A structurally preserved allosteric site in the MIF superfamily affects enzymatic activity and CD74 activation in D-dopachrome tautomerase

The macrophage migration inhibitory factor (MIF) family of cytokines contains multiple ligand-binding sites and mediates immunomodulatory processes through an undefined mechanism(s). Previously, we reported a dynamic relay connecting the MIF catalytic site to an allosteric site at its solvent channel. Despite structural and functional similarity, the MIF homolog D-dopachrome tautomerase (also called MIF-2) has low sequence identity (35%), prompting the question of whether this dynamic regulatory network is conserved. Here, we establish the structural basis of an allosteric site in MIF-2, showing with solution NMR that dynamic communication is preserved in MIF-2 despite differences in the primary sequence. X-ray crystallography and NMR detail the structural consequences of perturbing residues in this pathway, which include conformational changes surrounding the allosteric site, despite global preservation of the MIF-2 fold. Molecular simulations reveal MIF-2 to contain a comparable hydrogen bond network to that of MIF, which was previously hypothesized to influence catalytic activity by modulating the strength of allosteric coupling. Disruption of the allosteric relay by mutagenesis also attenuates MIF-2 enzymatic activity in vitro and the activation of the cluster of differentiation 74 receptor in vivo, highlighting a conserved point of control for nonoverlapping functions in the MIF superfamily.

Tetralone derivatives are MIF tautomerase inhibitors and attenuate macrophage activation and amplify the hypothermic response in endotoxemic mice

Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine playing crucial role in immunity. MIF exerts a unique tautomerase enzymatic activity that has relevance concerning its multiple functions and its small molecule inhibitors have been proven to block its pro-inflammatory effects. Here we demonstrate that some of the E-2-arylmethylene-1-tetralones and their heteroanalogues efficiently bind to MIF's active site and inhibit MIF tautomeric (enolase, ketolase activity) functions. A small set of the synthesised derivatives, namely compounds (4), (23), (24), (26) and (32), reduced inflammatory macrophage activation. Two of the selected compounds (24) and (26), however, markedly inhibited ROS and nitrite production, NF-κB activation, TNF-α, IL-6 and CCL-2 cytokine expression. Pre-treatment of mice with compound (24) exaggerated the hypothermic response to high dose of bacterial endotoxin. Our experiments suggest that tetralones and their derivatives inhibit MIF's tautomeric functions and regulate macrophage activation and thermal changes in severe forms of systemic inflammation.

Optimization of Pyrazoles as Phenol Surrogates to Yield Potent Inhibitors of Macrophage Migration Inhibitory Factor

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that is implicated in the regulation of inflammation, cell proliferation, and neurological disorders. MIF is also an enzyme that functions as a keto-enol tautomerase. Most potent MIF tautomerase inhibitors incorporate a phenol, which hydrogen bonds to Asn97 in the active site. Starting from a 113-μm docking hit, we report results of structure-based and computer-aided design that have provided substituted pyrazoles as phenol alternatives with potencies of 60-70 nm. Crystal structures of complexes of MIF with the pyrazoles highlight the contributions of hydrogen bonding with Lys32 and Asn97, and aryl-aryl interactions with Tyr36, Tyr95, and Phe113 to the binding.

Engineering a Promiscuous Tautomerase into a More Efficient Aldolase for Self-Condensations of Linear Aliphatic Aldehydes

The enzyme 4-oxalocrotonate tautomerase (4-OT) from Pseudomonas putida mt-2 takes part in a catabolic pathway for aromatic hydrocarbons, where it catalyzes the conversion of 2hydroxyhexa-2,4-dienedioate into 2-oxohexa-3-enedioate. This tautomerase can also promiscuously catalyze carbon-carbon bond-forming reactions, including various types of aldol reactions, by using its amino-terminal proline as a key catalytic residue. Here, we used systematic mutagenesis to identify two hotspots in 4-OT (Met45 and Phe50) at which single mutations give marked improvements in aldolase activity for the self-condensation of propanal. Activity screening of a focused library in which these two hotspots were varied led to the discovery of a 4-OT variant (M45Y/F50V) with strongly enhanced aldolase activity in the self-condensation of linear aliphatic aldehydes, such as acetaldehyde, propanal, and butanal, to yield α,β-unsaturated aldehydes. With both propanal and benzaldehyde, this double mutant, unlike the previously constructed single mutant F50A, mainly catalyzes the self-condensation of propanal rather than the cross-condensation of propanal and benzaldehyde, thus indicating that it indeed has altered substrate specificity. This variant could serve as a template to create new biocatalysts that lack dehydration activity and possess further enhanced aldolase activity, thus enabling the efficient enzymatic self-coupling of aliphatic aldehydes.

Discovery of Novel Inhibitors of the Tautomerase Activity of Macrophage Migration Inhibitory Factor (MIF)

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine associated with multiple diseases, including neurodegenerative disorders. With the ultimate goal of providing novel chemotypes as starting points for development of disease-modifying therapeutics for neurodegeneration, we endeavored to screen the GSK compound collection for MIF inhibitors using a miniaturized, activity-based kinetic assay. The assay monitors the increase in absorbance at 320 nm resulting from keto-to-enol tautomerization of 4-hydroxyphenylpyruvate, a reaction catalyzed by MIF. We ran a full-diversity screen evaluating the inhibitory activity of 1.6 million compounds. Primary hits were confirmed and retested in an orthogonal assay measuring tautomerization of l-dopachrome methyl ester by the decrease in absorbance at 475 nm in kinetic mode. Selected compounds were progressed to medium-throughput mode-of-inhibition studies, which included time dependence, enzyme concentration dependence, and reversibility of their inhibitory effect. With these results and after inspection of the physicochemical properties of compounds, 17 chemotypes were prioritized and progressed to further stages of validation and characterization to better assess their therapeutic potential.

MIF: metastasis/MDSC-inducing factor?

Myeloid-derived suppressor cells (MDSCs) promote tumor growth and metastasis. We have recently demonstrated that the pro-inflammatory cytokine macrophage migration inhibitory factor (MIF) enhances the immunosuppressive microenvironment by increasing the abundance of monocytic MDSCs within the tumor. Our results suggest that MIF is a potential therapeutic target for the prevention of metastasis as it regulates the tumor microenvironment.

A novel, macrophage migration inhibitory factor suicide substrate inhibits motility and growth of lung cancer cells

Although chemokine and growth factor receptors are attractive and popular targets for cancer therapeutic intervention, structure-based targeting of the ligands themselves is generally not considered practical. New evidence indicates that a notable exception to this is macrophage migration inhibitory factor (MIF). MIF, an autocrine- and paracrine-acting cytokine/growth factor, plays a pivotal role in both the initiation and maintenance of neoplastic diseases. MIF possesses a nonphysiologic enzymatic activity that is evolutionarily well-conserved. Although small molecule antagonists of MIFs enzymatic active site have been reported to inhibit biological activities of MIF, universally high IC(50)s have limited their clinical appeal. Using a computational virtual screening strategy, we have identified a unique small molecule inhibitor that serves as a suicide substrate for MIF, resulting in the covalent modification of the catalytically active NH(2)-terminal proline. Our studies further reveal that this compound, 4-iodo-6-phenylpyrimidine (4-IPP), is approximately 5x to 10x times more potent in blocking MIF-dependent catalysis and lung adenocarcinoma cell migration and anchorage-independent growth than the prototypical MIF inhibitor, ISO-1. Finally, using an in silico combinatorial optimization strategy, we have identified four unique congeners of 4-IPP that exhibit MIF inhibitory activity at concentrations 10x to 20x lower than that of parental 4-IPP.