Decitabine Up-regulates S100A2 Expression and Synergizes with IFN-γ to Kill Uveal Melanoma Cells

Abstract

Metastatic uveal melanoma is resistant to conventional chemotherapy and immunotherapy. In this study, we investigated the responsiveness of uveal melanoma cell lines to IFNs and the hypomethylating agent decitabine. The uveal melanoma cell lines 92-1, UW-1, OCM-1, and MKT-BR were exposed to varying concentrations of IFN-alpha, IFN-gamma, and decitabine, alone and in combination. The effects of decitabine on gene expression were examined using DNA microarray analysis. We found that IFN-gamma and decitabine induced cell death in uveal melanoma. Whereas a high concentration of IFN-gamma (1,000 units/mL) was required to induce cell death, we observed a dose-related increase in cell death when decitabine was used at a range of 0.1 to 10 micromol/L. Strikingly, 1 micromol/L decitabine synergized with 10 to 1,000 units/mL IFN-gamma to induce massive cell death. In contrast, decitabine had no effect on three cutaneous melanoma cell lines and exhibited no synergy with either IFN. In uveal melanoma, decitabine up-regulated the expression of genes involved in growth control and apoptosis and down-regulated genes that have been implicated in the malignant phenotype of cutaneous melanoma. The gene up-regulated to the greatest degree by decitabine and whose expression showed a dose-effect across the three concentrations of decitabine was S100A2, a putative tumor suppressor. The genes modulated by decitabine in uveal melanoma were largely unaffected in cutaneous melanoma. These findings form a basis for testing the decitabine/IFN-gamma combination in metastatic uveal melanoma and for exploring the role of S100A2 in the susceptibility of uveal melanoma to IFN-mediated cell death.