PRT062070: A Dual Syk/JAK Inhibitor with Potent Immune Regulatory Capacity in Rodent Models of Inflammation and Cancer.

Abstract 2764

The heterogeneity and severity of certain autoimmune diseases and B cell malignancies warrant simultaneous targeting of multiple disease-relevant pathways. Simultaneous inhibition of Syk and JAK represents such a strategy, and may have several benefits relative to selective kinase inhibition, such as gaining control over a broader array of disease etiologies, reducing probability of selection for alternate disease mechanisms, and the potential that an overall lower level suppression of multiple targets may be sufficient to modulate disease activity. To this end, we provide an update on the pre-clinical development of our lead dual Syk/JAK inhibitor; PRT062070.

Cellular assays demonstrate an impressive selectivity profile, with potency against Syk, JAK1, and JAK3 primarily maintained in whole blood assays. B cell antigen-receptor mediated cellular activation and FcεRI-mediated basophil degranulation were inhibited in whole blood by PRT062070 with Syk IC₅₀'s of 0.1μM and 0.23μM, respectively. PRT062070 preferentially inhibited JAK1 and JAK3 dependent cytokine mediated signaling and functional responses in various cell types. IL2 mediated STAT5 Y694 was inhibited with an IC₅₀ of 0.27μM, while IL4 mediated signaling to STAT6 Y641 and functional responses in B cells and monocytes, namely CD69, CD25, and CD23 up-regulation, were inhibited with IC₅₀'s within the range of 0.11μM to 0.57μM. PRT062070 also demonstrated potency in suppressing FcγR mediated neutrophil oxidative burst. Conversely, PRT062070 did not inhibit T cell antigen receptor or PMA-mediated signaling to ERK Y204, or T cell receptor mediated Lck activity as measured by ZAP70 Y319, providing evidence for selectivity of action. At 4uM (the highest concentration tested) only 20% inhibition against GM-CSF mediated STAT5 phophorylation in monocytes was observed, suggesting limited inhibition of JAK2. In tumor cell viability assays, several non-Hodgkins lymphoma cell lines demonstrated enhanced sensitivity to dual Syk/JAK inhibition relative to JAK inhibition alone.

Following oral dosing in rodents, PRT062070 suppressed inflammation in the mouse collagen antibody induced arthritis model, prevented splenomegaly in mice stimulated in vivo with BCR specific antibody, and diminished progression of a B cell non-Hodgkins lymphoma cell line in xenograft mice. Using the rat collagen induced arthritis treatment model, we report a dose-dependent inhibition of inflammation with complete suppression of disease progression at 0.3μM. The advantages of dually targeting Syk and JAK for inflammation and B cell cancers will be discussed, as well as plans for initial human studies.