Variations on a theme: the alternate translocations in APL

Polycomb repressor complex: Its function in human cancer and therapeutic target strategy

The Polycomb Repressor Complex (PRC) plays a pivotal role in gene regulation during development and disease, with dysregulation contributing significantly to various human cancers. The intricate interplay between PRC and cellular signaling pathways sheds light on cancer complexity. PRC presents promising therapeutic opportunities, with inhibitors undergoing rigorous evaluation in preclinical and clinical studies. In this review, we emphasize the critical role of PRC complex in gene regulation, particularly PcG proteins mediated chromatin compaction through phase separation. We also highlight the pathological implications of PRC complex dysregulation in various tumors, elucidating underlying mechanisms driving cancer progression. The burgeoning field of therapeutic strategies targeting PRC complexes, notably EZH2 inhibitors, has advanced significantly. However, we explore the need for combination therapies to enhance PRC targeted treatments efficacy, providing a glimpse into the future of cancer therapeutics.

An Outcome Analysis of Childhood Acute Promyelocytic Leukemia Treated with Atra and Arsenic Trioxide, and Limited Dose Anthracycline

The overall survival of Acute Promyelocytic Leukemia (APL), reported in recent studies, is approaching to 90% wherein, arsenic trioxide (ATO) and all-trans retinoic acid (ATRA) are used as the mainstay of treatment with either limited or no use of anthracycline and cytarabine. This study is aimed to ascertain the outcome of children with APL using similar approach. A total of 30 patients with APL, registered from January 2015 to December 2018, were reviewed. Diagnosis was established on bone marrow aspirate and confirmed by the presence of PML-RARA translocation. Treatment protocol was based on Australian APML 4 study performed by Australian Leukemia Lymphoma Group (ALLG). Lumbar puncture was not performed as it was not part of the protocol due to the risk of bleeding. The mean age in current cohort was 9 years with 53% males. Seven (23.3%) patients died and three (10%) abandoned treatment during induction. Twenty patients completed the intensive phase of chemotherapy and all (100%) of them attained molecular remission (MR). One patient dropped out after MR whereas, 19 remain on follow up with no evidence of disease, reflecting disease free survival (DFS) of 95%. With a median follow up of 2.5 years (range 2.1-4.8 years) the 5 years Kaplan-Meier estimate of OS was 63% and 73%, with and without abandonment, respectively. Analysis of outcome according to risk groups revealed inferior outcome of high risk (HR) group (38% and 50% with and without abandonment, respectively) in contrast to standard risk (SR) group which showed better outcome (82% and 88% with and without abandonment, respectively). The attainment of 100% molecular remission and absence of relapse supports the effectiveness of this regimen. Moreover, it is found to be less toxic and therefore, can be conveniently managed in day-care settings.

Acute Promyelocytic Leukemia: Update on Risk Stratification and Treatment Practices

Acute promyelocytic leukemia (APL) is a rare but highly curable form of acute myeloid leukemia (AML) whose genetic hallmark is the balanced reciprocal translocation t(15;17)(q22;q12) which fuses the promyelocytic leukemia (PML) and retinoic acid receptor alpha (RARα) genes (Wang and Chen in Blood 111:2505-2515, 2008; Lallem and-Breitenbach et al. in J Exp Med 189:1043-1052, 1999). It is a rare disease and accounts for 5-10% of adult AML with an estimated incidence of 0.1/100,000 in Western countries (Sant et al. in Blood 116:3724-3734, 2010). In the United States, 600-800 new cases are diagnosed every year although the incidence appears increased in patients originating from Latin America (Douer in Best Pract Res Clin Haematol 16:357-367, 2003). Notably, the median age at diagnosis is approximately 40 years which is significantly lower than in AML where the median age is 68 years.

Development and validation of a droplet digital PCR assay for the evaluation of PML-RARα fusion transcripts in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is an aggressive disease that requires prompt treatment. Promyelocytic leukemia protein-retinoic acid receptor α (PML-RARα) fusion genes resulting from reciprocal translocation are considered a molecular basis for diagnosing APL. Moreover, PML-RARα fusion gene testing is an essential tool for monitoring the response to therapy via minimal residual disease and providing a diagnosis before rapid disease progression in APL. The present study developed a novel droplet digital PCR (ddPCR) assay to rapidly detect two PML-RARα variants (bcr1 and bcr3) and compared its limit of detection (LOD) with quantitative PCR (qPCR). It was demonstrated that the LOD of ddPCR for PML-RARα reached 0.001%, and the evaluation of high copy number samples of PML-RARα by ddPCR correlated well with qPCR. Furthermore, clinical sample testing with ddPCR found that 34 and 24% samples were bcr-1-positive and bcr3-positive, respectively. However, according to qPCR, 30% of the samples were bcr1-positive and 20% were bcr3-positive. In addition, the concordance rate between ddPCR and qPCR reaction was 86%. While monitoring minimal residual disease, the PML-RARα mutation rate of three patients who recovered well decreased to 0.34%. However, one patient who was bcr3-positive and relapsed had a mutation rate of 13% while in remission, indicating that the bcr3 isoform may be an adverse prognostic factor affecting recovery. Therefore, the present results suggested that this novel ddPCR assay may be useful for monitoring and evaluating the treatment effects and prognosis of APL.

Treatment Outcome and the Genetic Characteristics of Acute Promyelocytic Leukemia in Children in Poland From 2005 to 2018

Background: The aim of the study was to analyze the treatment outcome and genetic characteristics of acute promyelocytic leukemia (APL) in children in Poland from 2005 to 2018. Methods: All 41 patients diagnosed with APL in Poland during the analysis period were eligible for the study. In period I (2005-2015), 33 patients were treated with chemotherapy and all-trans retinoic acid (ATRA), and in period II (2015-2018), 3 patients (high risk) received induction chemotherapy with ATRA and arsenic trioxide (ATO), and 5 patients (standard risk) received ATRA and ATO without chemotherapy. Results: Probability of 5-years overall survival (OS), event-free survival (EFS), and relapse-free survival (RFS) was 0.819 ± 0.069, 0.831 ± 0.063, and 0.961 ± 0.037, respectively, in the whole cohort. Four (11%) early deaths were observed. One patient died of severe infection in the course of disease progression. Relapse occurred in one patient, who died finally because of disease progression. All events occurred in the patients from period I. Variant APL was identified in one patient (successfully treated with chemotherapy with ATRA) and complex translocation in one patient (the only patient with relapse). Additional chromosomal aberrations were found in 26% of patients and FLT3-ITD mutation was detected in 44% of patients; none of those changes influenced clinical outcome. Conclusion: Treatment outcome in the analyzed group is similar to the results reported by other study groups. The main cause of death was coagulation disorders in the early stage of disease. Early, accurate diagnosis followed by specific treatment enables the reduction in the number of early deaths.

Structural Variants as a Basis for Targeted Therapies in Hematological Malignancies

Structural variants (SV) are changes in the genomic landscape that can alter gene expression levels and thus lead to disease development. The most common and best studied SVs in hematological malignancies are chromosomal translocations. Here, parts of two genes that are normally on different chromosomes come into close proximity due to a failure in DNA repair. As a consequence, fusion proteins which show a different function and/or cellular localization compared to the two original proteins are expressed, sometimes even at different levels. The identification of chromosomal translocations is often used to identify the specific disease a patient is suffering from. In addition, SVs such as deletions, duplications, inversions and single nucleotide polymorphisms (SNPs) can occur in hematopoietic cells and lead to their malignant transformations. Changes in the 3D genome structure have also recently been shown to impact disease development. In this review, we describe a variety of SVs occurring in different subtypes of hematological malignancies. Currently, most therapeutic approaches target fusion proteins which are the cellular product of chromosomal translocations. However, amplifications and SNPs also play a role in disease progression and can be targeted. We present some examples for different types of structural variants and how they are currently treated.

A case of acute myeloid leukemia with promyelocytic features characterized by expression of a novel RARG-CPSF6 fusion

Novel RARG-CPSF6 fusion in an AML case with promyelocytic features and no evidence of PML-RARA or X-RARA fusion. Gene fusions involving RARG can initiate AML with promyelocytic morphological features.

Secretome profiling of heterotypic spheroids suggests a role of fibroblasts in HIF-1 pathway modulation and colorectal cancer photodynamic resistance

PURPOSE

Previous analyses of the tumor microenvironment (TME) have resulted in a concept that tumor progression may depend on interactions between cancer cells and its surrounding stroma. An important aspect of these interactions is the ability of cancer cells to modulate stroma behavior, and vice versa, through the action of a variety of soluble mediators. Here, we aimed to identify soluble factors present in the TME of colorectal cancer cells that may affect relevant pathways through secretome profiling.

METHODS

To partially recapitulate the TME and its architecture, we co-cultured colorectal cancer cells (SW480, TC) with stromal fibroblasts (MRC-5, F) as 3D-spheroids. Subsequent characterization of both homotypic (TC) and heterotypic (TC + F) spheroid secretomes was performed using label-free liquid chromatography-mass spectrometry (LC-MS).

RESULTS

Through bioinformatic analysis using the NCI-Pathway Interaction Database (NCI-PID) we found that the HIF-1 signaling pathway was most highly enriched among the proteins whose secretion was enhanced in the heterotypic spheroids. Previously, we found that HIF-1 may be associated with resistance of colorectal cancer cells to photodynamic therapy (PDT), an antitumor therapy that combines photosensitizing agents, O₂ and light to create a harmful photochemical reaction. Here, we found that the presence of fibroblasts considerably diminished the sensitivity of colorectal cancer cells to photodynamic activity. Although the biological significance of the HIF-1 pathway of secretomes was decreased after photosensitization, this decrease was partially reversed in heterotypic 3D-spheroids. HIF-1 pathway modulation by both PDT and stromal fibroblasts was confirmed through expression assessment of the HIF-target VEGF, as well as through HIF transcriptional activity assessment.

CONCLUSION

Collectively, our results delineate a potential mechanism by which stromal fibroblasts may enhance colorectal cancer cell survival and photodynamic treatment resistance via HIF-1 pathway modulation.

[Effects of NPM1 gene expression on acute myeloid leukemia cell lines and its mechanism]

目的

探讨NPM1基因表达对急性髓系白血病（AML）细胞系的影响及其机制。

方法

选取AML细胞系U937和HL-60细胞，转染NPM1质粒至细胞系构建稳定克隆，采用Western blot法鉴定高表达NPM1蛋白的单克隆细胞。MTT法检测细胞增殖活性，流式细胞术检测细胞周期分布和细胞凋亡率，显微镜下计数检测集落形成能力，Western blot法检测细胞周期相关信号通路蛋白表达，实时荧光定量PCR（RQ-PCR）法检测初诊AML患者骨髓单个核细胞NPM1基因表达水平。

结果

①U937和HL-60细胞中NPM1高表达组相对细胞增殖率与对照组相比，差异无统计学意义（4.68±1.28对3.89±0.81，3.34±0.37对2.68±0.29，P值均>0.05）。②U937和HL-60细胞中NPM1高表达组S期细胞比例均明显高于对照组[（50.22±3.42）%对（39.78±3.80）%，（59.01±3.27）%对（43.94±2.08）%，P值均<0.05]。③U937细胞NPM1高表达组和对照组相比具有更强的抗凋亡能力[（48.67±3.22）%和（68.77±10.21）%，P<0.05]和集落形成能力（772.7±24.0和652.3±16.5，P<0.05），而HL-60细胞相应的两组细胞上述能力均相似。④NPM1高表达组细胞中CDK4、Cyclin D1、Cyclin D2及Cyclin E表达明显高于对照组，而Cyclin D3表达明显低于对照组。⑤细胞遗传学预后良好组AML患者NPM1定量水平低于预后中等组。

结论

NPM1蛋白能够促进更多的细胞进入S期，增强抗凋亡和细胞集落形成能力。NPM1定量水平可能预示细胞遗传学的危险度。

The genetics and clinical characteristics of children morphologically diagnosed as acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is characterized by t(15;17)(q22;q21), resulting in a PML-RARA fusion that is the master driver of APL. A few cases that cannot be identified with PML-RARA by using conventional methods (karyotype analysis, FISH, and RT-PCR) involve abnormal promyelocytes that are fully in accordance with APL in morphology, cytochemistry, and immunophenotype. To explore the mechanisms involved in pathogenesis and recurrence of morphologically diagnosed APL, we performed comprehensive variant analysis by next-generation sequencing in 111 pediatric patients morphologically diagnosed as APL. Structural variant (SV) analysis in 120 DNA samples from both diagnosis and relapse stage identified 95 samples with RARA rearrangement (including 94 with PML-RARA and one with NPM-RARA) and two samples with KMT2A rearrangement. In the eligible 13 RNA samples without any RARA rearrangement at diagnosis, one case each with CPSF6-RARG, NPM1-CCDC28A, and TBC1D15-RAB21 and two cases with a TBL1XR1-RARB fusion were discovered. These uncovered fusion genes strongly suggested their contributions to leukemogenesis as driver alternations and APL phenotype may arise by abnormalities of other members of the nuclear receptor superfamily involved in retinoid signaling (RARB or RARG) or even by mechanisms distinct from the formation of aberrant retinoid receptors. Single-nucleotide variant (SNV) analysis in 77 children (80 samples) with RARA rearrangement showed recurrent alternations of primary APL in FLT3, WT1, USP9X, NRAS, and ARID1A, with a strong potential for involvement in pathogenesis, and WT1 as the only recurrently mutated gene in relapsed APL. WT1, NPM1, NRAS, FLT3, and NSD1 were identified as recurrently mutated in 17 primary samples without RARA rearrangement and WT1, NPM1, TP53, and RARA as recurrently mutated in 9 relapsed samples. The survival of APL with RARA rearrangement is much better than without RARA rearrangement. Thus, patients morphologically diagnosed as APL that cannot be identified as having a RARA rearrangement are more reasonably classified as a subclass of AML other than APL, and individualized treatment should be considered according to the genetic abnormalities.

Molecular Malfeasance Mediating Myeloid Malignancies: The Genetics of Acute Myeloid Leukemia

A remarkable number of different, but recurrent, structural cytogenetic abnormalities have been observed in AML, and the 2016 WHO AML classification system incorporates numerous distinct entities associated with translocations or inversions, as well as others associated with single gene mutations into a category entitled "AML with recurrent genetic abnormalities." The AML classification is heavily reliant on cytogenetic and molecular information based on conventional genetic techniques (including karyotype, fluorescence in situ hybridization, reverse transcriptase polymerase chain reaction, single gene sequencing), but large-scale next generation sequencing is now identifying novel mutations. With targeted next generation sequencing panels now clinically available at many centers, detection of mutations, as well as alterations in epigenetic modifiers, is becoming part of the routine diagnostic evaluation of AML and will likely impact future classification schemes.

The discussion of t(1;17)(p11;q21) translocation in acute promyelocytic leukemia patient on molecular remission

Some chromosomal aberrations emerging in the course of treatment are probably not related to disease progression, but attribute to the germline alteration. Therefore, the dynamic genetic tests should be performed during the whole treatment process, which is significantly essential for efficacy evaluation and treatment decision‐ making.

Galectin-12 inhibits granulocytic differentiation of human NB4 promyelocytic leukemia cells while promoting lipogenesis

As a member of the galectin family of animal lectins, galectin-12 is preferentially expressed in adipocytes and leukocytes. In adipocytes, galectin-12 is associated with lipid droplets and regulates lipid metabolism and energy balance, whereas its role in leukocytes is not clear. Analysis of galectin-12 expression in a public data set of acute myeloid leukemia (AML) samples revealed that it is selectively overexpressed in the M3 subtype, which is also known as acute promyelocytic leukemia (APL). To investigate the role of galectin-12 in APL cells, we manipulated its expression in the APL cell line, NB4, and measured resultant effects on all-trans-retinoic acid (ATRA)-induced granulocytic differentiation. With a doxycycline-inducible gene knockdown system, we found that suppression of galectin-12 promoted ATRA-induced neutrophil differentiation but inhibited lipid droplet formation. Our results indicate that overexpression of galectin-12 contributes to a differentiation block in APL cells, and suppression of galectin-12 facilitates granulocytic differentiation. Furthermore, these data suggest that lipogenesis and other aspects of myeloid differentiation can be differentially regulated. Taken together, these findings suggest that galectin-12 may be a target for treatment of the ATRA-resistant subset of APL.

Molecular Characteristics and Clinical Significance of 12 Fusion Genes in Acute Promyelocytic Leukemia: A Systematic Review

Acute promyelocytic leukemia (APL) is characterized by the generation of the promyelocytic leukemia-retinoic acid (RA) receptor α (PML-RARα) fusion gene. PML-RARα is the central leukemia-initiating event in APL and is directly targeted by all-trans-RA (ATRA) as well as arsenic. In classic APL harboring PML-RARα transcripts, more than 90% of patients can achieve complete remission when treated with ATRA combined with arsenic trioxide chemotherapy. In the last 20 years, more than 10 variant fusion genes have been found and identified in APL patients. These variant APL cases present different clinical phenotypes and treatment outcomes. All variant APL cases show a similar breakpoint within the RARα gene, whereas its partner genes are variable. These fusion proteins have the ability to repress rather than activate retinoic targets. These chimeric proteins also possess different molecular characteristics, thereby resulting in variable sensitivities to ATRA and clinical outcomes. In this review, we comprehensively analyze various rearrangements in variant APL cases that have been reported in the literature as well as the molecular characteristics and functions of the fusion proteins derived from different RARα partner genes and their clinical implications.

Comprehensive mutational analysis of primary and relapse acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is a subtype of myeloid leukemia characterized by differentiation block at the promyelocyte stage. Besides the presence of chromosomal rearrangement t(15;17), leading to the formation of PML-RARA (promyelocytic leukemia-retinoic acid receptor alpha) fusion, other genetic alterations have also been implicated in APL. Here, we performed comprehensive mutational analysis of primary and relapse APL to identify somatic alterations, which cooperate with PML-RARA in the pathogenesis of APL. We explored the mutational landscape using whole-exome (n=12) and subsequent targeted sequencing of 398 genes in 153 primary and 69 relapse APL. Both primary and relapse APL harbored an average of eight non-silent somatic mutations per exome. We observed recurrent alterations of FLT3, WT1, NRAS and KRAS in the newly diagnosed APL, whereas mutations in other genes commonly mutated in myeloid leukemia were rarely detected. The molecular signature of APL relapse was characterized by emergence of frequent mutations in PML and RARA genes. Our sequencing data also demonstrates incidence of loss-of-function mutations in previously unidentified genes, ARID1B and ARID1A, both of which encode for key components of the SWI/SNF complex. We show that knockdown of ARID1B in APL cell line, NB4, results in large-scale activation of gene expression and reduced in vitro differentiation potential.

Acute Promyelocytic Leukemia: A Review and Discussion of Variant Translocations

The majority of patients with acute promyelocytic leukemia (APL) manifest the t(15;17)(q24.1;q21.2) translocation; however, a minor but significant proportion of patients with APL harbor complex, cryptic, or variant translocations, which typically involve RARA. With the exception of ZBTB16/RARA, these variants have similar morphologic and immunophenotypic features as classic APL. Study of the variant forms of APL not only gives insight into the pathogenesis of APL but also allows us to understand the mechanism of retinoid therapy. It is important to identify these cryptic and variant translocations because certain variants, including ZBTB16/RARA and STAT5B/RARA, are resistant to treatment with all-trans retinoic acid, arsenic trioxide, and anthracyclines.

The leukemic oncoprotein NPM1-RARA inhibits TP53 activity

The variant acute promyelocytic leukemia (APL) translocation t(5;17)(q35;q21) fuses the N-terminus of nucleophosmin (NPM1) to the retinoic acid receptor alpha (RARA). We found that ectopic NPM1-RARA expression decreased TP53 protein levels in target cells. NPM1-RARA impaired TP53-dependent transcription. Cells expressing NPM1-RARA were more resistant to apoptotic stimuli. This work identifies the TP53 tumor suppressor as a novel target through which NPM1-RARA impacts leukemogenesis, and confirms the importance of impairment of TP53 in establishment of the APL phenotype.

Microgranular variant of acute promyelocytic leukemia with der(17) ins(17;15): A case report and review of the literature

Acute promyelocytic leukemia (APL) with variant translocations is rare. The patient of the present case report, a 2-year-old male with a microgranular variant of APL carrying der(17) ins(17;15) translocation, exhibited fever and epistaxis. The complete blood count showed marked leukocytosis with 72% atypical promyelocytes, anemia and thrombocytopenia. Conventional cytogenetic analysis of the bone marrow cells revealed a karyotype of 47, XY, add(3)(q29), -7, ins(17;15)(q12;q14q22),+21,+mar. The promyelocytic leukemia/retinoic acid receptor α (PML/RARα) rearrangement and insertion were confirmed by fluorescence in situ hybridization. The PML/RARα transcripts were not detected by the reverse transcription polymerase chain reaction, and the patient was diagnosed with microgranular variant M3 APL. The patient achieved remission after a 30-day treatment and was still in remission during a recent follow-up. The present findings suggest that the ins(17;15) variant in APL may not be associated with an unfavorable prognosis. In summary, we reported an extremely rare case of APL with der(17) ins(17;15) abnormality in a pediatric patient and reviewed the literature.

Global characteristics of childhood acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) comprises approximately 5-10% of childhood acute myeloid leukemia (AML) cases in the US. While variation in this percentage among other populations was noted previously, global patterns of childhood APL have not been thoroughly characterized. In this comprehensive review of childhood APL, we examined its geographic pattern and the potential contribution of environmental factors to observed variation. In 142 studies (spanning >60 countries) identified, variation was apparent-de novo APL represented from 2% (Switzerland) to >50% (Nicaragua) of childhood AML in different geographic regions. Because a limited number of previous studies addressed specific environmental exposures that potentially underlie childhood APL development, we gathered 28 childhood cases of therapy-related APL, which exemplified associations between prior exposures to chemotherapeutic drugs/radiation and APL diagnosis. Future population-based studies examining childhood APL patterns and the potential association with specific environmental exposures and other risk factors are needed.

Retinoic acid receptors: from molecular mechanisms to cancer therapy

Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported.

Coexistence of t(15;17) and t(15;16;17) detected by fluorescence in situ hybridization in a patient with acute promyelocytic leukemia: A case report and literature review

Acute promyelocytic leukemia (APL) is characterized by the t(15;17)(q22;q21), which results in the fusion of the promyelocytic leukemia (PML) gene at 15q22 with the retinoic acid α-receptor (RARA) gene at 17q21. The current study presents the case of a 54-year-old female with APL carrying the atypical PML/RARA fusion signal due to a novel complex variant translocation t(15;16;17)(q22;q24;q21), as well as the classical PML/RARA fusion signal. Subsequent array comparative genomic hybridization revealed somatic, cryptic deletions on 3p25.3, 8q23.1 and 12p13.2-p13.1, and a duplication on 8q11.2; however, no genetic material loss or gain was observed in the breakpoint regions of chromosomes 15, 16 or 17. To the best of our knowledge, this is the first report of the coexistence of two abnormal clones, one classical and one variant, presenting simultaneously in addition to cryptic chromosome segmental imbalances in an adult APL patient.

The PML domain of PML-RARα blocks senescence to promote leukemia

In most acute promyelocytic leukemia (APL) cases, translocons produce a promyelocytic leukemia protein-retinoic acid receptor α (PML-RARα) fusion gene. Although expression of the human PML fusion in mice promotes leukemia, its efficiency is rather low. Unexpectedly, we find that simply replacing the human PML fusion with its mouse counterpart results in a murine PML-RARα (mPR) hybrid protein that is transformed into a significantly more leukemogenic oncoprotein. Using this more potent isoform, we show that mPR promotes immortalization by preventing cellular senescence, impeding up-regulation of both the p21 and p19(ARF) cell-cycle regulators. This induction coincides with a loss of the cancer-associated ATRX/Daxx-histone H3.3 predisposition complex and suggests inhibition of senescence as a targetable mechanism in APL therapy.

Acute Myelogenous Leukemia without Maturation with a Retinoic Alpha-Receptor Deletion: A Case Report

Acute promyelocytic leukemia (APL) is characterized by a t(15;17) which fuses the 17q retinoic acid alpha-receptor sequence to the 15q PML gene sequence. The resulting fusion product plays a role in the development and maintenance of APL, and is very rarely found in other acute myeloid leukemia (AML) subtypes. Rare complex APL genomic rearrangements have retinoic acid alpha-receptor sequence deletions. Here we report a retinoic acid alpha-receptor sequence deletion in a case of AML without differentiation. To our knowledge, this is the first example of a retinoic acid alpha-receptor sequence deletion in this AML subtype.

Extrinsic apoptosis is impeded by direct binding of the APL fusion protein NPM-RAR to TRADD

A subset of acute promyelocytic leukemia (APL) cases has been characterized by the t(5;17)(q35;q21) translocation variant, which fuses nucleophosmin (NPM) to retinoic acid receptor α (RARA). The resultant NPM-RAR fusion protein blocks myeloid differentiation and leads to a leukemic phenotype similar to that caused by the t(15;17)(q22;q21) PML-RAR fusion. The contribution of the N-terminal 117 amino acids of NPM contained within NPM-RAR has not been well studied. As a molecular chaperone, NPM interacts with a variety of proteins implicated in leukemogenesis. Therefore, a proteomic analysis was conducted to identify novel NPM-RAR-associated proteins. TNF receptor type I-associated DEATH domain protein (TRADD) was identified as a relevant binding partner for NPM-RAR. This interaction was validated by coprecipitation and colocalization analysis. Biologic assessment found that NPM-RAR expression impaired TNF-induced signaling through TRADD, blunting TNF-mediated activation of caspase-3 (CASP3) and caspase-8 (CASP8), to ultimately block apoptosis.

IMPLICATIONS

This study identifies a novel mechanism through which NPM-RAR affects leukemogenesis.

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.

Synergy against PML-RARa: targeting transcription, proteolysis, differentiation, and self-renewal in acute promyelocytic leukemia

Pandolfi et al. provide an in-depth discussion on the synergism between all-trans-retinoic acid and arsenic trioxide treatment and their mechanisms of action on acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL) is a hematological malignancy driven by a chimeric oncoprotein containing the C terminus of the retinoic acid receptor-a (RARa) fused to an N-terminal partner, most commonly promyelocytic leukemia protein (PML). Mechanistically, PML-RARa acts as a transcriptional repressor of RARa and non-RARa target genes and antagonizes the formation and function of PML nuclear bodies that regulate numerous signaling pathways. The empirical discoveries that PML-RARa–associated APL is sensitive to both all-trans-retinoic acid (ATRA) and arsenic trioxide (ATO), and the subsequent understanding of the mechanisms of action of these drugs, have led to efforts to understand the contribution of molecular events to APL cell differentiation, leukemia-initiating cell (LIC) clearance, and disease eradication in vitro and in vivo. Critically, the mechanistic insights gleaned from these studies have resulted not only in a better understanding of APL itself, but also carry valuable lessons for other malignancies.

How I treat children and adolescents with acute promyelocytic leukaemia

Acute promyelocytic leukaemia (APL) is a rare subtype of acute myeloid leukaemia. The outcome of paediatric APL has improved substantially over the past 20 years; cure rates above 80% are expected when all-trans retinoic acid (ATRA) is given with anthracycline-based regimens. The presenting features of paediatric APL may include severe bleeding and thrombotic complications, which contribute to the high early death rate. The incidence of leucocytosis and the microgranular subtype is greater in paediatric than adult APL, and children experience greater ATRA-related toxicity. It is crucial to begin ATRA therapy and intensive platelet and fibrinogen replacement on first suspicion of APL. Recent risk-adapted therapeutic trials have shown that patients at greater risk of relapse benefit from the introduction of high-dose cytarabine during consolidation. Combination therapy with ATRA and arsenic trioxide provides very effective frontline treatment and may reduce the need for subsequent anthracycline therapy.

Interaction with RXR is necessary for NPM-RAR-induced myeloid differentiation blockade

The t(5;17)(q35;q21) APL variant results in expression of a fusion protein linking the N-terminus of nucleophosmin (NPM) to the C-terminus of the retinoic acid receptor alpha (RAR). We have previously shown that NPM-RAR is capable of binding to DNA either as a homodimer or heterodimer with RXR. To determine the biological significance of NPM-RAR/RXR interaction, we developed two mutants of NPM-RAR that showed markedly diminished ability to bind RXR. U937 subclones expressing the NPM-RAR mutants showed significantly less inhibition of vitamin D3/TGFbeta-induced differentiation, compared with NPM-RAR. These results support the hypothesis that RXR interaction is necessary for NPM-RAR-mediated myeloid maturation arrest.

Molecular basis for the diagnosis and treatment of acute promyelocytic leukemia

Acute promyelocytic leukemia is characterized by gene rearrangements that always involve the retinoic acid receptor alpha on chromosome 15. In the majority of patients t(15;17) is detected, which generates the promyelocytic leukemia gene/retinoic acid receptor alpha rearrangement. This rearrangement interacts with several proteins, including the native promyelocytic leukemia gene, thus causing its delocalization from the nuclear bodies, impairing its function. The immunofluorescence staining technique using the anti-PML antibody may be used to provide a rapid diagnosis and to immediately start therapy using all-trans retinoic acid. The experience of the International Consortium on Acute Promyelocytic Leukemia has demonstrated that early mortality was significantly reduced by adopting the immunofluorescence technique. All-trans retinoic acid combined with chemotherapy is the standard therapy; this promotes complete remission rates greater than 90% and cure rates of nearly 80%. However, early mortality is still an important limitation and hematologists must be aware of the importance of treating newly diagnosed acute promyelocytic leukemia as a medical emergency.

An optimized technology platform for the rapid multiplex molecular analysis of genetic alterations associated with leukemia

Molecular methods play a critical role in the accurate diagnosis of leukemia by complementing morphologic, cytochemical, immunophenotypic, and cytogenetic analyses. We developed a multiplex reverse transcription-polymerase chain reaction (RT-PCR) method combined with liquid bead array cytometry for the rapid detection of genetic alterations associated with leukemia. Fusion transcripts corresponding to the most common recurrent chromosomal translocations were reproducibly detected in as low as 0.1-10 ng of total RNA with an analytical sensitivity of 0.01-1%. Multiday, multilot, multioperator, and multi-instrument precision studies, for a total of 678 independent measures in 46 runs, showed a very high reproducibility with 100% agreement among replicates. Using multiplex panels for four to 20 independent targets, we demonstrate the flexibility of the method to codetect rare splicing isoforms, discriminate among multiple variants generated by unique cytogenetic abnormalities, identify distinct chromosomal partners involved with 11q23 or 17q21 rearrangements, and assess cryptic abnormalities not detectable by standard cytogenetics such as the t(12;21), del(1p32), or NPM1 mutations. Overall, three different internal control transcripts and 34 variants resulting from 18 abnormal chromosomal sites were evaluated. These results underscore the value of the multiplex assay system as a sensitive and reliable technology platform for the characterization of relevant genetic alterations in leukemia.

Acute promyelocytic leukemia: an experience on 95 greek patients treated in the all-trans-retinoic Acid era

Acute promyelocytic leukemia (APL) is highly curable with the combination of all-transretinoic acid (ATRA) and anthracycline based chemotherapy, but the percentage of early deaths remains high. In the present study, we report the clinical, immunophenotypic, cytogenetic and molecular characteristics and outcome of APL patients diagnosed and treated in various Hospitals of Greece and Cyprus.We describe the data of ninety-five APL patients who were diagnosed during the last 15 years. Seven (7.4%) newly diagnosed APL patients died due to intracranial hemorrhage within 72 hours of presentation. All but two patients were induced with ATRA alone or ATRA plus chemotherapy. The early death rate was 14.9%. After induction all 80 evaluable patients achieved complete hematologic remission. The cumulative incidence of relapse was 18.3%. Eight of the ten relapsed patients were successfully salvaged, while both patients with molecularly resistant disease died during salvage treatment. Overall survival (OS) at 5 years was 78.4% and disease free survival (DFS) 73.6%. In multivariate analysis of OS age over 60 years, DIC at diagnosis and marginally major hemorrhage at presentation were identified as adverse prognostic factors. In the subgroup of patients with available data on FLT3 mutation status (49 out of 94), ITD positivity also remained as an independent prognostic factor in the final model of OS, together with major hemorrhage and marginally high Sanz score. We found a close correlation between the CD2 expression and the development of the differentiation syndrome (DS). In conclusion, the main problem in managing patients with APL is still the high early death rate.

Characterization of cryptic rearrangements, deletion, complex variants of PML, RARA in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is characterized by a reciprocal translocation t(15;17)(q22;q21) leading to the disruption of Promyelocytic leukemia (PML) and Retionic Acid Receptor Alpha (RARA) followed by reciprocal PML–RARA fusion in 90% of the cases. Fluorescence in situ hybridization (FISH) has overcome the hurdles of unavailability of abnormal and/or lack of metaphase cells, and detection of cryptic, submicroscopic rearrangements. In the present study, besides diagnostic approach we sought to analyze these cases for identification and characterization of cryptic rearrangements, deletion variants and unknown RARA translocation variants by application of D-FISH and RARA break-apart probe strategy on interphase and metaphase cells in a large series of 200 cases of APL. Forty cases (20%) had atypical PML–RARA and/or RARA variants. D-FISH with PML/RARA probe helped identification of RARA insertion to PML. By application of D-FISH on metaphase cells, we documented that translocation of 15 to 17 leads to 17q deletion which results in loss of reciprocal fusion and/or residual RARA on der(17). Among the complex variants of t(15;17), PML–RARA fusion followed by residual RARA insertion closed to PML–RARA on der(15) was unique and unusual. FISH with break-apart RARA probe on metaphase cells was found to be a very efficient strategy to detect unknown RARA variant translocations like t(11;17)(q23;q21), t(11;17)(q13;q21) and t(2;17)(p21;q21). These findings proved that D-FISH and break-apart probe strategy has potential to detect primary as well as secondary additional aberrations of PML, RARA and other additional loci. The long-term clinical follow-up is essential to evaluate the clinical importance of these findings.

Epigenetic factors in cancer development: polycomb group proteins

The role of chromatin-modifying factors in cancer biology emerged exponentially in the last 10 years, and increased attention has been focused on Polycomb group (PcG) proteins and their enzymatic activities. PcG proteins are repressive chromatin modifiers required for proliferation and development. The frequent deregulation of PcG activities in human tumors has direct oncogenic effects and results, essential for cancer cell proliferation. Here we will review the recent findings regarding PcG proteins in prospective tumor development, focusing on the molecular mechanisms that deregulate PcG expression in different tumors, at the downstream pathways to PcG expression (that contribute to cancer development) and at the mechanisms that regulate PcG recruitment to specific targets. Finally, we will speculate on the benefit of PcG inhibition for cancer treatment, reviewing potential pharmacological strategies.

Differentiation therapy of acute myeloid leukemia

Acute Myeloid Leukemia (AML) is a predominant acute leukemia among adults, characterized by accumulation of malignantly transformed immature myeloid precursors. A very attractive way to treat myeloid leukemia, which is now called 'differentiation therapy', was proposed as in vitro studies have shown that a variety of agents stimulate differentiation of the cell lines isolated from leukemic patients. One of the differentiation-inducing agents, all-trans retinoic acid (ATRA), which can induce granulocytic differentiation in myeloid leukemic cell lines, has been introduced into clinics to treat patients with acute promyelocytic leukemia (APL) in which a PML-RARA fusion protein is generated by a t(15;17)(q22;q12) chromosomal translocation. Because differentiation therapy using ATRA has significantly improved prognosis for patients with APL, many efforts have been made to find alternative differentiating agents. Since 1,25-dihydroxyvitamin D3 (1,25D) is capable of inducing in vitro monocyte/macrophage differentiation of myeloid leukemic cells, clinical trials have been performed to estimate its potential to treat patients with AML or myelodysplastic syndrome (MDS). Unfortunately therapeutic concentrations of 1,25D can induce potentially fatal systemic hypercalcemia, thus limiting clinical utility of that compound. Attempts to overcome this problem have focused on the synthesis of 1,25D analogs (VDAs) which retain differentiation inducing potential, but lack its hypercalcemic effects. This review aims to discuss current problems and potential solutions in differentiation therapy of AML.

Aberrant corepressor interactions implicated in PML-RAR(alpha) and PLZF-RAR(alpha) leukemogenesis reflect an altered recruitment and release of specific NCoR and SMRT splice variants

Human acute promyelocytic leukemia is causally linked to chromosomal translocations that generate chimeric retinoic acid receptor-α proteins (x-RARα fusions). Wild-type RARα is a transcription factor that binds to the SMRT/NCoR family of corepressors in the absence of hormone but releases from corepressor and binds coactivators in response to retinoic acid. In contrast, the x-RARα fusions are impaired for corepressor release and operate in acute promyelocytic leukemia as dominant-negative inhibitors of wild-type RARα. We report that the two most common x-RARα fusions, PML-RARα and PLZF-RARα, have gained the ability to recognize specific splice variants of SMRT and NCoR that are poorly recognized by RARα. These differences in corepressor specificity between the normal and oncogenic receptors are further magnified in the presence of a retinoid X receptor heteromeric partner. The ability of retinoids to fully release corepressor from PML-RARα differs for the different splice variants, a phenomenon relevant to the requirement for supraphysiological levels of this hormone in differentiation therapy of leukemic cells. We propose that this shift in the specificity of the x-RARα fusions to a novel repertoire of corepressors contributes to the dominant-negative and oncogenic properties of these oncoproteins and helps explain previously paradoxical aspects of their behavior.

Cryptic insertion of PML-RARA into the 3p25 locus in an acute promyelocytic leukemia with t(3;17)(p25;q21)

We studied a case of a 72-year-old man with acute promyelocytic leukemia and a t(3;17)(p25;q21). Fluorescence in situ hybridization failed to show rearrangement of the PML (promyelocytic leukemia protein) locus but did demonstrate relocalization of the retinoic acid receptor alpha (RARA) to chromosome 3. We performed a modified panhandle polymerase chain reaction analysis to investigate the unknown 5' partner. Our analysis indicates that the fusion partner is PML. This karyotype therefore results in a cryptic PML-RARA fusion inserted into the 3p25 locus. Our case highlights the need for molecular analysis of seemingly novel karyotypic abnormalities.

Role of nucleophosmin in acute myeloid leukemia

Nucleophosmin (NPM) is a nucleolar phosphoprotein implicated in the regulation of multiple cellular functions, which possesses both oncogenic and tumor-suppressor properties. Mutations of the NPM1 gene leading to the expression of a cytoplasmic mutant protein, NPMc+, are the most frequent genetic abnormalities found in acute myeloid leukemias. Acute myeloid leukemias with mutated NPM1 have distinct characteristics, including a significant association with a normal karyotype, involvement of different hematopoietic lineages, a specific gene-expression profile and clinically, a better response to induction therapy and a favorable prognosis. NPMc+ maintains the capacity of wild-type NPM to interact with a variety of cellular proteins, and impairs their activity by delocalizing them to the cytoplasm. In this review we summarize recent discoveries concerning NPM function, and discuss their possible impact on the pathogenesis of acute myeloid leukemias with mutated NPM1.