Blastic leukaemias (AML): a biologist's view

Current and Emerging Techniques for Diagnosis and MRD Detection in AML: A Comprehensive Narrative Review

Acute myeloid leukemia (AML) comprises a group of hematologic neoplasms characterized by abnormal differentiation and proliferation of myeloid progenitor cells. AML is associated with poor outcome due to the lack of efficient therapies and early diagnostic tools. The current gold standard diagnostic tools are based on bone marrow biopsy. These biopsies, apart from being very invasive, painful, and costly, have low sensitivity. Despite the progress uncovering the molecular pathogenesis of AML, the development of novel detection strategies is still poorly explored. This is particularly important for patients that check the criteria for complete remission after treatment, since they can relapse through the persistence of some leukemic stem cells. This condition, recently named as measurable residual disease (MRD), has severe consequences for disease progression. Hence, an early and accurate diagnosis of MRD would allow an appropriate therapy to be tailored, improving a patient's prognosis. Many novel techniques with high potential in disease prevention and early detection are being explored. Among them, microfluidics has flourished in recent years due to its ability at processing complex samples as well as its demonstrated capacity to isolate rare cells from biological fluids. In parallel, surface-enhanced Raman scattering (SERS) spectroscopy has shown outstanding sensitivity and capability for multiplex quantitative detection of disease biomarkers. Together, these technologies can allow early and cost-effective disease detection as well as contribute to monitoring the efficiency of treatments. In this review, we aim to provide a comprehensive overview of AML disease, the conventional techniques currently used for its diagnosis, classification (recently updated in September 2022), and treatment selection, and we also aim to present how novel technologies can be applied to improve the detection and monitoring of MRD.

Inhibition of UBE2L6 attenuates ISGylation and impedes ATRA-induced differentiation of leukemic cells

Ubiquitin/ISG15‐conjugating enzyme E2L6 (UBE2L6) is a critical enzyme in ISGylation, a post‐translational protein modification that conjugates the ubiquitin‐like modifier, interferon‐stimulated gene 15 (ISG15), to target substrates. Previous gene expression studies in acute promyelocytic leukemia (APL) cells showed that all‐trans‐retinoic acid (ATRA) altered the expression of many genes, including UBE2L6 (200‐fold) and other members of the ISGylation pathway. Through gene expression analyses in a cohort of 98 acute myeloid leukemia (AML) patient samples and in primary neutrophils from healthy donors, we found that UBE2L6 gene expression is reduced in primary AML cells compared with normal mature granulocytes. To assess whether UBE2L6 expression is important for leukemic cell differentiation—two cell line models were employed: the human APL cell line NB4 and its ATRA‐resistant NB4R counterpart, as well as the ATRA‐sensitive human AML HL60 cells along with their ATRA‐resistant subclone—HL60R. ATRA strongly induced UBE2L6 in NB4 APL cells and in ATRA‐sensitive HL60 AML cells, but not in the ATRA‐resistant NB4R and HL60R cells. Furthermore, short hairpin (sh)RNA‐mediated UBE2L6 depletion in NB4 cells impeded ATRA‐mediated differentiation, suggesting a functional role for UBE2L6 in leukemic cell differentiation. In addition, ATRA induced ISG15 gene expression in NB4 APL cells, leading to increased levels of both free ISG15 protein and ISG15 conjugates. UBE2L6 depletion attenuated ATRA‐induced ISG15 conjugation. Knockdown of ISG15 in NB4 APL cells inhibited ISGylation and also attenuated ATRA‐induced differentiation. In summary, we demonstrate the functional importance of UBE2L6 in ATRA‐induced neutrophil differentiation of APL cells and propose that this may be mediated by its catalytic role in ISGylation.

Toll-like receptor 9 negatively related to clinical outcome of AML patients

BACKGROUND

Acute myeloid leukemia (AML) can modulate toll-like receptor-9 (TLR9) expression and activation. This study was conducted to elucidate the expression of TLR9 in AML patients and its relation to the prognosis of the disease.

RESULTS

The study included 40 newly diagnosed AML patients managed in the hospital in addition to 20 sex and age matched normal volunteers as control. TLR9 expression assay was conducted on peripheral blood samples of AML cases before the start of treatment as well as the controls by immunophenotyping. TLR9 expression was ranging from 0.10 to 2.40% in AML patients with higher expression among the control, ranging from 0.94 to 8.25%. The median TLR9 expression in AML patients was significantly lower with advanced cytogenetic risk score. It is not significantly differing in relation to patients' sex, age group, and FAB type of AML. However, significant lower median expression was found in relation to clinical outcome. TLR9 expression ≤ 1% showed lower median overall survival time when compared to those with > 1% expression.

CONCLUSION

This study concluded that AML patients express TLR9 in leukemic cells with very low percentage. This expression was negatively related to the clinical outcome.

Functional Toll-Like Receptors (TLRs) Are Expressed by a Majority of Primary Human Acute Myeloid Leukemia Cells and Inducibility of the TLR Signaling Pathway Is Associated with a More Favorable Phenotype

Acute myeloid leukemia (AML) is a highly heterogeneous disease with regard to biological characteristics and receptor expression. Toll-like receptors (TLRs) are upstream to the transcription factor NFκB and part of the innate immune system. They are differentially expressed on AML blasts, and during normal hematopoiesis they initiate myeloid differentiation. In this study, we investigated the response upon TLR stimulation in an AML cohort (n = 83) by measuring the increase of NFκB-mediated cytokine secretion. We observed that TLR4 is readily induced in most patients, while TLR1/2 response was more restricted. General response to TLR stimulation correlated with presence of nucleophosmin gene mutations, increased mRNA expression of proteins, which are part of the TLR signaling pathway and reduced expression of transcription-related proteins. Furthermore, signaling via TLR1/2 appeared to be linked with prolonged patient survival. In conclusion, response upon TLR stimulation, and especially TLR1/2 induction, seems to be part of a more favorable phenotype, which also is characterized by higher basal cytokine secretion and a more mature blast population.

The Capacity of Long-Term in Vitro Proliferation of Acute Myeloid Leukemia Cells Supported Only by Exogenous Cytokines Is Associated with a Patient Subset with Adverse Outcome

Acute myeloid leukemia (AML) is an aggressive malignancy, which is highly heterogeneous with regard to chemosensitivity and biological features. The AML cell population is organized in a hierarchy that is reflected in the in vitro growth characteristics, with only a minority of cells being able to proliferate for more than two weeks. In this study, we investigated the ability of AML stem cells to survive and proliferate in suspension cultures in the presence of exogenous mediators but without supporting non-leukemic cells. We saw that a high number of maintained stem cells (i.e., a large number of clonogenic cells after five weeks of culture) was associated with decreased overall survival for patients receiving intensive chemotherapy; this prognostic impact was also detected in the multivariate/adjusted analysis. Furthermore, the patients with many clonogenic cells presented more frequently with mutations in transcription-related genes, and also showed a higher abundance of proteins involved in transcription at the time of diagnosis. In conclusion, the growth characteristics of the long-term proliferating leukemic stem cells seem to have an independent prognostic impact in human AML, and these characteristics appear to be reflected by the mutational landscape and the proteome of the patients at the time of diagnosis.

Lentiviral-Mediated shRNA Approaches: Applications in Cellular Differentiation and Autophagy

Acute myeloid leukemia (AML) is characterized by the accumulation of immature white blood cell precursors in the bone marrow and peripheral circulation. In essence, leukemic cells fail to differentiate and are stalled at a particular step of hematopoietic maturation and are unable to complete their development into functional blood cells with a finite life cycle. They are thus said to possess a "differentiation block." Pharmacological override of this block is one attractive avenue of therapy, termed "differentiation therapy." The most successful example of this therapeutic strategy is the use of the physiologic retinoid all-trans-retinoic acid (ATRA) in the treatment of acute promyelocytic leukemia (APL). In this chapter, we will outline the methods used to characterize the mechanisms mobilized by retinoid signaling and will use the activation of a key regulator of autophagy, ATG7, as an example of the functional characterization of a retinoid regulated gene during differentiation. We will discuss how lentiviral delivery of shRNA constructs into cultured APL cells, such as NB4, can be used to functionally deplete key proteins. We will also describe how the effect of protein knockdown on ATRA-induced differentiation and autophagy can be assessed using quantitative PCR, Western blotting, and flow cytometry.

Patients with acute myeloid leukemia can be subclassified based on the constitutive cytokine release of the leukemic cells; the possible clinical relevance and the importance of cellular iron metabolism

OBJECTIVE

Acute myeloid leukaemia (AML) is a heterogeneous malignancy; we studied how the constitutive cytokine release by the AML cells varies among patients.

METHODS

We investigated the constitutive release of 28 mediators during in vitro culture for 79 consecutive patients.

RESULTS

Constitutive cytokine release profiles differed among patients, and hierarchical clustering identified three subsets with high, intermediate and low release, respectively. The high-release subset showed high levels of most mediators, usually monocytic differentiation as well as altered mRNA expression of proteins involved in intracellular iron homeostasis and molecular trafficking; this subset also included 4 out of 6 patients with inv(16). Spontaneous in vitro apoptosis did not differ among the subsets. For the high-release patients, cytokines were released both by CD34⁺ and CD34^- cells. The mRNA and released protein levels showed statistically significant correlations only for eleven of the cytokines. The overall survival after intensive anti-leukemic therapy was significantly higher for high-release compared with low-release patients. Pharmacological targeting of iron metabolism (iron chelation, transferrin receptor blocking) altered the cytokine release profile.

CONCLUSIONS

Subclassification of AML patients based on the constitutive cytokine release may be clinically relevant and a part of a low-risk (i.e. chemosensitive) AML cell phenotype.

Leukemia Blast Crisis: A Simulation Case for Residents

INTRODUCTION

Oncologic emergencies are life-threatening and often require advanced team-management skills as well as a mastery of disease processes and therapeutic interventions. Simulation of an oncologic emergency case is a useful way to experience, reflect on, and practice these skills. This case involving a simulated patient in blast crisis was created as part of our Emergency Medicine (EM) Resident Simulation Curriculum at the Perelman School of Medicine at the University of Pennsylvania.

METHODS

This case is based on an actual patient seen in our emergency department and highlights specific teaching points and potential pitfalls in treatment algorithms. It details a 40-year-old female with history of acute myeloid leukemia presenting with fatigue for 2 days, tachycardia, and labored breathing. The patient develops worsening respiratory distress if not intervened upon and progresses to pulseless electrical activity arrest. Lab work is notable for markedly elevated white blood cell count and acidosis. A SimMan or SimMan3G is required for the simulation. The associated debriefing materials are Included in this educational resource. Evaluation of learner performance is mapped to the EM Milestones.

RESULTS

Eighteen of the 20 (90%) EM residents that participated in this simulation, responded to the Likert-scale postsession survey. Of those who responded, 83% agreed or strongly agreed that the case was realistic and 89% agreed or strongly agreed that the case was useful.

DISCUSSION

The simulation venue offers a unique opportunity to address team dynamics as well as provide a forum for didactic learning as it is often difficult to debrief a critical case while working in real-time patient care settings.

Class III Receptor Tyrosine Kinases in Acute Leukemia - Biological Functions and Modern Laboratory Analysis

Acute myeloid leukemia (AML) is a complex disease caused by deregulation of multiple signaling pathways. Mutations in class III receptor tyrosine kinases (RTKs) have been implicated in alteration of cell signals concerning the growth and differentiation of leukemic cells. Point mutations, insertions, or deletions of RTKs as well as chromosomal translocations induce constitutive activation of the receptor, leading to uncontrolled proliferation of undifferentiated myeloid blasts. Aberrations can occur in all domains of RTKs causing either the ligand-independent activation or mimicking the activated conformation. The World Health Organization recommended including RTK mutations in the AML classification since their detection in routine laboratory diagnostics is a major factor for prognostic stratification of patients. Polymerase chain reaction (PCR)-based methods are well-validated for the detection of fms-related tyrosine kinase 3 (FLT3) mutations and can easily be applied for other RTKs. However, when methodological limitations are reached, accessory techniques can be applied. For a higher resolution and more quantitative approach compared to agarose gel electrophoresis, PCR fragments can be separated by capillary electrophoresis. Furthermore, high-resolution melting and denaturing high-pressure liquid chromatography are reliable presequencing screening methods that reduce the sample amount for Sanger sequencing. Because traditional DNA sequencing is time-consuming, next-generation sequencing (NGS) is an innovative modern possibility to analyze a high amount of samples simultaneously in a short period of time. At present, standardized procedures for NGS are not established, but when this barrier is resolved, it will provide a new platform for rapid and reliable laboratory diagnostic of RTK mutations in patients with AML. In this article, the biological and physiological role of RTK mutations in AML as well as possible laboratory methods for their detection will be reviewed.

Long noncoding RNA, CCDC26, controls myeloid leukemia cell growth through regulation of KIT expression

Background

Accumulating evidence suggests that some long noncoding RNAs (lncRNAs) are involved in certain diseases, such as cancer. The lncRNA, CCDC26, is related to childhood acute myeloid leukemia (AML) because its copy number is altered in AML patients.

Results

We found that CCDC26 transcripts were abundant in the nuclear fraction of K562 human myeloid leukemia cells. To examine the function of CCDC26, gene knockdown (KD) was performed using short hairpin RNAs (shRNAs), and four KD clones, in which CCDC26 expression was suppressed to 1% of its normal level, were isolated. This down-regulation included suppression of CCDC26 intron-containing transcripts (the CCDC26 precursor mRNA), indicating that transcriptional gene suppression (TGS), not post-transcriptional suppression, was occurring. The shRNA targeting one of the two CCDC26 splice variants also suppressed the other splice variant, which is further evidence for TGS. Growth rates of KD clones were reduced compared with non-KD control cells in media containing normal or high serum concentrations. In contrast, enhanced growth rates in media containing much lower serum concentrations and increased survival periods after serum withdrawal were observed for KD clones. DNA microarray and quantitative polymerase chain reaction screening for differentially expressed genes between KD clones and non-KD control cells revealed significant up-regulation of the tyrosine kinase receptor, KIT, hyperactive mutations of which are often found in AML. Treatment of KD clones with ISCK03, a KIT-specific inhibitor, eliminated the increased survival of KD clones in the absence of serum.

Conclusions

We suggest that CCDC26 controls growth of myeloid leukemia cells through regulation of KIT expression. A KIT inhibitor might be an effective treatment against the forms of AML in which CCDC26 is altered.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0364-7) contains supplementary material, which is available to authorized users.

Autophagy in acute leukemias: a double-edged sword with important therapeutic implications

Macroautophagy, usually referred to as autophagy, is a degradative pathway wherein cytoplasmatic components such as aggregated/misfolded proteins and organelles are engulfed within double-membrane vesicles (autophagosomes) and then delivered to lysosomes for degradation. Autophagy plays an important role in the regulation of numerous physiological functions, including hematopoiesis, through elimination of aggregated/misfolded proteins, and damaged/superfluous organelles. The catabolic products of autophagy (amino acids, fatty acids, nucleotides) are released into the cytosol from autophagolysosomes and recycled into bio-energetic pathways. Therefore, autophagy allows cells to survive starvation and other unfavorable conditions, including hypoxia, heat shock, and microbial pathogens. Nevertheless, depending upon the cell context and functional status, autophagy can also serve as a death mechanism. The cohort of proteins that constitute the autophagy machinery function in a complex, multistep biochemical pathway which has been partially identified over the past decade. Dysregulation of autophagy may contribute to the development of several disorders, including acute leukemias. In this kind of hematologic malignancies, autophagy can either act as a chemo-resistance mechanism or have tumor suppressive functions, depending on the context. Therefore, strategies exploiting autophagy, either for activating or inhibiting it, could find a broad application for innovative treatment of acute leukemias and could significantly contribute to improved clinical outcomes. These aspects are discussed here after a brief introduction to the autophagic molecular machinery and its roles in hematopoiesis.

The pterocarpanquinone LQB-118 induces apoptosis in acute myeloid leukemia cells of distinct molecular subtypes and targets FoxO3a and FoxM1 transcription factors

Acute myeloid leukemia (AML) patients' outcome is usually poor, mainly because of drug resistance phenotype. The identification of new drugs able to overcome mechanisms of chemoresistance is essential. The pterocarpanquinone LQB-118 compound has been shown to have a potent cytotoxic activity in myeloid leukemia cell lines and patient cells. Our aim was to investigate if LQB-118 is able to target FoxO3a and FoxM1 signaling pathways while sensitizing AML cell lines. LQB-118 induced apoptosis in both AML cell lines HL60 (M3 FAB subtype) and U937 (M4/M5 FAB subtype). Cell death occurred independently of alterations in cell cycle distribution. In vivo administration revealed that LQB-118 was not cytotoxic to normal bone marrow-derived cells isolated from mice. LQB-118 induced FoxO3a nuclear translocation and upregulation of its direct transcriptional target Bim, in HL60 cells. However, LQB-118 induced FoxO3a nuclear exclusion, followed by Bim downregulation, in U937 cells. Concomitantly, LQB-118 exposure reduced FoxM1 and Survivin expression in U937 cells, but this effect was more subtle in HL60 cells. Taken together, our data suggest that LQB-118 has a selective and potent antitumor activity against AML cells with distinct molecular subtypes, and it involves differential modulation of the signaling pathways associated with FoxO3a and FoxM1 transcription factors.

WIPI-dependent autophagy during neutrophil differentiation of NB4 acute promyelocytic leukemia cells

Members of the WD-repeat protein interacting with phosphoinositides (WIPI) family are phosphatidylinositol 3-phosphate (PI3P) effectors that are essential for the formation of autophagosomes. Autophagosomes, unique double-membraned organelles, are characteristic for autophagy, a bulk degradation mechanism with cytoprotective and homeostatic function. Both, WIPI-1 and WIPI-2 are aberrantly expressed in several solid tumors, linking these genes to carcinogenesis. We now found that the expression of WIPI-1 was significantly reduced in a large cohort of 98 primary acute myeloid leukemia (AML) patient samples (complex karyotypes; t(8;21); t(15,17); inv(16)). In contrast, the expression of WIPI-2 was only reduced in acute promyelocytic leukemia (APL), a distinct subtype of AML (t(15,17)). As AML cells are blocked in their differentiation, we tested if the expression levels of WIPI-1 and WIPI-2 increase during all-trans retinoic acid (ATRA)-induced neutrophil differentiation of APL. According to the higher WIPI-1 expression in granulocytes compared with immature blast cells, WIPI-1 but not WIPI-2 expression was significantly induced during neutrophil differentiation of NB4 APL cells. Interestingly, the induction of WIPI-1 expression was dependent on the transcription factor PU.1, a master regulator of myelopoiesis, supporting our notion that WIPI-1 expression is reduced in AML patients lacking proper PU-1 activity. Further, knocking down WIPI-1 in NB4 cells markedly attenuated the autophagic flux and significantly reduced neutrophil differentiation. This result was also achieved by knocking down WIPI-2, suggesting that both WIPI-1 and WIPI-2 are functionally required and not redundant in mediating the PI3P signal at the onset of autophagy in NB4 cells. In line with these data, downregulation of PI3KC3 (hVPS34), which generates PI3P upstream of WIPIs, also inhibited neutrophil differentiation. In conclusion, we demonstrate that both WIPI-1 and WIPI-2 are required for the PI3P-dependent autophagic activity during neutrophil differentiation, and that PU.1-dependent WIPI-1 expression is significantly repressed in primary AML patient samples and that the induction of autophagic flux is associated with neutrophil differentiation of APL cells.

Benznidazole modulates cell proliferation in acute leukemia cells

CONTEXT

We have previously reported that benznidazole (BZL), known for its trypanocidal action, has anti-proliferative activity against different cell lines like HeLa and Raw 264.7 among others. At the moment, it has not been reported if the anti-proliferative effect of BZL is similar for non-adherent hematopoietic cells like was reported for adherent cancer cell lines.

OBJECTIVE

We aimed to investigate the efficacy of BZL on the growth of the leukemic cell lines THP-1 and OCI/AML3.

MATERIALS AND METHODS

We evaluated cell proliferation by [³H]-thymidine incorporation and MTT reduction as well as cell death by lactate dehydrogenase (LDH) activity. We assessed apoptosis by flow cytometry for detection of annexin V-positive and propidium iodide-negative cells, along with nuclear morphology by diamidino-2-phenolindole (DAPI) staining. Western blot studies were performed to evaluate changes in cell cycle proteins in BZL-treated cells.

RESULTS

BZL significantly reduced proliferation of both cell lines without inducing cell death. Likewise it produced no significant differences in apoptosis between treated cells and controls. In addition, flow cytometry analysis indicated that BZL caused a larger number of THP-1 cells in G0/G1 phase and a smaller number of cells in S phase than controls. This was accompanied with an increase in the expression of the CDK inhibitor p27 and of cyclin D1, with no significant differences in the protein levels of CDK1, CDK2, CDK4, cyclins E, A and B as compared to controls.

CONCLUSION

BZL inhibits the proliferation of leukemic non-adherent cells by controlling cell cycle at G0/G1 cell phase through up-regulation of p27.