Highly malignant cells with normal karyotype in G-banding

Karyotype evolution of the clonal rat liver cell line CL 52 during progression in vitro and in vivo

Liver cell line CL 52, derived from a diethylnitrosamine-treated rat at the stage of preneoplasia/early neoplasia, had an inconspicuous 2n karyotype when analyzed 6 months after in vitro propagation. Malignant progression was accompanied by cytogenetic alterations of chromosomes 1, 3, and 11. In addition, trisomy of chromosomes 4, 6, and 7 led to a significant reduction of the tumor latency period after retransplantation. During 4 years of cytogenetic observation, the once clonal 2n population showed a characteristic karyotype evolution: loss of diploidy, occurrence of polyploid sidelines, deletions followed by unbalanced rearrangements, clonal diversification, and selection of the in vitro most rapidly growing or in vivo most malignant cell type. The karyotype alterations in the four sublines of CL 52 are discussed with special reference to oncogenesis-related genes assigned to the involved rat chromosomes 1, 3, 11, 12, 4, 6, 7, 10. The observed karyotype evolution of this cell line exemplifies genetic/ chromosome instability of carcinogen-induced preneoplastic/early neoplastic liver cells and provides a tool for analyzing, under controlled conditions, stage-dependent sequences of molecular genetic alterations in liver carcinogenesis.

Cytogenetic heterogeneity: its role in tumor evolution

There is ample evidence that cytogenetic heterogeneity characterizes human solid tumors, despite the opposing influences of clonal origin and selection for tumor-specific chromosome aberrations. Different chromosome patterns are found within individual tumors and among phenotypically similar tumors. Some tumor cell populations contain mixtures of diploid and cytogenetically aberrant cells; others display multiple aberrant clones. The extent and biological significance of chromosomal heterogeneity is contrasted between examples of leukemias and of selected solid tumors (mainly of breast and central nervous system origin). Increasing degrees of chromosomal aberration appear correlated with increasingly malignant biological properties of tumors. Genic and chromosomal instability are potential sources for genetic diversity within all tumors. However, variations in local selective forces and differential survival within an expanding solid lesion may contribute to maintenance of a mixed cell population within the primary tumor. In turn, the resulting heterogeneity may permit selection and increase of aberrant cells that are responsible for tumor progression and metastasis.

Double nondisjunction during karyotypic progression of chemically induced Syrian hamster cell lines

The karyotypic evolution of three chemically induced cell lines of Syrian hamster embryo in culture are described. The only karyotypic alteration of one clone was a trisomy of chromosome #11, which presumably arose by nondisjunction after carcinogen treatment. A pure population of cells with the trisomy was observed repeatedly upon karyotyping of cells at the first three passages after cloning. However, at a late passage, apparently normal diploid cells appeared in the culture, which we propose resulted from a second nondisjunction of one chromosome #11, reverting the cells from trisomy 11 to disomy 11. The karyotypic evolution of two other cell lines also involved double nondisjunction, which resulted in duplication of a translocated chromosome and concurrent loss of the normal nonrearranged chromosome. Taken together with the reported findings of others, the results indicate that double nondisjunction is a mechanism in karyotypic progression during neoplastic development.

Cytogenetic changes during the early stages of liver carcinogenesis in Chinese hamster: an in vivo--in vitro comparison

Cytogenetic changes were investigated during the early stages of hepatic adenocarcinoma development in Chinese hamsters injected with a single dose of dimethylnitrosamine (DMN). An in vivo-in vitro comparison was made from 7 to 35 weeks after injection. A partial hepatectomy was used to stimulate mitosis for in vivo analysis, and the excised liver, grown to the primary culture stage, was used for chromosome analysis in vitro. Aneuploidy, tetraploidy, and chromosome aberrations increased significantly in the hepatic cells of DMN-treated animals in vivo, with no significant change over the 7- to 35-week period. No differences, however, could be detected between the primary cultures of control and DMN-treated animals because of an inherent tendency for all cultures to develop aneuploid stem lines at an early stage in culture. A preferential involvement of chromosome #6 in the single trisomic state was demonstrated in vitro and to a minor extent in vivo. The relevance of increased aneuploidy in early carcinogenesis and the differences between the in vivo and in vitro results are discussed.

Chromosome changes in rat embryo cell lines transformed by temperature-sensitive mutants and sheared DNA of herpes simplex virus

The chromosomes of six rat embryo cell lines transformed with herpes simplex virus (HSV) temperature-sensitive (ts) mutants were examined at different passages of in vitro cultivation. Two cell lines were predominantly diploid, one cell line was hyperdiploid, one cell line was pseudodiploid, and two cell lines were hypotetraploid. In near-diploid cell lines chromosome No. 9 was most frequently involved in chromosome changes. All three cell lines derived from tumors obtained after one transplantation of HSV-transformed cells into baby rats were pseudodiploid, but each had different marker chromosomes. Chromosome No. 15 was involved in the formation of two out of four marker chromosomes. Four cell lines derived from tumors developing after two and three transplantations were hypodiploid and showed large chromosome variation. The occurrence of 25 marker chromosomes in three tumor-derived cell lines resulted in gains in parts from chromosomes No. 2, 6, and 7. One marker chromosome had a homogeneously faintly stained region. Chromosomes No. 2, 3, 7, and 12 were more frequently involved in the formation of marker chromosomes. No chromosome change was found to be specifically associated with HSV-induced transformation of rat cells, but chromosome changes in tumor-derived cell lines may provide selective advantage for survival and autonomous growth in the host animal.

[Chromosomal abnormalities in human neoplasia (author's transl)]

Multiple connections exist between chromosomal aberrations and malignant tumors. It is the aim of the present article to summarize the data known so far in view of i) cancer-prone chromosome abnormalities, ii) chromosome abnormalities related to tumors and iii) chromosome abnormalities related to carcinogens. In some instances it seemed useful to discuss the findings in man in connection with the results of in vitro experimental data.

Editorial: Chromosomes and human neoplasms. Achievements using new staining techniques

Numerical and structural chromosome aberrations are frequently found in neoplastic cells. As demonstrated by the new chromosome banding techniques these aberrations are not random, but tend to show a specific occurrence. A model example is the leukemias where many cytogenetical investigations have been done to date. In leukemia chromosome analysis serves the following purposes: to identify a neoplastic process, to confirm and strengthen the hematological diagnosis, for the early diagnosis of transformation from a chronic leukemia into its blastic phase and for following up the clonal evolution of a leukemic cell line. In the discussion of chromosomes and neoplasms it must be mentioned that individuals demonstrating chromosomal instability and some trisomic patients show a greater tendency toward the development of a malignancy. Malignancy is primarily a cellular phenomenon caused by a disturbance in cellular regulation, whose fine events are not known. Therefore the exact role of the chromosomes in neoplastic processes cannot be stated. From experimental investigations it appears that the affected chromosomes carry cell growth regulating factors and also that a specific aberration is the result of the action of a specific agent.

Non-random chromosome changes in acute myeloid leukemia. Chromosome banding examination of 30 cases at diagnosis

Bone-marrow chromosomes were examined with the G-banding technique in 30 patients with acute myeloid leukemia at the time of diagnosis. In 13 of the 30 patients (43%) only normal diploid bone-marrow cells were found, and no deviations from the normal banding pattern could be detected in these cells. In bone-marrow cells of 17 patients (57%), distinct chromosome abnormalities were found; in 10 of the patients only abnormal cells were observed, whereas in 7 of the patients the abnormal cells coexisted with normal diploid cells without any visible chromosome banding abnormality. The results of the detailed analysis of the karyotypic aberrations demonstrated that when chromosome aberrations occurred they were clearly non-random. All patients except two displayed trisomy 8,9 or 21 or monosomy 7. Analysis of cases of acute leukemia from other laboratories indicated that the same consistent pattern of chromosome involvement prevailed in them.

Extremely long duration of chronic myeloid leukaemia with Ph1 negative and Ph1 positive bone marrow cells

A male patient still surviving 17 years after the diagnosis of chronic myeloid leukaemic (CML) is described. A chromosome analysis of the bone marrow 16 years after the diagnosis revealed 84% Ph1 negative and 16% Ph1 positive cells, all containing the Y chromosome. The disease has been very sensitive to treatment with busulphan but bone marrow hypoplasia has not been induced. It is probable that in some CML patients with such a double cell population the prognosis may be extraordinarily good and that they run a considerable risk of being overtreated due to a pronounced sensitivity to alkylating drugs. Such rare cases should not serve as arguments for aggressive treatment of CML.