Acriflavine targets oncogenic STAT5 signaling in myeloid leukemia cells

International audienc

The incidence of hypoxia on oxidative metabolism in acute myeloid leukemias : establishment and characterization of an in vitro leukemic niche model

Dans les leucémies aiguës myéloïdes (LAM), un taux élevé d’espèces réactives de l’oxygène (ROS) est connu pour favoriser la prolifération de blastes, alors qu’un niveau faible promeut la quiescence des cellules souches leucémiques. La faible oxygénation, ou hypoxie, de la niche médullaire pourrait contribuer à la chimiorésistance des LAM en diminuant le stress oxydatif. Les facteurs induits par l’hypoxie (HIF) sont impliqués dans le contrôle du métabolisme et des enzymes antioxydantes. Leur inhibition conduit à un stress et à la mort des cellules de LAM. Mon objectif était d’étudier un lien entre l’hypoxie, le métabolisme oxydatif et la chimiorésistance dans un modèle in vitro de culture de cellules de LAM. L’acquisition d’un profil hypoxique par les cellules souches hématopoïétiques (CSH), cultivées avec des cellules stromales mésenchymateuses (CSM) médullaires, a été montré. Nous avons postulé que les cellules leucémiques pouvaient également l’acquérir en coculture avec des CSM humaines. Pour le démontrer, nous avons cultivé des cellules de LAM primaires ou de la lignée MV4-11 sur des CSM humaines primaires ou de la lignée HS-27a. A l’instar des CSH, nous avons identifié trois populations leucémiques en fonction de leur capacité d’adhésion sur les CSM : en suspension, adhérentes aux CSM et nichées dans les CSM. Les cellules nichées, les plus adhérentes, ont une plus forte expression du CXCR4 que les autres. Elles sont aussi plus résistantes de 2 à 7 fois à la cytarabine. Cependant, aucune modification du phénotype souche et des capacités clonogéniques, de repopulation ou de xénogreffe, n’a pu être associée aux cellules nichées comparées aux deux autres populations. En revanche, les cellules nichées présentent un profil hypoxique, une plus faible prolifération avec une augmentation de la phase G0, et de plus faibles niveaux de ROS en lien avec une masse mitochondriale diminuée. Ceci suggère donc un lien entre la chimiorésistance et l’hypoxie ou le métabolisme, plutôt qu’avec une capacité souche. Nous avons aussi montré que l’acriflavine, un inhibiteur non spécifique des HIF, pouvait avoir un effet synergique avec la cytarabine sur les cellules nichées chimiorésistantes. Nos résultats montrent que le surnageant ou le simple contact avec les CSM ne suffisent pas à induire le changement métabolique et la résistance à la cytarabine. Nous pensons que l’hypoxie dans la niche peut moduler le métabolisme oxydatif et donc la chimiorésistance par des mécanismes directs et/ou indirects via l’expression de CXCR4, montré récemment comme impliqué dans la régulation du stress oxydatif des CSH.In acute myeloid leukemia, a high level of ROS is known to favor blasts proliferation, whereas a low level promotes stem cells quiescence. The low oxygenation, or hypoxia, of the bone marrow niche could contribute to chemoresistance of AML cells by reducing the oxidative stress. Hypoxia-inducible factors (HIF) are involved in the control of the cell metabolism and antioxidant enzymes. HIFs inhibition leads to AML cells stress and death. The purpose of this work was to study a link between hypoxia, oxidative metabolism and chemoresistance in an in vitro model of leukemic cell culture. The acquisition of a hypoxic profile by hematopoietic stem cells (HSC) cultured with medullary mesenchymal stromal cells (MSC), has been shown. We hypothesized that AML cells may also acquire such profile in a coculture with human MSCs. To demonstrate that, we cultivated primary AML cells or the MV4-11 cell line on primary human MSCs or the HS-27a cell line. Like HSCs, we identified three leukemic populations according to their adhesion capacity to MSCs: in suspension, adherent to MSCs and embedded in MSCs. Embedded cells, the most adherent, have stronger CXCR4 expression compared to the others. They are also 2- to 7-fold more resistance to cytarabine. However, no change in the stem cell phenotype profile and in the clonogenic, repopulation or xenograft capacities, could be associated with the embedded cells compared to other populations. In contrast, embedded cells present a hypoxic profile, a weak proliferation with increased G0 phase, and lower ROS level that may rely on lower mitochondrial mass. This suggests that chemoresistance mainly relies on hypoxia or cell metabolism rather than a higher stem cell capacity. Furthermore, we have shown that acriflavine, a non-specific HIF inhibitor, could synergize with the cytarabine to eliminate embedded chemoresistant cells. Our results show that the MSC supernatant or a simple contact are not sufficient to induce metabolic change and resistance to cytarabine. We assume that hypoxia in the niche may modulate the oxidative metabolism and the chemoresistance by direct mechanisms and/or indirect ones through CXCR4 expression, a chemokine receptor shown to be involved in the regulation of the oxidative stress in HSC

A Novel Inhibitor of STAT5 Signaling Overcomes Chemotherapy Resistance in Myeloid Leukemia Cells

International audienc

A comparative study of the capacity of mesenchymal stromal cell lines to form spheroids

International audienceMesenchymal stem cells (MSC)-spheroid models favor maintenance of stemness, ex vivo expansion and transplantation efficacy. Spheroids may also be considered as useful surrogate models of the hematopoietic niche. However, accessibility to primary cells, from bone marrow (BM) or adipose tissues, may limit their experimental use and the lack of consistency in methods to form spheroids may affect data interpretation. In this study, we aimed to create a simple model by examining the ability of cell lines, from human (HS-27a and HS-5) and murine (MS-5) BM origins, to form spheroids, compared to primary human MSCs (hMSCs). Our protocol efficiently allowed the spheroid formation from all cell types within 24 hours. Whilst hMSC-spheroids began to shrink after 24 hours, the size of spheroids from cell lines remained constant during three weeks. The difference was partially explained by the balance between proliferation and cell death, which could be triggered by hypoxia and induced oxidative stress. Our results demonstrate that, like hMSCs, MSC cell lines make reproductible spheroids that are easily handled. Thus, this model could help in understanding mechanisms involved in MSC functions and may provide a simple model by which to study cell interactions in the BM niche

Characterization of NADPH Oxidase Expression and Activity in Acute Myeloid Leukemia Cell Lines: A Correlation with the Differentiation Status

International audienceIn acute myeloid leukemia (AML), a low level of reactive oxygen species (ROS) is associated with leukemic stem cell (LSC) quiescence, whereas a high level promotes blast proliferation. ROS homeostasis relies on a tightly-regulated balance between the antioxidant and oxidant systems. Among the oxidants, NADPH oxidases (NOX) generate ROS as a physiological function. Although it has been reported in AML initiation and development, the contribution of NOX to the ROS production in AML remains to be clarified. The aim of this study was to investigate the NOX expression and function in AML, and to examine the role of NOX in blast proliferation and differentiation. First, we interrogated the NOX expression in primary cells from public datasets, and investigated their association with prognostic markers. Next, we explored the NOX expression and activity in AML cell lines, and studied the impact of NOX knockdown on cell proliferation and differentiation. We found that NOX2 is ubiquitously expressed in AML blasts, and particularly in cells from the myelomonocytic (M4) and monocytic (M5) stages; however, it is less expressed in LSCs and in relapsed AML. This is consistent with an increased expression throughout normal hematopoietic differentiation, and is reflected in AML cell lines. Nevertheless, no endogenous NOX activity could be detected in the absence of PMA stimulation. Furthermore, CYBB knockdown, although hampering induced NOX2 activity, did not affect the proliferation and differentiation of THP-1 and HL-60 cells. In summary, our data suggest that NOX2 is a marker of AML blast differentiation, while AML cell lines lack any NOX2 endogenous activity