The acetyl-histone H3 (Ac-H3) and acetyl-histone H4 (Ac-H4) levels in these primary tumor tissues confirmed a stronger inhibitory effect of ZN444B on histone deacetylases compared with SAHA, which confirmed the HDAC inhibitory effect of ZN444B on breast cancer in vivo (Fig. 3E, F). This evidence concerns the gene HDAC9 and breast cancer.