HDAC1-IN-5 is a potent HDAC1 inhibitor with IC 50 values of 15 nM and 20 nM for HDAC1 and HDAC6 , respectively. HDAC1-IN-5 can enhance the acetylation of histone H3 and α-tubulin , as well as promote the activation of caspase 3 in cancer cells, thereby inducing apoptosis. HDAC1-IN-5 induces chromatin damage by binding with DNA. HDAC1-IN-5 has strong inhibitory activity against tumor growth in xenograft mice.