1,25-Dihydroxyvitamin D₃ and cisplatin synergistically induce apoptosis and cell cycle arrest in gastric cancer cells.

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] plays an anticancer role in multiple types of cancer and potentiates the cytotoxic effects of several common chemotherapeutic agents. The hypercalcemia caused by 1,25(OH)2D3 alone or resistance to cisplatin weaken the anticancer effects of vitamin D. Thus, in this study, we aimed to investigate the synergistic effects of 1,25(OH)2D3 and cisplatin on the apoptosis and cell cycle progression of gastric cancer cells. BGC-823 human gastric cancer cells were treated with 1,25(OH)2D3 or cisplatin alone, or a combination of both agents. Cell apoptosis was assessed by TUNEL assay and flow cytometry. The expression of the apoptosis-related proteins, poly(ADP-ribose) polymerase (PARP), Bax, Bcl-2, caspase-3 and caspase-8, was examined using immunoblot analysis. ERK and AKT phosphorylation were examined by immunoblot analysis. The cell cycle distribution was determined by propidium iodide staining and flow cytometric analysis. p21 and p27 protein expression was also examined using immunoblot analysis. Our results revealed that co-treatment with 1,25(OH)2D3 enhanced cisplatin-induced apoptosis and upregulated the expression of Bax, and promoted the cleavage of PARP and caspase-3. The phosphorylation levels of ERK and AKT were reduced following combined treatment with 1,25(OH)2D3 and cisplatin. The percentage of cells in the G0/G1 phase was greater in the cells treated with the combined treatment than in those treated with either 1,25(OH)2D3 or cisplatin alone. p21 and p27 expression was upregulated following co-treatment with both agents. The results of this study suggest that 1,25(OH)2D3 potentiates cisplatin-mediated cell growth inhibition and cell apoptosis, which involves the upregulation of Bax, a decrease in ERK and AKT phosphorylation levels, and increased p21 and p27 levels.