Analysis of the p53 and MDM-2 gene in acute myeloid leukemia

Validation of aminodeoxychorismate synthase and anthranilate synthase as novel targets for bispecific antibiotics inhibiting conserved protein-protein interactions

Multi-resistant bacteria are a rapidly emerging threat to modern medicine. It is thus essential to identify and validate novel antibacterial targets that promise high robustness against resistance-mediating mutations. This can be achieved by simultaneously targeting several conserved function-determining protein-protein interactions in enzyme complexes from prokaryotic primary metabolism. Here, we selected two evolutionary related glutamine amidotransferase complexes, aminodeoxychorismate synthase and anthranilate synthase, that are required for the biosynthesis of folate and tryptophan in most prokaryotic organisms. Both enzymes rely on the interplay of a glutaminase and a synthase subunit that is conferred by a highly conserved subunit interface. Consequently, inhibiting subunit association in both enzymes by one competing bispecific inhibitor has the potential to suppress bacterial proliferation. We comprehensively verified two conserved interface hot-spot residues as potential inhibitor-binding sites in vitro by demonstrating their crucial role in subunit association and enzymatic activity. For in vivo target validation, we generated genomically modified Escherichia coli strains in which subunit association was disrupted by modifying these central interface residues. The growth of such strains was drastically retarded on liquid and solid minimal medium due to a lack of folate and tryptophan. Remarkably, the bacteriostatic effect was observed even in the presence of heat-inactivated human plasma, demonstrating that accessible host metabolite concentrations do not compensate for the lack of folate and tryptophan within the tested bacterial cells. We conclude that a potential inhibitor targeting both enzyme complexes will be effective against a broad spectrum of pathogens and offer increased resilience against antibiotic resistance.

IMPORTANCE

Antibiotics are indispensable for the treatment of bacterial infections in human and veterinary medicine and are thus a major pillar of modern medicine. However, the exposure of bacteria to antibiotics generates an unintentional selective pressure on bacterial assemblies that over time promotes the development or acquisition of resistance mechanisms, allowing pathogens to escape the treatment. In that manner, humanity is in an ever-lasting race with pathogens to come up with new treatment options before resistances emerge. In general, antibiotics with novel modes of action require more complex pathogen adaptations as compared to chemical derivates of existing entities, thus delaying the emergence of resistance. In this contribution, we use modified Escherichia coli strains to validate two novel targets required for folate and tryptophan biosynthesis that can potentially be targeted by one and the same bispecific protein-protein interaction inhibitor and promise increased robustness against bacterial resistances.

Discovery of JN122, a Spiroindoline-Containing Molecule that Inhibits MDM2/p53 Protein-Protein Interaction and Exerts Robust In Vivo Antitumor Efficacy

MDM2 and MDM4 cooperatively and negatively regulate p53, while this pathway is often hijacked by cancer cells in favor of their survival. Blocking MDM2/p53 interaction with small-molecule inhibitors liberates p53 from MDM2 mediated degradation, which is an attractive strategy for drug discovery. We reported herein structure-based discovery of highly potent spiroindoline-containing MDM2 inhibitor (-)60 (JN122), which also exhibited moderate activities against MDM4/p53 interactions. In a panel of cancer cell lines harboring wild type p53, (-)60 efficiently promoted activation of p53 and its target genes, inhibited cell cycle progression, and induced cell apoptosis. Interestingly, (-)60 also promoted degradation of MDM4. More importantly, (-)60 exhibited good PK properties and exerted robust antitumor efficacies in a systemic mouse xenograft model of MOLM-13. Taken together, our study showcases a class of potent MDM2 inhibitors featuring a novel spiro-indoline scaffold, which is promising for future development targeting cancer cells with wild-type p53.

Drivers of de novo Serine/Glycine synthesis in acute leukemia

Cancer cells hijack metabolic pathways in order to provide themselves with building blocks to support their proliferation and survival. Upregulation and addiction to de novo serine/glycine synthesis is an example of metabolic rewiring in cancer cells whereby serine and glycine are synthesised via a side branch of glycolysis. In this review, we focus on upregulation of endogenous serine/glycine production in acute leukemia, namely T-cell acute leukemia (T-ALL) and acute myeloid leukemia (AML). Several genetic lesions directly driving the serine/glycine addiction in acute leukemia have been established. Additionally, indirect regulation of de novo serine/glycine synthesis is observed in acute leukemia.

Reduced murine double minute 2 and 4 protein, but not messenger RNA , expression is associated with more severe disease in myelodysplastic syndromes and acute myeloblastic leukaemia

The human homologues of murine double minute 2 (MDM2) and 4 (MDM4) negatively regulate p53 tumour suppressor activity and are reported to be frequently overexpressed in human malignancies, prompting clinical trials with drugs that prevent interactions between MDM2/MDM4 and p53. Bone marrow samples from 111 patients with acute myeloblastic leukaemia, myelodysplastic syndrome or chronic myelomonocytic leukaemia were examined for protein (fluorescence-activated cell sorting) and messenger RNA (mRNA) expression (quantitative polymerase chain reaction) of MDM2, MDM4 and tumour protein p53 (TP53). Low protein expression of MDM2 and MDM4 was observed in immature cells from patients with excess of marrow blasts (>5%) compared with CD34⁺ /CD45^low cells from healthy donors and patients without excess of marrow blasts (<5%). The mRNA levels were indistinguishable in all samples examined regardless of disease status or blast levels. Low MDM2 and MDM4 protein expression were correlated with poor survival. These data show a poor correlation between mRNA and protein expression levels, suggesting that quantitative flow cytometry analysis of protein expression levels should be used to predict and validate the efficacy of MDM2 and MDM4 inhibitors. These findings show that advanced disease is associated with reduced MDM2 and MDM4 protein expression and indicate that the utility of MDM2 and MDM4 inhibitors may have to be reconsidered in the treatment of advanced myeloid malignancies.

MDM2 inhibitor APG-115 exerts potent antitumor activity and synergizes with standard-of-care agents in preclinical acute myeloid leukemia models

Acute myeloid leukemia (AML) is a clinically and genetically heterogeneous clonal disease associated with unmet medical needs. Paralleling the pathology of other cancers, AML tumorigenesis and propagation can be ascribed to dysregulated cellular processes, including apoptosis. This function and others are regulated by tumor suppressor P53, which plays a pivotal role in leukemogenesis. Opposing P53-mediated activities is the mouse double minute 2 homolog (MDM2), which promotes P53 degradation. Because the TP53 mutation rate is low, and MDM2 frequently overexpressed, in patients with leukemia, targeting the MDM2-P53 axis to restore P53 function has emerged as an attractive AML treatment strategy. APG-115 is a potent MDM2 inhibitor under clinical development for patients with solid tumors. In cellular cultures and animal models of AML, we demonstrate that APG-115 exerted substantial antileukemic activity, as either a single agent or when combined with standard-of-care (SOC) hypomethylating agents azacitidine (AZA) and decitabine (DAC), or the DNA-damaging agent cytarabine (Ara-C). By activating the P53/P21 pathway, APG-115 exhibited potent antiproliferative and apoptogenic activities, and induced cell cycle arrest, in TP53 wild-type AML lines. In vivo, APG-115 significantly reduced tumor burden and prolonged survival. Combinations of APG-115 with SOC treatments elicited synergistic antileukemic activity. To explain these effects, we propose that APG-115 and SOC agents augment AML cell killing by complementarily activating the P53/P21 pathway and upregulating DNA damage. These findings and the emerging mechanism of action afford a sound scientific rationale to evaluate APG-115 (with or without SOC therapies) in patients with AML.

An expert overview of emerging therapies for acute myeloid leukemia: novel small molecules targeting apoptosis, p53, transcriptional regulation and metabolism

INTRODUCTION

Acute myeloid leukemia (AML) is an aggressive malignancy of clonal myeloid precursor cells. Curative therapy has classically involved the use of intensive induction chemotherapy followed by consolidation with additional chemotherapy or allogeneic hematopoietic stem cell transplant. For many patients, such an approach is prohibitive because of high treatment-related toxicities. Advancements in the molecular understanding of AML have led to the introduction of new targeted therapies that are changing the treatment landscape for AML.

AREAS COVERED

We review emerging small molecule inhibitors that have shown preclinical efficacy for the treatment of AML. The compounds discussed affect apoptosis, p53-mediated interactions, transcriptional regulation, and cellular metabolism. We performed a literature search of PubMed and primarily included relevant sources published from 2000 to the present, though earlier sources are also referenced.

EXPERT OPINION

Most clinical trials for AML currently employ novel targeted therapies that demonstrate promising activity in preclinical models. We anticipate that new small molecule inhibitors will continue to enter the clinical realm and alter the treatment paradigm for AML. In a field where clinical advancement was comparatively slow for many years, it appears that we are now starting to see the rapid growth borne out of the deepening molecular understanding of AML.

DCK is an Unfavorable Prognostic Biomarker and Correlated With Immune Infiltrates in Liver Cancer

BACKGROUND

The biological function of deoxycytidine kinase in tumor is not yet clear, and there are a few studies relating to the correlation of deoxycytidine kinase gene with the occurrence and development of liver cancer.

METHODS

The messenger RNA expression of deoxycytidine kinase was analyzed with the use of the UALCAN and GEPIA database. Moreover, we assessed the function of deoxycytidine kinase on clinical prognosis with Kaplan-Meier plotter database. The relationship between deoxycytidine kinase and cancer immune infiltrates was investigated via Tumor Immune Estimation Resource site. Furthermore, Tumor Immune Estimation Resource was also used to evaluate the correlations between the expression of deoxycytidine kinase and gene marker sets of immune infiltrates.

RESULTS

The deoxycytidine kinase messenger RNA level significantly upregulated in patients with liver cancer compared to normal liver samples. Moreover, the increased expression of deoxycytidine kinase messenger RNA was closely associated with reduced overall survival and disease-free survival in all liver cancers. In addition, deoxycytidine kinase expression displayed a strong correlation with infiltrating levels of macrophages, neutrophils, and dendritic cells in liver cancer, and deoxycytidine kinase expression was positively correlated with diverse immune marker sets in liver cancer.

CONCLUSIONS

All the above findings suggested that increased expression of deoxycytidine kinase was significantly related to unfavorable prognosis in patients with liver cancer. And deoxycytidine kinase is correlated with immune infiltrating levels, including those of B cells, macrophages, neutrophils, and dendritic cells in patients with liver cancer. These findings suggest that deoxycytidine kinase can be used as a prognostic biomarker for determining prognosis and immune infiltration in liver cancer. And deoxycytidine kinase is a potential target for liver cancer therapy, and these preliminary findings require further study to determine whether deoxycytidine kinase-targeting reagents might be developed for clinical application in liver cancer.

Dual inhibition of MDMX and MDM2 as a therapeutic strategy in leukemia

The tumor suppressor p53 is often inactivated via its interaction with endogenous inhibitors mouse double minute 4 homolog (MDM4 or MDMX) or mouse double minute 2 homolog (MDM2), which are frequently overexpressed in patients with acute myeloid leukemia (AML) and other cancers. Pharmacological disruption of both of these interactions has long been sought after as an attractive strategy to fully restore p53-dependent tumor suppressor activity in cancers with wild-type p53. Selective targeting of this pathway has thus far been limited to MDM2-only small-molecule inhibitors, which lack affinity for MDMX. We demonstrate that dual MDMX/MDM2 inhibition with a stapled α-helical peptide (ALRN-6924), which has recently entered phase I clinical testing, produces marked antileukemic effects. ALRN-6924 robustly activates p53-dependent transcription at the single-cell and single-molecule levels and exhibits biochemical and molecular biological on-target activity in leukemia cells in vitro and in vivo. Dual MDMX/MDM2 inhibition by ALRN-6924 inhibits cellular proliferation by inducing cell cycle arrest and apoptosis in cell lines and primary AML patient cells, including leukemic stem cell-enriched populations, and disrupts functional clonogenic and serial replating capacity. Furthermore, ALRN-6924 markedly improves survival in AML xenograft models. Our study provides mechanistic insight to support further testing of ALRN-6924 as a therapeutic approach in AML and other cancers with wild-type p53.

Lanthanide-doped nanoparticles conjugated with an anti-CD33 antibody and a p53-activating peptide for acute myeloid leukemia therapy

Roughly one third of all human cancers are attributable to the functional inhibition of the tumor suppressor protein p53 by its two negative regulators MDM2 and MDMX, making dual-specificity peptide antagonists of MDM2 and MDMX highly attractive drug candidates for anticancer therapy. Two pharmacological barriers, however, remain a major obstacle to the development of peptide therapeutics: susceptibility to proteolytic degradation in vivo and inability to traverse the cell membrane. Here we report the design of a fluorescent lanthanide oxyfluoride nanoparticle (LONp)-based multifunctional peptide drug delivery system for potential treatment of acute myeloid leukemia (AML) that commonly harbors wild type p53, high levels of MDM2 and/or MDMX, and an overexpressed cell surface receptor, CD33. We conjugated to LONp via metal-thiolate bonds a dodecameric peptide antagonist of both MDM2 and MDMX, termed PMI, and a CD33-targeted, humanized monoclonal antibody to allow for AML-specific intracellular delivery of a stabilized PMI. The resultant nanoparticle antiCD33-LONp-PMI, while nontoxic to normal cells, induced apoptosis of AML cell lines and primary leukemic cells isolated from AML patients by antagonizing MDM2 and/or MDMX to activate the p53 pathway. Fluorescent antiCD33-LONp-PMI also enabled real-time visualization of a series of apoptotic events in AML cells, proving a useful tool for possible disease tracking and treatment response monitoring. Our studies shed light on the development of antiCD33-LONp-PMI as a novel class of antitumor agents, which, if further validated, may help targeted molecular therapy of AML.

Gene and protein analysis reveals that p53 pathway is functionally inactivated in cytogenetically normal Acute Myeloid Leukemia and Acute Promyelocytic Leukemia

Background

Mechanisms that inactivate the p53 pathway in Acute Myeloid Leukemia (AML), other than rare mutations, are still not well understood.

Methods

We performed a bioinformatics study of the p53 pathway function at the gene expression level on our collection of 1153 p53-pathway related genes. Publically available Affymetrix data of 607 de-novo AML patients at diagnosis were analyzed according to the patients cytogenetic, FAB and molecular mutations subtypes. We further investigated the functional status of the p53 pathway in cytogenetically normal AML (CN-AML) and Acute Promyelocytic Leukemia (APL) patients using bioinformatics, Real-Time PCR and immunohistochemistry.

Results

We revealed significant and differential alterations of p53 pathway-related gene expression in most of the AML subtypes. We found that p53 pathway-related gene expression was not correlated with the accepted grouping of AML subtypes such as by cytogenetically-based prognosis, morphological stage or by the type of molecular mutation. Our bioinformatic analysis revealed that p53 is not functional in CN-AML and APL blasts at inducing its most important functional outcomes: cell cycle arrest, apoptosis, DNA repair and oxidative stress defense. We revealed transcriptional downregulation of important p53 acetyltransferases in both CN-AML and APL, accompanied by increased Mdmx protein expression and inadequate Chk2 protein activation.

Conclusions

Our bioinformatic analysis demonstrated that p53 pathway is differentially inactivated in different AML subtypes. Focused gene and protein analysis of p53 pathway in CN-AML and APL patients imply that functional inactivation of p53 protein can be attributed to its impaired acetylation. Our analysis indicates the need in further accurate evaluation of p53 pathway functioning and regulation in distinct subtypes of AML.

Electronic supplementary material

The online version of this article (doi:10.1186/s12920-017-0249-2) contains supplementary material, which is available to authorized users.

Superior anti-tumor activity of the MDM2 antagonist idasanutlin and the Bcl-2 inhibitor venetoclax in p53 wild-type acute myeloid leukemia models

Background

Venetoclax, a small molecule BH3 mimetic which inhibits the anti-apoptotic protein Bcl-2, and idasanutlin, a selective MDM2 antagonist, have both shown activity as single-agent treatments in pre-clinical and clinical studies in acute myeloid leukemia (AML). In this study, we deliver the rationale and molecular basis for the combination of idasanutlin and venetoclax for treatment of p53 wild-type AML.

Methods

The effect of idasanutlin and venetoclax combination on cell viability, apoptosis, and cell cycle progression was investigated in vitro using established AML cell lines. In vivo efficacy was demonstrated in subcutaneous and orthotopic xenograft models generated in female nude or non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mice. Mode-of-action analyses were performed by means of cell cycle kinetic studies, RNA sequencing as well as western blotting experiments.

Results

Combination treatment with venetoclax and idasanutlin results in synergistic anti-tumor activity compared with the respective single-agent treatments in vitro, in p53 wild-type AML cell lines, and leads to strongly superior efficacy in vivo, in subcutaneous and orthotopic AML models. The inhibitory effects of idasanutlin were cell-cycle dependent, with cells arresting in G1 in consecutive cycles and the induction of apoptosis only evident after cells had gone through at least two cell cycles. Combination treatment with venetoclax removed this dependency, resulting in an acceleration of cell death kinetics. As expected, gene expression studies using RNA sequencing showed significant alterations to pathways associated with p53 signaling and cell cycle arrest (CCND1 pathway) in response to idasanutlin treatment. Only few gene expression changes were observed for venetoclax treatment and combination treatment, indicating that their effects are mediated mainly at the post-transcriptional level. Protein expression studies demonstrated that inhibition of the anti-apoptotic protein Mcl-1 contributed to the activity of venetoclax and idasanutlin, with earlier inhibition of Mcl-1 in response to combination treatment contributing to the superior combined activity. The role of Mcl-1 was confirmed by small hairpin RNA gene knockdown studies.

Conclusions

Our findings provide functional and molecular insight on the superior anti-tumor activity of combined idasanutlin and venetoclax treatment in AML and support its further exploration in clinical studies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0280-3) contains supplementary material, which is available to authorized users.

Regain control of p53: Targeting leukemia stem cells by isoform-specific HDAC inhibition

Leukemia stem cells (LSCs) are self-renewable, leukemia-initiating populations that are often resistant to traditional chemotherapy and tyrosine kinase inhibitors currently used for treatment of acute or chronic myeloid leukemia. The persistence and continued acquisition of mutations in resistant LSCs represent a major cause of refractory disease and/or relapse after remission. Understanding the mechanisms regulating LSC growth and survival is critical in devising effective therapies that will improve treatment response and outcome. Several recent studies indicate that the p53 tumor suppressor pathway is often inactivated in de novo myeloid leukemia through oncogenic-specific mechanisms, which converge on aberrant p53 protein deacetylation. Here, we summarize our current understanding of the various mechanisms underlying deregulation of histone deacetylases (HDACs), which could be exploited to restore p53 activity and enhance targeting of LSCs in molecularly defined patient subsets.

Rational Combinations of Targeted Agents in AML

Despite modest improvements in survival over the last several decades, the treatment of AML continues to present a formidable challenge. Most patients are elderly, and these individuals, as well as those with secondary, therapy-related, or relapsed/refractory AML, are particularly difficult to treat, owing to both aggressive disease biology and the high toxicity of current chemotherapeutic regimens. It has become increasingly apparent in recent years that coordinated interruption of cooperative survival signaling pathways in malignant cells is necessary for optimal therapeutic results. The modest efficacy of monotherapy with both cytotoxic and targeted agents in AML testifies to this. As the complex biology of AML continues to be elucidated, many “synthetic lethal” strategies involving rational combinations of targeted agents have been developed. Unfortunately, relatively few of these have been tested clinically, although there is growing interest in this area. In this article, the preclinical and, where available, clinical data on some of the most promising rational combinations of targeted agents in AML are summarized. While new molecules should continue to be combined with conventional genotoxic drugs of proven efficacy, there is perhaps a need to rethink traditional philosophies of clinical trial development and regulatory approval with a focus on mechanism-based, synergistic strategies.

p53 protein expression independently predicts outcome in patients with lower-risk myelodysplastic syndromes with del(5q)

Del(5q) myelodysplastic syndromes defined by the International Prognostic Scoring System as low- or intermediate-1-risk (lower-risk) are considered to have an indolent course; however, recent data have identified a subgroup of these patients with more aggressive disease and poorer outcomes. Using deep sequencing technology, we previously demonstrated that 18% of patients with lower-risk del(5q) myelodysplastic syndromes carry TP53 mutated subclones rendering them at higher risk of progression. In this study, bone marrow biopsies from 85 patients treated with lenalidomide in the MDS-004 clinical trial were retrospectively assessed for p53 expression by immunohistochemistry in association with outcome. Strong p53 expression in ≥ 1% of bone marrow progenitor cells, observed in 35% (30 of 85) of patients, was significantly associated with higher acute myeloid leukemia risk (P=0.0006), shorter overall survival (P=0.0175), and a lower cytogenetic response rate (P=0.009), but not with achievement or duration of 26-week transfusion independence response. In a multivariate analysis, p53-positive immunohistochemistry was the strongest independent predictor of transformation to acute myeloid leukemia (P=0.0035). Pyrosequencing analysis of laser-microdissected cells with strong p53 expression confirmed the TP53 mutation, whereas cells with moderate expression predominantly had wild-type p53. This study validates p53 immunohistochemistry as a strong and clinically useful predictive tool in patients with lower-risk del(5q) myelodysplastic syndromes. This study was based on data from the MDS 004 trial (clinicaltrials.gov identifier: NCT00179621).

Prognostic impact and targeting of CRM1 in acute myeloid leukemia

Chromosomal region maintenance 1 (CRM1) is a nuclear export receptor recognizing proteins bearing a leucine-rich nuclear export signal. CRM1 is involved in nuclear export of tumor suppressors such as p53. We investigated the prognostic significance of CRM1 in acute myeloid leukemia (AML) and effects of a novel small-molecule selective inhibitor of CRM1. CRM1 protein expression was determined in 511 newly diagnosed AML patients and was correlated with mouse double minute 2 (MDM2) and p53 levels. High CRM1 expression was associated with short survival of patients and remained an adverse prognostic factor in multivariate analysis. CRM1 inhibitor KPT-185 induced mainly full-length p53 and apoptosis in a p53-dependent manner, whereas inhibition of proliferation was p53 independent. Patient samples with p53 mutations showed low sensitivity to KPT-185. Nuclear retention of p53 induced by CRM1 inhibition synergized with increased levels of p53 induced by MDM2 inhibition in apoptosis induction. KPT-185 and Nutlin-3a, alone and in combination, induced synergistic apoptosis in patient-derived CD34(+)/CD38(-) AML, but not in normal progenitor cells. Data suggest that CRM1 exerts an antiapoptotic function and is highly prognostic in AML. We propose a novel combinatorial approach for the therapy of AML, aimed at maximal activation of p53-mediated apoptosis by concomitant MDM2 and CRM1 inhibition.

JAK2(V617F) negatively regulates p53 stabilization by enhancing MDM2 via La expression in myeloproliferative neoplasms

JAK2(V617F) is a gain of function mutation that promotes cytokine-independent growth of myeloid cells and accounts for a majority of myeloproliferative neoplasms (MPN). Mutations in p53 are rarely found in these diseases before acute leukemia transformation, but this does not rule out a role for p53 deregulation in disease progression. Using Ba/F3-EPOR cells and ex vivo cultured CD34(+) cells from MPN patients, we demonstrate that expression of JAK2(V617F) affected the p53 response to DNA damage. We show that E3 ubiquitin ligase MDM2 accumulated in these cells, due to an increased translation of MDM2 mRNA. Accumulation of the La autoantigen, which interacts with MDM2 mRNA and promotes its translation, was responsible for the increase in MDM2 protein level and the subsequent degradation of p53 after DNA damage. Downregulation of La protein or cell treatment with nutlin-3, a MDM2 antagonist, restored the p53 response to DNA damage and the cytokine-dependence of Ba/F3-EPOR-JAK2(V617F) cells. Altogether, these data indicate that the JAK2(V617F) mutation affects p53 response to DNA damage through the upregulation of La antigen and accumulation of MDM2. They also suggest that p53 functional inactivation accounts for the cytokine hypersensitivity of JAK2(V617F) MPN and might have a role in disease progression.

Integrated genomic analyses identify WEE1 as a critical mediator of cell fate and a novel therapeutic target in acute myeloid leukemia

Acute myeloid leukemia (AML) remains a therapeutic challenge despite increasing knowledge about the molecular origins of the disease, as the mechanisms of AML cell escape from chemotherapy remain poorly defined. We hypothesized that AML cells are addicted to molecular pathways in the context of chemotherapy and used complementary approaches to identify these addictions. Using novel molecular and computational approaches, we performed genome-wide shRNA screens to identify proteins that mediate AML cell fate after cytarabine exposure, gene expression profiling of AML cells exposed to cytarabine to identify genes with induced expression in this context, and examination of existing gene expression data from primary patient samples. The integration of these independent analyses strongly implicates cell cycle checkpoint proteins, particularly WEE1, as critical mediators of AML cell survival after cytarabine exposure. Knockdown of WEE1 in a secondary screen confirmed its role in AML cell survival. Pharmacologic inhibition of WEE1 in AML cell lines and primary cells is synergistic with cytarabine. Further experiments demonstrate that inhibition of WEE1 prevents S-phase arrest induced by cytarabine, broadening the functions of WEE1 that may be exploited therapeutically. These data highlight the power of integrating functional and descriptive genomics, and identify WEE1 as potential therapeutic target in AML.

p53 stabilization induces apoptosis in chronic myeloid leukemia blast crisis cells

Philadelphia chromosome positive chronic myeloid leukemia has a progressive course starting in a benign phase and terminating in a blastic phase. In this study, we show that human homolog double minute 2 (HDM2) inhibition, with MI-219-a novel compound, and consequently p53 stabilization induce chronic myeloid leukemia (CML) blast crisis cells to undergo apoptosis regardless of the presence of the T315I mutation in the BCR-ABL kinase domain. The response to MI-219 is associated with the downregulation of c-Myc and the induction of p21(WAF1). The p53 target and pro-apoptotic proteins PUMA, Noxa and Bax are induced, whereas full length Bid protein decreases with increased activity of pro-apoptotic cleaved Bid, and decrease of Mcl-1 is observed by increased caspase activity. CD95/FAS (FAS antigen) receptor is also induced by MI-219, indicating that both intrinsic and extrinsic apoptotic responses are transcriptionally induced. In addition, p53 protein accumulates in the mitochondrial fraction of treated cells involved in transcription-independent induction of apoptosis. We conclude that HDM-2 inhibition with MI-219 effectively induces p53-dependent apoptosis in most blast crisis CML cells, with or without BCR-ABL mutation(s).

p53 flow cytometry evaluation in leukemias: correlation to factors affecting clinical outcome

p53 is a cell cycle checkpoint control protein that assesses DNA damage and acts as a transcription factor regulating genes, which control cell growth, DNA repair, and apoptosis. p53 mutations have been found in a wide variety of different cancers including flow cytometric assessment of p53 protein expression using anti-p53 monoclonal antibodies. We studied p53 protein expression by flow cytometry (FC) assay in 223 blood and/or bone marrow samples from 72 patients with chronic myeloid leukemia (CML): 54 in chronic phase (CML-CP), 7 in accelerated phase (CML-AP), and 11 in blastic phase (CML-BP); 64 patients with chronic lymphoid leukemia (CLL): (34 at diagnosis, 21 in previously treated, and 9 with Richter's syndrome); 44 patients with acute lymphoid leukemia (ALL): 36 at diagnosis and 8 in relapse; and 43 acute myeloid leukemia (AML): 27 de novo, 7 in relapse, and 9 secondary. p53 protein expression was observed in 64 of 223 patient's samples: 14/64 (21.9%) CLL, 13/44 (29.5%) ALL, 19/43 (44.2%) AML, and 17/72 (23.6%) CML. Highest levels were detected in the advanced phases of CLL, ALL, and CML. In addition, in patients with AML, high levels of p53 expression were detected in secondary and relapse disease and also in de novo AML cases. Our results demonstrated that p53 expression levels are strongly associated with advanced disease. On the basis of these results, we concluded that FC can be a reliable approach to study p53 protein expression in leukemic patients.

Blockade of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase and murine double minute synergistically induces Apoptosis in acute myeloid leukemia via BH3-only proteins Puma and Bim

Molecular aberrations of the Ras/Raf/mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK)/ERK and/or Murine double minute (MDM2)/p53 signaling pathways have been reported in 80% and 50% of primary acute myeloid leukemia (AML) samples and confer poor outcome. In this study, antileukemic effects of combined MEK inhibition by AZD6244 and nongenotoxic p53 activation by MDM2 antagonist Nutlin-3a were investigated. Simultaneous blockade of MEK and MDM2 signaling by AZD6244 and Nutlin-3a triggered synergistic proapoptotic responses in AML cell lines [combination index (CI) = 0.06 +/- 0.03 and 0.43 +/- 0.03 in OCI/AML3 and MOLM13 cells, respectively] and in primary AML cells (CI = 0.52 +/- 0.01). Mechanistically, the combination upregulated levels of BH3-only proteins Puma and Bim, in part via transcriptional upregulation of the FOXO3a transcription factor. Suppression of Puma and Bim by short interfering RNA rescued OCI/AML3 cells from AZD/Nutlin-induced apoptosis. These results strongly indicate the therapeutic potential of combined MEK/MDM2 blockade in AML and implicate Puma and Bim as major regulators of AML cell survival.

Apoptosis in leukemias: regulation and therapeutic targeting

Nearly 25 years after the seminal publication of John Foxton Kerr that first described apoptosis, the process of regulated cell death, our understanding of this basic physiological phenomenon is far from complete [39]. From cardiovascular disease to cancer, apoptosis has assumed a central role with broad ranging therapeutic implications that depend on a complete understanding of this process, yet have also identified an incredibly complex regulatory system that is critical for development and is at the core of many diseases, challenging scientist and clinicians to step into its molecular realm and modulate its circuitry for therapeutic purposes. This chapter will review our understanding of the molecular circuitry that controls apoptosis in leukemia and the pharmacological manipulations of this pathway that may yield therapeutic benefit.

Simultaneous activation of p53 and inhibition of XIAP enhance the activation of apoptosis signaling pathways in AML

Activation of p53 by murine double minute (MDM2) antagonist nutlin-3a or inhibition of X-linked inhibitor of apoptosis (XIAP) induces apoptosis in acute myeloid leukemia (AML) cells. We demonstrate that concomitant inhibition of MDM2 by nutlin-3a and of XIAP by small molecule antagonists synergistically induced apoptosis in p53 wild-type OCI-AML3 and Molm13 cells. Knockdown of p53 by shRNA blunted the synergy, and down-regulation of XIAP by antisense oligonucleotide (ASO) enhanced nutlin-3a-induced apoptosis, suggesting that the synergy was mediated by p53 activation and XIAP inhibition. This is supported by data showing that inhibition of both MDM2 and XIAP by their respective ASOs induced significantly more cell death than either ASO alone. Importantly, p53 activation and XIAP inhibition enhanced apoptosis in blasts from patients with primary AML, even when the cells were protected by stromal cells. Mechanistic studies demonstrated that XIAP inhibition potentiates p53-induced apoptosis by decreasing p53-induced p21 and that p53 activation enhances XIAP inhibition-induced cell death by promoting mitochondrial release of second mitochondria-derived activator of caspases (SMAC) and by inducing the expression of caspase-6. Because both XIAP and p53 are presently being targeted in ongoing clinical trials in leukemia, the combination strategy holds promise for expedited translation into the clinic.

Tumor suppressor genes in myeloid differentiation and leukemogenesis

Tumor suppressor genes, such as p53, RB, the INK4-ARF family and PML, suppress malignant transformation by regulating cell cycle progression, ensuring the fidelity of DNA replication and chromosomal segregation, or by inducing apoptosis in response to potentially deleterious events. In myeloid leukemia, hematopoietic differentiation resulting from highly coordinated, stage-wise expression of myeloid transcription and soluble signaling factors is disrupted leading to a block in terminal differentiation and uncontrolled proliferation. This virtually always involves functional inactivation or genetic disruption of one or several tumor suppressor genes in order to circumvent their checkpoint control and apoptosis-inducing functions. Hence, reactivation of tumor suppressor gene function has therapeutic potential and can possibly enhance conventional cytotoxic chemotherapy. In this review, we focus on the role of different tumor suppressor genes in myeloid differentiation and leukemogenesis, and discuss implications for therapy.

The dual PI3 kinase/mTOR inhibitor PI-103 prevents p53 induction by Mdm2 inhibition but enhances p53-mediated mitochondrial apoptosis in p53 wild-type AML

Activation of the phosphatidylinositol-3 kinase/Akt/mammalian target of the rapamycin (PI3K/Akt/mTOR) pathway and inactivation of wild-type p53 by murine double minute 2 homologue (Mdm2) overexpression are frequent molecular events in acute myeloid leukemia (AML). We investigated the interaction of PI3K/Akt/mTOR and p53 pathways after their simultaneous blockade using the dual PI3K/mTOR inhibitor PI-103 and the Mdm2 inhibitor Nutlin-3. We found that PI-103, which itself has modest apoptogenic activity, acts synergistically with Nutlin-3 to induce apoptosis in a wild-type p53-dependent fashion. PI-103 synergized with Nutlin-3 to induce Bax conformational change and caspase-3 activation, despite its inhibitory effect on p53 induction. The PI-103/Nutlin-3 combination caused profound dephosphorylation of 4E-BP1 and decreased expression of many proteins including Mdm2, p21, Noxa, Bcl-2 and survivin, which can affect mitochondrial stability. We suggest that PI-103 actively enhances downstream p53 signaling and that a combination strategy aimed at inhibiting PI3K/Akt/mTOR signaling and activating p53 signaling is potentially effective in AML, where TP53 mutations are rare and downstream p53 signaling is intact.

Triptolide sensitizes AML cells to TRAIL-induced apoptosis via decrease of XIAP and p53-mediated increase of DR5

Acute myeloid leukemia (AML) cells are relatively resistant to tumor necrosis factor alpha-related apoptosis-inducing ligand (TRAIL). We previously reported that triptolide, a potent anticancer agent from a Chinese herb, decreases XIAP in leukemic cells. We evaluated the combination of triptolide and TRAIL and found synergistic promotion of apoptosis in AML cells. XIAP-overexpressing U937 cells (U937XIAP) were more resistant to TRAIL than U937neo cells, and inhibition of XIAP with the small-molecule inhibitor 1396-11 enhanced TRAIL-induced apoptosis, implying XIAP as a resistance factor in AML. Furthermore, triptolide increased DR5 levels in OCI-AML3, while the DR5 increase was blunted in p53-knockdown OCI-AML3 and p53-mutated U937 cells, confirming a role for p53 in the regulation of DR5. In support of this finding, disruption of MDM2-p53 binding with subsequent increase in p53 levels by nutlin3a increased DR5 levels and sensitized OCI-AML3 cells to TRAIL. The combination of 1396-11 plus nutlin3a plus TRAIL was more effective than either the 1396-11 and TRAIL or nutlin3a and TRAIL combinations in OCI-AML3 cells, further supporting the role of triptolide as a sensitizer to TRAIL-induced apoptosis in part by independent modulation of XIAP expression and p53 signaling. Thus, the combination of triptolide and TRAIL may provide a novel strategy for treating AML by overcoming critical mechanisms of apoptosis resistance.

Expression of the regulatory cell cycle proteins p21, p27, p14, p16, p53, mdm2, and cyclin E in bone marrow biopsies with acute myeloid leukemia. Correlation with patients' survival

Cell cycle control is a crucial event in normal hematopoiesis, and abnormalities of regulatory cell cycle genes have been found to contribute to the development of many hematologic malignancies. The present study investigates the immunohistochemical expression of seven essential cell cycle proteins (p21, p27, p14, p16, p53, mdm2, and cyclin E) in paraffin-embedded sections from 42 bone marrow biopsies obtained from an equal number of patients with newly diagnosed acute myeloid leukemia (AML). This study revealed (i) a high frequency of p53+/mdm2-/p21-phenotype, which is probably a result of p53 gene mutation and/or inhibition of mdm2 action by p14(ARF); (ii) expression of p27+/cyclinE-phenotype in most cases, suggesting that p27 may act as a potent cyclin-dependent kinase inhibitor; (iii) expression of p16 only in very few cases; and (iv) no relationship between the expression of any of the above proteins and survival as well as histologic subtype.

MDM2 is recognized as a tumor-associated antigen in chronic lymphocytic leukemia by CD8+ autologous T lymphocytes

OBJECTIVE

Tumor-associated antigens (TAA) are the basis for antigen-specific immunotherapy. The human homolog of the murine double-minute 2 oncoprotein (MDM2) is a putative TAA because it is overexpressed in several malignancies, including chronic lymphocytic leukemia (CLL) cells compared with normal B lymphocytes.

PATIENTS AND METHODS

Autologous, MDM2-specific human leukocyte antigen (HLA)-A2-restricted T cells were identified using interferon (IFN)-gamma-ELISPOT assays and HLA-A2/dimer-peptide staining after 4 weeks of in vitro culture.

RESULTS

Using native CLL cells as antigen-presenting cells (APCs), we demonstrate the generation of MDM2-specific T cells in 7/12 CLL patients that recognized specifically the MDM2-derived peptide MDM2(81-88) bound to HLA-A2-dimers while they were inactive against an unrelated MAGE-3 peptide (p = 0.002). After 4 weeks, up to 32.3% of the expanded CD8(+) T cells specifically recognized MDM2(81-88) by HLA-A2-dimer/peptide staining and up to 0.9% of all T cells expanded reacted specifically against this MDM2-derived peptide in the IFN-gamma-ELISPOT assay. If T cells were not expandable using native CLL cells as APC, leukemic cells were stimulated with CD40-ligand to increase the antigen-presenting capacity. This resulted in successful generation of MDM2-specific T cells in three of five remaining cases tested. Additionally, the factor that correlated best with successful generation of antigen-specific T cells in CLL patients was the ability of APCs to secrete IFN-gamma upon stimulation.

CONCLUSION

In summary, MDM2(81-88) was shown for the first time in humans to elicit a functional autologous immune response. MDM2 was demonstrated to be naturally processed and presented as TAA in primary human CLL cells enabling expansion of functional autologous tumor-specific T cells.

MDM2 antagonists induce p53-dependent apoptosis in AML: implications for leukemia therapy

Although TP53 mutations are rare in acute myeloid leukemia (AML), inactivation of wild-type p53 protein frequently occurs through overexpression of its negative regulator MDM2 (murine double minute 2). Recently, small-molecule antagonists of MDM2, Nutlins, have been developed that inhibit the p53-MDM2 interaction and activate p53 signaling. Here, we study the effects of p53 activation by Nutlin-3 in AML cells. Treatment with MDM2 inhibitor triggered several molecular events consistent with induction of apoptosis: loss of mitochondrial membrane potential, caspase activation, phosphatidylserine externalization, and DNA fragmentation. There was a positive correlation in primary AML samples with wild-type p53 between baseline MDM2 protein levels and apoptosis induced by MDM2 inhibition. No induction of apoptosis was observed in AML samples harboring mutant p53. Colony formation of AML progenitors was inhibited in a dose-dependent fashion, whereas normal CD34+ progenitor cells were less affected. Mechanistic studies suggested that Nutlin-induced apoptosis was mediated by both transcriptional activation of proapoptotic Bcl-2 family proteins, and transcription-independent mitochondrial permeabilization resulting from mitochondrial p53 translocation. MDM2 inhibition synergistically enhanced cytotoxicity of cytosine arabinoside and doxorubicin in AML blasts but not in normal hematopoietic progenitor cells. p53 activation by targeting the p53-MDM2 interaction might offer a novel therapeutic strategy for AML that retain wild-type p53.

Impairment of p53 acetylation, stability and function by an oncogenic transcription factor

Mutations of p53 are remarkably rare in acute promyelocytic leukemias (APLs). Here, we demonstrate that the APL-associated fusion proteins PML-RAR and PLZF-RAR directly inhibit p53, allowing leukemic blasts to evade p53-dependent cancer surveillance pathways. PML-RAR causes deacetylation and degradation of p53, resulting in repression of p53 transcriptional activity, and protection from p53-dependent responses to genotoxic stress. These phenomena are dependent on the expression of wild-type PML, acting as a bridge between p53 and PML-RAR. Recruitment of histone deacetylase (HDAC) to p53 and inhibition of p53 activity were abrogated by conditions that either inactivate HDACs or trigger HDAC release from the fusion protein, implicating recruitment of HDAC by PML-RAR as the mechanism underlying p53 inhibition.

Iron deprivation induces apoptosis independently of p53 in human and murine tumour cells

Iron deprivation induces apoptosis in some sensitive cultured tumour cells, while other cells are resistant. In order to elucidate the mechanisms involved in apoptosis induction by iron deprivation, we studied the expression of p53 and the expression of selected p53-regulated genes. To discriminate between changes coupled only with iron deprivation and changes involved in apoptosis induction by iron deprivation, we compared the expression of the genes in sensitive (human Raji, mouse 38C13) versus resistant (human HeLa, mouse EL4) cells under iron deprivation. Iron deprivation was achieved by incubation in a defined iron-free medium. The level of p53 mRNA decreased significantly under iron deprivation in sensitive cells, but it did not change in resistant cells. On the contrary, the level of the p53 protein under iron deprivation was slightly increased in sensitive cells while it was not changed in resistant cells. The activity of p53 was assessed by the expression of selected p53-regulated targets, i.e. p21(WAF1/CIP1) gene, mdm2, bcl-2 and bax. We did not detect any relevant change in mRNA levels as well as in protein levels of these genes under iron deprivation with the exception of p21(WAF1/CIP1). We detected a significant increase in the level of p21 mRNA in both (sensitive and resistant) mouse cell lines tested, however, we did not find any change in both (sensitive and resistant) human cell lines. Moreover, the p21(WAF1/CIP1) protein was accumulated in mouse-sensitive 38C13 cells under iron deprivation while all other cell lines tested, including human-sensitive cell line Raji, did not show any accumulation of p21(WAF1/CIP1) protein. It seems that the p21(WAF1/CIP1) mRNA, as well as protein accumulation, is not specifically coupled with apoptosis induction by iron deprivation and that it is rather cell-line specific. Taken together, we suggest that iron deprivation induces apoptosis at least in some cell types independently of the p53 pathway.

BCR/ABL activates mdm2 mRNA translation via the La antigen

In a BCR/ABL-expressing myeloid precursor cell line, p53 levels were markedly downmodulated. Expression of MDM2, the negative regulator of p53, was upregulated in a tyrosine kinase-dependent manner in growth factor-independent BCR/ABL-expressing cells, and in accelerated phase and blast crisis CML samples. Increased MDM2 expression was associated with enhanced mdm2 mRNA translation, which required the interaction of the La antigen with mdm2 5' UTR. Expression of MDM2 correlated with that of La and was suppressed by La siRNAs and by a dominant negative La mutant, which also enhanced the susceptibility to drug-induced apoptosis of BCR/ABL-transformed cells. By contrast, La overexpression led to increased MDM2 levels and enhanced resistance to apoptosis. Thus, La-dependent activation of mdm2 translation might represent an important molecular mechanism involved in BCR/ABL leukemogenesis.

Clonal evolution in marrows of patients with Shwachman-Diamond syndrome: a prospective 5-year follow-up study

OBJECTIVES

Shwachman-Diamond syndrome (SDS) is characterized by varying degrees of marrow failure. Retrospective studies suggested a high propensity for malignant myeloid transformation into myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). The study's aims were to determine the cellular and molecular characteristics as well as the clinical course of malignant myeloid transformation and clonal marrow disease in patients with SDS.

METHODS

This is a longitudinal prospective study of 14 patients recruited for annual hematological evaluations. Results of baseline and serial hematological assessments for up to 5 years are reported.

RESULTS

Clonal marrow cytogenetic abnormalities (CMCA) were detected in 4 patients (29%) on first testing or at follow-up. The abnormalities were del(20q) in two patients, i(7q) in one, and combined del(20q) and i(7q) in one. The following tests did not distinguish patients with CMCA from other SDS patients: severity of peripheral cytopenia, fetal hemoglobin levels, percentage of marrow CD34+ cells, colony growth from marrow CD34+ cells, cluster-to-colony ratio, marrow stromal function, percentage of marrow apoptosis cells, and granulocyte colony-stimulating factor receptor expression. RAS and p53 mutation analysis and AML blast colony assays were uniformly negative. No patients showed progression into more advanced stages of MDS or into AML. In one patient, the abnormal clone became undetectable after 2 years of follow-up.

CONCLUSIONS

We conclude that although CMCA in SDS is high, progression into advanced stages of MDS or to overt AML may be slow and difficult to predict. Treatment should be cautious since some abnormal clones can regress.

Tumor suppressor genes in normal and malignant hematopoiesis

Over the last decade, a growing number of tumor suppressor genes have been discovered to play a role in tumorigenesis. Mutations of p53 have been found in hematological malignant diseases, but the frequency of these alterations is much lower than in solid tumors. These mutations occur especially as hematopoietic abnormalities become more malignant such as going from the chronic phase to the blast crisis of chronic myeloid leukemia. A broad spectrum of tumor suppressor gene alterations do occur in hematological malignancies, especially structural alterations of p15(INK4A), p15(INK4B) and p14(ARF) in acute lymphoblastic leukemia as well as methylation of these genes in several myeloproliferative disorders. Tumor suppressor genes are altered via different mechanisms, including deletions and point mutations, which may result in an inactive or dominant negative protein. Methylation of the promoter of the tumor suppressor gene can blunt its expression. Chimeric proteins formed by chromosomal translocations (i.e. AML1-ETO, PML-RARalpha, PLZF-RARalpha) can produce a dominant negative transcription factor that can decrease expression of tumor suppressor genes. This review provides an overview of the current knowledge about the involvement of tumor suppressor genes in hematopoietic malignancies including those involved in cell cycle control, apoptosis and transcriptional control.

Mutations in the p53 gene in acute myeloid leukemia patients correlate with poor prognosis

Inactivation of tumor suppressor genes, whose products exert an inhibitory influence on cell cycle progression, can lead to neoplastic transformation. In acute myeloid leukemia (AML), the frequency of p53 gene mutations ranges from 4 to 15% in populations from USA and Europe. In an attempt to investigate the frequency of point mutations in the p53 gene in AML Brazilian patients, DNA samples of 35 patients were studied using PCR-SSCP techniques, screening exons 4-10. Mutations were identified in bone marrow DNA in 5 of the 35 AML patients (14.3%), a frequency similar to those reported for Northern American and European populations. The overall survival of patients with mutations in the p53 gene was significantly shorter than for patients without mutations.

Different p16INK4a and p14ARF expression patterns in acute myeloid leukaemia and normal blood leukocytes

The p16INK4a gene is often disrupted or transcriptionally silenced by CpG island methylation in human cancers. However, in acute myeloid leukaemia (AML) alterations of the INK4a-ARF tumour suppressor locus are rarely found despite the noted variable p16INK4a mRNA and protein levels. The p14ARF, an alternative reading frame protein encoded from the same INK4a-ARF locus, is a potent tumour suppressor functionally linked to p53. There is little known regarding the role of p14ARF in primary human tumours. Therefore, we analysed the expression patterns of these two tumour suppressors in 37 cases of AML. The relative expression of p16INK4a and p14ARF mRNA in AML blasts, measured by a specific p16INK4a/p14ARF multiplex RT-PCR, was significantly shifted towards p14ARF whereas relatively lower levels of p16INK4a were detected. Quantitative RT-PCR revealed significantly higher expression of both transcripts in AML blasts when compared to normal differentiated myeloid cells or CD34+ progenitor cells. Furthermore, a good correlation between p16INK4a protein and mRNA was observed, whereas no correlation was found with p14ARF. Our results suggest: a) increased levels of both p16INK4a and p14ARF may participate in the pathogenesis of AML, b) that high p14ARF mRNA expression might influence p16INK4a transcription and c) that post-transcriptional regulatory mechanisms are important for p14ARF expression.

Mutations with loss of heterozygosity of p53 are common in therapy-related myelodysplasia and acute myeloid leukemia after exposure to alkylating agents and significantly associated with deletion or loss of 5q, a complex karyotype, and a poor prognosis

PURPOSE

To study mutations and loss of heterozygosity (LOH) of p53 in therapy-related myelodysplasia (t-MDS) and acute myeloid leukemia (t-AML).

PATIENTS AND METHODS

Fifty-two unselected patients with t-MDS and 25 patients with t-AML were studied by polymerase chain reaction (PCR)-single-strand conformational polymorphism (SSCP) at the DNA level and by reverse transcriptase (RT)-PCR-SSCP at the mRNA level, and cases with aberrant SSCP patterns were sequenced.

RESULTS

Somatically acquired mutations of p53 were observed in 21 of 77 cases of t-MDS or t-AML, and 19 of these 21 patients had received alkylating agents. Single-base substitutions at A:T pairs were more common in t-MDS and t-AML, whereas single-base substitutions at G:C pairs are most common in MDS and AML de novo and in solid tumors. Six patients demonstrated a cytogenetic loss of 17p13, and these six and an additional nine patients with p53 mutations demonstrated LOH of p53 at the DNA or mRNA level. This suggests a cytogenetic loss of the normal p53 allele in these nine cases combined with duplication of the homologous chromosome 17 carrying the mutated p53 allele. Mutations of p53 were significantly associated with deletion or loss of 5q (P <.0001) and a complex karyotype (P =.0001), but surprisingly were not associated with deletion or loss of 7q (P =.73), and were infrequent in patients with balanced chromosome translocations (P =.03). Mutations of p53 were more common in older patients (P =.036) and were associated with an extremely poor prognosis (P =.014), apparently restricted to the 15 cases with LOH of p53 ( P =.046).

CONCLUSION

Mutations with loss of function of p53 are significantly associated with deletion or loss of 5q in t-MDS and t-AML after previous treatment with alkylating agents and are associated with genetic instability.

Induction of differentiation and apoptosis- a possible strategy in the treatment of adult acute myelogenous leukemia

A differentiation block with accumulation of immature myeloid cells characterizes acute myelogenous leukemia (AML). However, native AML cells often show some morphological signs of differentiation that allow a classification into different subsets, and further differentiation may be induced by exposure to various soluble mediators, e.g., all trans-retinoic acid (ATRA) and several cytokines. Combination therapy with ATRA and chemotherapy should now be regarded as the standard treatment for the acute promyelocytic leukemia variant of AML. Several agents can induce leukemic cell differentiation for other AML subtypes, although these effects differ between patients. Differentiation may then be associated with induction of apoptosis, and differentiation-inducing therapy may therefore become useful in combination with intensive chemotherapy to increase the susceptibility of AML blasts to drug-induced apoptosis. However, it should be emphasized that differentiation and apoptosis can occur as separate events with different regulation in AML cells, and future studies in AML should therefore focus on: A) the identification of new agents with more predictable effects on differentiation and apoptosis; B) the use of clinical and laboratory parameters to define new subsets of AML patients in which differentiation/apoptosis induction has a predictable and beneficial effect, and C) further characterization of how AML blast sensitivity to drug-induced apoptosis is modulated by differentiation induction.

Bcr-Abl protein tyrosine kinase activity induces a loss of p53 protein that mediates a delay in myeloid differentiation

Chronic myeloid leukaemia is a haemopoietic stem cell disorder, the hallmark of which is the expression of the Bcr-Abl Protein Tyrosine Kinase (PTK). We have previously reported that activation of a temperature sensitive Bcr-Abl PTK in the multipotent haemopoietic cell line FDCP-Mix for short periods resulted in subtle changes including, a transient suppression of apoptosis and no inhibition of differentiation. In contrast, activation of the Bcr-Abl PTK for 12 weeks results in cells that display a delay in differentiation at the early granulocyte stage. Flow cytometric analysis also indicates that the expression of cell surface differentiation markers and nuclear morphology are uncoupled. Furthermore, a significant number of the mature neutrophils display abnormal morphological features. Prolonged exposure to Bcr-Abl PTK results in interleukin-3 independent growth and decreased p53 protein levels. FDCP-Mix cells expressing a dominant negative p53 and p53null FDCP-Mix cells demonstrate that the reduction in p53 is causally related to the delay in development. Returning the cells to the restrictive temperature restores the p53 protein levels, the growth factor dependence and largely relieves the effects on development. We conclude that prolonged Bcr-Abl PTK activity within multipotent cells results in a reduction of p53 that drives a delayed and abnormal differentiation.

Enhanced p73 expression during differentiation and complex p73 isoforms in myeloid leukemia

The p53 homologue p73 is expressed in at least six different isoforms (alpha, beta, gamma, delta, epsilon, and zeta), but unlike p53 it has rarely been found mutated in human cancers. However, altered expression of this gene has been reported in cancer cells. In order to understand if p73 is involved in normal and malignant development of myeloid cells, we investigated the expression pattern of the different p73 isoforms in progenitor and mature normal myeloid cells as well as in cells derived from acute and chronic myeloid leukemias. The results show that expression of p73 is markedly enhanced during differentiation of myeloid leukemic cells and that leukemic blasts from patients show an increased expression of the shorter p73 isoforms (gamma, delta, epsilon, zeta). In particular the epsilon isoform is only expressed in leukemic cells and completely absent in mature myeloid cells. Altogether our data suggest that p73 is involved in myeloid differentiation and its altered expression is involved in leukemic degeneration.

Telomerase activity in primary and secondary glioblastomas multiforme as a novel molecular tumor marker

OBJECT

Telomerase activity is responsible for cell immortality. To examine the role of telomerase in the carcinogenesis of human glioblastomas multiforme (GBMs), the authors studied telomerase activity, telomerase component expression, and telomere lengths in 42 GBM samples.

METHODS

In all samples, EGFR and MDM2 amplifications and overexpressions were examined using Southern and Northern blot analyses. The p53 mutation was analyzed using polymerase chain reaction-single strand conformational polymorphism and by direct sequence analysis. Specimens of tissues were immunostained with p53, EGFR, and MDM2 antibodies. Allelic loss on chromosomes 17p and 10 was assessed by loss of heterozygosity (LOH) assays. Telomerase activity, expression of its components (human telomerase reverse transcriptase [hTERT], human telomerase RNA component [hTERC], and telomerase-associated protein [TEP1]), and telomere lengths were analyzed using the telomeric repeat amplification protocol (TRAP)-hybridization protection assay, reverse transcription-polymerase chain reaction, and Southern blot analysis. According to the results of assessments of EGFR and MDM2 amplifications, p53 mutation, LOHs in chromosomes 17p and 10, and the clinical course of the disease, the 42 samples were classified into 22 primary and 20 secondary glioblastomas. Twenty-six (61.9%) of all 42 samples demonstrated detectable telomerase activity during the TRAP assay. Secondary GBMs displayed significantly higher levels of telomerase activity and hTERT expression than primary GBMs. Tumors with a p53 gene mutation demonstrated significantly higher telomerase activity than those without a p53 mutation. Four samples with a codon 175 mutation demonstrated an exceptionally high amount of telomerase activity. In secondary GBMs, the increase in telomerase activity and the hTERT expression level correlated with the increased frequency of p53 mutations. There was no significant difference in telomere length between primary and secondary GBMs.

CONCLUSIONS

These results suggest that telomerase activity and p53 mutations both play important roles in the multistep carcinogenesis of GBMs. Telomerase activity and hTERT expression may be considered as novel distinctive factors in human GBMs.

Characteristics and analysis of normal and leukemic stem cells: current concepts and future directions

Acute myeloid leukemias (AML) are considered to be clonal disorders involving early hematopoietic progenitor cells. The recent advances in characterization of early stem cells give rise to the question whether it is possible to distinguish healthy progenitors from cells of the leukemic clone in leukemia patients. Differences and similarities in phenotype, genotype and biology are described for leukemic cells and normal hematological progenitors. Recent new insights into human stem cell development offer the perspective that distinction between benign and malignant progenitors might be possible in the future at a very early stage of maturation.

New strategies for the treatment of acute myelogenous leukemia: differentiation induction--present use and future possibilities

A differentiation block and an accumulation of immature myeloid cells characterize acute myelogenous leukemia (AML). However, native AML cells usually show some morphological signs of differentiation that allow a classification into different subsets, and further differentiation may be induced by exposure to various soluble mediators, for example, all-trans retinoic acid (ATRA) and several cytokines. Combination therapy with ATRA and chemotherapy should now be regarded as the standard treatment of the acute promyelocytic leukemia (APL) variant of AML. Although several agents can also induce leukemic cell differentiation for other AML subgroups, in vitro studies as well as clinical data have demonstrated that these agents often have heterogeneous effects on the leukemic progenitors. This makes the clinical impact of differentiation induction therapy for individual patients difficult to predict. However, differentiation induction should be regarded as a promising therapeutic approach, especially as a part of immunotherapy or in combination with intensive chemotherapy to increase the susceptibility of AML blasts to drug-induced apoptosis. Although the morphology-based French-American-British classification was used to identify APL as an AML subset that required a special treatment, it seems unlikely that this classification alone can be used to identify new subsets of AML patients with special therapeutic requirements. Future studies on differentiation induction in AML should therefore focus on A) the identification of therapeutic agents with more predictable effects; B) the use of clinical and laboratory parameters to define new subsets of AML patients in which differentiation induction has a predictable and beneficial effect, and C) the characterization of how AML blast sensitivity to drug-induced apoptosis is altered by differentiation induction.

Strong immunogenic potential of a B7 retroviral expression vector: generation of HLA-B7-restricted CTL response against selectable marker genes

The stimulation of a specific immune response is an attractive goal in cancer therapy. Gene transfer of co-stimulatory molecules and/or cytokine genes into tumor cells and the injection of these genetically modified cells leads to tumor rejection by syngeneic hosts and the induction of tumor immunity. However, the development of host immune response could be either due to the introduced immunomodulatory genes or due to vector components. In this study, human renal cell carcinoma cell lines were modified by a retrovirus to express the co-stimulatory molecule B7-1 together with the hygromycin/thymidine kinase fusion protein (HygTk) as positive and negative selection markers. These B7-1-transduced renal cell carcinoma cell lines were able significantly to activate allogeneic T cell proliferation. The cytolytic activity of these T cells was determined by employing several transduced and nontransduced renal cell carcinoma cell lines as targets. Evidence for a strong vector-specific T cell reactivity induced by the Hyg/Tk protein was obtained in autologous renal cell carcinoma systems. Antibody blocking experiments as well as peptide binding assays demonstrated an HLA-B7-restricted T cell response directed against both the Hyg and the Tk genes. Thus, the vector itself may mask the generation of immune reactivity against tumor antigens and may even detract from it. Vectors with immunogenic potential may be useful for tumor vaccination via cross priming in vivo, whereas antivector reactivities would be detrimental in situations where gene defects are being corrected and where long term expression of a therapeutic protein is required.