Background/Purpose:  CC-292, CC-90008, and ibrutinib are covalent Btk/Tec family kinase inhibitors that block Btk activity by binding with high affinity to the adenosine triphosphate (ATP) binding site of Btk and forming a covalent bond with cysteine 384 in the target Btk protein, providing rapid, complete, and prolonged inhibition of Btk activity. The objective of this study is to provide an immunoprofile of covalent modifiers of Btk that may impact the therapeutic opportunities of this class of compounds by assessing their impact on B-cells, T-cells, NK cells, monocytes, osteoclasts, dendritic cells, and basophils.

Methods:  B cell function was measured by BCR signaling and induced proliferation, plasmablast differentiation, IgG and IL-6 production, and surface expression of activation markers (CD86, CD40, CD54, and CD69). T cell function was measured by proliferation, cytokine production and CD8 T cell degranulation after TCR stimulation. NK function was measured by degranulation after exposure to K562 cells. Monocyte/macrophage activity was assessed by Fcγ Receptor-mediated TNFα production and basophil activity was measured by FcεR-mediated degranulation. Effects on osteoclastogenesis and TLR9 activation were measured in osteoclasts and dendritic cells, respectively.

Results:  The three Btk inhibitors tested here had both similarities and differences in the net activities observed on immunocyte function. All three inhibitors blocked Btk-mediated PLCγ2 phosphorylation in B-cells, FCεR-mediated degranulation in basophils, and osteoclastogenesis and bone degrading activity in myeloid-derived osteoclasts. Differences were observed in B-cell function depending on the stimulus. BCR-induced proliferation was inhibited by CC-292 and ibrutinib, but only weakly for CC-90008. Similarly, CC-292 and ibrutinib blocked BCR-induced ERK1/2 phosphorylation, but CC-90008 had no effect. Conversely ibrutinib was not active in assays where CC-292 and CC-9008 were active, including IL-6 production, plasmablast differentiation, and IgG secretion. CC-90008 and ibrutinib, but not CC-292 were potent inhibitors of T-cell proliferation. Yet, all three inhibited T-cell cytokine production and degranulation. In monocyte FCγR-mediated TNFα production, TLR9-mediated mDC activation, and NK degranulation, CC292 and ibrutinib showed inhibitory activity, but none was observed for CC-90008.

Conclusion:  The data gathered from the immunophenotyping of CC-292, CC-90008 and ibrutinib identified differential functional impact on various immunocyte functions, within and beyond the original identification of B-cell activities regulated by Btk. Clinical inflammatory disease indications for these Btk inhibitors would therefore need to be differentially assessed to match the relative importance of particular disease mechanisms to the differential activities beyond Btk. B-cell antibody production, T-cell proliferation and cytokine production, NK cell function, and myeloid and osteoclast function vary significantly among the three inhibitors with the only common features being basophil degranulation and osteoclast function.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/immunoprofiling-of-brutons-tyrosine-kinase-btktec-family-kinase-inhibitors-indicate-activities-beyond-btk-in-immunocyte-function/