Molecular markers in acute myeloid leukaemia

Transglutaminase 2 programs differentiating acute promyelocytic leukemia cells in all-trans retinoic acid treatment to inflammatory stage through NF-κB activation

Differentiation syndrome (DS) is a life-threatening complication arising during retinoid treatment of acute promyelocytic leukemia (APL). Administration of all-trans retinoic acid leads to significant changes in gene expression, among the most induced of which is transglutaminase 2, which is not normally expressed in neutrophil granulocytes. To evaluate the pathophysiological function of transglutaminase 2 in the context of immunological function and disease outcomes, such as excessive superoxide anion, cytokine, and chemokine production in differentiated NB4 cells, we used an NB4 transglutaminase knock-out cell line and a transglutaminase inhibitor, NC9, which inhibits both transamidase- and guanosine triphosphate-binding activities, to clarify the contribution of transglutaminase to the development of potentially lethal DS during all-trans retinoic acid treatment of APL. We found that such treatment not only enhanced cell-surface expression of CD11b and CD11c but also induced high-affinity states; atypical transglutaminase 2 expression in NB4 cells activated the nuclear factor kappa (κ)-light-chain-enhancer of the activated B-cell pathway, driving pathogenic processes with an inflammatory cascade through the expression of numerous cytokines, including tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β), and monocyte chemoattractant protein 1. NC9 decreased the amount of transglutaminase 2, p65/RelA, and p50 in differentiated NB4 cells and their nuclei, leading to attenuated inflammatory cytokine synthesis. NC9 significantly inhibits transglutaminase 2 nuclear translocation but accelerates its proteasomal breakdown. This study demonstrates that transglutaminase 2 expression induced by all-trans retinoic acid treatment reprograms inflammatory signaling networks governed by nuclear factor κ-light-chain-enhancer of activated B-cell activation, resulting in overexpression of TNF-α and IL-1β in differentiating APL cells, suggesting that atypically expressed transglutaminase 2 is a promising target for leukemia treatment.

Circulating tumor DNA dynamically predicts response and/or relapse in patients with hematological malignancies

A growing body of evidence suggests that tumor-derived fragmentary DNA, known as circulating tumor DNA (ctDNA), has the potential to serve as a non-invasive biomarker for disease monitoring. However, in the setting of hematological malignancy, few published studies support the utility of ctDNA. We retrospectively investigated ctDNA levels of 17 patients with various hematological malignancies who had achieved remission after first-line therapy. We identified somatic driver mutations by next-generation sequencing, and designed droplet digital PCR assays for each mutation to measure ctDNA. Variant allele frequencies of ctDNA changed in association with clinical response in all patients. Eight patients clinically relapsed after a median of 297 days post-first-line therapy (termed, "relapsed group"); the remaining nine patients remained disease-free for a median of 332 days (termed, "remission group"). Among patients in the relapsed group, ctDNA levels increased more than twofold at paired serial time points. In marked contrast, ctDNA levels of all patients in the remission group remained undetectable or stable during clinical remission. Notably, ctDNA-based molecular relapse demonstrated a median 30-day lead time over clinical relapse. In summary, ctDNA monitoring may help identify hematologic cancer patients at risk for relapse in advance of established clinical parameters.

Molecular landscape of acute myeloid leukemia in younger adults and its clinical relevance

Recent major advances in understanding the molecular basis of acute myeloid leukemia (AML) provide a double-edged sword. Although defining the topology and key features of the molecular landscape are fundamental to development of novel treatment approaches and provide opportunities for greater individualization of therapy, confirmation of the genetic complexity presents a huge challenge to successful translation into routine clinical practice. It is now clear that many genes are recurrently mutated in AML; moreover, individual leukemias harbor multiple mutations and are potentially composed of subclones with differing mutational composition, rendering each patient's AML genetically unique. In order to make sense of the overwhelming mutational data and capitalize on this clinically, it is important to identify (1) critical AML-defining molecular abnormalities that distinguish biological disease entities; (2) mutations, typically arising in subclones, that may influence prognosis but are unlikely to be ideal therapeutic targets; (3) mutations associated with preleukemic clones; and (4) mutations that have been robustly shown to confer independent prognostic information or are therapeutically relevant. The reward of identifying AML-defining molecular lesions present in all leukemic populations (including subclones) has been exemplified by acute promyelocytic leukemia, where successful targeting of the underlying PML-RARα oncoprotein has eliminated the need for chemotherapy for disease cure. Despite the molecular heterogeneity and recognizing that treatment options for other forms of AML are limited, this review will consider the scope for using novel molecular information to improve diagnosis, identify subsets of patients eligible for targeted therapies, refine outcome prediction, and track treatment response.

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.

Minimal residual disease testing in hematologic malignancies and solid cancer

Minimal residual disease (MRD) assays are of a great value to assess treatment efficacy and may provide prognostic information. This is particularly relevant in the era of targeted therapy where the introduction of MRD monitoring has fundamentally transformed the way in which cancer patients are managed. While MRD guidelines are well-established for chronic myeloid leukemia, acute promyelocytic leukemia and acute lymphoblastic leukemia, areas for continuing development are available. High level of standardization and regular external quality control rounds and recommendations for data interpretation remain essential to improve MRD monitoring. In this review, we describe the different applications of MRD assays in most frequent hematologic malignancies and solid cancer and provide an overview of the strengths and potential weaknesses of each method.

Acute myelogenous leukemia at Baylor Charles A. Sammons Cancer Center, 2010 to 2012: retrospective analysis of molecular genetic evaluation

Over the last several decades, advancements in the understanding of genetic and molecular origins of acute myeloid leukemia (AML) have brought about significant changes in how the disease is classified, diagnosed, and treated. The change from the traditional French-American-British classification system to that of the World Health Organization redefined how the disease is diagnosed not only morphologically but genetically. With genetic information proving to have prognostic value, the newer classification system, which incorporates results of cytogenetic and molecular analyses, allows better definition of disease and risk stratification, ultimately guiding treatment choices. As understanding and advancements in the molecular basis of AML continue to grow and influence patient management, the importance of an accurate and thorough initial patient evaluation is paramount. We performed a review of AML cases diagnosed at Baylor Charles A. Sammons Cancer Center from February 2010 to December 2012 to assess the thoroughness of initial diagnostic evaluations based on current guidelines, including up-to-date molecular analyses for mutations in NPM1, CEBPA, FLT3, and C-KIT. Results showed that patients newly diagnosed with AML undergo thorough diagnostic evaluation in keeping with current recommendations, and many had further genetic and molecular evaluations, which although considered optional or investigational, have prognostic significance. We identified potential areas of improvement for making this diagnostic evaluation more specific to the patient and the patient's disease. Currently, we are investigating having patients undergo reflex genetic testing if they meet certain criteria to better define their specific disease while avoiding unnecessary genetic evaluations that come at increased cost.

Relevance of leukemic stem cells in acute myeloid leukemia: heterogeneity and influence on disease monitoring, prognosis and treatment design

Acute myeloid leukemia is a bone marrow disease characterized by a block in differentiation of the myeloid lineage with a concomitant uncontrolled high proliferation rate. Development of acute myeloid leukemia from stem cells with specific founder mutations, leads to an oligoclonal disease that progresses into a very heterogeneous leukemia at diagnosis. Measurement of leukemic stem cell load and characterization of these cells are essential for prediction of relapse and target identification, respectively. Prediction of relapse by monitoring the disease during minimal residual disease detection is challenged by clonal shifts during therapy. To overcome this, characterization of the potential relapse-initiating cells is required using both flow cytometry and molecular analysis since leukemic stem cells can be targeted both on extracellular features and on stem-cell specific signal transduction pathways.

Perspectives of differentiation therapies of acute myeloid leukemia: the search for the molecular basis of patients' variable responses to 1,25-dihydroxyvitamin d and vitamin d analogs

The concept of differentiation therapy of cancer is ~40 years old. Despite many encouraging results obtained in laboratories, both in vitro and in vivo studies, the only really successful clinical application of differentiation therapy was all-trans-retinoic acid (ATRA)-based therapy of acute promyelocytic leukemia (APL). ATRA, which induces granulocytic differentiation of APL leukemic blasts, has revolutionized the therapy of this disease by converting it from a fatal to a curable one. However, ATRA does not work for other acute myeloid leukemias (AMLs). Since 1,25-dihydroxyvitamin D₃ (1,25D) is capable of inducing monocytic differentiation of leukemic cells, the idea of treating other AMLs with vitamin D analogs (VDAs) was widely accepted. Also, some types of solid cancers responded to in vitro applied VDAs, and hence it was postulated that VDAs can be used in many clinical applications. However, early clinical trials in which cancer patients were treated either with 1,25D or with VDAs, did not lead to conclusive results. In order to search for a molecular basis of such unpredictable responses of AML patients toward VDAs, we performed ex vivo experiments using patient’s blast cells. Experiments were also performed using 1,25D-responsive and 1,25D-non-responsive cell lines, to study their mechanisms of resistance toward 1,25D-induced differentiation. We found that one of the possible reasons might be due to a very low expression level of vitamin D receptor (VDR) mRNA in resistant cells, which can be increased by exposing the cells to ATRA. Our considerations concerning the molecular mechanism behind the low VDR expression and its regulation by ATRA are reported in this paper.

Retinoid receptor signaling and autophagy in acute promyelocytic leukemia

Retinoids are a family of signaling molecules derived from vitamin A with well established roles in cellular differentiation. Physiologically active retinoids mediate transcriptional effects on cells through interactions with retinoic acid (RARs) and retinoid-X (RXR) receptors. Chromosomal translocations involving the RARα gene, which lead to impaired retinoid signaling, are implicated in acute promyelocytic leukemia (APL). All-trans-retinoic acid (ATRA), alone and in combination with arsenic trioxide (ATO), restores differentiation in APL cells and promotes degradation of the abnormal oncogenic fusion protein through several proteolytic mechanisms. RARα fusion-protein elimination is emerging as critical to obtaining sustained remission and long-term cure in APL. Autophagy is a degradative cellular pathway involved in protein turnover. Both ATRA and ATO also induce autophagy in APL cells. Enhancing autophagy may therefore be of therapeutic benefit in resistant APL and could broaden the application of differentiation therapy to other cancers. Here we discuss retinoid signaling in hematopoiesis, leukemogenesis, and APL treatment. We highlight autophagy as a potential important regulator in anti-leukemic strategies.

Modeling normal and malignant human hematopoiesis in vivo through newborn NSG xenotransplantation

Various strains of immune-compromised mice have been developed to investigate human normal and malignant stem cells in vivo. NOD/SCID mice harboring complete null mutation of Il2rg (NSG mice) lack T cells, B cells, and NK cells, and support high levels of engraftment by human cord blood hematopoietic stem cells (CB HSCs) and acute myeloid leukemia stem cells (AML LSCs). In addition to achieving high levels of human hematopoietic cell engraftment, use of newborn NSG mice as recipients has enabled the investigation into how human CB HSCs generate mature immune subsets in vivo. Moreover, through establishing an in vivo model of human primary AML by xenotransplantation of human LSCs into newborn NSG mice, functional properties of human AML such as cell cycle, location, and self-renewal capacity can be examined in vivo. Newborn NSG xenogeneic transplantation model may facilitate the understanding of human normal and malignant hematopoiesis and contribute to the development of novel therapies against hematologic diseases.

Evaluation of prognostic factors in patients with therapy-related acute myeloid leukemia

Background

Therapy-related AML (t-AML) occurs as a late complication of chemotherapy administered to treat a prior disorder. Prognostic factors affecting the clinical outcome in t-AML have not yet been clearly defined; therefore, we evaluated these factors in this study.

Methods

Forty-eight patients diagnosed with t-AML within the past 10 years were enrolled, and their chemotherapy regimens categorized into 4 groups: alkylating agents (AK) only, topoisomerase II inhibitors (TI) and AK, TI only, and others. The prognostic factors affecting clinical outcome were evaluated.

Results

Five (10.4%), 21 (43.8%), 9 (18.8%), and 13 (27.0%) patients were treated with AK only, AK and TI, TI only, and others, respectively. Patients with an AML M3 phenotype showed significantly longer overall survival (OS; 55.1 vs. 14.3 months, P=0.040) and disease-free survival (DFS; 61.2 vs. 17.5 months, P=0.049) than other phenotypes. In contrast, patients with a complex karyotype showed significantly shorter OS (7.9 vs. 31.3 months, P=0.008) and DFS (9.5 vs. 38.6 months, P=0.046); additionally, patients with chromosome 5 or 7 abnormalities showed significantly shorter OS (9.1 vs. 30.7 months, P=0.011) than other phenotypes. Only the presence of a complex karyotype or AML M3 phenotype retained prognostic impact in a multivariate analysis.

Conclusion

Only the AML M3 phenotype was identified as having a good prognosis, and this might suggest that it exhibits unique clinical features in t-AML patients. Moreover, our findings indicated that karyotype was the strongest prognostic indicator and predicted a poor prognosis for t-AML patients with a complex karyotype.

Mitochondrial cytochrome c oxidase subunit II variations predict adverse prognosis in cytogenetically normal acute myeloid leukaemia

Alterations in the two catalytic genes cytochrome c oxidase subunits I and II (COI and COII) have recently been suggested to have an adverse impact on prognosis in patients with acute myeloid leukaemia (AML). In order to explore this in further detail, we sequenced these two mitochondrial genes in diagnostic bone marrow or blood samples in 235 patients with AML. In 37 (16%) patients, a non-synonymous variation in either COI or COII could be demonstrated. No patients harboured both COI and COII non-synonymous variations. Twenty-four (10%) patients had non-synonymous variations in COI, whereas 13 (6%) patients had non-synonymous variations in COII. The COI and COII are essential subunits of cytochrome c oxidase that is the terminal enzyme in the oxidative phosphorylation complexes. In terms of disease course, we observed that in patients with a normal cytogenetic analysis at disease presentation (CN-AML) treated with curative intent, the presence of a non-synonymous variation in the COII was an adverse prognostic marker for both overall survival and disease-free survival (DFS) in both univariate (DFS; hazard ratio (HR) 4.4, P = 0.006) and multivariate analyses (DFS; HR 7.2, P = 0.001). This is the first demonstration of a mitochondrial aberration playing an adverse prognostic role in adult AML, and we argue that its role as a potentially novel adverse prognostic marker in the subset of CN-AML should be explored further.

The evolving molecular genetic landscape in acute myeloid leukaemia

PURPOSE OF REVIEW

Acute myeloid leukaemia (AML) is a heterogeneous disease with a variable response to therapy. The heterogeneity of AML is evident from variations in morphology, immunophenotype, cytogenetics and molecular abnormalities. The introduction of genome-wide technologies has enabled an even more detailed molecular analysis of AML. As a result, the molecular landscape of AML is rapidly evolving. The purpose of this review is to discuss the recent advances made in this field, with a special focus on risk stratification of AML.

RECENT FINDINGS

Clinical AML has been analysed in great molecular detail by gene expression profiling and more recently through epigenetic profiling and next generation sequencing. This has resulted in the identification of novel biomarkers, some of which appear to have a consistent clinical impact in AML, that is mutations in the genes encoding DNA (cytosine-5)-methyltransferase 3 alpha (DNMT3A), additional sex combs-like 1 (ASXL1), tet methylcytosine dioxygenase 2 (TET2) and Runt-related transcription factor 1 (RUNX1). In addition, massively parallel sequencing has revealed a great mutational heterogeneity as well as temporal clonal evolution in AML.

SUMMARY

The list of acquired mutations with clinical value in AML is growing. Clinical implementation of this multitude of markers will require integrated approaches and selection of markers to facilitate AML risk stratification in the future. The revealed molecular heterogeneity and evolution in AML will have implications for developing targeted therapies.

Efficacy and resistance of gemtuzumab ozogamicin for acute myeloid leukemia

Seventy to 80 % of patients with acute myeloid leukemia (AML) achieve complete remission following intensive chemotherapy, but more than 50 % of patients in remission subsequently relapse, which is often associated with clinical drug resistance. Therapy based on monoclonal antibodies (mAbs) has been developed to increase the selectivity of cytotoxic agents by conjugating them with a mAb. Gemtuzumab ozogamicin (GO) is a conjugate of a cytotoxic agent, a calicheamicin derivative, linked to a recombinant humanized mAb directed against the CD33 antigen, which is expressed on leukemia cells from more than 90 % of patients with AML. This conjugated mAb was introduced following promising results from phase I and II studies. However, the initial phase III study did not confirm the efficacy of GO in combination with conventional chemotherapies. Several subsequent phase III studies have shown the efficacy of GO in favorable and intermediate risk AML. Several resistance mechanisms against GO have been reported. Multidrug resistant (MDR) P-glycoprotein (P-gp), a trans-membrane glycoprotein that pumps out many anti-leukemic agents from cells, also affects GO. For this reasons, GO has been used in combination with MDR modifiers, such as cyclosporine, and in cases without P-gp. Several investigators have reported successful results of the use of GO in acute promyelocytic leukemia (APL). GO has also been described as effective in cases relapsed after treatment with all-trans retinoic acid (ATRA), arsenic acid and conventional chemotherapeutic agents. The efficacy of GO will be studied mainly in a favorable risk of AML, such as core binding factor leukemia and APL. In addition, suitable combinations with other chemotherapies and administration schedules should be discussed.

Rapid detection of PML-RARA fusion gene by novel high-speed droplet-reverse transcriptase-polymerase chain reaction: possibility for molecular diagnosis without lagging behind the morphological analyses

BACKGROUND

Acute promyelocytic leukemia (APL) is an aggressive disease requiring prompt diagnosis and treatment. Rapid detection of the PML-RARA fusion gene provides the molecular basis for a highly effective therapy with all-trans retinoic acid. We developed a rapid assay by novel droplet-reverse transcriptase-polymerase chain reaction (droplet-RT-PCR) for the detection of the PML-RARA fusion gene in APL patients.

METHODS

RNA was extracted from 7 samples obtained from 5 APL patients with the PML-RARA fusion gene confirmed by nested RT-PCR and fluorescence in situ hybridization. Using these 7 samples, we evaluated the reaction time and amplification efficiency of the droplet-RT-PCR.

RESULTS

Using the droplet-RT-PCR, we could detect the PML-RARA fusion gene in all 7 samples. The reaction time for 50 cycles of droplet-RT-PCR was 27 min. The amplification by the droplet-RT-PCR assay was considered positive for the PML-RARA fusion gene in less than 22 min, at the point when the fluorescence exceeded the threshold level.

CONCLUSIONS

Our novel droplet-RT-PCR assay is specific for the detection of the PML-RARA fusion gene and has a markedly reduced reaction time. Thus, the novel droplet-RT-PCR assay contributes to the rapid diagnosis of APL without lagging behind the morphological assessment.