Abstract
Rheumatoid arthritis (RA) is a common systemic autoimmune disorder. Fibroblast-like synoviocytes (FLS) have emerged as an attractive target for nonimmunosuppressive RA therapy, but there are no approved drugs targeting FLS. The receptor protein tyrosine phosphatase sigma (PTPRS) negatively regulates FLS migration and has been proposed as a target for FLS-directed RA therapy. Here we examined the impact of sequence variations on efficacy of an FLS-targeted biologic composed of Fc-fused PTPRS IgG-like domains Ig1 and Ig2 (Ig1&2-Fc). Engineering the linker and Fc tag improved effectiveness of human Ig1&2-Fc in assays of FLS migration and a mouse model of arthritis. Treatment of mice with Ig1&2-Fc over 4 months revealed no signs of toxicity or organ pathology. Finally, we show potential of Ig1&2-Fc coadministration in combination or as a bispecific fusion with a tumor necrosis factor-α inhibitor. Combination treatment of mouse tumor necrosis factor receptor 2 (mTnfr2) with Ig1&2-Fc resulted in increased efficacy in suppressing arthritis beyond single-agent treatment. When administered as a dual-action bispecific, Ig1&2 fused to mTnfr2 proved more efficacious at suppressing arthritis than mTnfr2 alone. This study illustrates the potential of Ig1&2-Fc as a combination or bispecific therapy with disease-modifying antirheumatic drugs to improve patient outcomes in RA.