Structural Plasticity in the C-Terminal Region of Macrophage Migration Inhibitory Factor-2 Is Associated with an Induced Fit Mechanism for a Selective Inhibitor

The synthesis of 1,2,3-triazoles as binders of D-dopachrome tautomerase (D-DT) for the development of dual-targeting inhibitors

Despite recent advances in the treatment of cancer, the issue of therapy resistance remains one of the most significant challenges in the field. In this context, signaling molecules, such as cytokines have emerged as promising targets for drug discovery. Examples of cytokines include macrophage migration inhibitory factor (MIF) and its closely related analogue D-dopachrome tautomerase (D-DT). In this study we aim to develop a new chemical class of D-DT binders and subsequently create a dual-targeted inhibitor that can potentially trigger D-DT degradation via the Proteolysis Targeting Chimera (PROTAC) technology. Here we describe the synthesis of a novel library of 1,2,3-triazoles targeting D-DT. The most potent derivative 19c (IC50 of 0.5 ± 0.04 μM with high selectivity toward D-DT) was attached to a cereblon (CRBN) ligand through aliphatic amides, which were synthesized by a remarkably convenient and effective solvent-free reaction. Enzyme inhibition experiments led to the discovery of the compound 10d, which exhibited moderate inhibitory potency (IC50 of 5.9 ± 0.7 μM), but unfortunately demonstrated no activity in D-DT degradation experiments. In conclusion, this study offers valuable insight into the SAR of D-DT inhibition, paving the way for the development of novel molecules as tools to study D-DT functions in tumor proliferation and, ultimately, new therapeutics for cancer treatment.

The C-terminal Region of D-DT Regulates Molecular Recognition for Protein-Ligand Complexes

Systematic analysis of molecular recognition is critical for understanding the biological function of macromolecules. For the immunomodulatory protein D-dopachrome tautomerase (D-DT), the mechanism of protein-ligand interactions is poorly understood. Here, 17 carefully designed protein variants and wild type (WT) D-DT were interrogated with an array of complementary techniques to elucidate the structural basis of ligand recognition. Utilization of a substrate and two selective inhibitors with distinct binding profiles offered previously unseen mechanistic insights into D-DT-ligand interactions. Our results demonstrate that the C-terminal region serves a key role in molecular recognition via regulation of the active site opening, protein-ligand interactions, and conformational flexibility of the pocket's environment. While our study is the first comprehensive analysis of molecular recognition for D-DT, the findings reported herein promote the understanding of protein functionality and enable the design of new structure-based drug discovery projects.

Macrophage migration inhibitory factor (MIF) and its homolog D-dopachrome tautomerase (D-DT) are significant promotors of UVB- but not chemically induced non-melanoma skin cancer

Non-melanoma skin cancer (NMSC) is the most common cancer in Caucasians worldwide. We investigated the pathophysiological role of MIF and its homolog D-DT in UVB- and chemically induced NMSC using Mif-/-, D-dt-/- and Mif-/-/D-dt-/- mice on a hairless SKH1 background. Knockout of both cytokines showed similar attenuating effects on inflammation after acute UVB irradiation and tumor formation during chronic UVB irradiation, without additive protective effects noted in double knockout mice, indicating that both cytokines activate a similar signaling threshold. In contrast, genetic deletion of Mif and D-dt had no major effects on chemically induced skin tumors. To get insight into the contributing mechanisms, we used an in vitro 3D skin model with incorporated macrophages. Application of recombinant MIF and D-DT led to an accumulation of macrophages within the epidermal part that could be reversed by selective inhibitors of MIF and D-DT pathways. In summary, our data indicate that MIF and D-DT contribute to the development and progression of UVB- but not chemically induced NMSC, a role at least partially accounted by effects of both cytokines on epidermal macrophage accumulation. These data highlight that MIF and D-DT are both potential therapeutic targets for the prevention of photocarcinogenesis but not chemical carcinogenesis.

Ligand-induced conformational changes enable intersubunit communications in D-dopachrome tautomerase

D-Dopachrome tautomerase (D-DT; or MIF-2) is a multifunctional protein with immunomodulatory properties and a documented pathogenic role in inflammation and cancer that is associated with activation of the cell surface receptor CD74. Alongside D-DT, macrophage migration inhibitory factor (MIF) is also known to activate CD74, promoting pathogenesis. While the role of the MIF/CD74 axis has been extensively studied in various disease models, the late discovery of the D-DT/CD74 axis has led to a poor investigation into the D-DT-induced activation mechanism of CD74. A previous study has identified 4-(3-carboxyphenyl)-2,5-pyridinedicarboxylic acid (4-CPPC) as the first selective and reversible inhibitor of D-DT and reported its potency to block the D-DT-induced activation of CD74 in a cell-based model. In this study, we employ molecular dynamics simulations and nuclear magnetic resonance experiments to study 4-CPPC-induced changes to the dynamic profile of D-DT. We found that binding of the inhibitor remarkably promotes the conformational flexibility of C-terminal without impacting the structural stability of the biological assembly. Consequently, long-range intrasubunit (>11 Å) and intersubunit (>30 Å) communications are enabled between distal regions. Communication across the three subunits is accomplished via 4-CPPC, which serves as a communication bridge after Val113 is displaced from its hydrophobic pocket. This previously unrecognized structural property of D-DT is not shared with its human homolog, MIF, which exhibits an impressive C-terminal rigidity even in the presence of an inhibitor. Considering the previously reported role of MIF's C-terminal in the activation of CD74, our results break new ground for understanding the functionality of D-DT in health and disease.

Underrepresented Impurities in 4-Hydroxyphenylpyruvate Affect the Catalytic Activity of Multiple Enzymes

Macrophage migration inhibitory factor (MIF) is a key immunostimulatory protein with regulatory properties in several disorders, including inflammation and cancer. All the reported inhibitors that target the biological activities of MIF have been discovered by testing against its keto/enol tautomerase activity. While the natural substrate is still unknown, model MIF substrates are used for kinetic experiments. The most extensively used model substrate is 4-hydroxyphenyl pyruvate (4-HPP), a naturally occurring intermediate of tyrosine metabolism. Here, we examine the impact of 4-HPP impurities in the precise and reproducible determination of MIF kinetic data. To provide unbiased evaluation, we utilized 4-HPP powders from five different manufacturers. Biochemical and biophysical analyses showed that the enzymatic activity of MIF is highly influenced by underrepresented impurities found in 4-HPP. Besides providing inconsistent turnover results, the 4-HPP impurities also influence the accurate calculation of ISO-1's inhibition constant, an MIF inhibitor that is broadly used for in vitro and in vivo studies. The macromolecular NMR data show that 4-HPP samples from different manufacturers result in differential chemical shift perturbations of amino acids in MIF's active site. Our MIF-based conclusions were independently evaluated and confirmed by 4-hydroxyphenylpyruvate dioxygenase (HPPD) and D-dopachrome tautomerase (D-DT); two additional enzymes that utilize 4-HPP as a substrate. Collectively, these results explain inconsistencies in previously reported inhibition values, highlight the effect of impurities on the accurate determination of kinetic parameters, and serve as a tool for designing error-free in vitro and in vivo experiments.

2,5-Pyridinedicarboxylic acid is a bioactive and highly selective inhibitor of D-dopachrome tautomerase

Macrophage migration inhibitory factor (MIF) and D-dopachrome tautomerase (D-DT) are two pleotropic cytokines, which are coexpressed in various cell types to activate the cell surface receptor CD74. Via the MIF/CD74 and D-DT/CD74 axes, the two proteins exhibit either beneficial or deleterious effect on human diseases. In this study, we report the identification of 2,5-pyridinedicarboxylic acid (a.k.a. 1) that effectively blocks the D-DT-induced activation of CD74 and demonstrates an impressive 79-fold selectivity for D-DT over MIF. Crystallographic characterization of D-DT-1 elucidates the binding features of 1 and reveals previously unrecognized differences between the MIF and D-DT active sites that explain the ligand's functional selectivity. The commercial availability, low cost, and high selectivity make 1 the ideal tool for studying the pathophysiological functionality of D-DT in disease models. At the same time, our comprehensive biochemical, computational, and crystallographic analyses serve as a guide for generating highly potent and selective D-DT inhibitors.

D-dopachrome tautomerase in cardiovascular and inflammatory diseases-A new kid on the block or just another MIF?

Macrophage migration inhibitory factor (MIF) as well as its more recently described structural homolog D-dopachrome tautomerase (D-DT), now also termed MIF-2, are atypical cytokines and chemokines with key roles in host immunity. They also have an important pathogenic role in acute and chronic inflammatory conditions, cardiovascular diseases, lung diseases, adipose tissue inflammation, and cancer. Although our mechanistic understanding of MIF-2 is relatively limited compared to the extensive body of evidence available for MIF, emerging data suggests that MIF-2 is not only a functional phenocopy of MIF, but may have differential or even oppositional activities, depending on the disease and context. In this review, we summarize and discuss the similarities and differences between MIF and MIF-2, with a focus on their structures, receptors, signaling pathways, and their roles in diseases. While mainly covering the roles of the MIF homologs in cardiovascular, inflammatory, autoimmune, and metabolic diseases, we also discuss their involvement in cancer, sepsis, and chronic obstructive lung disease (COPD). A particular emphasis is laid upon potential mechanistic explanations for synergistic or cooperative activities of the MIF homologs in cancer, myocardial diseases, and COPD as opposed to emerging disparate or antagonistic activities in adipose tissue inflammation, metabolic diseases, and atherosclerosis. Lastly, we discuss potential future opportunities of jointly targeting MIF and MIF-2 in certain diseases, whereas precision targeting of only one homolog might be preferable in other conditions. Together, this article provides an update of the mechanisms and future therapeutic avenues of human MIF proteins with a focus on their emerging, surprisingly disparate activities, suggesting that MIF-2 displays a variety of activities that are distinct from those of MIF.

Thieno[2,3-d]pyrimidine-2,4(1H,3H)-dione Derivative Inhibits d-Dopachrome Tautomerase Activity and Suppresses the Proliferation of Non-Small Cell Lung Cancer Cells

The homologous cytokines macrophage migration inhibitory factor (MIF) and d-dopachrome tautomerase (d-DT or MIF2) play key roles in cancers. Molecules binding to the MIF tautomerase active site interfere with its biological activity. In contrast, the lack of potent MIF2 inhibitors hinders the exploration of MIF2 as a drug target. In this work, screening of a focused compound collection enabled the identification of a MIF2 tautomerase inhibitor R110. Subsequent optimization provided inhibitor 5d with an IC₅₀ of 1.0 μM for MIF2 tautomerase activity and a high selectivity over MIF. 5d suppressed the proliferation of non-small cell lung cancer cells in two-dimensional (2D) and three-dimensional (3D) cell cultures, which can be explained by the induction of cell cycle arrest via deactivation of the mitogen-activated protein kinase (MAPK) pathway. Thus, we discovered and characterized MIF2 inhibitors (5d) with improved antiproliferative activity in cellular models systems, which indicates the potential of targeting MIF2 in cancer treatment.

MIF but not MIF-2 recruits inflammatory macrophages in an experimental polymicrobial sepsis model

Excessive inflammation drives the progression from sepsis to septic shock. Macrophage migration inhibitory factor (MIF) is of interest because MIF promoter polymorphisms predict mortality in different infections, and anti-MIF antibody improves survival in experimental models when administered 8 hours after infectious insult. The recent description of a second MIF superfamily member, D-dopachrome tautomerase (D-DT/MIF-2), prompted closer investigation of MIF-dependent responses. We subjected Mif-/- and Mif-2-/- mice to polymicrobial sepsis and observed a survival benefit with Mif but not Mif-2 deficiency. Survival was associated with reduced numbers of small peritoneal macrophages (SPMs) that, in contrast to large peritoneal macrophages (LPMs), were recruited into the peritoneal cavity. LPMs produced higher quantities of MIF than SPMs, but SPMs expressed higher levels of inflammatory cytokines and the MIF receptors CD74 and CXCR2. Adoptive transfer of WT SPMs into Mif-/- hosts reduced the protective effect of Mif deficiency in polymicrobial sepsis. Notably, MIF-2 lacks the pseudo-(E)LR motif present in MIF that mediates CXCR2 engagement and SPM migration, supporting a specific role for MIF in the recruitment and accumulation of inflammatory SPMs.

D-dopachrome tautomerase activates COX2/PGE2 pathway of astrocytes to mediate inflammation following spinal cord injury

Background

Astrocytes are the predominant glial cell type in the central nervous system (CNS) that can secrete various cytokines and chemokines mediating neuropathology in response to danger signals. D-dopachrome tautomerase (D-DT), a newly described cytokine and a close homolog of macrophage migration inhibitory factor (MIF) protein, has been revealed to share an overlapping function with MIF in some ways. However, its cellular distribution pattern and mediated astrocyte neuropathological function in the CNS remain unclear.

Methods

A contusion model of the rat spinal cord was established. The protein levels of D-DT and PGE₂ synthesis-related proteinase were assayed by Western blot and immunohistochemistry. Primary astrocytes were stimulated by different concentrations of D-DT in the presence or absence of various inhibitors to examine relevant signal pathways. The post-injury locomotor functions were assessed using the Basso, Beattie, and Bresnahan (BBB) locomotor scale.

Results

D-DT was inducibly expressed within astrocytes and neurons, rather than in microglia following spinal cord contusion. D-DT was able to activate the COX2/PGE₂ signal pathway of astrocytes through CD74 receptor, and the intracellular activation of mitogen-activated protein kinases (MAPKs) was involved in the regulation of D-DT action. The selective inhibitor of D-DT was efficient in attenuating D-DT-induced astrocyte production of PGE₂ following spinal cord injury, which contributed to the improvement of locomotor functions.

Conclusion

Collectively, these data reveal a novel inflammatory activator of astrocytes following spinal cord injury, which might be beneficial for the development of anti-inflammation drug in neuropathological CNS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02186-z.

Structural and functional insights into macrophage migration inhibitory factor from Oncomelania hupensis, the intermediate host of Schistosoma japonicum

Oncomelania hupensis is the unique intermediate host of Schistosoma japonicum. As an irreplaceable prerequisite in the transmission and prevalence of schistosomiasis japonica, an in-depth study of this obligate host-parasite interaction can provide glimpse into the molecular events in the competition between schistosome infectivity and snail immune resistance. In previous studies, we identified a macrophage migration inhibitory factor (MIF) from O. hupensis (OhMIF), and showed that it was involved in the snail host immune response to the parasite S. japonicum. Here, we determined the crystal structure of OhMIF and revealed that there were distinct structural differences between the mammalian and O. hupensis MIFs. Noticeably, there was a projecting and structured C-terminus in OhMIF, which not only regulated the MIF's thermostability but was also critical in the activation of its tautomerase activity. Comparative studies between OhMIF and human MIF (hMIF) by analyzing the tautomerase activity, oxidoreductase activity, thermostability, interaction with the receptor CD74 and activation of the ERK signaling pathway demonstrated the functional differences between hMIF and OhMIF. Our data shed a species-specific light on structural, functional, and immunological characteristics of OhMIF and enrich the knowledge on the MIF family.

Separating cytokine twins with a small molecule

The cytokine macrophage migration inhibitory factor (MIF) has been characterized as a key immunomodulator and mediator of various diseases. Small molecule inhibitors based on the conserved enzymatic pocket of MIF have been valuable in elucidating MIF mechanisms and developing translational strategies. In contrast, our mechanistic understanding of the MIF homolog MIF-2/d-dopachrome tautomerase (d-DT) and its clinical translation has been hampered, partly because MIF-2-selective inhibitors have been elusive. Here, Tilstam et al. characterize a small-molecule inhibitor selective for MIF-2 that interferes with receptor binding and cell signaling. That could be a promising therapeutic lead and a valuable research tool.

Immune modulation by the macrophage migration inhibitory factor (MIF) family: D-dopachrome tautomerase (DDT) is not (always) a backup system

Human macrophage migration inhibition factor (MIF) is a protein with cytokine and chemokine properties that regulates a diverse range of physiological functions related to innate immunity and inflammation. Most research has focused on the role of MIF in different inflammatory diseases. D-dopachrome tautomerase (DDT), a different molecule with structural similarities to MIF, which shares receptors and biological functions, has recently been reported, but little is known about its roles and mechanisms. In this review, we sought to understand the similarities and differences between these molecules by summarizing what is known about their different structures, receptors and mechanisms regulating their expression and biological activities with an emphasis on immunological aspects.

The expression of macrophage migration inhibitory factor in the non-small cell lung cancer

Objective

The objective was to investigate the expression of macrophage migration inhibitory factor (MIF) in non-small cell lung cancer (NSCLC), as well as the effects of macrophage MIF on tumor cells.

Methods

The human NSCLC cell strains H358 and H524 were selected as research objects. The Real-Time Polymerase Chain Reaction (RT-PCR) and Western Blot were utilized to detect the expression levels of MIF in human NSCLC cell strains. The lentiviral plasmid was utilized for MIF-mRNA interference. The expression levels of MIF before and after transfection were compared. The cell strains were cultured and proliferated for cell count and comparison.

Results

H358 showed MIF high expression while H524 showed MIF low expression. Once the H358 cells were constructed as silent MIF expression, compared with the original H358 cells, the difference was statistically significant. Once the H524 cells were constructed as high MIF expression, compared with original H524 cells, the difference was statistically significant. Being cultured for respective 3, 5, and 7 days, the transfected H358 cells showed a significant decrease in proliferative activity compared with original H358 cells, while the transfected H524 cells showed a significant increase in proliferative activity compared with original H524 cells.

Conclusion

MIF has high expression in H358 cells while low expression in H524 cells. The expression of MIF could enhance the proliferative activity of NSCLC tumor cells.

A selective small-molecule inhibitor of macrophage migration inhibitory factor-2 (MIF-2), a MIF cytokine superfamily member, inhibits MIF-2 biological activity

Cytokine macrophage migration inhibitory factor-2 (MIF-2 or D-dopachrome tautomerase) is a recently characterized second member of the MIF cytokine superfamily in mammalian genomes. MIF-2 shares pro-inflammatory and tumorigenic properties with the clinical target MIF (MIF-1), but the precise contribution of MIF-2 to immune physiology or pathology is unclear. Like MIF-1, MIF-2 has intrinsic keto-enol tautomerase activity and mediates biological functions by engaging the cognate, common MIF family receptor CD74. Evidence that the catalytic site of MIF family cytokines has a structural role in receptor binding has prompted exploration of tautomerase inhibitors as potential biological antagonists and therapeutic agents, although few catalytic inhibitors inhibit receptor activation. Here we describe the discovery and biochemical characterization of a selective small-molecule inhibitor of MIF-2. An in silico screen of 1.6 million compounds targeting the MIF-2 tautomerase site yielded several hits for potential catalytic inhibitors of MIF-2 and identified 4-(3-carboxyphenyl)-2,5-pyridinedicarboxylic acid (4-CPPC) as the most functionally potent compound. We found that 4-CPPC has an enzymatic IC₅₀ of 27 μm and 17-fold selectivity for MIF-2 versus MIF-1. An in vitro binding assay for MIF-1/MIF-2 to the CD74 ectodomain (sCD74) indicated that 4-CPPC inhibits MIF-2-CD74 binding in a dose-dependent manner (0.01-10 μm) without influencing MIF-1-CD74 binding. Notably, 4-CPPC inhibited MIF-2-mediated activation of CD74 and reduced CD74-dependent signal transduction. These results open opportunities for development of more potent and pharmacologically auspicious MIF-2 inhibitors to investigate the distinct functions of this MIF family member in vivo.

Elucidating the role of an immunomodulatory protein in cancer: From protein expression to functional characterization

Several fundamental discoveries made over the last two decades, in the field of cancer biology, have increased our understanding of the complex tumor micro- and macroenvironments. This has shifted the current empirical cancer therapies to more rationalized treatments targeting immunomodulatory proteins. From the point of identification, a protein target undergoes several interrogations, which are necessary to truly define its druggability. Here, we outline some basic steps that can be followed for in vitro characterization of a potential immunomodulatory protein target. We describe procedures for recombinant protein expression and purification including key annotations on protein cloning, expression systems, purification strategies and protein characterization using structural and biochemical approaches. For functional characterization, we provide detailed protocols for using flow-cytometric techniques in cell lines or primary cells to study protein expression profiles, proliferation, apoptosis and cell-cycle changes. This multilevel approach can provide valuable, in-depth understanding of any protein target with potential immunomodulatory effects.

Role of MIF and D-DT in immune-inflammatory, autoimmune, and chronic respiratory diseases: from pathogenic factors to therapeutic targets

Macrophage migration inhibitory factor (MIF) is a protein that acts as a cytokine-, enzyme-, endocrine- and chaperon-like molecule. It binds to the cell-surface receptor CD74 in association with CD44, which activates the downstream signal transduction pathway. In addition, MIF acts also as a noncognate ligand for C-X-C chemokine receptor type 2 (CXCR2), type 4 (CXCR4), and type 7 (CXCR7). Recently, D-dopachrome tautomerase (D-DT), a second member of the MIF superfamily, was identified. From a pharmacological and clinical point of view, the nonredundant biological properties of MIF and D-DT anticipate potential synergisms from their simultaneous inhibition. Here, we focus on the role of MIF and D-DT in human immune-inflammatory, autoimmune, and chronic respiratory diseases, providing an update on the progress made in the identification of specific small-molecule inhibitors of these proteins.