Cytogenetically marked clones in human fibroblasts cultured from normal subjects

Stindl

Hehlmann

2000

157

115

The mutation rates of cancer cells to drug and multidrug resistance are paradoxically high, i.e., 10 ؊3 to 10 ؊6 , compared with those altering phenotypes of recessive genes in normal diploid cells of about 10 ؊12 . Here the hypothesis was investigated that these mutations are due to chromosome reassortments that are catalyzed by aneuploidy. Aneuploidy, an abnormal number of chromosomes, is the most common genetic abnormality of cancer cells and is known to change phenotypes (e.g., Down's syndrome). Moreover, we have shown recently that aneuploidy autocatalyzes reassortments of up to 2% per chromosome per mitosis because it unbalances spindle proteins, even centrosome numbers, via gene dosage. The hypothesis predicts that a selected phenotype is associated with multiple unselected ones, because chromosome reassortments unbalance simultaneously thousands of regulatory and structural genes. It also predicts variants of a selected phenotype based on variant reassortments. To test our hypothesis we have investigated in parallel the mutation rates of highly aneuploid and of normal diploid Chinese hamster cells to resistance against puromycin, cytosine arabinoside, colcemid, and methotrexate. The mutation rates of aneuploid cells ranged from 10 ؊4 to 10 ؊6 , but no drug-resistant mutants were obtained from diploid cells in our conditions. Further selection increased drug resistance at similar mutation rates. Mutants selected from cloned cells for resistance against one drug displayed different unselected phenotypes, e.g., polygonal or fusiform cellular morphology, flat or threedimensional colonies, and resistances against other unrelated drugs. Thus our hypothesis offers a unifying explanation for the high mutation rates of aneuploid cancer cells and for the association of selected with unselected phenotypes, e.g., multidrug resistance. It also predicts drug-specific chromosome combinations that could become a basis for selecting alternative chemotherapy against drugresistant cancer.

Section: ϫ6mentioning

confidence: 99%

Explaining the high mutation rates of cancer cells to drug and multidrug resistance by chromosome reassortments that are catalyzed by aneuploidy

Stindl

Hehlmann

2000

157

115

“…As a result, the risk of a given chromosome of a highly aneuploid cell being lost or doubled per mitosis is about 2% (44,45). In contrast, the risk of chromosomes of normal diploid cells being lost or doubled during mitosis is very low, ranging from 0% in human embryos (46) and adolescents (47) to 0.4% in adults, on the basis of finding trisomic chromosomes in 0.2% (48). Thus, the characteristic instability and heterogeneity of cancer-specific karyotypes and resulting phenotypes even among the cells of the same cancer (41,(49)(50)(51) are a direct consequence of aneuploidycatalyzed chromosome reassortments.…”

mentioning

confidence: 99%

Origin of multidrug resistance in cells with and without multidrug resistance genes: Chromosome reassortments catalyzed by aneuploidy

Stindl

Hehlmann

2001

Cancer cells and aneuploid cell lines can acquire resistance against multiple unrelated chemotherapeutic drugs that are over 3,000-fold those of normal levels and display spontaneous resistances up to 20-fold of normal levels. Two different mechanisms were proposed for this phenotype: (i) classical mutation of drug metabolizing genes or (ii) chromosome reassortments, catalyzed by cancer-and cell line-specific aneuploidy, which generate, via new gene dosage combinations, a plethora of cancer phenotypes, including drug resistance. To distinguish between these mechanisms, we have asked whether three mouse cell lines can become drug resistant, from which two or three genes have been deleted, and on which multidrug resistance is thought to depend: Mdr1a, Mdr1b, and Mrp1. Because all three lines could acquire multidrug resistance and were aneuploid, whereas diploid mouse cells could not, we conclude that aneuploid cells become drug resistant via specific chromosome assortments, independent of putative resistance genes. We have asked further whether aneuploid drug-resistant Chinese hamster cells revert spontaneously to drug sensitivity in the absence of cytotoxic drugs at the high rates that are typical of chromosome reassortments catalyzed by aneuploidy or at the very low or zero rates (i.e., deletion) of gene mutation. We found that four drug-resistant hamster cell lines reverted to drug sensitivity at rates of about 2-3% per generation, whereas two closely related lines remained resistant under our conditions. Thus, the karyotypic instability generated by aneuploidy emerges as the common source of the various levels of drug resistance of cancer cells: minor spontaneous resistances reflect accidental chromosome assortments, the high selected resistances reflect complex specific assortments, and multidrug resistance reflects new combinations of unselected genes located on the same chromosomes as selected genes.

“…Indeed, low levels of aneuploidy occur somatically in noncancerous cells of humans and animals (96)(97)(98)(99) and in cells maintained in vitro (8,11,19,73,80). The incidence increases with the age of the cell in the body or in the culture (8,19,94,(96)(97)(98)(99).…”

mentioning

confidence: 99%

“…The incidence increases with the age of the cell in the body or in the culture (8,19,94,(96)(97)(98)(99). According to this view, "initiation" of carcinogenesis by hydrocarbons (25) induces aneuploidy insufficient for carcinogenesis.…”

mentioning

confidence: 99%

Aneuploidy correlated 100% with chemical transformation of Chinese hamster cells

Yerganian

et al. 1997

162

111

Aneuploidy or chromosome imbalance is the most massive genetic abnormality of cancer cells. It used to be considered the cause of cancer when it was discovered more than 100 years ago. Since the discovery of the gene, the aneuploidy hypothesis has lost ground to the hypothesis that mutation of cellular genes causes cancer. According to this hypothesis, cancers are diploid and aneuploidy is secondary or nonessential. Here we reexamine the aneuploidy hypothesis in view of the fact that nearly all solid cancers are aneuploid, that many carcinogens are nongenotoxic, and that mutated genes from cancer cells do not transform diploid human or animal cells. By regrouping the gene pool-as in speciation-aneuploidy inevitably will alter many genetic programs. This genetic revolution can explain the numerous unique properties of cancer cells, such as invasiveness, dedifferentiation, distinct morphology, and specific surface antigens, much better than gene mutation, which is limited by the conservation of the existing chromosome structure. To determine whether aneuploidy is a cause or a consequence of transformation, we have analyzed the chromosomes of Chinese hamster embryo (CHE) cells transformed in vitro. This system allows (i) detection of transformation within 2 months and thus about 5 months sooner than carcinogenesis and (ii) the generation of many more transformants per cost than carcinogenesis. To minimize mutation of cellular genes, we have used nongenotoxic carcinogens. It was found that 44 out of 44 colonies of CHE cells transformed by benz[a]pyrene, methylcholanthrene, dimethylbenzanthracene, and colcemid, or spontaneously were between 50 and 100% aneuploid. Thus, aneuploidy originated with transformation. Two of two chemically transformed colonies tested were tumorigenic 2 months after inoculation into hamsters. The cells of transformed colonies were heterogeneous in chromosome number, consistent with the hypothesis that aneuploidy can perpetually destabilize the chromosome number because it unbalances the elements of the mitotic apparatus. Considering that all 44 transformed colonies analyzed were aneuploid, and the early association between aneuploidy, transformation, and tumorigenicity, we conclude that aneuploidy is the cause rather than a consequence of transformation.