OP0077 INNOVATIVE TRANSLATIONAL MODELS TO STUDY HUMAN SYNOVIAL PATHOLOGY: TARGET VALIDATION AND PRECLINICAL IMAGING
Authors: Irene DI Ceglie, Mathijs Broeren, Claire Waterborg, Daphne Dorst, R.M. Thurlings, Peter Laverman, Fons van de Loo, Peter van der Kraan, Peter van Lent, Marije Koenders
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background</h3> Many experiments to study inflammation, hyperplasia, and fibrosis in the synovium have been performed in animal models of RA and OA. However, the predictive value of these models for the screening of potential drugs in RA is variable and for OA, none were sufficiently effective in clinical trials. Translational arthritis research with human cells is often performed in monolayer culture where the absence of extracellular matrix and other cell types results in alterations of cell functions and loss of phenotype. <h3>Objectives</h3> To improve the predictive value of preclinical arthritis research by developing and optimizing innovative translational models to study human synovial pathology in vitro and in vivo. <h3>Methods</h3> Synovial biopsies from RA patients were obtained during joint replacement surgery and processed for either (1) explant cultures, (2) 3D-synovial micromasses, (3) RA-SCID transplantation studies, and/or (4) a biobank for corresponding mRNA and IHC profiling. For explant culture, 3mm biopsies were cultured for 24hr w/o various inhibitors, and cytokine production was analyzed by Luminex. 3D-micromasses were generated from primary RA FLS and CD14+ PBMCs, stimulated for 3 weeks with 10 ng/ml TNFα or TGFβ and analyzed by histology, IHC and QPCR. For target validation and preclinical imaging, 6mm biopsies were engrafted SC into SCID mice. Radionuclide- and fluorescently-labelled anti-CD64 antibodies were injected IV, and targeting was determined by biodistribution, µSPECT/CT and IVIS imaging analysis. <h3>Results</h3> Our first assay with RA synovium explants demonstrated to be highly suitable to test the therapeutic efficacy of inhibitors for TNFα, TLR4, p38 and the JAK-pathway, resulting in significantly reduced production of proinflammatory mediators after 24hr of culture. In contrast to the explant cultures, our 3D synovial micromasses could be followed for weeks. In this second translational model, lining formation was observed at day 7 and the micromasses could be stimulated to mimic RA- or OA-like features of synovial hyperplasia or fibrosis respectively. Long-term exposure to the RA-related cytokine TNFα lead to hyperplasia of the lining and an altered macrophage phenotype characterized by reduced CD163 expression. Conversely, the repair-related growth factor TGFβ induced fibrosis-like changes in the micromass lining, a hallmark of OA. This was accompanied by an increased expression of <i>PLOD2</i>, <i>COL1A1</i> and αSMA. Our third preclinical model, the RA synovium SCID mouse, was previously validated using adalimumab, secukinumab, and rituximab, and was now used to study CD64 as a potential marker to image synovitis. Gene expression of <i>FCGRI (CD64)</i> in synovial explants from RA patients was shown to correlate positively to gene expression of pro-inflammatory factors <i>IL1B, TNFA, IL8, S100A8, MCP1</i>, and with damage-associated genes <i>MMP2</i> and <i>MMP13</i>. Interestingly, dual-labelled <sup>111</sup>In-DTPA-IrDye800CW-anti-CD64 antibody showed high uptake in the synovial transplants of the SCID mice, and specifically visualized the subcutaneous synovial grafts by both µSPECT/CT and IVIS imaging. <h3>Conclusion</h3> The development of these translational models allows us to bridge the gap between preclinical and clinical drug development research. Whereas our synovial explant assay is ideal for short-term interventions, and the RA-SCID mouse a great translational model for in vivo preclinical studies, donor variability and access to sufficient tissue may be challenging. In such cases, the 3D synovial micromass model may be an excellent alternative. Especially in combined setting, these 3 translational approaches will improve target validation and preclinical development of novel anti-rheumatic drugs. <h3>Reference</h3> [1] Abdollahi-Roodsaz, J Clin Invest2008; Koenders, Arthritis Rheum 2012; Broeren, ALTEX 2019 <h3>Disclosure of Interests</h3> None declared