Direct confirmation of quiescence of CD34+CD38- leukemia stem cell populations using single cell culture, their molecular signature and clinicopathological implications

A new prognostic risk model for acute myeloid leukemia patients based on telomere-related genes

Telomere maintenance is critical to ensure unlimited cancer cell proliferation, but the role of telomere-related genes in acute myeloid leukemia (AML) has not yet been thoroughly discussed. This study aims to develop a new prognostic risk model based on telomere-related genes and analyze potential mechanisms and targets. Cox regression analyses were used to build the prognostic risk model. Kaplan-Meier (KM) survival analysis and receiver operating characteristic (ROC) curve were used to assess the model performance. At the same time, we analyzed the relationship between the risk score and chemotherapy and immunotherapy and preliminarily explored possible mechanisms of immune resistance. The real-time polymerase chain reaction (PCR) was used to detect the prognosis gene expression levels. Finally, a prognostic signature of six telomere-related genes (TGPS6) including ALDH2, CDK18, DNMT3B, FRAT2, LGALSL, and RBL2 was constructed. The TGPS6 score was confirmed as an independent prognostic factor (HR 2.74, CI [2.13-3.53], p < 0.001) in AML and the five-year area under the ROC curve (AUC) value of the score in the training and validation set reached 0.74, 0.81 respectively. In addition, the TGPS6 perfected the European LeukemiaNet (ELN) 2017 prognosis risk stratification and performed well in both AML and cytogenetically normal AML (CN-AML) cohorts. The TGPS6 score also provided a reference for chemotherapy and immunotherapy in patients with AML.

PTEN regulates hematopoietic lineage plasticity via PU.1-dependent chromatin accessibility

PTEN loss in fetal liver hematopoietic stem cells (HSCs) leads to alterations in myeloid, T-, and B-lineage potentials and T-lineage acute lymphoblastic leukemia (T-ALL) development. To explore the mechanism underlying PTEN-regulated hematopoietic lineage choices, we carry out integrated assay for transposase-accessible chromatin using sequencing (ATAC-seq), single-cell RNA-seq, and in vitro culture analyses using in vivo-isolated mouse pre-leukemic HSCs and progenitors. We find that PTEN loss alters chromatin accessibility of key lineage transcription factor (TF) binding sites at the prepro-B stage, corresponding to increased myeloid and T-lineage potentials and reduced B-lineage potential. Importantly, we find that PU.1 is an essential TF downstream of PTEN and that altering PU.1 levels can reprogram the chromatin accessibility landscape and myeloid, T-, and B-lineage potentials in Ptennull prepro-B cells. Our study discovers prepro-B as the key developmental stage underlying PTEN-regulated hematopoietic lineage choices and suggests a critical role of PU.1 in modulating the epigenetic state and lineage plasticity of prepro-B progenitors.

The contribution of single-cell analysis of acute leukemia in the therapeutic strategy

After decades during which the treatment of acute myeloblastic leukemia was limited to variations around a skeleton of cytarabine/anthracycline, targeted therapies appeared. These therapies, first based on monoclonal antibodies, also rely on specific inhibitors of various molecular abnormalities. A significant but modest prognosis improvement has been observed thanks to these new treatments that are limited by a high rate of relapse, due to the intrinsic chemo and immune-resistance of leukemia stem cell, together with the acquisition of these resistances by clonal evolution. Relapses are also influenced by the equilibrium between the pro or anti-tumor signals from the bone marrow stromal microenvironment and immune effectors. What should be the place of the targeted therapeutic options in light of the tumor heterogeneity inherent to leukemia and the clonal drift of which this type of tumor is capable? Novel approaches by single cell analysis and next generation sequencing precisely define clonal heterogeneity and evolution, leading to a personalized and time variable adapted treatment. Indeed, the evolution of leukemia, either spontaneous or under therapy selection pressure, is a very complex phenomenon. The model of linear evolution is to be forgotten because single cell analysis of samples at diagnosis and at relapse show that tumor escape to therapy occurs from ancestral as well as terminal clones. The determination by the single cell technique of the trajectories of the different tumor sub-populations allows the identification of clones that accumulate factors of resistance to chemo/immunotherapy ("pan-resistant clones"), making possible to choose the combinatorial agents most likely to eradicate these cells. In addition, the single cell technique identifies the nature of each cell and can analyze, on the same sample, both the tumor cells and their environment. It is thus possible to evaluate the populations of immune effectors (T-lymphocytes, natural killer cells) for the leukemia stress-induced alteration of their functions. Finally, the single cells techniques are an invaluable tool for evaluation of the measurable residual disease since not only able to quantify but also to determine the most appropriate treatment according to the sensitivity profile to immuno-chemotherapy of remaining leukemic cells.

Inactivation of APC Induces CD34 Upregulation to Promote Epithelial-Mesenchymal Transition and Cancer Stem Cell Traits in Pancreatic Cancer

Pancreatic cancer (PC) is a highly lethal malignancy due to the cancer routinely being diagnosed late and having a limited response to chemotherapy. Pancreatic ductal adenocarcinoma (PDAC) is the most common form of pancreatic malignant tumor, representing more than 85% of all pancreatic cancers. In the present study, we characterized the phenotypes of concomitant P53 and APC mutations in pancreatic neoplasms driven by the oncogene KRAS in genetically modified mice (GEMM). In this GEMM setting, APC haploinsufficiency coupled with P53 deletion and KRAS^G12D activation resulted in an earlier appearance of pancreatic intraepithelial neoplasia (PanIN) lesions and progressed rapidly to highly invasive and metastatic PDAC. Through a microarray analysis of murine PDAC cells derived from our APC-deficient PDAC model, we observed that APC loss leads to upregulated CD34 expression in PDAC. CD34 is a member of a family of single-pass transmembrane proteins and is selectively expressed in hematopoietic progenitor cells, vascular endothelial cells, interstitial precursor cells, and various interstitial tumor cells. However, the functional roles of CD34 in pancreatic cancer remain unclear. Thus, in this study, we explored the mechanisms regarding how CD34 promotes the deterioration of pancreatic malignancy. Our results demonstrated that the increased expression of CD34 induced by APC inactivation promotes the invasion and migration of PDAC cells, which may relate to PDAC metastasis in vivo. Collectively, our study provides first-line evidence to delineate the association between CD34 and the APC/Wnt pathway in PDAC, and reveals the potential roles of CD34 in PDAC progression.

Applicability and reproducibility of acute myeloid leukaemia stem cell assessment in a multi-centre setting

Leukaemic stem cells (LSC) have been experimentally defined as the leukaemia‐propagating population and are thought to be the cellular reservoir of relapse in acute myeloid leukaemia (AML). Therefore, LSC measurements are warranted to facilitate accurate risk stratification. Previously, we published the composition of a one‐tube flow cytometric assay, characterised by the presence of 13 important membrane markers for LSC detection. Here we present the validation experiments of the assay in several large AML research centres, both in Europe and the United States. Variability within instruments and sample processing showed high correlations between different instruments (R_pearson > 0·91, P < 0·001). Multi‐centre testing introduced variation in reported LSC percentages but was found to be below the clinical relevant threshold. Clear gating protocols resulted in all laboratories being able to perform LSC assessment of the validation set. Participating centres were nearly unanimously able to distinguish LSC^high (>0·03% LSC) from LSC^low (<0·03% LSC) despite inter‐laboratory variation in reported LSC percentages. This study proves that the LSC assay is highly reproducible. These results together with the high prognostic impact of LSC load at diagnosis in AML patients render the one‐tube LSC assessment a good marker for future risk classification.

Cell Density-Dependent Cytological Stage Profile and Its Application for a Screen of Cytostatic Agents Active Toward Leukemic Stem Cells

Proliferation and expansion of leukemia is driven by leukemic stem cells (LSCs). Multidrug resistance (MDR) of LSCs is one of the main reasons of failure and relapses in acute myeloid leukemia (AML) treatment. In this study, we show that maintaining HL-60 at low cell culture density or applying a 240-day treatment with anthrapyridazone (BS-121) increased the percentage of primitive cells, which include LSCs determining the overall stage profile. This change manifested in morphology, expression of both cell surface markers and redox-state proteins, as well as mitochondrial potential. Moreover, four sublines were generated, each with unique and characteristic stage profile and cytostatic sensitivity. Cell density-induced culture alterations (affecting stage profiles) were exploited in a screen of anthrapyridazones. Among the compound tested, C-123 was the most potent against primitive cell stages while generating relatively low amounts of reactive oxygen species (ROS). Furthermore, it had low toxicity in vivo and weakly affected blood morphology of healthy mice. The cell density-dependent stage profiles could be utilized in preliminary drug screens for activity against LSCs or in construction of patient-specific platforms to find drugs effective in case of AML relapse (drug extrapolation). The correlation between ROS generation in differentiated cells and toxic effect observed in HL-60 has a potential application in myelotoxicity predictions. The discovered properties of C-123 indicate its potential application in AML treatment, specifically in conditioned myeloablation preceding allogeneic transplantation and/or ex vivo treatment preceding autologous transplantation.

Reinforcing the utility of chick embryo model to in vivo evaluate engraftment of human leukemic stem cells

BACKGROUND AND OBJECTIVE

Development of appropriate translational in vivo models is a prerequisite for personalized management of leukemic patients. Indeed, several immunodeficient mice models were developed for leukemias with main limitations due to their high cost, demanding management, and elongated assessment intervals. In this report, we aimed at evaluating the engraftment of CD34⁺ cells, isolated from an acute myeloid leukemia (AML) patient, in naturally immunodeficient chick embryo model.

METHODS AND RESULTS

Mononuclear cells or immunomagnetic sorted CD34⁺ cells were injected into chick embryo chorioallantoic membrane (CAM) veins. Seven days post-injection, human CD34 transcript was detected by reverse transcription polymerase chain reaction (RT-PCR) in blood, bone marrow (BM), spleen and liver from embryos injected with human leukemic cells. Interestingly, an amplicon of the same length has been detected in both BM and spleen from PBS injected embryos, although analysis via bioinformatics tools revealed no matches in chicken; neither in transcriptome nor in genome databases. Importantly, splenomegaly and hepatic lesions were observed in some CD34⁺ cells injected embryos.

CONCLUSION

Collectively, our data confirm the engraftment of primary human CD34⁺ leukemic cells in chick embryo liver, but other experiments are required to verify engraftment in BM and spleen, and to confirm the identity of a putative CD34 orthologous transcript in these two organs.

Yi-qi-yang-yin-tang increases the sensitivity of KG1a leukemia stem cells to daunorubicin by promoting cell cycle progression and regulating the expression of PTEN, TOPOII and mTOR

The present study aimed to investigate the effects of serum containing a combination of yi-qi-yang-yin-tang (YQYYT) and daunorubicin (DNR) on multidrug resistance in KG1a leukemia stem cells (LSCs). The effects of YQYYT and DNR on proliferation, cell cycle progression and the expression of phosphatase and tensin homolog (PTEN), topoisomerase II (Topo II) and mechanistic target of rapamycin (mTOR) in KG1a cells were investigated in vitro using cell counting kit-8 assay, flow cytometry, reverse transcription-quantitative polymerase chain reaction and western blotting, respectively. It was revealed that YQYYT-containing serum did not affect proliferation of KG1a cells compared with the blank group. Furthermore, there were no significant differences on the inhibition of proliferation among different groups at various concentrations of YQYYT. Treatment with YQYYT-containing serum (volume, 20 and 40 µl) and DNR was able to significantly inhibit the proliferation of KG1a cells compared with the blank group. The inhibition rate in the treatment group with YQYYT-containing serum (40 µl) and DNR for 48 h (72.5%) was higher compared with treatment for 24 h (60.4%, P<0.01). Treatment with YQYYT-containing serum was able to promote G₀ phase of KG1a cells into cell cycle in a dose- and time-dependent manner, and significantly upregulated the mRNA expression of PTEN and Topo II, but did not affect mTOR expression compared with the blank group. Treatment with serum containing YQYYT alone did not directly affect the proliferation of KG1a cells, but when the cells were treated with a combination of YQYYT-containing serum and DNR, the proliferation of KG1a cells was significantly inhibited in a dose- and time-dependent manner. Furthermore, treatment with YQYYT-containing serum was able to promote cell cycle progression of KG1a cells in the G₀ phase and upregulate the expression of the negative regulatory genes PTEN and Topo II. These results indicated the potential of YQYYT to reverse multidrug resistance in LSCs.

Molecular characterization of breast cancer CTCs associated with brain metastasis

The enumeration of EpCAM-positive circulating tumor cells (CTCs) has allowed estimation of overall metastatic burden in breast cancer patients. However, a thorough understanding of CTCs associated with breast cancer brain metastasis (BCBM) is necessary for early identification and evaluation of treatment response to BCBM. Here we report that BCBM CTCs is enriched in a distinct sub-population of cells identifiable by their biomarker expression and mutational content. Deriving from a comprehensive analysis of CTC transcriptomes, we discovered a unique "circulating tumor cell gene signature" that is distinct from primary breast cancer tissues. Further dissection of the circulating tumor cell gene signature identified signaling pathways associated with BCBM CTCs that may have roles in potentiating BCBM. This study proposes CTC biomarkers and signaling pathways implicated in BCBM that may be used either as a screening tool for brain micro-metastasis detection or for making rational treatment decisions and monitoring therapeutic response in patients with BCBM.Characterization of CTCs derived from breast cancer patients with brain metastasis (BCBM) may allow for early diagnosis of brain metastasis and/or help for treatment choice and its efficacy. In this study, the authors identify a unique signature, based on patient-derived CTCs transcriptomes, for BCBM- CTCs that is different from primary tumors.

Prognostic impact of the CD34+/CD38- cell burden in patients with acute myeloid leukemia receiving allogeneic stem cell transplantation

In acute myeloid leukemia (AML), leukemia-initiating cells exist within the CD34+/CD38- cell compartment. They are assumed to be more resistant to chemotherapy, enriched in minimal residual disease cell populations, and responsible for relapse. Here we evaluated clinical and biological associations and the prognostic impact of a high diagnostic CD34+/CD38- cell burden in 169 AML patients receiving an allogeneic stem cell transplantation in complete remission. Here, the therapeutic approach is mainly based on immunological graft-versus-leukemia effects. Percentage of bone marrow CD34+/CD38- cell burden at diagnosis was measured using flow cytometry and was highly variable (median 0.5%, range 0%-89% of all mononuclear cells). A high CD34+/CD38- cell burden at diagnosis associated with worse genetic risk and secondary AML. Patients with a high CD34+/CD38- cell burden had shorter relapse-free and overall survival which may be mediated by residual leukemia-initiating cells in the CD34+/CD38- cell population, escaping the graft-versus-leukemia effect after allogeneic transplantation. Evaluating the CD34+/CD38- cell burden at diagnosis may help to identify patients at high risk of relapse after allogeneic transplantation. Further studies to understand leukemia-initiating cell biology and develop targeting therapies to improve outcomes of AML patients are needed.

Hyaluronan Upregulates Mitochondrial Biogenesis and Reduces Adenoside Triphosphate Production for Efficient Mitochondrial Function in Slow-Proliferating Human Mesenchymal Stem Cells

Hyaluronan-coated surfaces preserve the proliferation and differentiation potential of mesenchymal stem cells by prolonging their G1-phase transit, which maintains cells in a slow-proliferative mode. Mitochondria are known to play a crucial role in stem cell self-renewal and differentiation. In this study, for the first time, the metabolic mechanism underlying the hyaluronan-regulated slow-proliferative maintenance of stem cells was investigated by evaluating mitochondrial functions. Human placenta-derived mesenchymal stem cells (PDMSCs) cultured on hyaluronan-coated surfaces at 0.5, 3.0, 5.0, and 30 µg/cm² were found to have an average 58% higher mitochondrial mass and an increase in mitochondrial DNA copy number compared to noncoated tissue culture surfaces (control), as well as a threefold increase in the gene expression of the mitochondrial biogenesis-related gene PGC-1α. Increase in mitochondrial biogenesis led to a hyaluronan dose-dependent increase in mitochondrial membrane potential, ATP content, and oxygen consumption rate, with reactive oxygen species levels shown to be at least three times lower compared to the control. Although hyaluronan seemed to favor mitochondrial function, cell entry into a hyaluronan-regulated slow-proliferative mode led to a fivefold reduction in ATP production and coupling efficiency levels. Together, these results suggest that hyaluronan-coated surfaces influence the metabolic proliferative state of stem cells by upregulating mitochondrial biogenesis and function with controlled ATP production. This more efficiently meets the energy requirements of slow-proliferating PDMSCs. A clear understanding of the metabolic mechanism induced by hyaluronan in stem cells will allow future applications that may overcome the current limitations faced in stem cell culture. Stem Cells 2016;34:2512-2524.