OP0200 BLOCKING ROR2 IMPROVES CARTILAGE INTEGRITY AND PROVIDES PAIN RELIEF IN OSTEOARTHRITIS
Authors: A. S. Thorup, D. Strachan, S. Caxaria, B. Poulet, B. Thomas, S. Eldridge, G. Nalesso, J. Whiteford, C. Pitzalis, T. Aigner, R. Corder, J. Bertrand, F. Dell’accio
Journal: Annals of the Rheumatic Diseases (2021)

Background: Osteoarthritis (OA) is the leading cause of chronic disability worldwide, affecting 12% of the population, and yet we still do not have a disease-modifying treatment. Cartilage breakdown is the hallmark of OA, and patients suffer from pain and loss of joint function/independence, severely affecting quality of life. Therefore, there is a huge unmet clinical need. Receptor tyrosine kinase–like orphan receptor 2 (ROR2) is a non-canonical WNT receptor that regulates the planar cell polarity pathway, controlling limb outgrowth during development. During skeletal development, chondrocytes require ROR2 to undergo hypertrophy throughout the process of endochondral bone formation 1 . Loss of function mutations in humans causes Recessive Robinow Syndrome, leading to limb shortening and brachydactyly 2,3 . Although absent from healthy adult articular cartilage, our initial studies identified high expression levels of ROR2 in chondrocytes from patients with OA, suggesting a role in the disease process Objectives: To test the potential of ROR2 blockade as a disease-modifying treatment for OA. Methods: Human cartilage organoid model in nude mice, menisco-ligament injury (MLI) model of OA in mice, behavioural studies, in vitro studies in cells. Results: ROR2/WNT5A signaling was increased in osteoarthritic cartilage. Blocking ROR2 was sufficient to induce articular chondrogenesis and suppress expression of aggrecanases in a mesenchymal stem cell line, and to support cartilage formation in a human cartilage organoid model in nude mice using primary chondrocytes from patients with OA. In the MLI model of OA, blocking ROR2 in therapeutic regime using atelocollagen-conjugated siRNA resulted in reduced cartilage destruction and in rapid and sustained pain relief. Due to the limited expression pattern of ROR2 in adulthood, no systemic or local toxicity were expected, nor were any observed 4 . With the current technology, ROR2 blockade requires intra-articular (IA) injections of siRNA conjugated to atelocollagen every 5 days. Preliminary efficacy data of potentially longer-acting ROR2 blockers are promising. The mechanism of action of ROR2 blockade was independent of modulation of canonical WNT signaling. ROR2/WNT5A promoted nuclear localization of YAP, which required both Rho and G-proteins. YAP signaling downstream of ROR2 also required Rho, but not G-proteins. YAP and TEAD inhibition was required, but not sufficient, for the chondrogenic effect of blocking ROR2. Therefore, additional, yet unknown mechanisms must be involved downstream of ROR2. Conclusion: ROR2 blockade has potential as a disease-modifying treatment for OA, resulting in cartilage protection and rapid and sustained pain relief in a murine model. This will be crucial for clinical success of any treatment for OA and promote patient compliance. Our current siRNA-atelocollagen based technology requires IA injections too frequently to be acceptable for patients. We are developing ROR2 blockade which can be administered systemically or IA not more often than every 3 months - work funded by FOREUM. References: [1]DeChiara, T. M. et al. Ror2, encoding a receptor-like tyrosine kinase, is required for cartilage and growth plate development. Nat. Genet. 24 , 271–4 (2000). [2]Bokhoven, H. Van, Celli, J. &amp; Kayserili, H. Mutation of the gene encoding the ROR2 tyrosine kinase causes autosomal recessive Robinow syndrome. Nature 25 , 423–426 (2000). [3]Afzal, A., Rajab, A., Fenske, C. &amp; Oldridge, M. Recessive Robinow syndrome, allelic to dominant brachydactyly type B, is caused by mutation of ROR2. Nature 25 , 419–422 (2000). [4]Thorup, A.-S. et al. ROR2 blockade as a therapy for osteoarthritis. Sci. Transl. Med. 12 , eaax3063 (2020). Acknowledgements: We gratefully acknowledge funding support of this work by the Medical College of St Bartholomew’s Hospital Trust, the William Harvey Research Foundation, FOREUM foundation for research in rheumatology (1016807), the MRC (MR/L022893/1, MR/N010973/1, MR/P026362/1, MR/K013076/1), Versus Arthritis (21515, 20886, 21621, 20859), and the DFG Emmy-Noether program (BE4328/5-1). Disclosure of Interests: Anne-Sophie Thorup: None declared, Danielle Strachan: None declared, Sara Caxaria: None declared, Blandine Poulet: None declared, Bethan Thomas: None declared, Suzanne Eldridge: None declared, Giovanna Nalesso: None declared, James Whiteford: None declared, Costantino Pitzalis: None declared, Thomas Aigner: None declared, Roger Corder: None declared, Jessica Bertrand: None declared, Francesco Dell’Accio Consultant of: Samumed and UCB