Poster Presentation: Bor-Lin Huang

ABSTRACT

Targeted Inhibition of Pathogenic TGF-β Activity in Arthrofibrosis via Non-Cartilage-Permeating Antagonists

Bor-Lin Huang1, Satviki Singh1, Sedat Dogru1, Thomas P. Schaer2, Brian D. Snyder1, Matthew D. Layne 3, Mark W. Grinstaff1, Michael B. Albro1

1 College of Engineering, Boston University, MA 2 Department of Clinical Studies New Bolton Center, University of Pennsylvania, PA 3 Chobanian and Avedisian School of Medicine, Boston University, MA

Objectives: Arthrofibrosis (AF) is a debilitating fibrotic disorder of the diarthrodial joint synovium, leading to pain and limited joint motion. AF primarily initiates from TGF-β dysregulation in synovial fluid (SF) in aging or in the aftermath of trauma or surgery. Prior intra-articular drug therapies to inhibit pathogenic SF TGF-β have achieved limited success, encumbered by off-target inhibition of beneficial TGF-β in articular cartilage, leading to cartilage degeneration. Here, we propose a targeted therapeutic approach using non-cartilage-permeating inhibitors (NCPIs) which selectively inhibit pathogenic TGF-β in SF during arthrofibrosis while avoiding off-target inhibition of beneficial TGF-β signaling in articular cartilage. We evaluate the use of large, anionic TGF-β receptor (SolR) antagonist proteins, which possess high affinity to neutralize TGF-β in SF and show limited penetration into cartilage due to steric/electrostatic partitioning from the dense sulfated-glycosaminoglycan-rich cartilage EC.

Materials and Methods: The efficacy of two NCPIs (recombinant TGF-β type-II and type-III soluble receptors; SolR2 and SolR3) and a small-molecule cartilage-permeating inhibitor (CPI) (LY364947) to selectively inhibit pathogenic TGF-β in SF was assessed via an in vitro co-culture system consisting of bovine cartilage explants and synoviocyte-seeded collagen construct, allowing for simultaneous monitoring of TGF-β-induced synovium contraction (a surrogate measure of fibrosis) and off-target effects on cartilage mechanical properties.

Results: Pathogenic TGF-β levels induced 70% contraction of synoviocyte-seeded constructs (p<0.05), relative to TGF-β-free. LY364947 significantly reduced synovium contraction to 8%, relative to TGF-β-free, and induced a significant 60% reduction in cartilage Young’s modulus (EY) (p<0.05). In contrast, SolR2 and SolR3 reduced synovium contraction to 18.5% and 49%, respectively (p<0.05) and had no off-target effect on cartilage EY, thus supporting NCPI selective inhibition of pathogenic TGF-β in SF.

Conclusion: Non-cartilage-permeating antagonists represent a novel pharmacological approach for inhibiting pathogenic TGF-β in arthrofibrosis while minimizing the off-target effects on articular cartilage.