Screening of an FDA-approved drug library reveals MEK1/2 inhibitors block production of osteoarthritis mediators in activated human chondrocytes and synovial fibroblasts

The purpose of this study was to screen FDA-approved compounds for potential disease-modifying osteoarthritis drugs. An FDA-approved library of 2679 compounds was used for a high throughput screen (HTS) of primary human chondrocytes activated by a fibronectin fragment (FN7-10) used to model the chondrocyte OA phenotype. Inhibition of matrix metalloproteinase-13 (MMP-13) production measured using a fluorescent probe was the HTS readout. Secondary testing included dose response studies, an anabolic assay measuring chondrocyte glycosaminoglycan (GAG) production, and effects of compounds on expression and production of OA mediators by chondrocytes and synovial fibroblasts. 230 compounds in the HTS blocked MMP-13 production by >70% with low cytotoxicity. Mitogen-activated protein kinase kinase (MEK1/2) inhibitors were among the most enriched and potent inhibitors of MMP-13 production and the top enhancers of GAG production. The MEK1/2 inhibitor trametinib enhanced COL2A1 and ACAN expression and decreased levels of MMP-13 and IL-6 in chondrocytes isolated from OA patients. Trametinib also blocked production of pro-inflammatory cytokines and chemokines in cultures of chondrocytes and synovial fibroblasts, including CCL20, CCL7, LIF, CCL4, CXCL5, CCL5, and TNF-α. Signaling pathway analysis revealed trametinib blocked mitogen-activated protein kinase (MAPK) and c-Fos activation caused by FN7-10. Inhibition of the MAPK-activated transcription factor AP-1 was found to reduce MMP-13 and IL-6 in chondrocytes and synovial fibroblasts. A PROteolysis Targeting Chimera (PROTAC) that mediates degradation of MEK1/2 also reduced production of OA catabolic and inflammatory markers. These results suggest MEK1/2 should be explored as a potential therapeutic target for OA disease modification.