Abstract 2974: Targeting the oxidized form of macrophage migration inhibitory factor (oxMIF) with antibody ON203 activates the tumor microenvironment
Authors: Maurer Barbara , Haas Eric R. , Mirkina Irina , Mayer Julia , Schinagl Alexander , Guerriero Jennifer L. , Thiele Michael 
Published: April 2023

Abstract
Modulation of immunosuppressive tumor microenvironments (TMEs) can enhance immunotherapy response rates in solid cancers. One of the key TME regulators is the macrophage migration inhibitory factor (MIF). In addition to its role in tumor cell proliferation, angiogenesis and metastasis, MIF induces polarization of macrophages to a suppressive M2-like subtype, suppresses cytotoxic T cells and correlates with poor response to immune checkpoint therapy. Therapeutic interventions are hampered due to MIF’s ubiquitous expression and non-pathological roles. In contrast, the disease-related structural isoform of MIF, termed oxMIF, is exclusively present in solid tumor tissue, can be specifically targeted by antibodies and oxMIF neutralization blocks protumorigenic activities attributed to MIF. We determined the antitumorigenic and TME-modifying potential of the new oxMIF-specific antibody ON203 in preclinical models including fresh tumoroids retaining an intact TME isolated from colorectal adenocarcinoma (CRC) patients. 3D tumoroids were treated with ON203 and tumor cell killing was analyzed by high-content 3D computational bioimaging. ON203-induced TME modulation was assessed by secretome analysis and flow cytometry. To understand ON203’s action on the TME and to determine factors influencing the response to ON203 we performed dimensionality reduction (UMAP) to comparatively visualize the composition of the tumoroids. To further characterize the immune population differences between conditions, we employed multi-parameter clustering (FlowSOM/XShift) and compared the abundance of each cluster across conditions. We also investigated functional marker expression differences across each of the conditions. ON203 demonstrated excellent tumor penetration and retention and reduced tumor cell proliferation in mouse xenograft models. oxMIF presence was confirmed in all freshly isolated CRC tumoroids and correlated with a “cold” phenotype with high IL-10 and TGF-β levels. Four out of five ON203-treated CRC tumoroids responded with significant tumor cell death. In the responding tumoroids ON203 activated NK and NKT cells (upregulation of Granzyme B and CD107a) and supported an anti-tumor M1-like polarization and macrophage activation (upregulation of CD16 and HLA-DR). Taken together, the anti-oxMIF antibody ON203 demonstrated antitumorigenic effects by reducing tumor cell proliferation and by modulating the TME towards immunosupportive functions. In the upcoming clinical Phase 1 trial ON203’s safety, tolerability, pharmacokinetics, and pharmacodynamics in patients with solid tumors will be analyzed to evaluate its potential as a standalone or combinatorial therapy with immune checkpoint inhibitors.
Citation Format: Barbara Maurer, Eric R. Haas, Irina Mirkina, Julia Mayer, Alexander Schinagl, Jennifer L. Guerriero, Michael Thiele. Targeting the oxidized form of macrophage migration inhibitory factor (oxMIF) with antibody ON203 activates the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2974.