HDAC9 and cancer: The results show that both GSPs and Res acted as strong DNMT inhibitors as well as HDAC inhibitors in MDA-MB-231 and MCF-7 cells, and their combination resulted in a greater reduction in DNMT activity and HDAC activity than did GSPs and Res alone in both of the cell lines (Figure 5 and Figure 6), which may suggest that GSPs and Res synergistically inhibit MDA-MB-231 and MCF-7 cells by upregulating cancer suppressor genes through decreasing DNMT and HDAC activities.