Antiproliferative and proapoptotic actions of okra pectin on B16F10 melanoma cells

The proliferation and apoptosis of metastatic melanoma cells are often abnormal. We have evaluated the action of a pectic rhamnogalacturonan obtained by hot buffer extraction of okra pods (okra RG-I) on melanoma cell growth and survival in vitro. We added okra RG-I containing an almost pure RG-I carrying very short galactan side chains to 2D (on tissue culture polystyrene, tPS) and 3D (on poly(2-hydroxyethylmethacrylate), polyHEMA) cultures of highly metastatic B16F10 mouse melanoma cells. We then analyzed cell morphology, proliferation index, apoptosis, cell cycle progression and the expression of adhesion molecules. Immunostaining and western blotting were used to assay galectin-3 (Gal-3) protein.Incubation with okra RG-I altered the morphology of B16F10 cells and significantly reduced their proliferation on both tPS and polyHEMA. The cell cycle was arrested in G2/M, and apoptosis was induced, particularly in cells on polyHEMA. The expression of N-cadherin and alpha5 integrin subunit was reduced and that of the multifunctional carbohydrate-binding protein, Gal-3, at the cell membrane increased.These findings suggest that okra RG-I induces apoptosis in melanoma cells by interacting with Gal-3. As these interactions might open the way to new melanoma therapies, the next step will be to determine just how they occur.