Pharmacological properties of a novel PI3Kd inhibitor, DS-1515

Introduction: Phosphoinositide 3-kinase (PI3K) is a member of lipid kinase families that specifically phosphorylates phosphoinositides at the D3 position of the inositide ring. PI3Kδ is expressed in key cell types relevant to respiratory diseases including T cells, B cells and mast cells. Pharmacological and genetic intervention of PI3Kδ have revealed its roles in differentiation, proliferation and cytokine production of inflammatory cells. Based on such evidences, PI3Kδ is an attractive drug target candidate for respiratory disease including asthma. Objective: The objective of this study is to characterize DS-1515 in vitro as a selective PI3Kδ inhibitor. Methods: The in vitro inhibitory activity of DS-1515 for each PI3K isoform (α, β, γ, and δ) was measured in a cell free assay system. The inhibitory activity of PI3K in cells were detected by AKT phosphorylation by western blotting, flow cytometry, and/or mass cytometry. The inhibitory activity to cytokine production from PBMCs stimulated with phytohemagglutinin (PHA) was measured by ELISA. Results: DS-1515 inhibited human PI3K α, β, γ, and δ enzyme with an IC50 of 4931 nM, >10000 nM, 1318 nM, and 5.9 nM respectively. DS-1515 inhibited AKT phophorylation in Raji cell (PI3Kδ dominant cell) but not in MCF7 cell and T-47D cell (PI3K α/β dominant cells). DS-1515 inhibited PHA-induced or anti-CD3/CD28 antibody-induced AKT phosphorylation in PBMCs (B and T cells). DS-1515 also suppressed Th1/2/17 cytokine (IFN-γ/IL-5/IL-17) production from PBMCs with an IC50 of 23.08, 8.13, and 19.23 nM respectively. Conclusion: DS-1515 is a highly selective PI3Kδ inhibitor with the inhibitory activity to cytokine production.