Preclinical Development 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 nonSP (NSP) cells derived from a rat endometrial cell line expressing human [Val] KRAS (RK12V cells) and determined 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 gH2AX foci were increased byNaB treatment of both RK12V-SP cells and RK12V-NSP cells. The expression levels of gH2AX, 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 withNaB induced production of intracellular ROS andDNAdamage in both RK12V-SP andRK12V-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. Mol Cancer Ther; 10(8); 1–10. 2011 AACR.