PI3K Isoforms Research Articles

Functional Assessments of Gynecologic Cancer Models Highlight Differences Between Single-Node Inhibitors of the PI3K/AKT/mTOR Pathway and a Pan-PI3K/mTOR Inhibitor, Gedatolisib

Background/Objectives: The PI3K/AKT/mTOR (PAM) pathway is frequently activated in gynecological cancers. Many PAM inhibitors selectively target single PAM pathway nodes, which can lead to reduced efficacy and increased drug resistance. To address these limitations, multiple PAM pathway nodes may need to be inhibited. Gedatolisib, a well-tolerated panPI3K/mTOR inhibitor targeting all Class I PI3K isoforms, mTORC1 and mTORC2, could represent an effective treatment option for patients with gynecologic cancers. Methods: Gedatolisib and other PAM inhibitors (e.g., alpelisib, capivasertib, and everolimus) were tested in endometrial, ovarian, and cervical cancer cell lines by using cell viability, cell proliferation, and flow cytometry assays. Xenograft studies evaluated gedatolisib in combination with a CDK4/6 inhibitor (palbociclib) or an anti-estrogen (fulvestrant). A pseudo-temporal transcriptomic trajectory of endometrial cancer clinical progression was computationally modeled employing data from 554 patients to correlate non-clinical studies with a potential patient group. Results: Gedatolisib induced a substantial decrease in PAM pathway activity in association with the inhibition of cell cycle progression and the decreased cell viability in vitro. Compared to single-node PAM inhibitors, gedatolisib exhibited greater growth-inhibitory effects in almost all cell lines, regardless of the PAM pathway mutations. Gedatolisib combined with either fulvestrant or palbociclib inhibited tumor growth in endometrial and ovarian cancer xenograft models. Conclusions: Gedatolisib in combination with other therapies has shown an acceptable safety profile and promising preliminary efficacy in clinical studies with various solid tumor types. The non-clinical data presented here support the development of gedatolisib combined with CDK4/6 inhibitors and/or hormonal therapy for gynecologic cancer treatment.

The fatty acid receptor CD36 promotes macrophage infiltration via p110γ signaling to stimulate metastasis

IntroductionMetabolic regulators are key in controlling immune cell fate in the tumor microenvironment. The accumulation of tumor-associated macrophages (TAMs) in cancer greatly contributes to metastasis and poor outcome. However, the metabolic pathways responsible for TAM accumulation are largely unknown. ObjectiveThis study aims to elucidate the role of the fatty acid translocase CD36 in the regulation of TAM accumulation. MethodsThe immune profile was analyzed in patients with liver metastasis by CIBERSORT. Immunohistostaining of CD68 and CD36 was conducted in clinical specimens from patients with liver metastasis. Myeloid-specific CD36 knockout mice and their littermates were used to establish preclinical liver metastasis models. Subsequently, a series of experiments were used to explore the underlying mechanisms of how CD36 regulates TAM population. ResultsWe found that massive TAM accumulation in patients with liver metastasis is associated with an upregulation of CD36 on TAMs. Liver metastasis is abundantly infiltrated by TAMs that are derived from circulating monocytes, but not tissue-resident macrophages. Myeloid-specific CD36 knockout specifically reduced and inactivated monocyte-differentiated macrophages, resulting in diminished immune suppression and attenuated liver metastasis. The protect effects of CD36 knockout can be abrogated by blockade of macrophage recruitment through CCR2 or the p110γ isoform of PI3K downstream of it. Mechanically, CD36 reprogrammed the lipid metabolism of macrophages, in which sphingolipids were significantly downregulated, that contributed to weakened lipid raft-dependent activation of p110γ. ConclusionCD36 expands TAM population by promoting the recruitment of circulating monocytes through CCL2/CCR2/p110γ signaling. Our findings provide evidence for targeting CD36 as a therapeutic strategy against liver metastasis.

Assessments of prostate cancer cell functions highlight differences between a pan-PI3K/mTOR inhibitor, gedatolisib, and single-node inhibitors of the PI3K/AKT/mTOR pathway.

Metastatic castration-resistant prostate cancer (mCRPC) is characterized by loss of androgen receptor (AR) sensitivity and oncogenic activation of the PI3K/AKT/mTOR (PAM) pathway. Loss of the PI3K regulator PTEN is frequent during prostate cancer (PC) initiation, progression, and therapeutic resistance. Co-targeting the PAM/AR pathways is a promising mCRPC treatment strategy but is hampered by reciprocal negative feedback inhibition or feedback relief. Most PAM inhibitors selectively spare (or weakly inhibit) one or more key nodes of the PAM pathway, potentiating drug resistance depending on the PAM pathway mutation status of patients. We posited that gedatolisib, a uniformly potent inhibitor of all class I PI3K isoforms, as well as mTORC1 and mTORC2, would be more effective than inhibitors targeting single PAM pathway nodes in PC cells. Using a combination of functional and metabolic assays, we evaluated a panel of PC cell lines with different PTEN/PIK3CA status for their sensitivity to multi-node PAM inhibitors (PI3K/mTOR: gedatolisib, samotolisib) and single-node PAM inhibitors (PI3Kα: alpelisib; AKT: capivasertib; mTOR: everolimus). Gedatolisib induced anti-proliferative and cytotoxic effects with greater potency and efficacy relative to the other PAM inhibitors, independent of PTEN/PIK3CA status. The superior effects of gedatolisib were likely associated with more effective inhibition of critical PAM-controlled cell functions, including cell cycle, survival, protein synthesis, oxygen consumption rate, and glycolysis. Our results indicate that potent and simultaneous blockade of all class I PI3K isoforms, mTORC1, and mTORC2 could circumvent PTEN-dependent resistance. Gedatolisib, as a single agent and in combination with other therapies, reported promising preliminary efficacy and safety in various solid tumor types. Gedatolisib is currently being evaluated in a Phase 1/2 clinical trial in combination with darolutamide in patients with mCRPC previously treated with an AR inhibitor, and in a Phase 3 clinical trial in combination with palbociclib and fulvestrant in patients with HR+/HER2- advanced breast cancer.

Exploring the anti-inflammatory and immunomodulatory potential of licochalcone B against psoralidin-induced liver injury

Ethnopharmacological relevanceHerb-induced liver injury (HILI) represents an exacerbated inflammatory response, with Psoraleae fructus (PF) and its preparations recently associated with hepatotoxicity. Licorice, historically recognized as a detoxifying herbal remedy, is considered to possess hepatoprotective properties. Our previous research identified bavachin, bakuchiol, and psoralidin (PSO) as potential toxic constituents in PF, while licochalcone B (LCB) and echinatin were identified as bioactive components in licorice. However, evidence regarding the interactions of active compounds in herbs and their underlying mechanisms remains limited. Aim of the studyThe objective of this study is to assess the potential mechanisms through which LCB modulates immunological and anti-inflammatory responses to treat PSO-induced liver injury by using human hepatocyte cells (L02) and LPS-primed mice. MethodsThe ameliorative effects of LCB and echinatin on bavachin, bakuchiol, and PSO-induced liver injury were demonstrated in L02 cells. Subsequently, the efficacy of LCB on PSO-induced idiosyncratic liver injury was further validated in C57BL/6 mice under moderate inflammatory stress induced by LPS priming. The mechanisms were preliminarily explored with an integrated strategy of molecular docking, RT-PCR verification, and untargeted metabolomics. ResultsThe study shows that LCB significantly reduced cell injury induced by the three chemicals in PF and provided substantial protection against PSO-induced hepatic damage, as indicated by the levels of ALT, AST, and LDH. LCB normalized liver function and remarkedly alleviated hepatic lesions and inflammation caused by PSO in mice under moderate inflammatory stress. The mRNA profiles of both L02 cells and mice liver tissue revealed that LCB mitigated PSO-induced hepatotoxicity by regulating the gene expression of pro-inflammatory cytokines IL1B and TNF, as well as immunoinflammatory genes PIK3CA, AKT1, NFKB1, and NLRP3. Furthermore, untargeted metabolomics of liver tissue indicated that LCB could reverse the abnormal expression of 11 discriminatory metabolites, with the interrelationship between differential metabolites and target genes primarily clustering in glycerophospholipid metabolism, arachidonic acid metabolism, and phosphatidylinositol signaling system. ConclusionLCB demonstrated a superior anti-inflammatory and immunomodulatory effect on PSO-induced hepatotoxicity by modulating the inflammatory response and metabolic signaling system. Key interactive targets included phosphatidylcholine, phosphatidic acid, and subunit isoforms of PI3K.

A novel iheyamine A derivative L42 suppresses acute myeloid leukemia via dual regulation of the PI3K/AKT/FOXO3a axis and TNF signaling pathway

Acute myeloid leukemia (AML) is one of the most common hematopoietic malignancies and the development of new drugs is crucial for the treatment of this lethal disease. Iheyamine A is a nonmonoterpenoid azepinoindole alkaloid from the ascidian Polycitorella sp., and its anticancer mechanism has not been investigated in leukemias. Herein, we showed the significant antileukemic activity of L42 in AML cell lines HEL, HL-60 and THP-1. The IC50 values were 0.466±0.099 µM, 0.356±0.023 µM, 0.475±0.084 µM in the HEL, HL-60 and THP-1 cell lines, respectively, which were lower than the IC50 (2.594±0.271 µM) in the normal liver cell line HL-7702. Furthermore, L42 significantly inhibited the growth of peripheral blood mononuclear cells (PBMCs) from an AML patient. In vivo, L42 effectively suppressed leukemia progression in a mouse model induced by Friend murine leukemia virus (F-MuLV). Mechanistically, we showed that L42 induced cell cycle arrest and apoptosis in leukemia cell lines. RNA sequencing analysis of L42-treated THP-1 cells revealed that the differentially expressed genes (DEGs) were enriched in the cell cycle and apoptosis and predominantly enriched in the PI3K/AKT pathway. Accordingly, L42 decreased the expression of the phospho-PI3K (p85), phospho-AKT and phospho-FOXO3a. Docking and CETSA analysis indicated that L42 bound to the PI3K isoform p110α (PIK3CA), which was implicated in the suppression of the PI3K/AKT pathway. L42 was also shown to initiate the TNF signaling-mediated apoptosis. Moreover, L42 exhibited stronger anti-leukemia activity and sensitivity in IDH2-mutant HEL cells than in IDH2-wild-type control. In conclusion, L42 effectively suppresses cell proliferation and triggers apoptosis in AML cell lines in part through inhibition of the PI3K/AKT signaling pathway to restore FOXO3a expression and activation of the TNF signaling pathway. Thus, the iheyamine A derivative L42 represents a novel candidate for AML therapy.

PIK3CA inhibition in models of proliferative glomerulonephritis and lupus nephritis.

Proliferative glomerulonephritis is a severe condition that often leads to kidney failure. There is a significant lack of effective treatment for these disorders. Here, following the identification of a somatic PIK3CA gain-of-function mutation in podocytes of a patient, we demonstrate using multiple genetically engineered mouse models, single-cell RNA sequencing, and spatial transcriptomics the crucial role played by this pathway for proliferative glomerulonephritis development by promoting podocyte proliferation, dedifferentiation, and inflammation. Additionally, we show that alpelisib, a PI3Kα inhibitor, improves glomerular lesions and kidney function in different mouse models of proliferative glomerulonephritis and lupus nephritis by targeting podocytes. Surprisingly, we determined that pharmacological inhibition of PI3Kα affects B and T lymphocyte populations in lupus nephritis mouse models, with a decrease in the production of proinflammatory cytokines, autoantibodies, and glomerular complement deposition, which are all characteristic features of PI3Kδ inhibition, the primary PI3K isoform expressed in lymphocytes. Importantly, PI3Kα inhibition does not impact lymphocyte function under normal conditions. These findings were then confirmed in human lymphocytes isolated from patients with active lupus nephritis. In conclusion, we demonstrate the major role played by PI3Kα in proliferative glomerulonephritis and show that in this condition, alpelisib acts on both podocytes and the immune system.

Gedatolisib shows superior potency and efficacy versus single-node PI3K/AKT/mTOR inhibitors in breast cancer models

The PI3K, AKT, and mTOR (PAM) pathway is frequently dysregulated in breast cancer (BC) to accommodate high catabolic and anabolic activities driving tumor growth. Current therapeutic options for patients with hormone receptor (HR) + / HER2- advanced BC (ABC) include PAM inhibitors that selectively inhibit only one PAM pathway node, which can lead to drug resistance as cells rapidly adapt to maintain viability. We hypothesized that gedatolisib, which potently inhibits all Class I PI3K isoforms, as well as mTORC1 and mTORC2, may be more effective in BC cells than single-node PAM inhibitors by limiting adaptive resistances. By using multiple functional assays, a panel of BC cell lines was evaluated for their sensitivity to four different PAM inhibitors: gedatolisib (pan-PI3K/mTOR inhibitor), alpelisib (PI3Kα inhibitor), capivasertib (AKT inhibitor), and everolimus (mTORC1 inhibitor). Gedatolisib exhibited more potent and efficacious anti-proliferative and cytotoxic effects regardless of the PAM pathway mutational status of the cell lines compared to the single-node PAM inhibitors. The higher efficacy of gedatolisib was confirmed in three-dimensional culture and in BC PDX models. Mechanistically, gedatolisib decreased cell survival, DNA replication, cell migration and invasion, protein synthesis, glucose consumption, lactate production, and oxygen consumption more effectively than the other PAM inhibitors tested. These results indicate that inhibition of multiple PAM pathway nodes by a pan-PI3K/mTOR inhibitor like gedatolisib may be more effective at inducing anti-tumor activity than single-node PAM inhibitors. A global Phase 3 study is currently evaluating gedatolisib plus fulvestrant with and without palbociclib in patients with HR+/HER2− ABC.

Phosphoinositide 3-Kinase C2alpha controls cardiac contractility through regulation of beta2-adrenergic receptor recycling

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Doctoral fellowship Introduction Phosphoinositide 3-kinase C2α (PI3KC2α) is a ubiquitously expressed class II PI3K isoform, which has been previously shown to be involved in the control of vesicular trafficking. However, its role in the myocardium has not been investigated. The primary aim of this study is to elucidate the mechanism by which mechanism PI3KC2α controls cardiac pathophysiology. Methods Cardiomyocyte-specific PI3KC2α knockout (PI3KC2α KO) animals were generated by crossing mice expressing a tamoxifen-inducible Cre recombinase under the control of the αMHC promoter with PI3KC2αflox/flox mice. Zebrafish embryos were injected with a PI3KC2α (PI3KC2α morphants) or a control morpholino (control morphants) at 1-cell stage. HEK293 with stable overexpression of GFP-tagged β2-AR were generated and transfected with either scramble or PI3KC2α siRNAs. Results Our findings indicate that PI3KC2α KO mice display a reduced cardiac contractility compared to wildtype animals. Similarly, PI3KC2α morphants zebrafish exhibit lower heart rate and fractional shortening compared to controls, both at baseline and after isoproterenol (ISO) stimulation. A similar unresponsiveness to ISO was found in vivo in PI3KC2α KO mice where chronic treatment with the β-adrenergic receptor (β-AR) agonist failed to induce the classical β-AR-mediated remodeling, characterized by an increase of the left ventricular mass and of cardiomyocyte area. These findings suggest that PI3KC2α plays a critical role in the regulation of β-AR signaling. In agreement, cAMP levels failed to increase in response to ISO treatment in PI3KC2α morphants. Furthermore, silencing of PI3KC2α in HEK293-GFP-β2-AR cells resulted in an increased GFP-β2-AR internalization compared to control cells, both at baseline and after ISO stimulation. Interestingly, preliminary findings indicate that overexpression of constitutively active Rab11Q70L induced a redistribution of GFP-β2-AR at the plasma membrane in PI3KC2α-silenced cells. Conclusion Overall, we identify a key role for PI3KC2α in the control of cardiac contractility through the regulation of β2-AR trafficking to the plasma membrane through a Rab11-dependent mechanism.

Abstract PO1-24-04: Gedatolisib, a pan-PI3K/mTOR inhibitor, shows superior potency and efficacy relative to other PI3K/AKT/mTOR pathway inhibitors in breast cancer models

Abstract Background: The PI3K, AKT, and mTOR (PAM) pathway is frequently activated in breast cancer (BC). Current standard-of-care therapy options for patients with advanced BC (ABC) include PAM inhibitors (PAMi), such as everolimus and alpelisib, and hormonal therapy, such as letrozole and fulvestrant. Most PAMi selectively inhibit one or only a few PAM pathway components, which can lead to drug resistance. To minimize drug resistance, a more comprehensive inhibition of the multiple PI3K isoforms and downstream mTOR complexes may be required. We hypothesized that gedatolisib, which potently inhibits all Class I PI3K isoforms, as well as mTORC1 and mTORC2, can be more effective in BC cells than a PAMi targeting single PAM pathway components. Methods: A panel of BC cell lines with mutated or non-mutated PAM pathway genes (PIK3CA, PTEN, AKT) were evaluated for their sensitivity to gedatolisib and other PAMi (PI3K-α: alpelisib; AKT: capivasertib; mTORC1: everolimus; pan-PI3K/mTOR: gedatolisib). Cell viability, growth rate inhibition, and cell death were evaluated by luciferase- and fluorescence-based assays, both in monolayer cultures and three-dimensional (3D) cultures on reconstituted basement membrane. Flow cytometry analytical assays were conducted to assess DNA synthesis (EdU incorporation), protein synthesis (OPP incorporation), and PAM pathway activity (RPS6 and 4EBP1 phosphorylation). BC xenograft studies evaluating gedatolisib in vivo were also performed. Results: Gedatolisib strongly inhibited PAM pathway activity and reduced cell viability and growth rate in the cell lines tested. Compared to the other PAMi, gedatolisib exhibited more potent and efficacious anti-proliferative and cytotoxic effects, regardless of the cell lines’ PI3K pathway mutational status. Gedatolisib effects were confirmed in 3D culture on reconstituted basement membrane, where gedatolisib inhibited tumor cell spheroid growth and induced regression. Mechanistically, gedatolisib decreased both DNA and protein synthesis more effectively than the other PAMi tested. Gedatolisib also exerted superior anti-proliferative and cytotoxic effects relative to the other PAMi tested in estrogen receptor-positive BC cell lines concomitantly treated with fulvestrant. BC xenografts confirmed growth inhibitory effects of gedatolisib in vivo. Conclusions: The pan-PI3K/mTOR inhibitor, gedatolisib, may more effectively address potential drug resistance mechanisms associated with narrowly targeted PAM inhibitors. Gedatolisib has previously demonstrated promising preliminary clinical efficacy and safety data in ABC in combination with hormonal therapy. A Phase 3 study (VIKTORIA-1) evaluating gedatolisib plus fulvestrant with and without palbociclib is underway in patients with ABC. Citation Format: Stefano Rossetti, Aaron Broege, Adrish Sen, Salmaan Khan, Ian MacNeil, Jhomary Molden, Igor Gorbatchevsky, Brian F. Sullivan, Lance Laing. Gedatolisib, a pan-PI3K/mTOR inhibitor, shows superior potency and efficacy relative to other PI3K/AKT/mTOR pathway inhibitors in breast cancer models [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-24-04.

Abstract PO1-06-14: Preliminary results of a phase I dose escalation study of eribulin in combination with copanlisib in patients with metastatic triple negative breast cancer (TNBC)

Abstract Background: Aberrant PI3K pathway signaling is frequently observed in TNBC. Increasing evidence indicate that PI3K pathway activation maintains the stemness and chemoresistance of breast cancer stem cells (CSCs). PI3K inhibition sensitizes CSCs to chemotherapy. Eribulin (E), a non-taxane microtubule dynamics inhibitor, showed overall survival benefit in metastatic HER2 negative BC. Preclinically, the addition of copanlisib (C), a potent pan-class I PI3K inhibitor that is highly selective against α and δ PI3K isoforms, improved anti-tumor effect in both E-sensitive and resistant TNBC patient-derived xenograft models, irrespective of PIK3CA/PTEN alteration status. Here we report the preliminary data of the phase I dose escalation trial of E+C in patients with metastatic TNBC. Methods: This trial includes a phase I study to determine the dose limiting toxicity (DLT) and recommended phase 2 dose (RP2D) of E+C, followed by a randomized phase II study of E+C (at RP2D) versus E (stratified by tumor PIK3CA/PTEN mutation status) with progression-free survival (PFS) as the primary endpoint. Key eligibility included patients with: metastatic TNBC who progressed on ≤5 lines of chemotherapy, prior anthracycline/taxane chemotherapy (unless contraindicated), ECOG 0-1, adequate organ function and known tumor PIK3CA/PTEN/AKT mutation status. Key exclusions include: prior receipt of E or any PI3K/mTOR/AKT inhibitor, grade ≥2 neuropathy, presence of tumor AKT mutation, and uncontrolled diabetes, hypertension or congenital QT prolongation. A 3+3 design was used to determine the DLT and RP2D. Dose level 1 (DL1) started with E at 1.1 mg/m2 mg IV and C at 45 mg IV on days (D) 1/8 of 21-D cycle, with the potential to escalate to 2 additional dose levels – DL2: E 1.4 mg/m2 and C 45 mg on D 1/8; DL3: E 1.4 mg/m2 and C 60 mg on D 1/8. Results: Eight patients were enrolled in the phase I study and received at least 1 dose of E+C. The median age was 48.5 (range, 26-67) years. The majority of patients identified as White (additionally 2 Hispanic, 1 Black) and had an ECOG performance status of 1 (n=6, 75.0%). Tumor PIK3CA and PTEN alterations were each observed in 1 patient. Median number of cycles received were 2 (range, 1-5). All 8 patients had at least 1 treatment-related adverse event (TRAE). The most common TRAEs across all dose levels were: lymphopenia (n=5, 62.5%), neutropenia (n=5, 62.5%), hyperglycemia (n=4, 50.0%), anemia (n=4, 50.0%) and fatigue (n=4, 50.0%); most toxicities were grade (G) 1-2. G3 hyperglycemia and hypertension were observed in 1 patient each, were medically managed and did not lead to treatment interruption. 1 patient was diagnosed with pulmonary embolism, possibly attributed to study therapy and breast cancer. DLTs were reported in 2 of 2 patients treated at DL2 - 1 patient developed G3 rash responsive to oral corticosteroids, and 1 patient developed G3 acute kidney injury in the setting of hypovolemia and discontinued study therapy. No additional patients were enrolled in DL2. No DLTs were observed in all 6 patients treated at DL1. 1 patient treated at DL1 had possible G1 non-infectious pneumonitis that resolved spontaneously on short interval imaging. Stable disease was observed in 2 of 6 response-evaluable patients (33.3%). 1 patient achieved regression of cutaneous disease following 1 cycle of therapy as assessed by the treating investigator. DL1, E at 1.1 mg/m2 plus C at 45 mg IV, was determined to be the RP2D. Tumor tissue biomarker analysis is underway. Conclusion: These data indicate that E+C at DL1 is a well-tolerated regimen warranting further investigation. The study is actively enrolling patients to the phase II study. Clinical trial information: NCT04345913. Funding Source: National Cancer Institute. Citation Format: Nusayba Bagegni, Brittney Haas, Leslie Nehring, Jingqin Luo, Laura Kennedy, Meghna Trivedi, Manali Bhave, Rabih Said, Cynthia Ma. Preliminary results of a phase I dose escalation study of eribulin in combination with copanlisib in patients with metastatic triple negative breast cancer (TNBC) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-06-14.

TYM-3-98, a novel selective inhibitor of PI3Kδ, demonstrates promising preclinical antitumor activity in B-cell lymphomas

AimsPI3Kδ is expressed predominately in leukocytes and is commonly found to be aberrantly activated in human B-cell lymphomas. Although PI3Kδ has been intensively targeted for discovering anti-lymphoma drugs, the application of currently approved PI3Kδ inhibitors has been limited due to unwanted systemic toxicities, thus warranting the development of novel PI3Kδ inhibitors with new scaffolds. Main methodsWe designed TYM-3-98, an indazole derivative, and evaluated its selectivity for all four PI3K isoforms, as well as its efficacy against various B-cell lymphomas both in vitro and in vivo. Key findingsWe identified TYM-3-98 as a highly selective PI3Kδ inhibitor over other PI3K isoforms at both molecular and cellular levels. It showed superior antiproliferative activity in several B-lymphoma cell lines compared with the approved first-generation PI3Kδ inhibitor idelalisib. TYM-3-98 demonstrated a concentration-dependent PI3K/AKT/mTOR signaling blockage followed by apoptosis induction. In vivo, TYM-3-98 showed good pharmaceutical properties and remarkably reduced tumor growth in a human lymphoma xenograft model and a mouse lymphoma model. SignificanceOur findings establish TYM-3-98 as a promising PI3Kδ inhibitor for the treatment of B-cell lymphoma.

Gedatolisib in combination with palbociclib and endocrine therapy in women with hormone receptor-positive, HER2-negative advanced breast cancer: results from the dose expansion groups of an open-label, phase 1b study

The PI3K-mTOR pathway is frequently dysregulated in breast cancer. Combining an inhibitor targeting all class I PI3K isoforms and mTOR complex 1 (mTORC1)-mTOR complex 2 (mTORC2) with endocrine therapy and a CDK4/6 inhibitor might provide more effective tumour control than standard-of-care therapy. To evaluate this hypothesis, gedatolisib, a pan-PI3K-mTOR inhibitor, was assessed in a phase 1b trial combined with palbociclib and endocrine therapy in patients with hormone receptor-positive, HER2-negative, advanced breast cancer. Results from the dose expansion portion of this trial are reported herein. This multicentre, open-label, phase 1b study recruited female patients aged at least 18 years from 17 sites across the USA with hormone-receptor-positive, HER2-negative, advanced breast cancer and an Eastern Cooperative Oncology Group performance status of 0-1. Four patient groups were studied in the dose expansion portion of the study: treatment-naive in the advanced setting (first line; group A), progression on 1-2 lines of endocrine therapy but CDK4/6 inhibitor-naive (group B); and one or more previous lines (second-line and higher) of therapy, including a CDK4/6 inhibitor (groups C and D). Gedatolisib 180 mg was administered intravenously weekly in 28-day treatment cycles for groups A-C, and on days 1, 8, and 15 for group D. Letrozole (group A), fulvestrant (groups B-D), and palbociclib (all groups) were administered at standard doses and schedules. The primary endpoint was investigator-assessed objective response rate per RECIST version 1.1 in the evaluable analysis set. This trial is completed and registered with ClinicalTrials.gov, NCT02684032. Between Dec 19, 2017, and June 19, 2019, 103 female participants were enrolled in the dose expansion groups A (n=31), B (n=13), C (n=32), and D (n=27). Median follow-up was 16·6 months (IQR 5·7-48·4) for group A, 11·0 months (7·6-16·9) for group B, 3·6 months (1·8-7·5) for group C, and 9·4 months (5·3-16·7) for group D for the primary endpoint. Gedatolisib, palbociclib, and endocrine therapy induced an objective response in 23 (85·2%; 90% CI 69·2-94·8) of 27 evaluable first-line participants (group A). In the second-line and higher setting, an objective response was observed in eight (61·5%; 90% CI 35·5-83·4) of 13 evaluable group B participants, seven (25·0%; 12·4-41·9) of 28 evaluable group C participants, and 15 (55·6%; 38·2-72·0) of 27 evaluable group D participants; this included participants with both wild-type and mutated PIK3CA tumours. The most common grade 3-4 treatment-related adverse events were neutropenia (65 [63%] of 103), stomatitis (28 [27%]), and rash (21 [20%]). Grade 3-4 hyperglycaemia was reported in six (6%) participants. 23 (22%) of 103 participants had a treatment-related serious adverse event, and there were no treatment-related deaths. Nine (9%) participants discontinued treatment because of a treatment-emergent adverse event. Gedatolisib plus palbociclib and endocrine therapy showed a promising objective response rate compared with the published results for standard-of-care therapies and had an acceptable safety profile. Pfizer and Celcuity.

Abstract 1956: Discovery of a novel and potent mutant-selective inhibitor of PI3Kα

Abstract Gain-of-function mutations in hotspots of PI3Kα including H1047R, E545K, and E542K are well-recognized oncogenic drivers in human cancers. Prevalence of these mutations is enriched in many human malignancies, particularly in hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2−) breast cancer. PI3Kα inhibition showed clear clinical benefit in treating HR+/HER2− breast cancer and has been approved in combination with fulvestrant. First generation PI3Kα inhibitors such as alpelisib and inavolisib, however, have limited selectivity against wild-type (WT) PI3Kα; therefore, are associated with a variety of on-target adverse effects including grade 3 hyperglycemia, skin rash, and gastrointestinal toxicities. Discovery of a highly-selective inhibitor of mutant PI3Kα could enable deeper target coverage while reducing undesired effects of inhibiting WT PI3Kα. SNV-002 is a novel, proprietary, and mutant-selective inhibitor of PI3Kα. In cellular assays, SNV-002 inhibited Ser473 phosphorylation of AKT (pAKT) with single digit nanomolar potency in PI3Kα H1047R-mutant T47D cells and displayed greater than 50-fold selectivity over SKBR3 WT control. Similar inhibition of pAKT was also observed in other cell lines carrying PI3Kα hotspot mutations, such as CAL33, NCI-H1048, EFM19, and HCC1954. SNV-002 maintained selectivity in helical domain E545K-mutant cell lines including MCF7 and MDA-MB-361. This selectivity was further confirmed using MCF10A isogenic cell lines carrying either WT or mutant PI3Kα (H1047R and E545K). In cellular assays to assess inhibition of other isoforms of PI3K (PI3Kβ, PI3Kγ, and PI3Kδ), the IC50 of SNV-002 was over 10,000 nM. Similarly, a broad kinome screen showed no inhibition of activity of 371 kinases. Compared with alpelisib, SNV-002 showed improved potency and prolonged residence time in T47D breast cancer cells. Importantly, assays using H1047R-mutant cells in the presence of human whole blood showed SNV-002 potency to be less than 100 nM, which was over 10-fold more potent than that of alpelisib. Treatment of breast cancer cells with SNV-002 suppressed PI3K-AKT-mTOR pathway, as evidenced by reduced levels of phospho-S6 ribosomal protein and associated with loss of cell viability in mutant lines. The pharmacokinetic profile of SNV-002 was excellent across multiple species. Oral administration of HCC1954 tumor-bearing mice with SNV-002 resulted in dose-proportional exposure and >90% pharmacodynamic inhibition of pAKT in the tumor with doses of 10 mg/kg, and no sign of glucose dysregulation in contrast to alpelisib. Together, these data show that SNV-002 is a highly-selective and potent inhibitor of mutant PI3Kα with good drug-like properties that support further development of SNV-002 for treatment of cancers driven by oncogenic PI3Kα mutations. Citation Format: Mingming Gao, Chao Qi, Zhentian Li, Qipeng Fan, Liyang Wang, Fei Zhou, Lin You, Hewen Zheng, Yu Li, Liangxing Wu, Wenqing Yao, Phillip C. Liu. Discovery of a novel and potent mutant-selective inhibitor of PI3Kα [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1956.

Abstract 1954: Development of highly potent, covalent, and selective inhibitors to target PI3Kα in cancer

Abstract Aberrant PI3K signaling is linked to various forms of cancer and proliferative disease. Approved clinical therapies targeting overactive PI3K are scarce and often accompanied by severe adverse effects due to lack of PI3K isoform selectivity. We recently reported a proprietary covalent proximity scanning (CoPS) approach to selectively target distant cysteines outside of the ATP-binding pocket in kinases. Using CoPS, we developed isoform specific, irreversible covalent PI3Kα inhibitors (cPI3Kαi) with outstanding target engagement profiles. Here, we report structure-guided scaffold and linker-optimizations resulting in cPI3Kαi with long-term and rapid inhibition of PI3Kα. Cellular activity was improved exploiting additional protein-inhibitor interactions inspired by X-ray crystallographic data, and introduction of structural elements to increase cell permeability. The cPI3Kαi series showed enhanced cellular potency and excellent on-target engagement. Kinetic parameters and covalent bond formation were determined using TR-FRET, nanoBRET tracer displacement assays, and LCMS/MS based proteomics. With our new cPI3Kαi, IC50s of PKB/Akt phosphorylation, pPKB/Akt recovery after drug washout, and growth inhibition experiments were performed in cancer cell lines harboring activating PIK3CA or inactivating PTEN mutations. Efficient and long-lasting inhibition of PKB/Akt phosphorylation was observed in PIK3CA mutant cell lines, while loss of PTEN was associated with partial responses, consistent with contributions of other class I PI3K isoforms to signal reactivation. A dynamic FOXO cytosolic/nuclear translocation assay was used to monitor distal PI3K signaling: cPI3Kαi blunted PI3K signaling rapidly with rates identical to the reversible BYL719/alpelisib. After drug washout, inhibition by BYL719/alpelisib was relieved within minutes, while a complete and prolonged shutdown of downstream signaling events was observed in PIK3CA mutant cell lines but not in cell lines where PTEN function was lost. This relapse in downstream signaling explains the lack of efficacy of PI3Kα selective inhibitors in models with PTEN loss and demonstrates that persistent inhibition across the PI3K pathway is required for efficacy. In summary, the new cPI3Kαi display outstanding specificity and cellular activity in PIK3CA-mutated cancer cells, and support the further development of cPI3Kαi as future clinical candidates and an alternative to established reversible inhibitors. Citation Format: Luka Raguž, Theodora A. Constantin, Lukas Bissegger, Erhan Keleş, Clara Orbegozo, Thorsten Schäfer, Rohitha Sriramaratnam, Chiara Borsari, Matthias P. Wymann. Development of highly potent, covalent, and selective inhibitors to target PI3Kα in cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1954.

Abstract 1957: OPM-116, a highly potent and specific PI3Kγ inhibitor to enhance antitumor immunity

Abstract Tumor-associated macrophages are an integral part of the tumor microenvironment. They play a crucial role in cancer initiation and progression by orchestrating tumor proliferation, angiogenesis, extracellular matrix remodeling, metastasis, immunosuppression, and resistance to checkpoint blockade immunotherapy and chemotherapy (Gao J, 2022). On the other hand, when properly stimulated, macrophages can effectively interact with the innate and adaptive immune systems arms, promoting cancer cell phagocytosis and tumor destruction by T cell-mediated cytotoxicity (Mantovani A, 2022). PI3Kγ has a unique pattern of expression and biological function, and it has been investigated for a long time as a therapeutic target for different disorders, including cancer. Inhibition of PI3Kγ reprograms M2 macrophages into M1 cells in the tumor microenvironment which translates into the expansion of activated T cells by relieving macrophage suppression. Recent clinical data indicates the compelling role of PI3Ky in combination with PDL1 in anti-tumor activity, irrespective of PDL1 status (Hamilton E, 2021). PI3Ky selectivity has been difficult to achieve due to the high sequence homology across the class 1 PI3K isoforms (Drew SL, 2020). Macrocyclization of small molecules with a linear structure strongly reduces their conformational flexibility and alters a variety of their physicochemical and biological characteristics. The unexpected selectivity these compounds can exhibit, even amongst closely similar target molecules, is explained by the conformationally limited structure (Ma J, 2022). Here, we describe the discovery of a potent and selective, ATP-competitive inhibitor of PI3Kγ. OPM-116, macrocyclic compound display >300-fold selectivity for PI3Kγ over the other class I isoforms. Its selectivity in biochemical and cellular assays as well as in human PBMC assays is presented. In vitro, OPM-116 can inhibit the IL-4-induced polarization of M2 macrophages. Pharmacodynamic analysis performed in animals that received oral compound administration confirmed the absolute selectivity and good PK profiles of the drug. OPM-116 is a highly selective, PI3Kγ inhibitor that displays high potency and specificity and represents a promising step toward the identification of a clinical candidate. Drew S.L., et al. Discovery of potent and selective PI3Kγ inhibitors. J. Med. Chem. 2020. Ma J., et al. Development of small macrocyclic kinase inhibitors. Futur. Med. Chem. 2022. Gao J., et al. Shaping polarization of tumor-associated macrophages in cancer immunotherapy. Front. Immunol. 2022. Mantovani A, et al. Macrophages as tools and targets in cancer therapy. Nat Rev Drug Discovery. 2022. Hamilton E, et al. Mario-3 phase II study safety run-in evaluating a novel triplet combination of eganelisib, atezolizumab, and nab-paclitaxel as first-line therapy for locally advanced or metastatic TNBC. AACR, Cancer Res 2021. Citation Format: Kenji Shoji, Petra Blom, Maria Eugenia Riveiro, Jan Hoflack. OPM-116, a highly potent and specific PI3Kγ inhibitor to enhance antitumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1957.

Abstract 1230: MTX-531, a first-in-class pan-PI3K inhibitor spares hyperinsulinemia yielding durable tumor regressions and resilience to adaptive resistance

Abstract Adaptive resistance mechanisms compromise the long-term effectiveness of kinase-targeted agents dictating the need for strategic combination approaches. MTX-531 was computationally designed to selectively target both PI3K and wild type EGFR. MTX-531 exhibits low nanomolar potency against the PI3K isoform family and EGFR with a high degree of specificity predicted by co-crystal structural analyses. Full kinome screening confirmed that MTX-531 is exquisitely selective for its intended targets. We evaluated the pharmacological profile of MTX-531, whereupon single agent treatment with this lead molecule elicited a high incidence of durable tumor regressions in a broad panel of PIK3CA mutant CDX and PDX squamous head and neck (HNSCC) models. The combination of MTX-531 with RAS pathway inhibitors, including agents directed against KRAS G12C, led to durable regressions of KRAS mutant colorectal and pancreatic xenografts, resulting in striking increases in median survival. MTX-531 is exceptionally well tolerated in mice and uniquely does not lead to hyperglycemia and hyperinsulinemia commonly seen with predecessor pan PI3K inhibitors. MTX-531 acts as an agonist of PPARγ, a structural feature of the molecule that is thought to mitigate hyperglycemia induced by PI3K inhibition. This unique attribute of MTX-531 confers a favorable therapeutic index not typically seen with PI3K inhibitors. To the best of our knowledge, MTX-531 is the first reported pan-PI3K inhibitor that does not lead to hyperglycemia. The pharmaceutical profile of MTX-531 includes favorable cross-species oral bioavailability, microsomal stability, and a facile 3 step chemical synthesis. MTX-531, which has the unique capability of concurrently and selectively inhibiting PI3K and EGFR, illustrates the power of rational computational drug design to target multiple adaptive resistance mechanisms in a single molecule. The versatility of MTX-531 in both the single agent and combination settings offers a breadth of development strategies that continue to evolve as new combination candidates become available. MTX-531 is currently undergoing advanced preclinical development for anticipated first in human clinical trials in late 2024. Citation Format: Christopher E. Whitehead, Elizabeth K. Ziemke, Christy L. Frankowski-McGregor, Rachel A. Mumby, June Chung, Jinju Li, Nathaniel Osher, Oluwadara Coker, Michelle Norris, Scott Kopetz, Veera Baladandayuthapani, Melinda Hollingshead, Sharad Verma, Judith S. Sebolt-Leopold. MTX-531, a first-in-class pan-PI3K inhibitor spares hyperinsulinemia yielding durable tumor regressions and resilience to adaptive resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1230.

Class IA PI3K isoforms lead to differential signalling downstream of PKB/Akt

Abstract Objectives The catalytic subunits of Class IA PI3K, p110α, p110β, and p110δ, phosphorylates phosphatidylinositol 4,5-bisphosphate (PIP2) into phosphatidylinositol 3,4,5-trisphosphate (PIP3) on the plasma membrane. In cancer, these catalytic subunits are usually found to be altered or amplified. Because pan-PI3K inhibition results in systemic toxicities, finding specific targets for the ubiquitous PI3K isoforms offers considerable potential for enhancing the effectiveness of PI3K-targeted therapy. Methods We aim to delineate the isoform-specific druggable targets of the PI3K by deleting PIK3CA (encoding p110α) and PIK3CB (encoding p110β) by Cre mediated excision and ectopically expressing p110α, p110β, or p110δ with or without myristoylation (Myr) tag in mouse embryonic fibroblasts (MEFs). Myr is a lipidation signal that translocates proteins to plasma membrane permanently. This translocation renders p110s constitutively activated as they remain in close proximity to PIP2 on the membrane. Results Unique and redundant Akt targets are identified downstream of different PI3K isoforms. mTORC1, one of the targets of fully-activated Akt, has been observed to be differentially regulated in MEFs upon expression of p110α or p110β. The varying dependencies on mTORC1 and Rac1 led us to analyse a potential scaffolding function of p110β with Rac1 to mediate phosphorylation and activation of mTOR using platforms for the modeling of biomolecular complexes. We also documented that p110α and p110β support cell cycle kinetics differentially. Conclusions This study suggests differential regulation of protein translation, metabolism, cell cycle, and survival signaling downstream of unique p110 targets, underlying the importance of cancer treatment according to the deregulated p110 isoform.

Discovery of novel pyrido[3,2-d]pyrimidine derivatives as selective and potent PI3Kδ inhibitors.

The δ isoform of class I PI3K (PI3Kδ) has been shown as a promising target for the treatment of hematologic malignancies and immune diseases. Herein, a series of pyrido[3,2-d]pyrimidine derivatives were designed, synthesized and evaluated for the preliminary bioactivity. Compared with idelalisib, compound S5 exhibited excellent enzyme activity against PI3Kδ (IC50 = 2.82 nM) and strong antiproliferation activity against SU-DHL-6 cells (IC50 = 0.035 μM). Besides, S5 inhibited the phosphorylation of Akt, which is downstream of PI3Kδ, in concentration-dependent manner. In view of the significant improvement in potency of PI3Kδ and selectivity over other PI3K isoforms, Compound S5 deserved further investigation as a promising PI3Kδ inhibitor.

Cholesterol biogenesis is a PTEN-dependent actionable node for the treatment of endocrine therapy-refractory cancers.

PTEN and PIK3CA mutations are the most prevalent PI3K pathway alterations in prostate, breast, colorectal, and endometrial cancers. p110β becomes the prominent PI3K isoform upon PTEN loss. In this study, we aimed to understand the molecular mechanisms of PI3K dependence in the absence of PTEN. Using online bioinformatical tools, we examined two publicly available microarray datasets with aberrant PI3K activation. We found that the rate-limiting enzyme of cholesterol biogenesis, SQLE, was significantly upregulated in p110β-hyperactivated or PTEN-deficient mouse prostate tumors. Concomitantly, the expression of cholesterol biosynthesis pathway enzymes was directly correlated with PI3K activation status in microarray datasets and diminished upon PTEN re-expression in PTEN-null prostate cancer cells. Particularly, PTEN re-expression decreased SQLE protein levels in PTEN-deficient prostate cancer cells. We performed targeted metabolomics and detected reduced levels of cholesteryl esters as well as free cholesterol upon PTEN re-expression. Notably, PTEN-null prostate and breast cancer cell lines were more sensitive to pharmacological intervention with the cholesterol pathway than PTEN-replete cancer cells. Since steroid hormones use sterols as structural precursors, we studied whether cholesterol biosynthesis may be a metabolic vulnerability that enhances antihormone therapy in PTEN-null castration-resistant prostate cancer cells. Coinhibition of cholesterol biosynthesis and the androgen receptor enhanced their sensitivity. Moreover, PTEN suppression in endocrine therapy-resistant luminal-A breast cancer cells leads to an increase in SQLE expression and a corresponding sensitization to the inhibition of cholesterol synthesis. According to our data, targeting cholesterol biosynthesis in combination with the hormone receptor signaling axis can potentially treat hormone-resistant prostate and breast cancers.

Polymorphonuclear myeloid-derived suppressor cells and phosphatidylinositol-3 kinase gamma are critical to tobacco-mimicking oral carcinogenesis in mice

BackgroundOral squamous cell carcinoma (OSCC) is a devastating disease most often associated with tobacco consumption that induces a field of mutations from which a tumor arises. Identification of ways to...