Fig. 1.

Luminal breast cancer is sensitive to entinostat in vivo and in vitro. a Antiproliferative activities of entinostat in breast cancer cells. The effects of entinostat on the proliferation of various human or mouse cancer cell lines were determined by using the [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)2H-tetrazolium [21] assay (CellTiter 96® AQueous One Solution Cell Proliferation Assay, Promega). Cells were seeded into 96-well culture plates and treated with entinostat for 3 days, and then treated with MTS for 2 h. Cell viability was determined by measuring the absorbance at 490 nm. Inhibitory concentration (IC) curves are shown with IC₅₀ values in legend. b Short-term treatment responses for seven mouse models of mammary cancer. The models used were p53 null T2 and T11 which were chosen based on their similarity in gene expression to claudin-low subtype, 2396R, 2225L, and C3tag whose subtype was basal-like, WHIM8 and WHIM35 whose subtypes were HER2-enriched [24], and 2208L and MMTV/Neu whose subtypes were luminal [25]. Entinostat at 12 mg/kg was continuously administered via the chow. Tumor size was measured at baseline for all the models and at 7-day point for 2225L, 10-day point for 2396R and T2, 14-day point for 2208L, and 21-day point for T11, WHIM8, WHIM35, C3tag, and MMTV/Neu. Treatment periods were dependent on their faster growth rate. The change in tumor volume is plotted as whisker plots shown as measures of tumor responsiveness for entinostat-treated models with their matched untreated control. The error bars represent the 95% CIs. The number of animals in each treatment group is indicated in parentheses. Mann-Whitney tests were conducted between untreated control and entinostat-treated group for each mouse model. *, < 0.05; **, < 0.01; ***, < 0.001; ns, not significant. c A total of eight MMTV/Neu tumors from six mice showed complete response but finally became resistant to entinostat chow (12 mg/kg). 180226-Lt.Neck or 180165-Lt.inguinal were not detected at the beginning but appeared after 63 or 77 days of treatment, respectively