Abstract A181: Oxidized macrophage migration inhibitory factor (oxMIF) is a previously unrecognized, disease-related isoform of MIF and a potential new drug target in cancer.

Abstract

Abstract Background: Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine with pleiotropic biologic effects and which is pathologically associated with several types of cancer. MIF is markedly different from other cytokines in that it is constitutively expressed, is stored in the cytoplasm and is present in the circulation of healthy subjects. Thus, the concept of targeting MIF for therapeutic intervention suffers from the drawback of targeting a ubiquitous protein. Here we report the discovery of a previously unrecognized conformational isoform of MIF that can be mimicked in vitro by mild oxidation of recombinant MIF and has therefore been designated as oxidized MIF (oxMIF). Ex vivo studies show that oxMIF is produced in patients with cancer. Highly selective, fully human monoclonal antibodies that specifically target oxMIF, but do not bind the ubiquitous reduced MIF isoform (redMIF), were shown to inhibit downstream signaling pathways associated with tumor proliferation and progression in vitro and in vivo. Methods: New ELISA methods have been established that allow the detection of oxMIF and redMIF in plasma samples acquired from commercial providers. The effect of highly selective oxMIF-specific antibodies on human cancer cells was explored in vitro and in mouse xenograft models using the cell lines PC-3 (prostate cancer), IGROV-1 (ovarian cancer) and COLO-357 (pancreatic cancer). Results: The baseline level of MIF detected in the plasma of healthy subjects (median 5123 pg/ml, n=69) was as expected according to the literature. However, our analysis revealed that this represents the ubiquitous reduced isoform of MIF, redMIF. OxMIF was, in general, not detected in the plasma from healthy controls (median 0 pg/mL, n=69). By contrast, significantly increased concentrations of oxMIF were detected in plasma from patients with breast cancer (644 pg/mL, p<0.05, n=15), ovarian cancer (3483 pg/mL, p<0.0007, n=42) and prostate cancer (2445 pg/mL, p<0.0005, n=14). Animal studies and in vitro studies revealed that novel human antibodies that selectively target oxMIF (i) inhibit proliferation by reducing phosphorylation of ERK1/2 and AKT, and promote apoptosis by activating caspase 3, (ii) inhibit angiogenesis and metastasis by reduction of VEGF expression and blood vessel density within the tumor, and (iii) reduce cancer-associated inflammation of the tumor by downregulating the production of proinflammatory cytokines. Conclusion: Our studies demonstrate that the oxMIF isoform is associated with cancer. OxMIF is a potential marker for disease activity or disease progression and is a promising new drug target for the treatment of cancer. A phase 1 clinical study of a novel human antibody that selectively targets oxMIF is currently ongoing in patients with solid malignancies (ClinicalTrials.gov identifier: NCT01765790). Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A181. Citation Format: Michael Thiele, Patrice Douillard, Dirk Voelkel, Thorsten Hagemann, Michael Freissmuth, Hartmut Ehrlich, Friedrich Scheiflinger, Randolf J. Kerschbaumer. Oxidized macrophage migration inhibitory factor (oxMIF) is a previously unrecognized, disease-related isoform of MIF and a potential new drug target in cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A181.