Novel Cinnamyl Hydroxyamides and 2-Aminoanilides as Histone Deacetylase Inhibitors: Apoptotic Induction and Cytodifferentiation Activity

Four novel series of cinnamyl-containing histone deacetylase (HDAC) inhibitors 1–4 are described, containing hydroxamate (1 and 3) or 2-aminoanilide (2 and 4) derivatives. When screened against class I (maize HD1-B and human HDAC1) and class II (maize HD1-A and human HDAC4) HDACs, most hydroxamates and 2-aminoanilides displayed potent and selective inhibition toward class I enzymes. Immunoblotting analyses performed in U937 leukemia cells generally revealed high acetyl-H3 and low acetyl-α-tubulin levels. Exceptions are compounds 3 f–i, 3 m–o, and 4 k, which showed higher tubulin acetylation than SAHA. In U937 cells, cell-cycle blockade in either the G2/M or G1/S phase was observed with 1–4. Five hydroxamates (compounds 1 h–l) effected a two- to greater than threefold greater percent apoptosis than SAHA, and in the CD11c cytodifferentiation test some 2-aminoanilides belonging to both series 2 and 4 were more active than MS-275. The highest-scoring derivatives in terms of apoptosis (1 k, 1 l) or cytodifferentiation (2 c, 4 n) also showed antiproliferative activity in U937 cells, thus representing valuable tools for study in other cancer contexts.