Selective PI3Kδ inhibitors, a review of the patent literature

Pharmacological Properties of 2,4,6-Trihydroxy-3-Geranyl Acetophenone and the Underlying Signaling Pathways: Progress and Prospects

2,4,6-Trihydroxy-3-geranyl acetophenone (tHGA) is a bioactive phloroglucinol compound found in Melicope pteleifolia (Champ. ex Benth.) T.G.Hartley, a medicinal plant vernacularly known as “tenggek burung”. A variety of phytochemicals have been isolated from different parts of the plant including leaves, stems, and roots by using several extraction methods. Specifically, tHGA, a drug-like compound containing phloroglucinol structural core with acyl and geranyl group, has been identified in the methanolic extract of the young leaves. Due to its high nutritional and medicinal values, tHGA has been extensively studied by using various experimental models. These studies have successfully discovered various interesting pharmacological activities of tHGA such as anti-inflammatory, endothelial and epithelial barrier protective, anti-asthmatic, anti-allergic, and anti-cancer. More in-depth investigations later found that these activities were attributable to the modulatory actions exerted by tHGA on specific molecular targets. Despite these findings, the association between the mechanisms and signaling pathways underlying each pharmacological activity remains largely unknown. Also, little is known about the medicinal potentials of tHGA as a drug lead in the current pharmaceutical industry. Therefore, this mini review aims to summarize and relate the pharmacological activities of tHGA in terms of their respective mechanisms of action and signaling pathways in order to present a perspective into the overall modulatory actions exerted by tHGA. Besides that, this mini review will also pinpoint the unexplored potentials of this compound and provide some valuable insights into the potential applications of tHGA which may serve as a guide for the development of modern medication in the future.

PI3Kδ inhibitors for the treatment of cancer: a patent review (2015-present)

Introduction: PI3Kδ is an important subtype of PI3K kinases, which is mainly expressed in leukocytes and plays an important role in the proliferation, differentiation, maturation and self-reaction of B cells. It is an effective target in the treatment of hematological malignancies and autoimmune diseases such as rheumatoid arthritis. Therefore, many pharmaceutical companies and research institutions have focused on the PI3Kδ subtype in an attempt to develop potent and selective PI3Kδ inhibitors.Areas covered: This review aims to provide an overview of the patented selective PI3Kδ inhibitors in treating cancer from 2015 to present.Expert opinion: Due to the importance of PI3Kδ, the development of selective PI3Kδ inhibitors for the treatment of hematoma and autoimmune diseases is expected. On 23 July 2014, the world's first selective PI3Kδ inhibitor, idelalisib, was approved by the FDA for the treatment of CLL, FL and SLL. Moreover, there are still many small molecule selective PI3Kδ inhibitors at different stages of development. The future research effort for development of PI3Kδ inhibitors is to manage the toxicity and lower the side-effects.

Idelalisib inhibits osteoclast differentiation and pre-osteoclast migration by blocking the PI3Kδ-Akt-c-Fos/NFATc1 signaling cascade

Since increased number of osteoclasts could lead to impaired bone structure and low bone mass, which are common characteristics of bone disorders including osteoporosis, the pharmacological inhibition of osteoclast differentiation is one of therapeutic strategies for preventing and/or treating bone disorders and related facture. However, little data are available regarding the functional relevance of phosphoinositide 3-kinase (PI3K) isoforms in the osteoclast differentiation process. To elucidate the functional involvement of PI3Kδ in osteoclastogenesis, here we investigated how osteoclast differentiation was influenced by idelalisib (also called CAL-101), which is p110δ-selective inhibitor approved for the treatment of specific human B cell malignancies. Here, we found that receptor activator of nuclear factor kappa B ligand (RANKL) induced PI3Kδ protein expression, and idelalisib inhibited RANKL-induced osteoclast differentiation. Next, the inhibitory effect of idelalisib on RANKL-induced activation of the Akt-c-Fos/NFATc1 signaling cascade was confirmed by western blot analysis and real-time PCR. Finally, idelalisib inhibited pre-osteoclast migration in the last stage of osteoclast differentiation through down-regulation of the Akt-c-Fos/NFATc1 signaling cascade. It may be possible to expand the clinical use of idelalisib for controlling osteoclast differentiation. Together, the present results contribute to our understanding of the clinical value of PI3Kδ as a druggable target and the efficacy of related therapeutics including osteoclastogenesis.

Conformationally restricted quinazolone derivatives as PI3Kδ-selective inhibitors: the design, synthesis and biological evaluation

A series of structurally novel quinazolone-based PI3Kδ-selective inhibitors were designed and synthesized via the approach of conformational restriction. The majority of them exhibited two-digit to single-digit nanomolar IC50 values against PI3Kδ, along with low micromolar to submicromolar GI50 values against human malignant B-cell line SU-DHL-6. The representative compound, with the most potent PI3Kδ inhibitory activity (IC50 = 6.3 nM) and anti-proliferative activity (GI50 = 0.21 μM) in this series, was further evaluated for its PI3Kδ selectivity, capability to down-regulate PI3K signaling in SU-DHL-6 cells, in vitro metabolic stability, and pharmacokinetic (PK) properties. The experimental results illustrated that this compound, as a promising lead, merits extensive structural optimization for exploring novel PI3Kδ-selective inhibitors as clinical candidates.

Discovery of Potent, Efficient, and Selective Inhibitors of Phosphoinositide 3-Kinase δ through a Deconstruction and Regrowth Approach

A deconstruction of previously reported phosphoinositide 3-kinase δ (PI3Kδ) inhibitors and subsequent regrowth led to the identification of a privileged fragment for PI3Kδ, which was exploited to deliver a potent, efficient, and selective lead series with a novel binding mode observed in the PI3Kδ crystal structure.

Introduction of pyrrolidineoxy or piperidineamino group at the 4-position of quinazoline leading to novel quinazoline-based phosphoinositide 3-kinase delta (PI3Kδ) inhibitors

Phosphoinositide 3-kinase Delta (PI3Kδ) plays a key role in B-cell signal transduction and inhibition of PI3Kδ was confirmed to have clinical benefit in certain types of activation of B-cell malignancies. Herein, we reported a novel series of 4-pyrrolidineoxy or 4-piperidineamino substituted quinazolines, showing potent PI3Kδ inhibitory activities. Among these compounds, 12d, 14b and 14c demonstrated higher potency against PI3Kδ with the half maximal inhibitory concentration (IC50) values of 4.5, 3.0, and 3.9 nM, respectively, which were comparable to idelalisib (IC50 = 2.7 nM). The further PI3K isoforms selectivity evaluation showed that compounds 12d, 14b and 14c have excellent PI3Kδ selectivity over PI3Kα, PI3Kβ, and PI3Kγ. Moreover, compounds 12d, 14b and 14c also displayed different anti-proliferative profiles against a panel of four human B cell lines including Ramos, Raji, RPMI-8226, and SU-DHL-6. The molecular docking simulation indicated several key hydrogen bonding interactions were formed. This study suggests the introduction of pyrrolidineoxy or piperidineamino groups into the 4-position of quinazoline leads to new potent and selective PI3Kδ inhibitors.

LAT is essential for the mast cell stabilising effect of tHGA in IgE-mediated mast cell activation

Mast cells play a central role in the pathogenesis of allergic reaction. Activation of mast cells by antigens is strictly dependent on the influx of extracellular calcium that involves a complex interaction between signalling molecules located within the cells. We have previously reported that tHGA, an active compound originally isolated from a local shrub known as Melicope ptelefolia, prevented IgE-mediated mast cell activation and passive systemic anaphylaxis by suppressing the release of interleukin-4 (IL-4) and tumour necrosis factor (TNF)-α from activated rat basophilic leukaemia (RBL)-2H3 cells. However, the mechanism of action (MOA) as well as the molecular target underlying the mast cell stabilising effect of tHGA has not been previously investigated. In this study, DNP-IgE-sensitised RBL-2H3 cells were pre-treated with tHGA before challenged with DNP-BSA. To dissect the MOA of tHGA in IgE-mediated mast cell activation, the effect of tHGA on the transcription of IL-4 and TNF-α mRNA was determined using Real Time-Polymerase Chain Reaction (qPCR) followed by Calcium Influx Assay to confirm the involvement of calcium in the activation of mast cells. The protein lysates were analysed by using Western Blot to determine the effect of tHGA on various important signalling molecules in the LAT-PLCγ-MAPK and PI3K-NFκB pathways. In order to identify the molecular target of tHGA in IgE-mediated mast cell activation, the LAT and LAT2 genes in RBL-2H3 cells were knocked-down by using RNA interference to establish a LAT/LAT2 competition model. The results showed that tHGA inhibited the transcription of IL-4 and TNF-α as a result of the suppression of calcium influx in activated RBL-2H3 cells. The results from Western Blot revealed that tHGA primarily inhibited the LAT-PLCγ-MAPK pathway with partial inhibition on the PI3K-p65 pathway without affecting Syk. The results from RNAi further demonstrated that tHGA failed to inhibit the release of mediators associated with mast cell degranulation under the LAT/LAT2 competition model in the absence of LAT. Collectively, this study concluded that the molecular target of tHGA could be LAT and may provide a basis for the development of a mast cell stabiliser which targets LAT.

Discovery of a Novel Series of 7-Azaindole Scaffold Derivatives as PI3K Inhibitors with Potent Activity

The phosphoinositide 3-kinase (PI3K) inhibitors potently inhibit the signaling pathway of PI3K/AKT/mTOR, which provides a promising new approach for the molecularly targeted cancer therapy. In this work, a novel series of 7-azaindole scaffold derivatives was discovered by the fragment-based growing strategy. The structure-activity relationship profiles identified that the 7-azaindole scaffold derivatives exhibit potent activity against PI3K at molecular and cellular levels as well as cell proliferation in a panel of human tumor cells.

Identification of a Potent, Selective, and Efficacious Phosphatidylinositol 3-Kinase δ (PI3Kδ) Inhibitor for the Treatment of Immunological Disorders

PI3Kδ plays an important role controlling immune cell function and has therefore been identified as a potential target for the treatment of immunological disorders. This article highlights our work toward the identification of a potent, selective, and efficacious PI3Kδ inhibitor. Through careful SAR, the successful replacement of a polar pyrazole group by a simple chloro or trifluoromethyl group led to improved Caco-2 permeability, reduced Caco-2 efflux, reduced hERG PC activity, and increased selectivity profile while maintaining potency in the CD69 hWB assay. The optimization of the aryl substitution then identified a 4'-CN group that improved the human/rodent correlation in microsomal metabolic stability. Our lead molecule is very potent in PK/PD assays and highly efficacious in a mouse collagen-induced arthritis model.

Discovery of a series of 8-(1-phenylpyrrolidin-2-yl)-6-carboxamide-2-morpholino-4H-chromen-4-one as PI3Kβ/δ inhibitors for the treatment of PTEN-deficient tumours

Attempts to lock the active conformation of compound 4, a PI3Kβ/δ inhibitor (PI3Kβ cell IC₅₀ 0.015μM), led to the discovery of a series of 8-(1-phenylpyrrolidin-2-yl)-6-carboxamide-2-morpholino-4H-chromen-4-ones, which showed high levels of potency and selectivity as PI3Kβ/δ inhibitors. Compound 10 proved exquisitely potent and selective: PI3Kβ cell IC₅₀ 0.0011μM in PTEN null MDA-MB-468 cell and PI3Kδ cell IC₅₀ 0.014μM in Jeko-1 B-cell, and exhibited suitable physical properties for oral administration. In vivo, compound 10 showed profound pharmacodynamic modulation of AKT phosphorylation in a mouse PTEN-null PC3 prostate tumour xenograft after a single oral dose and gave excellent tumour growth inhibition in the same model after chronic oral dosing. Based on these results, compound 10 was selected as one of our PI3Kβ/δ preclinical candidates.

Discovery and Pharmacological Characterization of Novel Quinazoline-Based PI3K Delta-Selective Inhibitors

Inhibition of the lipid kinase PI3Kδ is a promising principle to treat B and T cell driven inflammatory diseases. Using a scaffold deconstruction-reconstruction strategy, we identified 4-aryl quinazolines that were optimized into potent PI3Kδ isoform selective analogues with good pharmacokinetic properties. With compound 11, we illustrate that biochemical PI3Kδ inhibition translates into modulation of isoform-dependent immune cell function (human, rat, and mouse). After oral administration of compound 11 to rats, proximal PD markers are inhibited, and dose-dependent efficacy in a mechanistic plaque forming cell assay could be demonstrated.

The PI3K/Akt/PTEN/mTOR pathway: a fruitful target for inducing cell death in rheumatoid arthritis?

PI3K/Akt/mTOR signaling regulates diverse cellular processes. Abnormal PI3K/Akt/mTOR signaling is a characteristic feature of cancer. As such inhibition of PI3K/Akt/mTOR signaling using small molecule inhibitors has been a focus of recently developed anticancer drugs. Rheumatoid arthritis and psoriatic arthritis are autoimmune-mediated inflammatory diseases. PI3K signaling could now be targeted to determine its contribution to rheumatoid and psoriatic arthritis where deregulated proliferation and aberrant survival of activated immune cells, macrophages, monocytes, dendritic cells and synovial fibroblasts significantly overlap with abnormal growth of cancer cells. The results of some recent studies in psoriatic arthritis using PI3K signaling inhibitors suggests that small molecule inhibitor strategies directed at PI3K signaling may be a useful future therapy for immune-mediated arthritis.

Discovery of a series of 8-(2,3-dihydro-1,4-benzoxazin-4-ylmethyl)-2-morpholino-4-oxo-chromene-6-carboxamides as PI3Kβ/δ inhibitors for the treatment of PTEN-deficient tumours

We report the discovery and optimisation of a series of 8-(2,3-dihydro-1,4-benzoxazin-4-ylmethyl)-2-morpholino-4-oxo-chromene-6-carboxamides, leading to compound 16 as a potent and selective PI3Kβ/δ inhibitor: PI3Kβ cell IC50 0.012 μM (in PTEN null MDA-MB-468 cell) and PI3Kδ cell IC50 0.047 μM (in Jeko-1 B-cell), with good pharmacokinetics and physical properties. In vivo, 16 showed profound pharmacodynamic modulation of AKT phosphorylation in a mouse PTEN-deficient PC3 prostate tumour xenograft after a single oral dose and gave excellent tumour growth inhibition in the same model after chronic oral dosing. Compound 16 was selected as a preclinical candidate for the treatment of PTEN-deficient tumours.

Evaluation of WO2014075392 and WO2014075393, Merck's first PI3Kδ inhibitor filings

INTRODUCTION

There is considerable interest in the development of selective PI3Kδ inhibitors for the treatment of inflammatory diseases and haematological cancers. Merck has no previous filings in this field but licensed Exelixis' programme, including its lead compound XL-499, in December 2011.

AREAS COVERED

Both applications claim novel 9-alkyl-6,8-disubstituted purine derivatives as selective δ inhibitors for the treatment of asthma, obstructive airways disease, arthritis and cancer. The two applications differ in the range of exemplified substituents, the first focusing on 8-heteroaryl substituted purines, the second on 8-aminopurine derivatives. Many of the exemplified compounds have IC50 values < 10 nM against PI3Kδ with a number having sub-nanomolar potency.

EXPERT OPINION

The compounds appear to be XL-499 derivatives, some of which are more potent than XL-499. The compounds claimed by Merck are some of the most potent PI3Kδ inhibitors yet described but it is unclear whether a development compound has been identified.

Idelalisib- a PI3Kδ targeting agent for B-cell malignancies

Idelalisib, the first in-class phosphotidlyinositol 3-kinase delta (PI3Kδ) inhibitor, was approved by the US Food and Drug Administration in July 2014. It simultaneously received breakthrough therapy designation in combination with rituximab for the treatment of relapsed chronic lymphocytic leukemia (CLL) as well as accelerated approval as monotherapy for the treatment of relapsed follicular lymphoma and relapsed small lymphocytic lymphoma. In a pivotal phase III study of 220 patients with relapsed CLL, the overall response rate of patients who received rituximab plus idelalisib was 81%. The median progression-free survival (PFS) was 5 months with rituximab plus placebo group, but was not reached in the idelalisib arm. At 24 weeks, the PFS in patients receiving idelalisib was 93%. In a phase II trial of 125 patients with relapsed or refractory indolent non-Hodgkin lymphoma who received idelalisib 150 mg twice daily, the response rate was 57%. Complete response was seen in 6% of patients. The median duration of response was 12.5 months, and median PFS was 11 months. Idelalisib is a promising new therapy for relapsed indolent B-cell malignancies.

Evaluation of WO2013116562A, an orally active PI3Kδ inhibitor for the treatment of asthma

(S)-4-amino-6-((1-(5-chloro-4-oxo-3-phenyl-3,4-dihydroquinazolin-2-yl)ethyl)amino)pyrimidine-5-carbonitrile is claimed as a highly selective, PI3Kδ inhibitor. It is claimed to be useful in the treatment of asthma and appears intended for oral administration. It is shown to be well absorbed after oral administration and to have reasonable metabolic stability.

Evaluation of WO2013136076: two crystalline forms of the phosphatidylinositol 3-kinase-δ inhibitor RV-1729

This application claims two crystalline forms and inhaled formulations of a the selective phosphatidylinositol 3-kinase-δ inhibitor (PI3Kδ) inhibitor 6-(2-((4-amino-3-(3-hydroxyphenyl)-1H-pyrazolo[3,4-d]pyrimidin-1-yl)methyl)-3-(2-chlorobenzyl)-4-oxo-3,4-dihydroquinazolin-5-yl)-N, N-bis(2-methoxyethyl)hex-5-ynamide. These formulations are claimed to be useful in the treatment of respiratory diseases including asthma and chronic obstructive pulmonary disease.

Follicular T-helper cell recruitment governed by bystander B cells and ICOS-driven motility

Germinal centres support antibody affinity maturation and memory formation. Follicular T-helper cells promote proliferation and differentiation of antigen-specific B cells inside the follicle. A genetic deficiency in the inducible co-stimulator (ICOS), a classic CD28 family co-stimulatory molecule highly expressed by follicular T-helper cells, causes profound germinal centre defects, leading to the view that ICOS specifically co-stimulates the follicular T-helper cell differentiation program. Here we show that ICOS directly controls follicular recruitment of activated T-helper cells in mice. This effect is independent from ICOS ligand (ICOSL)-mediated co-stimulation provided by antigen-presenting dendritic cells or cognate B cells, and does not rely on Bcl6-mediated programming as an intermediate step. Instead, it requires ICOSL expression by follicular bystander B cells, which do not present cognate antigen to T-helper cells but collectively form an ICOS-engaging field. Dynamic imaging reveals ICOS engagement drives coordinated pseudopod formation and promotes persistent T-cell migration at the border between the T-cell zone and the B-cell follicle in vivo. When follicular bystander B cells cannot express ICOSL, otherwise competent T-helper cells fail to develop into follicular T-helper cells normally, and fail to promote optimal germinal centre responses. These results demonstrate a co-stimulation-independent function of ICOS, uncover a key role for bystander B cells in promoting the development of follicular T-helper cells, and reveal unsuspected sophistication in dynamic T-cell positioning in vivo.

Phosphoinositide 3-kinase α inhibitors: a patent review

INTRODUCTION

The alpha isoform of the class 1A family of phosphatidylinositol 3-kinases (PI3Kα) has been extensively studied and exploited as a target for cancer drugs. A large number of compounds, from a wide variety of structural scaffolds, are in development. There is an ongoing debate about the desirability for selectivity between PI3Kα and the other isoforms.

AREAS COVERED

The article briefly outlines the nature and role of the class 1A PI3K in cell signalling and provides a table of representative inhibitors of these enzymes that have proceeded to clinical trial, with literature data on their isoform selectivity. It covers the published patent literature from 2011 to 2012 (search completed in December 2012), with a particular focus on compounds with a level of selective inhibition of PI3Kα. In most cases, representative examples of claimed compounds and data on their inhibitory effects are provided.

EXPERT OPINION

Features of the development of PI3K inhibitors to date have been the plasticity of the enzymes, which possess binding sites for a bewildering number of small molecule scaffolds, and the need to determine the optimal patterns of selectivity between both the PI3K isoforms and the related downstream serine/threonine kinase mammalian target of rapamycin (mTOR) for therapeutic effect. Both themes are apparent in the recent patents reviewed here, with a wide variety of drug types, including variations on existing scaffolds and completely new ones, being evident. While many of these are dual PI3K/mTOR inhibitors, the PI3Kα-selective pyrido[2,3-b]pyrazine heterocycles reported by Intellikine and the (thiazolyl)pyrrolidinecarboxamides of Novartis are of particular interest.

p110δ PI3 kinase pathway: emerging roles in cancer

Class IA PI3Ks consists of three isoforms of the p110 catalytic subunit designated p110α, p110β, and p110δ which are encoded by three separate genes. Gain-of-function mutations on PIK3CA gene encoding for p110α isoform have been detected in a wide variety of human cancers whereas no somatic mutations of genes encoding for p110β or p110δ have been reported. Unlike p110α and p110β which are ubiquitously expressed, p110δ is highly enriched in leukocytes and thus the p110δ PI3K pathway has attracted more attention for its involvement in immune disorders. However, findings have been accumulated showing that the p110δ PI3K plays a seminal role in the development and progression of some hematologic malignancies. A wealth of knowledge has come from studies showing the central role of p110δ PI3K in B-cell functions and B-cell malignancies. Further data have documented that wild-type p110δ becomes oncogenic when overexpressed in cell culture models and that p110δ is the predominant isoform expressed in some human solid tumor cells playing a prominent role in these cells. Genetic inactivation of p110δ in mice models and highly-selective inhibitors of p110δ have demonstrated an important role of this isoform in differentiation, growth, survival, motility, and morphology with the inositol phosphatase PTEN to play a critical role in p110δ signaling. In this review, we summarize our understanding of the p110δ PI3K signaling pathway in hematopoietic cells and malignancies, we highlight the evidence showing the oncogenic potential of p110δ in cells of non-hematopoietic origin and we discuss perspectives for potential novel roles of p110δ PI3K in cancer.

Inhibition of PI3K signaling spurs new therapeutic opportunities in inflammatory/autoimmune diseases and hematological malignancies

The phosphoinositide 3-kinase/mammalian target of rapamycin/protein kinase B (PI3K/mTOR/Akt) signaling pathway is central to a plethora of cellular mechanisms in a wide variety of cells including leukocytes. Perturbation of this signaling cascade is implicated in inflammatory and autoimmune disorders as well as hematological malignancies. Proteins within the PI3K/mTOR/Akt pathway therefore represent attractive targets for therapeutic intervention. There has been a remarkable evolution of PI3K inhibitors in the past 20 years from the early chemical tool compounds to drugs that are showing promise as anticancer agents in clinical trials. The use of animal models and pharmacological tools has expanded our knowledge about the contribution of individual class I PI3K isoforms to immune cell function. In addition, class II and III PI3K isoforms are emerging as nonredundant regulators of immune cell signaling revealing potentially novel targets for disease treatment. Further complexity is added to the PI3K/mTOR/Akt pathway by a number of novel signaling inputs and feedback mechanisms. These can present either caveats or opportunities for novel drug targets. Here, we consider recent advances in 1) our understanding of the contribution of individual PI3K isoforms to immune cell function and their relevance to inflammatory/autoimmune diseases as well as lymphoma and 2) development of small molecules with which to inhibit the PI3K pathway. We also consider whether manipulating other proximal elements of the PI3K signaling cascade (such as class II and III PI3Ks or lipid phosphatases) are likely to be successful in fighting off different immune diseases.

The Therapeutic Potential for PI3K Inhibitors in Autoimmune Rheumatic Diseases

The class 1 PI3Ks are lipid kinases with key roles in cell surface receptor-triggered signal transduction pathways. Two isoforms of the catalytic subunits, p110γ and p110δ, are enriched in leucocytes in which they promote activation, cellular growth, proliferation, differentiation and survival through the generation of the second messenger PIP3. Genetic inactivation or pharmaceutical inhibition of these PI3K isoforms in mice result in impaired immune responses and reduced susceptibility to autoimmune and inflammatory conditions. We review the PI3K signal transduction pathways and the effects of inhibition of p110γ and/or p110δ on innate and adaptive immunity. Focusing on rheumatoid arthritis and systemic lupus erythematosus we discuss the preclinical evidence and prospects for small molecule inhibitors of p110γ and/or p110δ in autoimmune disease.

Signal transduction via the T cell antigen receptor in naïve and effector/memory T cells

T cells play an indispensable role in immune defense against infectious agents, but can also be pathogenic. These T cells develop in the thymus, are exported into the periphery as naïve cells and participate in immune responses. Upon recognition of antigen, they are activated and differentiate into effector and memory T cells. While effector T cells carry out the function of the immune response, memory T cells can last up to the life time of the individual, and are activated by subsequent antigenic exposure. Throughout this life cycle, the T cell uses the same receptor for antigen, the T cell Receptor, a complex multi-subunit receptor. Recognition of antigen presented by peptide/MHC complexes on antigen presenting cells unleashes signaling pathways that control T cell activation at each stage. In this review, we discuss the signals regulated by the T cell receptor in naïve and effector/memory T cells.

Selective inhibitors of phosphoinositide 3-kinase delta: modulators of B-cell function with potential for treating autoimmune inflammatory diseases and B-cell malignancies

The delta isoform of the p110 catalytic subunit (p110δ) of phosphoinositide 3-kinase is expressed primarily in hematopoietic cells and plays an essential role in B-cell development and function. Studies employing mice lacking a functional p110δ protein, as well as the use of highly-selective chemical inhibitors of p110δ, have revealed that signaling via p110δ-containing PI3K complexes (PI3Kδ) is critical for B-cell survival, migration, and activation, functioning downstream of key receptors on B cells including the B-cell antigen receptor, chemokine receptors, pro-survival receptors such as BAFF-R and the IL-4 receptor, and co-stimulatory receptors such as CD40 and Toll-like receptors (TLRs). Similarly, this PI3K isoform plays a key role in the survival, proliferation, and dissemination of B-cell lymphomas. Herein we summarize studies showing that these processes can be inhibited in vitro and in vivo by small molecule inhibitors of p110δ enzymatic activity, and that these p110δ inhibitors have shown efficacy in clinical trials for the treatment of several types of B-cell malignancies including chronic lymphocytic leukemia (CLL) and non-Hodgkin lymphoma (NHL). PI3Kδ also plays a critical role in the activation, proliferation, and tissue homing of self-reactive B cells that contribute to autoimmune diseases, in particular innate-like B-cell populations such as marginal zone (MZ) B cells and B-1 cells that have been strongly linked to autoimmunity. We discuss the potential utility of p110δ inhibitors, either alone or in combination with B-cell depletion, for treating autoimmune diseases such as lupus, rheumatoid arthritis, and type 1 diabetes. Because PI3Kδ plays a major role in both B-cell-mediated autoimmune inflammation and B-cell malignancies, PI3Kδ inhibitors may represent a promising therapeutic approach for treating these diseases.

Does the PI3K pathway promote or antagonize regulatory T cell development and function?

Regulatory T cells (Tregs) prevent autoimmunity and inflammation by suppressing the activation of other T cells and antigen presenting cells. The role of phosphoinositide 3-kinase (PI3K) signaling in Treg is controversial. Some studies suggest that inhibition of the PI3K pathway is essential for the development of Tregs whereas other studies have shown reduced Treg numbers and function when PI3K activity is suppressed. Here we attempt to reconcile the different studies that have explored PI3K and the downstream effectors Akt, Foxo, and mTOR in regulatory T cell development and function and discuss the implications for health and therapeutic intervention.

Pharmacological targeting of phosphoinositide lipid kinases and phosphatases in the immune system: success, disappointment, and new opportunities

The predominant expression of the γ and δ isoforms of PI3K in cells of hematopoietic lineage prompted speculation that inhibitors of these isoforms could offer opportunities for selective targeting of PI3K in the immune system in a range of immune-related pathologies. While there has been some success in developing PI3Kδ inhibitors, progress in developing selective inhibitors of PI3Kγ has been rather disappointing. This has prompted the search for alternative targets with which to modulate PI3K signaling specifically in the immune system. One such target is the SH2 domain-containing inositol-5-phosphatase-1 (SHIP-1) which de-phosphorylates PI(3,4,5)P₃ at the D5 position of the inositol ring to create PI(3,4)P₂. In this article, we first describe the current state of PI3K isoform-selective inhibitor development. We then focus on the structure of SHIP-1 and its function in the immune system. Finally, we consider the current state of development of small molecule compounds that potently and selectively modulate SHIP activity and which offer novel opportunities to manipulate PI3K mediated signaling in the immune system.

PI3K-independent AKT activation in cancers: a treasure trove for novel therapeutics

AKT/PKB serine threonine kinase, a critical signaling molecule promoting cell growth and survival pathways, is frequently dysregulated in many cancers. Although phosphatidylinositol-3-OH kinase (PI3K), a lipid kinase, is well characterized as a major regulator of AKT activation in response to a variety of ligands, recent studies highlight a diverse group of tyrosine (Ack1/TNK2, Src, PTK6) and serine/threonine (TBK1, IKBKE, DNAPKcs) kinases that activate AKT directly to promote its pro-proliferative signaling functions. While some of these alternate AKT activating kinases respond to growth factors, others respond to inflammatory and genotoxic stimuli. A common theme emerging from these studies is that aberrant or hyperactivation of these alternate kinases is often associated with malignancy. Consequently, evaluating the use of small molecular inhibitors against these alternate AKT activating kinases at earlier stages of cancer therapy may overcome the pressing problem of drug resistance surfacing especially in patients treated with PI3K inhibitors.

Targeting PI3K isoforms and SHIP in the immune system: new therapeutics for inflammation and leukemia

PI3K is critical for the normal function of the immune system, however dysregulated PI3K mediated signaling has been linked to the development of many immune mediated pathologies. This review describes current progress in the development of isoform-specific PI3K inhibitors that hold promise for the treatment of hematopoietic malignancies as well as for inflammatory and autoimmune diseases. A SH2-domain containing inositol-5-phosphatase (SHIP) is a regulator of PI3K signaling, and is also discussed as a potential drug target for immunomodulation and the treatment of leukemia. Recent progress has been made in the development of small molecule compounds that potently and selectively modulate SHIP activity and hence provide a novel mechanism to alter PI3K mediated signaling.

Imidazo[1,2-a]pyrazines as novel PI3K inhibitors

Phosphoinositide-3-kinase (PI3K) is an important target for cancer therapeutics due to the deregulation of its signaling pathway in a wide variety of human cancers. We describe herein a novel series of imidazo[1,2-a]pyrazines as PI3K inhibitors.