Advantages of YAK540 over TMP269 are simple, straight-forward synthesis; improved solubility; 4-fold less toxic in non-cancer HEK293 cells; 200-fold stronger cellular HDAC activity but yet similar HDAC enzyme activity and class IIa selectivity; more efficacious in inducing caspase-mediated apoptosis; stronger synergy in 2 of 4 examined leukemia cell lines; stronger induction of p21; similar cytotoxic selectivity for leukemia versus HEK293 cells in combination with BTZ. This evidence concerns the gene HDAC9 and cancer.