Background/Purpose: Targeting intracellular pathways with oral small molecules is an attractive therapeutic approach for treating immune mediated inflammatory diseases. The mitogen-activated protein kinase (MAPK) pathway is activated by environmental stressors, growth factors and inflammatory cytokines. However, the inhibition of central MAPK proteins has so far had undesirable side effects. The MAPK-activated protein kinase 2 (MK2) is a downstream mediator in the MAPK signaling pathway and could therefore be inhibited without the same side effects. The objective of this study was to study the effects of a small molecule inhibiting MK2 on inflammation and structural changes in ex vivo models of immune mediated inflammatory arthritis.

Methods: Synovial fluid mononuclear cells (SFMCs), fibroblast like synovial cells (FLSs) and peripheral blood mononuclear cells (PBMCs) were obtained from a study population consisting of patients with active RA or peripheral SpA with at least one swollen joint (for obtaining synovial fluid) (n=14). SFMCs were cultured for 48 hours with and without addition of a MK2 inhibitor (Celgene) at 1000 nM, 333 nM and 111 nM and supernatants were analyzed by the Olink proseek multiplex interferon panel and commercially available ELISA assays. Because FLSs are only found in small amounts among SFMCs, autologous co-cultures of FLS and PBMCs and SFMCs were also used. SFMCs cultured for 21 days were used to study inflammatory macrophage differentiation and osteoclastogenesis.

Results: In SFMCs cultured for 48 hours, the MK2 inhibitor decreased the production of CXCL9 (P<0.001), CXCL10 (P<0.01), HGF (P<0.01), CXCL11 (P<0.01), TWEAK (P<0.05), and IL-12B (P<0.05) and increased the production of CXCL5 (P<0.0001), CXCL1 (P<0.0001), CXCL6 (P<0.001), TGFα (P=0.01), MCP-3 (P<0.01), LAP TGFβ (P<0.05) dose-dependently after Bonferroni correction (all corrected P values). At the highest concentration, the MK2 inhibitor also decreased MCP-1 production (P<0.05). In FLS-SFMC co-cultures, the MK2 inhibitor decreased MCP-1 production (P<0.05) but did not change the production of DKK1 and MMP3. In FLS-PBMC co-cultures, the MK2 inhibitor decreased the production of MCP-1 (P<0.0001), increased MMP3 production (P<0.05) but did not change DKK1 production. In SFMCs cultured for 21 days as a model of inflammatory macrophage differentiation and osteoclastogenesis, the MK2 inhibitor decreased the production of MCP-1 (P<0.05) and tartrate-resistant acid phosphatase (TRAP) (P<0.05) but did not change the production of IL-10.

Conclusion: This study reveals the effects of a MK2 inhibitor in ex vivo models of immune mediated inflammatory arthritis. The MK2 inhibitor changed the secretory profile of SFMCs and decreased inflammatory osteoclastogenesis. Taken together, this points to a role of this MK2 inhibitor in attenuating inflammatory and destructive arthritis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-mapk-activated-kinase-2-inhibitor-attenuates-inflammatory-and-destructive-arthritis-in-human-ex-vivo-models/