CD36 Drives Metastasis and Relapse in Acute Myeloid Leukemia

Identifying mechanisms underlying relapse is a major clinical issue for effective cancer treatment. The emerging understanding of the importance of metastasis in hematologic malignancies suggests that it could also play a role in drug resistance and relapse in acute myeloid leukemia (AML). In a cohort of 1,273 AML patients, we uncovered that the multifunctional scavenger receptor CD36 was positively associated with extramedullary dissemination of leukemic blasts, increased risk of relapse after intensive chemotherapy, and reduced event-free and overall survival. CD36 was dispensable for lipid uptake but fostered blast migration through its binding with thrombospondin-1. CD36-expressing blasts, which were largely enriched after chemotherapy, exhibited a senescent-like phenotype while maintaining their migratory ability. In xenograft mouse models, CD36 inhibition reduced metastasis of blasts and prolonged survival of chemotherapy-treated mice. These results pave the way for the development of CD36 as an independent marker of poor prognosis in AML patients and a promising actionable target to improve the outcome of patients.

SIGNIFICANCE

CD36 promotes blast migration and extramedullary disease in acute myeloid leukemia and represents a critical target that can be exploited for clinical prognosis and patient treatment.

Targeting PP2A-dependent autophagy enhances sensitivity to ruxolitinib in JAK2V617F myeloproliferative neoplasms

The Janus kinase 2 (JAK2)-driven myeloproliferative neoplasms (MPNs) are chronic malignancies associated with high-risk complications and suboptimal responses to JAK inhibitors such as ruxolitinib. A better understanding of cellular changes induced by ruxolitinib is required to develop new combinatory therapies to improve treatment efficacy. Here, we demonstrate that ruxolitinib induced autophagy in JAK2^V617F cell lines and primary MPN patient cells through the activation of protein phosphatase 2A (PP2A). Inhibition of autophagy or PP2A activity along with ruxolitinib treatment reduced proliferation and increased the death of JAK2^V617F cells. Accordingly, proliferation and clonogenic potential of JAK2^V617F-driven primary MPN patient cells, but not of normal hematopoietic cells, were markedly impaired by ruxolitinib treatment with autophagy or PP2A inhibitor. Finally, preventing ruxolitinib-induced autophagy with a novel potent autophagy inhibitor Lys05 improved leukemia burden reduction and significantly prolonged the mice's overall survival compared with ruxolitinib alone. This study demonstrates that PP2A-dependent autophagy mediated by JAK2 activity inhibition contributes to resistance to ruxolitinib. Altogether, our data support that targeting autophagy or its identified regulator PP2A could enhance sensitivity to ruxolitinib of JAK2^V617F MPN cells and improve MPN patient care.

C/EBPα Confers Dependence to Fatty Acid Anabolic Pathways and Vulnerability to Lipid Oxidative Stress-Induced Ferroptosis in FLT3-Mutant Leukemia

Although transcription factor CCAAT-enhancer binding protein α (C/EBPα) is critical for normal and leukemic differentiation, its role in cell and metabolic homeostasis is largely unknown in cancer. Here, multiomics analyses uncovered a coordinated activation of C/EBPα and Fms-like tyrosine kinase 3 (FLT3) that increased lipid anabolism in vivo and in patients with FLT3-mutant acute myeloid leukemia (AML). Mechanistically, C/EBPα regulated the fatty acid synthase (FASN)-stearoyl-CoA desaturase (SCD) axis to promote fatty acid (FA) biosynthesis and desaturation. We further demonstrated that FLT3 or C/EBPα inactivation decreased monounsaturated FA incorporation to membrane phospholipids through SCD downregulation. Consequently, SCD inhibition enhanced susceptibility to lipid redox stress that was exploited by combining FLT3 and glutathione peroxidase 4 inhibition to trigger lipid oxidative stress, enhancing ferroptotic death of FLT3-mutant AML cells. Altogether, our study reveals a C/EBPα function in lipid homeostasis and adaptation to redox stress, and a previously unreported vulnerability of FLT3-mutant AML to ferroptosis with promising therapeutic application.

SIGNIFICANCE

FLT3 mutations are found in 30% of AML cases and are actionable by tyrosine kinase inhibitors. Here, we discovered that C/EBPα regulates FA biosynthesis and protection from lipid redox stress downstream mutant-FLT3 signaling, which confers a vulnerability to ferroptosis upon FLT3 inhibition with therapeutic potential in AML. This article is highlighted in the In This Issue feature, p. 1501.

Oxidative phosphorylation fueled by fatty acid oxidation sensitizes leukemic stem cells to cold

Dependency on mitochondrial oxidative phosphorylation (OxPhos) is a potential weakness for leukemic stem cells (LSCs) that can be exploited for therapeutic purposes. Fatty acid oxidation (FAO) is a crucial OxPhos-fueling catabolic pathway for some acute myeloid leukemia (AML) cells, particularly chemotherapy-resistant AML cells. Here, we identified cold sensitivity at 4°C (cold killing challenge; CKC4), commonly used for sample storage, as a novel vulnerability that selectively kills AML LSCs with active FAO-supported OxPhos while sparing normal hematopoietic stem cells (HSCs). Cell death of OxPhos-positive leukemic cells was induced by membrane permeabilization at 4°C; by sharp contrast, leukemic cells relying on glycolysis were resistant. Forcing glycolytic cells to activate OxPhos metabolism sensitized them to CKC4. Lipidomic and proteomic analyzes showed that OxPhos shapes the composition of the plasma membrane and introduces variation of 22 lipid subfamilies between cold-sensitive and cold-resistant cells. Together, these findings indicate that steady-state energy metabolism at body temperature predetermines the sensitivity of AML LSCs to cold temperature, suggesting that cold sensitivity could be a potential OxPhos biomarker. These results could have important implications for designing experiments for AML research to avoid cell storage at 4°C.

Phenotypically-defined stages of leukemia arrest predict main driver mutations subgroups, and outcome in acute myeloid leukemia

Classifications of acute myeloid leukemia (AML) patients rely on morphologic, cytogenetic, and molecular features. Here we have established a novel flow cytometry-based immunophenotypic stratification showing that AML blasts are blocked at specific stages of differentiation where features of normal myelopoiesis are preserved. Six stages of leukemia differentiation-arrest categories based on CD34, CD117, CD13, CD33, MPO, and HLA-DR expression were identified in two independent cohorts of 2087 and 1209 AML patients. Hematopoietic stem cell/multipotent progenitor-like AMLs display low proliferation rate, inv(3) or RUNX1 mutations, and high leukemic stem cell frequency as well as poor outcome, whereas granulocyte-monocyte progenitor-like AMLs have CEBPA mutations, RUNX1-RUNX1T1 or CBFB-MYH11 translocations, lower leukemic stem cell frequency, higher chemosensitivity, and better outcome. NPM1 mutations correlate with most mature stages of leukemia arrest together with TET2 or IDH mutations in granulocyte progenitors-like AML or with DNMT3A mutations in monocyte progenitors-like AML. Overall, we demonstrate that AML is arrested at specific stages of myeloid differentiation (SLA classification) that significantly correlate with AML genetic lesions, clinical presentation, stem cell properties, chemosensitivity, response to therapy, and outcome.

SHED-Dependent Oncogenic Signaling of the PEAK3 Pseudo-Kinase

Simple Summary

The human kinome is composed of about 50 pseudo-kinases with unclear function, because they are predicted to be catalytically inactive; however, they are shown to play an important role in cancer, similar to active kinases. Understanding how these pseudo-kinases promote tumor formation despite their catalytic inactivity is a great challenge, which may lead to innovative anti-cancer therapies. The PEAK1 and 2 pseudo-kinases have emerged as important components of the protein tyrosine kinase pathway implicated in cancer progression. They can signal using a scaffolding mechanism via a conserved split helical dimerization (SHED) module. In this study, we uncovered a similar SHED-dependent oncogenic activity for PEAK3, a recently discovered new member of this family. We also show that this new signaling mechanism may be implicated in acute myeloid leukemia.

Abstract

The PEAK1 and Pragmin/PEAK2 pseudo-kinases have emerged as important components of the protein tyrosine kinase pathway implicated in cancer progression. They can signal using a scaffolding mechanism that involves a conserved split helical dimerization (SHED) module. We recently identified PEAK3 as a novel member of this family based on structural homology; however, its signaling mechanism remains unclear. In this study, we found that, although it can self-associate, PEAK3 shows higher evolutionary divergence than PEAK1/2. Moreover, the PEAK3 protein is strongly expressed in human hematopoietic cells and is upregulated in acute myeloid leukemia. Functionally, PEAK3 overexpression in U2OS sarcoma cells enhanced their growth and migratory properties, while its silencing in THP1 leukemic cells reduced these effects. Importantly, an intact SHED module was required for these PEAK3 oncogenic activities. Mechanistically, through a phosphokinase survey, we identified PEAK3 as a novel inducer of AKT signaling, independent of growth-factor stimulation. Then, proteomic analyses revealed that PEAK3 interacts with the signaling proteins GRB2 and ASAP1/2 and the protein kinase PYK2, and that these interactions require the SHED domain. Moreover, PEAK3 activated PYK2, which promoted PEAK3 tyrosine phosphorylation, its association with GRB2 and ASAP1, and AKT signaling. Thus, the PEAK1-3 pseudo-kinases may use a conserved SHED-dependent mechanism to activate specific signaling proteins to promote oncogenesis.

Mitochondrial inhibitors circumvent adaptive resistance to venetoclax and cytarabine combination therapy in acute myeloid leukemia

Therapy resistance represents a major clinical challenge in acute myeloid leukemia (AML). Here we define a 'MitoScore' signature, which identifies high mitochondrial oxidative phosphorylation in vivo and in patients with AML. Primary AML cells with cytarabine (AraC) resistance and a high MitoScore relied on mitochondrial Bcl2 and were highly sensitive to venetoclax (VEN) + AraC (but not to VEN + azacytidine). Single-cell transcriptomics of VEN + AraC-residual cell populations revealed adaptive resistance associated with changes in oxidative phosphorylation, electron transport chain complex and the TP53 pathway. Accordingly, treatment of VEN + AraC-resistant AML cells with electron transport chain complex inhibitors, pyruvate dehydrogenase inhibitors or mitochondrial ClpP protease agonists substantially delayed relapse following VEN + AraC. These findings highlight the central role of mitochondrial adaptation during AML therapy and provide a scientific rationale for alternating VEN + azacytidine with VEN + AraC in patients with a high MitoScore and to target mitochondrial metabolism to enhance the sensitivity of AML cells to currently approved therapies.

Activation of Vitamin D Receptor Pathway Enhances Differentiating Capacity in Acute Myeloid Leukemia with Isocitrate Dehydrogenase Mutations

Simple Summary

Around 15% of acute myeloid leukemia (AML) patients harbor mutations in isocitrate dehydrogenases (IDH), which lead to the production of the oncometabolite 2-hydroxyglutarate (2-HG). Inhibitors of mutant IDH enzymes and their 2-HG production have been approved by the FDA to be used in patients. However, 60% of IDH mutant AML patients do not respond to these inhibitors or develop mechanisms of resistance, leading to relapse. Among these mechanisms, some produce a 2-HG rebound. Alternative therapies exploiting the 2-HG-dependent molecular effects could therefore be of clinical interest. In this study, we demonstrate that 2-HG specifically activates vitamin D receptor (VDR) in IDH mutant AML cells leading to increased sensitivity to the combination of vitamin D (or VDR agonist) and all-trans retinoic acid and revealing a new therapeutic approach that can be readily applied to AML patients in this subgroup.

Abstract

Relapses and resistance to therapeutic agents are major barriers in the treatment of acute myeloid leukemia (AML) patients. These unfavorable outcomes emphasize the need for new strategies targeting drug-resistant cells. As IDH mutations are present in the preleukemic stem cells and systematically conserved at relapse, targeting IDH mutant cells could be essential to achieve a long-term remission in the IDH mutant AML subgroup. Here, using a panel of human AML cell lines and primary AML patient specimens harboring IDH mutations, we showed that the production of an oncometabolite (R)-2-HG by IDH mutant enzymes induces vitamin D receptor-related transcriptional changes, priming these AML cells to differentiate with pharmacological doses of ATRA and/or VD. This activation occurs in a CEBPα-dependent manner. Accordingly, our findings illuminate potent and cooperative effects of IDH mutations and the vitamin D receptor pathway on differentiation in AML, revealing a novel therapeutic approach easily transferable/immediately applicable to this subgroup of AML patients.

Mitochondrial metabolism supports resistance to IDH mutant inhibitors in acute myeloid leukemia

Mutations in IDH induce epigenetic and transcriptional reprogramming, differentiation bias, and susceptibility to mitochondrial inhibitors in cancer cells. Here, we first show that cell lines, PDXs, and patients with acute myeloid leukemia (AML) harboring an IDH mutation displayed an enhanced mitochondrial oxidative metabolism. Along with an increase in TCA cycle intermediates, this AML-specific metabolic behavior mechanistically occurred through the increase in electron transport chain complex I activity, mitochondrial respiration, and methylation-driven CEBPα-induced fatty acid β-oxidation of IDH1 mutant cells. While IDH1 mutant inhibitor reduced 2-HG oncometabolite and CEBPα methylation, it failed to reverse FAO and OxPHOS. These mitochondrial activities were maintained through the inhibition of Akt and enhanced activation of peroxisome proliferator-activated receptor-γ coactivator-1 PGC1α upon IDH1 mutant inhibitor. Accordingly, OxPHOS inhibitors improved anti-AML efficacy of IDH mutant inhibitors in vivo. This work provides a scientific rationale for combinatory mitochondrial-targeted therapies to treat IDH mutant AML patients, especially those unresponsive to or relapsing from IDH mutant inhibitors.

Dendrogenin A Enhances Anti-Leukemic Effect of Anthracycline in Acute Myeloid Leukemia

Simple Summary

Recently, several molecules have improved the clinical outcome of acute myeloid leukemia (AML) patients. Despite these recent advances, their prognosis remains poor and new strategies to improve the standard anthracycline and Ara-C-based chemotherapy are needed. We recently published that dendrogenin A (DDA), a mammalian cholesterol metabolite with tumor-suppressor properties, can potentiate the effect of Ara-C to kill AML cells. In this study, we find that DDA can also potentiate anthracycline against AML. The potentiation of Ara-C by DDA is due to a switch from a protective autophagy to a deadly autophagy. Regarding anthracyclines, the potentiation of daunorubicin is caused by the modulation of the efflux by the PgP pump, and that of idarubicin, to an increase in DNA damage and to the induction of a rapid and lethal autophagy. This is caused by rapid modulation of AKT/mTOR and JNK activity, two major pathways involved both in DNA repair and lethal autophagy.

Abstract

Dendrogenin A (DDA), a mammalian cholesterol metabolite with tumor suppressor properties, has recently been shown to exhibit strong anti-leukemic activity in acute myeloid leukemia (AML) cells by triggering lethal autophagy. Here, we demonstrated that DDA synergistically enhanced the toxicity of anthracyclines in AML cells but not in normal hematopoietic cells. Combination index of DDA treatment with either daunorubicin or idarubicin indicated a strong synergism in KG1a, KG1 and MV4-11 cell lines. This was confirmed in vivo using immunodeficient mice engrafted with MOLM-14 cells as well as in a panel of 20 genetically diverse AML patient samples. This effect was dependent on Liver X Receptor β, a major target of DDA. Furthermore, DDA plus idarubicin strongly increased p53BP1 expression and the number of DNA strand breaks in alkaline comet assays as compared to idarubicin alone, whereas DDA alone was non-genotoxic. Mechanistically, DDA induced JNK phosphorylation and the inhibition of AKT phosphorylation, thereby maximizing DNA damage induced by idarubicin and decreasing DNA repair. This activated autophagic cell death machinery in AML cells. Overall, this study shows that the combination of DDA and idarubicin is highly promising and supports clinical trials of dendrogenin A in AML patients.

Autophagy regulates fatty acid availability for oxidative phosphorylation through mitochondria-endoplasmic reticulum contact sites

Autophagy has been associated with oncogenesis with one of its emerging key functions being its contribution to the metabolism of tumors. Therefore, deciphering the mechanisms of how autophagy supports tumor cell metabolism is essential. Here, we demonstrate that the inhibition of autophagy induces an accumulation of lipid droplets (LD) due to a decrease in fatty acid β-oxidation, that leads to a reduction of oxidative phosphorylation (OxPHOS) in acute myeloid leukemia (AML), but not in normal cells. Thus, the autophagic process participates in lipid catabolism that supports OxPHOS in AML cells. Interestingly, the inhibition of OxPHOS leads to LD accumulation with the concomitant inhibition of autophagy. Mechanistically, we show that the disruption of mitochondria–endoplasmic reticulum (ER) contact sites (MERCs) phenocopies OxPHOS inhibition. Altogether, our data establish that mitochondria, through the regulation of MERCs, controls autophagy that, in turn finely tunes lipid degradation to fuel OxPHOS supporting proliferation and growth in leukemia.

How autophagy supports tumor cell metabolism is not fully clear. Here, the authors show that autophagy regulates lipid availability to support mitochondrial oxidative metabolism through mitochondria-endoplasmic reticulum contact sites, necessary for cell proliferation in AML.

Extracellular ATP and CD39 Activate cAMP-Mediated Mitochondrial Stress Response to Promote Cytarabine Resistance in Acute Myeloid Leukemia

Relapses driven by chemoresistant leukemic cell populations are the main cause of mortality for patients with acute myeloid leukemia (AML). Here, we show that the ectonucleotidase CD39 (ENTPD1) is upregulated in cytarabine-resistant leukemic cells from both AML cell lines and patient samples in vivo and in vitro. CD39 cell-surface expression and activity is increased in patients with AML upon chemotherapy compared with diagnosis, and enrichment in CD39-expressing blasts is a marker of adverse prognosis in the clinics. High CD39 activity promotes cytarabine resistance by enhancing mitochondrial activity and biogenesis through activation of a cAMP-mediated adaptive mitochondrial stress response. Finally, genetic and pharmacologic inhibition of CD39 ecto-ATPase activity blocks the mitochondrial reprogramming triggered by cytarabine treatment and markedly enhances its cytotoxicity in AML cells in vitro and in vivo. Together, these results reveal CD39 as a new residual disease marker and a promising therapeutic target to improve chemotherapy response in AML. SIGNIFICANCE: Extracellular ATP and CD39-P2RY13-cAMP-OxPHOS axis are key regulators of cytarabine resistance, offering a new promising therapeutic strategy in AML.This article is highlighted in the In This Issue feature, p. 1426.

Dendrogenin A synergizes with Cytarabine to Kill Acute Myeloid Leukemia Cells In Vitro and In Vivo

Dendrogenin A (DDA) is a mammalian cholesterol metabolite that displays potent antitumor properties on acute myeloid leukemia (AML). DDA triggers lethal autophagy in cancer cells through a biased activation of the oxysterol receptor LXRβ, and the inhibition of a sterol isomerase. We hypothesize that DDA could potentiate the activity of an anticancer drug acting through a different molecular mechanism, and conducted in vitro and in vivo combination tests on AML cell lines and patient primary tumors. We report here results from tests combining DDA with antimetabolite cytarabine (Ara-C), one of the main drugs used for AML treatment worldwide. We demonstrated that DDA potentiated and sensitized AML cells, including primary patient samples, to Ara-C in vitro and in vivo. Mechanistic studies revealed that this sensitization was LXRβ-dependent and was due to the activation of lethal autophagy. This study demonstrates a positive in vitro and in vivo interaction between DDA and Ara-C, and supports the clinical evaluation of DDA in combination with Ara-C for the treatment of AML.

Targeting Myeloperoxidase Disrupts Mitochondrial Redox Balance and Overcomes Cytarabine Resistance in Human Acute Myeloid Leukemia

Chemotherapies alter cellular redox balance and reactive oxygen species (ROS) content. Recent studies have reported that chemoresistant cells have an increased oxidative state in hematologic malignancies. In this study, we demonstrated that chemoresistant acute myeloid leukemia (AML) cells had a lower level of mitochondrial and cytosolic ROS in response to cytarabine (AraC) and overexpressed myeloperoxidase (MPO), a heme protein that converts hydrogen peroxide to hypochlorous acid (HOCl), compared with sensitive AML cells. High MPO-expressing AML cells were less sensitive to AraC in vitro and in vivo. They also produced higher levels of HOCl and exhibited an increased rate of mitochondrial oxygen consumption when compared with low MPO-expressing AML cells. Targeting MPO expression or enzyme activity sensitized AML cells to AraC treatment by triggering oxidative damage and sustaining oxidative stress, particularly in high MPO-expressing AML cells. This sensitization stemmed from mitochondrial superoxide accumulation, which impaired oxidative phosphorylation and cellular energetic balance, driving apoptotic death and selective eradication of chemoresistant AML cells in vitro and in vivo. Altogether, this study uncovers a noncanonical function of MPO enzyme in maintaining redox balance and mitochondrial energetic metabolism, therefore affecting downstream pathways involved in AML chemoresistance. SIGNIFICANCE: These findings demonstrate the role of myeloperoxidase in the regulation of ROS levels and sensitivity of AML cells to cytarabine, an essential chemotherapeutic backbone in the therapy of AML.

Dexamethasone in hyperleukocytic acute myeloid leukemia

Patients with acute myeloid leukemia and a high white blood cell count are at increased risk of early death and relapse. Because mediators of inflammation contribute to leukostasis and chemoresistance, dexamethasone added to chemotherapy could improve outcomes. This retrospective study evaluated the impact of adding or not adding dexamethasone to chemotherapy in a cohort of 160 patients with at least 50×10⁹ white blood cells. In silico studies, primary samples, leukemic cell lines, and xenograft mouse models were used to explore the antileukemic activity of dexamethasone. There was no difference with respect to induction death rate, response, and infections between the 60 patients in the dexamethasone group and the 100 patients in the no dexamethasone group. Multivariate analysis showed that dexamethasone was significantly associated with improved relapse incidence (adjusted sub-HR: 0.30; 95% CI: 0.14–0.62; P=0.001), disease-free survival (adjusted HR: 0.50; 95% CI: 0.29–0.84; P=0.010), event-free survival (adjusted HR: 0.35; 95% CI: 0.21–0.58; P<0.001), and overall survival (adjusted HR: 0.41; 95% CI: 0.22–0.79; P=0.007). In a co-culture system, dexamethasone reduced the frequency of leukemic long-term culture initiating cells by 38% and enhanced the cytotoxicity of doxorubicin and cytarabine. In a patient-derived xenograft model treated with cytarabine, chemoresistant cells were enriched in genes of the inflammatory response modulated by dexamethasone. Dexamethasone also demonstrated antileukemic activity in NPM1-mutated samples. Dexamethasone may improve the outcome of acute myeloid leukemia patients receiving intensive chemotherapy. This effect could be due to the modulation of inflammatory chemoresistance pathways and to a specific activity in acute myeloid leukemia with NPM1 mutation.

Chemotherapy-Resistant Human Acute Myeloid Leukemia Cells Are Not Enriched for Leukemic Stem Cells but Require Oxidative Metabolism

Chemotherapy-resistant human acute myeloid leukemia (AML) cells are thought to be enriched in quiescent immature leukemic stem cells (LSC). To validate this hypothesis in vivo, we developed a clinically relevant chemotherapeutic approach treating patient-derived xenografts (PDX) with cytarabine (AraC). AraC residual AML cells are enriched in neither immature, quiescent cells nor LSCs. Strikingly, AraC-resistant preexisting and persisting cells displayed high levels of reactive oxygen species, showed increased mitochondrial mass, and retained active polarized mitochondria, consistent with a high oxidative phosphorylation (OXPHOS) status. AraC residual cells exhibited increased fatty-acid oxidation, upregulated CD36 expression, and a high OXPHOS gene signature predictive for treatment response in PDX and patients with AML. High OXPHOS but not low OXPHOS human AML cell lines were chemoresistant in vivo. Targeting mitochondrial protein synthesis, electron transfer, or fatty-acid oxidation induced an energetic shift toward low OXPHOS and markedly enhanced antileukemic effects of AraC. Together, this study demonstrates that essential mitochondrial functions contribute to AraC resistance in AML and are a robust hallmark of AraC sensitivity and a promising therapeutic avenue to treat AML residual disease.Significance: AraC-resistant AML cells exhibit metabolic features and gene signatures consistent with a high OXPHOS status. In these cells, targeting mitochondrial metabolism through the CD36-FAO-OXPHOS axis induces an energetic shift toward low OXPHOS and strongly enhanced antileukemic effects of AraC, offering a promising avenue to design new therapeutic strategies and fight AraC resistance in AML. Cancer Discov; 7(7); 716-35. ©2017 AACR.See related commentary by Schimmer, p. 670This article is highlighted in the In This Issue feature, p. 653.

Abstract A23: Characterization of novel molecular vulnerabilities provoking replicative and energetic stresses in pancreatic cancer cells

Pancreatic cancer (PDAC) remains a deadly disease with no cure. In this dismal context, we demonstrated that non-viral gene therapy to sensitize cancer cells to chemotherapy was safe and feasible, and offers therapeutic benefit in patients (Thergap trial 2010-2012). However, alternative molecular pathways must be targeted to relieve resistance to treatment for best therapeutic benefit. We identified cytidine deaminase (CDA) that catalyzes the hydrolytic deamination of cytidine and deoxycytidine to uridine and deoxyuridine, as overexpressed (i) in cohorts of patients resisting to gemcitabine, (ii) in PDAC as compared to normal parenchyma, and (iii) in patients receiving gene therapy. Targeting CDA using genetic tools sensitizes cancer cells to chemotherapy both in vitro and in vivo, with very high efficacy in preclinical models of cancer. On the other hand, loss of CDA per se unexpectedly alters cell proliferation, cell cycle progression and tumor growth in vivo, when more than half of mice engrafted with CDA-null human pancreatic cancer cells remained free of tumors nor developed metastasis. Using a multi-omics approach, we found that both pyrimidine and purine levels are decreased, inducing replicative stress hallmarks in CDA-null cells, and TCA cycle is altered, strongly suggesting mitochondrial dysfunction, as we further demonstrate decreased mitochondrial ATP and down expression of key proteins of the mitochondrial OXPHOS complexes and β-oxidation. Consequently, mitochondrial ROS are elevated with major changes in the redox balance in PDAC cells. Remarkably, tumor cells retaliate using compensatory mechanisms resembling Pasteur effect with elevated lactate levels. These compensatory mechanisms served as secondary targets to (i) further strengthen the inhibition of cell proliferation and migration seen in CDA-null cells, and (ii) annihilate potential mechanisms of resistance to treatment. Taken together, our aforementioned results demonstrate for the first time that targeting CDA, an enzyme primarily thought to be restricted to the pyrimidine salvage pathway, strongly alters PDAC proliferation and tumor progression, via massive modification of cancer cell metabolism and alteration of cell cycle, in the absence of chemotherapy. To the best of our knowledge, the crosstalk between replicative and energetic pathways has been thus far totally underexplored in cancer. As specific inhibitors of CDA are underway, we postulate that PDAC rewiring following CDA targeting can be considered exploitable Achille’s eel or vulnerabilities for novel, DNA and metabolic-based, synthetic lethality strategies and the promise of targeted-approaches with high efficacy for PDAC therapy.

Note: This abstract was not presented at the conference.

Citation Format: Marion Gayral, Audrey Frances, Estelle Saland, Hubert Lulka, Naima Hanoun, Anthony Lemarié, Laetitia Ligat, Nathalie Saint-Laurent, Frédéric Lopez, Louis Buscail, Jean-Emmanuel Sarry, Pierre Cordelier.{Authors}. Characterization of novel molecular vulnerabilities provoking replicative and energetic stresses in pancreatic cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr A23.

CDC25A governs proliferation and differentiation of FLT3-ITD acute myeloid leukemia

We investigated cell cycle regulation in acute myeloid leukemia cells expressing the FLT3-ITD mutated tyrosine kinase receptor, an underexplored field in this disease. Upon FLT3 inhibition, CDC25A mRNA and protein were rapidly down-regulated, while levels of other cell cycle proteins remained unchanged. This regulation was dependent on STAT5, arguing for FLT3-ITD-dependent transcriptional regulation of CDC25A. CDC25 inhibitors triggered proliferation arrest and cell death of FLT3-ITD as well as FLT3-ITD/TKD AC-220 resistant cells, but not of FLT3-wt cells. Consistently, RNA interference-mediated knock-down of CDC25A reduced the proliferation of FLT3-ITD cell lines. Finally, the clonogenic capacity of primary FLT3-ITD AML cells was reduced by the CDC25 inhibitor IRC-083864, while FLT3-wt AML and normal CD34+ myeloid cells were unaffected. In good agreement, in a cohort of 100 samples from AML patients with intermediate-risk cytogenetics, high levels of CDC25A mRNA were predictive of higher clonogenic potential in FLT3-ITD+ samples, not in FLT3-wt ones.Importantly, pharmacological inhibition as well as RNA interference-mediated knock-down of CDC25A also induced monocytic differentiation of FLT3-ITD positive cells, as judged by cell surface markers expression, morphological modifications, and C/EBPα phosphorylation. CDC25 inhibition also re-induced monocytic differentiation in primary AML blasts carrying the FLT3-ITD mutation, but not in blasts expressing wild type FLT3. Altogether, these data identify CDC25A as an early cell cycle transducer of FLT3-ITD oncogenic signaling, and as a promising target to inhibit proliferation and re-induce differentiation of FLT3-ITD AML cells.

Isocitrate dehydrogenase 1 mutations prime the all-trans retinoic acid myeloid differentiation pathway in acute myeloid leukemia

Boutzen et al. show that the IDH1 mutation and its oncometabolite, (R)-2-hydroxyglutarate, dysregulate downstream target pathways of myeloid-specific TFs, especially CEBPα, priming mutant IDH1-R132H AML blasts to the granulomonocytic lineage.

Acute myeloid leukemia (AML) is characterized by the accumulation of malignant blasts with impaired differentiation programs caused by recurrent mutations, such as the isocitrate dehydrogenase (IDH) mutations found in 15% of AML patients. These mutations result in the production of the oncometabolite (R)-2-hydroxyglutarate (2-HG), leading to a hypermethylation phenotype that dysregulates hematopoietic differentiation. In this study, we identified mutant R132H IDH1-specific gene signatures regulated by key transcription factors, particularly CEBPα, involved in myeloid differentiation and retinoid responsiveness. We show that treatment with all-trans retinoic acid (ATRA) at clinically achievable doses markedly enhanced terminal granulocytic differentiation in AML cell lines, primary patient samples, and a xenograft mouse model carrying mutant IDH1. Moreover, treatment with a cell-permeable form of 2-HG sensitized wild-type IDH1 AML cells to ATRA-induced myeloid differentiation, whereas inhibition of 2-HG production significantly reduced ATRA effects in mutant IDH1 cells. ATRA treatment specifically decreased cell viability and induced apoptosis of mutant IDH1 blasts in vitro. ATRA also reduced tumor burden of mutant IDH1 AML cells xenografted in NOD–Scid–IL2rγ^null mice and markedly increased overall survival, revealing a potent antileukemic effect of ATRA in the presence of IDH1 mutation. This therapeutic strategy holds promise for this AML patient subgroup in future clinical studies.

Knockout of Vdac1 activates hypoxia-inducible factor through reactive oxygen species generation and induces tumor growth by promoting metabolic reprogramming and inflammation

Background

Mitochondria are more than just the powerhouse of cells; they dictate if a cell dies or survives. Mitochondria are dynamic organelles that constantly undergo fusion and fission in response to environmental conditions. We showed previously that mitochondria of cells in a low oxygen environment (hypoxia) hyperfuse to form enlarged or highly interconnected networks with enhanced metabolic efficacy and resistance to apoptosis. Modifications to the appearance and metabolic capacity of mitochondria have been reported in cancer. However, the precise mechanisms regulating mitochondrial dynamics and metabolism in cancer are unknown. Since hypoxia plays a role in the generation of these abnormal mitochondria, we questioned if it modulates mitochondrial function. The mitochondrial outer-membrane voltage-dependent anion channel 1 (VDAC1) is at center stage in regulating metabolism and apoptosis. We demonstrated previously that VDAC1 was post-translationally C-terminal cleaved not only in various hypoxic cancer cells but also in tumor tissues of patients with lung adenocarcinomas. Cells with enlarged mitochondria and cleaved VDAC1 were also more resistant to chemotherapy-stimulated cell death than normoxic cancer cells.

Results

Transcriptome analysis of mouse embryonic fibroblasts (MEF) knocked out for Vdac1 highlighted alterations in not only cancer and inflammatory pathways but also in the activation of the hypoxia-inducible factor-1 (HIF-1) signaling pathway in normoxia. HIF-1α was stable in normoxia due to accumulation of reactive oxygen species (ROS), which decreased respiration and glycolysis and maintained basal apoptosis. However, in hypoxia, activation of extracellular signal-regulated kinase (ERK) in combination with maintenance of respiration and increased glycolysis counterbalanced the deleterious effects of enhanced ROS, thereby allowing Vdac1^−/− MEF to proliferate better than wild-type MEF in hypoxia. Allografts of RAS-transformed Vdac1^−/− MEF exhibited stabilization of both HIF-1α and HIF-2α, blood vessel destabilization, and a strong inflammatory response. Moreover, expression of Cdkn2a, a HIF-1-target and tumor suppressor gene, was markedly decreased. Consequently, RAS-transformed Vdac1^−/− MEF tumors grew faster than wild-type MEF tumors.

Conclusions

Metabolic reprogramming in cancer cells may be regulated by VDAC1 through vascular destabilization and inflammation. These findings provide new perspectives into the understanding of VDAC1 in the function of mitochondria not only in cancer but also in inflammatory diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s40170-015-0133-5) contains supplementary material, which is available to authorized users.

Antileukemic Activity of 2-Deoxy-d-Glucose through Inhibition of N-Linked Glycosylation in Acute Myeloid Leukemia with FLT3-ITD or c-KIT Mutations

We assessed the antileukemic activity of 2-deoxy-d-glucose (2-DG) through the modulation of expression of receptor tyrosine kinases (RTK) commonly mutated in acute myeloid leukemia (AML). We used human leukemic cell lines cells, both in vitro and in vivo, as well as leukemic samples from AML patients to demonstrate the role of 2-DG in tumor cell growth inhibition. 2-DG, through N-linked glycosylation inhibition, affected the cell-surface expression and cellular signaling of both FTL3-ITD and mutated c-KIT and induced apoptotic cell death. Leukemic cells harboring these mutated RTKs (MV4-11, MOLM-14, Kasumi-1, and TF-1 c-KIT D816V) were the most sensitive to 2-DG treatment in vitro as compared with nonmutated cells. 2-DG activity was also demonstrated in leukemic cells harboring FLT3-TKD mutations resistant to the tyrosine kinase inhibitor (TKI) quizartinib. Moreover, the antileukemic activity of 2-DG was particularly marked in c-KIT-mutated cell lines and cell samples from core binding factor-AML patients. In these cells, 2-DG inhibited the cell-surface expression of c-KIT, abrogated STAT3 and MAPK-ERK pathways, and strongly downregulated the expression of the receptor resulting in a strong in vivo effect in NOD/SCID mice xenografted with Kasumi-1 cells. Finally, we showed that 2-DG decreases Mcl-1 protein expression in AML cells and induces sensitization to both the BH3 mimetic inhibitor of Bcl-xL, Bcl-2 and Bcl-w, ABT-737, and cytarabine. In conclusion, 2-DG displays a significant antileukemic activity in AML with FLT3-ITD or KIT mutations, opening a new therapeutic window in a subset of AML with mutated RTKs.

Metformin inhibits growth of human glioblastoma cells and enhances therapeutic response

High-grade gliomas, glioblastomas (GB), are refractory to conventional treatment combining surgery, chemotherapy, mainly temozolomide, and radiotherapy. This highlights an urgent need to develop novel therapies and increase the efficacy of radio/chemotherapy for these very aggressive and malignant brain tumors. Recently, tumor metabolism became an interesting potential therapeutic target in various cancers. Accordingly, combining drugs targeting cell metabolism with appropriate chemotherapeutic agents or radiotherapy has become attractive. In light of these perspectives, we were particularly interested in the anti-cancer properties of a biguanide molecule used for type 2 diabetes treatment, metformin. In our present work, we demonstrate that metformin decreases mitochondrial-dependent ATP production and oxygen consumption and increases lactate and glycolytic ATP production. We show that metformin induces decreased proliferation, cell cycle arrest, autophagy, apoptosis and cell death in vitro with a concomitant activation of AMPK, Redd1 and inhibition of the mTOR pathway. Cell sensitivity to metformin also depends on the genetic and mutational backgrounds of the different GB cells used in this study, particularly their PTEN status. Interestingly, knockdown of AMPK and Redd1 with siRNA partially, but incompletely, abrogates the induction of apoptosis by metformin suggesting both AMPK/Redd1-dependent and –independent effects. However, the primary determinant of the effect of metformin on cell growth is the genetic and mutational backgrounds of the glioma cells. We further demonstrate that metformin treatment in combination with temozolomide and/or irradiation induces a synergistic anti-tumoral response in glioma cell lines. Xenografts performed in nude mice demonstrate in vivo that metformin delays tumor growth. As current treatments for GB commonly fail to cure, the need for more effective therapeutic options is overwhelming. Based on these results, metformin could represent a potential enhancer of the cytotoxic effects of temozolomide and/or radiotherapy.

A robust and rapid xenograft model to assess efficacy of chemotherapeutic agents for human acute myeloid leukemia

Relevant preclinical mouse models are crucial to screen new therapeutic agents for acute myeloid leukemia (AML). Current in vivo models based on the use of patient samples are not easy to establish and manipulate in the laboratory. Our objective was to develop robust xenograft models of human AML using well-characterized cell lines as a more accessible and faster alternative to those incorporating the use of patient-derived AML cells. Five widely used AML cell lines representing various AML subtypes were transplanted and expanded into highly immunodeficient non-obese diabetic/LtSz-severe combined immunodeficiency IL2Rγ_c^null mice (for example, cell line-derived xenografts). We show here that bone marrow sublethal conditioning with busulfan or irradiation has equal efficiency for the xenotransplantation of AML cell lines. Although higher number of injected AML cells did not change tumor engraftment in bone marrow and spleen, it significantly reduced the overall survival in mice for all tested AML cell lines. On the basis of AML cell characteristics, these models also exhibited a broad range of overall mouse survival, engraftment, tissue infiltration and aggressiveness. Thus, we have established a robust, rapid and straightforward in vivo model based on engraftment behavior of AML cell lines, all vital prerequisites for testing new therapeutic agents in preclinical studies.

TOM1 is a PI5P effector involved in the regulation of endosomal maturation

Phosphoinositides represent a major class of lipids specifically involved in the organisation of signaling cascades, maintenance of the identity of organelles and regulation of multiple intracellular trafficking steps. We previously described that phosphatidylinositol 5-monophosphate (PI5P), produced by the Shigella flexneri phosphatase IpgD, is implicated in the endosomal sorting of the EGFR. Here, we show that the adaptor protein TOM1 is a new PI5P direct binding partner. We identify the domain of TOM1 involved in this interaction and characterize the binding motif. Finally, we demonstrate that the recruitment of TOM1 by PI5P on signaling endosomes is responsible for the delay in EGFR degradation and fluid-phase bulk endocytosis. Taken together, our data strongly suggest that PI5P-enrichment in signaling endosomes prevents endosomal maturation through the recruitment of TOM1, and point out to a new function of PI5P in regulating discrete maturation steps in the endosomal system.

Abstract 1336: Bortezomib induces the degradation of FLT3-ITD tyrosine kinase in acute myeloid leukemia through an autophagy-dependent mechanism

Internal tandem duplication mutations of the Fms-like tyrosine kinase 3 (FLT3-ITD) are found in 30% of Acute Myeloid Leukemias and are associated with a very poor outcome. Although the activity of FLT3 inhibitors such as AC-220 is currently evaluated in phase II and III trials with promising results, some studies suggest that leukemic cells can develop various mechanisms of resistance including mutations of the tyrosine kinase domain (TKD).

In the present work, we show that AML cell lines harboring FLT3-ITD mutation, MV4-11 and MOLM-14, are exquisitely sensitive to the proteasome inhibitor bortezomib. Importantly, although bortezomib induced apoptosis in all primary AML samples (n=24), FLT3-ITD mutated cells (n=13) are much more sensitive than non-mutated samples (n=11). Moreover we observed a positive correlation between FLT3-ITD mutation load (measured by the FLT3-ITD/FLT3wt ratio) and bortezomib activity among FLT3-ITD samples (p=0.0084, r=0.719). At the molecular level, bortezomib induced autophagy, as shown by an increase of LC3-II protein expression and by electron microscopy analysis. This autophagy was mainly cytotoxic as cell death was inhibited by the autophagy pharmacological inhibitor, 3-methyladenine. Before cell death occurs, we observed that bortezomib induced a downregulation of FLT3-ITD both in cell lines and primary samples. Accordingly, cell signalling dependent on FLT3-ITD (ERK/Akt/STAT5) was inhibited upon bortezomib treatment. Others proteasome inhibitors such as MG-132 or carfilzomib were also able to downregulate FLT3-ITD protein level. Interestingly, 3-methyladenine restored FLT3-ITD expression and signaling after bortezomib exposure, suggesting a role for autophagy in the downregulation of the mutated receptor. Using confocal microscopy, we showed a co-localization between FLT3-ITD and LC3 structures after bortezomib exposure. Electron microscopy analyses confirmed the presence of the receptor in autophagy vesicles. Furthermore, the membrane trafficking inhibitor dynasore inhibited autophagy, cell death and degradation of FLT3-ITD induced by bortezomib. We also showed that bortezomib overcomes the resistance to AC-220 in a MOLM-14 ITD/TKD model, by triggering the degradation of the receptor. Finally, in vivo studies using a mouse xenograft model, confirmed that bortezomib was able to decrease FLT3-ITD protein level and inhibit leukemic cell growth.

Altogether, our results show that proteasome inhibitors induce a downregulation of the oncogenic tyrosine kinase FLT3-ITD in an autophagic-dependent manner, suggesting that they could be used as an alternative strategy in AML with FLT3-ITD mutations.

Citation Format: Clément Larrue, Estelle Saland, Marion David, Jean-Emmanuel Sarry, Stéphane Manenti, Christian Récher. Bortezomib induces the degradation of FLT3-ITD tyrosine kinase in acute myeloid leukemia through an autophagy-dependent mechanism. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1336. doi:10.1158/1538-7445.AM2014-1336

Arabinogalactan protein 31 (AGP31), a putative network-forming protein in Arabidopsis thaliana cell walls?

BACKGROUND AND AIMS

Arabinogalactan protein 31 (AGP31) is a remarkable plant cell-wall protein displaying a multi-domain organization unique in Arabidopsis thaliana: it comprises a predicted signal peptide (SP), a short AGP domain of seven amino acids, a His-stretch, a Pro-rich domain and a PAC (PRP-AGP containing Cys) domain. AGP31 displays different O-glycosylation patterns with arabinogalactans on the AGP domain and Hyp-O-Gal/Ara-rich motifs on the Pro-rich domain. AGP31 has been identified as an abundant protein in cell walls of etiolated hypocotyls, but its function has not been investigated thus far. Literature data suggest that AGP31 may interact with cell-wall components. The purpose of the present study was to identify AGP31 partners to gain new insight into its function in cell walls.

METHODS

Nitrocellulose membranes were prepared by spotting different polysaccharides, which were either obtained commercially or extracted from cell walls of Arabidopsis thaliana and Brachypodium distachyon. After validation of the arrays, in vitro interaction assays were carried out by probing the membranes with purified native AGP31 or recombinant PAC-V5-6xHis. In addition, dynamic light scattering (DLS) analyses were carried out on an AGP31 purified fraction.

KEY RESULTS

It was demonstrated that AGP31 interacts through its PAC domain with galactans that are branches of rhamnogalacturonan I. This is the first experimental evidence that a PAC domain, also found as an entire protein or a domain of AGP31 homologues, can bind carbohydrates. AGP31 was also found to bind methylesterified polygalacturonic acid, possibly through its His-stretch. Finally, AGP31 was able to interact with itself in vitro through its PAC domain. DLS data showed that AGP31 forms aggregates in solution, corroborating the hypothesis of an auto-assembly.

CONCLUSIONS

These results allow the proposal of a model of interactions of AGP31 with different cell-wall components, in which AGP31 participates in complex supra-molecular scaffolds. Such scaffolds could contribute to the strengthening of cell walls of quickly growing organs such as etiolated hypocotyls.

Mitochondrial energetic and AKT status mediate metabolic effects and apoptosis of metformin in human leukemic cells

Previous reports demonstrate that metformin, an anti-diabetic drug, can decrease the risk of cancer and inhibit cancer cell growth. However, its mechanism in cancer cells is still unknown. Metformin significantly blocks cell cycle and inhibits cell proliferation and colony formation of leukemic cells. However, the apoptotic response to metformin varies. Furthermore, daily treatment with metformin induces apoptosis and reduces tumor growth in vivo. While metformin induces early and transient activation of AMPK, inhibition of AMPKα1/2 does not abrogate anti-proliferative or pro-apoptotic effects of metformin. Metformin decreases electron transport chain complex I activity, oxygen consumption and mitochondrial ATP synthesis, while stimulating glycolysis for ATP and lactate production, pentose phosphate pathway for purine biosynthesis, fatty acid metabolism, as well as anaplerotic and mitochondrial gene expression. Importantly, leukemic cells with high basal AKT phosphorylation, glucose consumption or glycolysis exhibit a markedly reduced induction of the Pasteur effect in response to metformin and are resistant to metformin-induced apoptosis. Accordingly, glucose starvation or treatment with deoxyglucose or an AKT inhibitor induces sensitivity to metformin. Overall, metformin elicits reprogramming of intermediary metabolism leading to inhibition of cell proliferation in all leukemic cells and apoptosis only in leukemic cells responding to metformin with AKT phosphorylation and a strong Pasteur effect.

The nucleophosmin-anaplastic lymphoma kinase oncogene interacts, activates, and uses the kinase PIKfyve to increase invasiveness

NPM-ALK is a chimeric tyrosine kinase detected in most anaplastic large cell lymphomas that results from the reciprocal translocation t(2,5)(p23;q35) that fuses the N-terminal domain of nucleophosmin (NPM) to the catalytic domain of the anaplastic lymphoma kinase (ALK) receptor. The constitutive activity of the kinase is responsible for its oncogenicity through the stimulation of several downstream signaling pathways, leading to cell proliferation, migration, and survival. We demonstrated previously that the high level of phosphatidylinositol 5-phosphate measured in NPM-ALK-expressing cells is controlled by the phosphoinositide kinase PIKfyve, a lipid kinase known for its role in vesicular trafficking. Here, we show that PIKfyve associates with NPM-ALK and that the interaction involves the 181-300 region of the oncogene. Moreover, we demonstrate that the tyrosine kinase activity of the oncogene controls PIKfyve lipid kinase activity but is dispensable for the formation of the complex. Silencing or inhibition of PIKfyve using siRNA or the PIKfyve inhibitor YM201636 have no effect on NPM-ALK-mediated proliferation and migration but strongly reduce invasive capacities of NPM-ALK-expressing cells and their capacity to degrade the extracellular matrix. Accordingly, immunofluorescence studies confirm a perturbation of matrix metalloproteinase 9 localization at the cell surface and defect in maturation. Altogether, these results suggest a role for PIKfyve in NPM-ALK-mediated invasion.