Tumor stromal alternatively activated macrophages are important determinants of anti-tumor T lymphocyte responses, intratumoral neovascularization and metastatic dissemination. Our recent efforts to investigate the mechanism of macrophage migration inhibitory factor (MIF) in antagonizing anti-melanoma immune responses reveal that macrophage-derived MIF participates in macrophage alternative activation in melanoma-bearing mice. Both peripheral and tumor-associated macrophages (TAMs) isolated from melanoma bearing MIF-deficient mice display elevated pro-inflammatory cytokine expression and reduced anti-inflammatory, immunosuppressive and pro-angiogenic gene products compared to macrophages from tumor bearing MIF wildtype mice. Moreover, TAMs and myeloid-derived suppressor cells (MDSCs) from MIF-deficient mice exhibit reduced T lymphocyte immunosuppressive activities than do those from their wildtype littermates. Corresponding with reduced tumor immunosuppression and neoangiogenic potential by TAMs, MIF-deficiency confers protection against transplantable subcutaneous melanoma outgrowth and melanoma lung metastatic colonization. Finally, we report for the first time that our previously discovered MIF small molecule antagonist, 4-iodo-6-phenylpyrimidine (4-IPP), recapitulates MIF-deficiency in vitro and in vivo and attenuates tumor polarized macrophage alternative activation, immunosuppression, neoangiogenesis and melanoma tumor outgrowth. These studies describe an important functional contribution by MIF to tumor-associated macrophage alternative activation and provide justification for immunotherapeutic targeting of MIF in melanoma patients.

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 wellconserved. 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 f5Â to 10Â 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 10Â to 20Â lower than that of parental 4-IPP. [Cancer Res 2008;68(18):7253-7]

Low oxygen tension-mediated transcription by hypoxiainducible factors (HIF) has been reported to facilitate tumor progression, therapeutic resistance, and metastatic adaptation. One previously described target of hypoxia-mediated transcription is the cytokine/growth factor macrophage migration inhibitory factor (MIF). In studies designed to better understand hypoxia-stimulated MIF function, we have discovered that not only is MIF induced by hypoxia in pancreatic adenocarcinoma but MIF is also necessary for maximal hypoxia-induced HIF-1A expression. Cells lacking MIF are defective in hypoxia-and prolyl hydroxylase inhibitor-induced HIF-1A stabilization and subsequent transcription of glycolytic and angiogenic gene products. Moreover, COP9 signalosome subunit 5 (CSN5), a component of the COP9 signalosome previously reported to functionally interact with MIF, has recently been shown to interact with and stabilize HIF-1A. Our results indicate that MIF interacts with CSN5 in pancreatic cancer cells and that MIF-depleted cells display marked defects in hypoxia-induced CSN5/HIF-1A interactions. This functional interdependence between HIF-1A and MIF may represent an important and previously unrecognized protumorigenic axis. [Cancer Res 2007;67(1):186-93]

Tumor-derived growth factors and cytokines stimulate neoangiogenesis from surrounding capillaries to support tumor growth. Recent studies have revealed that macrophage migration inhibitory factor (MIF) expression is increased in lung cancer, particularly non-small cell lung carcinomas (NSCLC). Because MIF has important autocrine effects on normal and transformed cells, we investigated whether autocrine MIF and its only known family member, d-dopachrome tautomerase (D-DT), promote the expression of proangiogenic factors CXCL8 and vascular endothelial growth factor in NSCLC cells. Our results demonstrate that the expression of CXCL8 and vascular endothelial growth factor are strongly reliant upon both the individual and cooperative activities of the two family members. CXCL8 transcriptional regulation by MIF and D-DT appears to involve a signaling pathway that includes the activation of JNK, c-jun phosphorylation, and subsequent AP-1 transcription factor activity. Importantly, HUVEC migration and tube formation induced by supernatants from lung adenocarcinoma cells lacking either or both MIF and D-DT are substantially reduced when compared with normal supernatants. Finally, we demonstrate that the cognate MIF receptor, CD74, is necessary for both MIF- and D-DT-induced JNK activation and CXCL8 expression, suggesting its potential involvement in angiogenic growth factor expression. This is the first demonstration of a biological role for D-DT, and its synergism with MIF suggests that the combined therapeutic targeting of both family members may enhance current anti-MIF-based therapies.

Macrophage migration inhibitory factor (MIF) is expressed and secreted in response to mitogens and integrin-dependent cell adhesion. Once released, autocrine MIF promotes the activation of RhoA GTPase leading to cell cycle progression in rodent fibroblasts. We now report that small interfering RNAmediated knockdown of MIF and MIF small molecule antagonism results in a greater than 90% loss of both the migratory and invasive potential of human lung adenocarcinoma cells. Correlating with these phenotypes is a substantial reduction in steady state as well as serum-induced effector binding activity of the Rho GTPase family member, Rac1, in MIF-deficient cells. Conversely, MIF overexpression by adenovirus in human lung adenocarcinoma cells induces a dramatic enhancement of cell migration, and co-expression of a dominant interfering mutant of Rac1 (Rac1 N17 ) completely abrogates this effect. Finally, our results indicate that MIF depletion results in defective partitioning of Rac1 to caveolin-containing membrane microdomains, raising the possibility that MIF promotes Rac1 activity and subsequent tumor cell motility through lipid raft stabilization.

Highly aggressive cancers “entrain” innate and adaptive immune cells to suppress anti-tumor lymphocyte responses. Circulating myeloid-derived suppressor cells (MDSCs) constitute the bulk of monocytic immunosuppressive activity in late stage melanoma patients. Previous studies revealed that monocyte-derived macrophage migration inhibitory factor (MIF) is necessary for the immune suppressive function of tumor-associated macrophages (TAMs) and MDSCs in mouse models of melanoma. In the current study we sought to determine whether MIF contributes to human melanoma MDSC induction and T-cell immunosuppression using melanoma patient-derived MDSCs and an ex vivo co-culture model of human melanoma-induced MDSC. We now report that circulating MDSCs isolated from late stage melanoma patients are reliant upon MIF for suppression of antigen-independent T-cell activation and that MIF is necessary for maximal reactive oxygen species (ROS) generation in these cells. Moreover, inhibition of MIF results in a functional reversion from immune suppressive MDSC to an immunostimulatory dendritic cell (DC)-like phenotype that is at least partly due to reductions in MDSC prostaglandin E2 (PGE2). These findings indicate that monocyte-derived MIF is centrally involved in human monocytic MDSC induction/immune suppressive function and that therapeutic targeting of MIF may provide a novel means of inducing anti-tumor DC responses in late stage melanoma patients.

Our previous studies demonstrated that the proinflammatory peptide, macrophage migration inhibitory factor (MIF), functions as an autocrine mediator of both growth factor-and integrin-dependent sustained ERK MAPK activation, cyclin D1 expression, and cell cycle progression. We now report that MIF promotes the activation of the canonical ERK MAPK cascade and cyclin D1 expression by stimulating the activity of the Rho GTPase and downstream signaling to stress fiber formation. Rho-dependent stress fiber accumulation promotes the sustained activation of ERK and subsequent cyclin D1 expression during G 1 -S phase cell cycle progression. This pathway is reported to be dependent upon myosin light chain (MLC) kinase, integrin clustering, and subsequent activation of focal adhesion kinase, leading to sustained MAPK activity. Our studies reveal that recombinant MIF induces cyclin D1 expression in a Rho-, Rho kinase-, MLC kinase-, and ERK-dependent manner in asynchronous NIH 3T3 fibroblasts. Moreover, MIF ؊/؊ murine embryonic fibroblasts display aberrant cyclin D1 expression that is linked to defective Rho activity, stress fiber formation, and MLC phosphorylation. These results suggest that MIF is an integral autocrine mediator of Rho GTPase-dependent signaling events and provide mechanistic insight into how MIF regulates proliferative, migratory, and oncogenic processes.Despite being one of the earliest cytokines discovered, macrophage migration inhibitory factor (MIF) 1 is arguably the least understood. MIF has been shown to exert effects on a variety of cell types and influence the regulatory functions of many diverse biological processes. These include inflammation, immune regulation, physiologic and pathophysiologic neovascularization, and cell replication (1-3). This broad array of effects of MIF on cellular functions is difficult to understand. Perhaps one unifying interpretation might be that MIF is elaborated in response to tissue wounding. MIF affects both ends of the complex cascade of reactions caused by injury, from inflammation to reparative cell replication. In this same vein, MIF production following growth factor or extracellular matrix stimulation would also be in accord with its involvement in cell replication. In the case of neoplastic cells, internal (oncogenic) or external (growth factors, extracellular matrix) signals could serve to increase MIF production that, in turn, may facilitate anchorage independence and loss of contact inhibition.Our previous studies have established that MIF, a protein historically associated with inflammation and immune regulation, stimulates the proliferation of mouse fibroblasts (4). This response is associated with the activation of the p44/p42 extracellular signal-regulated kinase (ERK) MAPKs. We further demonstrated that growth factors stimulate the rapid release of preformed MIF from adherent, quiescent fibroblasts. Importantly, the sustained activation of MAPK in serum-stimulated fibroblasts is dependent upon MIF autocrine action (4).In addition to the discovery t...

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