ABR-224050 A NOVEL DIHYDROOROTATE DEHYDROGENASE INHIBITOR SUPPRESSING DISEASE DEVELOPMENT IN COLLAGEN INDUCED ARTHRITIS IN DBA/1 MICE

Background: ABR-224050 was recently identified as a novel inhibitor of dihydroorotate dehydrogenase (DHODH), by applying structure-based drug design. DHODH is an enzyme controlling the rate limiting step in de novo pyrimidine biosynthesis. DHODH inhibition results in decreased cellular levels of pyrimidine nucleotides, thereby arresting proliferating cells in the G1 phase of the cell cycle. As rapidly proliferating human T cells have an exceptional requirement for de novo pyrimidine biosynthesis, DHODH inhibitors constitute an attractive therapeutic approach to autoimmune diseases such as rheumatoid arthritis (RA). ABR-224050 was tested in an experimental polyarthritis mouse model, collagen induced arthritis (CIA). This disease model has several features in common with the human disorder RA.Objectives: 1) To study the ability of ABR-224050 to inhibit T cell proliferation both in vitro and in vivo. 2) To study the effect of ABR-224050 as monotherapy or in combination with methotrexate on disease development in CIA.Methods: The effect of ABR-224050 on T cell proliferation in vitro was measured in a radioactivity-based cell proliferation assay or in a luminescent-based cell viability assay. Staphylococcus enterotoxin A (SEA) was used to induce proliferation of CFSE (CarboxyFluoroscein diacetate Succinmimidyl Ester)-labeled T cells in C57Bl/6 mice. The effect of ABR-224050 treatment on in vivo T cell proliferation was analysed by flow cytometry. In the CIA study, DBA/1 mice were immunized with bovine type II collagen emulsified in Complete Freund's Adjuvant. Treatment was initiated three days after immunization and continued daily throughout the experiment. Mice were inspected for signs of arthritis and scored three times per week. Cartilage degradation was measured in serum samples using animal Cartilage Oligmeric Matrix Protein (COMP) ELISA (AnaMar Medical).Results: ABR-224050 was shown to be a potent inhibitor of proliferation of the human T cell line Jurkat and mitogen-stimulated primary mouse and human lymphocytes (IC50 ∼ 0.1 μM) in vitro. Addition of exogenous uridine to the cell cultures reversed the antiproliferative effect. ABR-224050 also inhibited SEA induced proliferation of CD4 and CD8 T cells (by 78% and 90%, respectively) in vivo. Furthermore, ABR-224050 showed a significant inhibition of mean clinical score days 14-54 in the CIA study. ABR-224050 in combination with methotrexate showed an additive inhibitory effect on disease development compared to the monotherapies. All treated groups showed a significant inhibition of COMP in serum.Conclusion: ABR-224050 is a potent inhibitor of T cell proliferation. The mechanism of action for this proliferation block is inhibition of de novo pyrimidine synthesis. ABR-224050 also significantly inhibited the development of arthritis in CIA mice.The combination of ABR-224050 and methotrexate showed an additive inhibitory effect on disease development compared to the monotherapies. In addition, the level of COMP in serum was significantly inhibited in mice treated with ABR-224050 or methotrexate and the ABR-224050/methotrexate combination.Citation: Ann Rheum Dis, volume 66, supplement II, year 2007, page 299Session: RA: etiology, pathogenesis and animal models