Evaluation of the role of leukaemia inhibitory factor receptor antagonist in the pathogenesis of inflammatory arthritis

Abstract

Rheumatoid arthritis (RA) is a chronic, inflammatory, systemic, autoimmune disease that is characterized by acute inflammation of the synovium, cartilage destruction and bone damage. The exact cause of the disease has not been elucidated so far. Nevertheless, the pathogenesis of RA is quite complex, involving a repertoire of cytokines that act either collectively or individually to exert their pro-inflammatory effects, thereby debilitating the joint architecture. Despite the success of several anti-cytokine based therapies, particularly those targeting tumour necrosis factor (TNFα), in the treatment of rheumatoid arthritis (RA), there is still a need for development of alternative therapies to treat RA patients, who are either refractory to the existing therapies or, who discontinue the use of these drugs owing to their potential side effects and/or toxicities. Leukaemia inhibitory factor (LIF) is an IL-6 subfamily cytokine that has been well implicated in the pathogenesis of RA. Considering this, the development of anti-LIF therapeutics as an alternative to the currently available treatments in RA is a promising possibility that merits further study. Several LIF antagonists have been developed to block the biological activity of LIF. However, whether antagonism of LIF and the other related IL-6 subfamily cytokines would favourably influence the disease severity or outcome in RA has not been fully investigated so far. This study aimed at evaluating the role of a LIF receptor super antagonist, MH35BD, in the pathogenesis of inflammatory arthritis. MH35BD was observed to be exerting anti-inflammatory and chondroprotective effects in vitro. In addition, it was found to block the biological activity of other IL-6 subfamily cytokines, such as Oncostatin M (OSM), also implicated in the pathogenesis of RA. Antagonsim of LIFR by MH35BD reduced both LIF and OSM induced expression of proteolytic endopeptidases and their naturally occurring inhibitors by primary articular chondrocytes to basal levels. Furthermore, MH35BD had no effect on STAT3 phosphorylation in murine macrophages, thereby potentially blocking the gp130 receptor subunit-mediated signalling via the JAK/STAT pathway in macrophages. With the aim of increasing the serum half-life of MH3BD, the MH35BD:Fc fusion protein construct was generated and tested in vivo for its serum stability. However, the MH35BD:Fc fusion protein was found to be less stable in the serum as compared to its monomeric counterpart, MH35BD, since the serum levels of MH35BD:Fc decreased at a rapid rate than that of MH35BD. This highlights the importance of studying the binding characteristics of Fc based fusion proteins to neonatal Fc receptors, FcRn that determines their serum stability. When tested for it efficacy in animal models of arthritis, MH35BD did not exert any significant effect on the extent of joint inflammation in both K/BxN serum induced and antigen induced (AIA) models of arthritis. Nevertheless, it significantly inhibited the cutaneous delayed type hypersensitivity (DTH) reactions induced in arthritic mice, suggesting that the T cell initiated joint inflammation in AIA and DTH reactions may be regulated by independent mechanisms. The very aggressive nature of the disease in K/BxN serum induced model of arthritis and the issues pertaining to the completeness of the blockade of LIFR by MH35BD might have been responsible for the ineffectiveness of the anti-LIF therapy in this model of inflammatory arthritis. However, these issues were circumvented by inducing arthritis in LIF gene knockouts (LIF-/-) by K/BxN serum transfer. Complete absence of endogenous LIF production in the LIF knockouts ensured proper interpretation of the observed results, without any interference in respect to parameters such as sufficiency of dose and completeness of blockade of LIFR. It was found that although the LIF-/- mice were susceptible to arthritis induction by K/BxN serum transfer, the disease severity in LIF-/- mice was substantially ameliorated as compared to the wild-type diseased controls. In conclusion, this study provides a useful insight into the role of LIFR antagonist, MH35BD, as a potential therapeutic candidate for the treatment of rheumatoid arthritis and other related arthropathies. Compelling evidence has proved that LIF contributes to the induction and progression of inflammatory arthritis and joint tissue damage in the K/BxN serum induced arthritis. Thus, this study provides further impetus to test the effects of LIF blockade as a potential therapeutic strategy in rheumatoid arthritis.