Mitochondrial fusion is a therapeutic vulnerability of acute myeloid leukemia

Mitochondrial metabolism recently emerged as a critical dependency in acute myeloid leukemia (AML). The shape of mitochondria is tightly regulated by dynamin GTPase proteins, which drive opposing fusion and fission forces to consistently adapt bioenergetics to the cellular context. Here, we showed that targeting mitochondrial fusion was a new vulnerability of AML cells, when assayed in patient-derived xenograft (PDX) models. Genetic depletion of mitofusin 2 (MFN2) or optic atrophy 1 (OPA1) or pharmacological inhibition of OPA1 (MYLS22) blocked mitochondrial fusion and had significant anti-leukemic activity, while having limited impact on normal hematopoietic cells ex vivo and in vivo. Mechanistically, inhibition of mitochondrial fusion disrupted mitochondrial respiration and reactive oxygen species production, leading to cell cycle arrest at the G$_{0}$/G$_{1}$ transition. These results nominate the inhibition of mitochondrial fusion as a promising therapeutic approach for AML

Study of glucose metabolism in acute myeloid leukemia and implication of the mTORC1 signaling pathway

Les Leucémies Aigües Myéloïdes (LAM) sont des hémopathies malignes hétérogènes de mauvais pronostic qui se caractérisent par une expansion clonale de progéniteurs immatures. De nombreuses dérégulations de voies de signalisation sont retrouvées dans les cellules leucémiques et leur confèrent un avantage de prolifération et de survie. La voie de signalisation mTORC1, qui contrôle la traduction protéique, l’autophagie et plusieurs voies métaboliques, est ainsi constitutivement activée dans les cellules leucémiques. La reprogrammation métabolique notamment via « l’effet Warburg » est un phénomène bien décrit dans les cellules cancéreuses. L’augmentation de l’utilisation de la glycolyse, confère aux cellules tumorales un avantage de survie en favorisant une production rapide d’ATP et d’intermédiaires métaboliques nécessaires pour les biosynthèses de nucléotides, d’acides-aminés et de lipides. C’est donc dans ce contexte que j’ai étudié le métabolisme du glucose dans les cellules de LAM et l’implication de la voie de signalisation mTORC1 dans la dérégulation de ce métabolisme. J’ai tout d’abord identifié par une étude transcriptomique dans la lignée leucémique MOLM-14 que la signalisation mTORC1 contrôle plusieurs voies métaboliques notamment celles permettant l’utilisation du glucose. Ceci a été vérifié dans plusieurs lignées de LAM puisque l’inhibition ou la sur-activation de mTORC1 entrainent respectivement une diminution ou une augmentation de la consommation de glucose et de la production de lactate. De façon intéressante, le niveau d’activation de la voie mTORC1 détermine la sensibilité des cellules leucémiques à l’inhibition de la glycolyse. En effet, lorsque mTORC1 est activé, le blocage de la glycolyse induit de l’autophagie et l’apoptose des cellules leucémiques. A l’inverse, le blocage de mTORC1 induit une reprogrammation métabolique des cellules leucémiques qui utilisent alors principalement la phosphorylation oxydative pour produire l’ATP dont elles ont besoin. Leur survie devient alors indépendante du glucose. A l’inverse des cellules primaires de LAM, les cellules hématopoïétiques immatures normales CD34+ sont moins sensibles au blocage de la glycolyse. Le ciblage du métabolisme du glucose pourrait donc constituer une stratégie thérapeutique intéressante dans les LAM. Je me suis ensuite intéressée aux effets anti-leucémiques induits par l’inhibition de la voie des pentoses phosphates (PP) et plus particulièrement au ciblage de la G6PD (glucose-6-phosphate déshydrogénase) par le composé le 6-aminonicotinamide (6-AN). En effet, une étude de flux métabolique a permis de mettre en évidence qu’une proportion importante de glucose est dirigé vers la voie des PP, laissant suggérer que l’addiction des cellules leucémiques au glucose pourrait être liée à une utilisation augmentée de cette voie annexe. J’ai alors observé que le 6-AN induit une cytotoxicité in-vitro y compris dans les cellules primaires de patients, sans avoir d’effets sur les cellules hématopoïétiques normales et in-vivo dans un modèle de xénogreffe de la lignée MOLM-14 chez la souris NUDE. Cette étude a donc permis de montrer que l’activation constitutive de mTORC1 rend la survie des cellules de LAM dépendante de la glycolyse et crée une sensibilité spécifique à l’inhibition de la G6PD. La dérégulation de la signalisation mTORC1 étant quasi-constante dans les LAM, cibler la G6PD pourrait donc représenter une stratégie thérapeutique intéressante.Acute Myeloid Leukemia (AML) are heterogeneous hematological diseases with poor prognosis characterized by a clonal expansion of immature progenitors. Many deregulation of signaling pathways are found in leukemic cells and give them an advantage of proliferation and survival. The MTORC1 signaling pathway, which controls protein translation, autophagy and several metabolic pathways, is constitutively activated in leukemic cells. Metabolic reprogramming in particular the "Warburg effect" is a phenomenon well described in cancer cells. High rate of glycolysis has been considered to give tumour cells advantages through rapid production of ATP and intermediates for the synthesis of nucleotides, amino acids, and lipids. In this context, I studied glucose metabolism in AML cells and the involvement of the mTORC1 signaling pathway in the deregulation of this metabolism. First, I identified by a transcriptomic analysis in the MOLM-14 cell line that mTORC1 signaling controls several metabolic pathways including those for glucose utilization. This has been verified in several AML cell lines, since inhibition or over-activation of mTORC1 respectively induces a decrease or an increase in glucose consumption and lactate production. Interestingly, the level of activation of the mTORC1 signaling pathway determines the sensitivity of AML cells to the inhibition of glycolysis. Indeed, when mTORC1 is activated, the blockade of glycolysis induces autophagy and apoptosis of leukemic cells. Conversely, blocking mTORC1 induces metabolic reprogramming of leukemic cells, which then mainly use oxidative phosphorylation to produce ATP for their needs. AML cell survival become independent of glucose. Unlike primary AML cells, survival of normal immature hematopoietic cells CD34+ is only barely affected by the blockade of glycolysis. Thus, targeting the glucose metabolism may constitute an attractive therapeutic strategy in AML. I then investigated the anti-leukemic activity induced by the inhibition of the pentose phosphate pathway (PPP) and more particularly by the specific blockade of G6PD (glucose 6-phosphate dehydrogenase) with the 6-aminonicotinamide (6- AN) compound. Indeed, a metabolic flux analysis demonstrated that a significant proportion of glucose was directed towards the PPP. This result suggested that the addiction of leukemic cells toward glucose might be related to an increased use of PPP. I then observed that the 6-AN induced in vitro cytotoxicity including in primary AML cells from patients without effect on normal immature hematopoietic cells CD34+ and in vivo in a xenograft model of MOLM-14 cell line in the NUDE mouse. This study therefore demonstrated that the constitutive activation of mTORC1 makes AML cells survival dependent on glycolysis, and creates a specific vulnerability to the inhibition of G6PD. Given that deregulation of the mTORC1 signaling pathway is almost constant in AML, targeting G6PD may therefore represent an interesting therapeutic strategy

AMP-Activated Protein Kinase Contributes to Apoptosis Induced by the Bcl-2 Inhibitor Venetoclax in Acute Myeloid Leukemia

The treatment of acute myeloid leukemia (AML) remains a challenge especially among the elderly. The Bcl-2 inhibitor venetoclax recently showed significant survival benefits in AML patients when combined to low-dose cytarabine or azacitidine. Bcl-2 inhibition initiate mitochondrial apoptosis, but also respiration and cellular ATP production in AML. AMP-Activated Protein Kinase (AMPK) is a central energy sensor activated by increased AMP:ATP ratio to restore the cellular energy balance. Unexpectedly, we observed that venetoclax inhibited AMPK activity through caspase-dependent degradation of AMPK subunits in AML cells. On the other hand, genetic models of AMPK invalidation and re-expression suggested that AMPK participated to the early stages of apoptotic response through a negative regulation of multi-domain anti-apoptotic effectors such as Mcl-1 or Bcl-xL. Together our results suggested a new link between AMPK and Bcl-2-dependent mitochondrial apoptosis that participated to the anti-leukemic activity of venetoclax in AML.</p

Dual mTORC1/2 inhibition induces anti-proliferative effect in NF1-associated plexiform neurofibroma and malignant peripheral nerve sheath tumor cells

International audienceApproximately 30-50% of individuals with Neurofibromatosis type 1 develop benign peripheral nerve sheath tumors, called plexiform neurofibromas (PNFs). PNFs can undergo malignant transformation to highly metastatic malignant peripheral nerve sheath tumors (MPNSTs) in 5-10% of NF1 patients, with poor prognosis. No effective systemic therapy is currently available for unresectable tumors. In tumors, the NF1 gene deficiency leads to Ras hyperactivation causing the subsequent activation of the AKT/mTOR and Raf/MEK/ERK pathways and inducing multiple cellular responses including cell proliferation. In this study, three NF1-null MPNST-derived cell lines (90-8, 88-14 and 96-2), STS26T sporadic MPNST cell line and PNF-derived primary Schwann cells were used to test responses to AZD8055, an ATP-competitive "active-site" mTOR inhibitor. In contrast to rapamycin treatment which only partially affected mTORC1 signaling, AZD8055 induced a strong inhibition of mTORC1 and mTORC2 signaling in MPNST-derived cell lines and PNF-derived Schwann cells. AZD8055 induced full blockade of mTORC1 leading to an efficient decrease of global protein synthesis. A higher cytotoxic effect was observed with AZD8055 compared to rapamycin in the NF1-null MPNST-derived cell lines with IC50 ranging from 70 to 140 nM and antiproliferative effect was confirmed in PNF-derived Schwann cells. Cell migration was impaired by AZD8055 treatment and cell cycle analysis showed a G0/G1 arrest. Combined effects of AZD8055 and PD0325901 MEK inhibitor as well as BRD4 (BromoDomain-containing protein 4) inhibitors showed a synergistic antiproliferative effect. These data suggest that NF1-associated peripheral nerve sheath tumors are an ideal target for AZD8055 as a single molecule or in combined therapies

Co-activation of AMPK and mTORC1 Induce Cytotoxicity in Acute Myeloid Leukemia

International audienceGraphical Abstract Highlights d AMPK activation blocks AML propagation without toxicity to normal hematopoiesis d Cytotoxicity induced by an AMPK activator (GSK621) involves autophagy in AML d Co-activation of AMPK and mTORC1 is synthetically lethal in AML d AMPK and mTORC1 crosstalk requires eIF2a/ATF4 signalin

Pim kinases modulate resistance to FLT3 tyrosine kinase inhibitors in FLT3-ITD acute myeloid leukemia

Fms-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) is frequently detected in acute myeloid leukemia (AML) patients and is associated with a dismal long-term prognosis. FLT3 tyrosine kinase inhibitors provide short-term disease control, but relapse invariably occurs within months. Pim protein kinases are oncogenic FLT3-ITD targets expressed in AML cells. We show that increased Pim kinase expression is found in relapse samples from AML patients treated with FLT3 inhibitors. Ectopic Pim-2 expression induces resistance to FLT3 inhibition in both FLT3-ITD-induced myeloproliferative neoplasm and AML models in mice. Strikingly, we found that Pim kinases govern FLT3-ITD signaling and that their pharmacological or genetic inhibition restores cell sensitivity to FLT3 inhibitors. Finally, dual inhibition of FLT3 and Pim kinases eradicates FLT3-ITD(+) cells including primary AML cells. Concomitant Pim and FLT3 inhibition represents a promising new avenue for AML therapy

RAS activation induces synthetic lethality of MEK inhibition with mitochondrial oxidative metabolism in acute myeloid leukemia

International audienceDespite recent advances in acute myeloid leukemia (AML) molecular characterization and targeted therapies, a majority of AML cases still lack therapeutically actionable targets. In 127 AML cases with unmet therapeutic needs, as defined by the exclusion of ELN favorable cases and of FLT3-ITD mutations, we identified 51 (40%) cases with alterations in RAS pathway genes (RAS+, mostly NF1, NRAS, KRAS, and PTPN11 genes). In 79 homogeneously treated AML patients from this cohort, RAS+ status were associated with higher white blood cell count, higher LDH, and reduced survival. In AML models of oncogenic addiction to RAS-MEK signaling, the MEK inhibitor trametinib demonstrated antileukemic activity in vitro and in vivo. However, the efficacy of trametinib was heterogeneous in ex vivo cultures of primary RAS+ AML patient specimens. From repurposing drug screens in RAS-activated AML cells, we identified pyrvinium pamoate, an anti-helminthic agent efficiently inhibiting the growth of RAS+ primary AML cells ex vivo, preferentially in trametinib-resistant PTPN11- or KRAS-mutated samples. Metabolic and genetic complementarity between trametinib and pyrvinium pamoate translated into anti-AML synergy in vitro. Moreover, this combination inhibited the propagation of RA+ AML cells in vivo in mice, indicating a potential for future clinical development of this strategy in AML