[Cytogenetic monitoring acute myeloid leucosis in children].

Preliminary results of cytogenetic monitoring acute myeloid leukosis (AML) in children are presented. Repeated chromosomal analyses were accomplished in 23 patients that presented with cell clones showing various karyotype abnormalities prior to the onset of therapy. All the patients were treated following identical protocols. Complete hematological remission was achieved in 20 cases. The majority of patients did not have cells with chromosomal abnormalities changes after a 2-4 month follow up. Anomalous metaphases persisted in 6 patients although their occurrence decreased. Five of them poorly responded to therapy whereas simultaneous achievement of morphological and cytogenetic remission ensured more beneficial outcome of the treatment. Results of the study agree with recent reports of delayed reversion to normal karyotype under effect of AML therapy that as a rule predicts an unfavourable prognosis Repeated analysis during stable hematological remission did not reveal cells with karyotype abnormalities in bone marrow with the exception of a single patient who had marrow cells with chromosomal translocation (16:16) up to the 8th month of complete hematological remission. This patient remains under observation (duration of remission is now 15 months). It was shown that the relative amount of cells with abnormal karyotype in bone marrow frequently exceeds that of blast cells (usually before the onset of therapy and sometimes in the beginning of morphological remission). During stable remission, such an excess is an antecedent of relapse. It is concluded that cytogenetic analysis for monitoring AML extends the possibility of detecting leukemia cells.

[Chromosomal translocation t(8,21) in acute myeloid leukemia of children: prognostic value of additional karyotype abnormalities].

Prognostic significance of additional karyotype abnormalities was studied in 73 children with t(8,21) acute myeloid leukemia (AML). Additional chromosomal aberrations were documented in 61 cases (83.6%). The loss of sex chromosomes and/or deletion of the long arm of chromosome 9 (9q-) were predominant abnormalities, in agreement with the literature data. Other additional abnormalities detected in 14 cases were tentatively designated as "atypical". Comparison of pretreatment cytogenetic data and those obtained during relapses revealed the previously unknown rise in the frequency of atypical abnormalities in AML relapses (to 63.6% vs 19.2% at the first presentation, p < 0.005). It is supposed that atypical additional abnormalities reflect relatively late stages of leukemia, and their presence before therapy predicts poor prognosis. In fact, general, relapse-free, and uneventful survival rates in patients with atypical abnormalities were significantly lower that in the remaining patients with t(8;21) AML. Poor survival was associated not only with early relapses but also with high mortality from fatal infections soon after onset of treatment. The incidence of fatal infections in this group was significantly higher than in patients without atypical abnormalities (p = 0.027). Atypical additional abnormalities are rather variable and each variant should to be specifically characterized to estimate its prognostic significance. Our results need to be verified in a larger-scale multicentre study.

[Complex karyotype abnormalities in pediatric acute myeloid leukemia].

A majority of the data on the prognostic significance of distinct chromosome changes and combinations of them in pediatric acute myeloid leukemia (AML) has been derived from adult studies, with not numerous published data in pediatric patients. One of points needed to be clarified is prognostic significance of complex karyotype (at least 3 unrelated abnormalities). We investigated characteristic features of complex karyotype in newly diagnosed pediatric AML de novo. Cell clones with complex karyotype were found in 35 of 254 (13.8%) patients at the age from 0 to 15 years studied prior to therapy. The group was divided into 2 subgroups depending on presence of favorable chromosome abnormalities, i.e. (see symbols)(8;21), t(15;17) and inv(16). The abnormalities were absent in 20 cases (1st subgroup), in 15 remaining patients they were identified (2nd subgroup). In 2nd subgroup karyotypes were not so considerably changed and no adverse risk markers were detected as distinct from 1st subgroup. New data were obtained for complex karyotype differences of adult and pediatric AML. In the great majority (76%) of complex karyotypes in our adult patients chromosome abnormalities associated with adverse risk were found but in pediatric patients their frequency was significantly less (30%). The highest rate of complex karyotype we observed in children at the age from 0 to 3 years. Similar data were not published earlier. Complex karyotype is considered to be characteristic of older AML patients and in the majority of the patients the karyotype contains markers of adverse risk. Possibly, worse outcome in older AML patients is connected with the markers but not with multiple chromosome changes. New data of frequency and the peculiarities of complex karyotype in pediatric AML are important for understanding of AML pathogenesis and for development a more effective AML treatment.

P53-dependent effects of RAS oncogene on chromosome stability and cell cycle checkpoints.

Mutations activating the function of ras proto-oncogenes are often observed in human tumors. Their oncogenic potential is mainly due to permanent stimulation of cellular proliferation and dramatic changes in morphogenic reactions of the cell. To learn more on the role of ras activation in cancerogenesis we studied its effects on chromosome stability and cell cycle checkpoints. Since the ability of ras oncogenes to cause cell transformation may be dependent on activity of the p53 tumor-suppressor the cells with different p53 state were analysed. Ectopic expression of N-ras(asp12) caused in p53-deficient MDAH041 cell line an augmentation in the number of chromosome breaks in mitogenic cells, significant increase in the frequency of metaphases showing chromosome endoreduplication and accumulation of polyploid cells. Similar effects were induced by different exogenous ras genes (N-ras(asp12), H-ras(leu12), N-ras proto-oncogene) in Rat1 and Rat2 cells which have a defect in p53-upstream pathways. In contrast, in REF52 and human LIM1215 cells showing ras-induced p53 up-regulation, ras expression caused only slight increase in the number of chromosome breaks and did not enhance the frequency of endoreduplication and polyploidy. Inactivation in these cells of p53 function by transduction of dominant-negative C-terminal p53 fragment (genetic suppressor element #22, GSE22) or mutant p53s significantly increased the frequency of both spontaneous and ras-induced karyotypic changes. In concordance with these observations we have found that expression of ras oncogene caused in p53-defective cells further mitigation of ethyl-metansulphonate-induced G1 and G2 cell cycle arrest, but did not abrogate G1 and G2 cell cycle checkpoints in cells with normal p53 function. These data indicate that along with stimulation of cell proliferation and morphological transformation ras activation can contribute to cancerogenesis by increasing genetic instability.

Increased karyotype precision using fluorescence in situ hybridization and spectral karyotyping in patients with myeloid malignancies.

We studied seven patients with various malignant hematologic disorders using fluorescence in situ hybridization (FISH) and one of these patients with spectral karyotyping (SKY). With appropriate probes, the t(8;21) and inv(16) were confirmed in two patients and the karyotypic precision was increased in five others using FISH and SKY. Two of three patients with 12p rearrangements had a deletion of one TEL allele. Thus, these newer techniques are an important adjunct to accurate chromosome analysis in malignancy.

[Karyotypic anomalies and chromosomal sites of increased fragility in colorectal cancer]. / Anomalii kariotipa i saity povyshennoi lomskiti khromosom pri kolorektal'nykh rakakh.

Karyotypic structural aberrations in tumor cells and chromosome constitutive fragile sites (cFSs) in peripheral blood lymphocytes were studied in ten patients with colorectal adenocarcinoma Most chromosome breakpoints (38 out of 40, i.e., 95.0%) were shown to be located within cFSs in tumor cells. Expression of 24 out of 137 cFSs in patients was higher than that in healthy donors. Four of these cFSs (6q26, 7q36, 16q23, and 17q21), were involved in the formation of nonrandom tumor cell chromosome markers most characteristic of colorectal neoplasms. The frequency of damages induced within these sites was analyzed in each patient. Expression of 7q36, 16q23, and 17q21 was increased in blood cells of patients carrying specific chromosome rearrangements with the breakpoints within these sites. The association between nonrandom chromosome aberrations in tumor cells and cFSs in normal cells is discussed.

[p53 with a mutation in codon 273 increases the probability of amplifying the dhfr gene in Rat-1 and LIM1215 cells]. / p53 s mutatsiei v kodone 273 uvelichivaet veroiatnost' amplifikatsii gena dhfr v kletkakh Rat-1 i LIM1215.

The effect of the expression of the exogenous human mutant p53 (Arg-->His in codon 273) on the amplification rate of the gene dhfr in permissive Rat-1 and LIM1215 cells was studied. It was shown that injection of a retroviral construction with p53His273 resulted in the accumulation of methotrexate-resistant variants with an increased number of dhfr copies in populations of recipient cells. Luria-Delbruck fluctuation analysis revealed a four- to six-fold increase in the rate of appearance of new methotrexate-resistant cells. Chromosomal analysis demonstrated an extrachromosomal location of amplified DNA in cells containing p53His273, as was the case for control sublines. The data obtained indicate that modifications of p53 may induce gene amplification not only via removing the proliferation block of cells with amplified genes in selective medium, but also via some other mechanisms, that seem to increase the chromosomal recombination rate.

Regularities of karyotypic evolution during stepwise amplification of genes determining drug resistance.

Analysis of chromosomal alterations during stepwise development of mdr1, dhfr, or CAD gene amplifications in a large number of independently selected Djungarian hamster DM-15 and murine P388 sublines revealed typical patterns of karyotypic evolution, specific for multiplication of each of these genes in each cell type. Some principal similarities of karyotypic evolution were noted in at least two different systems. They include: (i) appearance at the first selection step of a new chromosomal arm bearing the resident gene copy followed at the next selection steps by the formation in these specific chromosomal arms of amplified DNA tandem arrays; (ii) translocations of amplified DNA from its initial site to other, also non-random, chromosomal sites; and (iii) emergence in the cell variants with high degrees of gene amplification of multiple extra-chromosomal elements. The most prominent distinctions among the systems were as follows: (i) different structures, evidently containing amplified DNAs, appeared at the initial steps of amplification of different genes--additional heterogeneously staining regions in specific chromosomal segments in the case of amplification of dhfr or CAD genes in DM-15 cells, and mini-chromosomes in the case of mdr1 gene amplification in both DM-15 and P380 cells; (ii) distinct patterns of location of the amplified mdr1 gene copies are characteristic of Djungarian hamster DM-15 and murine P388 cell derivatives after subsequent steps of selection--at the site of resident gene localization or in some other, also non-random, chromosomal sites in DM-15 sublines, and predominantly extra-chromosomal in P388 sublines. We propose that different mechanisms are responsible for the initial steps of amplification of dhfr and CAD genes on the one hand and the mdr1 gene on the other: non-equal sister-chromatid exchanges and autonomous replication of the extra-chromosomal elements. It seems, however, that both mechanisms may be involved in further rounds of amplification of each of these three genes.

Enhanced expression of 1p32 and 1p22 fragile sites in lymphocytes in cutaneous malignant melanomas.

Frequency and distribution of 5-fluorodeoxyuridine (5-FdU) plus caffeine-induced fragile sites on chromosomes of peripheral blood lymphocytes (PBL) from 10 patients with cutaneous melanoma were studied in comparison with 10 PBL samples from normal donors of corresponding sex and age. The total number of breaks showed a significant difference among individuals in both groups, however, the average frequencies of 5-FdU plus caffeine-induced, as well as spontaneous damages in PBL from melanoma patients, were higher than those from healthy volunteers. The analysis of the breakpoint distribution showed a statistically significant increase in the expression of several fragile sites. The highest enhancement was observed at 1p32 and 1p22 sites (p less than 0.001). Earlier, the increase in the expression of 1p32 fragile sites was reported for neuroblastoma patients. We believe that enhanced expression of fragile sites in 1p may play a yet-unknown pathogenetic role in the development of some neuroectodermal tumors.

[Segments of Djungarian hamster chromosomes, specific for translocation of integration of amplified mdr1 genes, do not possess increased instability]. / Uchastki khromosom dzhungarskogo khomiachka, spetsifichnye dlia translokatsii ili integratsii amplifitsirovannykh genov mdr1, ne obladaiut povyshennoi nestabil'nost'iu.

Earlier we have revealed in Djungarian hamster DM-15 cells three chromosomal segments (2p22, 5p1, 7q23-25) that are specific for transposition of amplified mdr1 genes from the site of location of resident gene copy (it was mapped to 4q21-23). In situ hybridization revealed in wild type cells no mdr1 homologous sequences in all these three segments. In this work we studied distribution of chromosomal breakages induced in DM-15 cells by aphidicolin, 5-fluorodeoxyuridine or N-phosphonacetyl-L-aspartate. The data obtained indicate that two of above mentioned segments. 2p22 and 7q23-25, contain no fragile sites. So, specificity of these segments for the transposition of amplified mdr1 genes is not due to their particular instability or to the presence in them of sequences homologous to amplifiable selectable gene.

Non-random karyotypic changes in Djungarian hamster tumors induced by 3-methylcholanthrene.

The karyotypes of 30 tumors (sarcomas and adenocarcinomas) induced with methylcholanthrene in Djungarian hamsters (Phodopus sungorus campbelli) have been investigated. In 23 tumors structural changes of the short arm of X-chromosome (Xp+ or Xp = type) were revealed. Non-random rearrangements of 3p, 7q and 8q were also observed. Other structural or numerical changes of the karyotype were accidential. For majority of tumors the presence of chromosome markers with long homogeneously staining regions or double minutes, structures are known as cytological manifestation of gene amplification, was typical. Induced tumors of the Djungarian hamster might serve as an interesting tool for studies of relationship of somatic cell genetic changes to different aspects of chemical carcinogenesis.

[Nonrandom karyotype changes in chemically induced tumors of the Djungarian hamster]. / Nesluchainye izmeneniia kariotipa v khimicheski indutsirovannykh opukholiakh dzhungarskogo khomiachka.

In the cells of tumors induced with methylcholanthrene in wild type and mutant (pink-eyed dilution) Djungarian hamsters non-random involvement in structural changes of certain chromosomes (Xp, 3p and 3q, 7q, 8q) was revealed. In addition, characteristic feature of the majority of tumors was varied number of double-minutes chromosomes (DMs). In some tumors, the markers with long homogeneously or differentially stained regions (HSRs and DSRs) were also present. The DMs, HSRs and DSRs are known as the structures containing amplified genes.

[Amplification of regions of the genome in the somatic cells of mammals resistant to colchicine. VII. Localization of the initial and amplified copies of gene mdr in one and the same segment of chromosome 4 of the Djungarian hamster]. / Amplifikatsiia uchastkov genoma v somaticheskikh kletkakh mlekopitaiushchikh, ustoichivykh k kolkhitsinu. Soobshchenie VII. Lokalizatsiia iskhodnoi i amplifitsirovannykh kopii gena mdr v odnom i tom zhe segmente khromosomy 4 dzhungarskogo khomiachka.

By in situ hybridization technique, the mdr gene which is amplified during the development of multiple drug resistance was mapped in the 4q15--21 segment of normal Djungarian hamster chromosome 4. As was shown earlier, this chromosomal region is specific for the location of amplified mdr gene copies. These results, as well as some data obtained by other authors, suggest that recombinations of amplified DNAs occur preferentially in or near the sites bearing homologous sequences.

[Cloning and characteristics of DNA sequences amplified in Djungarian hamster cells with multidrug resistance]. / Klonirovanie i kharakteristika uchastkov DNK, amplifitsirovannykh v kletkakh dzhungarskogo khomiachka, obladaiushchikh mnozhestvennoi ustoichivost'iu.

A number of DNA clones containing the amplified DNA sequences were isolated from the genomic library of multidrug-resistant (MDR) Djungarian hamster cells using the DNAC0t 10-250 hybridization probe. Five independent nonoverlapping clones were obtained that covered more than 100 kb of the amplified genomic region. These clones were used as hybridization probes in blot-hybridization with DNA from 7 independently derived MDR Djungarian hamster cell lines selected for the resistance to colchicine or actinomycin D. Some clones contained the DNA sequences amplified in all of the cell lines tested while the others contained the cell line specific amplified sequences. Hybridization in situ was used to localize the amplified DNA in metaphase chromosomes of a MDR cell line that contained about 140 copies of these sequences. The approximate size of an amplicon calculated on the basis of the obtained data is about 1-2 X 10(3) kb.

[Nomenclature of the metaphase chromosomes of the djungarian hamster]. / Nomenklatura metafaznykh khromosom dzhungarskogo khomiachka.

The proposed nomenclature of G-banded chromosomes of Phodopus sungorus campbelli is based on requisites and principles of the International System for Human Cytogenetic Nomenclature (ISCN).

[Isolation of DNA probes for the detection of sequences amplified in colchicine-resistant cells]. / Poluchenie DNK-zonda, predstavliaiushchego posledovatel'nosti, amplifitsirovannye v ustoichivykh k kolkhitsinu kletkakh.

Earlier we have found that the development of resistance to colchicine in mammalian cells in vitro is due to gene amplification leading to decreased plasma membrane permeability to the selective agent and some other unrelated drugs. By a stepwise self-renaturation procedure followed by chromatography on hydroxyapatite we isolated the fraction of middle-repeated sequences (DNAc0t = 10-250) enriched in amplified DNA from the DNA of colchicine-resistant Djungarian hamster cell line. Blotting-hybridization with [32P]DNAc0t = 10-250 performed in the presence of the excess of unlabelled DNA from wild type cells reveals amplified sequences in resistant cell lines. The comparison of DNAs from cell lines resistant to colchicine, adriablastin and actinomycin D showed that common but not identical DNA sequences are amplified in these cases. In situ hybridization with [3H]DNAc0t = 10-250 indicates that amplified sequences are located in the long homogeneously staining regions (HSRs) of the marker chromosomes. These results suggest that DNAc0t = 10-250 may be used for screening of recombinant molecules containing amplified sequences.

[Sensitivity of grey and beige Djungarian hamsters to the blastomogenic action of 7,12-dimethylbenz(a)anthracene and 3-methylcholanthrene]. / Chuvstvitel'nost' serykh i bezhevykh dzhungarskikh khomiachkov k blastomogennomu deistviiu 7,12-dimetilbenz(a)antratsena i 3-metilkholantrena.

Sensitivity of normal gray and mutant beige (pink-eyed dilution mutation) Djungarian hamsters to the carcinogenic activity of 7,12-dimethylbenz (a) anthracene (DMBA) and 3-methylcholanthrene (MC) was studied. No differences between these two groups of animals which were given pills with DMBA were revealed. At the same time the beige females were found to be more sensitive to MC than males and hamsters of wild (gray) colour. Among tumours induced both by DMBA and MC fibrosarcomas prevailed both in the gray and beige hamsters. Fibrous histiocytomas were detected only in the MC-infected hamsters. Epithelial tumours were found only in females.

[Possible role of the T antigen in inducing chromosome aberrations in SV40 virus-transformed cells]. / Vozmozhnaia rol' T-antigena v induktsii khromosomnykh aberratsii v kletkakh, transformirovannykh virusom SV40.

A possible role of the simian virus 40 T antigen in chromosome damages in transformed cells was examined. Two lines of Golden hamster embryonal fibroblasts, transformed by SV40 tsA30 and ts239 mutants (He30 and He239, respectively), were incubated at nonpermissive (40.5-41 degrees C) or permissive (33 degrees C) temperatures. Chromosome aberrations were registered in either subline after 3, 6, 9 and 12 weeks of cultivation under the above conditions. In the both cell lines kept at 33 degrees the frequency of aberrant metaphases and the number of chromosome breaks per cell increased drastically by week 3 of cultivation, and such a state was preserved up to week 12. The frequency of aberrant metaphases in cells cultivated at 41 degrees was maintained at the constant level (He239) or at slightly higher than that in the original culture (He30). The sublines He239, originally incubated at 33 or 40.5 degrees, were then shifted to 40.5 and 33 degrees, respectively. As a result the number of chromosome aberrations either decreased (33----40.5 degrees) or increased (40.5----33 degrees) as early as on day 2, and these patterns were stabilized at the level corresponding to the new conditions. We assayed the induction of DNA breaks in cells, grown at the permissive or nonpermissive temperatures, by using DNA sedimentation in the alkaline sucrose gradient. The DNA sedimentation peaks of cells cultured at 37 and 41 degrees coincided, whereas the DNA of cells cultured at 33 degrees was represented by shorter fragments.

A new cell system for the study of mouse mammary tumour virus.

A stable cell line derived from mammary gland cancer of Djungarian hamster is proposed for the study of oncogenic properties of mouse mammary tumour virus (MMTV). The conditions of infection and expression of the viral genome in this cell line are described in addition to the chromosomal composition or the original and infected cells. The MMTV-infected cells showed increased colony formation in semi-solid media. The advantages of the new cell system are discussed.