PTEN hamartoma tumour syndrome (PHTS), a rare disease caused by germline heterozygous PTEN variants, is associated with multi-organ/tissue overgrowth, autism spectrum disorder and increased cancer risk. Phenotypic variability in PHTS is partly due to diverse PTEN variants and the protein's multifaceted functions. PTEN is primarily a phosphatidylinositol(3,4,5)trisphosphate (PIP3) phosphatase regulating PI3K/AKT signalling but also maintains chromosomal stability through nuclear functions such as double-stranded (ds)DNA damage repair. Here, we show that PTEN-R173C, a pathogenic variant frequently found in PHTS and somatic cancer, has elevated PIP3 phosphatase activity that effectively regulates canonical PI3K/AKT signalling. However, PTEN-R173C is unstable and excluded from the nucleus. We generated Pten+/R173C mice which developed few tumours during their lifetime, aligning with normal PI3K/AKT signalling. However, they exhibited lymphoid hyperplasia, macrocephaly and brain abnormalities, associated with impaired nuclear functions of PTEN-R173C, demonstrated by reduced dsDNA damage repair. We integrated PHTS patient data with our mouse model results, and propose that defective nuclear functions of PTEN variants can predict the onset of PHTS phenotypes and that late-onset cancer in these individuals may arise from secondary genetic alterations, facilitated by compromised dsDNA repair.

Background Current immunotherapy regimens most often fail due to an insufficient T cell response and/or immune-related adverse events (irAEs) which lead to treatment discontinuation. Additionally, many cancers likely require combination immunotherapies which may further increase irAE. This is exemplified in our preclinical models of dual targeting of regulatory T cells with a phosphoinositide 3-kinase δ (PI3Kδ) inhibitor and antibodies to LAG-3. Indeed, while this approach in preclinical models of triple-negative breast cancer shows excellent tumor control, treatment is poorly tolerated and results in significant toxicity. Given the emerging relevance of these targets in human breast cancer, we explored strategies to sustain tumor immunity while mitigating toxicity using these therapeutic modalities.Methods Different approaches to combination immunotherapies employing a PI3Kδ inhibitor (PI-3065) with LAG-3 targeting treatments were tested in a mouse model of triple-negative breast cancer to optimize tumor control while limiting irAE.Results Systemic targeting of the LAG-3 ligand FGL1 did not provide additional anticancer benefit but markedly worsened irAE. Localized delivery of anti-LAG-3 antibodies to the tumor microenvironment promoted tumor control while reducing the overall number of animals experiencing severe irAE compared with those receiving systemic LAG-3 blockade. However, intermittent dosing of the PI3Kδ inhibitor in combination with anti-LAG-3 treatment prevented the initial development of irAE and enabled excellent tumor control without systemic adverse effects.Conclusions Our data demonstrated that refining immunotherapy delivery approaches can improve tolerability that ultimately transforms treatment success.

PTEN (phosphatase and tensin homolog deleted on chromosome ten) is a tumor suppressor, the function of which is impaired in many diverse cancers. It has phosphoinositide lipid phosphatase activity by which it suppresses activation of the oncogenic PI3K signaling network but in vitro also displays activity against protein substrates and is able to auto-dephosphorylate its Thr366 residue. Here we generate germline knock-in mice expressing PTEN-Y138L, a mutant enzyme which selectively lacks protein phosphatase activity and retains lipid phosphatase activity. Homozygous PtenY138L/Y138L mice die in utero before E10.5. Primary MEFs and thymocytes with only a single PtenY138L allele display normal low levels of AKT phosphorylation indicating effective regulation of PI3K signaling by endogenous PTEN-Y138L in vivo. Heterozygous Pten+/Y138L mice have reduced overall survival compared to wild-type littermates and develop tumors in multiple organs. Our data imply that in addition to its lipid phosphatase activity, the protein phosphatase activity of PTEN is also required for normal embryonic development and tumor suppression.

Among the PI3K isoforms, PI3Kδ has attracted particular attention from immunologists and hematologists. Despite earlier clinical setbacks, the PI3Kδ field has recently re-emerged with renewed promise. Here, I highlight key milestones in the evolving understanding of PI3Kδ signaling in immunity and cancer, and pivotal studies that have shaped this field.

The PI3K/AKT/mTOR pathway represents an excellent drug target, given its proven druggability and roles in cancer, immune regulation and genetic disorders. However, although some agents targeting this pathway have gained approval, drug development has faced challenges due to tolerability issues and resistance mechanisms, amongst other obstacles. New pharmacological approaches and improved biological and clinical understanding are now renewing interest and confidence in therapeutically modulating PI3K/AKT/mTOR signalling. This Perspective covers the challenges, lessons learned and new efforts in targeting this pathway.

Abstract PI3Kδ is a predominantly leukocyte-enriched class I PI3K consisting of the p110δ catalytic subunit (encoded by PIK3CD) and most commonly the p85α regulatory subunit (encoded by PIK3R1). PI3Kδ is an important regulator of B-cell function and has been the target of extensive drug development efforts for B-cell malignancies, with multiple inhibitors approved for this indication. Based on our pre-clinical studies, PI3Kδ inhibition is now also emerging as an immunotherapy approach for solid tumours. Regulatory T-cells (Treg) are exquisitely sensitive to PI3Kδ inhibition, therefore pharmacological PI3Kδ inhibitors preferentially target the Tregs, rebalancing the immune system in favour of an effector T cell-mediated anti-tumour immune response. This concept is currently under investigation in clinical trials in uveal melanoma and non-small cell lung cancer. Notably, we and others have also observed multiple solid tumour types including glioblastoma, melanoma, breast cancer, prostate cancer, neuroblastoma and hepatocellular carcinoma also express wild-type PIK3CD, often at much higher levels than their non-transformed cell types of origin. Some studies suggest PI3Kδ promotes proliferation in these tumour cells, but this remains unclear with the potential that inhibitors were used at non-PI3Kδ-specific concentrations, and these findings are not consistently confirmed with genetic approaches. This raises the questions of what function PI3Kδ plays in solid tumours and how the use of PI3Kδ inhibitors for immunotherapy will affect the tumour cells themselves via inhibition of cell-intrinsic PI3Kδ. Using highly-selective PI3Kδ inhibitors and CRISPR-Cas9-mediated PIK3CD deletion in solid tumour cell lines, we demonstrate that PI3Kδ inhibition does not affect cell proliferation in these models. However, through both in vitro and xenograft studies, we have identified cancer-relevant roles for PI3Kδ in solid tumours, the implications of which will be presented. Our data suggest the solid tumour cell-intrinsic PI3Kδ expression should be considered to inform PI3Kδ-targeting immunotherapy studies. Citation Format: Sarah E. Conduit, Elena Lopez-Guadamillas, Daniele Morelli, Harriet Howard, Wayne Pearce, Cheryl Scudamore, Bart Vanhaesebroeck. Solid tumor cell-intrinsic function of PI3Kδ [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 5750.

Abstract Cancer cells maintain oncogenic signalling within a survival “fitness zone”. While conventional targetαed therapies suppress this signalling below a critical threshold, excessive activation of the same pathways can also be lethal to cell, an observation currently being explored as a novel therapeutic approach in cancer. In this study, we report that hyperactivation of PI3Kα, one of the most frequently oncogenically activated PI3K isoforms, using the small-molecule PI3Kα activator UCL-TRO-1938 (further referred to as 1938) induces cytotoxicity in cancer cell lines while sparing non-transformed cells. This PI3K activation-induced cell death (PI3K-AICD) depends on AKT/mTORC1 activity, only occurs under serum starvation and is enhanced by low O2 levels. This hyperactivation lethality is mechanistically linked to an irreconcilable metabolic conflict by simultaneously activating anabolic PI3K/mTORC1 signalling in a catabolic (hypoxic) state, resulting in an unresolvable energy crisis and ultimately cell death. In serum-deprived lung cancer cell lines, 1938 induces a magnified endoplasmic reticulum stress response which, along with PI3K-AICD, can be mitigated by supplementation with unsaturated fatty acids, suggesting a critical metabolic dependency on lipid metabolism for driving this cell death response. Consequently, co-treatment with 1938 and inhibitors of stearoyl-CoA desaturase-1 (SCD1), an O2-dependent enzyme essential for fatty acid desaturation, amplifies the PI3K-AICD response. In summary, these findings demonstrate that enhancing an oncogenic pathway central to metabolic control can selectively kill cancer cells. Citation Format: Benoit Bilanges, Ralitsa Madsen, Daniele Morelli, Thomas Jones, Wayne Pearce, Etienne Leveille, Mustafa Kocak, Eden Bramson, Mark Bekala, Roger Williams, Nicholas McGranahan, Markus Muschen, William R. Sellers, Henning Walczak, Bart Vanhaesebroeck. Pharmacological activation of PI3Kα triggers cancer cell death under metabolic stress [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4738.

Abstract Neoadjuvant chemoradiotherapy (nCRT) is used in about one third of rectal cancer cases in the UK, but treatment response is heterogeneous, leading to difficulties in response prediction and sensitization. Phenotypic plasticity, driven by both cell-intrinsic mutations and cell-extrinsic signals from the tumour microenvironment (TME) has been shown to influence therapy resistance in colorectal cancer. This study explores the role of proliferative cancer stem cells (proCSCs) and revival cancer stem cells (revCSCs) in CRT response, and how phenotypic plasticity can be targeted to improve CRT sensitivity. Patient-derived organoids (PDOs) from a cohort of 10 patients with microsatellite-stable rectal cancer were subject to combinatorial perturbations of radiation, chemotherapy, exploratory radiosensitizers, and co-culture with cancer associated fibroblasts (CAFs). PDOs were analysed 3 hours and 48 hours after radiation in triplicate, totalling 2,400 experimental conditions. PDOs were analysed using single-cell thiol-organoid barcoding in situ mass cytometry (TOBis MC), enabling high-dimensional characterisation of CSC states, DNA damage responses, canonical signalling pathways, cell cycle, and apoptosis. PDOs displayed heterogeneous, patient-specific responses to CRT, and could be classified in the following manner: 1) high signalling response, high apoptosis; 2) high signalling response, low apoptosis; and 3) low signalling response, low apoptosis. Therapy-induced apoptosis did not correlate with on-target DNA damage, but instead strongly aligned with baseline stem cell index (SCI), a metric that describes the relative proCSC-revCSC ratio of each PDO. Higher rates of apoptosis were seen in PDOs that were proCSC-dominant at baseline (high-SCI), whereas revCSC-dominant PDOs (low-SCI) were more resistant apoptosis after treatment. In certain low-SCI PDOs, the proCSC population could be enriched using a PI3Ka activator before radiation, resulting in increased apoptosis after radiation with little toxicity. After CRT, a significant reduction in SCI was seen across the cohort. Blockade of revCSC transdetermination with a YAP/TEAD1 inhibitor also resulted in increased radiation-induced apoptosis. Highly plastic PDOs exhibiting large differences SCI following CRT were identified by high DACH1 expression. This study suggests that the initial level of on-target DNA-damage following CRT does not dictate cell death, rather, it is due to what state the cancer cell is in when the damage occurs. We find that rectal cancer cells in a proCSC state typically enter apoptosis in response to DNA damage, whereas cancer cells in the revCSC state survive therapy. We also find that pharmacologically enriching proCSCs and blocking access to the revCSC state can sensitize PDOs to CRT, and may have therapeutic importance in treating rectal cancer. Citation Format: Nick Li, Petra Vlckova, Alistair Wilkinson, Ewa Basiarz, Aurelie Dobric, Corinne Molyneux, Rhianna O'Sullivan, Shauna Crampsie, Benoit Bilanges, Bart Vanhaesebroeck, Maria A. Hawkins, Chris Tape. Stem cell transdetermination is a targetable driver of therapeutic response to neoadjuvant chemoradiotherapy in rectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 6623.

The 309G SNP in the second promoter of the gene encoding mouse double minute 2 (MDM2) has been implicated in multiple human diseases. The aims of this study were to determine whether MDM2 SNP309G is associated with proliferative diabetic retinopathy (PDR), and whether it contributes to pathological angiogenesis. Sanger DNA sequencing was used to determine the MDM2 SNP309 status in peripheral blood and fibrovascular membranes (FVMs) from individuals with PDR, as well as in epiretinal membranes from individuals with proliferative vitreoretinopathy (PVR). An ELISA was used to quantify the levels of the oxidative DNA damage biomarker 8-oxo-2′-deoxyguanosine in vitreous humour samples from individuals with PDR or PVR. Prime editing was employed to introduce MDM2 SNP309G into primary human retinal microvascular endothelial cells (HRECs), which were then assessed for in vitro angiogenic activities, including proliferation, migration and tube formation. A mouse model of oxygen-induced retinopathy (OIR) was used to evaluate pathological retinal neovascularisation in humanised mice carrying MDM2 SNP309T or SNP309G. Quantitative RT-PCR and western blot analyses were performed to assess gene and protein expression related to MDM2-mediated signalling pathways. An association between MDM2 SNP309G and PDR was identified. Among 110 individuals with PDR, 60.1

A, Modulation of expression of PSMA protein in CWR22 and 22RV1 cells by inhibitors with maximum upregulation induced by DS-7423 (3.4- and 5.6-fold, respectively). B, Detection of PSMA mRNA after treatment with DS-7423. Results are shown as mean with SE (n = 3; ***, P < 0.001).

The placenta is essential for embryonic development, in part by mediating nutrient transfer from mother to embryo. Placental insufficiency is the most common cause of intrauterine growth restriction which has long-term health consequences lasting into adulthood. p110β is a class IA phosphoinositide 3-kinase (PI3K) catalytic subunit, a family of lipid kinases which are critical regulators of adult metabolism, immunity and embryonic and placental development. However, unlike the other class IA PI3K isoforms, the in vivo functions of p110β remain unclear. While homozygous p110β kinase-dead mice are mostly embryonically lethal, some survive into adulthood with no apparent phenotypes, other than reduced fertility. The mechanism(s) underlying this embryonic lethality remain unclear. Therefore, we performed an in-depth characterisation of p110β kinase-dead embryos, revealing a previously unrecognised role for p110β in controlling the expression of system A amino acid transporters. We show that homozygous p110β kinase-dead embryos are phenotypically normal, but growth-restricted and exhibit placental insufficiency. The placenta is small with a reduced nutrient storing junctional zone and downregulation of the system A amino acid transporters, required for maternal-to-embryo amino acid transfer. These data suggest defective amino acid transfer drives embryonic growth restriction and partial lethality of p110β kinase-dead embryos. This predominantly embryonic p110β phenotype is consistent with the notion that system A amino acid transporters are more critical during development than in adult physiology. The greater significance of p110β in development than in adult homeostasis may also help explain why p110β inhibitors, compared to inhibitors of other PI3K isoforms, are well-tolerated in adults.

Phosphoinositide 3-kinase delta (PI3Kδ) is essential for immune cell functions, preventing immunodeficiency and inflammation; however, its role in dendritic cell (DC)-mediated immune regulation remains unknown. Here, we report a key role for DC-intrinsic PI3Kδ in linking microbial recognition with antigen presentation for effective T-cell priming. Using genetic and functional assays, we demonstrate that PI3Kδ deficiency in DCs leads to broad dysregulation of intestinal CD4⁺ T-cell immunity, characterized by impaired regulatory T-cell expansion and increased susceptibility to colitis. DC-based studies show that PI3Kδ links pattern-recognition-receptor signaling to MHC class I- and II-restricted presentation of phagosome-associated antigens by facilitating NOX2-dependent oxidative burst through RAC2, while mitigating inflammasome activation. In contrast, PI3Kδ deficiency disrupts phagosomal pH balance, leading to accelerated acidification and proteolysis of antigens, impairing T-cell activation. Our study identifies PI3Kδ as a key coordinator of phagosome dynamics, important for DC adaptive programming that shapes T-cell responses and supports intestinal immune homeostasis. ### Competing Interest Statement B.V. is a consultant for Pharming (Leiden, The Netherlands) and iOnctura (Geneva, Switzerland) and a shareholder of Open Orphan (Dublin, Ireland). The other authors declare no competing interests. Medical Research Council, MR/M023230/1 Barts Charity, MGU0488 Royal Society, IES\R2\212104 Arthritis Research UK, 19867 Great Ormond Street Hospital Children’s Charity, 1160024 Cancer Research UK, C23338/A10200 European Union Horizon 2020, 753567, 845908

The organismal roles of the class II PI3K isoform PI3K-C2α remain poorly understood. Recent studies have found PI3K-C2α to promote arterial thrombosis and breast cancer metastasis, generating interest in this kinase as a drug target, with small molecule PI3K-C2α inhibitors now available. However, the consequences of systemic PI3K-C2α inactivation in the nondiseased, postnatal state are largely unknown. Here, we show that induction of genetic PI3K-C2α inactivation in adult mice is well tolerated, without adverse effects on normal physiology. Surprisingly, however, mice with inactive PI3K-C2α display strong sensitization to challenge with bacterial lipopolysaccharide (LPS), a model of endotoxic shock. This sensitization is recapitulated by vascular endothelial-specific deletion of PI3K-C2α. Furthermore, sensitization to LPS can be fully rescued by disabling extrinsic induction of cell death by combined caspase-8- and RIPK3 deficiency. These observations validate the tolerability of systemic PI3K-C2α inhibition in principle but reveal an unexpected role for PI3K-C2α in the regulation of extrinsic cell death pathways.

PTEN Hamartoma Tumour Syndrome (PHTS) is a rare disorder characterized by germline heterozygous mutations in the PTEN tumour suppressor gene, leading to multi-organ/tissue overgrowth, autism spectrum disorder and increased cancer risk. PHTS individuals display heterogeneity in phenotypes, which has been linked in part to the diverse genetic alterations in the PTEN gene and the multifaceted functions of this protein. Indeed, while PTEN primarily functions as a PIP3 lipid phosphatase in the cytosol, regulating PI3K/AKT signalling, a pathway commonly deregulated in cancer, it also plays crucial roles in maintaining chromosomal stability through nuclear activities such as double strand (ds) DNA damage repair. Recent studies have identified a subset of missense PHTS variants that cause nuclear exclusion of PTEN, impairing its nuclear functions. Here, we present our findings from one such pathogenic variant, PTEN-R173C , frequently found in PHTS and somatic cancers. Using cell biological and mouse modelling approaches, we show that PTEN-R173C has higher PIP3 phosphatase activity than wild-type PTEN, resulting in effective regulation of canonical PI3K/AKT signalling. However, PTEN-R173C is unstable and excluded from the nucleus. Aligning with their near normal PI3K/AKT signalling, Pten+/R173C mice display a low incidence of solid tumours compared to Pten+/- mice. Pten+/R173C mice also exhibit lymphoid hyperplasia and macrocephaly which correlates with compromised nuclear functions of PTEN-R173C. That nuclear functions are compromised is demonstrated by reduced dsDNA damage repair in Pten+/R173C mice. Integrating PHTS patient data with findings from our mouse model, our study indicates that nuclear dysfunction of pathogenic PTEN variants is a key factor in predicting the onset of the different PHTS-associated phenotypes. We speculate that late-onset cancer in individuals with nuclear-excluded PTEN results from genetic alterations unrelated to PTEN itself, facilitated by impaired PTEN-mediated dsDNA damage repair. ### Competing Interest Statement BV is a consultant for Pharming (Leiden, The Netherlands) and iOnctura (Geneva, Switzerland) and a shareholder of Open Orphan (Dublin, Ireland) PTEN Research Foundation, https://ror.org/04b98dz04, UCL-16-001, UCL-20-001, UOC-17-001 Cancer Research UK, https://ror.org/054225q67, C416/A29287, CANTAC721\100022, C23338/A25722, C416/A25145 European Commission, https://ror.org/00k4n6c32, H2020-MSCA-IF-2018 GA: 838559 Biotechnology and Biological Sciences Research Council, https://ror.org/00cwqg982, BB/W007460/1, BB/N009061/1 Jean Shanks Foundation, https://ror.org/00wf6bs47 Fondation ARC pour la Recherche sur le Cancer, https://ror.org/0489qz649, ARCPJA2022060005118 La Ligue Contre le Cancer, https://ror.org/00rkrv905 Wellcome Trust, https://ror.org/029chgv08, 108726/Z/15/Z NIHR Cambridge Biomedical Research Centre, NIHR203312 Medical Research Council, https://ror.org/03x94j517, MC-A024-5PF91

Expression profile for indicated proteins in prostate cancer cells after treatment with PI3K, mTOR, or dual inhibitors for 48 hours. A, DS-7423 increased expression of HER2 (4.5-fold in CWR22, 7.3-fold in 22RV1, 1.8-fold in PC3, and 1.2-fold in Shmac5 cells), HER3 (5-fold in LNCap, 1.3-fold in CWR22, 18-fold in PC3, and 4.5-fold in Shmac5 cells), and AR (6.1-fold in LNCaP). B, Immunofluorescence images show the DS-7423–induced upregulation of HER2 (green) and HER3 (red) in CWR22 and 22RV1 cells. Nucleus stained with Hoechst33342 (blue); scale bar, 50 μm.

Mechanistic target of rapamycin (mTOR) is a highly conserved serine/threonine kinase that regulates key cellular processes including cell growth, autophagy and metabolism. Hyperactivation of the mTOR pathway causes a group of rare and ultrarare genetic diseases. mTOR pathway diseases have diverse clinical manifestations that are managed by distinct medical disciplines but share a common underlying molecular basis. There is a now a deep understanding of the molecular underpinning that regulates the mTOR pathway but effective treatments for most mTOR pathway diseases are lacking. Translating scientific knowledge into clinical applications to benefit the unmet clinical needs of patients is a major challenge common to many rare diseases. In this article we expound how mTOR pathway diseases provide an opportunity to coordinate basic and translational disease research across the group, together with industry, medical research foundations, charities and patient groups, by pooling expertise and driving progress to benefit patients. We outline the germline and somatic mutations in the mTOR pathway that cause rare diseases and summarise the prevalence, genetic basis, clinical manifestations, pathophysiology and current treatments for each disease in this group. We describe the challenges and opportunities for progress in elucidating the underlying mechanisms, improving diagnosis and prognosis, as well as the development and approval of new therapies for mTOR pathway diseases. We illustrate the crucial role of patient public involvement and engagement in rare disease and mTOR pathway disease research. Finally, we explain how the mTOR Pathway Diseases node, part of the Research Disease Research UK Platform, will address these challenges to improve the understanding, diagnosis and treatment of mTOR pathway diseases.

Model proposed describing the PSMA-mGluR1-HER2 mechanism of resistance to dual PI3K-mTOR inhibitor DS-7423 (created with BioRender.com). HER2/X represents the HER2-containing receptor protein complex (X = EGFR or HER3 in Supplementary Fig. S1E and S1F). A feedback mechanism that is activated in response to PI3K/mTOR inhibition involves upregulation of ErbB/HER protein (HER2 or HER3) according to the genetically diverse prostate cancer cell lines we have tested. Downstream effects include a PSMA increase upon DS-7423 treatment that is partially dependent on HER2 signaling. Targeting the PI3K/mTOR pathway has unraveled a complex relationship between PSMA increase and HER2 upregulation via mGluR1 activity (Fig. 4B).

Cancer mutations in the PIK3CA gene cause congenital disorders. The endothelium is among the most frequently affected tissues in these disorders, displaying aberrant vascular overgrowth in the form of malformations. Pathological PIK3CA vascular phenotypes are found in veins and capillaries but rarely in arteries for reasons that are unclear at present. Here, using lineage tracing, we show that expression of mutated PIK3CAH1047R in endothelial cells leads to marked clonal expansions in capillary and venous endothelial cells. In contrast, mature arterial endothelial cells are refractory to PIK3CA mutation under these conditions and never display pathological phenotypes. Moreover, PIK3CAH1047R expression in arterial precursors interrupts arterial differentiation, thereby driving fate switch towards venous identity. This fate rewiring offers an additional layer of protection to prevent arterial damage in response to PIK3CA genetic perturbation. Molecularly, the PIK3CAH1047R-driven arterial-to-venous fate switch is orchestrated by upregulation of the vein-specifying transcription factor Nr2f2/COUP-TFII. Our findings reveal that pathogenic responses to PIK3CAH1047R greatly depend on the diferentation stage and fate trajectory of the targeted cell. Arteries are thus shielded against PIK3CA mutation, solving the long-standing question on the rarity of PIK3CA-related arterial malformations observed in patients ### Competing Interest Statement M.G. has a research agreement with Relay Therapeutics, Inc., A Delaware corporation having a principal place of business at 399 Binney Street Cambridge, MA 02139 United States. E.B. is co-founder of Venthera; PI of the clinical trial [NCT04589650][1] (Novartis) and Advisor for Novartis. B.V. is a consultant for Pharming (Leiden, The Netherlands) and iOnctura (Geneva, Switzerland) and a shareholder of Open Orphan (Dublin, Ireland). [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT04589650&atom=%2Fbiorxiv%2Fearly%2F2025%2F02%2F25%2F2025.02.25.640041.atom

Future OncologyAhead of Print InterviewOpen Access30 years of PI3K: an interview with Bart VanhaesebroeckBart VanhaesebroeckBart Vanhaesebroeck *Author for correspondence: E-mail Address: bart.vanh@ucl.ac.ukhttps://orcid.org/0000-0002-7074-3673Cancer Institute, University College London, Paul O'Gorman Building, 72 Huntley Street, London WC1E 6BT, UKPublished Online:7 May 2024https://doi.org/10.2217/fon-2024-0215AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinkedInRedditEmail Keywords: cell signalingPI3KalphaPI3KdeltaCould you please introduce yourself & provide a brief summary of your career to date?Many thanks for this interview – my answers below are targeted at a wider nonspecialist audience.I am a basic scientist with a keen interest in applying newly acquired knowledge to understand and treat human disease. Throughout my research career, I have always been involved in fundamental research that could be applied to drug development. I have had the pleasure that some of our discoveries have made it all the way to approved drugs for leukemia.Following training in Biology/Biochemistry, I obtained a PhD in a laboratory in Belgium that was among the first to clone human genes to produce so-called recombinant proteins. This was in the early days of molecular biology, when scientists like Walter Fiers, my PhD mentor, were looking to exploit DNA technology to produce large amounts of 'natural' products from the human body to use as medicines, such as insulin to activate metabolism or natural immune stimulators. This was the beginning of the biotech industry, which at the time spawned companies such as Biogen and Genentech. Doing a PhD in an environment where research was being applied in so-called translational research was a huge privilege and shaped my thinking on how I wanted to do future research.My PhD studies focused on investigating the basic biology of some of these recombinant proteins such as Tumour Necrosis Factor and Interleukin-2. This also meant that when I finished my PhD, I had not yet had a chance to clone a gene myself. I subsequently picked up these skills in my postdoctoral lab at the Ludwig Institute for Cancer Research in London where my colleagues and I cloned genes for so-called PI 3-kinases (PI3Ks), an area I have been working in for over 30 years now.PI3Ks control cell behavior and are involved in many different types of diseases, in particular cancer and immune deregulation. With my laboratory and our collaborators, we made a new type of mouse model to uncover the functions of these PI3Ks in the organism. This allowed us to publish impactful papers, but also to identify some PI3K family members as new drug targets. Together with studies from other laboratories, these findings led to extensive development efforts of PI3K inhibitor drugs. It was great to see how others also saw the potential therapeutic application of our findings, and it was an interesting experience for my laboratory to become involved in drug development, something I really enjoyed. Drugs against some PI3Ks are now approved for cancer and PI3K-associated rare diseases.Not every discovery you make in science is easily translatable to drug development. I intentionally picked this type of 'druggable' research subject because I wanted to eventually apply our scientific discoveries. Over the years, I have been fortunate enough to find myself in the space between basic scientists, technologists, drug developers and clinicians, and learning to speak the different languages used in these sectors and to understand their specific challenges.Some of our discoveries have led to the development and eventual approval of drugs, something I am very proud of.For the benefit of our patient & non-scientific readers, could you please give a brief overview of the PI3K pathway & emphasize its importance in cancer research?We are all made up of cells, and cells respond to their environment. Information from the outside must be relayed to the inside of the cell to execute specific functions. PI3K is one of these so-called signal transducers. Proteins like these organize 'signal transduction pathways' in the cell, which are a bit like the metro networks in a large town which allow you to go to from one place to another. PI3K is a very important underground metro station that you often must travel through and is therefore a key player in cells.In the case of PI3K, there are eight family members which perform different functions in cells. To find out what each of the PI3K family members is doing in cells and in the organism has kept us busy for about 20 years. Interestingly, it turns out it is possible to make drugs against every PI3K family member. As we will explain in more detail below, we think it is also possible to make activators of each PI3K.Cancer cells 'hijack' PI3K to switch on signals in cells without a normal signal coming from the outside. Cancer cells use PI3K to become a bit like self-starters, something that we try to block with drugs. PI3Ks can also become over-stimulated in the immune system, and inhibitors have been developed to block that response. Somewhat counter-intuitively, inhibitors against PI3Ks that are expressed in white blood cells can rebalance the immune system to induce an anti-cancer immune response. These inhibitors are currently being tested in so-called cancer immunotherapy.I've really enjoyed your use of analogies throughout your talk today & in your explanations of the role of PI3K within the cell. Could you tell us more about those?Yes, in my experience, simple analogies are often the only thing that people remember from scientific talks. I use this also in daily life, somewhat to the frustration of my now grown-up children.In fact, my daughter came up with an analogy which I now use to describe some key aspects of our ongoing research. This revolves around the question whether in cancer, one needs to activate or inhibit PI3K to kill cancer cells. My daughter compared a cancer cell with a balloon full of air. PI3K inhibitors/blockers are squeezing the air out of the balloon and make it go floppy but the balloon does not pop. When the time is right, the balloon can be inflated again, similar to when cancer returns after some time. In contrast, if you put 10% more air in a fully-blown balloon, it will pop and it will never be possible to blow up the balloon again, and the cancer will not come back. Therefore, one should activate PI3K rather than inhibit it to kill cancer cells, something we are currently exploring in the lab, as explained further below.I always tell my staff to try to use simple language to explain their science, similar to 'Children's BBC'. In these programs, concepts are presented factually correct but simplified to the core, using simple analogies. This is actually very challenging for most scientists. What is the concept? What are you trying to do?Talking at lab tours to non-scientifically-trained visitors such as sponsors and patients is a really good exercise. For example, when someone in the lab is showing how to 'genotype mice', this is looking at the offspring of mouse A bred to mouse B and looking which genes the pups have inherited. This is in fact the same as a 'maternity/paternity' test, something people can relate to. We often, jokingly, propose for the visitors to give us some DNA to see if they are related to each other. People giggle at this but suddenly see the practical application of the rather complicated lab stuff they are being shown. Scientists should do more of this because it's important to communicate your science without saying the wrong thing. This is not the same as dumbing things down. We should also remember that we have a duty to explain our science and methods – ultimately most of the research is paid for by donations from the public and the taxpayer!Could you please describe the projects that you & your team are currently undertaking at UCL?Our research covers three main strands. The first is basic research – there is still a lot unknown about PI3Ks, for example what's happening in cells when PI3K is mutated such as in cancer.We are also testing whether PI3K inhibitors, when given at low doses, can prevent or stop cancer from developing. This can be of specific importance in hereditary cancers where the risk of cancer development is well-known. The idea is to keep cancer at bay, winning time before the cancer develops. For these studies, we use genetically-modified mice which carry the same mutations as in humans, resulting in the development of different cancer types within a year. Our preliminary data look promising, with some well-tolerated drugs able to prevent cancer and extend life in mice. It is hoped that similar approaches will one day be possible in the wider human population.After having inhibited PI3Ks for over 30 years, we are now also exploring whether we can activate PI3K using small molecules. PI3Ks do a lot of good things in the body, and the idea is to test whether we can harness this by activating PI3K for short periods of time when needed. This can be useful in tissue regeneration such as wound healing and diabetic wounds and nerve regeneration. We have just published a paper in Nature on this concept. We have good indications that a PI3K activator can be used to make nerves regenerate faster, something we are trying to develop further in a spin-out company for which we are currently seeking investment. We are also exploring if PI3K activation could be used to stimulate the immune response (for example during vaccination). Paradoxically, short-term overactivation of PI3K could also be useful in killing cancer cells, as explained above with my daughter's balloon analogy. The idea here is to over-stimulate cancer which is already under stress. This is probably one of our most controversial ideas, and I hope to be able to secure funding to explore this further – it is definitely a new modality to interfere with cancer!I think myself extremely lucky to be in an environment where we have the freedom to explore new ideas and, with a bit of luck and hard work, help to alleviate some human diseases.In September 2023, you organized a Biochemical Society Meeting on PI3K pathway. What were some of the highlights of this meeting & do you plan to organize similar events in future?This oversubscribed meeting clearly illustrated renewed interest in PI3K. Scientific discovery and drug development go in waves – this also applies to PI3K research and development which has gone through a dip over the last couple of years, following disappointing outcomes of clinical trials with first generation PI3K inhibitors. In the early days of PI3K, clinical expectations were somewhat inflated, with massive drug development before the pathway was properly understood. The highlights at the meeting were that we now understand the PI3K pathway and its challenges and pitfalls for clinical application much better. It was hugely interesting to see basic scientists, clinicians, drug developers and patients interacting at the meeting. We organized a session with patients which was really inspiring. For example, we had a 16-year-old boy explaining his diagnosis of a PI3K-associated rare disease, what the challenges are and how PI3K drugs have helped him.Our Barcelona meeting clearly illustrated the momentum to organize a follow-on PI3K meeting in the near future. It would also be great to link up PI3K with some other signal transduction pathways, there is a risk for research to end up in so-called 'silos' – cancer for example is a hugely complicated disease which need to be attacked from all angles.What are the challenges to developing novel therapeutics based on the PI3K pathway & how do you think they could be overcome?The most important aspect in my view is to follow the science. When PI3Ks were first discovered, this generated enormous interest, given that these enzymes are over-active in cancer and immune malfunctions but importantly, could also be targeted by small molecules. This created a rush and high expectations which were not always in line with the basic findings on PI3Ks. The fact is that the biology and science will always eventually show up in the clinic, and it is better to be prepared for what could come. Examples are serious side effects of PI3K drugs on metabolism, side effects such as colitis and the toxicity of blocking many PI3K family members at once. Having said this, it is worth trying some of these avenues in challenging diseases such as cancer, as one cannot really predict how drugs will work in the clinic. We now better understand the PI3K pathway and now know what (not) to do.Another big challenge is to convince investors to come back to the field – there is some reluctance not only because of previous negative experience in the PI3K inhibitor field, but also because the regulatory landscape has changed, with PI3K having been singled out in high-profile US FDA reports as a troublesome field, for which more complex clinical trials are now requested. This is a huge challenge for some cancer types for which there are not many patients but also from a return-on-investment perspective.Do you have any colleagues that you look up to or are inspired by? Did you have any role models as a student or in your early career?As a group, I greatly admire my clinical colleagues who perform research. This is a challenging and demanding combination, both from a personal and logistic perspective. It must not always be easy to switch from difficult clinical sessions with cancer patients to lab research, where people might be complaining about relatively small problems compared with what some of these patients must go through.As individual role models, I often refer to Walter Fiers, my PhD supervisor mentioned earlier. He was an agricultural engineer who applied his biochemical knowledge from the brewing industry to make natural medicines, exploiting new technologies in molecular biology that he helped to develop. The same applied to the laboratory next door, led by Marc Van Montagu and Jeff Shell, who invented ways to make plants take up genes, for example to make rice that contains added vitamins, or are resistant to pests. These people were pioneers in their field and often had to work under difficult financial circumstances in Belgium. Toward the end of their careers, the Flemish government began to appreciate their work and that of other pioneers in Belgium and set up the Flemish Institute for Biotechnology (VIB), a hugely successful inter-university organization which produces some of the best in fundamental science but is at the same time very applied and translational. Many of my friends and colleagues are still there, they are doing the same thing as me, but on a much larger scale. I hugely admire people like Walter Fiers and Van Montagu for their vision and foresight, the opportunities they gave to people and their perseverance and vision. We need more of those!Interview disclosureThe opinions expressed in this interview are those of B Vanhaesebroeck and do not necessarily reflect the views of Taylor and Francis.Financial disclosureThe authors have no financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.Competing interests disclosureB Vanhaesebroeck is a consultant for iOnctura (Geneva, Switzerland) and Pharming (Leiden, the Netherlands) and a shareholder of Open Orphan (Dublin, Ireland). The authors have no other competing interests or relevant affiliations with any organization or entity with the subject matter or materials discussed in the manuscript apart from those disclosed.Writing disclosureNo writing assistance was utilized in the production of this manuscript.Open accessThis work is licensed under the Attribution-NonCommercial-NoDerivatives 4.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/4.0/FiguresReferencesRelatedDetails Ahead of Print STAY CONNECTED Metrics History Received 10 October 2023 Accepted 12 March 2024 Published online 7 May 2024 Information© 2024 Bart VanhaesebroeckKeywordscell signalingPI3KalphaPI3KdeltaInterview disclosureThe opinions expressed in this interview are those of B Vanhaesebroeck and do not necessarily reflect the views of Taylor and Francis.Financial disclosureThe authors have no financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.Competing interests disclosureB Vanhaesebroeck is a consultant for iOnctura (Geneva, Switzerland) and Pharming (Leiden, the Netherlands) and a shareholder of Open Orphan (Dublin, Ireland). The authors have no other competing interests or relevant affiliations with any organization or entity with the subject matter or materials discussed in the manuscript apart from those disclosed.Writing disclosureNo writing assistance was utilized in the production of this manuscript.Open accessThis work is licensed under the Attribution-NonCommercial-NoDerivatives 4.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/4.0/PDF download

Oncogenic PIK3CA mutations generate large clones in aging human esophagus. Here we investigate the behavior of Pik3ca mutant clones in the normal esophageal epithelium of transgenic mice. Expression of a heterozygous Pik3caH1047R mutation drives clonal expansion by tilting cell fate toward proliferation. CRISPR screening and inhibitor treatment of primary esophageal keratinocytes confirmed the PI3K-mTOR pathway increased mutant cell competitive fitness. The antidiabetic drug metformin reduced mutant cell advantage in vivo and in vitro. Conversely, metabolic conditions such as type 1 diabetes or diet-induced obesity enhanced the competitive fitness of Pik3caH1047R cells. Consistently, we found a higher density of PIK3CA gain-of-function mutations in the esophagus of individuals with high body mass index compared with those with normal weight. We conclude that the metabolic environment selectively influences the evolution of the normal epithelial mutational landscape. Clinically feasible interventions to even out signaling imbalances between wild-type and mutant cells may limit the expansion of oncogenic mutants in normal tissues.