SCE induction by cytostatics and its relation to iatrogenic leukemogenesis

Alkaline single-cell gel electrophoresis and human biomonitoring for genotoxicity: a pilot study on breast cancer patients undergoing chemotherapy including cyclophosphamide

Alkaline single-cell gel electrophoresis (the 'comet assay') was used to evaluate DNA damage in lymphocytes from 17 breast cancer patients before and 1-21 h after chemotherapy including cyclophosphamide (600-1800 mg/m2). In order to control for the experimental variability over time, freshly isolated lymphocytes from female mice given physiological saline or cyclophosphamide (150 mg/kg b.wt.) were included as 'internal standards' in each individual electrophoresis run. There was an upward tendency of DNA damage in the mouse lymphocytes over the study period, but cyclophosphamide was constantly found to induce significant damage at all time points investigated (1-48 h). Although patients given up to 11 prior cycles of chemotherapy showed the same basal level of DNA damage as the patients coming to the clinic for their first treatment, the chemotherapy given at the time of the present blood sampling was associated with significant DNA damage in most samples. Considerable interindividual variations were observed both before and after the treatment. DNA single-strand breaks and alkali-labile sites in peripheral lymphocytes as evaluated by the comet assay seem to be useful molecular biomarkers for exposure to DNA damaging agents when monitoring ongoing exposures, but less impressive when monitoring accumulated exposures, at least in patients given high doses of cyclophosphamide and other antineoplastic agents.

DNA-damaging effect of cyclophosphamide on human blood cells in vivo and in vitro studied with the single-cell gel test (comet assay)

The single-cell gel (SCG) test was used to study the induction and persistence of DNA damage by cyclophosphamide (CP) in human blood cells after treatment in vitro and in vivo. S9-mix-activated CP (from 0.1 mM upward) induced DNA effects in a concentration-dependent manner in the in-vitro SCG test. Blood cells from various donors showed considerable intra- and interindividual variability. Incubation of CP-treated blood samples at 37 degrees C caused a rapid decrease in DNA effects, but DNA migration was still significantly increased 1 hr after the end of the CP treatment. Comparative studies with the in vitro sister chromatid exchange (SCE) test were performed that demonstrated that much lower CP concentrations (about 100 times) were required for a significant induction of SCEs. A group of 11 patients who suffered from vasculitis/collagen disease and were treated with low CP doses (50-200 mg/day) exhibited an elevated level of DNA damage in the SCG test with peripheral blood cells, compared with a group of 11 control persons or 5 patients without chemotherapy. Increases in DNA damage were variable and not clearly related to the CP dose. SCE tests could successfully be performed with 5 out of the 11 CP-treated patients; all showed significantly increased SCE frequencies. For six patients no result could be obtained with the SCE test due to a failure of lymphocyte proliferation. Three multiple sclerosis patients who received high doses of CP were investigated with the SCG test before, during, and after the treatment. The results indicate that CP-induced DNA effects that are detectable with the SCG test persist in vivo for a period of several days, but for less than 2 weeks. The results of our study provide information with regard to the use of the SCG test in human monitoring. The advantages and limitations of the test are discussed.

Evaluation of sister chromatid exchange as an indicator of sensitivity to N-ethyl-N-nitrosourea-induced carcinogenesis in rats

Sister chromatid exchange (SCE) frequencies in peripheral lymphocytes are a frequently used endpoint to indicate exposures to genotoxins in groups of humans. The aim of this study was to ascertain, in an experimental design, whether or not SCE rates have any association with the risk of cancer at the individual level in rats exposed to a known carcinogen. Individual SCE rates were determined in three consecutive analyses in cultured blood lymphocytes of 50 adult male Wistar rats. Analyses were done before as well as 24 hr and 7 days after a single intraperitoneal administration of 0, 25, 50, or 75 mg/kg of N-ethyl-N-nitrosourea (ENU). The animals were followed until death; also, the relationship between SCEs and carcinogenic outcome, i.e., the presence or absence of tumors, and their latency period were examined. ENU significantly decreased the life expectancy of the rats. The tumor types most clearly associated with ENU treatment were various gliomas and thyroid-gland and testicular tumors. ENU induced a moderate (maximally 1.6-fold) increase in the mean frequency of SCEs/cell at both sampling times after treatment. The effect was somewhat more pronounced 1 day rather than 1 week after treatment. The mean SCE rates in rats with ENU-specific cancers or in animals with early or multiple tumors did not differ from those in animals that survived no less than 65 weeks or longer without developing tumors. In ENU-treated animals with tumors, no relationship was found between the mean SCE rate and survival time. It is concluded that in outbred Wistar rats the SCE response in cultured lymphocytes does not indicate individual susceptibility to the carcinogenic action of ENU. On a group basis, however, animals with high SCE rates were shown to have increased risk of cancer.