800 - Selective Tyrosine Kinase Inhibition by Imatinib Mesylate for the Treatment of Autoimmune Arthritis

William H. Robinson, Ricardo T. Paniagua, Peggy P. Ho, Steven M. Chan, Orr Sharpe, Paul J. Utz, Mark C. Genovese. Stanford University, Stanford, CA
Presentation Number: 800

Objective: RA is characterized by the accumulation and proliferation of inflammatory cells in the synovial lining, resulting in the formation of pannus tissue which invades and destroys adjacent cartilage and bone. Macrophage, mast cells, and fibroblast-like synoviocytes (FLS) become activated in and are thought to play significant roles in the synovial inflammation and joint destruction in RA. Imatinib mesylate (Gleevec, formerly STI-571) is a tyrosine kinase inhibitor developed to treat Bcr-Abl expressing leukemias. We investigated protein tyrosine kinase inhibition with imatinib as a therapeutic strategy using the collagen-induced arthritis (CIA) model for RA.
Methods: DBA1/J mice were immunized with collagen type II in complete Freund’s adjuvant to provoke CIA (n = 15 per group), and mice were dosed twice daily with Gleevec (33 or 100 mg/kg; previously demonstrated by others to result in a pharmacokinetic profile similar to a mid-range dose of 400 mg once-daily in humans) or vehicle-control starting either at CIA induction (Prevention) or at the first clinical signs of arthritis (Treatment). We performed reverse phase protein microarray analysis of phospho-proteins, conventional immunoblot analysis of phospho-proteins, 3H-thymidine incorporation proliferation assays, and bead-array cytokine analysis to characterize the mechanisms by which imatinib inhibits cellular responses and signal transduction pathways in a mast cell line (C1.MC/57.1), murine peritoneal macrophage, as well as in FLS and synovial fluid mononuclear cells derived from human RA patients.
Results: We demonstrate that imatinib potently prevents and treats established CIA. Histopathologic analyses demonstrated statistically significant reductions in inflammation, erosion, and pannus scores in imatinib-treated mice with CIA. We show that micromolar concentrations of imatinib abrogate multiple signal transduction pathways implicated in RA pathogenesis, including mast cell c-Kit signaling and TNF-alpha release, macrophage c-Fms activation and cytokine production, and fibroblast PDGFR-beta signaling and proliferation. We extended our studies to synovial fluid mononuclear cells and FLS derived from human RA patients, in which imatinib attenuated fibroblast-like synoviocyte (FLS) PDGFR-beta signaling and synovial fluid mononuclear cell TNF-alpha production. At higher concentrations, imatinib also inhibited autoreactive T and B lymphocyte function.
Conclusion: We have demonstrated that imatinib potently prevents and treats CIA by selectively inhibiting a spectrum of signal transduction pathways central to the pathogenesis of RA. Our results provide further rationale for prospective clinical trials to determine if imatinib provides efficacy in RA. Selective tyrosine kinase inhibition by imatinib and other pharmacologic agents represents a promising strategy for the treatment of RA and other inflammatory diseases.

 W.H. Robinson, None; R.T. Paniagua, None; P.P. Ho, None; S.M. Chan, None; O. Sharpe, None; P.J. Utz, None; M.C. Genovese, None.