Modification of the cap group of biphenylacrylohydroxamic acid-based HDAC inhibitors led to the identification of a new derivative (3) characterized by an indolyl-substituted 4-phenylcinnamic skeleton. Molecular docking was used to predict the optimal conformation in the class I HDACs active site. Compound 3 showed HDAC inhibitory activity and antiproliferative activity against a panel of tumor cell lines, in the low μM range. The compound was further tested in vitro for acetylation of histone H4 and other non-histone proteins, and in vivo in a colon carcinoma model, showing significant proapoptotic and antitumor activities.