Background/Purpose: The current biologic treatment for Ankylosing Spondylitis (AS) and Psoriatic Arthritis (PsA) are limited to TNF-a inhibitors (TNFi) and, more recently, IL-17A monoclonal antibodies. These treatments work in a percentage of patients and are not effective against all the disease manifestations. Targeting cellular pathways leading to the production of inflammatory cytokines is a new and appealing therapeutic approach for inflammatory conditions. The inhibition of the mitogen-activated protein kinase (MAPK), attempted in the past in Rheumatoid Arthritis (RA), yielded undesirable effects, including toxicity and tachyphylaxis. We aimed to assess the in vitro efficacy of a small molecule inhibiting the MAPK-associated protein kinase 2 (MK2) in limiting the cytokine response in T-cells (including Th17), and in monocytes derived from patients with inflammatory arthritis.

Methods: CD4+ T cells and monocytes were isolated from peripheral blood mononuclear cells (PBMCs) of AS (n=16), PsA (n=12), RA patients (n=11) and healthy controls (HC, n=7) and stimulated for six days under either neutral (Th0) or Th17-promoting conditions in the presence of MK2 inhibitor (CC0786512, Celgene) or control (DMSO). The level of IL-17A, IFN-g, GM-CSF, IL-17F in the culture was measured using Cytokine Bead Array (CBA). Cells were also stained for intracellular cytokines and Foxp3 and analysed by flow cytometry. Cytotoxicity and proliferation were also assessed with Annexin V/7-AAD staining and CFSE dilution. Monocytes were stimulated with lipopolysaccharide (LPS) for 18 hours and treated with CC0786512 and the secretion of TNF-a, IL-6, MIP-1a, MCP-1, GM-CSF measured with ELISA or CBA.

Results: CC0786512 effectively inhibited secretion of IL-17A, GM-CSF and IL-17F in CD4+ T cells from AS and PsA (Figure), with negligible effects on viability or cell proliferation. The compound worked on T cells cultured both in neutral (Th0) and in vitro Th17 polarising conditions, with effects in samples derived from TNFi-treated and TNFi-naive patients. The inhibition of MK2 reduced the number of Th17 cells generated under Th17 driving conditions, and in particular of Th17 cells co-expressing IFN-g. In monocytes, the MK2 inhibition resulted in reduced TNF-a, MIP-1a and MCP-1 secretion.

Conclusion: Our results indicate that the MK2 inhibitor significantly inhibits both Th17 T cell and monocyte immune responses in cells derived from patients with AS and PsA. Our results encourage further investigation and make MK2 a promising novel therapeutic target in the treatment of Spondyloarthritis.