The grape and wine polyphenol piceatannol is a potent inducer of apoptosis in human SK-Mel-28 melanoma cells

Summary. Background & aim: The resveratrol analogue piceatannol (3,5,3,4-tetrahydroxy-trans-stilbene; PICE) is a polyphenol present in grapes and wine. PICE is a protein kinase inhibitor that modifies multiple cellular targets exerting immunosuppressive, antileukemic and antitumorigenic activities in several cell lines and animal models. The present work aims to evaluate the antimelanoma effect of PICE on human melanoma cells for the first time. To this purpose, the pro-apoptotic capacity, uptake and metabolism of PICE as well as its effect on cell cycle and cyclins A, E and B1 expression will be studied. Methods: Human SK-Mel-28 melanoma cells were incubated with PICE (1–200 µM) for 72 hours. Cell cycle and viability were examined using flow cytometry analysis. Apoptosis was determined using the annexin V assay and also by fluorescence microscopy. Cyclins A, E and B1 were detected by Western blotting. Stability, cellular uptake and metabolism of PICE were evaluated using HPLC-DAD-MS-MS. Results: The lowest PICE concentration assayed (1 µM) increased about 6-fold over the control the apoptotic population of melanoma cells (10.2% at 8 hours which remained constant during 48 h). 100 µM PICE induced 13% apoptosis at 8 h increasing up to 41.5% at 48 h. The decrease in cell viability was highly correlated with the increase of apoptotic cells (R = 0.996; P < 0.0001) revealing that significant cytotoxic, unspecific effects did not occur in melanoma cells upon incubation with PICE. Cell cycle was arrested at G₂ phase which was supported by the down-regulation of cyclins A, E and B1. Two methyl-PICE derived metabolites, 3,5,4-trihydroxy-3-methoxy-trans-stilbene and 3,5,3-trihydroxy-4-methoxy-trans-stilbene (corresponding to 36% of the initially PICE added) were excreted by cells to the medium. The same methyl-PICE derivatives were also found inside the cells (0.01% of the initially PICE added; 0.0183 picograms/cell). Conclusion: The antimelanoma properties of dietary piceatannol cannot be ruled out taking into account its fast and potent pro-apoptotic capacity at low concentration (1 µM).