Molecular genetics in acute leukemia

The role of miR-128 in cancer development, prevention, drug resistance, and immunotherapy

A growing body of evidence has revealed that microRNA (miRNA) expression is dysregulated in cancer, and they can act as either oncogenes or suppressors under certain conditions. Furthermore, some studies have discovered that miRNAs play a role in cancer cell drug resistance by targeting drug-resistance-related genes or influencing genes involved in cell proliferation, cell cycle, and apoptosis. In this regard, the abnormal expression of miRNA-128 (miR-128) has been found in various human malignancies, and its verified target genes are essential in cancer-related processes, including apoptosis, cell propagation, and differentiation. This review will discuss the functions and processes of miR-128 in multiple cancer types. Furthermore, the possible involvement of miR-128 in cancer drug resistance and tumor immunotherapeutic will be addressed.

IKZF1 rs4132601 and rs11978267 Gene Polymorphisms and Acute Lymphoblastic Leukemia: Relation to Disease Susceptibility and Outcome

(IKZF1) rs4132601 and rs11978267 are common gene polymorphisms and have been associated with the risk of acute lymphoblastic leukemia. However, these associations are less evident in races and/or ethnicities other than European and Hispanic. Therefore, we investigated the association between these single-nucleotide polymorphisms and acute lymphoblastic leukemia susceptibility and disease outcome. Real-time polymerase chain reaction typing was performed for IKZF1 rs4132601 and rs11978267 for 128 pediatric acute lymphoblastic leukemia (pALL), 45 adult acute lymphoblastic leukemia (aALL), and 436 healthy controls. The G allele-containing and G-containing genotypes (GG+GT) of rs4132601 were significantly higher in pALL (P=0.003, odds ratio [OR]=1.65, 0.009, OR=1.42, respectively) and aALL (P=0.016, OR=1.81 and 0.011, OR=1.61, respectively). However, the GG haplotype was associated with the risk of pALL (P=0.044), the GA haplotype was associated with the risk of aALL (P=0.007). In aALL, the GG genotype of rs4132601 was associated with absence of remission and poor overall survival (P=0.003 and 0.041, respectively). The IKZF1 rs4132601 single-nucleotide polymorphism can be considered a susceptibility risk factor for the development of pALL and aALL in the studied cohort of Egyptian patients. The GG genotype of IKZF1 rs4132601 may be a risk factor for poor outcome in aALL patients.

Genetic, epigenetic, and lineage-directed mechanisms in benzene-induced malignancies and hematotoxicity targeting hematopoietic stem cells niche

Benzene is a known hematotoxic and leukemogenic agent with hematopoietic stem cells (HSCs) niche being the potential target. Occupational and environmental exposure to benzene has been linked to the incidences of hematological disorders and malignancies. Previous studies have shown that benzene may act via multiple modes of action targeting HSCs niche, which include induction of chromosomal and micro RNA aberrations, leading to genetic and epigenetic modification of stem cells and probable carcinogenesis. However, understanding the mechanism linking benzene to the HSCs niche dysregulation is challenging due to complexity of its microenvironment. The niche is known to comprise of cell populations accounted for HSCs and their committed progenitors of lymphoid, erythroid, and myeloid lineages. Thus, it is fundamental to address novel approaches via lineage-directed strategy to elucidate precise mechanism involved in benzene-induced toxicity targeting HSCs and progenitors of different lineages. Here, we review the key genetic and epigenetic factors that mediate hematotoxicological effects by benzene and its metabolites in targeting HSCs niche. Overall, the use of combined genetic, epigenetic, and lineage-directed strategies targeting the HSCs niche is fundamental to uncover the key mechanisms in benzene-induced hematological disorders and malignancies.

A Ranking Approach for Probe Selection and Classification of Microarray Data with Artificial Neural Networks

Acute leukemia classification into its myeloid and lymphoblastic subtypes is usually accomplished according to the morphology of the tumor. Nevertheless, the subtypes may have similar histopathological appearance, making screening procedures difficult. In addition, approximately one-third of acute myeloid leukemias are characterized by aberrant cytoplasmic localization of nucleophosmin (NPMc(+)), where the majority has a normal karyotype. This work is based on two DNA microarray datasets, available publicly, to differentiate leukemia subtypes. The datasets were split into training and test sets, and feature selection methods were applied. Artificial neural network classifiers were developed to compare the feature selection methods. For the first dataset, 50 genes selected using the best classifier was able to classify all patients in the test set. For the second dataset, five genes yielded 97.5% accuracy in the test set.

Chromosome-wide aneuploidy study of cultured circulating myeloid progenitor cells from workers occupationally exposed to formaldehyde

Formaldehyde (FA) is an economically important industrial chemical to which millions of people worldwide are exposed environmentally and occupationally. Recently, the International Agency for Cancer Research concluded that there is sufficient evidence that FA causes leukemia, particularly myeloid leukemia. To evaluate the biological plausibility of this association, we employed a chromosome-wide aneuploidy study approach, which allows the evaluation of aneuploidy and structural chromosome aberrations (SCAs) of all 24 chromosomes simultaneously, to analyze cultured myeloid progenitor cells from 29 workers exposed to relatively high levels of FA and 23 unexposed controls. We found statistically significant increases in the frequencies of monosomy, trisomy, tetrasomy and SCAs of multiple chromosomes in exposed workers compared with controls, with particularly notable effects for monosomy 1 [P = 6.02E-06, incidence rate ratio (IRR) = 2.31], monosomy 5 (P = 9.01E-06; IRR = 2.24), monosomy 7 (P = 1.57E-05; IRR = 2.17), trisomy 5 (P = 1.98E-05; IRR = 3.40) and SCAs of chromosome 5 (P = 0.024; IRR = 4.15). The detection of increased levels of monosomy 7 and SCAs of chromosome 5 is particularly relevant as they are frequently observed in acute myeloid leukemia. Our findings provide further evidence that leukemia-related cytogenetic changes can occur in the circulating myeloid progenitor cells of healthy workers exposed to FA, which may be a potential mechanism underlying FA-induced leukemogenesis.

The ordered acquisition of Class II and Class I mutations directs formation of human t(8;21) acute myelogenous leukemia stem cell

The cellular properties of leukemia stem cells (LSCs) are achieved at least through Class I and Class II mutations that generate signals for enhanced proliferation and impaired differentiation, respectively. Here we show that in t(8;21) acute myelogenous leukemia (AML), hematopoietic stem cells (HSCs) transform into LSCs via definitively-ordered acquisition of Class II (AML1/ETO) and then Class I (c-KIT mutant) abnormalities. Six t(8;21) AML patients with c-KIT mutants maintaining > 3 years of complete remission were analyzed. At diagnosis, all single LSCs had both AML1/ETO and c-KIT mutations. However, in remission, 16 out of 1,728 CD34(+)CD38(-) HSCs and 89 out of 7,187 single HSC-derived myeloerythroid colonies from these patients had AML1/ETO, whose breakpoints were identical to those found in LSCs. These cells had wild-type c-KIT, which expressed AML1/ETO at a low level, and could differentiate into mature blood cells, suggesting that they may be the persistent preleukemic stem cells. Microarray analysis suggested that mutated c-KIT signaling provides LSCs with enhanced survival and proliferation. Thus, in t(8;21) AML, the acquisition of AML1/ETO is not sufficient, and the subsequent upregulation of AML1/ETO and the additional c-KIT mutant signaling are critical steps for transformation into LSCs.

Epigenetic silencing of Bcl-2, CEBPA and p14(ARF) by the AML1-ETO oncoprotein contributing to growth arrest and differentiation block in the U937 cell line

The AML1-ETO fusion transcription factor generated by the t(8;21) translocation is considered to deregulate the expression of genes that are crucial for normal differentiation and proliferation of hematopoietic progenitors, resulting in acute myelogenous leukemia by recruiting co-repressor complexes to DNA. To investigate the role of AML1-ETO in leukemogenesis, we transfected the cloned AML1-ETO cDNA and expressed the AML1-ETO protein in U937 myelomonocytic leukemia cells. By focusing on the anti-apoptotic gene Bcl-2, the key regulator gene of granulocytic differentiation CCAAT/enhancer-binding protein α (CEBPA) and the tumor suppressor gene p14(ARF), we found that both AML1-ETO-expressing cell lines and t(8;21) leukemia samples displayed low levels of these three genes. Chromatin immunoprecipitation assays demonstrated that Bcl-2, CEBPA and p14(ARF) were direct transcriptional targets of AML1-ETO. The universal binding of AML1-ETO to genomic DNA resulted in recruitment of methyl-CpG binding protein 2 (MeCP2), reduction of histone H3 or H4 acetylation and increased trimethylation of histone H3 lysine 9 as well as lysine 27 indicating that AML1-ETO induced heterochromatic silencing of Bcl-2, CEBPA and p14(ARF). These results suggested that the aberrant transcription factor AML1-ETO epigenetically silenced the function of the Bcl-2, CEBPA and p14(ARF) genes by inducing repressed chromatin configurations at their promoters through histone modifications.

Generation of monoclonal antibodies to the AML1-ETO fusion protein: strategies for overcoming high homology

The chromosomal translocation t(8;21) often found in acute myeloid leukemia generates an oncogenic fusion protein AML1-ETO. This chimeric oncoprotein disrupts wild-type AML1 function and dysregulates genes important for normal myelopoiesis. Monoclonal antibodies that can capture and detect the AML1-ETO fusion protein would help with early diagnosis and treatment prognosis of acute myeloid leukemia. We report the development of murine monoclonal antibodies (MAbs) that specifically bind epitopes encoded by either AML1 or ETO. Since alignment to the human ETO protein indicated almost 100% homology to the mouse ortholog, a strategy was needed to instruct humoral immunity in mice to focus and respond to self-epitopes. Our strategy to develop capture/detector reagents involved producing MAbs that would bind to epitopes within the non-fused myelopic protein (i.e., either AML1 or ETO). This included a process to select antibodies for their ability to also recognize the translocated chromosomal AML1-ETO fusion protein and to identify complementary capture/detector antibody pairs. Construction of a peptide hapten-carrier complex and use of a rapid immunization protocol resulted in IgM-IgG ETO specific MAbs. These MAbs bound specifically to a recombinant form of AML1-ETO fusion protein expressed in HEK and to an endogenous AML1-ETO form of the fusion protein expressed in Kasumi-1. We report the development of murine hybridoma MAbs derived from immunizations with a peptide "self-epitope." Our findings provide a potential strategy to instruct humoral immunity in mice to focus and respond to self-epitopes. This strategy has been validated with the oncogenic fusion protein AML1-ETO involved in acute myeloid leukemia.

Identifying an indoor air exposure limit for formaldehyde considering both irritation and cancer hazards

Formaldehyde is a well-studied chemical and effects from inhalation exposures have been extensively characterized in numerous controlled studies with human volunteers, including asthmatics and other sensitive individuals, which provide a rich database on exposure concentrations that can reliably produce the symptoms of sensory irritation. Although individuals can differ in their sensitivity to odor and eye irritation, the majority of authoritative reviews of the formaldehyde literature have concluded that an air concentration of 0.3 ppm will provide protection from eye irritation for virtually everyone. A weight of evidence-based formaldehyde exposure limit of 0.1 ppm (100 ppb) is recommended as an indoor air level for all individuals for odor detection and sensory irritation. It has recently been suggested by the International Agency for Research on Cancer (IARC), the National Toxicology Program (NTP), and the US Environmental Protection Agency (US EPA) that formaldehyde is causally associated with nasopharyngeal cancer (NPC) and leukemia. This has led US EPA to conclude that irritation is not the most sensitive toxic endpoint and that carcinogenicity should dictate how to establish exposure limits for formaldehyde. In this review, a number of lines of reasoning and substantial scientific evidence are described and discussed, which leads to a conclusion that neither point of contact nor systemic effects of any type, including NPC or leukemia, are causally associated with exposure to formaldehyde. This conclusion supports the view that the equivocal epidemiology studies that suggest otherwise are almost certainly flawed by identified or yet to be unidentified confounding variables. Thus, this assessment concludes that a formaldehyde indoor air limit of 0.1 ppm should protect even particularly susceptible individuals from both irritation effects and any potential cancer hazard.

Hidden Aberrations Diagnosed by Interphase FluorescenceIn SituHybridisation and Spectral Karyotyping in Childhood Acute Lymphoblastic Leukaemia

Acute lymphoblastic leukaemia (ALL) is the most common oncologic disease in childhood, accounting for approximately 25% of all paediatric malignancies. Based on clinical risk criteria and modern laboratory investigations including immunophenotyping, cytogenetics and molecular genetics, patients can be divided into prognostic groups and assigned to risk-adjusted treatment protocols. The karyotype is an independent prognostic indicator and has for some aberrations that are associated with a poor outcome a direct impact on the choice of treatment. Cytogenetic analysis in ALL is often hampered by poor chromosome morphology, few malignant metaphases, undetectable chromosomal rearrangements due to regions of a similar size and banding pattern and sometimes only normal metaphases derived from normal cells are found after cell culture. Structural as well as numerical aberrations may therefore remain undetected using conventional G-banding. The application of modern molecular cytogenetic techniques including a broad set of fluorescence in situ hybridisation (FISH) methods and recent developments in comparative genomic hybridisation to DNA microarrays, together with molecular methods such as Southern blotting and RT-PCR has greatly improved the detection rate of genetic changes in ALL. This review emphasises the value of increasing the resolving power of the cytogenetic investigation by spectral karyotyping (SKY) and interphase FISH in identifying prognostically important and novel chromosomal rearrangements as a complement to conventional banding analysis. The results of investigations performed on cases with ALL have shown that interphase FISH is valuable and in many cases even mandatory for the detection of prognostically important genetic abnormalities and should therefore consistently be employed in the routine cytogenetic investigations in ALL. Likewise, SKY is a valuable tool for the cytogenetic analysis. Thus, the results of several different investigations described in this review revealed that SKY yielded additional information in 97/157 (62%) cases with chromosomal aberrations detected by G-banding, and in 10/66 (15%) cases with normal G-banding.

Is exposure to formaldehyde in air causally associated with leukemia?--A hypothesis-based weight-of-evidence analysis

Recent scientific debate has focused on the potential for inhaled formaldehyde to cause lymphohematopoietic cancers, particularly leukemias, in humans. The concern stems from certain epidemiology studies reporting an association, although particulars of endpoints and dosimetry are inconsistent across studies and several other studies show no such effects. Animal studies generally report neither hematotoxicity nor leukemia associated with formaldehyde inhalation, and hematotoxicity studies in humans are inconsistent. Formaldehyde's reactivity has been thought to preclude systemic exposure following inhalation, and its apparent inability to reach and affect the target tissues attacked by known leukemogens has, heretofore, led to skepticism regarding its potential to cause human lymphohematopoietic cancers. Recently, however, potential modes of action for formaldehyde leukemogenesis have been hypothesized, and it has been suggested that formaldehyde be identified as a known human leukemogen. In this article, we apply our hypothesis-based weight-of-evidence (HBWoE) approach to evaluate the large body of evidence regarding formaldehyde and leukemogenesis, attending to how human, animal, and mode-of-action results inform one another. We trace the logic of inference within and across all studies, and articulate how one could account for the suite of available observations under the various proposed hypotheses. Upon comparison of alternative proposals regarding what causal processes may have led to the array of observations as we see them, we conclude that the case for a causal association is weak and strains biological plausibility. Instead, apparent association between formaldehyde inhalation and leukemia in some human studies is better interpreted as due to chance or confounding.

Chromosome-wide aneuploidy study (CWAS) in workers exposed to an established leukemogen, benzene

Evidence suggests that de novo, therapy-related and benzene-induced acute myeloid leukemias (AML) occur via similar cytogenetic and genetic pathways, several of which involve aneuploidy, the loss or gain of chromosomes. Aneuploidy of specific chromosomes has been detected in benzene-related leukemia patients as well as in healthy benzene-exposed workers, suggesting that aneuploidy precedes and may be a potential mechanism underlying benzene-induced leukemia. Here, we analyzed the peripheral blood lymphocytes of 47 exposed workers and 27 unexposed controls using a novel OctoChrome fluorescence in situ hybridization (FISH) technique that simultaneously detects aneuploidy in all 24 chromosomes. Through this chromosome-wide aneuploidy study (CWAS) approach, we found heterogeneity in the monosomy and trisomy rates of the 22 autosomes when plotted against continuous benzene exposure. In addition, statistically significant, chromosome-specific increases in the rates of monosomy [5, 6, 7, 10, 16 and 19] and trisomy [5, 6, 7, 8, 10, 14, 16, 21 and 22] were found to be dose dependently associated with benzene exposure. Furthermore, significantly higher rates of monosomy and trisomy were observed in a priori defined 'susceptible' chromosome sets compared with all other chromosomes. Together, these findings confirm that benzene exposure is associated with specific chromosomal aneuploidies in hematopoietic cells, which suggests that such aneuploidies may play roles in benzene-induced leukemogenesis.

C-KIT mutation cooperates with full-length AML1-ETO to induce acute myeloid leukemia in mice

The full-length AML1-ETO (AE) fusion gene resulting from t(8;21)(q22;q22) in human acute myeloid leukemia (AML) is not sufficient to induce leukemia in animals, suggesting that additional mutations are required for leukemogenesis. We and others have identified activating mutations of C-KIT in nearly half of patients with t(8;21) AML. To test the hypothesis that activating C-KIT mutations cooperate with AE to cause overt AML, we generated a murine transduction and transplantation model with both mutated C-KIT and AE. To overcome the intracellular transport block of human C-KIT in murine cells, we engineered hybrid C-KIT (HyC-KIT) by fusing the extracellular and transmembrane domains of the murine c-Kit in-frame to the intracellular signaling domain of human C-KIT. We showed that tyrosine kinase domain mutants HyC-KIT N822K and D816V, as well as juxtamembrane mutants HyC-KIT 571+14 and 557-558Del, could transform murine 32D cells to cytokine-independent growth. The protein tyrosine kinase inhibitor dasatinib inhibited the proliferation of 32D cells expressing these C-KIT mutants, with potency in the low nanomolar range. In mice, HyC-KIT N822K induced a myeloproliferative disease, whereas HyC-KIT 571+14 induces both myeloproliferative disease and lymphocytic leukemia. Interestingly, coexpression of AE and HyC-KIT N822K led to fatal AML. Our data have further enriched the two-hit model that abnormalities of both transcription factor and membrane/cytosolic signaling molecule are required in AML pathogenesis. Furthermore, dasatinib prolonged lifespan of mice bearing AE and HyC-KIT N822K-coexpressing leukemic cells and exerted synergic effects while combined with cytarabine, thus providing a potential therapeutic for t(8;21) leukemia.

A unique complex translocation involving six different chromosomes in a case of childhood acute lymphoblastic leukemia with the Philadelphia chromosome and adverse prognosis

Acute lymphoblastic leukemia (ALL) is the most common childhood malignancy. Approximately 84% of cases of ALL are classified as B-precursor ALL, 14% of cases are T-cell and 2% of cases are B-cell (B-)ALL. About one third of B-ALL cases show an abnormal karyotype. Combining data obtained by immunophenotyping, karyotyping and molecular cytogenetic analyses allows for a better understanding of this heterogeneous disease. This study reports an exceptional B-ALL case with a poor prognosis and unique complex chromosomal aberrations not previously observed, i.e., a translocation involving the six chromosomal regions 1q42, 4q21, 4q24, 4q35 (twice), 8q22 and 10p15.3 besides 9q34 and 22q11.2.

Acquired genomic copy number aberrations and survival in adult acute myelogenous leukemia

Genomic aberrations are of predominant importance to the biology and clinical outcome of patients with acute myelogenous leukemia (AML), and conventional karyotype-based risk classifications are routinely used in clinical decision making in AML. One of the known limitations of cytogenetic analysis is the inability to detect genomic abnormalities less than 5 Mb in size, and it is currently unclear whether overcoming this limitation with high-resolution genomic single-nucleotide polymorphism (SNP) array analysis would be clinically relevant. Furthermore, given the heterogeneity of molecular mechanisms/aberrations that underlie the conventional karyotype-based risk classifications, it is likely that further refinements in genomic risk prognostication can be achieved. In this study, we analyzed flow cytometer-sorted, AML blast-derived, and paired, buccal DNA from 114 previously untreated prospectively enrolled AML patients for acquired genomic copy number changes and loss of heterozygosity using Affymetrix SNP 6.0 arrays, and we correlated genomic lesion load and specific chromosomal abnormalities with patient survival. Using multivariate analyses, we found that having ≥ 2 genomic lesions detected through SNP 6.0 array profiling approximately doubles the risk of death when controlling for age- and karyotype-based risk. Finally, we identified an independent negative prognostic impact of p53 mutations, or p53 mutations and 17p-loss of heterozygosity combined on survival in AML.

NF1 inactivation in adult acute myelogenous leukemia

PURPOSE

This study was conducted to identify novel genes with importance to the biology of adult acute myelogenous leukemia (AML).

EXPERIMENTAL DESIGN

We analyzed DNA from highly purified AML blasts and paired buccal cells from 95 patients for recurrent genomic microdeletions using ultra-high density Affymetrix single nucleotide polymorphism 6.0 array-based genomic profiling.

RESULTS

Through fine mapping of microdeletions on 17q, we derived a minimal deleted region of approximately 0.9-Mb length that harbors 11 known genes; this region includes Neurofibromin 1 (NF1). Sequence analysis of all NF1 coding exons in the 11 AML cases with NF1 copy number changes identified acquired truncating frameshift mutations in two patients. These NF1 mutations were already present in the hematopoetic stem cell compartment. Subsequent expression analysis of NF1 mRNA in the entire AML cohort using fluorescence-activated cell sorting sorted blasts as a source of RNA identified six patients (one with a NF1 mutation) with absent NF1 expression. The NF1 null states were associated with increased Ras-bound GTP, and short hairpin RNA-mediated NF1 suppression in primary AML blasts with wild-type NF1 facilitated colony formation in methylcellulose. Primary AML blasts without functional NF1, unlike blasts with functional NF1, displayed sensitivity to rapamycin-induced apoptosis, thus identifying a dependence on mammalian target of rapamycin (mTOR) signaling for survival. Finally, colony formation in methylcellulose ex vivo of NF1 null CD34+/CD38- cells sorted from AML bone marrow samples was inhibited by low-dose rapamycin.

CONCLUSIONS

NF1 null states are present in 7 of 95 (7%) of adult AML and delineate a disease subset that could be preferentially targeted by Ras or mammalian target of rapamycin-directed therapeutics.

Detection of fetomaternal genotype associations in early-onset disorders: evaluation of different methods and their application to childhood leukemia

Several designs and analytical approaches have been proposed to dissect offspring from maternal genetic contributions to early-onset diseases. However, lack of parental controls halts the direct verification of the assumption of mating symmetry (MS) required to assess maternally-mediated effects. In this study, we used simulations to investigate the performance of existing methods under mating asymmetry (MA) when parents of controls are missing. Our results show that the log-linear, likelihood-based framework using a case-triad/case-control hybrid design provides valid tests for maternal genetic effects even under MA. Using this approach, we examined fetomaternal associations between 29 SNPs in 12 cell-cycle genes and childhood pre-B acute lymphoblastic leukemia (ALL). We identified putative fetomaternal effects at loci CDKN2A rs36228834 (P = .017) and CDKN2B rs36229158 (P = .022) that modulate the risk of childhood ALL. These data further corroborate the importance of the mother's genotype on the susceptibility to early-onset diseases.

MicroRNAs expression signatures are associated with lineage and survival in acute leukemias

MicroRNAs (miRNAs) are small ( approximately 22 nucleotide) non-coding RNAs whose altered expression has been associated with various types of cancers, including leukemia. In the present study, we conducted a quantitative PCR (qPCR) analysis of expression of 23 human precursor miRNAs in bone marrow specimens of 85 Chinese primary leukemia patients, including 53 acute myeloid leukemia (AML) and 32 acute lymphoblastic leukemia (ALL) cases. We show that 16 miRNAs were differentially expressed between AMLs and ALLs. Of them, eight were previously reported (i.e., miR-23a, miR-27a/b, miR-128a, miR-128b, miR-221, miR-222, miR-223, and let-7b) and eight were newly identified (i.e., miR-17, miR-20a, miR-29a/c, miR-29b, miR-146a, miR-150, miR-155, and miR-196b). More importantly, through correlating miRNA expression signatures with outcome of patients, we further show that expression signatures of a group of miRNAs are associated with overall survival of patients. Of them, three (i.e., miR-146a, miR-181a/c, and miR-221), five (i.e., miR-25, miR-26a, miR-29b, miR-146a, and miR-196b), and three (i.e., miR-26a, miR-29b, and miR-146a) miRNAs are significantly associated with overall survival (P<0.05) of the 32 ALL, 53 AML, and 40 non-M3 AML patients, respectively. Particularly, the expression signature of miR-146a is significantly inversely correlated with overall survival of both ALL and AML patients. The prognostic significance of miR-146a in AML has been confirmed further in an independent study of 61 Chinese new AML patient samples. We also identified 622 putative target genes of miR-146a that are predicted by at least three out of the five major prediction programs (i.e., TragetScan, PicTar, miRanda, miRBase Targets, and PITA). Through gene ontology analysis, we found that these genes were particularly enriched (2- to 9-fold higher than expected by chance) in the GO categories of "negative regulation of biology processes," "negative regulation of cellular processes," "apoptosis," and "cell cycle," which may be related to the association of miR-146a with poor survival.

Occupational exposure to formaldehyde, hematotoxicity, and leukemia-specific chromosome changes in cultured myeloid progenitor cells

There are concerns about the health effects of formaldehyde exposure, including carcinogenicity, in light of elevated indoor air levels in new homes and occupational exposures experienced by workers in health care, embalming, manufacturing, and other industries. Epidemiologic studies suggest that formaldehyde exposure is associated with an increased risk of leukemia. However, the biological plausibility of these findings has been questioned because limited information is available on the ability of formaldehyde to disrupt hematopoietic function. Our objective was to determine if formaldehyde exposure disrupts hematopoietic function and produces leukemia-related chromosome changes in exposed humans. We examined the ability of formaldehyde to disrupt hematopoiesis in a study of 94 workers in China (43 exposed to formaldehyde and 51 frequency-matched controls) by measuring complete blood counts and peripheral stem/progenitor cell colony formation. Further, myeloid progenitor cells, the target for leukemogenesis, were cultured from the workers to quantify the level of leukemia-specific chromosome changes, including monosomy 7 and trisomy 8, in metaphase spreads of these cells. Among exposed workers, peripheral blood cell counts were significantly lowered in a manner consistent with toxic effects on the bone marrow and leukemia-specific chromosome changes were significantly elevated in myeloid blood progenitor cells. These findings suggest that formaldehyde exposure can have an adverse effect on the hematopoietic system and that leukemia induction by formaldehyde is biologically plausible, which heightens concerns about its leukemogenic potential from occupational and environmental exposures.

MLL rearrangements in pediatric acute lymphoblastic and myeloblastic leukemias: MLL specific and lineage specific signatures

Background

The presence of MLL rearrangements in acute leukemia results in a complex number of biological modifications that still remain largely unexplained. Armstrong et al. proposed MLL rearrangement positive ALL as a distinct subgroup, separated from acute lymphoblastic (ALL) and myeloblastic leukemia (AML), with a specific gene expression profile. Here we show that MLL, from both ALL and AML origin, share a signature identified by a small set of genes suggesting a common genetic disregulation that could be at the basis of mixed lineage leukemia in both phenotypes.

Methods

Using Affymetrix^® HG-U133 Plus 2.0 platform, gene expression data from 140 (training set) + 78 (test set) ALL and AML patients with (24+13) and without (116+65) MLL rearrangements have been investigated performing class comparison (SAM) and class prediction (PAM) analyses.

Results

We identified a MLL translocation-specific (379 probes) signature and a phenotype-specific (622 probes) signature which have been tested using unsupervised methods. A final subset of 14 genes grants the characterization of acute leukemia patients with and without MLL rearrangements.

Conclusion

Our study demonstrated that a small subset of genes identifies MLL-specific rearrangements and clearly separates acute leukemia samples according to lineage origin. The subset included well-known genes and newly discovered markers that identified ALL and AML subgroups, with and without MLL rearrangements.

Commonality but diversity in cancer gene fusions

Recent findings of gene fusions in carcinomas recapitulate the discovery of chromosomal abnormalities in leukemias and sarcomas decades ago. A recurring feature of carcinoma gene fusions, in contrast to those in hematopoietic and mesenchymal malignancies, is that they result in aberrant cell signaling. This may reflect differences in the differentiation programs of these tissues.

Molecular and chromosomal alterations: new therapies for relapsed acute myeloid leukemia

Acute myeloid leukemia (AML) remains the most common form of leukemia and the most common cause of leukemia death. Although conventional chemotherapy can cure between 25 and 45% of AML patients, the majority of patients die after relapse or of complications associated with treatment. Thus, more specific and less toxic treatments for AML patients are needed, especially for elderly patients. An indispensable prerequisite to investigate tailored approaches for AML is the recent progress in the understanding the molecular features that distinguish leukemia progenitors from normal hematopoietic counterparts and the identification of a variety of dysregulated molecular pathways. This in turn would allow the identification of tumor-specific characteristics that provide a rational basis for the development of more tailored, and hence potentially more effective and less toxic, therapeutic approaches. In this review, we describe some of the signaling pathways that are aberrantly regulated in AML, with a specific focus on their pathogenetic and therapeutic significance, and we examine some recent therapies directed against these targets, used in clinical trial for relapsed patients or unfit for conventional chemotherapy.

MicroRNA expression signatures accurately discriminate acute lymphoblastic leukemia from acute myeloid leukemia

Acute lymphoblastic leukemia (ALL) is the most common childhood cancer, whereas acute myeloid leukemia (AML) is the most common acute leukemia in adults. In general, ALL has a better prognosis than AML. To understand the distinct mechanisms in leukemogenesis between ALL and AML and to identify markers for diagnosis and treatment, we performed a large-scale genome-wide microRNA (miRNA, miR) expression profiling assay and identified 27 miRNAs that are differentially expressed between ALL and AML. Among them, miR-128a and -128b are significantly overexpressed, whereas let-7b and miR-223 are significantly down-regulated in ALL compared with AML. They are the most discriminatory miRNAs between ALL and AML. Using the expression signatures of a minimum of two of these miRNAs resulted in an accuracy rate of >95% in the diagnosis of ALL and AML. The differential expression patterns of these four miRNAs were validated further through large-scale real-time PCR on 98 acute leukemia samples covering most of the common cytogenetic subtypes, along with 10 normal control samples. Furthermore, we found that overexpression of miR-128 in ALL was at least partly associated with promoter hypomethylation and not with an amplification of its genomic locus. Taken together, we showed that expression signatures of as few as two miRNAs could accurately discriminate ALL from AML, and that epigenetic regulation might play an important role in the regulation of expression of miRNAs in acute leukemias.

Leukemia: stem cells, maturation arrest, and differentiation therapy

Human myeloid leukemias provide models of maturation arrest and differentiation therapy of cancer. The genetic lesions of leukemia result in a block of differentiation (maturation arrest) that allows myeloid leukemic cells to continue to proliferate and/or prevents the terminal differentiation and apoptosis seen in normal white blood cells. In chronic myeloid leukemia, the bcr-abl (t9/22) translocation produces a fusion product that is an activated tyrosine kinase resulting in constitutive activation cells at the myelocyte level. This activation may be inhibited by imatinib mesylate (Gleevec, STI-571), which blocks the binding of ATP to the activated tyrosine kinase, prevents phosphorylation, and allows the leukemic cells to differentiate and undergo apoptosis. In acute promyelocytic leukemia, fusion of the retinoic acid receptor-alpha with the gene coding for promyelocytic protein, the PML-RAR alpha (t15:17) translocation, produces a fusion product that blocks the activity of the promyelocytic protein, which is required for formation of the granules of promyelocytes and prevents further differentiation. Retinoic acids bind to the retinoic acid receptor (RAR alpha) component of the fusion product, resulting in degradation of the fusion protein by ubiquitinization. This allows normal PML to participate in granule formation and differentiation of the promyelocytes. In one common type of acute myeloid leukemia, which results in maturation arrest at the myeloid precursor level, there is a mutation of FLT3, a transmembrane tyrosine kinase, which results in constitutive activation of the IL-3 receptor. This may be blocked by agents that inhibit farnesyl transferase. In each of these examples, specific inhibition of the genetically altered activation molecules of the leukemic cells allows the leukemic cells to differentiate and die. Because acute myeloid leukemias usually have mutation of more than one gene, combinations of specific inhibitors that act on the effects of different specific genetic lesions promises to result in more effective and permanent treatment.

Inducible expression of AML1-ETO fusion protein endows leukemic cells with susceptibility to extrinsic and intrinsic apoptosis

AML1-ETO, a leukemia-associated fusion protein generated by the frequently occurred chromosome translocation t(8;21) in acute myeloid leukemia, was shown to exert dichotomous functions in leukemic cells, that is, growth arrest versus differentiation block. By the analysis of oligonucleotide microarray, AML1-ETO was shown to modulate the expressions of an impressive array of pro- and anti-apoptotic genes. Here, we investigate potential effects of the ecdysone inducible AML1-ETO expression on apoptosis of leukemic U937 cell line. We show that AML1-ETO significantly stabilizes death receptor Fas protein and increases proapoptotic Bak in addition to reducing Bcl-2 expression. Accordingly, inducible AML1-ETO expression is followed by apoptosis to a lower degree. Especially, AML1-ETO endows leukemic cells with the susceptibility to anti-Fas agonist antibody, ultraviolet light and camptothecin analog NSC606985-induced apoptosis with increased activation of caspase-3/8. Considering that apoptosis-enhancing effect of AML1-ETO would not be favorable to the leukemogenesis harboring the t(8;21) translocation, it must be overcome to fulfill their leukemogenic potential. Complementary to this prediction is that two AML1-ETO-carrying leukemic cells, Kasumi-1 and SKNO-1, present similar sensitivity to apoptosis induction with AML1-ETO-negative leukemic cells. Therefore, genetic and/or epigenetic screenings of apoptosis-related genes modulated by AML1-ETO deserve to be explored for understanding the mechanisms of AML1-ETO-induced leukemogenesis.

High-dose cytosine arabinoside in the treatment of acute myeloid leukemia: Review of three randomized trials

BACKGROUND

The use of high-dose cytosine arabinoside (HDAraC) during induction may improve outcomes in patients with acute myeloid leukemia (AML) compared with standard-dose AraC (SDAraC). The objective of this review was to assess the impact of HDAraC during induction therapy for patients with AML based on results from randomized trials.

METHODS

All randomized trials in the field were identified by using a predefined search strategy. Trials that assessed the impact of HDAraC compared with SDAraC as induction therapy for adult patients with AML in a randomized fashion and that reported the relevant endpoints were included. Data were extracted from each trial by both reviewers according to prespecified criteria.

RESULTS

No differences between HDAraC and SDAraC were found with regard to complete remission rates (relative risk, 1.00; 95% confidence interval [95% CI], 0.92-1.10). The weighted mean difference (WMD) for median recurrence-free survival (RFS) was 4.19 in favor of HDAraC (95% CI, 0.59-7.78; P = .02). The WMD for 4-year RFS was 10.98 in favor of HDAraC (95% CI, 1.02-20.94; P = .03). The WMD for median overall survival (OS) was - 0.22 for HDAraC compared with SDAraC (95% CI, - 2.76-2.32; P = .9). Data regarding the median OS was heterogeneous between studies (chi-square P = .00), with 2 studies in favor of HDAraC and 2 studies in favor of SDAraC. The WMD for 4-year OS was 6.21 in favor of HDAraC (95% CI, 2.70-9.72; P = .0005).

CONCLUSIONS

Induction therapy with HDAraC improved long-term disease control and overall survival in adults age < 60 years with de novo AML. It remains unknown whether patients should receive HDAraC during induction or if it is to be given during postremission therapy. Further analyses should focus on this issue and on the effects of HDAraC in prognostically different subgroups of patients with AML.

Effect of gamma-linolenic acid and prostaglandins E1 on gamma-radiation and chemical-induced genetic damage to the bone marrow cells of mice

The effect of gamma-linolenic acid (GLA) and prostaglandin E1 (PGE1) on gamma-radiation, diphenylhydantoin (DPH), benzo(a)pyrene (BP), and 4-alpha-phorbol-induced genetic damage to the bone marrow cells of mice, using the sensitive micronucleus (MN) test was investigated. PGE1 and its precursor GLA prevented gamma-radiation, DPH, BP, and 4-alpha-phorbol-induced genetic damage.

Simultaneous localization of MLL, AF4 and ENL genes in interphase nuclei by 3D-FISH: MLL translocation revisited

Background

Haematological cancer is characterised by chromosomal translocation (e.g. MLL translocation in acute leukaemia) and two models have been proposed to explain the origins of recurrent reciprocal translocation. The first, established from pairs of translocated genes (such as BCR and ABL), considers the spatial proximity of loci in interphase nuclei (static "contact first" model). The second model is based on the dynamics of double strand break ends during repair processes (dynamic "breakage first" model). Since the MLL gene involved in 11q23 translocation has more than 40 partners, the study of the relative positions of the MLL gene with both the most frequent partner gene (AF4) and a less frequent partner gene (ENL), should elucidate the MLL translocation mechanism.

Methods

Using triple labeling 3D FISH experiments, we have determined the relative positions of MLL, AF4 and ENL genes, in two lymphoblastic and two myeloid human cell lines.

Results

In all cell lines, the ENL gene is significantly closer to the MLL gene than the AF4 gene (with P value < 0.0001). According to the static "contact first" model of the translocation mechanism, a minimal distance between loci would indicate a greater probability of the occurrence of t(11;19)(q23;p13.3) compared to t(4;11)(q21;q23). However this is in contradiction to the epidemiology of 11q23 translocation.

Conclusion

The simultaneous multi-probe hybridization in 3D-FISH is a new approach in addressing the correlation between spatial proximity and occurrence of translocation. Our observations are not consistent with the static "contact first" model of translocation. The recently proposed dynamic "breakage first" model offers an attractive alternative explanation.

Saccharomyces cerevisiae as a model system to define the chromosomal instability phenotype

Translocations, deletions, and chromosome fusions are frequent events seen in cancers with genome instability. Here we analyzed 358 genome rearrangements generated in Saccharomyces cerevisiae selected by the loss of the nonessential terminal segment of chromosome V. The rearrangements appeared to be generated by both nonhomologous end joining and homologous recombination and targeted all chromosomes. Fifteen percent of the rearrangements occurred independently more than once. High levels of specific classes of rearrangements were isolated from strains with specific mutations: translocations to Ty elements were increased in telomerase-defective mutants, potential dicentric translocations and dicentric isochromosomes were associated with cell cycle checkpoint defects, chromosome fusions were frequent in strains with both telomerase and cell cycle checkpoint defects, and translocations to homolog genes were seen in strains with defects allowing homoeologous recombination. An analysis of human cancer-associated rearrangements revealed parallels to the effects that strain genotypes have on classes of rearrangement in S. cerevisiae.

Both V(D)J coding ends but neither signal end can recombine at the bcl-2 major breakpoint region, and the rejoining is ligase IV dependent

The t(14;18) chromosomal translocation is the most common translocation in human cancer, and it occurs in all follicular lymphomas. The 150-bp bcl-2 major breakpoint region (Mbr) on chromosome 18 is a fragile site, because it adopts a non-B DNA conformation that can be cleaved by the RAG complex. The non-B DNA structure and the chromosomal translocation can be recapitulated on intracellular human minichromosomes where immunoglobulin 12- and 23-signals are positioned downstream of the bcl-2 Mbr. Here we show that either of the two coding ends in these V(D)J recombination reactions can recombine with either of the two broken ends of the bcl-2 Mbr but that neither signal end can recombine with the Mbr. Moreover, we show that the rejoining is fully dependent on DNA ligase IV, indicating that the rejoining phase relies on the nonhomologous DNA end-joining pathway. These results permit us to formulate a complete model for the order and types of cleavage and rejoining events in the t(14;18) translocation.

Use of OctoChrome fluorescence in situ hybridization to detect specific aneuploidy among all 24 chromosomes in benzene-exposed workers

Benzene is an established human leukemogen. The mechanism of benzene-induced leukemogenesis, however, remains unclear, but chromosomal damage is thought to play a critical role. We previously reported that the loss of chromosomes 5 and 7 (monosomy 5 and 7) and the gain of chromosomes 8 and 21 (trisomy 8 and 21) are significantly increased in benzene-exposed workers in comparison to matched controls. To determine if selective effects of benzene can occur, we employed three-color painting on an 8-square slide to screen numerical changes in all 24 human chromosomes (OctoChrome FISH) in a pilot study of 11 subjects (6 exposed to >5 ppm benzene and 5 age- and sex-matched controls). The effects of benzene on each chromosome were assessed as the incidence rate ratio (IRR) from a Poisson regression model with the strongest effects being reflected by the highest IRR values. Monosomy of chromosomes 5, 6, 7 and 10 had the highest IRRs and statistical significance in this preliminary study (IRR>2.5, p<0.01). On the other hand, the monosomy levels of six other chromosomes (1, 4, 9, 11, 22 and Y) were unchanged in the exposed workers with IRRs close to 1.0. Similarly, selective effects were also observed on trisomy induction with chromosomes 8, 9, 17, 21 and 22 (IRR>2.5, p<0.01). These results suggest that benzene has the capability of producing selective effects on certain chromosomes, which is supported by our in vitro findings showing that chromosomes 5 and 7 are more sensitive to loss than other chromosomes following exposure to benzene metabolites. We are currently investigating potential mechanisms for this induction of selective aneuploidy.

Rearrangement of the MLL gene in acute myeloblastic leukemia: report of two rare translocations

Band 11q23 is known to be involved in translocations and insertions with a variety of partner chromosomes. They lead to MLL rearrangement, resulting in a fusion with numerous genes. We report here 2 male adults in whom a diagnosis of acute myelomonoblastic leukemia (FAB M4) and acute monoblastic leukemia (FAB M5) was made. Conventional cytogenetic techniques showed a 45,XY,t(1;11)(p32;q23),-7 karyotype in the first case and a 46,XY, t(11;17)(q23;q21) in the second case. Fluorescent in situ hybridization (FISH) with a specific MLL probe showed the gene to be disrupted, the 3' region being translocated on the derivative chromosomes 1 and 17, respectively. Fourteen and 24 patients, including ours, with acute myeloblastic leukemia associated with a t(1;11)(p32;q23) and a t(11;17)(q23;q21), respectively have been reported in the literature. Several patients with the latter translocation have also been identified to have acute lymphoblastic leukemia (ALL). Although both translocations are preferentially associated with monocytic differentiation, the t(11;17)(q23;q21) is more common in adults and has been reported in many patients with ALL, compared to the t(1;11)(p32;q23).

Location ofMyc,Igh, andIgk on Robertsonian fusion chromosomes is inconsequential forMyc translocations and plasmacytoma development in mice, but Rb(6.15)-carrying tumors preferIgk-Myc inversions over translocations

The location of the Myc and immunoglobulin (Ig) loci on metacentric Robertsonian (Rb) fusion chromosomes may affect the development of mouse plasmacytomas (Pcts) by changing the probability with which chromosomal Myc-Ig translocations occur. To test this hypothesis, we induced Pcts in BALB/c (C) mice that carried Rb(4.12) and/or Rb(6.15) chromosomes. The Rb mice developed Pcts (n = 198) with similar onset and incidence to that in the inbred C mice. Karyotyping of 70 Rb-carrying Pcts demonstrated that in these tumors, just as in their counterparts in inbred C mice, the Igh heavy-chain locus was translocated with Myc more often than was the Igk light-chain locus. Pcts harboring Igh or Igk on normal and Rb chromosomes showed no bias toward either in generating Myc translocations. These findings indicated that the location of Myc, Igh, and Igk on normal or Rb chromosomes is inconsequential for Myc translocation and Pct development. In contrast, in Rb(6.15) mice, in which chromosomal inversions competed with chromosomal translocations for Igk-Myc juxtapositions, the former occurred more frequently than the latter in the resulting Pcts. This suggested that spatial proximity of Igk and Myc on the same chromosome facilitates the rearrangement of these loci. Myc translocation-dependent mouse Pct may provide a good model system for furthering our understanding of the relationship of higher-order genome organization in the interphase nucleus, origin of chromosomal translocations, and development of cancer.

Constitutional chromosome aberrations as pathogenetic events in hematologic malignancies

A predisposition to tumor development is associated with some constitutional chromosomal abnormalities. Investigations of families with an apparent hereditary cancer and constitutional chromosome rearrangements have led to the molecular identification of tumor suppressor genes. Under the somatic mutation theory for the development of cancer, two mutational events are required. The first step may be a constitutional event and the second an acquired genetic mutation. Cytogenetic studies were performed on 5633 bone marrow specimens from patients with hematologic malignancies from a single institution. Fifty cases of constitutional chromosome aberrations were detected. Data collected from the literature and from our series are reviewed and compared with the incidence of specific constitutional chromosome aberrations in the newborn population. Possible mechanisms that may predispose individuals with constitutional chromosome aberrations to the development of a hematologic malignancy are reviewed.

Molecular events in follicular thyroid tumors

Knowledge of the molecular events that govern human thyroid tumorigenesis has grown considerably in the past ten years. Key genetic alterations and new oncogenic pathways have been identified. Molecular genetic aberrations in thyroid carcinomas bear noteworthy resemblance to those in acute myelogenous leukemias. Thyroid carcinomas and myeloid leukemias both possess transcription factor gene rearrangements-PPARgamma-related translocations in thyroid carcinoma and RARalpha-related and CBF-related translocations (amongst others) in myeloid leukemia. PPARgamma and RARalpha are closely related members ofthe same nuclear receptor subfamily, and the PML-RARalpha and PAX8-PPARgamma fusion proteins both function as dominant negative inhibitors of their wild-type parent proteins. Thyroid carcinomas and myeloid leukemias also both harbor NRAS mutations (15-25% of both cancers) and receptor tyrosine kinase mutations--RET mutations in thyroid carcinomas and FLT3 mutations in myeloid leukemias. The NRAS and tyrosine receptor kinase mutations are not observed in the same thyroid carcinoma or leukemia patients, suggesting that multiple initiating pathways exist in both. Lastly, thyroid carcinomas and myeloid leukemias possess p53 mutations at relatively low frequency (10-15%) in patients who tend to be older and have more aggressive, therapy resistant disease. Such parallels are unlikely to occur by chance alone and argue that common mechanisms underlie these diverse epithelial and hematologic cancers. The comparison of thyroid carcinomas and myeloid leukemias may highlight areas of thyroid cancer investigation worthy of further focus. For example, few collaborating mutations have been defined in thyroid carcinomas even though they play a clear role in myeloid leukemias, as exemplified by RARalpha rearrangements and FLT3 mutations that together dictate the promyleocytic leukemia phenotype. Functional interactions between collaborating mutations are possible at multiple levels, and it is tempting to speculate that some thyroid carcinomas might develop through an unique combination or co-activation of RET and RAS and/or RET and PPARgamma (and/or other) signaling systems. In fact, the ELE1-RET (PTC3) fusion protein contains the ELE1 nuclear receptor co-activator domain and it appears to physically associate with and inhibit wild-type PPARgamma in some papillary carcinomas. The similarities of the fusion proteins in thyroid carcinoma and myeloid leukemia suggest that a more directed search for fusion genes in non-thyroid carcinomas is warranted. In fact, novel fusion genes have been identified recently in aggressive midline, secretory breast, and renal cell carcinomas, although the epithelial nature of the latter is not well-documented. Interestingly, these cancers all tend to present more frequently in adolescence and young adulthood in a manner similar to thyroid and myeloid malignancies that have fusion genes. The analyses of cancers that present earlier in life may enhance fusion gene recognition in other carcinoma types. Definition and biologic characterization of the precursor cells that give rise to thyroid carcinoma will also be important. Myeloid leukemias are thought to arise from stem/progenitor cells that acquire disturbed self-renewal and differentiation capacities but retain characteristics of the myeloid lineages. Although the presence of comparable stem/progenitor cells in the thyroid are not defined, distinct thyroid cancer lineages and patterns of differentiation exist and candidate stem/progenitor cells such as the p63-immunoreactive solid cell nests are apparent. A last important area is development of molecular-based therapies for thyroid carcinoma patients resistant to standard radio-iodine treatment. Treatments for such cancers are limited and pathways defined by thyroid cancer mutations are prime targets for pharmacologic interventions with molecular inhibitors. Tyrosine kinase inhibitors and nuclear receptor ligands have proven dramatically effective in some myeloid leukemia patients. Various molecular inhibitors are being investigated now in thyroid cancer models. Such developments predict that the thyroid cancer model will continue to provide biologic insights into human carcinoma biology and that improved pathologic diagnosis and treatment for thyroid cancer patients sit on the not too distant horizon.

Standardization and quality control studies of ‘real-time’ quantitative reverse transcriptase polymerase chain reaction of fusion gene transcripts for residual disease detection in leukemia – A Europe Against Cancer Program

Detection of minimal residual disease (MRD) has proven to provide independent prognostic information for treatment stratification in several types of leukemias such as childhood acute lymphoblastic leukemia (ALL), chronic myeloid leukemia (CML) and acute promyelocytic leukemia. This report focuses on the accurate quantitative measurement of fusion gene (FG) transcripts as can be applied in 35-45% of ALL and acute myeloid leukemia, and in more than 90% of CML. A total of 26 European university laboratories from 10 countries have collaborated to establish a standardized protocol for TaqMan-based real-time quantitative PCR (RQ-PCR) analysis of the main leukemia-associated FGs within the Europe Against Cancer (EAC) program. Four phases were scheduled: (1) training, (2) optimization, (3) sensitivity testing and (4) patient sample testing. During our program, three quality control rounds on a large series of coded RNA samples were performed including a balanced randomized assay, which enabled final validation of the EAC primer and probe sets. The expression level of the nine major FG transcripts in a large series of stored diagnostic leukemia samples (n=278) was evaluated. After normalization, no statistically significant difference in expression level was observed between bone marrow and peripheral blood on paired samples at diagnosis. However, RQ-PCR revealed marked differences in FG expression between transcripts in leukemic samples at diagnosis that could account for differential assay sensitivity. The development of standardized protocols for RQ-PCR analysis of FG transcripts provides a milestone for molecular determination of MRD levels. This is likely to prove invaluable to the management of patients entered into multicenter therapeutic trials.

Genetic and biological subgroups of low-stage follicular thyroid cancer

Investigations of cancer-specific gene rearrangements have increased our understanding of human neoplasia and led to the use of the rearrangements in pathological diagnosis of blood cell and connective tissue malignancies. Here, we have investigated 3p25 rearrangements of the peroxisome proliferator-activated receptor gamma (PPAR gamma) gene in follicular epithelial tumors of the human thyroid gland. Eleven of 42 (26%) low-stage follicular carcinomas, 0 of 40 follicular adenomas, 1 of 30 Hurthle cell carcinomas, 1 of 90 papillary carcinomas, and 0 of 10 nodular goiters had 3p25 rearrangements by interphase fluorescence in situ hybridization. All 11 follicular carcinomas with 3p25 rearrangement exhibited strong, diffuse nuclear immunoreactivity for PPAR gamma, consistent with expression of PPAR gamma fusion protein. Twelve of 42 (29%) low-stage follicular carcinomas had 3p25 aneusomy without PPAR gamma rearrangement (P = 0.01), suggesting that PPAR gamma rearrangement and aneuploidy are independent early events in follicular cancer. Eleven of 12 follicular carcinomas with 3p25 aneusomy exhibited no PPAR gamma immunoreactivity, supporting the existence of two independent pathways. Follicular carcinoma patients with PPAR gamma rearrangement more frequently had vascular invasion (P = 0.01), areas of solid/nested tumor histology (P < 0.001), and previous non-thyroid cancers (P < 0.01) compared with follicular carcinoma patients without PPAR gamma rearrangement. Our experiments identify genetic subgroups of low-stage follicular thyroid cancer and provide evidence that follicular carcinomas with PPAR gamma rearrangement are a distinct biological entity. The findings support a model in which separate genetic alterations initiate distinct pathways of oncogenesis in thyroid carcinoma subtypes.

Karyotype instability between diagnosis and relapse in 117 patients with acute myeloid leukemia: implications for resistance against therapy

The instability of the karyotype may play a role in the development of refractoriness of acute myeloid leukemia (AML) to anti-leukemic therapy. Therefore, in the current study cytogenetic analyses were performed in 117 patients with AML both at diagnosis and at relapse. Changes in karyotype were observed in 38% (36% of initially normal karyotypes, 39% of initially aberrant karyotypes). An evolution of karyotype, ie the acquisition of further aberrations in addition to those present at diagnosis, occurred more frequently in patients with unfavorable karyotypes at diagnosis as compared to all others (60% vs 32%, P = 0.0095). The duration from initial diagnosis to relapse was significantly shorter in cases with an evolution of the aberrant karyotype as compared to cases with no changes in the aberrant karyotype between diagnosis and relapse or with solely regression of aberrations at relapse (9.2 +/- 4.4 vs14.0 +/- 8.5 months, P = 0.0081). In an additional analysis, another cohort of 120 patients with refractory and relapsed AML who were treated uniformly within the respective trial of the German AML Cooperative Group was analyzed cytogenetically at diagnosis and at relapse to further prove the prognostic impact of karyotype aberrations at relapse. Karyotypes were prognostically favorable, intermediate, unfavorable and not available in 8%, 50%, 17% and 25% at diagnosis and in 8%, 49%, 21% and 22% at relapse, respectively. Karyotype aberrations at diagnosis had no impact on response to therapy (P = 0.32) but influenced survival and event-free survival significantly (P = 0.03 and P = 0.02). In contrast, karyotype aberrations at relapse strongly influenced response to therapy (P = 0.05), survival (P = 0.01), and event-free survival (P = 0.002). These data suggest that the instability of the karyotype between diagnosis and relapse and thus karyotype aberrations at relapse in particular contribute to the refractoriness of AML to anti-leukemic therapy.

Oral manifestations of acute myelomonocytic leukemia: a case report and review of the classification of leukemias

BACKGROUND

Oral signs and symptoms may indicate a serious underlying systemic disease. The most frequently observed oral findings of leukemia are mucosal bleeding and ulceration, petechiae, and gingival hyperplasia. This case report describes a 53-year-old male who presented with gingival enlargement and bleeding, fatigue, and recent weight loss as initial manifestations of acute myelomonocytic leukemia.

METHODS

A gingival biopsy was performed, revealing the presence of a hypercellular infiltrate of atypical myeloid and monocytic cells. Further work-up consisted of a complete blood count, bone marrow biopsy, and immunohistochemical and histochemical analysis of biopsy material and flow cytometry of peripheral blood.

RESULTS

Flow cytometry results confirmed that the infiltrate was of a myelomonocytic origin, and a diagnosis of acute myelomonocytic leukemia was rendered. The patient responded well to a chemotherapeutic induction regimen of cytosine arabinoside and idarubicin hydrochloride, with regression of gingival enlargement and remission of disease. The patient continued with consolidation chemotherapy and an autologous bone marrow transplant, but eventually died 22 months after initial diagnosis.

CONCLUSIONS

Oral health care professionals, especially periodontists, must recognize that gingival enlargement may represent an initial manifestation of an underlying systemic disease. Acute myelogenous leukemia is a hematological disorder with a predilection for gingival involvement.

Evidence for two commonly deleted regions on mouse chromosome 2 in gamma ray-induced acute myeloid leukemic cells

OBJECTIVE

The objective of this study was to delineate a precise molecular map of the commonly deleted region (CDR) on mouse chr2 in radiation-induced mouse acute myeloid leukemic (AML) cells.

MATERIALS AND METHODS

We used a PCR-based loss of heterozygosity (LOH) assay to map the chr2-CDR in AML cells isolated from F1 hybrid mice (BALB/cJ x CBA/CaJ) which developed AML following exposure to a single dose of 3 Gy of 137Cs gamma rays. A total of 30 polymorphic microsatellite markers, mapping within or close to chr2(D-E), were used under optimized PCR conditions that generate a single major band for each marker on a nondenaturing polyacrylamide gel.

RESULTS

Detailed LOH mapping identified two distinct AML-CDRs: one localized to a 4.6 centiMorgan (cM) interval between markers D2Mit272 and D2Mit394; the other mapped to a 0.8 cM interval between markers D2Mit276 and D2Mit444. Both CDRs span the mouse chr2E region.

CONCLUSION

The data present, for the first time, evidence for two distinctly noncontiguous CDRs on mouse chr2 harboring gene(s) involved in AML development. These CDRs are orthologous to human chromosomes 11p11-13 and 15q11-15 that have been implicated in subsets of AML. This finding indicates the region of mouse chr2 that must be searched for candidate genes involved in radiation-induced AML.

A novel selection system for chromosome translocations in Saccharomyces cerevisiae

Chromosomal translocations are common genetic abnormalities found in both leukemias and solid tumors. While much has been learned about the effects of specific translocations on cell proliferation, much less is known about what causes these chromosome rearrangements. This article describes the development and use of a system that genetically selects for rare translocation events using the yeast Saccharomyces cerevisiae. A translocation YAC was created that contains the breakpoint cluster region from the human MLL gene, a gene frequently involved in translocations in leukemia patients, flanked by positive and negative selection markers. A translocation between the YAC and a yeast chromosome, whose breakpoint falls within the MLL DNA, physically separates the markers and forms the basis for the selection. When RAD52 is deleted, essentially all of the selected and screened cells contain simple translocations. The detectable translocation rates are the same in haploids and diploids, although the mechanisms involved and true translocation rates may be distinct. A unique double-strand break induced within the MLL sequences increases the number of detectable translocation events 100- to 1000-fold. This novel system provides a tractable assay for answering basic mechanistic questions about the development of chromosomal translocations.

Differential response to stem cell factor and Flt3 ligand by the FAB subtype in acute myeloid leukemia clonogenic cells

Proliferative response of blast clonogenic cells to various hematopoietic growth factors (HGF), including stem cell factor (SCF) and flt3 ligand (FL) was investigated in 100 patients with acute myeloid leukemia (AML) and chronic myelogenous leukemia (CML) in myeloid crisis (MC). The frequency of spontaneous colony formation was significantly high in CML in MC (55%) and AML French-American-British (FAB) subtype M4 (48%) compared with M2 (16%). No spontaneous colony was formed in any of the patients with M1 and M3. The frequency of proliferative response to various HGF alone and in combination according to FAB subtype and CML in MC was as follows: that to granulocyte colony-stimulating factor (G-CSF) was lowest in M1 and CML in MC (50%) compared with other FAB subtypes (>or=86%), that to granulocyte-macrophage CSF (GM-CSF) was lowest in CML in MC (44%) compared with FAB subtypes (>or=74%), and that to interleukin-3 (IL-3) was lowest in CML in MC (30%) compared with FAB subtypes (>or=78%). SCF and FL stimulated blast colony formation in 11% and 17% of patients with M3, respectively, but there was no response to both, and in 60% and 57% of patients with CML in MC, respectively, with 14% showing a response to both. The frequency of proliferative response to both SCF and FL increased in the order of M1 (33%), M2 (63%), M4-5 (95%), and M6 (100%). The results are summarized as follows: absence of spontaneous colony formation and response to HGF other than SCF and FL, designated as HGF-dependent growth (M3); spontaneous colony formation and lowest response to HGF, designated as autonomous growth (CML in MC); and spontaneous colony formation and highest response to HGF including SCF and FL, designated as autocrine growth (M4-6). M1 and M2 were intermediate between CML in MC and M4-6. The relation between in vitro growth pattern of blast clonogenic cells and prognosis in AML FAB subtype and CML in MC is discussed.