Inactivation of PI3Kgamma and PI3Kdelta distorts T-cell development and causes multiple organ inflammation

Advancements in dual-target inhibitors of PI3K for tumor therapy: Clinical progress, development strategies, prospects

Phosphoinositide 3-kinases (PI3Ks) modify lipids by the phosphorylation of inositol phospholipids at the 3'-OH position, thereby participating in signal transduction and exerting effects on various physiological processes such as cell growth, metabolism, and organism development. PI3K activation also drives cancer cell growth, survival, and metabolism, with genetic dysregulation of this pathway observed in diverse human cancers. Therefore, this target is considered a promising potential therapeutic target for various types of cancer. Currently, several selective PI3K inhibitors and one dual-target PI3K inhibitor have been approved and launched on the market. However, the majority of these inhibitors have faced revocation or voluntary withdrawal of indications due to concerns regarding their adverse effects. This article provides a comprehensive review of the structure and biological functions, and clinical status of PI3K inhibitors, with a specific emphasis on the development strategies and structure-activity relationships of dual-target PI3K inhibitors. The findings offer valuable insights and future directions for the development of highly promising dual-target drugs targeting PI3K.

Simultaneous Inhibition of PI3Kgamma and PI3Kdelta Deteriorates T-cell Function With Implications for Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a common and incurable B-cell malignancy. Recent therapeutic approaches that target the B-cell receptor signaling pathway include inhibition of phosphatidylinositol-3-kinase (PI3K). The PI3K isoform delta is constitutively active in CLL, making it an attractive therapeutic target. However, the expression of PI3K isoforms is not exclusive to leukemic cells, as other immune cells in the tumor microenvironment also rely on PI3K activity. Subsequently, therapeutic inhibition of PI3K causes immune-related adverse events (irAEs). Here, we analyzed the impact of the clinically approved PI3Kδ inhibitors idelalisib and umbralisib, the PI3Kγ inhibitor eganelisib, and the dual-γ and -δ inhibitor duvelisib on the functional capacity of T cells. All investigated inhibitors reduced T-cell activation and proliferation in vitro, which is in line with PI3K being a crucial signaling component of the T-cell receptor signaling. Further, dual inhibition of PI3Kγ and PI3Kδ showed strong additive effects suggesting a role also for PI3Kγ in T cells. Extrapolation of this data to a clinical setting could provide an explanation for the observed irAEs in CLL patients undergoing treatment with PI3K inhibitors. Consequently, this highlights the need for a close monitoring of patients treated with PI3K inhibitors, and particularly duvelisib, due to their potentially increased risk of T-cell deficiencies and associated infections.

Metabolic regulation of T cell development

T cell development in the thymus is tightly controlled by complex regulatory mechanisms at multiple checkpoints. Currently, many studies have focused on the transcriptional and posttranslational control of the intrathymic journey of T-cell precursors. However, over the last few years, compelling evidence has highlighted cell metabolism as a critical regulator in this process. Different thymocyte subsets are directed by distinct metabolic pathways and signaling networks to match the specific functional requirements of the stage. Here, we epitomize these metabolic alterations during the development of a T cell and review several recent works that provide insights into equilibrating metabolic quiescence and activation programs. Ultimately, understanding the interplay between cellular metabolism and T cell developmental programs may offer an opportunity to selectively regulate T cell subset functions and to provide potential novel therapeutic approaches to modulate autoimmunity.

Quantitative systems pharmacology model-based investigation of adverse gastrointestinal events associated with prolonged treatment with PI3-kinase inhibitors

Several PI3K inhibitors are in clinical development for the treatment of various forms of cancers, including pan-PI3K inhibitors targeting all four PI3K isoforms (α, β, γ, and δ), and isoform-selective inhibitors. Diarrhea and immune-mediated colitis are among the adverse events observed with PI3K inhibition which limits the maximal tolerated dose. A quantitative systems pharmacology model was developed to investigate PI3K-inhibitor-induced colitis. The effects of individual PI3K isoforms on relevant cellular pathways were incorporated into a mechanistic representation of mucosal inflammation. A virtual clinical population captures the observed clinical variability in the onset timing and rates of diarrhea and colitis for seven clinically tested PI3K inhibitors. Model-based analysis suggests that colitis development is governed by both the inhibition of PI3Kδ, which drives T cell differentiation and proliferation, and PI3Kα, which regulates epithelial barrier integrity. Specifically, when PI3Kα is inhibited below a given threshold, epithelial barrier dysfunction precipitates an exaggerated T effector response due to PI3Kδ-inhibition, leading to risk of diarrhea and colitis. This synergy explains why the lowest diarrhea and colitis rates are seen with the weakest PI3Kδ inhibition (alpelisib), and higher rates are seen with strong PI3Kδ inhibition if PI3Kα is even mildly inhibited (e.g., idelalisib), whereas strong PI3Kδ inhibition in the absence of PI3Kα inhibition does not result in high colitis rates (umbralisib). Thus, the model-based analysis suggests that PI3Kα and δ inhibition play unique but synergistic roles in driving colitis. Finally, we explore if and how dose-regimen might influence colitis rates for molecules that inhibit both PI3Kα and PI3Kδ.

Regulation of activated T cell survival in rheumatic autoimmune diseases

Adaptive immune responses rely on the proliferation of T lymphocytes able to recognize and eliminate pathogens. The magnitude and duration of the expansion of activated T cell clones are finely regulated to minimize immunopathology and avoid autoimmunity. In patients with rheumatic autoimmune diseases, such as systemic lupus erythematosus and rheumatoid arthritis, activated lymphocytes survive and exert effector functions for prolonged periods, defying the mechanisms that normally curb their capacities during acute and chronic infections. Here, we review the molecular mechanisms that limit the duration of immune responses in health and discuss the factors that alter such regulation in the setting of systemic lupus erythematosus and rheumatoid arthritis. We highlight defects that could contribute to the development and progression of autoimmune disease and describe how chronic inflammation can alter the regulation of activated lymphocyte survival, promoting its perpetuation. These concepts might contribute to the understanding of the mechanisms that underlie the chronicity of inflammation in the context of autoimmunity.

Trends in TREC values according to age and gender in Chinese children and their clinical applications

T cell receptor excision circles (TRECs) are small circularized DNA elements produced during rearrangement of T cell receptor (TCR) genes. Because TRECs are fairly stable, do not replicate during mitosis, and are not diluted during division of naïve T cells (Dion et al. [1]), they are suitable for assessing the number of newly formed T cells (Ping and Denise [2]). In this study, we detected TRECs in 521 healthy Chinese children aged 0-18 years in different clinical settings. The TRECs decrease with aging and show lower levels in preterm and low birth weight (BW) babies compared to those in full-term infants, while the preterm babies can also show comparable levels of TRECs when they have a gestation age (GA)-matched BW. We found a strong correlation between TRECs and peripheral CD4 naïve T cell numbers, which was age-related. We also analyzed the TRECs in different PIDs. Since T cell defects vary in PIDs, TREC levels change inconsistently. For example, in Wiskott-Aldrich syndrome (WAS), combining the level of TREC with lymphocyte subsets can help to distinguish subtypes of disease.Conclusion: We established the reference value range for TRECs by evaluating children below 18 years old in China, which could be used to screen for PIDs during early life. What is Known: • The TREC levels are decreased with age, and there is a positive correlation between TRECs and the numbers of naïve T cells. What is New: • This is the largest study to determine TREC reference levels in healthy Chinese pediatric, we provide solid data showing a correlation between CD4 naïve T cell counts and TREC levels according to age. We point out the GA matched BW is need to be considered during the SCID newborn screening. We are the first group showed that TREC levels can help clinician distinguish different WAS phenotype.

Integrated safety analysis of umbralisib, a dual PI3Kδ/CK1ε inhibitor, in relapsed/refractory lymphoid malignancies

Phosphoinositide 3-kinase-δ (PI3Kδ) inhibitors are active in lymphoid malignancies, although associated toxicities can limit their use. Umbralisib is a dual inhibitor of PI3Kδ and casein kinase-1ε (CK1ε). This study analyzed integrated comprehensive toxicity data from 4 open-label, phase 1 and 2 studies that included 371 adult patients (median age, 67 years) with relapsed/refractory non-Hodgkin lymphoma (follicular lymphoma [n = 147]; marginal zone lymphoma [n = 82]; diffuse large B-cell lymphoma/mantle cell lymphoma [n = 74]; chronic lymphocytic leukemia [n = 43]; and other tumor types [n = 25]) who were treated with the recommended phase 2 dose of umbralisib 800 mg or higher once daily. At data cutoff, median duration of umbralisib treatment was 5.9 months (range, 0.1-75.1 months), and 107 patients (28.8%) received umbralisib for ≥12 months. Any-grade treatment-emergent adverse events (AEs) occurred in 366 (98.7%) of 371 patients, with the most frequent being diarrhea (52.3%), nausea (41.5%), and fatigue (31.8%). Grade 3 or higher treatment-emergent AEs occurred in 189 (50.9%) of 371 patients and included neutropenia (11.3%), diarrhea (7.3%), and increased aminotransferase levels (5.7%). Treatment-emergent serious AEs occurred in 95 (25.6%) of 371 patients. AEs of special interest were limited and included pneumonia (29 of 371 [7.8%]), noninfectious colitis (9 of 371 [2.4%]), and pneumonitis (4 of 371 [1.1%]). AEs led to discontinuation of umbralisib in 51 patients (13.7%). Four patients (1.1%) died of AEs, none of which was deemed related to umbralisib. No cumulative toxicities were reported. The favorable long-term tolerability profile and low rates of immune-mediated toxicities support the potential use of umbralisib for the benefit of a broad population of patients with lymphoid malignancies.

PI3K inhibitors are finally coming of age

Overactive phosphoinositide 3-kinase (PI3K) in cancer and immune dysregulation has spurred extensive efforts to develop therapeutic PI3K inhibitors. Although progress has been hampered by issues such as poor drug tolerance and drug resistance, several PI3K inhibitors have now received regulatory approval - the PI3Kα isoform-selective inhibitor alpelisib for the treatment of breast cancer and inhibitors mainly aimed at the leukocyte-enriched PI3Kδ in B cell malignancies. In addition to targeting cancer cell-intrinsic PI3K activity, emerging evidence highlights the potential of PI3K inhibitors in cancer immunotherapy. This Review summarizes key discoveries that aid the clinical translation of PI3Kα and PI3Kδ inhibitors, highlighting lessons learnt and future opportunities.

PI3K in T Cell Adhesion and Trafficking

PI3K signalling is required for activation, differentiation, and trafficking of T cells. PI3Kδ, the dominant PI3K isoform in T cells, has been extensively characterised using PI3Kδ mutant mouse models and PI3K inhibitors. Furthermore, characterisation of patients with Activated PI3K Delta Syndrome (APDS) and mouse models with hyperactive PI3Kδ have shed light on how increased PI3Kδ activity affects T cell functions. An important function of PI3Kδ is that it acts downstream of TCR stimulation to activate the major T cell integrin, LFA-1, which controls transendothelial migration of T cells as well as their interaction with antigen-presenting cells. PI3Kδ also suppresses the cell surface expression of CD62L and CCR7 which controls the migration of T cells across high endothelial venules in the lymph nodes and S1PR1 which controls lymph node egress. Therefore, PI3Kδ can control both entry and exit of T cells from lymph nodes as well as the recruitment to and retention of T cells within inflamed tissues. This review will focus on the regulation of adhesion receptors by PI3Kδ and how this contributes to T cell trafficking and localisation. These findings are relevant for our understanding of how PI3Kδ inhibitors may affect T cell redistribution and function.

PI3-Kinase p110α Deficiency Modulates T Cell Homeostasis and Function and Attenuates Experimental Allergic Encephalitis in Mature Mice

Class I phosphoinositide 3-kinases (PI3K) are involved in the development of normal and autoimmune responses, including Experimental Autoimmune Encephalomyelitis (EAE), a mouse model for human multiple sclerosis (MS). Here, the role of the ubiquitously expressed class IA PI3K p110α catalytic subunits in EAE has been analyzed using a model of Cre/flox mediated T cell specific deletion of p110α catalytic chain (p110αΔT). Comparison of two month-old (young) and six month-old (mature) p110αΔT mice and their wild type (WT) counterparts indicated loss of spleen CD4⁺ T cells that increased with age, indicating a role of p110α in their homeostasis. In contrast, CD4⁺ T regulatory (Treg) cells were enhanced in mature p110αΔT mice when compared to WT mice. Since Myelin Oligodendrocyte Glycoprotein (MOG) peptide-induced EAE is dependent on, or mediated by CD4⁺ T cells and CD4⁺ T cell-derived cytokines and controlled by Treg cells, development of EAE in young and mature WT or p110αΔT mice was analyzed. EAE clinical symptoms and disease scores in six month p110αΔT mice were significantly lower than those of mature WT, or young WT and p110αΔT mice. Furthermore, ex vivo antigen activation of lymph node cells from MOG immunized mature p110αΔT mice induced significantly lower levels of IFN-γ and IL-17A than young p110αΔT or young and mature WT mice. Other cytokines including IL-2, IL-10 or TNF-α showed no significant differences between p110αΔT and WT mature mice. Our data show a lower incidence of MOG-induced EAE in mature p110αΔT mice linked to altered T cell homeostasis and lower secretion of inflammatory cytokines.

A Case for Phosphoinositide 3-Kinase-Targeted Therapy for Infectious Disease

PI3Ks activate critical signaling cascades and have multifaceted regulatory functions in the immune system. Loss-of-function and gain-of-function mutations in the PI3Kδ isoform have revealed that this enzyme can substantially impact immune responses to infectious agents and their products. Moreover, reports garnered from decades of infectious disease studies indicate that pharmacologic inhibition of the PI3K pathway could potentially be effective in limiting the growth of certain microbes via modulation of the immune system. In this review, we briefly highlight the development and applications of PI3K inhibitors and summarize data supporting the concept that PI3Kδ inhibitors initially developed for oncology have immune regulatory potential that could be exploited to improve the control of some infectious diseases. This repurposing of existing kinase inhibitors could lay the foundation for alternative infectious disease therapy using available therapeutic agents.

Umbralisib, a Dual PI3Kδ/CK1ε Inhibitor in Patients With Relapsed or Refractory Indolent Lymphoma

PURPOSE

Phosphatidylinositol-3-kinase (PI3K) inhibitors have shown activity in relapsed or refractory (R/R) indolent non-Hodgkin lymphoma (iNHL). PI3K inhibitors have been hampered by poor long-term tolerability and toxicity, which interfere with continuous use. Umbralisib, a dual inhibitor of PI3Kδ/casein kinase-1ε, exhibits improved selectivity for PI3Kδ compared with other PI3K inhibitors. This phase IIb trial was designed to evaluate the efficacy and safety of umbralisib in patients with R/R iNHL.

PATIENTS AND METHODS

In this multicohort, open-label, phase IIb study, 208 patients with R/R marginal zone, follicular, or small lymphocytic lymphoma (MZL, FL, or SLL) unresponsive to prior treatments (≥ 1 MZL; ≥ 2 FL/SLL), including ≥ 1 anti-CD20-based therapy, were administered umbralisib 800 mg orally once daily until disease progression, unacceptable toxicity, or study withdrawal. Primary end point is overall response rate; secondary end points include time to response, duration of response, progression-free survival, and safety.

RESULTS

The median follow-up is 27.7 months (efficacy) and 21.4 months (safety). The overall response rate was 47.1%, and tumor reduction occurred in 86.4% of patients. The median time to response was 2.7-4.6 months. The median duration of response was not reached for MZL, 11.1 months for FL, and 18.3 months for SLL. Median progression-free survival was not reached for MZL, 10.6 months for FL, and 20.9 months for SLL. At least one grade ≥ 3 treatment-emergent adverse event (TEAE) was reported in 53.4% of patients. TEAEs led to umbralisib discontinuation in 32 patients (15.4%). A total of 31 patients (14.9%) discontinued because of a treatment-related adverse event. Grade ≥ 3 TEAEs reported in ≥ 10% of patients: neutropenia (11.5%) and diarrhea (10.1%). Increased ALT/AST (grade ≥ 3) occurred in 6.7%/7.2% of patients.

CONCLUSION

Umbralisib achieved meaningful clinical activity in heavily pretreated patients with iNHL. The safety profile was manageable, with a relatively low incidence of immune-mediated toxicities and adverse event-related discontinuations.

Phosphatidylinositol 3-Kinase δ Inhibitor-Induced Immunomodulation and Secondary Opportunistic Infection in the Cynomolgus Monkey (Macaca fascicularis)

Phosphatidylinositol 3-kinases (PI3Ks) regulate intracellular signaling events for multiple cell surface receptors. Phosphatidylinositol 3-kinase δ, 1 of 4 class I PI3K isoforms, is primarily found in leukocytes and regulates immune cell functions. Here, we report changes in the immune and digestive systems that were associated with AMG2519493, a highly selective small-molecule PI3Kδ inhibitor. Following 1- or 3-month oral repeat dosing in the cynomolgus monkey, changes were observed in circulating B cells, lymphoid tissues (spleen, lymph nodes, gut-associated lymphoid tissue, tonsil), and the digestive tract. Decreased circulating B cells and lymphoid cellularity in B cell-rich zones in lymphoid tissues were attributed to the intended pharmacologic activity of AMG2519493. Dose- and duration-dependent digestive system toxicity was characterized by inflammation in the large intestine and secondary opportunistic infections restricted to the digestive tract. Digestive tract changes were associated with moribundity and mortality at high-dose levels, and the effect level decreased with increased duration of exposure. These observations demonstrate the role of PI3Kδ in regulation of the immune system and of host resistance to opportunistic infections of the digestive tract.

Effects of AS2819899, a novel selective PI3Kδ inhibitor, in a NZB/W F1 mouse lupus-like nephritis model

Phosphoinositide 3-kinases generate lipid-based second messengers that control an array of intracellular signaling pathways. In particular, phosphoinositide 3-kinases delta (PI3Kδ) is expressed primarily in hematopoietic cells and plays an important role in B-cell development and function. B cells play a critical role in autoimmune diseases by producing autoantibodies. Studies have therefore increasingly focused on PI3Kδ as a therapeutic target for the treatment of inflammatory and autoimmune diseases. One such autoimmune disease is systemic lupus erythematosus (SLE). SLE is a chronic systemic autoimmune disease with repeated recurrence and remission, and autoantibodies play an important role in its pathogenesis. Here, we examined the pharmacological profile of the novel PI3Kδ selective inhibitor AS2819899 and investigated its therapeutic potential against SLE in a NZB/W F1 mouse lupus-like nephritis model, a widely-used SLE mouse model. AS2819899 prevented B and T cell activation in vitro, and inhibited antibody production in a T-cell independent de novo antibody production mouse model. In the spontaneous NZB/W F1 mouse model, AS2819899 treatment significantly reduced anti-dsDNA antibody titers and improved kidney dysfunction. Further, AS2819899 inhibited the memory recall reaction in a T-cell dependent antibody production mouse model, suggesting that AS2819899 can potentially maintain remission of SLE. Moreover, we identified a pharmacodynamics marker for AS2819899 that may be useful in clinical studies. These results indicate that AS2819899 may be an attractive therapeutic candidate for SLE, including the maintenance of remission.

Loss of Phosphatidylinositol 3-Kinase Activity in Regulatory T Cells Leads to Neuronal Inflammation

Class I PI3K enzymes are critical for the maintenance of effective immunity. In T cells, PI3Kα and PI3Kδ are activated by the TCR and costimulatory receptors, whereas PI3Kγ is activated by G protein-coupled chemokine receptors. PI3Kδ is a key regulator of regulatory T (Treg) cell function. PI3K isoform-selective inhibitors are in development for the treatment of diseases associated with immune dysregulation, including chronic inflammatory conditions, cancer, and autoimmune diseases. Idelalisib (PI3Kδ), alpelisib (PI3Kα), duvelisib (PI3Kδ/γ), and copanlisib (pan-PI3K) have recently been approved for use in cancer treatment. Although effective, these therapies often have severe side effects associated with immune dysregulation and, in particular, loss of Treg cells. Therefore, it is important to gain a better understanding of the relative contribution of different PI3K isoforms under homeostatic and inflammatory conditions. Experimental autoimmune encephalitis is a mouse model of T cell-driven CNS inflammation, in which Treg cells play a key protective role. In this study, we show that PI3Kδ is required to maintain normal Treg cell development and phenotype under homeostatic conditions but that loss of PI3Kδ alone in Treg cells does not lead to autoimmunity. However, combined loss of PI3Kα and PI3Kδ signaling resulted in increased experimental autoimmune encephalitis disease severity. Moreover, mice lacking PI3Kα and PI3Kδ in Treg cells developed spontaneous peripheral nerve inflammation. These results show a key role for PI3K signaling in Treg cell-mediated protection against CNS inflammation.

The Genetics and Mechanisms of T-Cell Acute Lymphoblastic Leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy derived from early T-cell progenitors. The recognition of clinical, genetic, transcriptional, and biological heterogeneity in this disease has already translated into new prognostic biomarkers, improved leukemia animal models, and emerging targeted therapies. This work reviews our current understanding of the molecular mechanisms of T-ALL.

Degeneration of the intestinal microbial community in PI3Kγ-knockout mice

BACKGROUND AND AIM

PI3Kγ is closely related to inflammation and cardiovascular diseases and thus, PI3Kγ inhibitors are candidate drugs for the treatment of these disorders. Considering the potential effect of the intestinal microbiome on inflammation and cardiovascular diseases, this study aimed to identify characteristics of the intestinal microbial community under PI3Kγ deficiency, to help reveal the potential influence of PI3Kγ inhibitors mediated by the microbial community.

METHODS

Exon 2 of the PI3Kγ gene was knocked out in a Balb/c mouse by using single-guide RNAs. Homozygous PI3Kγ-knockout (PI3Kγ-/-) mice were obtained by embryo transfer and hybridization. PI3Kγ-/- and wild-type (WT) mice were raised in the same specific pathogen-free conditions until 8 weeks of age. Then, colonic tissues and feces from the middle segment of the colon were collected and analyzed by Illumina MiSeq sequencing. Differences in intestinal microbial community between the PI3Kγ-/- and WT mice were detected by bioinformatics analysis.

RESULTS

The richness and alpha diversity of the colonic microbial community were decreased in PI3Kγ-/- mice. The alpha diversity of the microbial community in feces did not differ between PI3Kγ-/- and WT mice. The beta diversity of the microbial community in feces of PI3Kγ-/- mice was obviously different from that in WT mice, whereas the within-group variation in Bray-Curtis distances of the mucosal microbial community was significantly decreased in PI3Kγ-/- mice. The topological structure of the species-related network of the colonic microbial community in PI3Kγ-/- mice was more polarized. Finally, we predicted that PI3Kγ deficiency might affect the synthesis of some antibiotics, bile acid, and thiamine through effects on the microbial community.

CONCLUSIONS

PI3Kγ dysfunction led to degeneration of the intestinal microbial community and might alter the synthesis of some antibiotics, bile acids, and thiamine. The usage of PI3Kγ inhibitors for inflammation and cardiovascular diseases might lead to knock-on effect on our organism through intestinal microbiota.

Immunological characterization of HM5023507, an orally active PI3Kδ/γ inhibitor

Phosphoinositide 3-kinases, delta (PI3Kδ) and gamma (PI3Kγ) are enriched in immune cells and regulate the development and function of innate and adaptive immunity. Dual PI3Kδγ inhibitors are considered high value targets for their potential to treat a variety of immune-mediated diseases, but their discovery has been challenging. Here we describe the preclinical pharmacology of HM5023507, an orally active dual inhibitor of δγ isoforms in immune signaling. HM5023507 inhibited PI3Kδ and PI3Kγ isoforms with greater than 100-fold selectivity against PI3Kα and PI3Kβ in recombinant enzymatic assays and in primary human immune cells with an exquisite selectivity against other targets. HM5023507 attenuated the PI3Kδ/γ signaling in human basophils (IC50: 42/340 nmol/L; selectivity ratio ~1:8). HM5023507 attenuated the activation and function of human B and T cells, Th17 differentiation of CD4 T cells in the blood of healthy donors and rheumatoid arthritis patients, and cytokine and IgG production in human T and B cell cocultures, in vitro. Orally dosed HM5023507 attenuated PI3K δ/γ-mediated immune signaling in the rat in a dose-related manner. In addition, HM5023507 inhibited semiestablished collagen-induced arthritic inflammation in the rats (ED50 of 0.25mg/kg, p.o. BID or 0.5 mg/kg, QD, AUC: 1422 ng/mL*h), improved histopathology- and micro-computed tomography (µCT)-based indices of joint damage, bone destruction, and attenuated the levels of anti-collagen antibody, with an overall anti-inflammatory profile matching that of a TNFα neutralizing antibody. The PI3K δγ inhibitory profile of HM5023507 and its selectivity make it a useful tool to further delineate immunobiology of dual PI3K δγ targeting.

Function, Regulation and Biological Roles of PI3Kγ Variants

Phosphatidylinositide 3-kinase (PI3K) γ is the only class IB PI3K member playing significant roles in the G-protein-dependent regulation of cell signaling in health and disease. Originally found in the immune system, increasing evidence suggest a wide array of functions in the whole organism. PI3Kγ occur as two different heterodimeric variants: PI3Kγ (p87) and PI3Kγ (p101), which share the same p110γ catalytic subunit but differ in their associated non-catalytic subunit. Here we concentrate on specific PI3Kγ features including its regulation and biological functions. In particular, the roles of its non-catalytic subunits serving as the main regulators determining specificity of class IB PI3Kγ enzymes are highlighted.

PI3K p110δ inactivation antagonizes chronic lymphocytic leukemia and reverses T cell immune suppression

Targeted therapy with small molecules directed at essential survival pathways in leukemia represents a major advance, including the phosphatidylinositol-3'-kinase (PI3K) p110δ inhibitor idelalisib. Here, we found that genetic inactivation of p110δ (p110δD910A/D910A) in the Eμ-TCL1 murine chronic lymphocytic leukemia (CLL) model impaired B cell receptor signaling and B cell migration, and significantly delayed leukemia pathogenesis. Regardless of TCL1 expression, p110δ inactivation led to rectal prolapse in mice resembling autoimmune colitis in patients receiving idelalisib. Moreover, we showed that p110δ inactivation in the microenvironment protected against CLL and acute myeloid leukemia. After receiving higher numbers of TCL1 leukemia cells, half of p110δD910A/D910A mice spontaneously recovered from high disease burden and resisted leukemia rechallenge. Despite disease resistance, p110δD910A/D910A mice exhibited compromised CD4+ and CD8+ T cell response, and depletion of CD4+ or CD8+ T cells restored leukemia. Interestingly, p110δD910A/D910A mice showed significantly impaired Treg expansion that associated with disease clearance. Reconstitution of p110δD910A/D910A mice with p110δWT/WT Tregs reversed leukemia resistance. Our findings suggest that p110δ inhibitors may have direct antileukemic and indirect immune-activating effects, further supporting that p110δ blockade may have a broader immune-modulatory role in types of leukemia that are not sensitive to p110δ inhibition.

The p110δ isoforme of phosphatidylinositol 3-kinase plays an important role in host defense against chlamydial lung infection through influencing CD4+ T-cell function

PI3Ks display integrant significance in T-cell development and differentiation, which is related to host defense against infections. Here, we investigated the role of p110δ isoform of PI3Ks in host defense against chlamydial lung infection in a mouse model. Our data showed that lung infection with Chlamydia muridarum (Cm) activated PI3K/AKT signaling pathway. Compared to WT mice, p110δD910A mice, mice with an inactivating knockin mutation in the p110δ Isoform of PI3Ks, showed more sever disease phenotype and slower recovery, which was associated with reduced Chlamydia-specific Th1 and Th17 immune responses following infection. Further adoptive transfer experiment showed that mice which received CD4+ T cells from infected p110δD910A mice exhibited greater body weight loss and higher bacterial loads in the lung than those which received CD4+ T cells from WT mice following challenge infection. These results provide in vivo evidence that p110δ isoform of PI3Ks plays an important role in host defense against chlamydial infection by promoting CD4+ T-cell immunity.

A common molecular signature of patients with sickle cell disease revealed by microarray meta-analysis and a genome-wide association study

A chronic inflammatory state to a large extent explains sickle cell disease (SCD) pathophysiology. Nonetheless, the principal dysregulated factors affecting this major pathway and their mechanisms of action still have to be fully identified and elucidated. Integrating gene expression and genome-wide association study (GWAS) data analysis represents a novel approach to refining the identification of key mediators and functions in complex diseases. Here, we performed gene expression meta-analysis of five independent publicly available microarray datasets related to homozygous SS patients with SCD to identify a consensus SCD transcriptomic profile. The meta-analysis conducted using the MetaDE R package based on combining p values (maxP approach) identified 335 differentially expressed genes (DEGs; 224 upregulated and 111 downregulated). Functional gene set enrichment revealed the importance of several metabolic pathways, of innate immune responses, erythrocyte development, and hemostasis pathways. Advanced analyses of GWAS data generated within the framework of this study by means of the atSNP R package and SIFT tool identified 60 regulatory single-nucleotide polymorphisms (rSNPs) occurring in the promoter of 20 DEGs and a deleterious SNP, affecting CAMKK2 protein function. This novel database of candidate genes, transcription factors, and rSNPs associated with SCD provides new markers that may help to identify new therapeutic targets.

Pitfalls of Combining Novel Agents in Lymphoma

OPINION STATEMENT

As our knowledge of lymphoma and its intricate signaling pathways has grown, so has the development of novel agents. While their mechanisms of action vary considerably, these therapies supplement and in some cases offer alternatives to standard chemotherapy. Initial studies have highlighted tolerable side effects though in the majority of instances limited efficacy when used as monotherapy. Research has focused on combining these novel agents to improve outcomes and perhaps offer refined treatment options. Novel combinations represent new territory, inherently dissimilar to combination chemotherapy with new pitfalls and challenges given their unique mechanisms of action. Though promising, it is crucial to consider the complex interplay that can occur. While there is potential for improved outcomes, there is also the possibility of unexpected toxicities. For this reason, it is critical that novel combinations be carefully considered and tested in clinical trials before widespread use. Thus far, research has shown that combination therapies are successful when not only avoiding overlapping toxicity but also capitalizing on synergy. We believe that more specific targets and an improved understanding of their off-/on-target effects will further successful novel combinations.

T-Cell-Specific Loss of the PI-3-Kinase p110α Catalytic Subunit Results in Enhanced Cytokine Production and Antitumor Response

Class IA phosphatidylinositol 3-kinase (PI3K) catalytic subunits p110α and p110δ are targets in cancer therapy expressed at high levels in T lymphocytes. The role of p110δ PI3K in normal or pathological immune responses is well established, yet the importance of p110α subunits in T cell-dependent immune responses is not clear. To address this problem, mice with p110α conditionally deleted in CD4⁺ and CD8⁺ T lymphocytes (p110α^-/-ΔT) were used. p110α^-/-ΔT mice show normal development of T cell subsets, but slightly reduced numbers of CD4⁺ T cells in the spleen. "In vitro," TCR/CD3 plus CD28 activation of naive CD4⁺ and CD8⁺ p110α^-/-ΔT T cells showed enhanced effector function, particularly IFN-γ secretion, T-bet induction, and Akt, Erk, or P38 activation. Tfh derived from p110α^-/-ΔT cells also have enhanced responses when compared to normal mice, and IL-2 expanded p110α^-/-ΔT CD8⁺ T cells had enhanced levels of LAMP-1 and Granzyme B. By contrast, the expansion of p110α^-/-ΔT iTreg cells was diminished. Also, p110α^-/-ΔT mice had enhanced anti-keyhole limpet hemocyanin (KLH) IFN-γ, or IL-4 responses and IgG1 and IgG2b anti-KLH antibodies, using CFA or Alum as adjuvant, respectively. When compared to WT mice, p110α^-/-ΔT mice inoculated with B16.F10 melanoma showed delayed tumor progression. The percentage of CD8⁺ T lymphocytes was higher and the percentage of Treg cells lower in the spleen of tumor-bearing p110α^-/-ΔT mice. Also, IFN-γ production in tumor antigen-activated spleen cells was enhanced. Thus, PI3K p110α plays a significant role in antigen activation and differentiation of CD4⁺ and CD8⁺ T lymphocytes modulating antitumor immunity.

Emerging role of BCR signaling inhibitors in immunomodulation of chronic lymphocytic leukemia

Approved therapies that target the B-cell receptor (BCR) signaling pathway, such as ibrutinib and idelalisib, are known to show activity in chronic lymphocytic leukemia (CLL) via their direct effects on crucial survival pathways in malignant B cells. However, these therapies also have effects on T cells in CLL by mediating toxicity and possibly controlling disease. By focusing on the effects of BCR signaling inhibitors on the T-cell compartment, we may gain new insights into the comprehensive biological outcomes of systemic treatment to further understand mechanisms of drug efficacy, predict the toxicity or adverse events, and identify novel combinatorial therapies. Here, we review T-cell abnormalities in preclinical models and patient samples, finding that CLL T cells orchestrate immune dysfunction and immune-related complications. We then continue to address the effects of clinically available small molecule BCR signaling inhibitors on the immune cells, especially T cells, in the context of concomitant immune-mediated adverse events and implications for future treatment strategies. Our review suggests potentially novel mechanisms of action related to BCR inhibitors, providing a rationale to extend their use to other cancers and autoimmune disorders.

Deficiency of PI3-Kinase catalytic isoforms p110γ and p110δ in mice enhances the IL-17/G-CSF axis and induces neutrophilia

Background

Phosphoinositide 3-kinase γ (PI3Kγ) and PI3Kδ are second messenger-generating enzymes with key roles in proliferation, differentiation, survival, and function of leukocytes. Deficiency of the catalytic subunits p110γ and p110δ of PI3Kγ and PI3Kδ in p110γ/δ^−/− mice leads to defective B- and T-cell homeostasis. Here we examined the role of p110γ and p110δ in the homeostasis of neutrophils by analyzing p110γ^−/−, p110δ^−/− and p110γ/δ^−/− mice.

Methods

Neutrophils and T cells in leukocyte suspensions from the bone marrow (BM), blood, spleen and lung were analyzed by flow cytometry. Serum concentrations of IL-17, of the neutrophilic growth factor G-CSF, and of the neutrophil mobilizing CXC chemokines CXCL1/KC and CXCL2/MIP-2 were measured by Bio-Plex assay. Production of G-CSF and CXCL1/KC by IL-17-stimulated primary lung tissue cells were determined by ELISA, whereas IL-17-dependent signaling in lung tissue cells was analyzed by measuring Akt phosphorylation using immunoblot.

Results

We found that in contrast to single knock-out mice, p110γ/δ^−/− mice exhibited significantly elevated neutrophil counts in blood, spleen, and lung. Increased granulocytic differentiation stages in the bone marrow of p110γ/δ^−/− mice were paralleled by increased serum concentrations of G-CSF, CXCL1/KC, and CXCL2/MIP-2. As IL-17 induces neutrophilia via the induction of G-CSF and CXC chemokines, we measured IL-17 and IL-17-producing T cells. IL-17 serum concentrations and frequencies of IL-17⁺ splenic T cells were significantly increased in p110γ/δ^−/− mice. Moreover, IFN-γ⁺, IL-4⁺, and IL-5⁺ T cell subsets were drastically increased in p110γ/δ^−/− mice, suggesting that IL-17⁺ T cells were up-regulated in the context of a general percentage increase of other cytokine producing T cell subsets.

Conclusions

We found that p110γ/δ deficiency in mice induces complex immunological changes, which might in concert contribute to neutrophilia. These findings emphasize a crucial but indirect role of both p110γ and p110δ in the regulation of neutrophil homeostasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-017-0185-y) contains supplementary material, which is available to authorized users.

First-in-human studies of seletalisib, an orally bioavailable small-molecule PI3Kδ inhibitor for the treatment of immune and inflammatory diseases

PURPOSE

PI3Ks are potential therapeutic targets in immune-inflammatory diseases. These studies aimed to investigate the safety, tolerability and PK profile of seletalisib, a selective inhibitor of PI3Kδ in humans.

METHODS

These phase I, randomised, double-blind, placebo-controlled, single-centre studies (NCT02303509, NCT02207595) evaluated single and multiple oral doses of seletalisib (5-90 mg QD and 30 mg BID) in healthy adults and subjects with mild-to-moderate psoriasis (Study-1). Pharmacodynamic effects on markers of inflammation were assessed via changes in ex vivo basophil degranulation and histological assessment of psoriatic skin biopsies.

RESULTS

Seletalisib was well tolerated at doses ≤15 mg (Study-1) and ≤45 mg QD (Study-2) for 14 days. No safety concerns or dose-limiting toxicities were identified (Study-1). Incidence of gastrointestinal-related AEs was not dose related but higher incidences of rash AEs were associated with higher-dose seletalisib (Study-2 rash AEs: 18 in 12 seletalisib-treated subjects versus 1 in 1 placebo-treated subject). Mean seletalisib plasma concentration-time profiles increased with increasing doses after single and multiple dosing, with no major deviations from dose-proportionality. There was no unexpected accumulation or loss of exposure after multiple dosing (time-independent pharmacokinetic profile). Apparent t 1/2 values were supportive of once-daily dosing (geometric mean t1/2: Study-1, 17.7-21.1 h; Study-2, 18.1-22.4 h). No clinically significant food effect was observed (Study-1). Pharmacodynamic findings demonstrated ex vivo inhibition of basophil degranulation, improvements in histological assessment of skin biopsies and other markers of psoriatic biology and preliminary evidence of target engagement in psoriatic skin tissue.

CONCLUSIONS

Seletalisib safety, tolerability and pharmacokinetic/pharmacodynamic profiles support its continued clinical development in immune-inflammatory diseases.

Seletalisib: Characterization of a Novel, Potent, and Selective Inhibitor of PI3Kδ

Phosphoinositide 3-kinases (PI3K) are key signaling enzymes regulating cellular survival, development, and function. Expression of the PI3Kδ isoform is largely restricted to leukocytes and it plays a key role in immune cell development and function. Seletalisib is a novel small-molecule inhibitor of PI3Kδ that was evaluated in biochemical assays, cellular assays of adaptive and innate immunity, and an in vivo rat model of inflammation. Our findings show that seletalisib is a potent, ATP-competitive, and selective PI3Kδ inhibitor able to block protein kinase B (AKT) phosphorylation following activation of the B-cell receptor in a B-cell line. Moreover, seletalisib inhibited N-formyl peptide-stimulated but not phorbol myristate acetate-stimulated superoxide release from human neutrophils, consistent with a PI3Kδ-specific activity. No indications of cytotoxicity were observed in peripheral blood mononuclear cells (PBMCs) or other cell types treated with seletalisib. Findings from cellular assays of adaptive immunity demonstrated that seletalisib blocks human T-cell production of several cytokines from activated T-cells. Additionally, seletalisib inhibited B-cell proliferation and cytokine release. In human whole blood assays, seletalisib inhibited CD69 expression upon B-cell activation and anti-IgE-mediated basophil degranulation. Seletalisib showed dose-dependent inhibition in an in vivo rat model of anti-CD3-antibody-induced interleukin 2 release. Collectively, these data characterize seletalisib as a selective PI3Kδ inhibitor and potential therapeutic candidate for the treatment of B-cell malignancies and autoimmune diseases driven by dysregulated proinflammatory cytokine secretion.

Inhibition of Hematopoietic Cell Kinase Activity Suppresses Myeloid Cell-Mediated Colon Cancer Progression

Aberrant activation of the SRC family kinase hematopoietic cell kinase (HCK) triggers hematological malignancies as a tumor cell-intrinsic oncogene. Here we find that high HCK levels correlate with reduced survival of colorectal cancer patients. Likewise, increased Hck activity in mice promotes the growth of endogenous colonic malignancies and of human colorectal cancer cell xenografts. Furthermore, tumor-associated macrophages of the corresponding tumors show a pronounced alternatively activated endotype, which occurs independently of mature lymphocytes or of Stat6-dependent Th2 cytokine signaling. Accordingly, pharmacological inhibition or genetic reduction of Hck activity suppresses alternative activation of tumor-associated macrophages and the growth of colon cancer xenografts. Thus, Hck may serve as a promising therapeutic target for solid malignancies.

Better Understanding of Phosphoinositide 3-Kinase (PI3K) Pathways in Vasculature: Towards Precision Therapy Targeting Angiogenesis and Tumor Blood Supply

The intracellular PI3K-AKT-mTOR pathway is involved in regulation of numerous important cell processes including cell growth, differentiation, and metabolism. The PI3Kα isoform has received particular attention as a novel molecular target in gene therapy, since this isoform plays critical roles in tumor progression and tumor blood flow and angiogenesis. However, the role of PI3Kα and other class I isoforms, i.e. PI3Kβ, γ, δ, in the regulation of vascular tone and regional blood flow are largely unknown. We used novel isoform-specific PI3K inhibitors and mice deficient in both PI3Kγ and PI3Kδ (Pik3cg(-/-)/Pik3cd(-/-)) to define the putative contribution of PI3K isoform(s) to arterial vasoconstriction. Wire myography was used to measure isometric contractions of isolated murine mesenteric arterial rings. Phenylephrine-dependent contractions were inhibited by the pan PI3K inhibitors wortmannin (100 nM) and LY294002 (10 µM). These vasoconstrictions were also inhibited by the PI3Kα isoform inhibitors A66 (10 µM) and PI-103 (1 µM), but not by the PI3Kβ isoform inhibitor TGX 221 (100 nM). Pik3cg(-/-)/Pik3cd(-/-)-arteries showed normal vasoconstriction. We conclude that PI3Kα is an important downstream element in vasoconstrictor GPCR signaling, which contributes to arterial vasocontraction via α1-adrenergic receptors. Our results highlight a regulatory role of PI3Kα in the cardiovascular system, which widens the spectrum of gene therapy approaches targeting PI3Kα in cancer cells and tumor angiogenesis and regional blood flow.

Microenvironmental cues for T-cell acute lymphoblastic leukemia development

Intensive chemotherapy regimens have led to a substantial improvement in the cure rate of patients suffering from T-cell acute lymphoblastic leukemia (T-ALL). Despite this progress, about 15% and 50% of pediatric and adult cases, respectively, show resistance to treatment or relapse with dismal prognosis, calling for further therapeutic investigations. T-ALL is an heterogeneous disease, which presents intrinsic alterations leading to aberrant expression of transcription factors normally involved in hematopoietic stem/progenitor cell development and mutations in genes implicated in the regulation of cell cycle progression, apoptosis, and T-cell development. Gene expression profiling allowed the classification of T-ALL into defined molecular subgroups that mostly reflects the stage of their differentiation arrest. So far this knowledge has not translated into novel, targeted therapy. Recent evidence points to the importance of extrinsic signaling cues in controlling the ability of T-ALL to home, survive, and proliferate, thus offering the perspective of new therapeutic options. This review summarizes the present understanding of the interactions between hematopoietic cells and bone marrow/thymic niches during normal hematopoiesis, describes the main signaling pathways implicated in this dialog, and finally highlights how malignant T cells rely on specific niches to maintain their ability to sustain and propagate leukemia.

Selective Sparing of Human Tregs by Pharmacologic Inhibitors of the Phosphatidylinositol 3-Kinase and MEK Pathways

Phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase/extracellular signal-regulated (MEK) signaling are central to the survival and proliferation of many cell types. Multiple lines of investigation in murine models have shown that control of the PI3K pathway is particularly important for regulatory T cell (Treg) stability and function. PI3K and MEK inhibitors are being introduced into the clinic, and we hypothesized that pharmacologic inhibition of PI3K, and possibly MEK, in mixed cultures of human mononuclear cells would preferentially affect CD4(+) and CD8(+) lymphocytes compared with Tregs. We tested this hypothesis using four readouts: proliferation, activation, functional suppression, and signaling. Results showed that Tregs were less susceptible to inhibition by both δ and α isoform-specific PI3K inhibitors and by an MEK inhibitor compared with their conventional CD4(+) and CD8(+) counterparts. These studies suggest less functional reliance on PI3K and MEK signaling in Tregs compared with conventional CD4(+) and CD8(+) lymphocytes. Therefore, the PI3K and MEK pathways are attractive pharmacologic targets for transplantation and treatment of autoimmunity.

p110γ/δ Double-Deficiency Induces Eosinophilia and IgE Production but Protects from OVA-Induced Airway Inflammation

The catalytical isoforms p110γ and p110δ of phosphatidylinositide 3-kinase γ (PI3Kγ) and PI3Kδ play an important role in the pathogenesis of asthma. Two key elements in allergic asthma are increased levels of eosinophils and IgE. Dual pharmacological inhibition of p110γ and p110δ reduces asthma-associated eosinophilic lung infiltration and ameliorates disease symptoms, whereas the absence of enzymatic activity in p110γ^KOδ^D910A mice increases IgE and basal eosinophil counts. This suggests that long-term inhibition of p110γ and p110δ might exacerbate asthma. Here, we analysed mice genetically deficient for both catalytical subunits (p110γ/δ^-/-) and determined basal IgE and eosinophil levels and the immune response to ovalbumin-induced asthma. Serum concentrations of IgE, IL-5 and eosinophil numbers were significantly increased in p110γ/δ^-/- mice compared to single knock-out and wildtype mice. However, p110γ/δ^-/- mice were protected against OVA-induced infiltration of eosinophils, neutrophils, T and B cells into lung tissue and bronchoalveolar space. Moreover, p110γ/δ^-/- mice, but not single knock-out mice, showed a reduced bronchial hyperresponsiveness. We conclude that increased levels of eosinophils and IgE in p110γ/δ^-/- mice do not abolish the protective effect of p110γ/δ-deficiency against OVA-induced allergic airway inflammation.

Phosphatidylinositol 3-Kinase p110δ Isoform Regulates CD8+ T Cell Responses during Acute Viral and Intracellular Bacterial Infections

The p110δ isoform of PI3K is known to play an important role in immunity, yet its contribution to CTL responses has not been fully elucidated. Using murine p110δ-deficient CD8(+) T cells, we demonstrated a critical role for the p110δ subunit in the generation of optimal primary and memory CD8(+) T cell responses. This was demonstrated in both acute viral and intracellular bacterial infections in mice. We show that p110δ signaling is required for CD8(+) T cell activation, proliferation and effector cytokine production. We provide evidence that the effects of p110δ signaling are mediated via Akt activation and through the regulation of TCR-activated oxidative phosphorylation and aerobic glycolysis. In light of recent clinical trials that employ drugs targeting p110δ in certain cancers and other diseases, our study suggests caution in using these drugs in patients, as they could potentially increase susceptibility to infectious diseases. These studies therefore reveal a novel and direct role for p110δ signaling in in vivo CD8(+) T cell immunity to microbial pathogens.

Inhibition of G-Protein βγ Signaling Decreases Levels of Messenger RNAs Encoding Proinflammatory Cytokines in T Cell Receptor-Stimulated CD4(+) T Helper Cells

Background: Inhibition of G-protein βγ (Gβγ) signaling was found previously to enhance T cell receptor (TCR)-stimulated increases in interleukin 2 (IL-2) mRNA in CD4⁺ T helper cells, suggesting that Gβγ might be a useful drug target for treating autoimmune diseases, as low dose IL-2 therapy can suppress autoimmune responses. Because IL-2 may counteract autoimmunity in part by shifting CD4⁺ T helper cells away from the Type 1 T helper cell (TH1) and TH17 subtypes towards the TH2 subtype, the purpose of this study was to determine if blocking Gβγ signaling affected the balance of TH1, TH17, and TH2 cytokine mRNAs produced by CD4⁺ T helper cells.

Methods: Gallein, a small molecule inhibitor of Gβγ, and siRNA-mediated silencing of the G-protein β₁ subunit (Gβ₁) were used to test the effect of blocking Gβγ on mRNA levels of cytokines in primary human TCR-stimulated CD4⁺ T helper cells.

Results: Gallein and Gβ₁ siRNA decreased interferon-γ (IFN-γ) and IL-17A mRNA levels in TCR-stimulated CD4⁺ T cells grown under TH1-promoting conditions. Inhibiting Gβγ also decreased mRNA levels of STAT4, which plays a positive role in TH1 differentiation and IL-17A production. Moreover, mRNA levels of the STAT4-regulated TH1-associated proteins, IL-18 receptor β chain (IL-18Rβ), mitogen-activated protein kinase kinase kinase 8 (MAP3K8), lymphocyte activation gene 3 (LAG-3), natural killer cell group 7 sequence (NKG7), and oncostatin M (OSM) were also decreased upon Gβγ inhibition. Gallein also increased IL-4, IL-5, IL-9, and IL-13 mRNA levels in TCR-stimulated memory CD4⁺ T cells grown in TH2-promoting conditions.

Conclusions: Inhibiting Gβγ to produce these shifts in cytokine mRNA production might be beneficial for patients with autoimmune diseases such as rheumatoid arthritis (RA), Crohn’s disease (CD), psoriasis, multiple sclerosis (MS), and Hashimoto’s thyroiditis (HT), in which both IFN-γ and IL-17A are elevated.

Inhibition of G-protein βγ signaling enhances T cell receptor-stimulated interleukin 2 transcription in CD4+ T helper cells

G-protein-coupled receptor (GPCR) signaling modulates the expression of cytokines that are drug targets for immune disorders. However, although GPCRs are common targets for other diseases, there are few GPCR-based pharmaceuticals for inflammation. The purpose of this study was to determine whether targeting G-protein βγ (Gβγ) complexes could provide a useful new approach for modulating interleukin 2 (IL-2) levels in CD4⁺ T helper cells. Gallein, a small molecule inhibitor of Gβγ, increased levels of T cell receptor (TCR)-stimulated IL-2 mRNA in primary human naïve and memory CD4⁺ T helper cells and in Jurkat human CD4⁺ leukemia T cells. Gβ₁ and Gβ₂ mRNA accounted for >99% of Gβ mRNA, and small interfering RNA (siRNA)-mediated silencing of Gβ₁ but not Gβ₂ enhanced TCR-stimulated IL-2 mRNA increases. Blocking Gβγ enhanced TCR-stimulated increases in IL-2 transcription without affecting IL-2 mRNA stability. Blocking Gβγ also enhanced TCR-stimulated increases in nuclear localization of nuclear factor of activated T cells 1 (NFAT1), NFAT transcriptional activity, and levels of intracellular Ca²⁺. Potentiation of IL-2 transcription required continuous Gβγ inhibition during at least two days of TCR stimulation, suggesting that induction or repression of additional signaling proteins during T cell activation and differentiation might be involved. The potentiation of TCR-stimulated IL-2 transcription that results from blocking Gβγ in CD4⁺ T helper cells could have applications for autoimmune diseases.

Two birds with one stone: dual p110δ and p110γ inhibition

In this issue of Chemistry & Biology, Winkler and colleagues describe the discovery and preclinical development of IPI-145, a new inhibitor of the phosphoinositide 3-kinase (PI3K) isoforms p110δ and p110γ that have entered clinical trials.

PI3K signalling in inflammation

PI3Ks regulate several key events in the inflammatory response to damage and infection. There are four Class I PI3K isoforms (PI3Kα,β,γ,δ), three Class II PI3K isoforms (PI3KC2α, C2β, C2γ) and a single Class III PI3K. The four Class I isoforms synthesise the phospholipid 'PIP3'. PIP3 is a 'second messenger' used by many different cell surface receptors to control cell movement, growth, survival and differentiation. These four isoforms have overlapping functions but each is adapted to receive efficient stimulation by particular receptor sub-types. PI3Kγ is highly expressed in leukocytes and plays a particularly important role in chemokine-mediated recruitment and activation of innate immune cells at sites of inflammation. PI3Kδ is also highly expressed in leukocytes and plays a key role in antigen receptor and cytokine-mediated B and T cell development, differentiation and function. Class III PI3K synthesises the phospholipid PI3P, which regulates endosome-lysosome trafficking and the induction of autophagy, pathways involved in pathogen killing, antigen processing and immune cell survival. Much less is known about the function of Class II PI3Ks, but emerging evidence indicates they can synthesise PI3P and PI34P2 and are involved in the regulation of endocytosis. The creation of genetically-modified mice with altered PI3K signalling, together with the development of isoform-selective, small-molecule PI3K inhibitors, has allowed the evaluation of the individual roles of Class I PI3K isoforms in several mouse models of chronic inflammation. Selective inhibition of PI3Kδ, γ or β has each been shown to reduce the severity of inflammation in one or more models of autoimmune disease, respiratory disease or allergic inflammation, with dual γ/δ or β/δ inhibition generally proving more effective. The inhibition of Class I PI3Ks may therefore offer a therapeutic opportunity to treat non-resolving inflammatory pathologies in humans. This article is part of a Special Issue entitled Phosphoinositides.

Proline-rich tyrosine kinase 2 controls PI3-kinase activation downstream of the T cell antigen receptor in human T cells

TCR-induced signaling controls T cell activation that drives adaptive immunity against infections, but it can also induce dysfunctional T cell responses that promote pathologic disease. The PI3K pathway regulates many downstream effector responses after TCR stimulation. However, the molecular mechanisms that induce PI3K function downstream of the TCR are not fully understood. We have previously shown that Pyk2 is activated downstream of the TCR in a PI3K-independent manner. Although Pyk2 controls adhesion, proliferation, and cytokine production in T cells, the mechanisms by which it controls these processes are not known. In this study, we generated Pyk2-deficient human T cells to elucidate further the role that this kinase plays in TCR-induced effector functions and signaling. We observed that Pyk2 localized with the p85 regulatory subunit of PI3K at the LAT complex and that PI3K-dependent signaling was impaired in Pyk2-deficient T cells. Likewise, functions downstream of PI3K, including IFN-γ production and proliferation, were also suppressed in human T cells deficient in Pyk2. Collectively, these data demonstrate that Pyk2 is a critical regulator of PI3K function downstream of the TCR.

Role of phosphoinositide 3-kinase in the pathogenesis of acute pancreatitis

A large body of experimental and clinical data supports the notion that inflammation in acute pancreatitis has a crucial role in the pathogenesis of local and systemic damage and is a major determinant of clinical severity. Thus, research has recently focused on molecules that can regulate the inflammatory processes, such as phosphoinositide 3-kinases (PI3Ks), a family of lipid and protein kinases involved in intracellular signal transduction. Studies using genetic ablation or pharmacologic inhibitors of different PI3K isoforms, in particular the class I PI3Kδ and PI3Kγ, have contributed to a greater understanding of the roles of these kinases in the modulation of inflammatory and immune responses. Recent data suggest that PI3Ks are also involved in the pathogenesis of acute pancreatitis. Activation of the PI3K signaling pathway, and in particular of the class IB PI3Kγ isoform, has a significant role in those events which are necessary for the initiation of acute pancreatic injury, namely calcium signaling alteration, trypsinogen activation, and nuclear factor-κB transcription. Moreover, PI3Kγ is instrumental in modulating acinar cell apoptosis, and regulating local neutrophil infiltration and systemic inflammatory responses during the course of experimental acute pancreatitis. The availability of PI3K inhibitors selective for specific isoforms may provide new valuable therapeutic strategies to improve the clinical course of this disease. This article presents a brief summary of PI3K structure and function, and highlights recent advances that implicate PI3Ks in the pathogenesis of acute pancreatitis.

Inhibition of PI3Kδ reduces kidney infiltration by macrophages and ameliorates systemic lupus in the mouse

Systemic lupus erythematosus (SLE) is a human chronic inflammatory disease generated and maintained throughout life by autoreactive T and B cells. Class I phosphoinositide 3-kinases (PI3K) are heterodimers composed of a regulatory and a catalytic subunit that catalyze phosphoinositide-3,4,5-P3 formation and regulate cell survival, migration, and division. Activity of the PI3Kδ isoform is enhanced in human SLE patient PBLs. In this study, we analyzed the effect of inhibiting PI3Kδ in MRL/lpr mice, a model of human SLE. We found that PI3Kδ inhibition ameliorated lupus progression. Treatment of these mice with a PI3Kδ inhibitor reduced the excessive numbers of CD4(+) effector/memory cells and B cells. In addition, this treatment reduced serum TNF-α levels and the number of macrophages infiltrating the kidney. Expression of inactive PI3Kδ, but not deletion of the other hematopoietic isoform PI3Kγ, reduced the ability of macrophages to cross the basement membrane, a process required to infiltrate the kidney, explaining MRL/lpr mice improvement by pharmacologic inhibition of PI3Kδ. The observations that p110δ inhibitor prolonged mouse life span, reduced disease symptoms, and showed no obvious secondary effects indicates that PI3Kδ is a promising target for SLE.

Cellular metabolism on T-cell development and function

Cell metabolism is closely related to the host immunity in many respects. We herein briefly summarized the recent progress on the roles of cellular metabolism in T-cell development, homeostasis, differentiation and functions. Relatively quiescent naïve T cells only require energy for survival and migration, and they mainly metabolize glucose to carbon dioxide through oxidative phosphorylation. However, activated T cells engage in robust cell proliferation, produce of a range of effector molecules and migrate through peripheral tissues, so they utilizes glycolysis to convert glucose to lactate (termed aerobic glycolysis) to meet the significantly increased metabolic demands. Importantly, the differentiation of T-cell subsets and memory T cells (Tm) was also significantly shaped by distinct cellular metabolic pathways including glucose, amino acids (AA), fatty acids (FA), and others. Understanding the regulatory metabolic networks on immunity may offer new insights into the immune-related disorders and open novel potential therapies to prevent and treat immune diseases.

PI3Kδ inhibition hits a sensitive spot in B cell malignancies

A PI3Kδ-selective inhibitor shows impressive clinical activity in chronic lymphocytic leukemia and indolent B cell non-Hodgkin's lymphomas. In these malignancies, the PI3K pathway is not mutationally activated as in many other cancers, but it is important for mediating supportive cues from the cancer microenvironment and the B cell antigen receptor.

The polycomb protein Ezh2 regulates differentiation and plasticity of CD4(+) T helper type 1 and type 2 cells

After antigen encounter by CD4(+) T cells, polarizing cytokines induce the expression of master regulators that control differentiation. Inactivation of the histone methyltransferase Ezh2 was found to specifically enhance T helper 1 (Th1) and Th2 cell differentiation and plasticity. Ezh2 directly bound and facilitated correct expression of Tbx21 and Gata3 in differentiating Th1 and Th2 cells, accompanied by substantial trimethylation at lysine 27 of histone 3 (H3K27me3). In addition, Ezh2 deficiency resulted in spontaneous generation of discrete IFN-γ and Th2 cytokine-producing populations in nonpolarizing cultures, and under these conditions IFN-γ expression was largely dependent on enhanced expression of the transcription factor Eomesodermin. In vivo, loss of Ezh2 caused increased pathology in a model of allergic asthma and resulted in progressive accumulation of memory phenotype Th2 cells. This study establishes a functional link between Ezh2 and transcriptional regulation of lineage-specifying genes in terminally differentiated CD4(+) T cells.

Role of inositol poly-phosphatases and their targets in T cell biology

T lymphocytes play a critical role in host defense in all anatomical sites including mucosal surfaces. This not only includes the effector arm of the immune system, but also regulation of immune responses in order to prevent autoimmunity. Genetic targeting of PI3K isoforms suggests that generation of PI(3,4,5)P3 by PI3K plays a critical role in promoting effector T cell responses. Consequently, the 5'- and 3'-inositol poly-phosphatases SHIP1, SHIP2, and phosphatase and tensin homolog capable of targeting PI(3,4,5)P3 are potential genetic determinants of T cell effector functions in vivo. In addition, the 5'-inositol poly-phosphatases SHIP1 and 2 can shunt PI(3,4,5)P3 to the rare but potent signaling phosphoinositide species PI(3,4)P2 and thus these SHIP1/2, and the INPP4A/B enzymes that deplete PI(3,4)P2 may have precise roles in T cell biology to amplify or inhibit effectors of PI3K signaling that are selectively recruited to and activated by PI(3,4)P2. Here we summarize recent genetic and chemical evidence that indicates the inositol poly-phosphatases have important roles in both the effector and regulatory functions of the T cell compartment. In addition, we will discuss future genetic studies that might be undertaken to further elaborate the role of these enzymes in T cell biology as well as potential pharmaceutical manipulation of these enzymes for therapeutic purposes in disease settings where T cell function is a key in vivo target.

Phosphoinositide 3-kinase δ/γ inhibition does not prevent concanavalin A-induced hepatitis

An increasing number of studies have suggested that phosphoinositide 3-kinase-γ (PI3Kγ) and PI3Kδ are involved in the pathogenesis of autoimmune and inflammatory diseases, such as asthma and atherosclerosis. However, the underlying mechanism of acute hepatitis remains unknown. The present study aimed to determine the effect of PI3Kδ/γ inhibition on hepatic injury in a murine model of hepatitis induced by concanavalin A (ConA). It was demonstrated that the pharmacological inhibition of PI3Kδ/γ by TG100-115 did not prevent liver damage following ConA challenge. Furthermore, the PI3Kδ/γ inhibition resulted in elevated transaminase activity in the serum, aggravated hepatic lesions characterized by hepatic necrosis, increased inflammatory cell infiltration and apoptosis of hepatocytes. Survival tests demonstrated that TG100-115 significantly increased the death rate of mice following ConA challenge. In addition, TG100-115 increased the serum levels of the proinflammatory cytokine IL-2 following ConA injection. These results may oppose the development of PI3Kδ/γ inhibitors as therapeutic agents, particularly for the treatment of human hepatitis.

Novel PI3Kγ mutation in a 44-year-old man with chronic infections and chronic pelvic pain

A 44-year-old man is presented here with 14 years of chronic purulent sinusitis, a chronic fungal rash of the scrotum, and chronic pelvic pain. Treatment with antifungal therapy resulted in symptom improvement, however he was unable to establish an effective long-term treatment regimen, resulting in debilitating symptoms. He had undergone extensive work-up without identifying a clear underlying etiology, although Candida species were cultured from the prostatic fluid. 100 genes involved in the cellular immune response were sequenced and a missense mutation was identified in the Ras-binding domain of PI3Kγ. PI3Kγ is a crucial signaling element in leukotaxis and other leukocyte functions. We hypothesize that his mutation led to his chronic infections and pelvic pain.

The microRNA miR-181 is a critical cellular metabolic rheostat essential for NKT cell ontogenesis and lymphocyte development and homeostasis

Regulation of metabolic pathways in the immune system provides a mechanism to actively control cellular function, growth, proliferation, and survival. Here, we report that miR-181 is a nonredundant determinant of cellular metabolism and is essential for supporting the biosynthetic demands of early NKT cell development. As a result, miR-181-deficient mice showed a complete absence of mature NKT cells in the thymus and periphery. Mechanistically, miR-181 modulated expression of the phosphatase PTEN to control PI3K signaling, which was a primary stimulus for anabolic metabolism in immune cells. Thus miR-181-deficient mice also showed severe defects in lymphoid development and T cell homeostasis associated with impaired PI3K signaling. These results uncover miR-181 as essential for NKT cell development and establish this family of miRNAs as central regulators of PI3K signaling and global metabolic fitness during development and homeostasis.