P126/O29 mTOR blockade by rapamycin decreases arthritis and spondylitis development and severity in HLA-B27 transgenic rats
Authors: S Chen, M Van Tok, V Knaup, L Kraal, D Pots, J Taurog, D Baeten, L van Duivenvoorde, M van de Sande
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Career situation of first and presenting author</h3> Student for a master or a PhD. <h3>Introduction</h3> TNF and IL-17A have been demonstrated as key inflammatory cytokines in Spondyloarthritis (SpA), whereas targeting bone remodeling remains an unmet clinical need in SpA. The mammalian target of rapamycin (mTOR) regulates IL-17 expression and osteogenesis and could therefore be a promising therapeutic target in SpA. <h3>Objectives</h3> To investigate if blockade of mTOR with rapamycin inhibits the pathological processes in inflammation and bone in SpA. <h3>Methods</h3> Cytokines were measured by ELISA in the supernatant from SpA patient PBMCs stimulated with anti-CD3/CD28, with various concentrations of rapamycin. SpA FLS were cultured in osteogenesis conditions with rapamycin, supplemented with TNF, IL-17A or both cytokines and stained for alkaline phosphatase (ALP) and Alizarin red. 6-weeks-old HLA-B27/Huβ2m transgenic rats were immunized with 60–90 µg heat-inactivated <i>M. tub</i> in IFA. Rats were treated with 1.5 mg/kg rapamycin or vehicle intraperitoneally (3x a week) in prophylactic and therapeutic settings and monitored for spondylitis and arthritis incidence and severity. Inflammation, bone destruction and formation were evaluated by histology after 5 weeks of treatment. <i>IL-17A</i>, <i>IL-17F</i> and <i>TNF</i> mRNA expression were tested in the metacarpophalangeal (MCP) joints. <h3>Results</h3> TNF and IL-17A protein production by SpA PBMCs after stimulation were decreased in the presence of 1 nM rapamycin (p&lt;0.05). Rapamycin also reduced ALP and Alizarin red staining during SpA FLS osteogenesis (p&lt;0.05)<i>. In vivo</i>, prophylactic rapamycin treatment decreased the incidence of spondylitis (18.2% (2/11)) and arthritis (36.7% (4/11)) compared to controls (92.3% (12/13; p&lt;0.0001) and 100% (13/13; p&lt;0.05)). Rapamycin treatment reduced arthritis severity (0.5 versus 7.2 on a 0–12 scale (p&lt;0.0001)) and spondylitis severity (0.2 versus 2.1 on a 0–3 scale (p&lt;0.0001)). In line with the clinical findings, histological analyses revealed diminished inflammation (p&lt;0.0001), reduced bone, cartilage destruction (p&lt;0.001) and less new bone formation (p&lt;0.001) in peripheral joints. Comparably, therapeutic treatment with rapamycin decreased spondylitis severity (1 versus 2.8; p&lt;0.05) and arthritis severity (4 versus 8.8; p&lt;0.05) compared to controls. In the rapamycin treatment group, <i>IL-17A</i> (p&lt;0.05) and<i> IL-17F</i> (p&lt;0.05) mRNA were decreased in the MCP joints. <h3>Conclusions</h3> mTOR blockade decreases IL-17A and TNF production <i>in vitro</i> in Spa PBMCs and reduces osteoblastic differentiation of human SpA FLS. In the <i>M. tub</i> induced HLA-B27 transgenic rat model of SpA, mTOR blockade reduces arthritis and spondylitis development and severity by targeting inflammation and bone remodeling. <h3>Disclosure of Interest</h3> None declared.