Some comments on sister chromatid exchange (SCE) in human neoplasia

The incidence of sister chromatid exchange (SCE) in bone marrow cells and/or lymphocytes of patients with various leukemias and the effects of drugs on the SCE incidence in the cells of patients with leukemia or cancer are presented and discussed. The possible use of SCE for screening antileukemic drugs, mutagenic and/or carcinogenic agents and susceptible human populations is presented.     

On monosegmental sister chromatid exchanges (SCE)

Considerations are given to special features of the nuclear envelope that might occasion segmental exchange between sister chromatids. The underlying dynamics may lead to illegal apposition of originally distant sequences and/or to modulations in the topologic orientation of genes on chromatid segments involved in such exchanges.     

Induction and reduction of sister chromatid exchange by CCNU in human lymphocytes in vitro

Sister chromatid exchange (SCE) was studied in human lymphocytes treated with 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) in vitro. A dose-dependent increase of SCE was observed in cells exposed to 10(-5) - 10(-4) M CCNU. The maximal increase was 25-35 SCEs/cell over the control level, which is similar to the increase found in patients treated with CCNU in vivo. In the presence of rat liver microsomes (S-9 fraction) the frequency of CCNU-induced SCE was slightly higher than in parallel cultures without S-9, suggesting that microsomal metabolism may enhance the rate of decomposition of CCNU into reactive products. The CCNU-induced increase of SCE was greater in cells treated for longer time periods (up to 70 hr) than in cells subjected to a 1-hr treatment. This effect was most pronounced at higher concentrations of the drug (5 X 10(-5) M). The frequency of CCNU-induced SCE was also found to be dependent on the time of treatment in the cell cycle. A treatment for 1 hr during early G1-phase (about 20 hr before the first S-phase) gave rise to a higher increase of SCE than a 1 hr treatment immediately before or during the first or second S-phase. Thus, the CCNU-induced DNA damage leading to SCE seems to persist and may even increase during the prereplicative phase of the cell cycle. After replication in BrdUrd-free medium, the frequency of CCNU-induced SCEs decreased to the control level. The present results, taken together with other studies of strand break and cross-link formation by CCNU in mammalian cells in vitro, suggest that the major SCE-inducing damage by CCNU is DNA interstrand cross-links. These lesions then appear to be slowly removed, if at all, during the prereplicative phase of the cell cycle, and to disappear during or after replication in BrdUrd-free medium in vitro.     

X irradiation and sister chromatid exchange in cultured human lymphocytes

Sister chromatid exchange (SCE) frequency was not increased in G₀ lymphocytes following irradiation up to 400 rads. Lymphocytes irradiated after 42 or 60 hours of culture showed a dose-dependent increase in exchange frequency at 100 and 200 rads. SCE was not increased in cells irradiated in G₂ (68.5 hours). Lymphocytes maintained in a 5-Bromodeoxyuridine (BrdUrd) free medium and irradiated 42 hours after culture initiation showed an increase in SCE if BrdUrd was added immediately after irradiation, but no increase was found if there was a 5 hour holding period prior to the addition of BrdUrd. The effect on induced SCE frequency of heightened radiosensitivity due to increased amounts of BrdUrd was also investigated. When the BrdUrd concentration was increased from 10 μg/ml to 50 μg/ml, the percent increase in X-ray-induced SCE was lower at 50 μg/ml. In addition, increased BrdUrd concentration only slightly increased the sensitivity of the SCE technique to irradiation doses of 50 rads.     

Increased frequencies of sister chromatid exchange in soldiers deployed to Kuwait

Frequencies of sister chromatid exchange (SCE), a measure ofgenotoxic exposure, were assessed in military troops deployedto Kuwait in 1991. Soldiers completed health questionnairesand had blood collected prior to, during and following deploymentto Kuwait. Frequency of spontaneous SCE was determined on bloodsamples as a measure of mutagenic exposure. Compared to pre-deploymentbaseline SCE frequency means, levels obtained 2 months intothe Kuwait deployment were significantly increased (P > 0.001)and persisted for at least 1 month after return to Germany.Outcome was unaffected by known personal SCE effect modifiersincluding smoking, age and diet. Potential sources of the apparentmutagenic exposure are discussed. ⁸Present address: US Department of Labor/Occupational Safetyand Health Administration, 200 Constitution Avenue NW, Washington,DC 20210, USA ¹⁰This work represents the professional opinion of the authorand not necessarily that of the US DOL/OSHA ⁹Previous position: Occupational and Environmental MedicineDivision, US Army Environmental Hygiene Agency, Aberdeen ProvingGround, MD 21010–5422, USA      

Variation in the baseline sister chromatid exchange frequency in human lymphocytes

The utility of the sister chromatid exchange (SCE) assay for human population studies is potentially limited by the variability associated with individual baseline SCE frequencies. This investigation identifies and quantifies the major sources of preparative and biological variation associated with the determination of baseline SCE frequencies in cultured human lymphocytes. Much of the variation in lymphocyte SCE frequencies is attributable to the amount of bromodeoxyuridine (BrdUrd) available per lymphocyte; the pooled coefficient of variation (CV) over the dose range of 10 to 160 μM is about 18%. Other variations in the baseline frequency result from culture-to-culture and slide-to-slide differences. The pooled coefficient of variation among donors is about 10%. The effect of cell-to-cell differences in baseline SCE frequency among donors can be minimized by increasing the number of cells scored per donor. When 20 cells are analyzed per individual the pooled cell-to-cell variation is 9% but when 40 or 80 cells are analyzed it is reduced to 6 and 4% respectively. For a single individual the cell-to-cell coefficient of variation at 100 μM BrdUrd is 40.8%. Under our experimental conditions, a 30% increase in SCE frequency between two cohort populations can be detected with a 95% probability at a 5% level of significance when 11 individuals per cohort are studied. For a longitudinal or in vitro dose response study of a single individual, a 50% increase in SCE frequency can be detected with a 95% probability at a 5% level of significance when 25 cells per sample are analyzed. These results indicate the feasibility of applying the SCE bioassay to humans as a measure of environmental stress.     

Proliferative characteristics and sister chromatid exchange (SCE) of colony-forming cells (CFU-S) in acute myelogenous leukemia

Sister chromatid exchange (SCE) and cell cycle progression of colony-forming cells (CFU-S) from patients with acute myelogenous leukemia were studied using bromodeoxyuridine (BrdU) incorporation and sister chromatid differential staining. The mean SCE rate of CFU-S was 7.99, which is similar to that reported for human peripheral blood lymphocytes. Cultures treated with BrdU at culture initiation and then harvested 72-120 hr later indicated a cell cycle time (TC) of approximately 60 hr. However, cells allowed to proliferate for 72-120 hr prior to the addition of BrdU showed TC values of 12-36 hr. Analysis of serial cultures from one patient revealed a heterogeneous population with a mean TC of 19.5 hr. These cell cycle times are considerably shorter than previously published reports and suggest that leukemic cells have the potential to divide rapidly.     

锌对镉诱导人淋巴细胞姊妹染色单体交换的影响

目的：探讨镉与锌的致突变性以及锌对镉致突变性的影响。 方法： 采用正常人外周血淋巴细胞体外培养的方法，观察镉、锌以及镉和锌的混合物诱导细胞姊妹染色单体交换（SCE）频率增加的情况。 结果： 镉在1×10-8mol/L－1×10-6mol/L浓度范围内具有诱发人外周血淋巴细胞SCE频率增加的作用，而锌在1×10-6mol/L－1×10-4mol/L浓度范围内不具有诱发人外周血淋巴细胞SCE频率增加的作用。锌可拮抗镉诱导SCE频率的增加，并且在1×10-6mol/L－1×10-4mol/L浓度范围内随着锌浓度的增加，其抑制作用也增强，并有明显的剂量-效应关系。 结论： 锌在体外培养的细胞中对镉的致突变性具有一定程度的抑制作用。     

Duplication 9p due to unequal sister chromatid exchange.

A case of trisomy 9p syndrome is reported. The karyotype showed a tandem duplication of the short arm and of the inverted heterochromatic block of chromosome 9. Unequal sister chromatid exchange seems to be the only possible cause of this finding.     

Growth rate and sister chromatid exchange (SCE) incidence of bone marrow cells in Acute Myeloblastic Leukemia (AML)

The sister chromatid exchange (SCE) incidence and growth kinetics have been studied by means of an in vitro bromodeoxyuridine (BrdU) chromosome labeling method in the bone marrow cells of 17 acute myeloblastic leukemia (AML) patients with only diploid cells at diagnosis, remission, and relapse of the disease. At diagnosis, the cells tended to exhibit a low SCE frequency as compared to that during remission. An increased SCE frequency was observed after chemotherapy during remission or relapse. At diagnosis and relapse, when leukemic blast cells predominated in the marrow, they were characterized by the predominance of cells that had undergone only one cell cycle after BrdU exposure. In contrast, the marrow cells during remission tended to resemble the control pattern of growth kinetics, with a predominance of cells undergoing second and third cell cycles in the presence of BrdU. These results suggest that the growth rate of leukemic and nonleukemic cells is different, and that chemotherapy can cause an increased SCE frequency in the marrow cells of AML patients irrespective of the state of the disease.     

Sister chromatid exchange (SCE) rates in human melanoma cells as an index of mutagenesis

Melanomas are highly clonogenic. Genetic variability and polymorphismof tumour cell populations have been reported. However, no directevidence of imitator activity as a source of genetic polymorphismfor melanoma cells has been described. Some intermediates ofmelanin synthesis are cytotoxic and genotoxic and their mutagenicpower has been described. We show here that the rate of sisterchromatid exchange (SCE) of the line of human melanoma cellsused varies with the concentration of the melanin precursorL-tyrosine, in the culture medium. An increase of melanin synthesisresults in increased SCE rates. The highest values of SCEs arefound in melanotic melanoma cells compared with the amelanoticones. Indeed we present evidence that melanoma cells show higherlevels of SCE when compared with normal human lymphocytes, andto the SCE frequencies derived from the literature on the lymphocytesof familial malignant melanoma, sporadic malignant melanomapatients and the lymphocytes of relatives of familial and sporadicmelanoma patients. ³To whom correspondence should be addressed     

Frequency of sister chromatid exchange in peripheral lymphocytes of male pesticide applicators

In the present study 61 male pesticide applicators who worked in cotton fields and regularly sprayed pesticides such as DDT, BHC, endosulfan, malathion, methyl parathion, phosphamidon, dimethoate, monocrotophos, quinalphos fenvelrate, and cypermethrin were analyzed for sister chromatid exchanges, mitotic index, and cell cycle kinetics in peripheral lymphocytes. Subjects who handled pesticides were non-smokers and teetotalers and the data were compared with the matched control group. Statistical analysis revealed that the frequency of sister chromatid exchanges was significantly higher among the pesticide applicators at all the durations of exposure when compared to controls. Subjects exposed to pesticides also showed cell cycle delay and decrease in mitotic index when compared to the control group.     

Adriamycin-induced sister chromatid exchange and chromosomal aberrations in Down's syndrome lymphocytes.

Blood samples from six Down's syndrome (DS) and six age- and sex-matched controls were cultured for 72 h in the presence of BrdUrd. Lymphocytes were then analysed at their second mitosis for sister chromatid exchange (SCE) and at their first mitosis for chromosome aberrations. Treatment with adriamycin (30 and 60 ng) showed a significant increase in frequency of SCE and chromosome aberrations in DS lymphocytes compared to normal lymphocytes at initiation of culture. Cells treated with adriamycin (ADR) for the last 24 h also showed a significant increase in SCE in DS lymphocytes compared to normal lymphocytes. A significant increase in chromatid-type aberrations was also recorded in DS lymphocytes after both treatments cultured for the last 24 h.     

牛白血病姐妹染色单体交换频率与微量元素变化、泰氏锥虫感染相关性的研究

用外周血淋巴细胞短期培养法,对64头奶牛进行姐妹染色单体交换(SCE)频率的观察,结果表明,淋巴肉瘤牛、血检和MID双阳性牛、MID单阳性牛以及健康对照牛SCE/细胞值分别为9.36±0.349(S·E),6.60±0.495,4.89±0.379和3.59±0.328,各组之间有极显著差异(P<0.01)。同时,用等离子体源发射光谱分析法对牛毛Zn、Ni、Mn、Cu、Co、Pb、Mo、Cr、Ba、B10种元素进行测定,发现MID单阳性牛、血检和MID双阳性牛、淋巴肉瘤牛被毛中Mn含量依次显著降低(P<0.05),与SCE呈显著性负相关(r=-0.969);Co含量依次增高,与SCE呈正相关(r=0.814);Cu/Zn值与SCE呈正相关(r=0.783)。用泰氏锥虫间接红细胞凝集试验(IHA)检测泰氏锥虫感染情况,发现血检和MID双阳性中、MID单阳性牛以及健康对照牛IHA阳性率分别为86.18%,4(?).45%,和31.25%,而淋巴肉瘤牛均为阳性,与SCE呈正相关(r=0.753),具有显著性意义(P<0.05)。     

Normal sister chromatid exchange frequencies during growth of a transplantable murine myeloid leukemia

Frequencies of sister chromatid exchange (SCE) were analyzed in normal and coexisting leukemic cells harvested from the bone marrow of mice 10, 15, 18, and 21 days after transplantation of myeloid leukemic cells. These posttransplantation stages correspond to no abnormal physical or clinical symptoms (day 10) through the terminal stage of leukemia (day 21). The data indicate that the SCE frequencies in normal cells of leukemic mice did not differ from those in normal cells of normal mice. Furthermore, the frequencies in the coexisting normal and leukemic cells remained statistically constant throughout the posttransplantation period. It is concluded from this study that spontaneous cellular SCE frequencies may not be altered by the presence or growth of leukemic cells.     

Sister chromatid exchange (SCE) of the kinetochore carrying segment, KS

The mechanism of SCE discussed in previous papers (3, 4) is adapted to account for the absence of kinks on chromatids experiencing an exchange limited to their KSs. The paper ends with a brief digression on kinks. Equivalent to solitons, such dynamic malformations can function as carriers of information along the chromatid stack.     

A comparison of induced sister chromatid exchange levels in Chinese hamster ovary cells and cultured human lymphocytes

Human lymphocytes and Chinese hamster ovary cells were exposed to DNA damaging agents for two cell cycles, and the induced sister chromatid exchange (SCE) rate was compared. CHO cells showed a significant increase in SCE following treatment with bleomycin and vincristine whereas human lymphocytes did not. Both CHO cells and lymphocytes showed an increase in SCE with 5-bromodeoxyuridine (BrdUrd) and tritiated uridine (3H-Urd) but the increase was greater in CHO cells. SCE levels were similar after exposure to proflavine and colcemid did not increase the exchange frequency in either cell type. Apparently CHO cells are more sensitive than human lymphocytes to the actions of bleomycin, vincristine, BrdUrd, and 3H-Urd. SCE analysis in response to mutagens and carcinogens should therefore be based on more than one cell type.     

On the importance of DNA strand breaks as the first event to initiate sister chromatid exchange (SCE): Experiments with restriction endonucleaseBglI

The exact molecular mechanism of sister chromatid exchange (SCE) is still unknown, despite the many reports dealing with this cytogenetic end point published in the last 40 years. One point to be investigated is the nature of the original lesion(s) in DNA leading to the production of SCE. Whereas, for chromosomal aberrations, the importance of DNA double-strand breaks has been well established, there is still controversy about the relative importance of strand breaks and base modifications for triggering the process of SCE formation. In the present paper, we have taken advantage of the ability of the restriction endonucleaseBglI to induce SCE and have exploited the fact that preincubation with 2,3-butanedione results in the loss ofBglI ability to cut DNA, while it is still able to recognize its sequence in DNA and bind to it, to see whether this alone is enough to initiate SCE formation, or if a physical DNA double-strand break is required. Our results seem to support the necessity of DNA breaks for SCE production.accepted for publication by J. S. (Pat) Heslop-Harrison