Background Bruton tyrosine kinase (BTK), a Tec family kinase, is involved in B cell activation and osteoclast formation. As BTK plays a central role in B cell receptor (BCR) signaling and B cell development, BTK might be an attractive therapeutic target for autoimmune diseases including rheumatoid arthritis (RA) [1–3].

Objectives To investigate the effects of HM7122, a novel BTK inhibitor, on human B cell activation and osteoclast formation.

Methods In vitro biochemical inhibition assay was performed using Invitrogen kinase assay. Peripheral blood mononuclear cells (PBMCs) from healthy controls were activated with anti-human IgM in increasing concentrations of HM71224. Phosphorylationof BTK and its down-stream signaling molecules PLCγ2 and ERK were examined using phospho-flow and phospho-blots. The BTK occupancy was measured in PBMCs using ELISA. The expression of B cell activation marker CD40, CD69 and CD86 were examined by flow cytometry. Osteoclasts were generated from isolated monocytes in the presence of M-CSF and RANKL and the inhibition of osteoclast generation by HM71224 was examined.

Results In vitro, HM71224 effectively bound to BTK (IC₅₀ =2nM) but not to STAT5 (IC₅₀ >1000 nM), STAT6 (IC₅₀ =445 nM) and EGFR (IC₅₀ =800 nM). HM71224 blocked phosphorylation of BTK, PLCγ2 and ERK (IC50 =1nM, 1nM, and 100 nM, respectively). The BTK occupancy in human PBMCs showed an effective binding of HM71224 to BTK protein (IC₅₀ =69.9±14 nM). Upregulation of the activation marker CD40, CD69 and CD86 on stimulated human B cells were inhibited by HM71224 in a dose-dependent manner (Figure A). Furthermore, osteoclast formation was suppressed in the presence of HM71224 as well (Figure B).

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Conclusions HM71224 is a novel BTK inhibitor that effectively inhibits B cell activation and osteoclastogenesis. HM71224 might offer a new therapeutic option to treat autoimmune diseases associated with B cell activation.

References

1. Edwards J.C.W. et al, B-cell targeting in rheumatoid arthritis and other autoimmune diseases. Nature Reviews Immunology, 2006, 6: 394-403.

2. Rickert R.C. New insights into pre-BCR and BCR signaling with relevance to B cell malignancies. Nature Reviews Immunology, 2013, 13:578-591.

3. Swanson D.C. et al, Tyrosine kinases as targets for the treatment of rheumatoid arthritis. Nature Reviews Rheumatology, 2009, 5: 317-324.

Disclosure of Interest : J. K. Park: None declared, J. A. Park: None declared, Y. J. Lee: None declared, J. Song: None declared, J. I. Oh: None declared, Y.-M. Lee: None declared, K. H. Suh: None declared, J. Son: None declared, E. B. Lee Grant/research support: Hanmi Pharm Co Ltd

DOI 10.1136/annrheumdis-2014-eular.2783