Investigation of Toll-Like Receptor (TLR) 4 Inhibitor TAK-242 as a New Potential Antirheumatoid Arthritis Drug

Snigdha Samarpita; Joo Young Kim; Mahaboob Khan Rasool; Kyoung Soo Kim

Disclosures

Arthritis Res Ther. 2020;22(16) 

In This Article

Abstract and Introduction

Abstract

Background: Proper blocking of toll-like receptor (TLR) activation during disease progression has been reported to have inhibitory effect on the pathogenesis of rheumatoid arthritis (RA). We tested whether the TLR4 inhibitor TAK-242 had potential as a remedy for rheumatoid arthritis.

Methods: The therapeutic effect of TAK-242 was tested in vitro using the human rheumatoid fibroblast-like synoviocyte (FLS) line MH7A or primary human FLS and in an adjuvant-induced arthritis (AIA) rat model.

Results: TAK-242 dose dependently inhibited the increased expression of IL-6, IL-8, MMP-1, and VEGF in LPS-stimulated MH7A cells. It also inhibited the expression of IL-6 and IL-8 in poly(I:C), TLR3 activator-stimulated primary FLS, but not in IL-1β-stimulated primary FLS. These findings suggest that TAK-242 blocks a specific signaling pathway to some degree. Further, TAK-242 slightly inhibited mobilization of NF-κB into nuclei. In the AIA rat model, TAK-242 significantly reversed the body weight and paw thickness of AIA rats to the normal state at a dose of 5 mg/kg, but not at 3 mg/kg, and reduced the increased serum level of IL-6 and VEGF in AIA rats. It also significantly ameliorated inflammatory symptoms of joint tissues at day 21 of treatment, according to histology and RT-PCR.

Conclusions: Based on the drug repositioning concept, TAK-242, which is used for the treatment of TLR4-mediated inflammatory diseases, shows potential for cost-effective development as a remedy for rheumatoid arthritis or to control the progression of RA.

Introduction

Tissue and cells are injured during chronic and persistent inflammation of rheumatoid arthritis (RA). Endogenous molecules such as nuclear proteins, RNA, and DNA may be released into synovial fluid and then activate inflammatory responses through the signaling pathway of toll-like receptors (TLRs) expressed in cells such as macrophages, synovial cells, and preosteoclasts located in joints.[1] Although TLRs are the front line of innate immunity, they have been known to play an important role in triggering immune responses by recognizing various molecules released from damaged cells known as damage-associated molecular patterns (DAMPs) as well as pathogen-associated molecular patterns (PAMPs) such as bacterial lipopolysaccharides (LPS), viral RNA, CpG-containing DNA, and flagellin.[2,3] The specific bindings of PAMPs and DAMPs to TLRs may trigger main adaptor protein MyD88-dependent or independent pathways.[4] All these inflammatory responses through TLRs signaling pathways remove harmful stimuli or repair damaged tissues. However, such endogenous damage signals can induce an inappropriate innate response, resulting in harmful inflammation that can lead to more destruction than the original injury.[5,6]

The relevance of TLRs to RA has been investigated through experimental models. TLR2 and TLR4 have been extensively studied, and TLR5 and TLR7 have recently gained attention in RA pathology.[1] TLR4 is mainly expressed in monocytes, macrophages, granulocytes, and the spleen, but the additional expression of TLR4 in chondrocytes, osteoblasts, and synoviocytes implicates TLR4 in the pathophysiology of the musculoskeletal system.[7] Thus, TLR4 appears to be more important than other TLRs in RA.[8] Accordingly, proper blocking of TLR4 activation during disease progression may help control RA.

TLR4 antagonists have been developed to beneficially block TLR4 signaling in various diseases such as sepsis, septic shock, lung inflammation, and RA.[4] TLR4 antagonists, anti-TLR4 antibodies, decoy peptides, and small molecule inhibitors inhibit the interaction of ligands with TLR4 to block triggering of the TLR4 signaling pathway in an extracellular or intracellular manner.[4,9] In particular, cell-permeable TAK-242 (resatorvid) selectively binds to TLR4 and interferes with interactions between TLR4 and two adaptor molecules of TLR4, toll/interleukin-1 receptor domain-containing adaptor protein (TIRAP), or toll/interleukin-1 receptor domain-containing adaptor protein inducing interferon-β-related adaptor molecule (TRAM).[10] TAK-242 is a small molecule suppressor of pathogen-induced release of inflammatory cytokines and acts by inhibiting TLR-4-mediated signaling. It also shows inhibitory effects on the production of nitric oxide (NO) or tumor necrosis factor (TNF)-alpha induced by the TLR4-specific ligand LPS.[11] Because of its suppression of cytokine levels, TAK-242 is known as an effective treatment for severe sepsis and may be a new therapeutic agent for other inflammatory diseases. Under the concept of drug repositioning, we wanted to determine the potential for TAK-242 to have a therapeutic effect against RA. In this study, we show that TAK-242 inhibits the expression of inflammatory cytokines in LPS-stimulated FLS and demonstrate anti-arthritic effects in a complete Freund's adjuvant (CFA)-induced arthritis (AIA) rat model.

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