Suberoylanilide hydroxamic acid (SAHA) enhances the anti-tumor effects of olaparib in an MDA-MB-231 xenograft model. (A) A mouse xenograft model with MDA-MB-231 human breast cancer cells was established. The mice were treated with 30 mg/kg olaparib (n = 8), 30 mg/kg SAHA (n = 8), 30 mg/kg olaparib plus 30 mg/kg SAHA (n = 8), or vehicle alone (n = 8) daily for 28 d. Tumor volumes for each mouse were measured and are presented in a graph with the SD. Olaparib plus SAHA significantly inhibited tumor growth in a MDA-MB-231 mouse xenograft model (*P <0.001). (B) Changes in mouse body weight were measured to estimate the toxicity of each treatment. (C) The tumors were removed from the mice 10 d after drug treatment ended, and immunohistochemical staining for Ki-67 along with a TUNEL assay were conducted. Representative images from this study are presented with scale bars representing 25 μM (400× magnification). Arrows indicate positive staining. (D) Total cell proteins were extracted from tissues and the expression of molecules associated with proliferation, apoptosis, and autophagy were evaluated with western blotting.