Acute promyelocytic leukemia: PML/RARalpha and the leukemic stem cell

Role of APR3 in cancer: apoptosis, autophagy, oxidative stress, and cancer therapy

APR3 (Apoptosis-related protein 3) is a gene that has recently been identified to be associated with apoptosis. The gene is located on human chromosome 2p22.3 and contains both transmembrane and EGF (epidermal growth factor)-like domains. Additionally, it has structural sites, including AP1, SP1, and MEF2D, that indicate NFAT (nuclear factor of activated T cells) and NF-κB (nuclear factor kappa-B) may be transcription factors for this gene. Functionally, APR3 participates in apoptosis due to the induction of mitochondrial damage to release mitochondrial cytochrome C. Concurrently, APR3 affects the cell cycle by altering the expression of Cyclin D1, which, in turn, affects the incidence and growth of malignancies and promotes cell differentiation. Previous reports indicate that APR3 is located in lysosomal membranes, where it contributes to lysosomal activity and participates in autophagy. While further research is required to determine the precise role and molecular mechanisms of APR3, earlier studies have laid the groundwork for APR3 research. There is growing evidence supporting the significance of APR3 in oncology. Therefore, this review aims to examine the current state of knowledge on the role of the newly discovered APR3 in tumorigenesis and to generate fresh insights and suggestions for future research.

Arsenic in medicine: past, present and future

Arsenicals are one of the oldest treatments for a variety of human disorders. Although infamous for its toxicity, arsenic is paradoxically a therapeutic agent that has been used since ancient times for the treatment of multiple diseases. The use of most arsenic-based drugs was abandoned with the discovery of antibiotics in the 1940s, but a few remained in use such as those for the treatment of trypanosomiasis. In the 1970s, arsenic trioxide, the active ingredient in a traditional Chinese medicine, was shown to produce dramatic remission of acute promyelocytic leukemia similar to the effect of all-trans retinoic acid. Since then, there has been a renewed interest in the clinical use of arsenicals. Here the ancient and modern medicinal uses of inorganic and organic arsenicals are reviewed. Included are antimicrobial, antiviral, antiparasitic and anticancer applications. In the face of increasing antibiotic resistance and the emergence of deadly pathogens such as the severe acute respiratory syndrome coronavirus 2, we propose revisiting arsenicals with proven efficacy to combat emerging pathogens. Current advances in science and technology can be employed to design newer arsenical drugs with high therapeutic index. These novel arsenicals can be used in combination with existing drugs or serve as valuable alternatives in the fight against cancer and emerging pathogens. The discovery of the pentavalent arsenic-containing antibiotic arsinothricin, which is effective against multidrug-resistant pathogens, illustrates the future potential of this new class of organoarsenical antibiotics.

Single-cell analysis of transcription factor regulatory networks reveals molecular basis for subtype-specific dysregulation in acute myeloid leukemia

Highly heterogeneous acute myeloid leukemia (AML) exhibits dysregulated transcriptional programs. Transcription factor (TF) regulatory networks underlying AML subtypes have not been elucidated at single-cell resolution. Here, we comprehensively mapped malignancy-related TFs activated in different AML subtypes by analyzing single-cell RNA sequencing data from AMLs and healthy donors. We first identified six modules of regulatory networks which were prevalently dysregulated in all AML patients. AML subtypes featured with different malignant cellular composition possessed subtype-specific regulatory TFs associated with differentiation suppression or immune modulation. At last, we validated that ERF was crucial for the development of hematopoietic stem/progenitor cells by performing loss- and gain-of-function experiments in zebrafish embryos. Collectively, our work thoroughly documents an abnormal spectrum of transcriptional regulatory networks in AML and reveals subtype-specific dysregulation basis, which provides a prospective view to AML pathogenesis and potential targets for both diagnosis and therapy.

Mechanical phenotyping reveals unique biomechanical responses in retinoic acid-resistant acute promyelocytic leukemia

All-trans retinoic acid (ATRA) is an essential therapy in the treatment of acute promyelocytic leukemia (APL), but nearly 20% of patients with APL are resistant to ATRA. As there are no biomarkers for ATRA resistance that yet exist, we investigated whether cell mechanics could be associated with this pathological phenotype. Using mechano-node-pore sensing, a single-cell mechanical phenotyping platform, and patient-derived APL cell lines, we discovered that ATRA-resistant APL cells are less mechanically pliable. By investigating how different subcellular components of APL cells contribute to whole-cell mechanical phenotype, we determined that nuclear mechanics strongly influence an APL cell's mechanical response. Moreover, decondensing chromatin with trichostatin A is especially effective in softening ATRA-resistant APL cells. RNA-seq allowed us to compare the transcriptomic differences between ATRA-resistant and ATRA-responsive APL cells and highlighted gene expression changes that could be associated with mechanical changes. Overall, we have demonstrated the potential of "physical" biomarkers in identifying APL resistance.

Skp2 promotes APL progression through the stabilization of oncoprotein PML-RARα and the inhibition of JunB expression

AIMS

To investigate the role of Skp2 and JunB on acute promyelocytic leukemia (APL) progression and the related mechanism.

MATERIALS AND METHODS

The expression of Skp2 in NB4 cell line was depleted to explore its effect on proliferation and differentiation both in vitro and in vivo assays. Western blot and quantitative RT-PCR analysis were performed to explore Skp2-regulated downstream target genes. Luciferase and co-immunoprecipitation analysis indicated that PML-RARα inhibited the transactivation of JunB by interacting with the PU.1 protein. The western blot analysis confirmed that Skp2 could maintain the stability of PML-RARα.

KEY FINDINGS

We report that the progression of APL and the attenuation of APL sensitivity to ATRA are positively associated with Skp2. Elevated Skp2 expression promotes APL progression by decreasing the expression of lncRNA HOTAIRM1 and inactivation of GSK3β, causing autophagy inhibition followed by the suppression of PML-RARα ubiquitylation and degradation, which represses JunB transcriptional activation through PU.1/PML-RARα transcriptional complex to block cell differentiation. Coupled with ATRA or GSK3β inhibitor treatment, genetic or pharmacological inhibition of Skp2 strikingly induces JunB expression by accelerating the degradation of PML-RARα, which contributes to the eradication of APL. Additionally, the expressions of Skp2 and JunB are negatively correlated in mice subcutaneous leukemia xenograft tumors.

SIGNIFICANCE

Collectively, this study uncovers the roles of Skp2 in PML-RARα stabilization and in APL oncogenic functions. We reveal a novel mechanism of PML-RARα degradation and JunB regulation that constitute an important signaling network of Skp2-GSK3β-PML/RARα-JunB.

The Bone Marrow Microenvironment Mechanisms in Acute Myeloid Leukemia

Bone marrow (BM) is a highly complex tissue that provides important regulatory signals to orchestrate hematopoiesis. Resident and transient cells occupy and interact with some well characterized niches to produce molecular and cellular mechanisms that interfere with differentiation, migration, survival, and proliferation in this microenvironment. The acute myeloid leukemia (AML), the most common and severe hematological neoplasm in adults, arises and develop in the BM. The osteoblastic, vascular, and reticular niches provide surface co-receptors, soluble factors, cytokines, and chemokines that mediate important functions on hematopoietic cells and leukemic blasts. There are some evidences of how AML modify the architecture and function of these three BM niches, but it has been still unclear how essential those modifications are to maintain AML development. Basic studies and clinical trials have been suggesting that disturbing specific cells and molecules into the BM niches might be able to impair leukemia competencies. Either through niche-specific molecule inhibition alone or in combination with more traditional drugs, the bone marrow microenvironment is currently considered the potential target for new strategies to treat AML patients. This review describes the cellular and molecular constitution of the BM niches under healthy and AML conditions, presenting this anatomical compartment by a new perspective: as a prospective target for current and next generation therapies.

MYC: a multipurpose oncogene with prognostic and therapeutic implications in blood malignancies

MYC oncogene is a transcription factor with a wide array of functions affecting cellular activities such as cell cycle, apoptosis, DNA damage response, and hematopoiesis. Due to the multi-functionality of MYC, its expression is regulated at multiple levels. Deregulation of this oncogene can give rise to a variety of cancers. In this review, MYC regulation and the mechanisms by which MYC adjusts cellular functions and its implication in hematologic malignancies are summarized. Further, we also discuss potential inhibitors of MYC that could be beneficial for treating hematologic malignancies.

Retinoic Acid-Induced Gene G(RIG-G) as a Novel Monitoring Biomarker in Leukemia and Its Clinical Applications

Retinoic acid inducible gene G (RIG-G) is an inducible gene produced during the treatment of acute promyelocytic leukemia with all-trans retinoic acid (ATRA). However, it is unclear the expression level of RIG-G gene in the peripheral blood of healthy subjects and patients with acute promyelocytic leukemia (APL or AML-M3). In the present study, we established the TaqMan-MGB fluorescent probe qPCR (real-time polymerase chain reaction) method for the first time to detect the expression of RIG-G gene in APL. Twenty APL patients were selected, and their RIG-G expression levels were quantified to assess the correlation between the expression of peripheral blood and bone marrow samples. U test was used to analyze the expression level of RIG-G in the peripheral blood of 40 normal specimens and 20 APL patients to observe the prognostic monitoring effect of RIG-G gene in the ATRA treatment process. ROC (receiver operating characteristic curve) was used to analyze and test the diagnostic efficiency of RIG-G gene for APL patients. There is a strong positive correlation between the expression of RIG-G in peripheral blood and bone marrow of APL patients. The expression level of RIG-G in peripheral blood of APL patients is significantly lower than that in healthy controls (p < 0.001). The changes in the expression level of RIG-G in peripheral blood changed indicates the remission and recurrence of APL patients after ATRA treatment, and the ROC curve shows that it has a better diagnostic power for APL. In summary, the TaqMan-MGB real-time PCR method we have established has successfully run. The detection of RIG-G gene expression in peripheral blood can effectively monitor the disease changes of APL patients and avoid harmful bone marrow puncture injury.

Environmental and Health Hazards of Chromated Copper Arsenate-Treated Wood: A Review

Copper chrome arsenate (CCA) water-borne solution used to be widely used to make timber highly resistant to pests and fungi, in particular, wood products designed for outdoor use. Nowadays, CCA is a restricted chemical product in most countries, since potential environmental and health risks were reported due to dermal contact with CCA residues from treated structures and the surrounding soil, as well as the contamination of soils. However, large quantities of CCA-treated timber are still in use in framings, outdoor playground equipment, landscaping, building poles, jetty piles, and fencing structures around the world, thus CCA remains a source of pollutants to the environment and of increasing toxic metal/metalloid exposure (mainly in children). International efforts have been dedicated to the treatment of materials impregnated with CCA, however not only does some reuse of CCA-treated timber still occur, but also existing structures are leaking the toxic compounds into the environment, with impacts on the environment and animal and human health. This study highlights CCA mechanisms and the documented consequences in vivo of its exposure, as well as the adverse environmental and health impacts.

Current and emerging molecular and epigenetic disease entities in acute myeloid leukemia and a critical assessment of their therapeutic modalities

Acute myeloid leukemia (AML) is the most frequently diagnosed acute leukemia, and its incidence increases with age. Although the etiology of AML remains unknown, exposure to genotoxic agents or some prior hematologic disorders could lead to the development of this condition. The pathogenesis of AML involves the development of malignant transformation of hematopoietic stem cells that undergo successive genomic alterations, ultimately giving rise to a full-blown disease. From the disease biology perspective, AML is considered to be extremely complex with significant genetic, epigenetic, and phenotypic variations. Molecular and cytogenetic alterations in AML include mutations in those subsets of genes that are involved in normal cell proliferation, maturation and survival, thus posing significant challenge to targeting these pathways without attendant toxicity. In addition, multiple malignant cells co-exist in the majority of AML patients. Individual subclones are characterized by unique genetic and epigenetic abnormalities, which contribute to the differences in their response to treatment. As a result, despite a dramatic progress in our understanding of the pathobiology of AML, not much has changed in therapeutic approaches to treat AML in the past four decades. Dose and regimen modifications with improved supportive care have contributed to improved outcomes by reducing toxicity-related side effects. Several drug candidates are currently being developed, including targeted small-molecule inhibitors, cytotoxic chemotherapies, monoclonal antibodies and epigenetic drugs. This review summarizes the current state of affairs in the pathobiological and therapeutic aspects of AML.

NLS-RARα blocks cell differentiation by inhibiting the retinoic acid signalling pathway

A majority of acute promyelocytic leukaemia (APL) cases are characterized by the PML-RARα fusion gene. Previous studies have shown that neutrophil elastase (NE) can cleave PML-RARα and is important for the development of APL. Here, we demonstrate that one of the cleavage products of PML-RARα, NLS-RARα, can block cell differentiation by repressing the expression of the target genes within the retinoic acid signalling pathway. The results of reverse transcriptase polymerase chain reaction (RT-PCR) and Western blot analysis showed that NLS-RARα depressed the expression of the cell differentiation marker protein, CD11b and CEBPβ, as well as the retinoic acid signalling pathway target genes, RARβ and CEBPε. Studies have shown that NLS-RARα forms heterodimers with retinoid X receptor α(RXRα) and interacts with SMRT. When treated with all-trans retinoic acid (ATRA), NLS-RARα exhibits diminished transcriptional activity compared to RARα. Moreover, in the presence of high doses of ATRA, NLS-RARα could be degraded along with the consequent transactivation of retinoic acid signalling pathway target genes and cell differentiation induction in a dose- and time-dependent manner. Together, these results indicate that NLS-RARα blocks cell differentiation by inhibiting the retinoic acid signalling pathway.

Primaquine phosphate induces the apoptosis of ATRA-resistant acute promyelocytic leukemia cells by inhibition of the NF-κB pathway

As a subtype of acute myeloid leukemia (AML), acute promyelocytic leukemia (APL) is characterized by a chromosomal translocation, most of which result in the production of a PML-RAR alpha fusion protein. Although the overall survival rate of APL patients has improved dramatically due to all-trans retinoic acid (ATRA) treatment, ATRA-resistance remains a clinical challenge in the management of APL. Therefore, alternative agents should be considered for ATRA-resistant APL patients. Here, we report that antimalaria drug primaquine phosphate (PRQ) exhibits an anti-leukemia effect on both ATRA-sensitive cell line NB4 and ATRA-resistant APL cell lines, NB4-LR2, NB4-LR1, and NB4-MR2. Moreover, PRQ significantly inhibited primary colony formation of untreated or relapsed APL patients. Further study showed that PRQ could induce the apoptosis of APL cells by inhibiting NF-κB signaling pathway. The in vivo study showed that PRQ significantly inhibited NB4-LR2 xenograft tumors growth. These results suggest that PRQ is a potential therapeutic agent for ATRA-resistant APL patients.

Epigenetic mechanisms underlying the therapeutic effects of HDAC inhibitors in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a hematological disorder caused by the oncogenic BCR-ABL fusion protein in more than 90% of patients. Despite the striking improvements in the management of CML patients since the introduction of tyrosine kinase inhibitors (TKis), the appearance of TKi resistance and side effects lead to treatment failure, justifying the need of novel therapeutic approaches. Histone deacetylase inhibitors (HDACis), able to modulate gene expression patterns and important cellular signaling pathways through the regulation of the acetylation status of both histone and non-histone protein targets, have been reported to display promising anti-leukemic properties alone or in combination with TKis. This review summarizes pre-clinical and clinical studies that investigated the mechanisms underlying the anticancer potential of HDACis and discusses the rationale for a combination of HDACis with TKis as a therapeutic option in CML.

PML/RARa blocks the differentiation and promotes the proliferation of acute promyelocytic leukemia through activating MYB expression by transcriptional and epigenetic regulation mechanisms

The promyelocytic leukemia (PML)/retinoic acid receptor-alpha (RARα) onco-fusion protein that is generated from t(15;17) chromosome translocation is crucial for the leukemogenesis of acute promyelocytic leukemia (APL) and is well documented as a transcriptional repressor. To understand the relationship between PML/RARα and the oncogene in the development of APL, we investigate the regulation mechanism of PML/RARα to MYB proto-oncogene and the role of this regulation on the proliferation and differentiation of APL cells. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) assays show that MYB expression was significantly higher in PML/RARα positive cell lines. Microarray data verify that the MYB expression was significantly higher in APL patient samples than in normal promyelocyte samples. Further expression analysis from RT-qPCR and microarray data verifies that the expression of MYB is upregulated by PML/RARα. Transcriptional factor binding analysis shows that MYB is directly bound by PML/RARα and its cofactors. Luciferase assays show that PML/RARα transactivated MYB promoter activity through the RARα binding site and the coexistence of CCAAT enhancer binding protein ε. We also find that PML/RARα increases the acetylation level of the promoter region of MYB. Further evidence demonstrates that PML/RARα regulates MYB expression through long-range interaction. Functionally, PML/RARα increases the cell proliferation and blocks the differentiation through activating MYB expression. Collectively, this study uncovers a novel mechanism of PML/RARα-mediated transcriptional activation and enriches our knowledge of the onco-fusion protein-mediated transcription activation.

Expression of the promyelocytic leukemia protein without the nuclear localization signal as a novel diagnostic marker for acute promyelocytic leukemia

Promyelocytic leukemia-retinoic acid receptor α (PML-RARα) is a fusion protein generated by the t(15;17)(q22;q12) translocation associated with acute promyelocytic leukemia (APL). PML-RARα is cleaved by neutrophil elastase, an early myeloid-specific serine protease, leading to translocation of the nuclear localization signal (NLS) of the PML protein to the N-terminal of RARα, and the mutational product PML(NLS-). The present study was designed to analyze the role of the NLS in mediating PML transport into the nucleus and to evaluate the value of measuring NLS translocation in the early diagnosis of APL. PML and PML(NLS-) localization was examined by immunofluorescence (IF). The interaction between PML/PML(NLS-) and importin α was detected by an in vivo binding assay using co-immunoprecipitation and double IF labeling. Twenty-seven untreated APL patients with PML-RARα and 22 non-APL controls were evaluated. PML(NLS-) was detected in primary APL, but not non-APL cells. IF showed that PML was localized to the nucleus, interacted with importin α in vivo, and co-localized in the PML nuclear bodies. PML(NLS-) was primarily localized in the cytoplasm and the interaction with importin α was lost. IF had a sensitivity and specificity of 92.6 and 77.3%, respectively, for diagnosing APL. These data suggest that PML(NLS-) may be a novel diagnostic biomarker for APL.

From molecular interaction to acute promyelocytic leukemia: Calculating leukemogenesis and remission from endogenous molecular-cellular network

Acute promyelocytic leukemia (APL) remains the best example of a malignancy that can be cured clinically by differentiation therapy. We demonstrate that APL may emerge from a dynamical endogenous molecular-cellular network obtained from normal, non-cancerous molecular interactions such as signal transduction and translational regulation under physiological conditions. This unifying framework, which reproduces APL, normal progenitor, and differentiated granulocytic phenotypes as different robust states from the network dynamics, has the advantage to study transition between these states, i.e. critical drivers for leukemogenesis and targets for differentiation. The simulation results quantitatively reproduce microarray profiles of NB4 and HL60 cell lines in response to treatment and normal neutrophil differentiation, and lead to new findings such as biomarkers for APL and additional molecular targets for arsenic trioxide therapy. The modeling shows APL and normal states mutually suppress each other, both in "wiring" and in dynamical cooperation. Leukemogenesis and recovery under treatment may be a consequence of spontaneous or induced transitions between robust states, through "passes" or "dragging" by drug effects. Our approach rationalizes leukemic complexity and constructs a platform towards extending differentiation therapy by performing "dry" molecular biology experiments.

Onco-microRNA miR-130b promoting cell growth in children APL by targeting PTEN

OBJECTIVE

To study the expression of microRNA-130b (miR-130b) in children acute promyelocytic leukemia (APL) and its role for regulating PTEN expression.

METHODS

A total of 50 children APL marrow tissues and 15 normal marrow tissues between January and December in 2012 were collected into our study. The expression of miR-130b in APL and normal marrow tissues were detected by quantitative real-time polymerase chain reaction. MiR-130b inhibitor was transfected into HL-60 cells. Cell Counting Kit-8 assay and flow cytometry were used to measure cell proliferation and apoptosis, respectively. The expression of PTEN, a potential target of miR-130b, and its downstream genes, Bcl-2 and Bax, in transformed cells were detected by quantitative real-time polymerase chain reaction and western-blot.

RESULTS

The expression of miR-130b was significantly higher in children APL marrow tissues than in normal marrow tissues (P < 0.05). Down-regulation of miR-130b could significantly suppress cell proliferation and induce apoptosis in HL-60 cells (P < 0.05). PTEN expression was upregulated when miR-130b was knocking-down (P < 0.05). As downstream genes of PTEN, the expression of Bcl-2 and Bax were regulated as well.

CONCLUSIONS

MiR-130b is overexpressed in children APL marrow tissues and associated with cell growth. MiR-130b may promote children APL progression by inducing cell proliferation and inhibiting apoptosis.

Arsenic trioxide binding to serum proteins

Arsenic trioxide (ATO) also known as Trisenox, is an anticancer chemotherapeutic drug which has been used in treating diagnosed and relapsed patients with acute promyelocytic leukemia (APL). Serum albumin is the most abundant of the proteins in blood plasma and is the major transporter for delivering several drugs in vivo. The current study was designed to evaluate the potential ability of human and bovine serum albumin for delivering arsenic trioxide. Therefore, interaction of arsenic trioxide with HSA and BSA was investigated in aqueous solution at physiological conditions using a constant protein concentration and various drug contents. FTIR and UV-Vis spectroscopic methods were used to analyze arsenic trioxide and protein binding modes, the binding constants and the effect of drug complexation on HSA and BSA stability and conformation. Results of this study showed that drug complexation altered protein conformation by major reduction of α-helix and increase of turn structure which is indicative of a partial protein destabilization. Structural analysis revealed that arsenic trioxide bind HSA and BSA with overall binding constants of KATO-HSA=1.07 (±0.01)×10(4) M(-1) and KATO-BSA=1.27(±0.02)×10(4) M(-1). It could be concluded that serum albumins can be considered as good carriers for delivering arsenic trioxide to target tissue.

Establishment of a humanized APL model via the transplantation of PML-RARA-transduced human common myeloid progenitors into immunodeficient mice

Recent advances in cancer biology have revealed that many malignancies possess a hierarchal system, and leukemic stem cells (LSC) or leukemia-initiating cells (LIC) appear to be obligatory for disease progression. Acute promyelocytic leukemia (APL), a subtype of acute myeloid leukemia characterized by the formation of a PML-RARα fusion protein, leads to the accumulation of abnormal promyelocytes. In order to understand the precise mechanisms involved in human APL leukemogenesis, we established a humanized in vivo APL model involving retroviral transduction of PML-RARA into CD34⁺ hematopoietic cells from human cord blood and transplantation of these cells into immunodeficient mice. The leukemia well recapitulated human APL, consisting of leukemic cells with abundant azurophilic abnormal granules in the cytoplasm, which expressed CD13, CD33 and CD117, but not HLA-DR and CD34, were clustered in the same category as human APL samples in the gene expression analysis, and demonstrated sensitivity to ATRA. As seen in human APL, the induced APL cells showed a low transplantation efficiency in the secondary recipients, which was also exhibited in the transplantations that were carried out using the sorted CD34⁻ fraction. In order to analyze the mechanisms underlying APL initiation and development, fractionated human cord blood was transduced with PML-RARA. Common myeloid progenitors (CMP) from CD34⁺/CD38⁺ cells developed APL. These findings demonstrate that CMP are a target fraction for PML-RARA in APL, whereas the resultant CD34⁻ APL cells may share the ability to maintain the tumor.

Biomedical implications of heavy metals induced imbalances in redox systems

Several workers have extensively worked out the metal induced toxicity and have reported the toxic and carcinogenic effects of metals in human and animals. It is well known that these metals play a crucial role in facilitating normal biological functions of cells as well. One of the major mechanisms associated with heavy metal toxicity has been attributed to generation of reactive oxygen and nitrogen species, which develops imbalance between the prooxidant elements and the antioxidants (reducing elements) in the body. In this process, a shift to the former is termed as oxidative stress. The oxidative stress mediated toxicity of heavy metals involves damage primarily to liver (hepatotoxicity), central nervous system (neurotoxicity), DNA (genotoxicity), and kidney (nephrotoxicity) in animals and humans. Heavy metals are reported to impact signaling cascade and associated factors leading to apoptosis. The present review illustrates an account of the current knowledge about the effects of heavy metals (mainly arsenic, lead, mercury, and cadmium) induced oxidative stress as well as the possible remedies of metal(s) toxicity through natural/synthetic antioxidants, which may render their effects by reducing the concentration of toxic metal(s). This paper primarily concerns the clinicopathological and biomedical implications of heavy metals induced oxidative stress and their toxicity management in mammals.

Associations between age, cytogenetics, FLT3-ITD, and marrow leukemia cells identified by flow cytometry

OBJECTIVES

To explore the relationships between age, cytogenetic subgroups, molecular markers, and cells with leukemic aberrant immunophenotype in patients with acute myeloid leukemia (AML).

METHODS

In this study, we evaluated the correlations between age, cytogenetic subgroups (normal, balanced and unbalance karyotype), molecular mutations (NPM1, FLT3-ITD, and CEBPA mutations) and marrow leukemia cells (LC) identified by flow cytometry in 256 patients with de novo AML.

RESULTS

From age group 10-19 years to age group ≥ 60 years, the percentage of LC decreased from 67.0 ± 18.4% to 49.0 ± 25.1% (F = 2.353, P = 0.041). LC percentage was higher in patients with balanced karyotypes (65.7 ± 22.4%), than those with unbalanced karyotypes (46.0 ± 26.6%) (u = 3.444, P = 0.001) or a normal karyotype (49.9 ± 22.1%) (u = 5.093, P < 0.001). Patients with FLT3-ITD (64.3 ± 19.5%) had higher LC percentages compared with those without (54.2 ± 24.3%) (u = 2.794, P = 0.007).

CONCLUSIONS

Associations between age, cytogenetics, molecular markers, and marrow leukemia cells may offer beneficial information to understand the biology and pathogenesis of AML.

Polymorphisms in microRNA target sites modulate risk of lymphoblastic and myeloid leukemias and affect microRNA binding

BACKGROUND

MicroRNA dysregulation is a common event in leukemia. Polymorphisms in microRNA-binding sites (miRSNPs) in target genes may alter the strength of microRNA interaction with target transcripts thereby affecting protein levels. In this study we aimed at identifying miRSNPs associated with leukemia risk and assessing impact of these miRSNPs on miRNA binding to target transcripts.

METHODS

We analyzed with specialized algorithms the 3' untranslated regions of 137 leukemia-associated genes and identified 111 putative miRSNPs, of which 10 were chosen for further investigation. We genotyped patients with acute myeloid leukemia (AML, n = 87), chronic myeloid leukemia (CML, n = 140), childhood acute lymphoblastic leukemia (ALL, n = 101) and healthy controls (n = 471). Association between SNPs and leukemia risk was calculated by estimating odds ratios in the multivariate logistic regression analysis. For miRSNPs that were associated with leukemia risk we performed luciferase reporter assays to examine whether they influence miRNA binding.

RESULTS

Here we show that variant alleles of TLX1_rs2742038 and ETV6_rs1573613 were associated with increased risk of childhood ALL (OR (95% CI) = 3.97 (1.43-11.02) and 1.9 (1.16-3.11), respectively), while PML_rs9479 was associated with decreased ALL risk (OR = 0.55 (0.36-0.86). In adult myeloid leukemias we found significant associations between the variant allele of PML_rs9479 and decreased AML risk (OR = 0.61 (0.38-0.97), and between variant alleles of IRF8_ rs10514611 and ARHGAP26_rs187729 and increased CML risk (OR = 2.4 (1.12-5.15) and 1.63 (1.07-2.47), respectively). Moreover, we observed a significant trend for an increasing ALL and CML risk with the growing number of risk genotypes with OR = 13.91 (4.38-44.11) for carriers of ≥3 risk genotypes in ALL and OR = 4.9 (1.27-18.85) for carriers of 2 risk genotypes in CML. Luciferase reporter assays revealed that the C allele of ARHGAP26_rs187729 creates an illegitimate binding site for miR-18a-3p, while the A allele of PML_rs9479 enhances binding of miR-510-5p and the C allele of ETV6_rs1573613 weakens binding of miR-34c-5p and miR-449b-5p.

CONCLUSIONS

Our study implicates that microRNA-binding site polymorphisms modulate leukemia risk by interfering with the miRNA-mediated regulation. Our findings underscore the significance of variability in 3' untranslated regions in leukemia.

Cytogenetics in benzene-associated myelodysplastic syndromes and acute myeloid leukemia: new insights into a disease continuum

Hematopoiesis in health and disease results from complex interactions between primitive hematopoietic stem cells (HSCs) and the extrinsic influences of other cells in the bone marrow (BM) niche. Advances in stem cell biology, molecular genetics, and computational biology reveal that the immortality, self-renewal, and maintenance of blood homeostasis generally attributed to individual HSCs are functions of the cells' behavior in the normal BM environment. Here we discuss how these advances, together with results of outcomes-based clinical epidemiology studies, provide new insight into the importance of epigenetic events in leukemogenesis. For the chemical benzene (Bz), development of myeloid neoplasms depends predominantly on alterations within the microenvironments in which they arise. The primary persistent disease in Bz myelotoxicity is myelodysplastic syndrome, which precedes cytogenetic injury. Evidence indicates that acute myeloid leukemia arises as a secondary event, subsequent to evolution of the leukemia-initiating cell phenotype within the altered BM microenvironment. Further explorations into the nature of chemical versus de novo disease should consider this mechanism, which is biologically distinct from previous models of clonal cytogenetic injury. Understanding alterations of homeostatic regulation in the BM niche is important for validation of models of leukemogenesis, monitoring at-risk populations, and development of novel treatment and prevention strategies.

Acute myeloid leukemia following exposure to benzene more closely resembles de novo than therapy related-disease

Benzene (Bz) is widely regarded as a prototype environmental leukemogen and individuals chronically exposed are at risk for myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). It is widely assumed that initiation and pathogenesis of AML following Bz exposure (Bz-AML) is similar or identical to therapy-related AML (t-AML), in which clonal cytogenetic abnormalities, including aneuploidy, are initiating events. However, this assumption is not supported by studies reporting actual disease outcomes together with cytogenetic analyses. Here, using clinically relevant cytogenetic, hematologic, and epidemiological methods, we directly show for 722 consecutive AML cases that the pattern of clonal cytogenetic abnormalities encountered in Bz-exposed cases (n = 78) more closely resembles de novo-AML than t-AML. The prevalence of aneuploidy in Bz-exposed- and de novo-AML cases was identical (23%), and no significant increases in -5/5q- (RR = 0.79) (95% CI: 0.29-2.12) or -7/7q- (RR = 1.27) (95% CI: 0.55-2.92) abnormalities were observed between Bz- vs de novo-AML, respectively. Previous studies have suggested a role for autoimmunity in Bz related MDS including immune mediated inflammatory features and positive responses to immunosuppressive therapy which are indistinguishable from those reported in MDS with low risk of progression to AML. These observations are more consistent with an epigenetic model for initiation of Bz-AML in which altered homeostatic regulation in the bone marrow niche, not direct cytogenetic injury, predominates in the initial development of the leukemic stem cell phenotype, a mechanism biologically distinct from previous models of clonal cytogenetic injury. These findings are important for further understanding the biological basis of AML, particularly in environmental and occupational settings.

Targeting the acute promyelocytic leukemia-associated fusion proteins PML/RARα and PLZF/RARα with interfering peptides

In acute promyelocytic leukemia (APL), hematopoietic differentiation is blocked and immature blasts accumulate in the bone marrow and blood. APL is associated with chromosomal aberrations, including t(15;17) and t(11;17). For these two translocations, the retinoic acid receptor alpha (RARα) is fused to the promyelocytic leukemia (PML) gene or the promyelocytic zinc finger (PLZF) gene, respectively. Both fusion proteins lead to the formation of a high-molecular-weight complex. High-molecular-weight complexes are caused by the "coiled-coil" domain of PML or the BTB/POZ domain of PLZF. PML/RARα without the "coiled-coil" fails to block differentiation and mediates an all-trans retinoic acid-response. Similarly, mutations in the BTB/POZ domain disrupt the high-molecular-weight complex, abolishing the leukemic potential of PLZF/RARα. Specific interfering polypeptides were used to target the oligomerization domain of PML/RARα or PLZF/RARα. PML/RARα and PLZF/RARα were analyzed for the ability to form high-molecular-weight complexes, the protein stability and the potential to induce a leukemic phenotype in the presence of the interfering peptides. Expression of these interfering peptides resulted in a reduced replating efficiency and overcame the differentiation block induced by PML/RARα and PLZF/RARα in murine hematopoietic stem cells. This expression also destabilized the PLZF/RARα-induced high-molecular-weight complex formation and caused the degradation of the fusion protein. Targeting fusion proteins through interfering peptides is a promising approach to further elucidate the biology of leukemia.

Leukemia-associated antigens and their relevance to the immunotherapy of acute myeloid leukemia

The graft-versus-leukemia effect of allogeneic hematopoietic stem cell transplantation (HSCT) has shown that the immune system is capable of eradicating acute myeloid leukemia (AML). This knowledge, along with the identification of the target antigens against which antileukemia immune responses are directed, has provided a strong impetus for the development of antigen-targeted immunotherapy of AML. The success of any antigen-specific immunotherapeutic strategy depends critically on the choice of target antigen. Ideal molecules for immune targeting in AML are those that are: (1) leukemia-specific; (2) expressed in most leukemic blasts including leukemic stem cells; (3) important for the leukemic phenotype; (4) immunogenic; and (5) clinically effective. In this review, we provide a comprehensive overview on AML-related tumor antigens and assess their applicability for immunotherapy against the five criteria outlined above. In this way, we aim to facilitate the selection of appropriate target antigens, a task that has become increasingly challenging given the large number of antigens identified and the rapid pace at which new targets are being discovered. The information provided in this review is intended to guide the rational design of future antigen-specific immunotherapy trials, which will hopefully lead to new antileukemia therapies with more selectivity and higher efficacy.

Sulindac sulfide reverses aberrant self-renewal of progenitor cells induced by the AML-associated fusion proteins PML/RARα and PLZF/RARα

Chromosomal translocations can lead to the formation of chimeric genes encoding fusion proteins such as PML/RARα, PLZF/RARα, and AML-1/ETO, which are able to induce and maintain acute myeloid leukemia (AML). One key mechanism in leukemogenesis is increased self renewal of leukemic stem cells via aberrant activation of the Wnt signaling pathway. Either X-RAR, PML/RARα and PLZF/RARα or AML-1/ETO activate Wnt signaling by upregulating γ-catenin and β-catenin. In a prospective study, a lower risk of leukemia was observed with aspirin use, which is consistent with numerous studies reporting an inverse association of aspirin with other cancers. Furthermore, a reduction in leukemia risk was associated with use of non-steroidal anti-inflammatory drug (NSAID), where the effects on AML risk was FAB subtype-specific. To better investigate whether NSAID treatment is effective, we used Sulindac Sulfide in X-RARα-positive progenitor cell models. Sulindac Sulfide (SSi) is a derivative of Sulindac, a NSAID known to inactivate Wnt signaling. We found that SSi downregulated both β-catenin and γ-catenin in X-RARα-expressing cells and reversed the leukemic phenotype by reducing stem cell capacity and increasing differentiation potential in X-RARα-positive HSCs. The data presented herein show that SSi inhibits the leukemic cell growth as well as hematopoietic progenitors cells (HPCs) expressing PML/RARα, and it indicates that Sulindac is a valid molecular therapeutic approach that should be further validated using in vivo leukemia models and in clinical settings.

Effector caspases and leukemia

Caspases, a family of aspartate-specific cysteine proteases, play a major role in apoptosis and a variety of physiological and pathological processes. Fourteen mammalian caspases have been identified and can be divided into two groups: inflammatory caspases and apoptotic caspases. Based on the structure and function, the apoptotic caspases are further grouped into initiator/apical caspases (caspase-2, -8, -9, and -10) and effector/executioner caspases (caspase-3, -6, and -7). In this paper, we discuss what we have learned about the role of individual effector caspase in mediating both apoptotic and nonapoptotic events, with special emphasis on leukemia-specific oncoproteins in relation to effector caspases.

Pharicin B stabilizes retinoic acid receptor-α and presents synergistic differentiation induction with ATRA in myeloid leukemic cells

All-trans retinoic acid (ATRA), a natural ligand for the retinoic acid receptors (RARs), induces clinical remission in most acute promyelocytic leukemia (APL) patients through the induction of differentiation and/or eradication of leukemia-initiating cells. Here, we identify a novel natural ent-kaurene diterpenoid derived from Isodon pharicus leaves, called pharicin B, that can rapidly stabilize RAR-α protein in various acute myeloid leukemic (AML) cell lines and primary leukemic cells from AML patients, even in the presence of ATRA, which is known to induce the loss of RAR-α protein. Pharicin B also enhances ATRA-dependent the transcriptional activity of RAR-α protein in the promyelocytic leukemia-RARα-positive APL cell line NB4 cells. We also showed that pharicin B presents a synergistic or additive differentiation-enhancing effect when used in combination with ATRA in several AML cell lines and, especially, some primary leukemic cells from APL patients. In addition, pharicin B can overcome retinoid resistance in 2 of 3 NB4-derived ATRA-resistant subclones. These findings provide a good example for chemical biology-based investigations of pathophysiological and therapeutic significances of RAR-α and PML-RAR-α proteins. The effectiveness of the ATRA/pharicin B combination warrants further investigation on their use as a therapeutic strategy for AML patients.

Enhancement of specific cellular immune response induced by DNA vaccines encoding PML-RARalpha and hIL-2 genes

A DNA vaccine encoding PML-RAR alpha fusion gene is thought to be a promising approach for acute promyelocytic leukemia patients to enhance immune responses after attaining complete remission. In this study, we sought to enhance cellular immunity by coexpressing human interleukin (hIL)-2 genes. Successfully constructed plasmids PML-RAR alpha-hIL-2-pIRES, PML-RAR alpha-pIRES and hIL-2-pIRES were delivered intramuscularly in BALB/C mice at 14-day intervals for three cycles. The cellular immune responses with respect to the specific cytotoxicity of spleen cells; interferon-gamma secretion in sera, and the T-cell receptor rearrangement excision circles of thymocyte were significantly increased from PML-RARalpha-hIL-2-pIRES immunized mice. Our results indicate that a DNA vaccine with PML fusion gene segment and hIL-2 together might elicit increased cellular immune responses in mice.

L-Ascorbate protects rat hepatocytes against sodium arsenite--induced cytotoxicity and oxidative damage

Sodium arsenite-exposed hepatocytes of rat showed higher production of nitric oxide (NO) and increased lipid peroxidation (LPO) level vis-a-vis activity of superoxide dismutase (SOD) and catalase (CAT) were significantly lowered. Subsequently, the cell proliferation index (CPI) and cell viability were also reduced. Treatment with L-ascorbate was found effective in normalizing the arsenic-induced alteration of SOD and CAT activity and LPO level in rat hepatocytes. These observations indicated that L-ascorbate also has potent cytoprotective role as it could reduce the NO production and normalize the cell proliferation and viability of hepatocytes. Therefore, the in vitro study suggested that ascorbic acid is helpful to ameliorate the arsenic-induced cytotoxicity and oxidative stress of rat hepatocytes.

Reciprocal t(9;22) ABL/BCR fusion proteins: leukemogenic potential and effects on B cell commitment

Background

t(9;22) is a balanced translocation, and the chromosome 22 breakpoints (Philadelphia chromosome – Ph⁺) determine formation of different fusion genes that are associated with either Ph⁺ acute lymphatic leukemia (Ph⁺ ALL) or chronic myeloid leukemia (CML). The “minor” breakpoint in Ph⁺ ALL encodes p185^BCR/ABL from der22 and p96^ABL/BCR from der9. The “major” breakpoint in CML encodes p210^BCR/ABL and p40^ABL/BCR. Herein, we investigated the leukemogenic potential of the der9-associated p96^ABL/BCR and p40^ABL/BCR fusion proteins and their roles in the lineage commitment of hematopoietic stem cells in comparison to BCR/ABL.

Methodology

All t(9;22) derived proteins were retrovirally expressed in murine hematopoietic stem cells (SL cells) and human umbilical cord blood cells (UCBC). Stem cell potential was determined by replating efficiency, colony forming - spleen and competitive repopulating assays. The leukemic potential of the ABL/BCR fusion proteins was assessed by in a transduction/transplantation model. Effects on the lineage commitment and differentiation were investigated by culturing the cells under conditions driving either myeloid or lymphoid commitment. Expression of key factors of the B-cell differentiation and components of the preB-cell receptor were determined by qRT-PCR.

Principal Findings

Both p96^ABL/BCR and p40^ABL/BCR increased proliferation of early progenitors and the short term stem cell capacity of SL-cells and exhibited own leukemogenic potential. Interestingly, BCR/ABL gave origin exclusively to a myeloid phenotype independently from the culture conditions whereas p96^ABL/BCR and to a minor extent p40^ABL/BCR forced the B-cell commitment of SL-cells and UCBC.

Conclusions/Significance

Our here presented data establish the reciprocal ABL/BCR fusion proteins as second oncogenes encoded by the t(9;22) in addition to BCR/ABL and suggest that ABL/BCR contribute to the determination of the leukemic phenotype through their influence on the lineage commitment.

Epigenetic therapies in haematological malignancies: searching for true targets

Epigenetic alterations complement genetic mutations as a molecular mechanism leading to cell transformation, and maintenance of the cancer phenotype. Of note, they are reversible by pharmacological manipulation of the enzymes responsible for chromatin modification: indeed, epigenetic drugs (histone deacetylase inhibitors and DNA demethylating agents) are currently on the market, inducing proliferative arrest and death of tumor cells. These drugs, however, have been effective only in a few tumor types: the lack of consistent clinical results is mainly due to their use in a poorly targeted approach, since the epigenetic alterations present in cancer cells are mostly unknown. In a few cases (notably, leukemias expressing RAR and MLL fusion proteins), the molecular mechanisms underlying tumor-selective and tumor-specific epigenetic alterations have started to be deciphered. These studies are revealing a dazzling complexity in the mechanisms leading to alterations of the epigenome, and the need of combination therapies targeting different chromatin modifiers to reach an effective reversion of epigenetic alterations.

Differential cell fates induced by all-trans retinoic acid-treated HL-60 human leukemia cells

HL-60 human leukemia cells, differentiated into a neutrophil lineage by all-trans retinoic acid (ATRA) treatment, express three members of the carcinoembryonic antigen (CEA) gene family, CEA-related cell adhesion molecule 1 (CEACAM1; CD66a), CEACAM3 (CD66d), and CEACAM6 (CD66c). CD66d is a neutrophil lineage-specific marker, and CD66a and CD66c are found on epithelial and other cells. HL-60 cells continuously treated with ATRA underwent apoptosis, and cells transiently treated for 1 day underwent cell-cycle arrest, entered into senescence, and exhibited reduced apoptosis with CD66-positive cells accounting for the majority of live cells. CD66 antigens were also induced in NB4 leukemic cells upon continuous treatment with ATRA. NB4 cells underwent apoptosis with a higher frequency in transient versus continuous-treated cells (38% vs. 19% at Day 5), in contrast to HL-60 cells that underwent cell-cycle arrest and senescence when transiently treated with ATRA. CD66 antigens were not induced in transient, ATRA-treated NB4 cells compared with HL-60 cells. Cell-cycle arrest in HL-60 cells involved reduction in expression levels of p21, cyclins D and E, while Rb1 exhibited reduction in protein levels without changes in mRNA levels over the time course of ATRA treatment. Analysis of several proapoptotic proteins implicated the activation of calpain and cleavage of Bax in the intrinsic apoptotic pathway, similar to published studies about the apoptosis of neutrophils. CD1d expression was also induced by ATRA in HL-60 cells and ligation with anti-CD1d antibody-induced apoptosis. In contrast, CD1d-positive primary monocytes were protected from spontaneous apoptosis by CD1d ligation. These studies demonstrate distinct cell fates for ATRA-treated HL-60 cells that provide new insights into ATRA-induced cell differentiation.

Apoptosis related protein 3, an ATRA-upregulated membrane protein arrests the cell cycle at G1/S phase by decreasing the expression of cyclin D1

Human Apr3 was first cloned from HL-60 cells treated by ATRA. In this study, we further demonstrated that Apr3 could be obviously upregulated by ATRA in many other ATRA sensitive cells, suggesting a common role of Apr3 in ATRA effects. Indirect immunofluorescence assay indicates that Apr3 is a membrane protein, while its truncated form without the predicted transmembrane and intracellular domain, was likely a secreted one. Furthermore, FACS analysis showed that Apr3 overexpression could cause an obvious G1/S phase arrest which might be induced by dramatic reduction of cyclin D1 expression. Strikingly, the truncated Apr3 antagonized the negative role of Apr3 on cell cycle and cyclin D1. Taken together, our data suggest that Apr3 should play an important role in ATRA signal pathway and the predicted transmembrane and/or the intracellular domain mediates Apr3 membrane localization and is vital for the negative regulation on cell cycle and cyclin D1.

Phosphoinositide 3-kinase/Akt signaling pathway and its therapeutical implications for human acute myeloid leukemia

The phosphoinositide 3-kinase (PI3K)/Akt signaling pathway is crucial to many aspects of cell growth, survival and apoptosis, and its constitutive activation has been implicated in the both the pathogenesis and the progression of a wide variety of neoplasias. Hence, this pathway is an attractive target for the development of novel anticancer strategies. Recent studies showed that PI3K/Akt signaling is frequently activated in acute myeloid leukemia (AML) patient blasts and strongly contributes to proliferation, survival and drug resistance of these cells. Upregulation of the PI3K/Akt network in AML may be due to several reasons, including FLT3, Ras or c-Kit mutations. Small molecules designed to selectively target key components of this signal transduction cascade induce apoptosis and/or markedly increase conventional drug sensitivity of AML blasts in vitro. Thus, inhibitory molecules are currently being developed for clinical use either as single agents or in combination with conventional therapies. However, the PI3K/Akt pathway is important for many physiological cellular functions and, in particular, for insulin signaling, so that its blockade in vivo might cause severe systemic side effects. In this review, we summarize the existing knowledge about PI3K/Akt signaling in AML cells and we examine the rationale for targeting this fundamental signal transduction network by means of selective pharmacological inhibitors.

Neoplastic stem cells: A novel therapeutic target in clinical oncology

Cancer is among the leading causes of morbidity and mortality in the Western world. Despite recent advances, most therapeutic approaches fail to eradicate the entire neoplastic clone. The remaining cells often develop metastasis and/or recurrences and therefore may represent attractive targets of therapy. A new exciting concept in this regard suggests that each neoplasm represents a heterogeneous population of cells that pertain to long-term tumor growth both in vivo in the natural host and in experimental animals. This concept postulates the existence of small fractions of 'tumor stem cells' that exhibit a capacity for self-renewal and unlimited growth and therefore are distinct from their progeny. Based on these hypotheses, the targeting of neoplastic stem cells is considered indispensable for eradication of the entire clone and for the development of curative treatment approaches. However, tumor stem cells often may be quiescent cells and may express a different profile of targets compared with 'more mature' tumor cells. Therefore, current efforts have attempted to characterize target expression profiles in cancer stem cells in various malignancies. In the this review, the authors have provided a brief summary of the current knowledge of neoplastic stem cells and the application of respective concepts in translational oncology with the ultimate objective of improving anticancer therapy.

Increased expression of cyclin A1 protein is associated with all-trans retinoic acid-induced apoptosis

Deregulated cell growth and inhibition of apoptosis are hallmarks of cancer. All-trans retinoic acid induces clinical remission in patients with acute promyelocytic leukemia by inhibiting cell growth and inducing differentiation and apoptosis of the leukemic blasts. An important role of the cell cycle regulatory protein, cyclin A1, in the development of acute myeloid leukemia has previously been demonstrated in a transgenic mouse model. We have recently shown that there was a direct interaction between cyclin A1 and a major all-trans retinoic acid receptor, RAR alpha, following all-trans retinoic acid treatment of leukemic cells. In the present study, we investigated whether cyclin A1 might be involved in all-trans retinoic acid-induced apoptosis in U-937 leukemic cells. We found that all-trans retinoic acid-induced apoptosis was associated with concomitant increase in cyclin A1 expression. However, there was no induction of cyclin A1 mRNA expression following the all-trans retinoic acid-induced apoptosis. Treatment of cells with a caspase inhibitor was not able to prevent all-trans retinoic acid-induced up-regulation of cyclin A1 expression. Interestingly, induced cyclin A1 expression in U-937 cells led to a significant increase in the proportion of apoptotic cells. Further, U-937 cells overexpressing cyclin A1 appeared to be more sensitive to all-trans retinoic acid-induced apoptosis indicating the ability of cyclin A1 to mediate all-trans retinoic acid-induced apoptosis. Induced cyclin E expression was not able to initiate cell death in U-937 cells. Our results indicate that cyclin A1 might have a role in apoptosis by mediating all-trans retinoic acid-induced apoptosis.

Clinical Pharmacokinetic Study of Arsenic Trioxide in an Acute Promyelocytic Leukemia (APL) Patient: Speciation of Arsenic Metabolites in Serum and Urine

The pharmacokinetics of arsenic species in a Japanese patient with relapsed acute promyelocytic leukemia (APL) treated with arsenic trioxide at a daily dose of 0.08 mg/kg was investigated. After achieving complete remission on Day 35 during the induction therapy of arsenic trioxide, we collected the serum and urine samples on Days 4 and 5 during the consolidation therapy of arsenic trioxide. The concentrations of inorganic arsenic and the methylated metabolites in serum and urine were measured by HPLC/ICP-MS. The patient restricted taking the seafood for 3 d before the start of administration and during the sampling period in order to avoid the influence of arsenic derived from seafood. Arsenite (As(III)), methylarsonic acid (MMAs(V)), and dimethylarsinic acid (DMAs(V)) were detected in serum and urine. The total concentration of As(III), MMAs(V) and DMAs(V) in serum ranged from 18 to 41 microg/l (240-547 nM) during 24 h on Day 4. The amount of total arsenic (As(III)+MMAs(V)+DMAs(V)) in urine was 4464 microg/d on Day 4. These results suggest that not the micro-molar but the nano-molar order of arsenic in serum is sufficient to produce the therapeutic effect on APL cells.

Phosphoinositide 3-kinase/Akt inhibition increases arsenic trioxide-induced apoptosis of acute promyelocytic and T-cell leukaemias

Recent studies suggest that the prosurvival signal transduction pathway involving phosphoinositide 3-kinase (PI3K)/Akt can confer an aggressive, apoptosis-resistant phenotype to acute leukaemia cells. We have investigated the effect of modulating this signalling pathway on the sensitivity of leukaemic cell lines (NB-4, CEM, Jurkat, MOLT-4) and acute promyelocytic primary blasts to apoptosis induced by 1 micromol/l As2O3. Whereas parental NB-4 cells did not display any phosphorylated (active) Akt, CEM, Jurkat and MOLT-4 cells exhibited high levels of Akt activation. Consistently, treatment of NB-4 cells with pharmacological inhibitors of the PI3K/Akt pathway (LY294002, wortmannin) did not increase sensitivity of these cells to arsenic trioxide (As2O3), whereas siRNA knock-down of Akt enhanced As2O3-induced apoptosis of CEM, Jurkat and MOLT-4 cells. Overexpression of a constitutively active Akt cDNA rendered NB-4 cells less susceptible to As2O3. Upon prolonged exposure to As2O3, we isolated a NB-4 cell clone that was resistant to As2O3 and displayed high levels of active Akt. LY294002 treatment of acute promyelocytic primary blasts with elevated Akt phosphorylation levels resulted in an increased sensitivity to As2O3. These results may provide a rationale for the development of combined or sequential treatment with PI3K/Akt inhibitors to improve the efficacy of As2O3 on acute leukaemias and also to overcome As2O3 resistance.

Retinoid/arsenic combination therapy of promyelocytic leukemia: induction of telomerase-dependent cell death

Acute promyelocytic leukemia (APL) is efficiently treated with a cell differentiation inducer, all-trans retinoic acid (ATRA). However, a significant percentage of patients still develop resistance to this treatment. Recently, arsenic trioxide (As2O3), alone or in combination with ATRA, has been identified as an alternative therapy in patients with both ATRA-sensitive and ATRA-resistant APL. Previous investigations restricted the mechanism of this synergism to the modulation and/or degradation of PML-RARalpha oncoprotein through distinct pathways. In this study, using several ATRA maturation-resistant APL cell lines, we demonstrate in vitro that the success of ATRA/As2O3 treatment in APL pathology can be explained, at least in part, by a synergistic effect of these two drugs in triggering downregulation of telomerase efficient enough to cause telomere shortening and subsequent cell death. Such long-term low-dose combinatorial therapy strategies, developed also to avoid acute side effects, reinforce the notion that the antitelomerase strategy, based on a combination of active agents, should now be considered and evaluated not only in APL but also in other malignancies.

Retinoid-induced activation of NF-κB in APL cells is not essential for granulocytic differentiation, but prolongs the life span of mature cells

All-trans retinoic acid (ATRA) significantly improves the survival of patients with acute promyelocytic leukemia (APL) by inducing granulocytic differentiation of leukemia cells. Since an activation of the transcription factor NF-kappaB occurs during ATRA-induced maturation of APL cells, a mechanistic link between these two processes was investigated. Using an in vitro model for APL, we report that ectopic overexpression of a repressor of NF-kappaB activation did not affect granulocytic differentiation. Importantly, NF-kappaB inhibition markedly resulted in a decreased viability of the differentiated cells, which correlated with increased apoptosis. Apoptosis was accompanied by a sustained activation of the c-Jun N-terminal kinase (JNK). Inhibition of JNK by the specific inhibitor SP600125 or by transfection of a dominant-negative mutant of JNK1 reduced the percentage of apoptotic cells, thus showing that JNK activation constitutes a death signal. Furthermore, impairment of NF-kappaB activation resulted in increased levels of reactive oxygen species (ROS) upon ATRA treatment. ROS accumulation was suppressed by the antioxidant butylated hydroxyanisol, which also abolished ATRA-induced JNK activation and apoptosis. Altogether, our results demonstrate an anti-apoptotic effect of NF-kappaB activation during ATRA-induced differentiation of NB4 cells and identify repression of ROS-mediated JNK activation as a mechanism for this effect. Our observations also suggest that NF-kappaB signalling may contribute to an accumulation of mature APL cells and participate in the development of ATRA syndrome.

The Integrity of the Charged Pocket in the BTB/POZ Domain Is Essential for the Phenotype Induced by the Leukemia-Associated t(11;17) Fusion Protein PLZF/RARα

Acute myeloid leukemia is characterized by a differentiation block as well as by an increased self-renewal of hematopoietic precursors in the bone marrow. This phenotype is induced by specific acute myeloid leukemia-associated translocations, such as t(15;17) and t(11;17), which involve an identical portion of the retinoic acid receptor alpha (RARalpha) and either the promyelocytic leukemia (PML) or promyelocytic zinc finger (PLZF) genes, respectively. The resulting fusion proteins form high molecular weight complexes and aberrantly bind several histone deacetylase-recruiting nuclear corepressor complexes. The amino-terminal BTB/POZ domain is indispensable for the capacity of PLZF to form high molecular weight complexes. Here, we studied the role of dimerization and binding to histone deacetylase-recruiting nuclear corepressor complexes for the induction of the leukemic phenotype by PLZF/RARalpha and we show that (a) the BTB/POZ domain mediates the oligomerization of PLZF/RARalpha; (b) mutations that inhibit dimerization of PLZF do the same in PLZF/RARalpha; (c) the PLZF/RARalpha-related block of differentiation requires an intact BTB/POZ domain; (d) the mutations interfering with either folding of the BTB/POZ domain or with its charged pocket prevent the self-renewal of PLZF/RARalpha-positive hematopoietic stem cells. Taken together, these data provide evidence that the dimerization capacity and the formation of a functionally charged pocket are indispensable for the PLZF/RARalpha-induced leukemogenesis.