Macrophage Migration Inhibitory Factor (MIF) Tautomerase Inhibitors as Potential Novel Anti-Inflammatory Agents: Current Developments

Macrophage migration inhibitory factor (MIF), the pro-inflammatory cytokine, first described in 1966, plays an essential role in both, innate and adaptive immune response. It has been implicated in tumour growth and angiogenesis and it exerts an antagonistic action against glucocorticoid immunosuppressive effect. Its perplexing enzymatic tautomerase activity has attracted considerable interest in the last decade. It has been suggested, that a multitude of autoimmune/ inflammatory/neoplastic disease states might benefit from therapeutic measures, targeting MIF. Hence, small molecule inhibitors of MIF are relentlessly sought as potential anti-inflammatory (antitumour) agents, while a true in vivo substrate for MIF still remains unidentified. One of the first studied MIF inhibitor group was the D-dopachrome family, and its carboxyderivatives have shown good inhibitory effect, as well as the fluorosubstituted phenylpyruvic acid class. The substance ISO-1 of isoxazoline skeleton was the first small molecular inhibitor of MIF, not related to its known substrates. N-acetyl-p-benzoquinone, an acetaminophen metabolite and its synthetic derivatives exerted submicromolar IC50 values. An acetylenic compound, the 2-oxo-4-phenyl-3-butynoate is a potent active-site-directed irreversible inhibitor of the phenyl pyruvate tautomerase activity of MIF. Some oxygen heterocycles, coumarines and chromenes, have also drawn attention as MIF inhibitors. The α,β-unsaturated carbonyl compounds constitute a large novel class of MIF inhibitors. Several potent inhibitors were found among the cinnamic acid derivatives, the α,β-unsaturated cyclic ketones, and the natural curcuminoids. Some other plant derived compounds were also studied. One of the latest developments in the field is the synthesis of AVP-13546, an exceptionally potent inhibitor. The structural pattern of MIF enzyme inhibitors exhibits wide variety; compounds having quite different molecular backbones belong to the MIF inhibitor family. In this paper, the separate classes of MIF inhibitors are discussed.