Novel Pyridine-Based Hydroxamates and 2'-Aminoanilides as Histone Deacetylase Inhibitors: Biochemical Profile and...

Starting from the N-hydroxy-3-(4-(2-phenylbutanoyl)amino)phenyl)acrylamide (5 b) previously described by us as a HDAC inhibitor, we prepared four aza-analogues, 6-8, 9 b, as regioisomers containing the pyridine nucleus. Preliminary screening against mHDAC1 highlighted the N-hydroxy-5-(2-(2-phenylbutanoyl)amino)pyridyl)acrylamide (9 b) as the most potent inhibitor. Thus, we further developed both pyridylacrylic- and nicotinic-based hydroxamates (9 a, 9 c-f, and 11 a-f) and 2'-aminoanilides (10 a-f and 12 a-f), related to 9 b, to be tested against HDACs. Among them, the nicotinic hydroxamate 11 d displayed sub-nanomolar potency (IC₅₀ : 0.5 nM) and selectivity up to 34 000 times that of HDAC4 and from 100 to 1300 times that of all the other tested HDAC isoforms. The 2'-aminoanilides were class I-selective HDAC inhibitors, generally more potent against HDAC3, with the nicotinic anilide 12 d being the most effective (IC₅₀^HDAC3 =0.113 μM). When tested in U937 leukemia cells, the hydroxamates 9 e, 11 c, and 11 d blocked over 80 % of cells in G2/M phase, whereas the anilides did not alter cell-cycle progress. In the same cell line, the hydroxamate 11 c and the anilide 10 b induced about 30 % apoptosis, and the anilide 12 c displayed about 40 % cytodifferentiation. Finally, the most potent compounds in leukemia cells 9 b, 11 c, 10 b, 10 e, and 12 c were also tested in K562, HCT116, and A549 cancer cells, displaying antiproliferative IC₅₀ values at single-digit to sub-micromolar level.