Figure 3. The HDAC inhibitor, entinostat, enhances peptide vaccine therapy in a castration resistant prostate cancer model.

A and B, Entinostat enhances the antitumor effect of the survivin vaccine, SurVaxM. FVB mice were castrated and subcutaneously inoculated with small castration resistant tumor pieces. Approximately 7 days after inoculation when tumors reached an average size of 50 mm², mice were treated three weeks with vehicle, entinostat (5 mg/kg, 1 dose/day, 5 days/wk), survivin vaccine SurVaxM (100 µg/dose, 1 dose/wk), or combination. A, Single tumor growth graph lines were generated by serial caliper measurements. B, Tumors were harvested at the end of treatment and weighed (combination vs. survivin vaccine, p = 0.003). C, Entinostat treatment reduced Foxp3 levels in Tregs from CR Myc-CaP tumor-bearing mice. After 5 days of treatment, peripheral blood cells were collected from mice, stained for CD4 and Foxp3, and subjected to FACS analysis. Quantitation of Foxp3 mean fluorescence intensity (Foxp3 MFI) (vehicle vs. entinostat, p = 0.0002; combination vs. survivin, p = 0.0004).