POS0229 ELUCIDATING THE MECHANISM OF ACTION DOWNSTREAM OF ROR2 BLOCKADE: A PHOSPHOPROTEOMIC APPROACH

Background Osteoarthritis (OA) affects 12% of the population, and yet we still have no disease-modifying treatment. Cartilage breakdown is hallmark OA, patients suffer from pain loss joint function/independence, severely affecting quality life. Therefore, there a huge unmet clinical need. Receptor tyrosine kinase–like orphan receptor 2 (ROR2) non-canonical WNT that regulates planar cell polarity pathway, controlling limb outgrowth. During skeletal development chondrocytes require ROR2 to undergo hypertrophy in process endochondral bone formation (1). Loss function mutations humans causes Recessive Robinow Syndrome (limb shortening brachydactyly (2,3)). Although absent healthy adult articular cartilage, our initial studies identified high expression with suggesting role disease process. In murine model blocking therapeutic regime using siRNA resulted reduced cartilage destruction rapid sustained relief. Due limited pattern adulthood, systemic or local toxicity were expected, nor any observed. We also found supports human organoid nude mice proposed blockade as potential OA The mechanism action was independent modulation canonical signaling. YAP inhibition required, but not sufficient, for chondrogenic effect (4). additional, unknown mechanisms must be involved downstream blockade. Objectives To study phosphorylation events ROR2, further understanding Methods Phosphoproteomics (label free liquid chromatography tandem-mass spectrometry TiO2 based phospho-enrichment), vitro cells, CRISPR. Results WNT5A most well established ligand ROR2. confirmed stimulation leads time-dependent ERK C3H10T1/2 cells. then deleted cells by CRISPR, performed phosphoproteomics analysis on wildtype (control) ROR2-CRISPR stimulated 100ng/ml recombinant 5 15 minutes. ROR2-dependant targets defined proteins differentially phosphorylated control upon stimulation, did occur manner. WNT5A/ROR2 modulated signaling pathway at other levels. KEGG revealed pathways known roles pathogenesis enhanced, including NF-KB, mTOR cellular senescence. With current technology, requires intra-articular injections conjugated atelocollagen every days. Preliminary efficacy data potentially longer-acting blockers are promising. Conclusion has treatment resulting protection relief model. Here, studied approach. novel processes regulated WNT5A/ROR2. Further needed clarify their OA. Our siRNA-atelocollagen technology too frequently acceptable patients. developing which can administered systemically intra-articularly more often than 3 months. References [1]DeChiara, T. M. et al. Nat. Genet. 24 , 271–4 (2000). [2]Bokhoven, H. Van, Celli, J. & Kayserili, Nature 25 423–426 [3]Afzal, A., Rajab, Fenske, C. Oldridge, 419–422 [4]Thorup, A.-S. Sci. Transl. Med. 12 eaax3063 (2020). Disclosure Interests Anne-Sophie Thorup: None declared, Jacob Wilson: Pedro Cutillas: Francesco Dell’Accio Consultant of: Samumed - related this abstract, Grant/research support from: UCB abstract