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Background IMU-838 (vidofludimus calcium) is a well-tolerated and orally available small molecule inhibitor of dihydroorotate dehydrogenase (DHODH) and is currently in phase 2 clinical development for ulcerative colitis (UC). Here, we investigated the effect of IMU-838 on different immune cell subsets and analysed the mechanism of action in more detail in T cells. Methods The effect of IMU-838 on regulatory macrophages (Mregs) was investigated by adding IMU-838 or anti-TNFα antibodies (infliximab, adalimumab), alone or in combination, in a mixed lymphocyte reaction assay, determining Mregs (CD206+CD14+) by FACS analysis. To investigate the effect of IMU-838 on human T and B cells, PBMC were stimulated with PHA (48h) or Oligonucleotide 2006-PTO (70h), respectively. An affinity-dependent effect of IMU-838 was assessed on CD8 T cells from OT-I and OT-III mice, containing a high and a low affinity T cell receptor (TCR), respectively, for OVA257-264 peptide. These cells were stimulated with ovalbumin (OVA) peptide loaded splenocytes or anti-CD3/anti-CD28 for 3 days. Oxidative phosphorylation (OXPHOS) and glycolysis in murine T cells was investigated by the Seahorse/Agilent technique in murine CD4 and CD8 T cells activated with anti-CD3/anti-CD28 with or without IMU-838. Results IMU-838 slightly induced Mregs, but strongly and dose-dependently decreased TNFα and IL-6 secretion. Anti-TNFα antibodies alone strongly induced Mregs, but also increased IL-6 levels. When IMU-838 was added, Mregs induction was even higher, and IL-6 was reduced. Besides reducing proinflammatory cytokines secreted by macrophages, IMU-838 also inhibits proliferation of activated B and T cells, as well as inflammatory T cell cytokine secretion, IL-17A, IL-17F and IFNγ, and increased apoptosis up to 3-fold compared to vehicle control. By investigating IMU-838’s role on affinity related activity status of T cells, it was shown that IMU-838 strongly inhibited cell proliferation in the peptide stimulated high affinity, but not in the low affinity, CD8 T cells. Peptide stimulated high affinity T cells show an upregulation of OXPHOS and glycolysis pathways, which are involved in the generation of the cell’s energy supply, compared to low affinity cells. IMU-838 strongly inhibited OXPHOS and glycolysis in both CD4 and CD8 T cells. Conclusion IMU-838 reduces the proinflammatory immune cell response by inducing Mregs, reducing pro-inflammatory cytokine secretion and reducing immune cell proliferation. DHODH is only important in cells that received a strong stimulus and are highly metabolically active. Therefore, IMU-838 will only specifically target these cells and will still allow for a normal immune response, representing a huge safety advantage for treatment of IBD patients.

journal of crohn's and colitis

P064 IMU-838, a Small Molecule DHODH Inhibitor in Phase 2 Clinical Trial for Ulcerative Colitis, Shows Potent Anti-inflammatory Activity in Cell-Culture-Based and In Vivo Systems