The Selective Phosphoinoside-3-Kinase p110δ Inhibitor IPI-3063 Potently Suppresses B Cell Survival, Proliferation, and Differentiation.

Honyin Chiu,David A Fruman,Karen Mcgovern,Phuongthao Nguyen,Jeffery L Kutok,Erin E Brophy,Annie Mai,Sharmila Mallya,Jonathan P Dinitto,Leandra V Jackson,David G Winkler

doi:10.3389/fimmu.2017.00747

Honyin Chiu, David A Fruman + Show 9 more

Open Access

https://doi.org/10.3389/fimmu.2017.00747

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Abstract

The class I phosphoinoside-3-kinases (PI3Ks) are important enzymes that relay signals from cell surface receptors to downstream mediators driving cellular functions. Elevated PI3K signaling is found in B cell malignancies and lymphocytes of patients with autoimmune disease. The p110δ catalytic isoform of PI3K is a rational target since it is critical for B lymphocyte development, survival, activation, and differentiation. In addition, activating mutations in PIK3CD encoding p110δ cause a human immunodeficiency known as activated PI3K delta syndrome. Currently, idelalisib is the only selective p110δ inhibitor that has been FDA approved to treat certain B cell malignancies. p110δ inhibitors can suppress autoantibody production in mouse models, but limited clinical trials in human autoimmunity have been performed with PI3K inhibitors to date. Thus, there is a need for additional tools to understand the effect of pharmacological inhibition of PI3K isoforms in lymphocytes. In this study, we tested the effects of a potent and selective p110δ inhibitor, IPI-3063, in assays of B cell function. We found that IPI-3063 potently reduced mouse B cell proliferation, survival, and plasmablast differentiation while increasing antibody class switching to IgG1, almost to the same degree as a pan-PI3K inhibitor. Similarly, IPI-3063 potently inhibited human B cell proliferation in vitro. The p110γ isoform has partially overlapping roles with p110δ in B cell development, but little is known about its role in B cell function. We found that the p110γ inhibitor AS-252424 had no significant impact on B cell responses. A novel dual p110δ/γ inhibitor, IPI-443, had comparable effects to p110δ inhibition alone. These findings show that p110δ is the dominant isoform mediating B cell responses and establish that IPI-3063 is a highly potent molecule useful for studying p110δ function in immune cells.

Highlights

Phosphoinoside-3-kinase (PI3K) enzymes are lipid kinases that produce 3′-phosphorylated phosphoinositides, which act as second messengers to relay signals from cell-surface receptors to downstream mediators
Activating mutations in PIK3CD encoding p110δ cause a human immunodeficiency known as activated PI3K delta syndrome (APDS), which is associated with chronically activated lymphocytes that undergo apoptosis or senescence [6, 7]
We assessed the effects of both IPI-3063 and IPI-443 on PI3K activity in mouse primary B cells stimulated with αIgM + IL-4, by evaluating phosphorylation of AKT at the serine 473 residue (Figures 1A,C) as well as the phosphorylation of ERK1/2 on Thr202/Tyr204 residues (Figures 1B,C)

Summary

Introduction

Phosphoinoside-3-kinase (PI3K) enzymes are lipid kinases that produce 3′-phosphorylated phosphoinositides, which act as second messengers to relay signals from cell-surface receptors to downstream mediators. The class I PI3Ks produce phosphatidylinositol-3,4,5-triphosphate (PIP3) that recruits cytoplasmic proteins to the membrane to drive downstream signaling responses. Class IA PI3Ks are heterodimers composed of two subunits, a regulatory subunit (p85) and one of three catalytic subunits (p110α, p110β, p110δ). The class IB PI3K is composed of unique regulatory subunits (p101 or p84) with the catalytic subunit p110γ. Whereas p110α and p110β are ubiquitously expressed, p110δ and p110γ expression is mainly restricted to leukocytes. The importance of PI3K activation in various cancers has led to development of many small molecule PI3K inhibitors targeting individual isoforms or subgroups [1]

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