CBP30, a selective CBP/p300 bromodomain inhibitor, suppresses human Th17 responses.

Th17 responses are critical to a variety of human autoimmune diseases, and therapeutic targeting with monoclonal antibodies against IL-17 and IL-23 has shown considerable promise. Here, we report data to support selective bromodomain blockade of the transcriptional coactivators CBP (CREB binding protein) and p300 as an alternative approach to inhibit human Th17 responses. We show that CBP30 has marked molecular specificity for the bromodomains of CBP and p300, compared with 43 other bromodomains. In unbiased cellular testing on a diverse panel of cultured primary human cells, CBP30 reduced immune cell production of IL-17A and other proinflammatory cytokines. CBP30 also inhibited IL-17A secretion by Th17 cells from healthy donors and patients with ankylosing spondylitis and psoriatic arthritis. Transcriptional profiling of human T cells after CBP30 treatment showed a much more restricted effect on gene expression than that observed with the pan-BET (bromo and extraterminal domain protein family) bromodomain inhibitor JQ1. This selective targeting of the CBP/p300 bromodomain by CBP30 will potentially lead to fewer side effects than with the broadly acting epigenetic inhibitors currently in clinical trials.

RN486, a selective Bruton's tyrosine kinase inhibitor, abrogates immune hypersensitivity responses and arthritis in rodents.

Genetic mutation and pharmacological inhibition of Bruton's tyrosine kinase (Btk) both have been shown to prevent the development of collagen-induced arthritis (CIA) in mice, providing a rationale for the development of Btk inhibitors for treating rheumatoid arthritis (RA). In the present study, we characterized a novel Btk inhibitor, 6-cyclopropyl-8-fluoro-2-(2-hydroxymethyl-3-{1-methyl-5-[5-(4-methyl-piperazin-1-yl)-pyridin-2-ylamino]-6-oxo-1,6-dihydro-pyridin-3-yl}-phenyl)-2H-isoquinolin-1-one (RN486), in vitro and in rodent models of immune hypersensitivity and arthritis. We demonstrated that RN486 not only potently and selectively inhibited the Btk enzyme, but also displayed functional activities in human cell-based assays in multiple cell types, blocking Fcε receptor cross-linking-induced degranulation in mast cells (IC(50) = 2.9 nM), Fcγ receptor engagement-mediated tumor necrosis factor α production in monocytes (IC(50) = 7.0 nM), and B cell antigen receptor-induced expression of an activation marker, CD69, in B cells in whole blood (IC(50) = 21.0 nM). RN486 displayed similar functional activities in rodent models, effectively preventing type I and type III hypersensitivity responses. More importantly, RN486 produced robust anti-inflammatory and bone-protective effects in mouse CIA and rat adjuvant-induced arthritis (AIA) models. In the AIA model, RN486 inhibited both joint and systemic inflammation either alone or in combination with methotrexate, reducing both paw swelling and inflammatory markers in the blood. Together, our findings not only demonstrate that Btk plays an essential and conserved role in regulating immunoreceptor-mediated immune responses in both humans and rodents, but also provide evidence and mechanistic insights to support the development of selective Btk inhibitors as small-molecule disease-modifying drugs for RA and potentially other autoimmune diseases.