HDAC9 and cancer: In the present study, five sulfur-containing compounds from our previous study (11), ten isolated compounds from the roots of Ferula flabelliloba and three constituents from the roots of Ferula ovina (Figure 1), were screened for their cytotoxic activity against four different cancer cell lines that typically overexpress HDAC enzymes, including colon (HCT116), human cervical (HeLa), lung (A549) and ovarian (A2780) cancer cells (12-14).