Phosphoinositide 3-kinase Isoforms Research Articles

Rational Design of a Novel 6H-Benzo[c]chromen Series as Selective PI3Kα Inhibitors.

The phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) signaling pathway is a frequently dysregulated pathway in human cancer, and PI3Kα is one of the most frequently mutated kinases in human cancer. A selective PI3Kα inhibitor may provide the opportunity to spare patients the side effects associated with broader inhibition of the class I PI3K family. Here, we describe our efforts to discover a novel series of selective PI3Kα inhibitors using structure-based drug design and molecular docking to inform the design of 6H-benzo[c]chromen inhibitors. XJTU-L453 (21) was identified with PI3Kα inhibitory potency and unique selectivity over other PI3K isoforms and all other kinases tested. Further evaluation of pharmacokinetic properties and in vivo efficacy led to the identification of the preclinical potential of XJTU-L453 (21).

Molecular mechanisms of PI3K isoform dependence in embryonic growth.

The phosphoinositide 3-kinase (PI3K) pathway is an important signaling mechanism for cell proliferation and metabolism. Mutations that activate PIK3CA may make cells p110α dependent, but when phosphatase tensin homolog (PTEN) is lost, the p110β isoform of PI3Ks becomes more important. However, the exact mechanism underlying the prevalence of p110s remains unclear. In this study, our aim was to elucidate the processes behind PI3K isoform dependency in a cellular model of embryonic development. In order to understand PI3K isoform prevalence, mouse embryonic fibroblasts (MEFs) were used and p110β, PTEN and Rac1 activity was modulated using retroviral plasmids. Expression levels and cellular growth were assessed by performing immunoblots and crystal violet assays. The levels of PTEN had only a partial effect on the prevalence of PI3K isoforms in MEFs. The dependency on p110α diminished when PTEN was depleted. Of note, when PTEN expression was repressed, there was no full transition in dependency from one PI3K isoform to the other. Interestingly, the viability of PTEN-depleted MEFs became less dependent on p110α and more dependent on p110β when p110β was overexpressed. Nevertheless, the overexpression of p110β in conjunction with PTEN knock-downs did not result in a complete shift of isoforms in PI3Ks. Finally, we investigated Rac1 activation with a mutant allele and determined a more potent increase in p110β prominence in MEFs. These findings suggest that multiple cellular parameters, including PTEN status, PI3K isoform levels, and Rac1 activity, combine to influence PI3K isoform prevalence, rather than a single determinant.

PI3Kγδ inhibition suppresses key disease features in a rat model of asthma

BackgroundTwo isoforms of Phosphoinositide 3-kinase (PI3K), p110γ and p110δ, are predominantly expressed in leukocytes and represent attractive therapeutic targets for the treatment of allergic asthma. The study aim was to assess the impact of administration of an inhaled PI3Kγδ inhibitor (AZD8154) in a rat model of asthma.MethodsFirstly, we checked that the tool compound, AZD8154, inhibited rat PI3K γ & δ kinases using rat cell-based assays. Subsequently, a time-course study was conducted in a rat model of asthma to assess PI3K activity in the lung and how it is temporally associated with other key transcription pathways and asthma like features of the model. Finally, the impact on lung dosed AZD8154 on target engagement, pathway specificity, airway inflammation and lung function changes was assessed.ResultsData showed that AZD8154 could inhibit rat PI3K γ & δ isoforms and, in a rat model of allergic asthma the PI3K pathway was activated in the lung. Intratracheal administration of AZD8154 caused a dose related suppression PI3K pathway activation (reduction in pAkt) and unlike after budesonide treatment, STAT and NF-κB pathways were not affected by AZD8154. The suppression of the PI3K pathway led to a marked inhibition of airway inflammation and reduction in changes in lung function.ConclusionThese data show that a dual PI3Kγδ inhibitor suppress key features of disease in a rat model of asthma to a similar degree as budesonide and indicate that dual PI3Kγδ inhibition may be an effective treatment for people suffering from allergic asthma.

Abstract LB175: Discovery of HP567, a highly potent, brain-penetrating, and H1047R-selective PI3Kα inhibitor for the treatment of tumors bearing H1047R mutation

Abstract The phosphoinositide 3 kinase (PI3K)-protein kinase B (PKB/AKT) is one of the most altered pathways in human cancer and its hyperactivation promotes tumor growth and survival. H1047R increases kinase activity and is the most common PI3Kα mutation with a mutation rate of 7.8% in all cancers, and 21%, 5% and 3% in breast cancer, endometrium, and ovarian cancer, respectively. Alpelisib is an FDA approved PI3Kα inhibitor targeting both wild-type (WT) and mutant PI3Kα, yet its clinical benefit is limited by the toxicities including hyperglycemia and rash (which are considered on target effects of WT- PI3Kα inhibition). Here, we report an allosteric and brain-penetrating PI3Kα inhibitor, HP567 that is 14-fold selective for PI3Kα H1047R over PI3Kα WT and is 80-fold selective over other PI3K isoforms. HP567 strongly inhibits proliferation and p-AKT (S473) in H1047R mutant cell lines with an average IC50 of 138 nM and 8 nM, respectively, and has no activity against PI3Kα WT cell lines. HP567 strongly inhibits growth of tumors bearing H1047R in multiple CDX models including breast cancers (MDA-MB-453, T47D, and CAL-148), ovarian cancer (SK-OV-3), tongue squamous cell carcinoma (CAL-33), and a brain-metastatic breast cancer (MDA-MB-453), without causing hyperglycemia or increases in plasma insulin levels. In conclusion, HP567 is a novel, potent, and brain-penetrating PI3Kα H1047R selective inhibitor. The pre-clinical data supports the clinical development of HP567 for the treatment of tumors bearing PI3Kα H1047R mutations. Structure of HP567 will not be disclosed. Citation Format: Jing Li, Lei Fan, Chengcheng Liu, Yao Luo, Xiaohui Chu, Hua Yu, Fei Wang, Xinghai Li. Discovery of HP567, a highly potent, brain-penetrating, and H1047R-selective PI3Kα inhibitor for the treatment of tumors bearing H1047R mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB175.

A high affinity pan-PI3K binding module supports selective targeted protein degradation of PI3Kα.

Class I phosphoinositide 3-kinases (PI3Ks) control cellular growth, but are also essential in insulin signaling and glucose homeostasis. Pan-PI3K inhibitors thus generate substantial adverse effects, a reality that has plagued drug development against this target class. We present here evidence that a high affinity binding module with the capacity to target all class I PI3K isoforms can facilitate selective degradation of the most frequently mutated class I isoform, PI3Kα, when incorporated into a cereblon-targeted (CRBN) degrader. A systematic proteomics study guided the fine tuning of molecular features to optimize degrader selectivity and potency. Our work resulted in the creation of WJ112-14, a PI3Kα-specific nanomolar degrader that should serve as an important research tool for studying PI3K biology. Given the toxicities observed in the clinic with unselective PI3Kα inhibitors, the results here offer a new approach toward selectively targeting this frequently mutated oncogenic driver.

PI3K-C2β limits mTORC1 signaling and angiogenic growth.

Phosphoinositide 3-kinases (PI3Ks) phosphorylate intracellular inositol lipids to regulate signaling and intracellular vesicular trafficking. Mammals have eight PI3K isoforms, of which class I PI3Kα and class II PI3K-C2α are essential for vascular development. The class II PI3K-C2β is also abundant in endothelial cells. Using in vivo and in vitro approaches, we found that PI3K-C2β was a critical regulator of blood vessel growth by restricting endothelial mTORC1 signaling. Mice expressing a kinase-inactive form of PI3K-C2β displayed enlarged blood vessels without corresponding changes in endothelial cell proliferation or migration. Instead, inactivation of PI3K-C2β resulted in an increase in the size of endothelial cells, particularly in the sprouting zone of angiogenesis. Mechanistically, we showed that the aberrantly large size of PI3K-C2β mutant endothelial cells was caused by mTORC1 activation, which sustained growth in these cells. Consistently, pharmacological inhibition of mTORC1 with rapamycin normalized vascular morphogenesis in PI3K-C2β mutant mice. Together, these results identify PI3K-C2β as a crucial determinant of endothelial signaling and illustrate the importance of mTORC1 regulation during angiogenic growth.

Duvelisib for Cytokine Release Syndrome Prophylaxis during CD19-Targeted CAR T Cell Therapy

Chimeric antigen receptor (CAR) T-cell therapy has transformed the treatment of patients with advanced non-Hodgkin lymphoma (NHL). However, treatment toxicity, including cytokine release syndrome (CRS) and immune cell-associated neurotoxicity syndrome (ICANS), can be significant. Effective prophylactic strategies may reduce the frequency and/or severity of CAR T cell therapy while also expanding the pool of patients eligible for such therapy. Duvelisib is an oral inhibitor of the gamma and delta isoforms of phosphoinositide 3-kinases (PI3K), which is an active therapy for CLL/NHL with an established safety profile. In addition, prior work from our group and others has demonstrated that PI3K inhibition can prevent CRS in an in vitro model (Amatya et al. ASH 2022) and can enhance antitumor cytotoxicity of CAR-T cells. Consequently, we performed a trial of duvelisib for CRS prophylaxis in patients undergoing standard-of-care (SoC) CAR T-cell therapy for NHL (NCT05044039). This was a phase I trial with a 3 + 3 dose escalation and two-arm dose expansion phase. The trial enrolled patients with NHL eligible for SoC CAR T-cell therapy and adequate organ function. Herein, we report data from the dose escalation cohort and the first dose expansion cohort, treated with duvelisib BID from day -2 to +28. The primary outcome was safety and tolerability. Secondary outcomes included the incidence and severity of CRS and ICANS, overall response rate (ORR), and progression-free survival (PFS). 17 patients are included in this analysis, including 6 patients in dose escalation and 11 of 14 planned patients in dose expansion cohort A, with full enrollment of cohort A expected prior to presentation. Median age was 68 years (range: 28 - 79) and 53% were male. Diagnoses included DLBCL (n = 13), MCL (2), FL (1) and PBMCL (1). For CAR-T cell therapy, patients received axi-cel (10), liso-cel (4), brexu-cel (2) and tisa-cel (1). 3 patients were enrolled on dose level 1 (15 mg BID) and 3 patients were enrolled on dose level 2 (25 mg BID). No patients experienced a dose-limiting toxicity (DLT) during dose escalation and consequently, 25 mg BID was selected as the recommended dose for expansion. 75 adverse events (AEs) were considered possibly (73) or probably (2) related to duvelisib by study investigators, including 14 severe (grade ≥3) AEs. The most common AEs were blood count abnormalities (41), liver function test abnormalities (12), fatigue (8) and nausea (6). The majority of severe AEs were cytopenias (13) and one patient had grade 3 hypokalemia. 13 patients (77%) had AEs attributed to duvelisib, including 6 patients (35%) with severe AEs. 76% of patients (13/17) experienced CRS at a median of 5 days following cell infusion (range 2 - 9) (Figure 1A). In 71% of patients (12/17), the onset of CRS was after day 3. Most were grade 1 (65%) and no patients experienced severe (grade 3 - 4) CRS. The median duration of CRS was 1 day (range: 1 - 7). ICANS occurred in 41% of patients (7/17) at a median of 7 days (range 4 - 10) and 12% of patients experienced severe (grade 3-4) ICANS. The median duration of ICANS was 5.5 days (range: 4 - 11 days). Toclizumab was given to 65% of patients for treatment of CRS and 53% received steroids for CRS and/or ICANS. All 17 patients were evaluable for disease response. At day +30, the overall response rate (ORR) was 71% (12/17) with 47% achieving complete response (CR) rate. At day +100, the ORR was 64% (9/14) with 50% CR. Best response was CR in 71% of patients and stable disease in 18% of patients. No patients had progressive disease (PD) as best response. CAR T cell expansion by flow cytometry was robust at all dose levels, consistent with prior reports (Figure 1B). With a median follow up of 93 days (range: 28 - 406), 53% of patients were alive and in remission. PD occurred in 6/17 (35%) patients with a median time to progression of 89 days (range: 28 - 182). Three patients enrolled on the study have died. One died from disease progression on day +266. Two died in remission from neutropenic sepsis (day +50) and vaping-induced lung injury (day +144). Data from this ongoing phase I study suggests that duvelisib with SoC CAR T-cell therapy is safe and tolerable. Preliminary data from this study suggest that the addition of duvelisib to CAR T-cell therapy may prevent grade 3-4 CRS and also delay the onset of CRS. Although limited follow-up is available, the depth and duration of response is similar to published data for CAR T-cells in this setting.

Abstract OT3-26-02: A Phase 3 study of gedatolisib plus fulvestrant with and without palbociclib in patients with HR+/HER2- advanced breast cancer previously treated with a CDK4/6 inhibitor plus a non-steroidal aromatase inhibitor (VIKTORIA-1)

Abstract Background: Gedatolisib is a potent reversible dual inhibitor that selectively targets all Class I isoforms of phosphoinositide 3-kinase (PI3K) and mechanistic target of rapamycin (mTOR). Two separate pivotal clinical trials demonstrated that PI3K and mTOR inhibitors are active in combination with endocrine therapy and prolong progression-free survival (PFS) among patients with hormone receptor positive (HR+)/HER2-negative (HER2-) advanced breast cancer (ABC) who had previously received endocrine therapy (SOLAR-1, BOLERO-2). CDK4/6 inhibitor (CDK4/6i) therapy has been approved in the front-line setting. However, patients eventually experience disease progression on CDK4/6i based therapy. Available data indicates that resistance to CDK4/6i is a transient adaptive mechanism that may be reversed by adding inhibitors of the PI3K/mTOR pathway (PI3K/mTORi). Thus, combination of PI3K/mTORi and CDK4/6i in patients whose disease progressed on prior CDK4/6i could potentially both restore sensitivity to CDK4/6i and prevent adaptive activation of the PI3K/mTOR pathway. This hypothesis was evaluated in a Phase 1b study (Layman SABCS 2021). Subjects with HR+/HER2- ABC who were CDK4/6i pretreated received gedatolisib (180 mg IV weekly for 3 weeks, then one week off) in combination with standard doses of palbociclib and fulvestrant. Median PFS was 12.9 months, and overall response rate was 63%. Grade 3-4 adverse events (AE) were observed at a low rate, and toxicity was overall easily managed with available standards of care, and few patients discontinued treatment due to treatment-related adverse events (4%). The most common AE was stomatitis; hyperglycemia of any grade occurred in 26% of patients. This preliminary data, dosing schedule, and study population characteristics form the basis for the Phase 3 trial, VIKTORIA-1. Trial design: This Phase 3, open-label, randomized, multinational two-part clinical trial will evaluate the efficacy and safety of gedatolisib and fulvestrant with or without palbociclib in patients with HR+/HER2- ABC previously treated with any CDK4/6i in combination with non-steroidal aromatase inhibitor therapy. Those without tumor PIK3CA mutations will be assigned to Study 1 and those with PIK3CA mutations will be assigned to Study 2. Study 1 will include up to 351 subjects randomized in a 1:1:1 ratio to Arm A (gedatolisib, palbociclib, and fulvestrant), Arm B (gedatolisib plus fulvestrant), or Arm C (fulvestrant). For subjects in Arm C whose disease progresses, crossover to Arm A or B is allowed. Study 2 will include up to 350 subjects randomized in a 3:3:1 ratio to Arm D (gedatolisib, palbociclib, and fulvestrant), Arm E (alpelisib plus fulvestrant), or Arm F (gedatolisib plus fulvestrant). Key eligibility criteria include adults with confirmed metastatic or locally advanced breast cancer, any menopausal status for females, radiologically evaluable disease, and prior CDK4/6i treatment with non-steroidal AI. Prior therapy with SERD, including fulvestrant is allowed. Key exclusion criteria include prior treatment with a PI3K, protein kinase B (Akt), or mTOR inhibitor, prior treatment with chemotherapy for advanced disease, more than two lines of prior endocrine therapy, bone only disease with no soft tissue components, active CNS metastases, and type 1 diabetes or uncontrolled type 2 diabetes. The primary endpoint is PFS assessed by blinded independent central review (BICR) per RECIST v1.1. Secondary endpoints included overall survival (OS), safety and tolerability, ORR, duration of response, time to response, CBR, quality of life, and pharmacokinetics. This trial is open for enrollment. Citation Format: Sara Hurvitz, Fabrice Andre, Massimo Cristofanilli, Giuseppe Curigliano, Antonio Giordano, Hyo S. Han, Miguel Martín, Barbara Pistilli, Hope Rugo, Robert Wesolowski, Samuel Suzuki, Sarah C. Mutka, Igor Gorbatchevsky, Sibylle Loibl. A Phase 3 study of gedatolisib plus fulvestrant with and without palbociclib in patients with HR+/HER2- advanced breast cancer previously treated with a CDK4/6 inhibitor plus a non-steroidal aromatase inhibitor (VIKTORIA-1) [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT3-26-02.

An open label trial of nemiralisib, an inhaled PI3 kinase delta inhibitor for the treatment of Activated PI3 kinase Delta Syndrome

Activated PI3Kδ Syndrome (APDS) is a rare inherited inborn error of immunity caused by mutations that constitutively activate the p110 delta isoform of phosphoinositide 3-kinase (PI3Kδ), resulting in recurring pulmonary infections. Currently no licensed therapies are available. Here we report the results of an open-label trial in which five subjects were treated for 12 weeks with nemiralisib, an inhaled inhibitor of PI3Kδ, to determine safety, systemic exposure, together with lung and systemic biomarker profiles (Clinicaltrial.gov: NCT02593539).Induced sputum was captured to measure changes in phospholipids and inflammatory mediators, and blood samples were collected to assess pharmacokinetics of nemiralisib, and systemic biomarkers.Nemiralisib was shown to have an acceptable safety and tolerability profile, with cough being the most common adverse event, and no severe adverse events reported during the study. No meaningful changes in phosphatidylinositol (3,4,5)-trisphosphate (PIP3; the enzyme product of PI3Kδ) or downstream inflammatory markers in induced sputum, were observed following nemiralisib treatment. Similarly, there were no meaningful changes in blood inflammatory markers, or lymphocytes subsets. Systemic levels of nemiralisib were higher in subjects in this study compared to previous observations.While nemiralisib had an acceptable safety profile, there was no convincing evidence of target engagement in the lung following inhaled dosing and no downstream effects observed in either the lung or blood compartments. We speculate that this could be explained by nemiralisib not being retained in the lung for sufficient duration, suggested by the increased systemic exposure, perhaps due to pre-existing structural lung damage.In this study investigating a small number of subjects with APDS, nemiralisib appeared to be safe and well-tolerated. However, data from this study do not support the hypothesis that inhaled treatment with nemiralisib would benefit patients with APDS.

Selective Inhibition of PI3K Isoforms in Brain Tumors Suppresses Tumor Growth by Increasing Radiosensitivity.

Glioblastoma (GBM) is a malignant brain tumor with poor prognosis. Radioresistance is a major challenge in the treatment of brain tumors. The development of several types of tumors, including GBM, involves the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway. Upon activation, this pathway induces radioresistance. In this study, we investigated whether additional use of selective inhibitors of PI3K isoforms would enhance radiosensitivity in GBM. We evaluated whether radiation combined with PI3K isoform selective inhibitors can suppress radioresistance in GBM. Glioma 261 expressing luciferase (GL261-luc) and LN229 were used to confirm the effect of combination of radiation and PI3K isoform inhibitors in vitro. Cell viability was confirmed by clonogenic assay, and inhibition of PI3K/AKT signaling activation was observed by Western blot. To confirm radiosensitivity, the expression of phospho-γ-H2AX was observed by immunofluorescence. In addition, to identify the effect of a combination of radiation and PI3K-α isoform inhibitor in vivo, an intracranial mouse model was established by implanting GL261-luc. Tumor growth was observed by IVIS imaging, and survival was analyzed using Kaplan-Meier survival curves. Suppression of the PI3K/AKT signaling pathway increased radiosensitivity, and PI3K-α inhibition had similar effects on PI3K-pan inhibition in vitro. The combination of radiotherapy and PI3K-α isoform inhibitor suppressed tumor growth and extended survival in vivo. This study verified that PI3K-α isoform inhibition improves radiosensitivity, resulting in tumor growth suppression and extended survival in GBM mice.

Investigation of morpholine isosters for the development of a potent, selective and metabolically stable mTOR kinase inhibitor

Upregulation of mechanistic target of rapamycin (mTOR) signaling drives various types of cancers and neurological diseases. Rapamycin and its analogues (rapalogs) are first generation mTOR inhibitors, and selectively block mTOR complex 1 (TORC1) by an allosteric mechanism. In contrast, second generation ATP-binding site inhibitors of mTOR kinase (TORKi) target both TORC1 and TORC2. Here, we explore 3,6-dihydro-2H-pyran (DHP) and tetrahydro-2H-pyran (THP) as isosteres of the morpholine moiety to unlock a novel chemical space for TORKi generation. A library of DHP- and THP-substituted triazines was prepared, and molecular modelling provided a rational for a structure activity relationship study. Finally, compound 11b [5-(4-(3-oxa-8-azabicyclo[3.2.1]octan-8-yl)-6-(tetrahydro-2H-pyran-4-yl)-1,3,5-triazin-2-yl)-4-(difluoromethyl)pyridin-2-amine] was selected due its potency and selectivity for mTOR kinase over the structurally related class I phosphoinositide 3-kinases (PI3Ks) isoforms. 11b displayed high metabolic stability towards CYP1A1 degradation, which is of advantage in drug development. After oral administration to male Sprague Dawley rats, 11b reached high concentrations both in plasma and brain, revealing an excellent oral bioavailability. In a metabolic stability assay using human hepatocytes, 11b was more stable than PQR620, the first-in-class brain penetrant TORKi. Compound 11b also displayed dose-dependent anti-proliferative activity in splenic marginal zone lymphoma (SMZL) cell lines as single agent and when combined with BCL2 inhibition (venetoclax). Our results identify the THP-substituted triazine core as a novel scaffold for the development of metabolically stable TORKi for the treatment of chronic diseases and cancers driven by mTOR deregulation and requiring drug distribution also to the central nervous system.

Dual PI3Kδγ inhibition demonstrates potent anticancer effects in diffuse large B-cell lymphoma models: Discovery and preclinical characterization of LL-00084282

Phosphoinositide 3-kinase (PI3K) pathway mediates key signaling events downstream to B-cell receptor (BCR) for survival of mature B-cells, and overexpression or overactivation of PI3Kδ is crucial for B-cell malignancies such as diffuse large B-cell lymphoma (DLBCL). Small molecule PI3Kδγ inhibitors, with a known potential to reduce activated B-cell (ABC)-DLBCL transformation, form an important class of therapeutics approved for follicular lymphoma (FL), chronic lymphocytic leukemia (CLL), small lymphocytic lymphoma (SLL). In this study, we describe discovery of a potent, selective and efficacious dual PI3Kδγ inhibitor, LL-00084282, having a differentiated efficacy profile in human ABC- and germinal center B-cell (GCB)-DLBCL cell lines. LL-00084282 displayed high potency and superior PI3Kδγ engagement with excellent selectivity over other PI3K isoforms at both IC50/90 concentrations in biochemical and cell-based assays. In contrast to selective PI3Kδ inhibitors, LL-00084282 showed superior and potent anticancer activity in both ABC- and GCB-DLBCL cell lines. LL-00084282 demonstrated in-vivo efficacy in OCI-Ly10 and SU-DHL-6 xenografts with good tolerability. Furthermore, LL-00084282 inhibited pro-inflammatory cytokine secretion and reduced basophil activation in human PBMCs, showing potential implications in immunoinflammatory conditions. Good pharmacokinetic properties in higher species and desirable efficacy profile highlights potential of this novel PI3Kδγ inhibitor for further clinical evaluation in DLBCL patients.

DDDR-19. NEXT-GENERATION PI3K INHIBITOR FOR GLIOBLASTOMA TREATMENT

Abstract High-grade gliomas are especially problematic because of the limited treatment options available to patients. The phosphoinositide 3-kinase (PI3K) pathway has become a significant research target within the field of cancer drug discovery due to the pathway’s promotion of cell proliferation and inhibition of apoptosis. While many new PI3K inhibitory medications show promise in preventing cancer growth, many are toxic because they inhibit multiple PI3K catalytic subunit isoforms making these drugs ineffective treatment options. Our novel peptide drug, Selectide-18, overcomes this toxicity by specifically targeting the p110β isoform of PI3K, which was shown to be the most impactful isoform in many cancer types, including several high-grade gliomas. We designed Selectide-18 after discovering an 18-residue motif unique to p110β. Selectide-18 is a mimetic peptide modeled after this motif. Our in silico analyses show that our drug works by binding to the PI3K regulatory subunit, p85α, thus preventing the binding of catalytic subunit p110β and leaving PI3K inactive. These findings were supported by coimmunoprecipitation. Using a PI3K cell-free kinase assay, we confirmed that our drug specifically targets p110β and does not inhibit p110α, p110δ, or p110γ. The IC50 of Selectide-18 was determined to be approximately 100nM using the same PI3K cell-free kinase assay. We tested several drugs in an MTS viability assay, including Selectide-18, a scrambled 18-residue negative control peptide, and PI3K inhibitor GSK2636771 to compare levels of cancer cell viability. Selectide-18 successfully killed glioblastoma cells within lines with high p110β activity. The drug had no effect in cell lines with low p110β activity. In conclusion, Selectide-18 is explicitly tailored for p110β-high gliomas and has shown promise to treat high-grade glioma effectively. We believe this model of peptide drug can usher in a new generation of p110β specific PI3K inhibitors.

The Pro-Fibrotic Response to Lens Injury Is Signaled in a PI3K Isoform-Specific Manner.

The signaling inputs that function to integrate biochemical and mechanical cues from the extracellular environment to alter the wound-repair outcome to a fibrotic response remain poorly understood. Here, using a clinically relevant post-cataract surgery wound healing/fibrosis model, we investigated the role of Phosphoinositide-3-kinase (PI3K) class I isoforms as potential signaling integrators to promote the proliferation, emergence and persistence of collagen I-producing alpha smooth muscle actin (αSMA+) myofibroblasts that cause organ fibrosis. Using PI3K isoform specific small molecule inhibitors, our studies revealed a requisite role for PI3K p110α in signaling the CD44+ mesenchymal leader cell population that we previously identified as resident immune cells to produce and organize a fibronectin-EDA rich provisional matrix and transition to collagen I-producing αSMA+ myofibroblasts. While the PI3K effector Akt was alone insufficient to regulate myofibroblast differentiation, our studies revealed a role for Rac, another potential PI3K effector, in this process. Our studies further uncovered a critical role for PI3K p110α in signaling the proliferation of CD44+ leader cells, which is important to the emergence and expansion of myofibroblasts. Thus, these studies identify activation of PI3K p110α as a critical signaling input following wounding to the development and progression of fibrotic disease.

Design, Synthesis, and Development of Pyrazolo[1,5-a]pyrimidine Derivatives as a Novel Series of Selective PI3Kδ Inhibitors: Part II-Benzimidazole Derivatives.

Phosphoinositide 3-kinase (PI3K) is the family of lipid kinases participating in vital cellular processes such as cell proliferation, growth, migration, or cytokines production. Due to the high expression of these proteins in many human cells and their involvement in metabolism regulation, normal embryogenesis, or maintaining glucose homeostasis, the inhibition of PI3K (especially the first class which contains four subunits: α, β, γ, δ) is considered to be a promising therapeutic strategy for the treatment of inflammatory and autoimmune diseases such as systemic lupus erythematosus (SLE) or multiple sclerosis. In this work, we synthesized a library of benzimidazole derivatives of pyrazolo[1,5-a]pyrimidine representing a collection of new, potent, active, and selective inhibitors of PI3Kδ, displaying IC50 values ranging from 1.892 to 0.018 μM. Among all compounds obtained, CPL302415 (6) showed the highest activity (IC50 value of 18 nM for PI3Kδ), good selectivity (for PI3Kδ relative to other PI3K isoforms: PI3Kα/δ = 79; PI3Kβ/δ = 1415; PI3Kγ/δ = 939), and promising physicochemical properties. As a lead compound synthesized on a relatively large scale, this structure is considered a potential future candidate for clinical trials in SLE treatment.

Mechanical checkpoint regulates monocyte differentiation in fibrotic niches.

Myelofibrosis is a progressive bone marrow malignancy associated with monocytosis, and is believed to promote the pathological remodelling of the extracellular matrix. Here we show that the mechanical properties of myelofibrosis, namely the liquid-to-solid properties (viscoelasticity) of the bone marrow, contribute to aberrant differentiation of monocytes. Human monocytes cultured in stiff, elastic hydrogels show proinflammatory polarization and differentiation towards dendritic cells, as opposed to those cultured in a viscoelastic matrix. This mechanically induced cell differentiation is blocked by inhibiting a myeloid-specific isoform of phosphoinositide 3-kinase, PI3K-γ. We further show that murine bone marrow with myelofibrosis has a significantly increased stiffness and unveil a positive correlation between myelofibrosis grading and viscoelasticity. Treatment with a PI3K-γ inhibitor in vivo reduced frequencies of monocyte and dendritic cell populations in murine bone marrow with myelofibrosis. Moreover, transcriptional changes driven by viscoelasticity are consistent with transcriptional profiles of myeloid cells in other human fibrotic diseases. These results demonstrate that a fibrotic bone marrow niche can physically promote a proinflammatory microenvironment.

Neutrophil Survival Signaling During Francisella tularensis Infection.

Neutrophils are the most abundant and shortest-lived leukocytes in humans and tight regulation of neutrophil turnover via constitutive apoptosis is essential for control of infection and resolution of inflammation. Accordingly, aberrant neutrophil turnover is hallmark of many disease states. We have shown in previous work that the intracellular bacterial pathogen Francisella tularensis markedly prolongs human neutrophil lifespan. This is achieved, in part, by changes in neutrophil gene expression. Still unknown is the contribution of major neutrophil pro-survival signaling cascades to this process. The objective of this study was to interrogate the contributions of ERK and p38 MAP kinase, Class I phosphoinositide 3-kinases (PI3K), AKT, and NF-κB to neutrophil survival in our system. We demonstrate that both ERK2 and p38α were activated in F. tularensis-infected neutrophils, but only p38α MAPK was required for delayed apoptosis and the rate of cell death in the absence of infection was unchanged. Apoptosis of both infected and uninfected neutrophils was markedly accelerated by the pan-PI3K inhibitor LY2094002, but AKT phosphorylation was not induced, and neutrophil death was not enhanced by AKT inhibitors. In addition, isoform specific and selective inhibitors revealed a unique role for PI3Kα in neutrophil survival after infection, whereas only simultaneous inhibition of PI3Kα and PI3kδ accelerated death of the uninfected controls. Finally, we show that inhibition of NF-κB triggered rapid death of neutrophil after infection. Thus, we defined roles for p38α, PI3Kα and NF-κB delayed apoptosis of F. tularensis-infected cells and advanced understanding of Class IA PI3K isoform activity in human neutrophil survival.

Selected Articles from This Issue

Highlights| June 01 2022 Selected Articles from This Issue Author & Article Information Online Issn: 1557-3265 Print Issn: 1078-0432 ©2022 American Association for Cancer Research2022American Association for Cancer Research Clin Cancer Res (2022) 28 (11): 2199. https://doi.org/10.1158/1078-0432.CCR-28-11-HI Related Content A commentary has been published: A Phase I Study Investigating AZD8186, a Potent and Selective Inhibitor of PI3Kβ/δ, in Patients with Advanced Solid Tumors A commentary has been published: Infigratinib in Patients with Recurrent Gliomas and FGFR Alterations: A Multicenter Phase II Study A commentary has been published: First Clinical Results of Fluorescence Lifetime-enhanced Tumor Imaging Using Receptor-targeted Fluorescent Probes View more A commentary has been published: Venetoclax Cooperates with Ionizing Radiation to Attenuate Diffuse Midline Glioma Tumor Growth View less Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Cite Icon Cite Search Site Article Versions Icon Versions Version of Record June 1 2022 Citation Selected Articles from This Issue. Clin Cancer Res 1 June 2022; 28 (11): 2199. https://doi.org/10.1158/1078-0432.CCR-28-11-HI Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest Search Advanced Search The phosphoinositide 3-kinase (PI3K) signaling pathway plays an important role in many tumor types, but development of PI3K inhibitors is challenging because of toxicity risks associated with inhibiting multiple PI3K isoforms. AZD8186 is a potent, selective inhibitor of PI3Kβ. In a phase I open-label study Choudhury and colleagues evaluated the safety, tolerability, and recommended phase II dose of AZD8186 monotherapy and in combination with abiraterone acetate or vistusertib. Eligible patients had advanced prostate cancer, triple-negative breast cancer, or squamous non-small-cell lung cancer, and patients with other solid tumor types were eligible if they were PTEN-deficient/mutated or PIK3CB-mutated/amplified. As monotherapy and in combination, AZD8186 was well tolerated, with few dose-limiting toxicities reported. Both monotherapy and combination therapy showed preliminary evidence of antitumor activity, which merits further assessment in subsequent studies. FGFR alterations occur in ∼8% of gliomas, with most detected in FGFR1 and FGFR3. Although FGFR fusions have proven oncogenic potential... You do not currently have access to this content.

Republication: Targeting PI3KC2β Impairs Proliferation and Survival in Acute Leukemia, Brain Tumours and Neuroendocrine Tumours.

Eight human catalytic phosphoinositide 3-kinase (PI3K) isoforms exist which are subdivided into three classes. While class I isoforms have been well-studied in cancer, little is known about the functions of class II PI3Ks. The expression pattern and functions of the class II PI3KC2β isoform were investigated in a panel of tumour samples and cell lines. Overexpression of PI3KC2β was found in subsets of tumours and cell lines from acute myeloid leukemia (AML), glioblastoma multiforme (GBM), medulloblastoma (MB), neuroblastoma (NB), and small cell lung cancer (SCLC). Specific pharmacological inhibitors of PI3KC2β or RNA interference impaired proliferation of a panel of human cancer cell lines and primary cultures. Inhibition of PI3KC2β also induced apoptosis and sensitised the cancer cells to chemotherapeutic agents. Together, these data show that PI3KC2β contributes to proliferation and survival in AML, brain tumours and neuroendocrine tumours, and may represent a novel target in these malignancies.

Combining radiation with PI3K isoform-selective inhibitor administration increases radiosensitivity and suppresses tumor growth in non-small cell lung cancer.

Non-small cell lung cancer (NSCLC) is a malignant lung tumor with a dismal prognosis. The activation of the phosphoinositide 3-kinase (PI3K)/AKT signaling pathway is common in many tumor types including NSCLC, which results in radioresistance and changes in the tumor microenvironment. Although pan-PI3K inhibitors have been tested in clinical trials to overcome radioresistance, concerns regarding their excessive side effects led to the consideration of selective inhibition of PI3K isoforms. In this study, we assessed whether combining radiation with the administration of the PI3K isoform-selective inhibitors reduces radioresistance and tumor growth in NSCLC. Inhibition of the PI3K/AKT pathway enhanced radiosensitivity substantially, and PI3K-α inhibitor showed superior radiosensitizing effect similar to PI3K pan-inhibitor, both in vitro and in vivo. Additionally, a significant increase in DNA double-strand breaks (DSB) and a decrease in migration ability were observed. Our study revealed that combining radiation and the PI3K-α isoform improved radiosensitivity that resulted in a significant delay in tumor growth and improved survival rate.