bims-pideca Biomed News
on Class IA PI3K signalling in development and cancer
Issue of 2021‒05‒16
fourteen papers selected by
Ralitsa Radostinova Madsen
University College London Cancer Institute

  1. Eur J Cancer. 2021 May 05. pii: S0959-8049(21)00209-4. [Epub ahead of print]151 49-62
      BACKGROUND AND PURPOSE: Combined mTORC1 inhibition with everolimus (EVE) and phosphatidylinositol 3-kinase catalytic subunit p110α blockade with alpelisib (ALP) has demonstrated synergistic efficacy in preclinical models and supports testing the combination of ALP and EVE in the clinical setting. The primary objective was to determine the maximum tolerated dose (MTD)/recommended dose for expansion (RDE) of ALP in combination with EVE and in combination with EVE and exemestane (EXE) and subsequently assess safety, preliminary efficacy and effect of ALP on the pharmacokinetics of EVE and determine the magnitude of the drug-drug interaction.PATIENTS AND METHODS: Dose escalation phases were conducted in patients with advanced solid tumours and in postmenopausal women with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC). The dose expansion phase was conducted in patients with pancreatic neuroendocrine tumour and renal cell carcinoma (RCC) (both mechanistic target of rapamycin inhibitor [mTORi]-naive), in patients with mTORi-pretreated solid tumours and in postmenopausal women with HR+, HER2- ABC.
    RESULTS: During the doublet escalation phase, dose-limiting toxicities (DLTs) were reported in 5 of 10 (50%) patients: one patient had grade (Gr) 2 hyperglycemia and one patient had Gr 3 diarrhoea in the 300 mg dose group, one patient had Gr 2 hyperglycemia and one patient had Gr 4 hypocalcaemia in the 250 mg dose group, and one patient in the 200 mg dose group had Gr 3 diarrhoea and Gr 3 stomatitis. The combination of ALP 250 mg + EVE 2.5 mg was declared as the MTD/RDE in subjects with advanced solid tumours. In the triplet escalation phase, one patient who received ALP 200 mg + EVE 2.5 mg + EXE 25 mg had a DLT of Gr 3 acute kidney injury. This dose combination was declared as the MTD and RDE in subjects with advanced HR-positive HER2-negative BC. The common adverse events (≥30% patients), occurring across all phases, were hyperglycaemia, stomatitis, diarrhoea, nausea, asthenia, decreased appetite and fatigue. The sixteen-week progression-free survival rate was 52.4% (90% confidence interval [CI]: 32.8, 71.4) in the RCC cohort, 35.3% (90% CI: 16.6, 58.0) in the prior pNET cohort and 30.0% (90% CI: 8.7, 60.7) in the prior mTORi cohort. The pharmacokinetics of 2.5 mg of EVE was largely unchanged in the presence of ALP, independent of the dose (250 mg or 300 mg). There were no clinically relevant drug-drug interactions observed between ALP and EVE.
    CONCLUSION: The overall safety profile of ALP with EVE and EXE is manageable and reversible; no unexpected safety signals were noted compared with the individual safety profiles. Pharmacokinetics of ALP, EVE and EXE was largely unchanged in combination with each other.
    Keywords:  Advanced breast cancer; Alpelisib; Everolimus; Exemestane; Hormone receptor–positive; Human epidermal growth factor receptor 2–negative; Maximum tolerated dose; PI3K; Pharmacokinetics; Recommended dose for expansion
  2. Autophagy. 2021 May 12. 1-11
      Glioblastoma (GBM), a very aggressive and incurable tumor, often results from constitutive activation of EGFR (epidermal growth factor receptor) and of phosphoinositide 3-kinase (PI3K). To understand the role of autophagy in the pathogenesis of glial tumors in vivo, we used an established Drosophila melanogaster model of glioma based on overexpression in larval glial cells of an active human EGFR and of the PI3K homolog Pi3K92E/Dp110. Interestingly, the resulting hyperplastic glia express high levels of key components of the lysosomal-autophagic compartment, including vacuolar-type H+-ATPase (V-ATPase) subunits and ref(2)P (refractory to Sigma P), the Drosophila homolog of SQSTM1/p62. However, cellular clearance of autophagic cargoes appears inhibited upstream of autophagosome formation. Remarkably, downregulation of subunits of V-ATPase, of Pdk1, or of the Tor (Target of rapamycin) complex 1 (TORC1) component raptor prevents overgrowth and normalize ref(2)P levels. In addition, downregulation of the V-ATPase subunit VhaPPA1-1 reduces Akt and Tor-dependent signaling and restores clearance. Consistent with evidence in flies, neurospheres from patients with high V-ATPase subunit expression show inhibition of autophagy. Altogether, our data suggest that autophagy is repressed during glial tumorigenesis and that V-ATPase and MTORC1 components acting at lysosomes could represent therapeutic targets against GBM.
    Keywords:  Autophagy; V-ATPase; cancer model; fruit fly; glioblastoma; lysosomes; neurospheres; ref(2)P
  3. EMBO Rep. 2021 May 13. e52173
      Lysosomal positioning and mTOR (mammalian target of rapamycin) signaling coordinate cellular responses to nutrient levels. Inadequate nutrient sensing can result in growth delays, a hallmark of Lowe syndrome. OCRL mutations cause Lowe syndrome, but the role of OCRL in nutrient sensing is unknown. Here, we show that OCRL is localized to the centrosome by its ASH domain and that it recruits microtubule-anchoring factor SSX2IP to the centrosome, which is important in the formation of the microtubule-organizing center. Deficiency of OCRL in human and mouse cells results in loss of microtubule-organizing centers and impaired microtubule-based lysosome movement, which in turn leads to mTORC1 inactivation and abnormal nutrient sensing. Centrosome-targeted PACT-SSX2IP can restore microtubule anchoring and mTOR activity. Importantly, boosting the activity of mTORC1 restores the nutrient sensing ability of Lowe patients' cells. Our findings highlight mTORC1 as a novel therapeutic target for Lowe syndrome.
    Keywords:  OCRL; lowe syndrome; lysosome positioning; mTOR; microtubule nucleation
  4. Immunity. 2021 May 11. pii: S1074-7613(21)00170-9. [Epub ahead of print]54(5): 976-987.e7
      Aerobic glycolysis-the Warburg effect-converts glucose to lactate via the enzyme lactate dehydrogenase A (LDHA) and is a metabolic feature of effector T cells. Cells generate ATP through various mechanisms and Warburg metabolism is comparatively an energy-inefficient glucose catabolism pathway. Here, we examined the effect of ATP generated via aerobic glycolysis in antigen-driven T cell responses. Cd4CreLdhafl/fl mice were resistant to Th17-cell-mediated experimental autoimmune encephalomyelitis and exhibited defective T cell activation, migration, proliferation, and differentiation. LDHA deficiency crippled cellular redox balance and inhibited ATP production, diminishing PI3K-dependent activation of Akt kinase and thereby phosphorylation-mediated inhibition of Foxo1, a transcriptional repressor of T cell activation programs. Th17-cell-specific expression of an Akt-insensitive Foxo1 recapitulated the defects seen in Cd4CreLdhafl/fl mice. Induction of LDHA required PI3K signaling and LDHA deficiency impaired PI3K-catalyzed PIP3 generation. Thus, Warburg metabolism augments glycolytic ATP production, fueling a PI3K-centered positive feedback regulatory circuit that drives effector T cell responses.
    Keywords:  ATP; LDHA; PI3K; Th17 cell; autoimmunity; glycolysis; redox balance
  5. Mol Cell. 2021 Apr 30. pii: S1097-2765(21)00324-5. [Epub ahead of print]
      The TSC complex is a critical negative regulator of the small GTPase Rheb and mTORC1 in cellular stress signaling. The TSC2 subunit contains a catalytic GTPase activating protein domain and interacts with multiple regulators, while the precise function of TSC1 is unknown. Here we provide a structural characterization of TSC1 and define three domains: a C-terminal coiled-coil that interacts with TSC2, a central helical domain that mediates TSC1 oligomerization, and an N-terminal HEAT repeat domain that interacts with membrane phosphatidylinositol phosphates (PIPs). TSC1 architecture, oligomerization, and membrane binding are conserved in fungi and humans. We show that lysosomal recruitment of the TSC complex and subsequent inactivation of mTORC1 upon starvation depend on the marker lipid PI3,5P2, demonstrating a role for lysosomal PIPs in regulating TSC complex and mTORC1 activity via TSC1. Our study thus identifies a vital role of TSC1 in TSC complex function and mTORC1 signaling.
    Keywords:  TSC; X-ray crystallography; lysosomes; mTORC1; membrane binding; phosphatidylinositol phosphate
  6. EMBO J. 2021 May 14. e106412
      The mammalian target of rapamycin complex 1 (mTORC1) integrates nutrients, growth factors, stress, and energy status to regulate cell growth and metabolism. Amino acids promote mTORC1 lysosomal localization and subsequent activation. However, the subcellular location or interacting proteins of mTORC1 under amino acid-deficient conditions is not completely understood. Here, we identify ADP-ribosylation factor GTPase-activating protein 1 (ArfGAP1) as a crucial regulator of mTORC1. ArfGAP1 interacts with mTORC1 in the absence of amino acids and inhibits mTORC1 lysosomal localization and activation. Mechanistically, the membrane curvature-sensing amphipathic lipid packing sensor (ALPS) motifs that bind to vesicle membranes are crucial for ArfGAP1 to interact with and regulate mTORC1 activity. Importantly, ArfGAP1 represses cell growth through mTORC1 and is an independent prognostic factor for the overall survival of pancreatic cancer patients. Our study identifies ArfGAP1 as a critical regulator of mTORC1 that functions by preventing the lysosomal transport and activation of mTORC1, with potential for cancer therapeutics.
    Keywords:  ArfGAP1; amino acids; lysosome; mTORC1; vesicle trafficking
  7. Expert Opin Ther Pat. 2021 May 10.
      INTRODUCTION: The phosphatidylinositol 3-kinase/protein kinase-B/mammalian target of rapamycin (PI3K/AKT/mTOR) signaling pathway plays a central role in regulating cell growth and proliferation and thus have been considered as effective anticancer drug targets. Many PI3K inhibitors have been developed and progressed to various stages of clinical trials and some even have been approved in recent years by the regulatory agency as anticancer treatment. In this review, we discuss the drug design and clinical development of PI3K inhibitors in the past four years. We review in details the selectivity and potency of forty-seven PI3K inhibitors, classified based on the mechanism of action. Structural determinants for increasing selectivity toward PI3K subtype-selectivity or mutant selectivity are discussed. Future research direction and current clinical development in combination therapy of inhibitors involving in the PI3Ks are also discussed.Area covered: This review covers clinical trial reports and patent literature on PI3K inhibitors and their selectivity published between 2016 and 2020.Expert opinion: To address the gain-of-function of PI3Kα mutants (E542K, E545K, and H1047R), it is highly desirable to design and develop mutant-specific PI3K inhibitors. It is also necessary to develop subtype-selective PI3Kα inhibitors to minimize toxicity. To reduce drug resistance and to improve efficacy, future studies should include combination therapy of PI3K inhibitors with existing anticancer drugs from different pathways.
    Keywords:  PI3K; cancer; clinical trials; combination therapy; inhibitors; trafficking cascade
  8. Elife. 2021 May 11. pii: e59696. [Epub ahead of print]10
      Metastasis suppression by high-dose, multi-drug targeting is unsuccessful due to network heterogeneity and compensatory network activation. Here we show that targeting driver network signaling capacity by limited inhibition of core pathways is a more effective anti-metastatic strategy. This principle underlies the action of a physiological metastasis suppressor, Raf Kinase Inhibitory Protein (RKIP), that moderately decreases stress-regulated MAP kinase network activity, reducing output to transcription factors such as pro-metastastic BACH1 and motility-related target genes. We developed a low-dose four-drug mimic that blocks metastatic colonization in mouse breast cancer models and increases survival. Experiments and network flow modeling show limited inhibition of multiple pathways is required to overcome variation in MAPK network topology and suppress signaling output across heterogeneous tumor cells. Restricting inhibition of individual kinases dissipates surplus signal, preventing threshold activation of compensatory kinase networks. This low-dose multi-drug approach to decrease signaling capacity of driver networks represents a transformative, clinically-relevant strategy for anti-metastatic treatment.
    Keywords:  cancer biology; human; mouse
  9. Nat Commun. 2021 May 10. 12(1): 2589
      Patients with Tuberous Sclerosis Complex (TSC) show aberrant wiring of neuronal connections formed during development which may contribute to symptoms of TSC, such as intellectual disabilities, autism, and epilepsy. Yet models examining the molecular basis for axonal guidance defects in developing human neurons have not been developed. Here, we generate human induced pluripotent stem cell (hiPSC) lines from a patient with TSC and genetically engineer counterparts and isogenic controls. By differentiating hiPSCs, we show that control neurons respond to canonical guidance cues as predicted. Conversely, neurons with heterozygous loss of TSC2 exhibit reduced responses to several repulsive cues and defective axon guidance. While TSC2 is a known key negative regulator of MTOR-dependent protein synthesis, we find that TSC2 signaled through MTOR-independent RHOA in growth cones. Our results suggest that neural network connectivity defects in patients with TSC may result from defects in RHOA-mediated regulation of cytoskeletal dynamics during neuronal development.
  10. Elife. 2021 May 14. pii: e62233. [Epub ahead of print]10
      Age-related changes to histone levels are seen in many species. However, it is unclear whether changes to histone expression could be exploited to ameliorate the effects of ageing in multicellular organisms. Here we show that inhibition of mTORC1 by the lifespan-extending drug rapamycin increases expression of histones H3 and H4 post-transcriptionally, through eIF3-mediated translation. Elevated expression of H3/H4 in intestinal enterocytes in Drosophila alters chromatin organization, induces intestinal autophagy through transcriptional regulation, prevents age-related decline in the intestine. Importantly, it also mediates rapamycin-induced longevity and intestinal health. Histones H3/H4 regulate expression of an autophagy cargo adaptor Bchs (WDFY3 in mammals), increased expression of which in enterocytes mediates increased H3/H4-dependent healthy longevity. In mice, rapamycin treatment increases expression of histone proteins and Wdfy3 transcription, and alters chromatin organisation in the small intestine, suggesting the mTORC1-histone axis is at least partially conserved in mammals and may offer new targets for anti-ageing interventions.
    Keywords:  D. melanogaster; cell biology; chromosomes; gene expression; mouse
  11. Nat Commun. 2021 May 10. 12(1): 2580
      Combining genetic and cell-type-specific proteomic datasets can generate biological insights and therapeutic hypotheses, but a technical and statistical framework for such analyses is lacking. Here, we present an open-source computational tool called Genoppi ( that enables robust, standardized, and intuitive integration of quantitative proteomic results with genetic data. We use Genoppi to analyze 16 cell-type-specific protein interaction datasets of four proteins (BCL2, TDP-43, MDM2, PTEN) involved in cancer and neurological disease. Through systematic quality control of the data and integration with published protein interactions, we show a general pattern of both cell-type-independent and cell-type-specific interactions across three cancer cell types and one human iPSC-derived neuronal cell type. Furthermore, through the integration of proteomic and genetic datasets in Genoppi, our results suggest that the neuron-specific interactions of these proteins are mediating their genetic involvement in neurodegenerative diseases. Importantly, our analyses suggest that human iPSC-derived neurons are a relevant model system for studying the involvement of BCL2 and TDP-43 in amyotrophic lateral sclerosis.
  12. Mol Metab. 2021 May 05. pii: S2212-8778(21)00091-0. [Epub ahead of print] 101246
      OBJECTIVE: Stress-induced hyperglycemia is associated with poor outcomes in nearly all critical illnesses. This acute elevation in glucose after injury or illness is associated with increased morbidity and mortality including multiple organ failure. Stress-induced hyperglycemia is often attributed to insulin resistance as controlling glucose levels via exogenous insulin improves outcomes, but mechanisms are unclear. Forkhead box O (FOXO) transcription factors are direct targets of insulin signaling in the liver that regulate glucose homeostasis via direct and indirect pathways. Loss of hepatic FOXO transcription factors reduces hyperglycemia in chronic insulin-resistance; however, the role of FOXOs in stress-induced hyperglycemia is unknown.METHODS: We subjected mice lacking FOXO transcription factors in liver to a model of injury known to cause stress-induced hyperglycemia. Glucose, insulin, glycerol, fatty acids, cytokines, and adipokines were assessed before and after injury. Liver and adipose tissue were analyzed for changes in glycogen, FOXO target gene expression, and insulin signaling.
    RESULTS: Stress-induced hyperglycemia was associated with reduced hepatic insulin signaling and increased hepatic FOXO target gene expression while loss of FOXO1, 3, and 4 in the liver attenuated hyperglycemia and prevented hyperinsulinemia. Mechanistically, loss of FOXO transcription factors mitigated the stress-induced hyperglycemia response by directly altering gene expression and glycogenolysis in the liver and indirectly suppressing lipolysis in adipose tissue. Reductions were associated with decreased IL-6, TNF-α, and follistatin and increased FGF21, suggesting that cytokines and FOXO-regulated hepatokines contribute to the stress-induced hyperglycemia response.
    CONCLUSIONS: This work implicates FOXO transcription factors as a predominant driver of stress-induced hyperglycemia through means that include cross talk between liver and adipose, highlighting a novel mechanism underlying acute hyperglycemia and insulin resistance in stress.
    Keywords:  AKT; FOXO; Insulin resistance; Lipolysis; Stress-induced hyperglycemia
  13. Cell. 2021 Apr 30. pii: S0092-8674(21)00495-5. [Epub ahead of print]
      Cancer cell genetic variability and similarity to host cells have stymied development of broad anti-cancer therapeutics. Our innate immune system evolved to clear genetically diverse pathogens and limit host toxicity; however, whether/how innate immunity can produce similar effects in cancer is unknown. Here, we show that human, but not murine, neutrophils release catalytically active neutrophil elastase (ELANE) to kill many cancer cell types while sparing non-cancer cells. ELANE proteolytically liberates the CD95 death domain, which interacts with histone H1 isoforms to selectively eradicate cancer cells. ELANE attenuates primary tumor growth and produces a CD8+T cell-mediated abscopal effect to attack distant metastases. Porcine pancreatic elastase (ELANE homolog) resists tumor-derived protease inhibitors and exhibits markedly improved therapeutic efficacy. Altogether, our studies suggest that ELANE kills genetically diverse cancer cells with minimal toxicity to non-cancer cells, raising the possibility of developing it as a broad anti-cancer therapy.
    Keywords:  CD95; cancer; histone H1; neutrophil estate; neutrophils; therapeutics; tumor immunology
  14. Cell. 2021 May 13. pii: S0092-8674(21)00372-X. [Epub ahead of print]184(10): 2525-2531
      Human cell lines (CLs) are key assets for biomedicine but lack ancestral diversity. Here, we explore why genetic diversity among cell-based models is essential for making preclinical research more equitable and widely translatable. We lay out practical actions that can be taken to improve inclusivity in study design.
    Keywords:  GWAS; HeLa; ancestry; cell lines; diversity; drug discovery; pharmacogenomics; precision medicine