Proteases such as serine proteases and matrix metalloproteases (MMPs) are involved in cartilage destruction in rheumatoid arthritis. The effects of gene transfer of plasmin inhibitors and tissue inhibitors of metalloproteinases (TIMPs) on cartilage degradation and invasion by rheumatoid synovial fibroblasts were investigated.

Replication defective adenoviral vectors were used for transduction. Genes encoding the following inhibitors were used: the plasmin inhibitor, bovine pancreatic trypsin inhibitor (BPTI); a cell surface-targeted plasmin inhibitor, ATF.BPTI, a hybrid protein of BPTI and a ligand of the cell surface uPA-receptor, ATF; TIMP-1; and TIMP-3. Cartilage degradation was investigated in an in vitro model using a radiolabeled cartilage-like matrix. The invasive behavior of rheumatoid synovial fibroblasts was studied in vitro in a Transwell model and in vivo in the SCID mouse co-implantation model.

Cartilage degradation was significantly reduced by gene transfer of BPTI and ATF.BPTI. The effect of ATF.BPTI was significantly stronger than that of BPTI suggesting that targeting protease inhibition to the cell surface improves the inhibitory effect. Gene transfer of ATF.BPTI, TIMP-1 and TIMP-3 significantly inhibited cartilage invasion. These results indicate that cartilage degradation and invasion can be inhibited by gene transfer of inhibitors of plasmin and MMPs. Inhibition of proteases at the site of joint destruction through gene transfer may provide a novel therapeutic strategy to limit the progression of joint destruction in rheumatoid arthritis.