Sodium butyrate inhibits the self-renewal capacity of endometrial tumor side-population cells by inducing a DNA damage response

We previously isolated side-population (SP) cells from a human endometrial cancer cell line, Hec1, and determined that Hec1-SP cells have cancer stem-like cell features. In this study, we isolated SP cells and non-SP (NSP) cells derived from a rat endometrial cell line expressing human [12Val] KRAS (RK12V cells) anddetermined the SP phenotype. RK12V-SP cells showed self-renewal capacity, the potential to develop into stromal cells, reduced expression levels of differentiation markers, long-term proliferating capacity in cultures, and enhanced tumorigenicity, indicating that RK12V-SP cells have cancer stem-like cell features. RK12V-SP cells also display higher resistance to conventional chemotherapeutic drugs. In contrast, treatment with a histone deacetylases (HDAC) inhibitor, sodium butyrate (NaB), reduced self-renewal capacity and completely suppressed colony formation of RK12V-SP cells in a soft agar. The levels of intracellular reactive oxygen species (ROS) and the number of γH2AX foci were increased by NaB treatment of both RK12V-SP cells and RK12V-NSP cells. The expression levels of γH2AX, p21, p27, and phospho-p38 mitogen-activated protein kinase were enhanced in RK12V-SP cells compared with RK12V-NSP cells. These results imply that treatment with NaB induced production of intracellular ROS and DNA damage in both RK12V-SP and RK12V-NSP cells. Following NaB treatment, DNA damage response signals were enhanced more in RK12V-SP cells than in RK12V-NSP cells. This is the first article on an inhibitory effect of NaB on proliferation of endometrial cancer stem-like cells. HDAC inhibitors may represent an attractive antitumor therapy based upon their inhibitory effects on cancer stem-like cells.