Synergistic anticancer activity of valproate combined with nicotinamide enhances anti-proliferation response and apoptosis in MIAPaca2 cells.

Histone deacetylase is strongly associated with epigenetic regulation and carcinogenesis, and its inhibitors can induce cell cycle arrest and apoptosis of the cancer cells. In this study we aimed to examine the antiproliferative effects a combination of the valproate with nicotinamide in MIAPaca2 cell line. We revealed that valproate acted in a synergistic/additive with nicotinamide to inhibit the proliferation and induction of apoptosis in MIAPaca2 cancer cell line. MIAPaca2 was treated with various concentrations of valproate. The MTT assay and colony formation in soft agar indicated that valproate at 0.5 mM, when used alone weakly, suppressed proliferation of cells (37 ± 3.02%) whereas the combination treatment of valproate + nicotinamide significantly suppressed cell proliferation (58 ± 3.5%). The effect of nicotinamide at 25 mM on cell proliferation and cell colonization induced 50% apoptosis of MIAPaca2 cells. To identify the anti-proliferation and apoptotic effects of valproate and nicotinamide we performed flow cytometric and microscopic analyses. The results indicated significant apoptosis induction and nuclear morphological alterations greater than when valproate was used alone. Furthermore, western blot analyses was performed to study the role of acetyl-histone H3 levels, and quantitative RNA expression analyses were performed on expression of thrombospondin (TSP) and maspin genes in MIAPaca2. We found that the combination treatment of valproate + nicotinamide enhanced the expression of maspin and TSP genes and the biological response of the cell line was correlated with the increase of histone H3 acetylation after nicotinamide and valproate application. Together our findings indicate that valproate which act as inhibitor of cell proliferation and inducer of apoptosis in human cancer MIAPaca2 cells when used in combination with nicotinamide makes it a potentially good candidate for new anticancer drug development.