Background BTK is a member of the Tec family kinase of non-receptor protein tyrosine kinases1. BTK is mostly expressed in hematopoietic cells such as B cells, mast cells and macrophages2. BTK plays key roles in multiple cell signaling pathways including BCR and FcγR signaling cascades and is an essential mediator not only in B-cell dependent but also in myeloid cell dependent inflammatory arthritis3–5. HM71224 which is a novel BTK Inhibitor and clinically studied in phase 1 stage, has been evaluated as a therapeutic agent for the treatment of autoimmune diseases such as rheumatoid arthritis (RA).
Objectives In this report, we present a highly potent and selective, orally available a small molecule BTK inhibitor and its efficacies in rodent models of rheumatoid arthritis.
Methods In vitro inhibition activity of HM71224 against diverse kinases was evaluated using recombinant enzymes. Also, inhibition effect on intracellular signaling pathways was assessed by Western blot analyses of the phosphorylated substrates in cell lysates. In vivo efficacy of HM71224 was evaluated in several models of RA such as collagen-induced arthritis (CIA) using DBA1 male mice5 and Lewis rat6.
Results Enzyme-based and cell-based in vitro assays were conducted to assess the activity of HM71224 against BTK and other related kinases. HM71224 highly selective inhibited BTK (2.6 nM). In cell-based studies, HM71224 showed potent inhibition activity against the phosphorylation of BTK (1.0 nM) and a downstream kinase PLCγ2 (1.0 nM) in Ramos B cell, being well correlated with the inhibition activity for BTK kinase. On the other hand, HM71224 did not meaningfully inhibit the phosphorylation of STAT5 (>1,000 nM) in CTLL T cell. Anti-arthritic in vivo efficacy of HM71224 was tested in a collagen induced arthritis model using DBA1/J mouse. At the oral dose of 10 mg/kg (QD), HM71224 showed excellent anti-arthritic effect in terms of clinical and histopathological arthritic scores, pannus formation, synovitis index, bone erosion index, joint cartilage index, serum autoantibody IgG level and serum cytokine level without body weight loss (the efficacious dose as ED90 was calculated to 6.0 mg/kg/day). Similarly, HM71224 also displayed excellent anti-arthritic efficacy in a CIA model using Lewis rat. The nearly complete inhibition of p-BTK and BTK target occupancy was observed after 4 hr at the doses of 10 mg/kg, which are the efficacious doses inducing remission in arthritis score.
Conclusions Our data demonstrated that HM71224, acting through selective inhibition of BTK activation, exhibited significantly beneficial effects in rodent models of rheumatoid arthritis. These results strongly support further development of HM71224 as a promising new agent for the treatment of rheumatoid arthritis.
Nature 1993; 361, 226-233
The Journal of Immunology 1994; 152, 557-565
Annual Review Immunology 2009; 27, 199-227
International Immunopharmacology 2009; 9, 10-25
Immunological Reviews 2009; 228, 58-73
Nature Protocol 2007; 2, 1269-1275
Journal of Musculoskeletal and Neuronal Interactions 2001; 1, 377-385
Disclosure of Interest None declared