Hydroxamate derivatives, including coumarin-, tetrahydro-β-carboline-, quinazolinone-, estratriene-, and urushiol-based scaffolds, have underscored potent and selective inhibition of various HDAC isoforms, especially HDAC1, HDAC6, and HDAC8, leading to cell cycle arrest, induction of apoptosis, and enhanced histone acetylation in multiple cancer models. This evidence concerns the gene HDAC9 and cancer.