Potentiation of Alu I-induced chromosome aberrations by high salt concentrations in Chinese hamster ovary cells

The restriction endonuclease Alu I induces chromosome-type aberrations in Chinese hamster ovary cells whose frequencies are considerably elevated in the presence of high concentrations of MgCl2, (NH4)2SO4, CaCl2 or NaCl. The most plausible explanation for these findings is that salt leads to partial dehistonization of the chromatin which makes more recognition sites available for Alu I.     

Effects of sodium butyrate on X-ray and bleomycin-induced chromosome aberrations in human peripheral blood lymphocytes.

Peripheral blood lymphocytes from normal human volunteers or from Down syndrome patients were pre-treated with sodium butyrate (a compound which is known to induce structural modifications in the chromatin through hyperacetylation of nucleosomal core histones) and exposed to X-irradiation or treated with bleomycin in vitro in the G0 and/or G1 stage(s) of the cell cycle. The frequencies of chromosomal aberrations in the first mitosis after treatment were scored. The results show an enhancement in the yield of aberrations in the butyrate pre-treated groups. However, the absolute frequencies of chromosomal aberrations as well as the relative increases with butyrate pre-treatment varied between blood samples from different donors suggesting the existence of inter-individual variations. There is a parallelism between the effects of X-irradiation or of combined treatments in G0 and G1 stages and between effects observed in the X-ray and bleomycin series. The increase in the yields of chromosomal aberrations in butyrate-treated and X-irradiated lymphocytes (relative to those which received X-irradiation alone) is interpreted as a consequence of the inhibition of repair of DNA damage by butyrate.     

Cancer progression by non-clonal chromosome aberrations

The establishment of the correct conceptual framework is vital to any scientific discipline including cancer research. Influenced by hematologic cancer studies, the current cancer concept focuses on the stepwise patterns of progression as defined by specific recurrent genetic aberrations. This concept has faced a tough challenge as the majority of cancer cases follow non-linear patterns and display stochastic progression. In light of the recent discovery that genomic instability is directly linked to stochastic non-clonal chromosome aberrations (NCCAs), and that cancer progression can be characterized as a dynamic relationship between NCCAs and recurrent clonal chromosome aberrations (CCAs), we propose that the dynamics of NCCAs is a key element for karyotypic evolution in solid tumors. To support this viewpoint, we briefly discuss various basic elements responsible for cancer initiation and progression within an evolutionary context. We argue that even though stochastic changes can be detected at various levels of genetic organization, such as at the gene level and epigenetic level, it is primarily detected at the chromosomal or genome level. Thus, NCCA-mediated genomic variation plays a dominant role in cancer progression. To further illustrate the involvement of NCCA/CCA cycles in the pattern of cancer evolution, four cancer evolutionary models have been proposed based on the comparative analysis of karyotype patterns of various types of cancer.     

Hyperthermic potentiation of chromosome aberrations by anticancer antibiotics

In view of the success of hyperthermia as a modality in cancer treatment, we have studied its effect on chromosomes in combination with anticancer antibiotics. Three classes of chemicals, one with a non-delayed type of effect (adriamycin), one with a delayed type of effect (mitomycin C), and one with a truely radio-mimetic effect (bleomycin) were selected for study on human lymphocytes and Chinese hamster K-1 cells. Propane sultone was also included because its effect on plants is suppressed by hyperthermia. The data show increased because its effect on plants is suppressed by hyperthermia. The data show increased potential of these chemicals to induce chromosome aberrations when applied at temperatures higher than 37 degrees C, irrespective of the phase of cell cycle. The potentiation may be due to true synergism (bleomycin) of facilitation of entry of larger quantities of the drug (adriamycin). No potentiating effect was observed on the induction of sister chromatid exchanges (SCEs).     

Potentiation of arsenic trioxide-induced apoptosis by 8-bromo-7-methoxychrysin in human leukemia cells involves depletion of intracellular reduced glutathione

The novel chrysin analog 8-bromo-7-methoxychrysin (BrMC) has been reported to induce apoptosis of various cancer cell lines. Arsenic trioxide (ATO) treatment induces clinical remission in acute promyelocytic leukemia patients. The combination of ATO with other agents has been shown to improve therapeutic effectiveness in vitro and in vivo. In this report, the mechanism of apoptosis induced by treatment with ATO alone or in combination with BrMC was studied in U937, HL-60, and Jurkat cells. Our results demonstrated that BrMC cooperated with ATO to induce apoptosis in human leukemia cells. This co-treatment caused mitochondrial transmembrane potential dissipation and stimulated the mitochondrial apoptotic pathway, as evidenced by cytochrome c release, down-regulation of X-linked inhibitor of apoptosis (XIAP) and Bcl-XL, and up-regulation of Bax. BrMC alone or in combination with ATO, decreased Akt phosphorylation as well as intracellular reduced glutathione (GSH) content. The thiol antioxidant N-acetylcysteine and exogenous GSH restored GSH content and attenuated apoptosis induced by co-treatment with ATO plus BrMC. In contrast, the non-thiol antioxidant butylated hydroxyanisole and mannitol failed to do so. These findings suggest that GSH depletion explains at least in part the potentiation of ATO-induced apoptosis by BrMC.     

Stochastic cancer progression driven by non-clonal chromosome aberrations

Cancer research has previously focused on the identification of specific genes and pathways responsible for cancer initiation and progression based on the prevailing viewpoint that cancer is caused by a stepwise accumulation of genetic aberrations. This viewpoint, however, is not consistent with the clinical finding that tumors display high levels of genetic heterogeneity and distinctive karyotypes. We show that chromosomal instability primarily generates stochastic karyotypic changes leading to the random progression of cancer. This was accomplished by tracing karyotypic patterns of individual cells that contained either defective genes responsible for genome integrity or were challenged by onco-proteins or carcinogens that destabilized the genome. Analysis included the tracing of patterns of karyotypic evolution during different stages of cellular immortalization. This study revealed that non-clonal chromosomal aberrations (NCCAs) (both aneuploidy and structural aberrations) and not recurrent clonal chromosomal aberrations (CCAs) are directly linked to genomic instability and karyotypic evolution. Discovery of "transitional CCAs" during in vitro immortalization clearly demonstrates that karyotypic evolution in solid tumors is not a continuous process. NCCAs and their dynamic interplay with CCAs create infinite genomic combinations leading to clonal diversity necessary for cancer cell evolution. The karyotypic chaos observed within the cell crisis stage prior to establishment of the immortalization further supports the ultimate importance of genetic aberrations at the karyotypic or genome level. Therefore, genomic instability generated NCCAs are a key driving force in cancer progression. The dynamic relationship between NCCAs and CCAs provides a mechanism underlying chromosomal based cancer evolution and could have broad clinical applications.     

Structural aberrations of chromosome 18

Summary 3 cases of the 18q — syndrome, 2 boys and 1 girl, are presented, and a comparison with data from the literature is given. The following features are typical of the syndrome: short stature, mental retardation, muscular hypotonia, a peculiar dysmorphia of the face and ears, cryptorchidism and small scrotum in males, proximally implanted thumbs, tapering fingers, excess of whorls on the fingertips, and dorsally implanted second toes. Midface hypoplasia with hypertelorism and cleft palate, as well as strabismus, were present in 2 of our patients, whereas all 3 showed nystagmus and prominence of anthelix and antitragus. In addition, 2 patients exhibited narrow ear canals and impaired hearing. One patient had coloboma of the iris and choroid, pale optic discs, and cleft lip; another had umbilical and inguinal hernias. Two cases represented de novo deletions of the long arm of chromosomes 18, whereas the karyotype of the father of the third case revealed a balanced translocation t(15;18)(q24;q21).

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Zusammenjassung 3 Patienten mit dem 18q — Syndrom, 2 Knaben und 1 Mädchen, werden vorgestellt und mit den Fällen der Literatur verglichen. Die folgenden typischen Merkmale des 18q — Syndroms fanden sich bei ihnen: Kleinwuchs, Schwachsinn, muskuläre Hypotonie, Gesichts- und Ohrdysmorphie, Kryptorchismus bei den Knaben sowie zurückversetzte Daumen, konisch zulaufende Finger, Häufung von Wirbelmustern auf den Fingerbeeren und nach dorsal versetzte 2. Zehen. 2 Patienten zeigten die für das 18q — Syndrom typische Mittelgesichtsdysplasie sowie Hypertelorismus und Strabismus, hingegen wiesen alle drei Nystagmus und eine charakteristische Ohrdysmorphie mit Vortreten von Anthelix und Antitragus auf. Je 2 Patienten waren schwerhörig bzw. hatten auffallend enge Gehörgänge. Bei einem Fall fanden sich noch ein Iris- und Chorioideakolobom, Opticusatrophie und eine Lippenspatle, bei einem anderen eine Nabel- und Leistenhernie. Bei 2 Patienten war die Deletion des langen Arms von Chromosome 18 neu entstanden, bei einem war der Vater Träger einer balancierten Translokation t(15;18)(q24;q21).

     

The fate of chromosome aberrations

Chromosomal aberrations rapidly disappear from populations of dividing cells, but little is known about the details of the process. One may ask, for example, whether a cell with an acentric fragment is virtually certain to die after the first mitosis or whether it has a high probability of surviving to the second. Some recent data on aberrations in cultured human lymphocytes lead to estimates that fragments (and presumably the cells containing them) survive to the next mitosis about 30% of the time and dicentric chromosomes about 50%. These estimates were made without regard for the proliferation of normal cells, however, and so must be somewhat in error. In fact, when cell proliferation is taken into account, the most likely value of survival of the fragment itself is about 80% (when both daughter cells are considered). Probable ranges of this value and of the other parameters considered are presented. It is hoped that this explicit formulation of a mathematical model will encourage further experimental examination of the effect of various aberrations upon cell populations.     

Effect of DMSO on radiation-induced chromosome aberrations analysed by FISH

The purpose of the present work was to determine if the described reduction in the frequency of radiation-induced chromosome aberrations by DMSO is homogeneous within different human chromosomes. Blood samples were irradiated with 4 Gy of X-rays in absence and presence of 0.5 M DMSO. FISH painting was carried out independently for human chromosomes 1, 2, 3, 4, 7, 11 and 12. The observed frequencies of apparently simple translocations and dicentrics for all these chromosomes, showed a homogeneous reduction when the irradiation was done in the presence of DMSO. Moreover, a better fit between the observed and expected frequencies was obtained when (DNA content)2/3 was used to calculate the expected frequencies, instead of just the DNA content. This result supports the idea that for exchange type aberrations, a better adjustment is obtained when the surface area of spherical chromosome territories is considered.