Amplified c-MYC sequences localized by fluorescence in-situ hybridization on double minute chromosomes in acute myeloid leukemias

FLT3 Amplification as Double Minute Chromosomes in a Patient with Chronic Myelomonocytic Leukemia

Double minute chromosomes (dmins) are a form of gene amplification presenting as small spherical paired chromatin bodies. Dmins are rare in hematologic malignancies and are generally associated with a poor prognosis. Some case reports identified MYC or MLL gene amplification performing as dmin in myeloid neoplasms. FLT3 (FMS-related tyrosine kinase 3) acts as an oncogene in myeloid neoplasms which is associated with several signal transduction pathways. Genomic amplification of FLT3 has not been reported in hematological disease. The current study attempts to demonstrate the existence of double minute chromosomes via FLT3 gene amplification in a patient diagnosed with chronic myelomonocytic leukemia (CMML). Routine G-banded karyotype, array-based comparative genomic hybridization, and fluorescence in situ hybridization analyses were used to characterize the cytogenetic abnormality in the patient's bone marrow. FLT3 amplification as dmins in a patient with CMML was revealed. This case study reports a rare double minute chromosome via FLT3 amplification in CMML by using array-based comparative genomic hybridization and fluorescence in situ hybridization analyses. The study also proposed another possible mechanism of FLT3 genes in leukemogenesis.

Double minute chromosomes in acute myeloid leukemia, myelodysplastic syndromes, and chronic myelomonocytic leukemia are associated with micronuclei, MYC or MLL amplification, and complex karyotype

Double minute chromosomes (dmin) are small, paired chromatin bodies that lack a centromere and represent a form of extrachromosomal gene amplification. Dmin are rare in myeloid neoplasms and are generally associated with a poor prognosis. Most studies of dmin in myeloid neoplasms are case reports or small series. In the current study, we present the clinicopathologic and cytogenetic features of 22 patients with myeloid neoplasms harboring dmin. These neoplasms included acute myeloid leukemia (AML) (n = 18), myelodysplastic syndrome (MDS) (n = 3), and chronic myelomonocytic leukemia (CMML) (n = 1). The AML cases consisted of AML with myelodysplasia-related changes (n = 13) and therapy-related AML (n = 5). Dmin were detected in initial pre-therapy samples in 14 patients with AML or CMML; they were acquired during the disease course in 8 patients who had AML or MDS. The presence of dmin was associated with micronuclei (18/18; 100%), complex karyotype (17/22; 77.3%), and amplification of MYC (12/16; 75%) or MLL (4/16; 25%). Immunohistochemical staining for MYC performed on bone marrow core biopsy or clot sections revealed increased MYC protein in all 19 cases tested. Except for one patient, most patients failed to respond to risk-adapted chemotherapies. At last follow up, all patients had died of disease after a median of 5 months following dmin detection. In conclusion, dmin in myeloid neoplasms commonly harbor MYC or MLL gene amplification and manifest as micronuclei within leukemic blasts. Dmin are often associated with myelodysplasia or therapy-related disease, and complex karyotypes.

Double minutes and MYC amplification: a combined May-Grunwald Giemsa and fluorescence in situ hybridization study

OBJECTIVES

To report the demonstration of double minutes with MYC amplification in a case of myeloproliferative neoplasm with monocytosis in transformation by a combination of standard karyotyping and interphase and metaphase fluorescence in situ hybridization (FISH).

METHODS

To determine the lineage involvement, we applied combined morphology and an interphase FISH study using dual-color break-apart probes for MYC on peripheral blood film.

RESULTS

MYC amplification was demonstrated in both myeloid and monocytic cells but not lymphocytes. The MYC amplification was not associated with loss of MYC signals at the homologous 8q24 regions where the genes were located. Furthermore, the extent of MYC amplification has been shown to diminish as the granulocytes mature.

CONCLUSIONS

Combined morphology and FISH study has shown a pluripotent myeloid disorder and also an inverse relationship between cell maturity and MYC amplification.

Gene amplification in myeloid leukemias elucidated by fluorescence in situ hybridization

Gene amplification in hematologic malignancies is uncommon. When karyotyping leukemia cells, gene amplification is generally seen as double-minute (dmin) chromosomes and homogeneously staining regions (hsr). One of the more commonly amplified regions is MYC at 8q24.21, but amplification of MLL at 11q23 and regions on 9p, 19q, and elsewhere on 11q have been reported. Increased copy number of these genes has been associated with poor prognosis. Over an 11-year period, we identified 31 cases of possible gene amplification, 27 of which had enough sample material for further investigations. A total of 17 cases had dmin only, 13 cases had hsr only, and 1 case had both dmin and hsr in the karyotype. Fluorescence in situ hybridization (FISH) analysis identified amplification of MYC in 12 cases, all on dmin, and amplification of MLL in eight cases, all on hsr. Regions other than MYC and MLL were amplified in eight cases and, using multicolor FISH and multicolor banding, we identified a number of novel regions of amplification: 13q11 approximately q12.1, 15q26.1 approximately q26.3, and 17q12. We also identified one case where two different chromosomal regions were simultaneously amplified in the same cell line.

Double minutes, cytogenetic equivalents of gene amplification, in human neoplasia - a review

Double minutes are tiny spherical chromatin bodies of a few mega-base pairs of size which are found occasionally in hematopoietic neoplasia and more or less often in human solid tumors. They have been associated with worse prognosis and poor outcome of the malignancies where present. With the beginning era of molecular cytogenetics they could be defined as cytogenetic equivalents of amplified DNA sequences. The identification of involved chromosomal segments and their molecular nature led to the development of molecular genetic techniques for a rapid and reliable detection of prognostically important oncogene amplifications in human tumors and,as a consequence, to gene-targeted therapy.

Trisomy 4 associated with double minute chromosomes and MYC amplification in acute myeloblastic leukemia

A case of de novo acute myeloblastic leukemia (AML) M2, with trisomy 4 and double minute (dmin) chromosomes is reported. Amplification of the MYC gene ascertained by FISH was associated with dmin. A review of the literature of trisomy 4-dmin-associated AML shows that this entity preferentially occurs in elderly women and is not always associated with previously identified exposition to mutagens.

Double minute chromosomes in monoblastic (M5) and myeloblastic (M2) acute myeloid leukemia: two case reports and a review of literature

Double minutes (dmin) are small, paired chromatin bodies that lack a centromere and represent a form of extrachromosomal gene amplification. Although they have been found in a variety of solid tumors, their presence in hematological malignancies, especially acute myeloid leukemia (AML), is rare. In addition, the presence of dmin may be a mechanism for upregulated oncogene expression and is generally associated with a poor prognosis. We describe two patients who had dmin at initial presentation of AML, including the first case of M5a with C-MYC amplification on dmin, and another case with C-MYC amplification as the only cytogenetic finding. We review here a total of 33 cases with dmin in AML. C-MYC was amplified by the dmin in 25 cases, while other putative oncogenes were amplified in the other 8.

ABL oncogene amplification with p16(INK4a) gene deletion in precursor T-cell acute lymphoblastic leukemia/lymphoma: report of the first case

Gene amplification is a relatively rare event in hematologic malignancies. The ABL gene on chromosome band 9q34 is a proto-oncogene and is the well-known translocation partner of the BCR gene on 22q11 giving rise to t(9;22)(q34;q11), which is the hallmark of chronic myeloid leukemia and is the most common chromosomal abnormality in adult acute lymphoblastic leukemia (ALL). Amplification of ABL is an exceedingly rare event, with only less than 5 cases reported in the literature. The p16(INK4a) (or CDKN2A) gene on 9p21 is a tumor suppressor gene, and deletion thereof is recently recognized as one of the most common genetic abnormalities in ALL. The authors herein describe an 8-year-old male patient with precursor T-cell ALL harboring both ABL gene amplification and p16(INK4a) gene deletion. Fluorescence in situ hybridization (FISH) analysis using BCR/ABL probes revealed five or more ABL signals, indicating amplification in 51.5% of interphase nuclei. FISH using p16(INK4a) gene probes showed heterozygous p16(INK4a) deletion in 71.0%. On conventional cytogenetic analysis, however, only 10 metaphases were available, which showed the normal karyotype, 46,XY[10], serving no evidence for the findings on FISH. This is the first report of an ALL case with ABL amplification, and the authors speculate that both ABL proto-oncogene amplification and the p16(INK4a) tumor suppressor gene deletion have been implicated in leukemogenesis in the present case, although whether the ABL amplification truly contributes to the leukemogenesis or merely an epiphenomenon representing underlying genomic instability remains to be determined.

Additional cytogenetic abnormalities in adults with Philadelphia chromosome-positive acute lymphoblastic leukaemia: a study of the Cancer and Leukaemia Group B

We analysed the nature and prognostic significance of secondary cytogenetic changes in 111 newly diagnosed adults with acute lymphoblastic leukaemia (ALL) and t(9;22)(q34;q11.2) or its variants. Secondary aberrations were seen in 75 (68%) patients. They included, in order of descending frequency: +der(22)t(9;22), +21, abnormalities of 9p, high hyperdiploidy (>50 chromosomes), +8, -7, +X and abnormalities resulting in loss of material from 8p, gain of 8q, gain of 1q and loss of 7p. Eighty patients (72%) had > or =1 normal metaphase in their karyotype. There were four balanced and 12 unbalanced translocations previously unreported in ALL with t(9;22). The t(2;7)(p11;p13) and der(18)t(8;18)(q11.2;p11.2) were seen in two cases each, and have never before been reported in haematological malignancy. All but four patients were treated on front-line Cancer and Leukaemia Group B clinical protocols. The presence of -7 as a sole secondary abnormality was associated with a lower complete remission (CR) rate (P = 0.004), while the presence of > or =3 aberrations was associated with a higher CR rate (P = 0.009) and +der(22)t(9;22) with a higher cumulative incidence of relapse (P = 0.02). It will be of interest to see if newly diagnosed t(9;22)-positive adult ALL patients with these and other secondary aberrations respond differently to treatment regimens that include imatinib mesylate.

Expression of the p14ARF tumor suppressor predicts survival in acute myeloid leukemia

Cell cycle aberrations are associated with therapy outcome in many types of cancer. We analyzed mRNA expression levels of 18 cell cycle-related genes in bone marrow samples from 78 acute myeloid leukemia (AML) patients and six controls using high-throughput quantitative RT-PCR. Samples of AML patients contained significantly increased mRNA expression levels of the mdm2 and c-myc oncogenes. Also, the average expression levels of p14ARF and p16INK4A were higher in patient samples compared to controls. Leukemic blasts and control bone marrow samples did not differ significantly in the expression levels of proliferation-associated genes such as cyclin A2 and pcna. When single genes were analyzed for prognostic significance in Kaplan-Meier and Cox regression analyses, a low p14ARF level emerged as a strong and independent predictor for poor survival (P=0.04 and 0.029). Subsequently, p14ARF mRNA levels were analyzed in a second, independent patient population (n=57). Again, low p14ARF levels were associated with a worse outcome. Finally, immunohistochemistry analysis of AML tissue arrays confirmed the widespread expression of c-myc and p14ARF in AML on the protein level. Taken together, the expression of the p53 regulators mdm2 and p14ARF are altered in AML, and low p14ARF levels indicate a poor prognosis.

Prognostic significance of trisomy 4 as the sole cytogenetic abnormality in acute myeloid leukemia

Trisomy 4 is a recurrent but rare cytogenetic abnormality reported in patients with acute myeloblastic leukemia (AML). The prognostic significance of this abnormality in patients with AML is not clear. We report here four cases of trisomy 4 as the sole cytogenetic abnormality in AML patients treated at our institute during the last 15 years and systematically review all reported cases of trisomy 4 as a solitary cytogenetic abnormality in AML with the aim of studying the disease demography and prognostic significance of this abnormality. Collective data on 30 patients (including four in the present report) showed complete remission (CR) rates of 76.6%. Median relapse free survival and overall survival were 7 months (95% CI 5-17) and 9 months (95% CI 3-17), respectively. Given the limitations of reported literature, the prognosis of AML patients with trisomy 4 appears to be poor compared with the intermediate risk cytogenetics. Collaborations between major institutions and cooperative groups are needed to collect better quality data to understand the prognostic significance of such rare karyotypic abnormalities.

Radiation therapy depletes extrachromosomally amplified drug resistance genes and oncogenes from tumor cells via micronuclear capture of episomes and double minute chromosomes

PURPOSE

To determine if clinically relevant doses of ionizing radiation are capable of inducing extrachromosomal DNA loss in transformed human cell lines.

MATERIALS AND METHODS

The multidrug-resistant (MDR) human epidermoid KB-C1 cell line and the human neuroendocrine colon carcinoma line COLO320, which contain extrachromosomally amplified MDR1 drug resistance genes and MYCC oncogenes, were irradiated with 2 Gy fractions up to a total dose of 28 Gy. To track the fate of extrachromosomally amplified genes, cells surviving radiation therapy and unirradiated control cells were analyzed by fluorescent in situ hybridization of chromosomes using MDR1 and MYCC-specific cosmid DNA probes. In addition, total DNA and protein isolated from irradiated and control cells was subjected to Southern and Western blotting procedures, respectively, to determine amplified gene copy number and protein expression levels. Dose-response assays to follow loss of function of the MDR1 gene from KB-C1 cells were also performed.

RESULTS

A significant reduction in extrachromosomal DNA, amplified gene copy number, and expression was detected in surviving cells after relatively low doses of radiation. Entrapment of extrachromosomal DNA into micronuclei was a consistent feature of irradiated cells.

CONCLUSIONS

Clinically relevant doses of radiation can deplete extrachromosomal DNA in viable human malignant cells and alter their phenotype. Depletion of extrachromosomally amplified genes from tumor cells occurs via entrapment in radiation-induced micronuclei.

Double minute chromosomes in acute myeloid leukemia and myelodysplastic syndrome: identification of new amplification regions by fluorescence in situ hybridization and spectral karyotyping

Double minute chromosomes (dmin) are small chromatin bodies consisting of genes amplified in an extrachromosomal location. dmins are uncommon in hematologic malignancies; they are seen primarily in acute myeloid leukemia, with amplification of the MYC oncogene or, less frequently, the MLL transcription factor. Nine patients with hematologic malignancies with dmin were seen at the Roswell Park Cancer Institute between 1985 and 2000; eight had acute myeloid leukemia and one a myelodysplastic syndrome. Fluorescence in situ hybridization (FISH) demonstrated MYC amplification on dmin in four patients, but MLL amplification was not seen. Spectral karyotyping showed that the dmin derived from chromosome 11 in one patient and from chromosome 19 in two others without MYC or MLL amplification; derivation from these chromosomes was confirmed by FISH with chromosome paint probes. The dmin of chromosome 11 origin hybridized to a bacterial artificial chromosome (BAC) RP11-112M22 that maps to 11q24.3 and is predicted to contain ETS1 and other markers, including D11S11351 and D11S4091. The dmin of chromosome 19 origin in one patient hybridized to BACs RP11-46I12 and RP11-110J19; in the other patient, these clones did not hybridize with the dmin, but were found to be amplified on a marker chromosome that was derived from chromosome 19 in that patient's cells. These BACs have been mapped to 19q12-19q13.1 and 19q11-19q13.1, respectively, and are predicted to contain the markers D19S409 and D19S919 and the gene for ubiquinol-cytochrome C reductase, Rieske iron-sulfur polypeptide1 (UQCRFS1). dmin originating from chromosome 19 have not been reported previously in hematologic malignancies.

A new case of acute nonlymphocytic leukemia (French-American-British subtype M1) with double minutes and c-MYC amplification

Herein, we present a new case of acute nonlymphocytic leukemia (ANLL) French-American-British M1 subtype with presence of multiple double minutes (dmin) derived from the amplification of the c-MYC oncogene. A review of dmins in ANLL is presented.

Duplication or amplification of chromosome band 11q23, including the unrearranged MLL gene, is a recurrent abnormality in therapy-related MDS and AML, and is closely related to mutation of the TP53 gene and to previous therapy with alkylating agents

Gene amplification is a rare phenomenon in acute leukemia, but recently amplification of specific chromosome bands containing genes rearranged in leukemia-specific balanced chromosome translocations has been reported in a few cases. We detected duplication or amplification of chromosome band 11q23 with 3-7 copies of the MLL gene by fluorescence in situ hybridization in 12 out of 70 unselected patients with therapy-related myelodysplasia or acute myeloid leukemia (17%). In all but one case, the supernumerary copies of MLL were located to previously unidentified marker chromosomes or unbalanced translocations. In 4 of the 12 patients, 2-6 copies were located together on the same chromosome arm representing amplification, 7 patients had single, extra duplicated copies of MLL, whereas both amplification and duplication were observed in the same cell in 1 patient. Comparative genomic hybridization demonstrated gain of varying, often large parts of 11q in five patients. The MLL gene was shown to be unrearranged in all 12 patients. Seven out of eight patients with duplication or amplification of MLL had mutations of TP53. Patients with supernumerary copies of MLL were in general older (P = 0.007) and had a shorter survival (P < 0.001) compared to other patients. Duplication or amplification of MLL was significantly associated with a complex karyotype (P = 0.002), with deletion or loss of 5q (P = 0.001), and with prior therapy with alkylating agents. These results support the existence of a specific genetic pathway in t-MDS and t-AML with many previously unidentified chromosome aberrations demonstrated to represent extra copies of parts of 11q, including the unrearranged MLL gene.

Trisomy 4 and double minutes in acute myeloid leukemia: further evidence that double minutes can occur as the primary cytogenetic abnormality

The specific association of trisomy 4 and double minutes (dmin) is rare and is usually reported in patients with acute myeloid leukemia (AML), primarily M2 and M4 subtypes. Several previous reports describing this combination suggested that trisomy 4 was the primary cytogenetic abnormality, and that the presence of the dmin was secondary. We describe a 79-year-old male who presented with myelodysplasia, transforming to AML-M2. Cytogenetic analysis of bone marrow aspirate cultures showed a 46,XY,dmin[12]/47,XY,+4,dmin[7]/46, XY[6] karyotype. The number of dmin ranged from 1 to 150. Fluorescence in situ hybridization (FISH) analysis showed that the dmin were derived from amplification of the MYC oncogene. Dual-color interphase FISH analysis was performed with D4Z1 and MYC probes and showed no evidence of a clone containing trisomy 4 without dmin. These data suggest that dmin may also occur as the primary cytogenetic abnormality in patients with trisomy 4 and dmin.

Double minutes and c-MYC amplification in acute myelogenous leukemia: Are they prognostic factors?

A case of acute myelogenous leukemia (AML) with double minutes (dmin) and X chromosome loss is presented. Using comparative genomic hybridization (CGH), a region of high-level DNA amplification was detected at 8q24, the locus of the c-MYC proto-oncogene. Fluorescence in situ hybridization (FISH) with a DNA probe specific for the human c-MYC gene confirmed the extrachromosomal amplification of this proto-oncogene in the dmin of the leukemic cells. During the course of the disease, three relapses occurred; two complete remissions could be achieved by treatment with various chemotherapy regimens. The patient's survival time of 25 months was considerably longer than in most reported cases of AML with extrachromosomal c-MYC amplification. Therefore, the present case challenges the view that the occurrence of dmin in AML is generally an indication of poor prognosis.

Nuclear topography of the c-myc gene in human leukemic cells

The c-myc gene plays an essential role in the regulation of the cell cycle and differentiation. Therefore, changes of the c-myc positioning during differentiation are of great interest. As a model system of cell differentiation, the HL-60 and U-937 human leukemic cell lines were used in our experiments. These cells can be induced to differentiation into granulocytes that represent one of the pathways of blood cell maturation. In this study, changes of the topographic characteristics of the c-myc gene (8q24), centromeric region of chromosome 8 and chromosome 8 domain during differentiation of HL-60 and U-937 cells were detected using fluorescence in-situ hybridisation (FISH). FISH techniques and fluorescence microscopy combined with image acquisition and analysis (high-resolution cytometry) were used in order to detect the topographic features of nuclear chromatin. Increased centre of nucleus-to-gene and gene-to-gene distances of c-myc genes, centromeric region of chromosome 8 and chromosome 8 domains were found early after the induction of granulocytic differentiation by dimethyl sulfoxide (DMSO) or retinoic acid (RA); the size of the chromosome 8 domains was rapidly reduced. In differentiated cells, c-myc is located at greater distances from the centromeric regions of chromosome 8. These results support the idea that relocation of the c-myc gene to the nuclear periphery and the condensation of the chromosome 8 domain might be associated with the c-myc gene expression due to common kinetics during granulocytic differentiation.

MYC oncogenes and human neoplastic disease

c-myc, N-myc and L-myc are the three members of the myc oncoprotein family whose role in the pathogenesis of many human neoplastic diseases has received wide empirical support. In this review, we first summarize data, derived mainly from non-clinical studies, indicating that these oncoproteins actually serve quite different roles in vivo. This concept necessarily lies at the heart of the basis for the observation that the deregulated expression of each MYC gene is reproducibly associated with only certain naturally occurring malignancies in humans and that these genes are not interchangeable with respect to their aberrant functional consequences. We also review evidence implicating each of the above MYC genes in specific neoplastic diseases and have attempted to identify unresolved questions which deserve further basic or clinical investigation. We have made every attempt to review those diseases for which significant and confirmatory evidence, based on studies with primary tumor material, exists to implicate MYC members in their causation and/or progression.

Molecular genetics and cytogenetics of myeloproliferative disorders

The myeloproliferative disorders are believed to represent clonal malignancies resulting from transformation of a pluripotent stem cell. X-inactivation patterns of peripheral blood cells have been proposed as a useful diagnostic tool but this method is limited by the finding of a clonal X-inactivation pattern in a significant proportion of normal elderly women. There is no pathognomonic chromosomal abnormality associated with the myeloproliferative disorders. However, consistent acquired cytogenetic changes include del(20q), del(13q), trisomy 8 and 9 and duplication of segments of 1q, all of which have been observed at diagnosis or before cytoreductive therapy and therefore represent early lesions which contribute to the pathogenesis of these disorders. Although, the acquired molecular defects underlying most myeloproliferative disorders have not yet been elucidated, translocations associated with the rare 8p11 syndrome have permitted identification of a novel fusion protein. The role of a number of candidate genes in the other myeloproliferative disorders has also been studied, but no mutations have been identified so far. It is likely that a number of genes will be involved, given the varied phenotypes of the diseases. Identification of causal genes will be of considerable interest to both clinicians, who currently lack a specific and sensitive diagnostic test, and scientists interested in fundamental issues of stem cell behaviour.