Phosphoinositide 3-kinase Gamma Research Articles

IRF5 governs macrophage adventitial infiltration to fuel abdominal aortic aneurysm formation.

Abdominal aortic aneurysm (AAA) is a chronic inflammatory disease characterized by the expansion of the aortic wall. One of the most significant features is the infiltration of macrophages in the adventitia, which drives vasculature remodeling. The role of macrophage-derived interferon regulatory factor 5 (IRF5) in macrophage infiltration and AAA formation remains unknown. RNA sequencing of AAA adventitia identified Irf5 as the top significantly increased transcription factor that is predominantly expressed in macrophages. Global and myeloid cell-specific deficiency of Irf5 reduced AAA progression, with a marked reduction in macrophage infiltration. Further cellular investigations indicated that IRF5 promotes macrophage migration by direct regulation of downstream phosphoinositide 3-kinase γ (PI3Kγ, Pik3cg). Pik3cg ablation hindered AAA progression, and myeloid cell-specific salvage of Pik3cg restored AAA progression and macrophage infiltration derived from Irf5 deficiency. Finally, we found that IRF5 and PI3Kγ expression in the adventitia is significantly increased in patients with AAA. These findings reveal that the IRF5-dependent regulation of PI3Kγ is essential for AAA formation.

Defining a Targetable Leukemia Intrinsic Dependency on Noncanonical PI3Kgamma Signaling

There are overlapping clinical and pathologic characteristics between poor prognosis subsets of acute myeloid leukemia (AML) and blastic plasmacytoid dendritic cell neoplasm (BPDCN), but common dependencies are ill-defined. We hypothesized that identifying novel shared targets and biomarkers could elucidate biology and nominate new therapies for both malignancies. We performed genome-wide CRISPR interference in BPDCN cells and identified 327 dependency genes, which were then analyzed informatically and functionally in AML, ALL, and BPDCN cells and patient-derived xenografts (PDXs). We defined a leukemia subset characterized by PIK3R5 activation and sensitivity to phosphoinositide 3-kinase gamma (PI3Kγ) inhibition via a noncanonical downstream pathway. The PI3Kγ complex includes an enzymatic subunit p110γ encoded by PIK3CG and a regulatory subunit p101 encoded by PIK3R5. Intriguingly, despite elevation of both p110γ and p101 proteins in this leukemia subset, only the PIK3R5 mRNA is overexpressed. To investigate this disconnection, we measured protein half-life and found that p110γ stability is positively regulated by PIK3R5/p101, associated with reduced p110γ ubiquitination. This suggested that increased expression of PIK3R5/p101 leads to posttranslational p110γ elevation by protecting it from ubiquitin proteasome-mediated degradation. To identify the upstream activator of PIK3R5, we analyzed RNA-seq data in >200 leukemia PDXs and found that AMLs with activated PIK3R5 are enriched for an innate immune response signature (IIRS). Supporting this model and indicating potential clinical relevance, analysis of TCGA AML patients revealed that the IIRS, which includes PIK3R5, was associated with M4/M5 monocytic AML and poor prognosis, independent of age, cytogenetics, or somatic mutations. Furthermore, in cells with low baseline expression, PIK3R5 was induced by the Toll-like receptor agonist resiquimod, showing that PIK3R5 is activated by inflammatory signaling and consistent with a monocytic/dendritic lineage association. By integrated analysis of ATAC-seq and ChIP-seq in PIK3R5 high vs low leukemias, as well as gene dependency scores, we identified the transcription factor PU.1 as responsible for PIK3R5 activation. Treatment with resiquimod enhanced the interaction between PU.1 and the PIK3R5 promoter, while depletion of PU.1 nullified the ability of resiquimod to activate PIK3R5. To elucidate molecular events downstream of p101/PI3Kγ, we studied consequences of pathway inactivation using PIK3R5 interference or the PI3Kγ-selective inhibitor eganelisib. Surprisingly, there was no effect of PI3Kγ inactivation on AKT phosphorylation or canonical PI3K-AKT-mTOR mRNA targets. Therefore, we performed phosphoproteomics and found that PAK1 S144, a phosphorylation site not previously associated with PI3K signaling, was suppressed by PIK3R5/PI3Kγ inhibition ( panel a). Selective inhibitors of PAK1, but not AKT, replicated the effect of eganelisib. Furthermore, introduction of constitutively active PAK1, but not inactive PAK1, eliminated sensitivity of leukemias to eganelisib, supporting the functional relationship between PAK1 phosphorylation and PI3Kγ dependency. PI3Kγ inhibitors are being tested in solid tumor trials to repolarize macrophages and potentiate immune checkpoint blockade, but their cancer cell-intrinsic role has not been explored. To assess PI3Kγ inhibition in vivo, we first performed intradermal xenografting assays using BPDCN derived from a patient's skin tumor. Eganelisib achieved comparable efficacy to cytarabine chemotherapy and the combination of eganelisib and cytarabine exerted significant synergy (combination index=0.63, p<0.0001). Next, we measured the effect of PI3Kγ inhibition on survival in disseminated PDX models. As predicted, single agent eganelisib significantly prolonged survival in AML, ALL, and BPDCN with high PIK3R5, while having no benefit in cases with low PIK3R5. To our surprise, the combination of eganelisib/cytarabine synergistically increased survival in all cases, regardless of baseline PIK3R5 ( panel b). We conclude that inflammatory signaling-activated PIK3R5 is a biomarker for sensitivity to PI3Kγ inhibition via an unappreciated PI3Kγ-PAK1 axis. Synergy with cytarabine unmasked eganelisib sensitivity in additional leukemias, expanding the therapeutic potential of targeting PI3Kγ.

Dual inhibition of phosphoinositide 3-kinases delta and gamma reduces chronic B cell activation and autoantibody production in a mouse model of lupus.

Phosphoinositide 3-kinase delta (PI3Kδ) plays key roles in normal B cell activation and is chronically activated in malignant B cells. Targeting of PI3Kδ using FDA-approved drugs Idelalisib or Umbralisib has shown efficacy in treatment of multiple B cell malignancies. Duvelisib, an inhibitor targeting both PI3Kδ and PI3Kγ (PI3Kδγi) has also been used for treatment of several leukemias and lymphomas and was suggested to offer potential additional benefits in supressing T cell and inflammatory responses. Transcriptomics analyses indicated that while most B cell subsets predominantly express PI3Kδ, plasma cells upregulate PI3Kγ. We thus assessed whether PI3Kδγi treatment can impact chronic B cell activation in the context of an autoantibody-mediated disease. Using the TAPP1R218LxTAPP2R211L (TAPP KI) mouse model of lupus-like disease driven by dysregulated PI3K pathway activity, we performed 4 week PI3Kδγi treatments and found significant reduction in CD86+ B cells, germinal center B cells, follicular helper T cells and plasma cells in multiple tissues. This treatment also significantly attenuated the abnormally elevated serum levels of IgG isotypes observed in this model. The profile of autoantibodies generated was markedly altered by PI3Kδγi treatment, with significant reductions in IgM and IgG targeting nuclear antigens, matrix proteins and other autoantigens. Kidney pathology was also impacted, with reduced IgG deposition and glomerulonephritis. These results indicate that dual inhibition of PI3Kδ and PI3Kγ can target autoreactive B cells and may have therapeutic benefits in autoantibody-mediated disease.

Abstract 5162: Discovery of INCB098377: a potent inhibitor of phosphoinositide 3-kinase gamma (PI3Kγ)

Abstract Immune checkpoint blockade has shown impressive efficacy in patients with inflamed tumors, although minimal activity has been observed in tumors lacking T cells. Myeloid cells are one of the most abundant cell types in both inflamed and non-inflamed tumors, and may contribute to immune checkpoint blockade resistance. The plasticity of macrophages enables them to directly and indirectly modulate T cell responses, and directly kill tumor cells via phagocytosis. This suggests that targeting myeloid cells could be an effective therapeutic approach. Class I PI3Ks are a family of dual specificity lipid and protein kinases. Unlike other class I PI3Ks, PI3Kγ is predominantly expressed in myeloid cells. PI3Kγ has been shown to be a key mediator that drives the immunosuppressive macrophage program by stimulating AKT/mTOR signaling and promote C/EBPβ expression while inhibiting NF-кB activity (Keneda MM. Nature. 2016;17:437-442). Here, we present the discovery and characterization of INCB098377, a potent and selective PI3Kγ inhibitor. Specific inhibition of PI3Kγ with INCB098377 may induce anti-tumor activity by reshaping the tumor immune microenvironment. In cell-based assays, INCB098377 has an IC50 of 1.4 nM and is greater than 100-fold selective over other PI3K isoforms. It also shows a favorable PK profile in several animal species. Treatment of M2 polarized macrophages with INCB098377 resulted in changes towards a more pro-inflammatory phenotype. CD163 and CD206 were decreased, whereas HLA-DR and co-stimulatory CD80/86 molecules were increased. MHC-I expression was unchanged, suggesting a role for these macrophages in MHC-II-mediated antigen presentation. Furthermore, INCB098377 treatment reduced macrophage-mediated immunosuppression and restored T cell proliferation in M2 polarized macrophages co-cultured with allogeneic human T cells. In vivo, significant tumor growth inhibition was observed with once-daily dosing of 10 mg/kg INCB098377 in both syngeneic and humanized mouse tumor models without toxicity. Moreover, efficacy was observed in inflamed and non-inflamed tumor models. Consistent with the proposed mechanism of action, INCB098377 inhibited phospho-AKT levels in vivo and in human PBMCs. Treatment with INCB098377 induced pro-inflammatory responses without macrophage depletion suggests that robust tumor microenvironment changes are responsible for observed anti-tumor efficacy. In addition, INCB098377 inhibited neutrophil migration in the Carrageenan-induced paw inflammation model. INCB098377, a potent and selective inhibitor of PI3Kγ, shows effective anti-tumor activity in a variety of mouse and humanized cancer models through the inhibition of immunosuppressive cells trafficking into the tumor, modulation of myeloid cell function, and enhancement of T cell proliferation. Acknowledgments: Diana Alvarez Arias and Stephen Douglass contributed equally to this study. Citation Format: Diana A. Arias, Stephen Douglass, Lisa Truong, Qian Wang, Kathy H. Wang, Gengjie Yang, Michael Hansbury, Sybil O’Connor, Kevin Bowman, Robert Collins, Matthew Stubbs, Leslie Hall, Christina Stevens, Christopher Maddage, Brent Douty, Maryanne Covington, Lynn Leffet, Eddy Yue, Andrew Combs, Sunkyu Kim, Niu Shin, Holly Koblish, Rodrigo Hess. Discovery of INCB098377: a potent inhibitor of phosphoinositide 3-kinase gamma (PI3Kγ). [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5162.

Leveraging molecular structure and bioactivity with chemical language models for de novo drug design

Generative chemical language models (CLMs) can be used for de novo molecular structure generation by learning from a textual representation of molecules. Here, we show that hybrid CLMs can additionally leverage the bioactivity information available for the training compounds. To computationally design ligands of phosphoinositide 3-kinase gamma (PI3Kγ), a collection of virtual molecules was created with a generative CLM. This virtual compound library was refined using a CLM-based classifier for bioactivity prediction. This second hybrid CLM was pretrained with patented molecular structures and fine-tuned with known PI3Kγ ligands. Several of the computer-generated molecular designs were commercially available, enabling fast prescreening and preliminary experimental validation. A new PI3Kγ ligand with sub-micromolar activity was identified, highlighting the method’s scaffold-hopping potential. Chemical synthesis and biochemical testing of two of the top-ranked de novo designed molecules and their derivatives corroborated the model’s ability to generate PI3Kγ ligands with medium to low nanomolar activity for hit-to-lead expansion. The most potent compounds led to pronounced inhibition of PI3K-dependent Akt phosphorylation in a medulloblastoma cell model, demonstrating efficacy of PI3Kγ ligands in PI3K/Akt pathway repression in human tumor cells. The results positively advocate hybrid CLMs for virtual compound screening and activity-focused molecular design.

Phosphoinositide 3-kinase gamma at the crossroad between autophagy and metabolic control in doxorubicin-induced cardiomyopathy

Phosphoinositide 3-kinase gamma at the crossroad between autophagy and metabolic control in doxorubicin-induced cardiomyopathy

A PI3Kγ signal regulates macrophage recruitment to injured tissue for regenerative cell survival.

The interaction between immune cells and injured tissues is crucial for regeneration. Previous studies have shown that macrophages attenuate inflammation caused by injuries to support the survival of primed regenerative cells. Macrophage loss in zebrafish mutants like cloche (clo) causes extensive apoptosis in the regenerative cells of the amputated larval fin fold. However, the mechanism of interaction between macrophage and injured tissue is poorly understood. Here, we show that a phosphoinositide 3-kinase gamma (PI3Kγ)-mediated signal is essential for recruiting macrophages to the injured tissue. PI3Kγ inhibition by the PI3Kγ-specific inhibitor, 5-quinoxalin-6-ylmethylene-thiazolidine-2,4-dione (AS605240 or AS), displayed a similar apoptosis phenotype with that observed in clo mutants. We further show that PI3Kγ function during the early regenerative stage is necessary for macrophage recruitment to the injured site. Additionally, protein kinase B (Akt) overexpression in the AS-treated larvae suggested that Akt is not the direct downstream mediator of PI3Kγ for macrophage recruitment, while it independently plays a role for the survival of regenerative cells. Together, our study reveals that PI3Kγ plays a role for recruiting macrophages in response to regeneration.

QSAR analysis on a large and diverse set of potent phosphoinositide 3-kinase gamma (PI3K\u03b3) inhibitors using MLR and ANN methods

Phosphorylation of PI3Kγ as a member of lipid kinases-enzymes, plays a crucial role in regulating immune cells through the generation of intracellular signals. Deregulation of this pathway is involved in several tumors. In this research, diverse sets of potent and selective isoform-specific PI3Kγ inhibitors whose drug-likeness was confirmed based on Lipinski’s rule of five were used in the modeling process. Genetic algorithm (GA)-based multivariate analysis was employed on the half-maximal inhibitory concentration (IC50) of them. In this way, multiple linear regression (MLR) and artificial neural network (ANN) algorithm, were used to QSAR models construction on 245 compounds with a wide range of pIC50 (5.23–9.32). The stability and robustness of the models have been evaluated by external and internal validation methods (R2 0.623–0.642, RMSE 0.464–0.473, F 40.114, Q2LOO 0.600, and R2y-random 0.011). External verification using a wide variety of structures out of the training and test sets show that ANN is superior to MLR. The descriptors entered into the model are in good agreement with the X-ray structures of target-ligand complexes; so the model is interpretable. Finally, Williams plot-based analysis was applied to simultaneously compare the inhibitory activity and structural similarity of training, test and validation sets.

Computational design of phosphoinositide 3-kinase gamma (PI3Kg) inhibitors as a newer therapy for rheumatoid arthritis


 
 
 
 Purpose: To develop a potential therapy for rheumatoid arthritis (RA) by altering factors involved in the pathogenesis of the disease.
 Methods: Molecular docking simulation-based virtual screening was performed against phosphoinositide-3-kinase gamma (PI3Kg) to identify potential leads that may serve as anti-rheumatoid arthritic agents through their interactions and binding energies with the target receptor, followed by their optimization for improvement of their pharmacokinetics and toxicity profiles.
 Results: Molecular docking simulation-based virtual screening and computational toxicity profiling predicted that the lead compounds ZINC04376856, ZINC01729526, ZINC01045089, ZINC03954520, ZINC01738764, and ZINC01163259 were potent PI3Kg inhibitors.
 Conclusion: These lead compounds exert potent inhibitory effects on human PI3Kg receptor. Thus, they need to be experimentally validated for use in the development of novel drugs for treating RA in humans.
 
 
 

Inhibition of Phosphoinositide 3-Kinase Gamma Protects Endothelial Cells via the Akt Signaling Pathway in Sepsis-Induced Acute Kidney Injury

Introduction: Sepsis is a primary cause of death in critically ill patients and is characterized by multiple organ dysfunction, including sepsis-induced acute kidney injury (AKI), which contributes to high mortality in sepsis. However, its pathophysiological mechanisms remain unclear. The kidney has one of the richest and most diversified endothelial cell populations in the body. This study was designed to investigate the effects of endothelial dysfunction in sepsis-induced AKI and explore possible intervention measures to offer new insight into the pathogenesis and treatment of sepsis-induced AKI. Methods: The circulating levels of endothelial adhesion molecules were detected in patients with sepsis and healthy controls to observe the role of endothelial damage in sepsis and sepsis-induced AKI. A murine sepsis model induced by cecal ligation and perforation was pretreated with a phosphoinositide 3-kinase gamma (PI3Kγ) inhibitor (CZC24832), and survival, kidney damage, and renal endothelial injury were assessed by pathological examination, immunohistochemistry, quantitative polymerase chain reaction, and Western blotting. Lipopolysaccharides and CZC24832 were administered to human umbilical vein endothelial cells in vitro, and endothelial cell function and the expression of adhesion molecules were evaluated. Results: Endothelial damage was more serious in sepsis-induced AKI than that in non-AKI, and the inhibition of PI3Kγ alleviates renal endothelial injury in a murine sepsis model, protecting endothelial cell function and repairing endothelial cell injury through the Akt signaling pathway. Conclusions: In this study, endothelial cell dysfunction plays an important role in sepsis-induced AKI, and the inhibition of PI3Kγ alleviates endothelial cell injury in sepsis-induced AKI through the PI3Kγ/Akt pathway, providing novel targets for treating sepsis and related kidney injury.

Pyrazole substituted resorcinol derivatives with PI3K inhibitory potential

Phosphoinositide 3-kinase gamma enzymes play significant roles in inflammatory cell recruitment to tumors and accordingly lot of studies have targeted development of small molecule inhibitors against these enzymes for managing various chronic inflammatory disorders. In this study, a number of Pyrazole substituted Resorcinol derivatives have been synthesized in the laboratory and then were evaluated for the inhibitory potential against the gamma isozyme. Highest inhibitory potential was observed from the introduction of non-polar phenyl or methylbenzyl substitution (66.4% and 59.5%) on the OH group of the resorcinol. Addition of relatively polar moiety resulted in decrease in the inhibitory potential and lowest inhibition was observed from 4-pyridyl methyl and 2-morpholino ethyl moieties (23.6% and 24.5% inhibition respectively). The results were encouraging due to remarkable inhibition showed by these compounds against the PI3K enzyme. Thus the scaffold appears as interesting pharmacophore suitable for further development.

PI3Kγ Regulatory Protein p84 Determines Mast Cell Sensitivity to Ras Inhibition-Moving Towards Cell Specific PI3K Targeting?

Mast cells are the major effector cells in immunoglobulin E (IgE)-mediated allergy. The high affinity IgE receptor FcεRI, as well as G protein-coupled receptors (GPCRs) on the mast cell surface signals to phosphoinositide 3-kinase γ (PI3Kγ) to initiate degranulation, cytokine release, and chemotaxis. PI3Kγ is therefore considered as a target for treatment of allergic disorders. However, leukocyte PI3Kγ is key to many functions in innate and adaptive immunity, and attenuation of host defense mechanisms is an expected adverse effect that complicates treatment of chronic illnesses. PI3Kγ operates as a p110γ/p84 or p110γ/p101 complex, where p110γ/p84 requires Ras activation. Here we investigated if modulation of Ras-isoprenylation could target PI3Kγ activity to attenuate PI3Kγ-dependent mast cell responses without impairment of macrophage functions. In murine bone marrow-derived mast cells, GPCR stimulation triggers activation of N-Ras and H-Ras isoforms, which is followed by the phosphorylation of protein kinase B (PKB/Akt) relayed through PI3Kγ. Although K-Ras is normally not activated in Ras wild-type cells, it is able to compensate for genetically deleted N- and H-Ras isoforms. Inhibition of Ras isoprenylation with farnesyltransferase inhibitor FTI-277 leads to a significant reduction of mast cell degranulation, cytokine production, and migration. Complementation experiments expressing PI3Kγ adaptor proteins p84 or p101 demonstrated a differential sensitivity towards Ras-inhibition depending on PI3Kγ complex composition. Mast cell responses are exclusively p84-dependent and were effectively controlled by FTI-277. Similar results were obtained when GTP-Ras was inactivated by overexpression of the GAP-domain of Neurofibromin-1 (NF-1). Unlike mast cells, macrophages express p84 and p101 but are p101-dominated and thus remain functional under treatment with FTI-277. Our work demonstrates that p101 and p84 have distinct physiological roles, and that Ras dependence of PI3Kγ signaling differs between cell types. FTI-277 reduces GPCR-activated PI3Kγ  responses in p84-expressing but not p101-containing bone marrow derived cells. However, prenylation inhibitors have pleiotropic effects beyond Ras and non-tolerable side-effects that disfavor further clinical validation. Statins are, however, clinically well-established drugs that have previously been proposed to block mast cell degranulation by interference with protein prenylation. We show here that Simvastatin inhibits mast cell degranulation, but that this does not occur via Ras-PI3Kγ pathway alterations.

Impact of ambient temperature on inflammation-induced encephalopathy in endotoxemic mice\u2014role of phosphoinositide 3-kinase gamma

BackgroundSepsis-associated encephalopathy (SAE) is an early and frequent event of infection-induced systemic inflammatory response syndrome. Phosphoinositide 3-kinase γ (PI3Kγ) is linked to neuroinflammation and inflammation-related microglial activity. In homeotherms, variations in ambient temperature (Ta) outside the thermoneutral zone lead to thermoregulatory responses, mainly driven by a gradually increasing sympathetic activity, and may affect disease severity. We hypothesized that thermoregulatory response to hypothermia (reduced Ta) aggravates SAE in PI3Kγ-dependent manner.MethodsExperiments were performed in wild-type, PI3Kγ knockout, and PI3Kγ kinase-dead mice, which were kept at neutral (30 ± 0.5 °C) or moderately lowered (26 ± 0.5 °C) Ta. Mice were exposed to lipopolysaccharide (LPS, 10 μg/g, from Escherichia coli serotype 055:B5, single intraperitoneal injection)—evoked systemic inflammatory response (SIR) and monitored 24 h for thermoregulatory response and blood–brain barrier integrity. Primary microglial cells and brain tissue derived from treated mice were analyzed for inflammatory responses and related cell functions. Comparisons between groups were made with one-way or two-way analysis of variance, as appropriate. Post hoc comparisons were made with the Holm–Sidak test or t tests with Bonferroni’s correction for adjustments of multiple comparisons. Data not following normal distribution was tested with Kruskal-Wallis test followed by Dunn’s multiple comparisons test.ResultsWe show that a moderate reduction of ambient temperature triggers enhanced hypothermia of mice undergoing LPS-induced systemic inflammation by aggravated SAE. PI3Kγ deficiency enhances blood–brain barrier injury and upregulation of matrix metalloproteinases (MMPs) as well as an impaired microglial phagocytic activity.ConclusionsThermoregulatory adaptation in response to ambient temperatures below the thermoneutral range exacerbates LPS-induced blood–brain barrier injury and neuroinflammation. PI3Kγ serves a protective role in suppressing release of MMPs, maintaining microglial motility and reinforcing phagocytosis leading to improved brain tissue integrity. Thus, preclinical research targeting severe brain inflammation responses is seriously biased when basic physiological prerequisites of mammal species such as preferred ambient temperature are ignored.

LncRNA CANT1 suppresses retinoblastoma progression by repellinghistone methyltransferase in PI3K\u03b3 promoter

Retinoblastoma (RB) is the most common malignant intraocular tumor of childhood. Recent studies have shown that long noncoding RNAs (lncRNAs), which are longer than 200 bp and without protein-coding ability, are key regulators of tumorigenesis. However, the role of lncRNAs in retinoblastoma remains to be elucidated. In this study, we found that the expression of lncRNA CASC15-New-Transcript 1 (CANT1) was significantly downregulated in RB. Notably, overexpression of CANT1 significantly inhibited RB growth both in vitro and in vivo. Furthermore, lncRNA CANT1, which was mainly located in the nucleus, occupied the promoter of phosphoinositide 3-kinase gamma (PI3Kγ) and blocked histone methyltransferase hSET1 from binding to the PI3Kγ promoter, thus abolishing hSET1-mediated histone H3K4 trimethylation of the PI3Kγ promoter and inhibiting PI3Kγ expression. Furthermore, we found that silencing PI3Kγ either by lncRNA CANT1 overexpression or by PI3Kγ siRNA, reduced the activity of PI3K/Akt signaling and suppressed RB tumorigenesis. In summary, lncRNA CANT1 acts as a suppressor of RB progression by blocking gene-specific histone methyltransferase recruitment. These findings outline a new CANT1 modulation mechanism and provide an alternative option for the RB treatment.

A non-catalytic function of PI3Kγ drives smooth muscle cell proliferation after arterial damage.

Arterial remodeling in hypertension and intimal hyperplasia involves inflammation and disrupted flow, both of which contribute to smooth muscle cell dedifferentiation and proliferation. In this context, our previous results identified phosphoinositide 3-kinase γ (PI3Kγ) as an essential factor in inflammatory processes of the arterial wall. Here, we identify for the first time a kinase-independent role of nonhematopoietic PI3Kγ in the vascular wall during intimal hyperplasia using PI3Kγ-deleted mice and mice expressing a kinase-dead version of the enzyme. Moreover, we found that the absence of PI3Kγ in vascular smooth muscle cells (VSMCs) leads to modulation of cell proliferation, associated with an increase in intracellular cAMP levels. Real-time analysis of cAMP dynamics revealed that PI3Kγ modulates the degradation of cAMP in primary VSMCs independently of its kinase activity through regulation of the enzyme phosphodiesterase 4. Importantly, the use of an N-terminal competing peptide of PI3Kγ blocked primary VSMC proliferation. These data provide evidence for a kinase-independent role of PI3Kγ in arterial remodeling and reveal novel strategies targeting the docking function of PI3Kγ for the treatment of cardiovascular diseases.

Rational Design of Novel Phosphoinositide 3-Kinase Gamma (PI3Kγ) Selective Inhibitors: A Computational Investigation Integrating 3D-QSAR, Molecular Docking and Molecular Dynamics Simulation.

Phosphoinositide 3-kinase gamma (PI3Kγ) draws an increasing attention due to its link with deadly cancer, chronic inflammation and allergy. But the development of PI3Kγ selective inhibitors is still a challenging endeavor because of the high sequence homology with the other PI3K isoforms. In order to acquire valuable information about the interaction mechanism between potent inhibitors and PI3Kγ, a series of PI3Kγ isoform-selective inhibitors were analyzed by a systematic computational method, combining 3D-QSAR, molecular docking, molecular dynamic (MD) simulations, free energy calculations and decomposition. The general structure-activity relationships were revealed and some key residues relating to selectivity and high activity were highlighted. It provides precious guidance for rational virtual screening, modification and design of selective PI3Kγ inhibitors. Finally, ten novel inhibitors were optimized and P10 showed satisfactory predicted bioactivity, demonstrating the feasibility to develop potent PI3Kγ inhibitors through this computational modeling and optimization.

Discovery of a novel phosphoinositide 3-kinase gamma (PI3Kγ) inhibitor against hematologic malignancies and theoretical studies on its PI3Kγ-specific binding mechanisms.

Class IB phosphoinositide 3-kinase gamma (PI3Kγ) is vital for regulating intracellular signaling pathways and has become an attractive drug target for the treatment of malignant tumors. In the present study, one potent PI3Kγ inhibitor (JN-PK1) with a novel scaffold against hematologic malignancies was identified based on a series of biological experiments, and then the selective mechanism of PI3Kγ inhibition was explored by a systematic computational method. JN-PK1 shows an effective antiproliferative activity on several cancer cell lines, especially blood cancer cells. Cell-free enzymatic studies demonstrated that JN-PK1 specifically inhibits PI3Kγ at low micromolar concentrations without affecting other isoforms of PI3K. In the cellular context, JN-PK1 potently inhibits PI3K/Akt/mTOR signaling pathway in a time- and concentration-dependent manner, which leads to the apoptosis of cancer cells. Further, the specific binding mode of JN-PK1 with PI3Kγ was illustrated by molecular docking, and the selective inhibition mechanism of PI3Kγ by JN-PK1 was revealed by molecular dynamics simulation. Finally, some key residues of PI3Kγ required for specificity and activity were identified. Taken together, JN-PK1 may be developed as a promising therapeutic agent for the treatment of hematologic malignancies.

The Combination of Duvelisib, a PI3K-δ,γ Inhibitor, and Romidepsin Is Highly Active in Relapsed/Refractory Peripheral T-Cell Lymphoma with Low Rates of Transaminitis: Results of Parallel Multicenter, Phase 1 Combination Studies with Expansion Cohorts

Introduction: Most therapies for relapsed/refractory (rel/ref) T-cell lymphomas (TCLs) induce responses in about 25%-30% of pts. Phosphoinositide-3-kinase (PI3K) delta has a role in survival and proliferation of malignant T cells as well as T-cell receptor and cytokine signaling in nonmalignant T cells. Inhibition of PI3K gamma can reprogram macrophages and promote tumor phagocytosis. A phase I study of the PI3K-δ/γ inhibitor duvelisib (D) in pts with rel/ref TCLs showed promising activity, but high rates of grade (Gr) 3/4 ALT elevation at the MTD of 75 mg BID (Horwitz et al, Blood 2018). Based on in vitro evidence of synergy, we initiated a phase I/II study of D combined with either romidepsin (R) or bortezomib (B).Methods: Pts were enrolled into parallel phase I dose escalation arms utilizing a 3+3 design to define the maximum tolerated dose (MTD) of D combined with either R (Arm A) or B (Arm B) in cycle 1. D was dosed at 25 mg, 50mg, or 75 mg BID on days 1-28 with either R (10 mg/m2 on days 1, 8, & 15) or B (1 mg/m2 on days 1, 4, 8, & 11) each on 28-day cycles. Once the MTD was established with each combination, preplanned expansion cohorts were enrolled to further characterize safety and describe subtype-specific efficacy (PTCL and CTCL). Based upon promising safety and efficacy, a total of 39 pts were treated on Arm A (33 at the MTD, D 75 mg BID + R 10 mg/m2). All pts received prophylaxis against Varicella and Pneumocystis. Response assessments were performed q2 cycles for 6 months and then q3 cycles. To assess biomarkers of response and resistance to single-agent D, 10 pts in Arm A (75 mg BID) and 10 pts in Arm B (25 mg BID) were each treated with 1 cycle of D alone, with pretreatment and on-treatment biopsies. Pts who did not achieve CR on D alone at the end of cycle 1 proceeded to combination therapy.Results: The MTD was not reached in Arm A (R+D); thus, dose level 3(DL3); (D 75 mg BID + R 10 mg/m2 days 1, 8, & 15) was deemed the MTD and used for expansion. In Arm B there were no cycle 1 DLTs. However, Gr 3 elevations of ALT or AST following cycle 2 were observed in 3 pts at DL2 (D 50mg BID) and 2 pts at DL3 (D 75mg BID) leading to DL1 (D 25mg BID + B 1mg/m2 days 1, 4, 8, & 11) being accepted as MTD for expansion.Of Arm A pts at the MTD, 21/32 (65%) had adverse events (AEs) ≥Gr 3, possibly related to study drug. Events occurring in ≥10% of pts included: increased ALT/AST (n=5, 15%), neutropenia (n=6, 18%), and hyponatremia (n=4, 12%). Three pts had ≥Gr 3 diarrhea. There were no Gr 5 AEs related to protocol therapy. Strikingly, 4 of 5 pts with elevated transaminases (ALT [4], AST [1]) on combination began on the D-only Lead-In Arm at 75 mg BID. In contrast, only 1 of 22 (4%) pts receiving combination R+D in cycle 1 had Gr 3-4 transaminitis (p=.0242). Of the pts with Gr 3-4 diarrhea, 2 of 3 were on Lead-In (p=.0793).In Arm A, 35/39 pts were evaluable for response. Overall response rate (ORR) across all DLs was 51% (18/35) and CR rate (CR) was 17% (6/35). PTCL, ORR and CR rates were 55% (12/22) and 27% (6/22) respectively. Among CTCL, ORR was 46% (6/13), no CR. Reponses by histology are detailed in Table 1. Of these responders, 3 proceeded to allogeneic stem cell transplantation (allo SCT) with curative intent. Of note, 4 pts were not evaluable for response, described in Table 1. Median PFS for Arm A (all DL) was 8.8 m (PTCL) and 5.4 m (CTCL). Median follow up was 5.8 m, and median duration of response was 9.1 m.Of Arm B pts at the MTD, 10/22 (45%) had AEs ≥Gr 3, possibly related to study drug, of these, only neutropenia (n=4, 18%) occurred in ≥10% of pts at the MTD. There was 1 Gr 5 event, Stevens-Johnson syndrome, possibly related to protocol therapy.In Arm B, the ORR across all DLs was 32% (9/28), the CR rate was 11% (3/28). ORR in PTCL was36% (5/14), 21% (3/14) achieved CR. ORR in CTCL was 28% (4/14), no CR. Responses by histology are detailed in Table 2. Of these responders, 1 proceeded to allo SCT with curative intent. Median PFS for Arm B (all DL) was 3.5 m (PTCL) and 4.6 m (CTCL). Median follow up was 7.2 m, and median duration of response was 9.3 m.Conclusion: Duvelisib in combination with romidepsin is highly active in pts with PTCL with tolerable side effects. Duvelisib can be safely combined with romidepsin at a 3-fold higher dose than with bortezomib (75 mg BID vs 25 mg BID) with much lower rate of Gr 3-4 transaminitis than single-agent duvelisib at the same dose. The high response rates and safety of Arm A (Duvelisib + Romidepsin) in PTCL appears to be a potential therapeutic advance and warrants further evaluation in a larger study. DisclosuresHorwitz:Portola: Consultancy; Innate Pharma: Consultancy; Forty Seven: Consultancy, Research Funding; Kyowa-Hakka-Kirin: Consultancy, Research Funding; ADC Therapeutics: Consultancy, Research Funding; Seattle Genetics: Consultancy, Research Funding; Millennium/Takeda: Consultancy, Research Funding; Mundipharma: Consultancy; Corvus: Consultancy; Celgene: Consultancy, Research Funding; Infinity/Verastem: Consultancy, Research Funding; Aileron Therapeutics: Consultancy, Research Funding; Spectrum: Research Funding; Trillium: Consultancy. Moskowitz:Takeda: Honoraria; Incyte: Research Funding; Seattle Genetics: Consultancy, Honoraria, Research Funding; Bristol Myers-Squibb: Consultancy, Research Funding; Merck: Research Funding; ADC Therapeutics: Research Funding. Jacobsen:Seattle Genetics: Consultancy; Merck: Consultancy. Mehta-Shah:Spectrum: Consultancy; Bristol-Myers Squibb: Research Funding; Celgene: Research Funding; Genetech: Research Funding; Verastem: Research Funding. Khodadoust:Innate Pharma: Research Funding. Fisher:Seattle Genetics Inc.: Membership on an entity's Board of Directors or advisory committees; Genetech: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees. Kim:Medivir: Membership on an entity's Board of Directors or advisory committees; Portola: Research Funding; miRagen: Research Funding; Kyowa-Kirin-Pharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; Neumedicine: Consultancy, Research Funding; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees; Innate Pharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Tetralogic: Research Funding; Merck: Research Funding; Galderma: Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Horizon Pharma: Consultancy, Research Funding; Forty Seven Inc: Research Funding; Soligenix: Research Funding; Eisai: Membership on an entity's Board of Directors or advisory committees, Research Funding. Weinstock:Travera: Equity Ownership; Astra Zeneca, JAX, Samumed, Regeneron, Sun Pharma, Prescient: Patents & Royalties; Novartis, Dragonfly, Travera, DxTerity, Travera: Consultancy; Novartis, Astra Zeneca, Abbvie, Aileron, Surface Oncology, Daiichi Sankyo: Research Funding; Novartis: Consultancy, Research Funding; Genentech/Roche, Monsanto: Consultancy.

Immuno-oncology agent IPI-549 is a modulator of P-glycoprotein (P-gp, MDR1, ABCB1)-mediated multidrug resistance (MDR) in cancer: In vitro and in vivo

Phosphoinositide 3-kinase gamma isoform (PI3Kγ) plays a critical role in myeloid-derived cells of the immunosuppressive tumor microenvironment. IPI-549, a recently discovered small molecule selective PI3Kγ inhibitor, is currently under immuno-oncology clinical trials in combination with nivolumab, an anti-PD-1 monoclonal antibody immune checkpoint blocker. The purpose of this study is to investigate whether IPI-549 could reverse P-glycoprotein (P-gp)-mediated MDR when combined with chemotherapeutic substrates of P-gp. Cytotoxicity assays showed that IPI-549 reverses P-gp-mediated MDR in SW620/Ad300 and LLC-PK-MDR1 cells. IPI-549 increases the amount of intracellular paclitaxel and inhibits the efflux of paclitaxel out of SW620/Ad300 cells. ABCB1-ATPase assay showed that IPI-549 stimulates the activity of ABCB1-ATPase. IPI-549 does not alter the expression and does not affect the subcellular localization of P-gp in SW620/Ad300 cells. The combination of IPI-549 with paclitaxel showed that IPI-549 potentiates the anti-tumor effects of paclitaxel in P-gp-overexpressing MDR SW620/Ad300 xenograft tumors. With clinical trials beginning to add newly approved immune checkpoint-based immunotherapy into standard-of-care immunogenic chemotherapy to improve patient outcomes, our findings support the rationale of adding IPI-549 to both the chemotherapeutic and immunotherapeutic aspects of cancer combination treatment strategies.

8e Protects against Acute Cerebral Ischemia by Inhibition of PI3Kγ-Mediated Superoxide Generation in Microglia.

The inflammatory response mediated by microglia plays a critical role in the progression of ischemic stroke. Phosphoinositide 3-kinase gamma (PI3Kγ) has been implicated in multiple inflammatory and autoimmune diseases, making it a promising target for therapeutic intervention. The aim of this study was to evaluate the efficacy of 8e, a hydrogen sulfide (H2S) releasing derivative of 3-n-butylphthalide (NBP), on brain damage and PI3Kγ signaling following cerebral ischemia injury. 8e significantly reduced sensorimotor deficits, focal infarction, brain edema and neural apoptosis at 72 h after transient middle cerebral artery occlusion (tMCAO). The NOX2 isoform of the NADPH oxidase family is considered a major enzymatic source of superoxide. We found that the release of superoxide, together with the expression of NOX2 subunits p47phox, p-p47phox, and the upstream PI3Kγ/AKT signaling were all down-regulated by 8e, both in the penumbral region of the rat brain and in the primary cultured microglia subjected to oxygen-glucose deprivation (OGD). With the use of siRNA and pharmacological inhibitors, we further demonstrated that 8e regulates the formation of superoxide in activated microglia through the PI3Kγ/AKT/NOX2 signaling pathway and subsequently prevents neuronal death in neighboring neurons. Our experimental data indicate that 8e is a potential candidate for the treatment of ischemic stroke and PI3Kγ-mediated neuroinflammation.