fashion. Forty-three percent inhibition of growth was found at an amiloride concentration of 400 μm after 4 days of treatment. The inhibitory effect of amiloride on growth of HT-29 cells was reversible since removal of amiloride by a media change after 48 h treatment lead to rapid regrowth to control levels. The reversibility of growth inhibition suggests that amiloride is not a non-specific cytotoxin for HT-29 cells. We examined the possible mechanisms for the inhibitory effects of amiloride. Amiloride (400 μM) completely abolished serum-stimulated ODC activity and inhibited difluoromethylornithine (DMFO)-stimulated putrescine uptake by 56%. We conclude that amiloride inhibits the in vitro growth of human colon cancer cells; since ODC-activity and polyamine transport were both inhibited, the inhibitory effects may be mediated in part by polyamine-dependent processes. Amiloride may be a useful agent in the treatment of colon cancer.