Introduction/Rationale: STAT6 is a transcription factor downstream of IL-4 and IL-13 signaling that acts as a key driver of type 2 inflammation, which is associated with atopic dermatitis and asthma. Inhibition of the IL-4/IL-13 pathway is clinically validated for treatment of allergic diseases. Our aim is to develop an oral small molecule that selectively inhibits activation of STAT6 for the treatment of allergic diseases.
Methods: Binding affinity and mechanism of action were determined using SPR and a nuclear translocation assay, respectively. Compound potency against human STAT6 was assessed in PBMC by measuring phosphorylated STAT6. Selectivity was examined utilizing STAT SH2 scan, KINOMEscan, and cellular assays for STATs 1-5. Inhibition of Th2 biomarkers, TARC and periostin, and cellular proliferation were assessed in cellular assays. Ex vivo target engagement was measured in mouse whole blood.
Results: EPS-3903 is an orally bioavailable allosteric inhibitor of STAT6 with strong binding affinity (Kd = 0.42 nM) that exhibited robust selectivity against other STAT family members, as well as a broad kinase panel. EPS-3903 suppressed STAT6 nuclear translocation in the human lung cell line A549 with an IC50 of 14 nM. In PBMC, EPS-3903 inhibited IL4-induced STAT6 phosphorylation and TARC production with IC50s of 5 and 11 nM, respectively. EPS-3903 potently prevented IL-13-induced periostin production in primary bronchial cells and STAT6-mediated proliferation in human TF-1 erythroblast cells with IC50s of 3.3 and 7.5 nM, respectively. In mouse whole blood, EPS-3903 suppressed pSTAT6 by >90% for 24 h.
Conclusion: EPS-3903 is a potent and selective allosteric inhibitor of STAT6 and demonstrated effectiveness in preventing STAT6 activation and downstream Th2 biomarker production. EPS-3903 suppressed STAT6 activation in vivo by >90% for 24 h. EPS-3903 may offer an oral therapeutic potential for treating allergic diseases including asthma and atopic dermatitis.
