Background/Purpose: Spleen tyrosine kinase (SYK) and Janus kinase (JAK) mediate signaling in immune cells and hematopoietic cells important for the initiation and progression of rheumatoid arthritis (RA). JAK inhibitors have demonstrated clinical efficacy in RA and exert their biological activity principally by blockade of proinflammatory cytokine signaling. ASN002 is a novel potent dual inhibitor of SYK and JAK kinases, currently in clinical development for auto-immune (atopic dermatitis) and oncology indications. To date, more than 70 patients and subjects have received single or multiple oral, daily doses of ASN002. Here we demonstrate that ASN002 inhibits both SYK and JAK signaling pathways and cellular functions in both immune cells and osteoclasts; and is efficacious in both early and late stage rat models of collagen induced arthritis (CIA).

Methods: Cell lines, osteoclast progenitors, fresh human peripheral blood mononuclear cells (PBMCs) or isolated immune cells were cultured with various stimulating agents and inhibition of JAK or SYK mediated cell signaling or functions were measured by flow cytometry, proliferation assays or cytokine production. Osteoclast differentiation and bone resorption were assessed using the tartrate resistant acid phosphatase (TRAP) activity assay and collagen type 1c telopeptide (CTx) release by ELISA. ASN002, was tested for in vivo efficacy in an early and late stage rat CIA model. Dosing was initiated at either Day 14 (early model) or Day 18 (late model). Efficacy measures were arthritic scores, edema, and histopathology and radiographic assessments of the ankles.

Results: ASN002 is a potent inhibitor of SYK, JAK1, JAK2, JAK3 and TYK2 kinases with IC50 values of 5, 46, 4, 11, and 8 nM in biochemical assays respectively. In mechanistic cell-based studies, ASN002 strongly suppressed the SYK and JAK family kinase signaling pathways as measured by phosphorylation of LAT (a SYK substrate), and phosphorylation of signal transducers and activators of transcription (STAT). Cytokine induced phosphorylation of STAT in fresh human PBMCs was also suppressed. Human T and B cell proliferation and other cellular functions such as cytokine release were inhibited by AN002 at nM levels. ASN002 also demonstrated nM level inhibition of osteoclast progenitor differentiation and bone resorption by osteoclasts. In the rat CIA model, ASN002 showed dose-dependent efficacy (3-30 mg/kg/day) and significantly reduced arthritic scores and paw edema in both early and late stage models. ASN002 showed a greater decrease in histopathology scores (82%) at 10 mg/kg, than either Tofacitinib (39%) or Fostamatinib (37%) alone.

Conclusion: ASN002 is an orally bioavailable, potent dual inhibitor of SYK and JAK kinases. It effectively inhibits SYK and JAK mediated cell signaling and functions. ASN002 significantly improved all efficacy measures in the rat CIA model, at lower exposures than those achieved in human studies to date. These data support the development of ASN002 for the treatment of autoimmune and inflammatory diseases, including rheumatoid arthritis and psoriatic arthritis. A Phase Ib study in patients with atopic dermatitis is in progress.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/asn002-a-novel-dual-sykjak-inhibitor-demonstrates-strong-efficacy-in-a-rat-model-of-collagen-induced-arthritis/