Changes in the proliferation of human lymphocytes induced by several cytostatics and revealed by the premature chromosome condensation technique

Genotoxic and aneugenic properties of an imidazole derivative

To contribute to a more accurate characterization of the mutagenic and aneugenic effects of thiabendazole (TBZ), a widely used antiparasitic and food preservative drug, the induction of sister chromatid exchanges (SCEs) and mitotic spindle anomalies as cytogenetic end-points were investigated. Studies were carried out in Chinese hamster ovary (CHO) cells and human peripheral blood lymphocytes. A significant dose-dependent increase in SCE frequency was observed in CHO cells with S9-Mix (P < 0.01) in the 50-100 microg ml(-1) dose-range, while in the absence of S9-Mix, an enhancement of the SCE frequency was exhibited at the highest dose (P < 0.01). In CHO-K1 cells a significant increase in mitotic spindle anomalies (P < 0.01) was observed with the highest concentration assayed reflecting the specific effect of TBZ formulation at the microtubule level. Cell proliferation kinetics (CPK) were not modified by the addition of this pharmaceutical product. In human lymphocyte cultures, exposure to 100 microg ml(-1) TBZ formulation resulted in a significant decrease of the mitotic index (MI) (P < 0.003) and changes in the replication index (RI) (P < 0.05).

Evaluation of the genotoxicity of cis-bis(3-aminoflavone)dichloroplatinum(II) in comparison with cis-DDP

Short-term tests that detect genetic damage have provided information needed for evaluating carcinogenic risks of chemicals to man. The mutagenicity of cis-bis(3-aminoflavone)dichloroplatinum(II) (cis-[Pt(AF)2Cl2]) in comparison with cis-diamminedichloroplatinum(II) (cis-DDP) was evaluated in the standard plate-incorporation assay in four strains of Salmonella typhimurium: TA97a, TA98, TA100 and TA102, in experiments with and without metabolic activation. It was shown that cis-[Pt(AF)2Cl2] acts directly and is mutagenic for three strains of S. typhimurium: TA97a, TA98 and TA100. In comparison with cis-DDP this compound showed a weaker genotoxicity. Contrary to cis-DDP it has not shown toxic properties in the tester bacteria. The genotoxicity of both tested compounds was evaluated using chromosomal aberration, sister chromatid exchange and micronucleus assays, without and with metabolic activation, in human lymphocytes in vitro. The inhibitory effects of both compounds on mitotic activity, cell proliferation kinetics and nuclear division index were also compared. In all test systems applied, cis-[Pt(AF)2Cl2] was a less effective clastogen and a weaker inducer of both sister chromatid exchanges and micronuclei in comparison with cis-DDP, with and without metabolic activation. cis-[Pt(AF)2Cl2] has a direct mechanism of action and is less cytostatic and cytotoxic than the other compound. These results provide important data on the genotoxicity of cis-[Pt(AF)2Cl2] and indicate its beneficial properties as a potential anticancer drug, especially in comparison with cis-DDP.

Selective mitomycin C and cyclophosphamide induction of apoptosis in differentiating B lymphocytes compared to T lymphocytes in vivo

Differentiating B and T lymphocytes differ in sensitivity to a number of environmental toxins and anticancer agents. B lymphocytes are susceptible and T lymphocytes resistant to killing by cyclophosphamide (Cy) metabolites capable of forming DNA interstrand cross-links. However, the mechanisms responsible for the rapid killing and loss of bursal-resident B lymphocytes are unknown. Therefore, we investigated the cellular mechanisms of selective toxicity of two cross-linking drugs, mitomycin C (MMC) and Cy, towards differentiating B and T lymphocyte populations using the chicken embryo model system. Viability of bursal-resident B lymphocytes (bursacytes) decreased starting at 5 h post exposure (PE) to MMC, and was maximally reduced by 71.6% by 10 h PE at the highest dose examined (9.0 micrograms MMC/g). Dose-dependent increases in the percentage of apoptotic bursacytes were observed as early as 5 h PE, and increased to 72% by 10 h PE. This was accompanied by reductions in bursacyte numbers. Cy also induced apoptosis in bursacytes. In contrast, thymus-resident lymphocytes (thymocytes) were much more resistant to the toxic effects of MMC and Cy. Viability of thymocytes was reduced by only 10% in the 9.0 micrograms/g MMC treatment group. In addition, the percentage of thymocytes engaged in apoptosis was much lower than that for bursacytes. MMC induced modest cell cycle inhibition in bursacytes and thymocytes. These data strongly suggest that MMC and Cy-induced diferential toxicity involves primarily early and extensive triggering of apoptosis in differentiating B lymphocytes, leading to rapid reduction of lymphocyte numbers in the embryonic bursa.

Schedule dependent variation in human lymphocyte sensitivity to bleomycin and repair of chromosomal aberrations in G2

Bleomycin (BLM) induced chromosomal damage in G2 phase and its repair kinetics in normal human lymphocytes were studied following different treatment schedules. As a first step, a dose-response curve was obtained (concentrations of 5-50 micrograms/ml). For repair kinetics studies, blood samples were treated with BLM at a concentration of 20 micrograms/ml. Continuous treatment produced equal numbers of breaks per cell (br/c) when the cells were treated 3, 4 or 5 h before fixation. If the treatment time was extended to 6 h, the level of br/c was increased 2-fold (p < 0.001) as a result of an increased number of cells with more than 3 br/c. The curves obtained after pulse treatment showed maximal chromosome damage at time 3 (45 min BLM treatment, followed by 2 h repair in drug free medium). When the time after treatment was extended to 4 h (treatment time 5), a 50% reduction in chromosome damage was measured. It was found out that at treatment points 3, 4 and 5 the differences in breaks per cell at the different schedules applied were statistically highly significant. If caffeine (CAF) was added, the continuous treatment, BLM+CAF, induced a statistically significant increase in the frequency of br/c at every treatment point, but the shape of the curve illustrating the kinetics of chromosomal damage remained unchanged. Moreover, the addition of CAF at continuous BLM treatment brings the level of br/c close to that measured at the pulse BLM treatment except for treatment time 3. When applied in a combination with BLM, CAF considerably modified the kinetics of chromosome damage for a pulse (BLM alone) treatment. The possible reasons for the changes in the level of br/c as well as a tentative scheme for assessment of chromosome damage repair capacity after BLM treatment are discussed.

Are mitotic index and lymphocyte proliferation kinetics reproducible endpoints in genetic toxicology testing?

Lymphocyte proliferation kinetics is an endpoint used in genetic toxicology which has recently been proposed as an alternative for the screening of new cytostatic drugs. Although great variability for this parameter has been reported, there are few reports about the intra- and inter-individual variation of the effects of chemicals on this endpoint. For this reason, experiments were conducted to evaluate the reproducibility of the effects of a well-known cytostatic, mitomycin C (MMC), on the proliferation of PHA-stimulated human lymphocytes, both over time and among samples from several donors. Although inter-individual variability was shown in both parameters in untreated and treated cultures, this variation was not significant. Intra-individual variation was significantly detected only in cultures treated with 0.1 microM MMC.