Background: The oxidized Macrophage Migration Inhibitory Factor (oxMIF) is the pathogenic and immunologically distinct isoform of the versatile MIF cytokine that has been reported to be a key regulator in chronic inflammatory diseases, including Rheumatoid Arthritis (RA). OxMIF is generated in inflamed tissue by oxidative processes and can be neutralized with isoform-specific antibodies that effectively inhibit the pathological functions attributed to MIF.

Objectives: First, the presence of oxMIF in the circulation of RA patients was investigated. Once confirmed, therapeutic efficacy of the anti-oxMIF antibody ON104 was evaluated in a preclinical mouse model of RA. Additionally, we determined the pharmacokinetic (PK) profile of ON104 in both healthy and arthritic mice, to better understand the pharmacokinetic and pharmacodynamic relationship.

Methods: The fully human anti-oxMIF antibody ON104 was generated by antibody engineering and used in an ELISA assay to detect oxMIF in the plasma of RA patients. ON104 was then tested in the type II Collagen-Induced Arthritis (CIA) model in DBA/1j mice. At the onset of the disease, mice were treated with different doses of ON104 twice weekly for 21 days. Clinical disease scoring, paw swelling, and histological evaluations were performed for all individual animals. To evaluate the PK profile, ON104 was injected intraperitoneally into arthritic mice at pharmacological relevant doses (2.5, 10, or 20 mg/kg) and referenced to healthy control mice. Blood samples were collected at 1-, 4-, 8-, 24-, 48-, 72-, and 168-hours post ON104 administration.

Results: In patients diagnosed with RA, plasma levels of oxMIF were significantly elevated (median 5.185 ng/mL, n=15) while in healthy subjects no oxMIF was detectable (lower detection limit 0.027 ng/mL, n=9). The anti-oxMIF antibody ON104, that shows specificity for both, human and murine oxMIF, led to a significant improvement in clinical signs of arthritis and a reduction of synovial and cartilage damage in the murine CIA model. Further, F4/80 macrophage infiltration within the inflamed joints was significantly reduced upon ON104 treatment. In a dose titration study in CIA mice, a linear dose response of ON104 with an ED ₅₀ of 1-2 mg/kg was observed. In addition, an excellent dose linearity of ON104 plasma exposure (expressed as Area Under the Curve or AUC) was observed in both arthritic and healthy mice, with arthritic mice exhibiting 60-80 % lower AUC values compared to healthy mice.

Conclusion: Here we describe for the first time the involvement of oxMIF in the pathogenesis of RA by demonstrating that oxMIF is present in the circulation of RA patients and that oxMIF-specific neutralization ameliorates clinical and histological signs of arthritis in a preclinical model of RA. Altogether, our data support that the anti-oxMIF antibody ON104 opens up an innovative treatment option for patients with RA with a new anti-inflammatory mechanism of action - either as monotherapy or in combination with other anti-rheumatic drugs.

REFERENCES: NIL.

Acknowledgements: NIL.

Disclosure of Interests: Christine Landlinger has been a full-time employee of OncoOne R&D at the time of the study, Maroua Ferhat has been a full-time employee of OncoOne R&D at the time of the study, Gregor Rossmüller has been a full-time employee of OncoOne R&D at the time of the study, Katia Mangano received a sponsorship from OncoOne to conduct the in vivo experiments, Ferdinando Nicoletti received a sponsorship from OncoOne to conduct the in vivo experiments, Michael Thiele holds ownership interests including shares of OncoOne R&D, and has been a full-time employee of OncoOne R&D at the time of the study.