ACR Meeting Abstracts

ACR Meeting Abstracts

Abstract Number: 2326

Discovery of a Highly Potent, Selective Reversible Covalent  Inhibitor of JAK3 Kinase

Ronald J. Hill1, Angelina Bisconte1, J. Michael Bradshaw1, Ken Brameld2, Eun Ok Kim1, Xiaoyan Li2, Tim Owens2, Erik Verner2 and David M. Goldstein2, 1Biology, Principia Biopharma, South San Francisco, CA, 2Chemistry, Principia Biopharma

Meeting: 2012 ACR/ARHP Annual Meeting

Keywords: , , ,

Session Information

Title: T-cell Biology and Targets in Autoimmune Disease

Session Type: Abstract Submissions (ACR)

Background/Purpose: Targeting of the JAK-STAT pathway has been shown to be efficacious for treatment of patients with rheumatoid arthritis through the successful use of pan-JAK inhibitors in clinical trials. To date, lack of selective JAK3 inhibitors has hindered the assessment of the role of JAK3 in autoimmune disorders. A JAK3 inhibitor has the potential benefit of alleviating undesirable side effects of JAK1 and JAK2 inhibition such as dyslipidemia and suppression of hematopoiesis, respectively. A new approach is presented to achieve potent, selective and durable inhibition of JAK3 by application of Principia’s reversible covalent platform targeting a cysteine residue in the active site of JAK3 that is absent from other JAK family members. Ability of these inhibitors to block IL-2 and IL-4 signaling is presented.

Methods: Enzyme potencies were measured using the Caliper platform at Nanosyn Inc. (Santa Clara, CA). IL-2 stimulated phospho-STAT5 was measured in Ficoll separated human peripheral blood mononuclear cells (PBMCs) by flow cytometry. IL-4 stimulated STAT6 activation was measured in Ramos B cells based on a STAT6 reporter assay (Invitrogen, Madison, WI). Kinase profiling was performed at DiscoveRx (San Diego, CA).

Results: We have developed a series of molecules that are highly potent and selective for JAK3. Compound 1 inhibited JAK3 enzymatic activity with an IC50 of 0.5 ± 0.3 nM, but not JAK1, JAK2, or TYK2 up to a concentration of 5 uM.  The selectivity among other kinases within the Cys sub-family was also high with no inhibition exceeding 60% at 1 uM. Profiling against a panel of 442 kinases confirmed the exceptional selectivity of the series. Compound 1 forms a durable yet reversible Cys interaction with JAK3 in biochemical assays with a dissociation half-life of 9 hours.

In cell-based assays, Compound 1 completely inhibited IL-2 stimulated STAT5 phosphorylation (IC50 = 206 ± 11 nM) in hPBMCs, IL-4 stimulated STAT6 phosphorylation (IC50 = 58 ± 10 nM) in Ramos B cells and IL-2 driven IFNgamma secretion (IC50 = 248 ± 8 nM) in hPBMCs. IL-6 stimulated STAT3 phosphorylation was not inhibited up to 5 uM indicating complete cellular selectivity for JAK3 over JAK1. In addition, NFAT activation downstream of TCR stimulation in Jurkat T cells was not blocked.

Conclusion: Compound 1 is a potent, selective and durable inhibitor of JAK3 and has the potential to be an efficacious treatment for rheumatoid arthritis or other T cell driven diseases with a potential for differentiation from pan-JAK inhibitors.

Disclosure:

R. J. Hill,

Principia Biopharma,

3;

A. Bisconte,

Principia Biopharma,

3;

J. M. Bradshaw,

Principia Biopharma,

3;

K. Brameld,

Principia Biopharma,

3;

E. O. Kim,

Principia Biopharma,

3;

X. Li,

Principia Biopharma,

3;

T. Owens,

Principia Biopharma,

3;

E. Verner,

Principia Biopharma,

3;

D. M. Goldstein,

Principia Biopharma,

3.

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