HDAC9 and neoplasm: To further clarify whether the enhancement of the cytotoxic effect of etoposide by NaBut is specific to the engineered mERas cell line or if HDAC inhibitors can sensitize other Ras-mutant tumor cells as well, we examined two tumor cell lines harboring mutations in the ras gene and having varying sensitivity to HDAC inhibitors: HCT116 and A549.