Background/Purpose:  CC-292 and CC-90008 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. Despite similar inhibitory potencies towards Btk enzyme inhibition, CC-292 and CC-90008 differ significantly in their impact on B and T cell, basophil, monocyte, and mDC functions. The objective of this study was to compare the efficacy of two covalent modifiers of Btk/Tec family kinases with different, but overlapping in vitro functional immunoprofiles in the MRL/lpr model of SLE and determine which in vitro immunocyte functions best translate to pathological endpoints.

Methods:  Immunoprofiling of B cell function was measured by 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, and cytokine production. CD8 T cell and NK function was measured by degranulation assays. Monocyte/macrophage and basophil activity was measured by Fcγ Receptor-mediated TNFα production and FcεR-mediated degranulation, respectively. Osteoclast and dendritic cell effects were each assessed by differentiation endpoints from precursor cells. Pathology in the MRL/lpr SLE model was assessed by body, spleen, and lymph node weight gain, dsDNA and ANA autoantibody titers, skin lesions, and kidney function (proteinurea) and lesions (histological assessment).

Results:  In vitro, CC-292 and CC-90008 were most similar in their ability to inhibit plasmablast differentiation, antibody secretion, basophil IgE degranulation, T-cell cytokine inhibition, and osteoclastogenesis. Differences were observed in that CC-292 inhibited macrophage Fcγ-induced TNFα, mDC differentiation and weakly inhibited T-cell proliferation, while CC-90008 had no effect on these macrophage and mDC functions and strongly inhibited T cell proliferation. In the MRL/lpr SLE model, CC-292 and CC-90008 both reduced dsDNA and ANA autoantibody titers, proteinurea and kidney pathology. In contrast, CC-90008 inhibited increases in body weight, skin lesions, splenomegaly, and lymphadenopathy, while CC-292 had only partial effects.

Conclusion:  The in vitro immunophenotyping of CC-292 and CC-90008 on immunocyte function had translatable correlates to SLE pathology in the MRL/lpr model. While plasmablast differentiation and antibody production correlated with in vitro B cell measures and in vivo autoantibody and kidney pathologies, the in vitro T-cell functions correlated with splenomegaly, lymphadenopathy, and skin pathology. These results indicate that while BTK and associated antibody and kidney function treat an important part of lupus pathology, activity associated with T-cell inhibition may be required for effects on skin and secondary lymphoid organ pathology.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/translatable-in-vitro-immunocyte-functional-measures-of-cc-292-and-cc-90008-inhibitors-of-the-brutons-tyrosine-kinase-btktec-family-and-the-pathology-observed-in-the-mlrlpr-mouse-model-of-system/