d-δ-Tocotrienol-mediated cell cycle arrest and apoptosis in human melanoma cells.

Nicolle V Fernandes, Praveen K Guntipalli, Huanbiao Mo

Index: Anticancer Res. 30(12) , 4937-44, (2010)

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Abstract

The rate-limiting enzyme of the mevalonate pathway, 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, provides essential intermediates for the prenylation or dolichylation of growth-related proteins. d-δ-tocotrienol, a post-transcriptional down-regulator of HMG CoA reductase, suppresses the proliferation of murine B16 melanoma cells. Dietary d-δ-tocotrienol suppresses the growth of implanted B16 melanomas without toxicity to host mice.The proliferation of human A2058 and A375 melanoma cells following a 72 h incubation in 96-well plates was measured by CellTiter 96® Aqueous One Solution. Cell cycle distribution was determined by flow cytometry. Fluorescence microscopy following acridine orange and ethidium bromide dual staining and procaspase-3 cleavage were used to detect apoptosis. Western-blot was employed to measure protein expression.d-δ-Tocotrienol induced dose-dependent suppression of cell proliferation with 50% inhibitory concentrations (IC(50)) of 37.5 ± 1.4 (A2058) and 22.3 ± 1.8 (A375) μmol/l, respectively (data are reported as mean ± standard deviation). d-δ-Tocotrienol-mediated cell cycle arrest at the G(1) phase was accompanied by reduced expression of cyclin-dependent kinase 4. Concomitantly, d-δ-tocotrienol induced caspase-3 activation and apoptosis. The impact of d-δ-tocotrienol on A2058 cell proliferation was potentiated by lovastatin (IC(50)=3.1 ± 0.5 μmol/l), a competitive inhibitor of HMG CoA reductase.d-δ-Tocotrienol may have potential application in melanoma chemoprevention and/or therapy.