The activity of bleomycin and modifiers of its clastogenic effect on the interphase chromatin of Indian muntjak fibroblasts

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.

Anticlastogenicity in cultured mammalian cells

Basic and applied research on anticlastogenicity has not only revealed valuable evidence on the mechanisms governing the induction of chromosomal aberrations by environmental mutagens, but also contributed effective ideas on a practical employment of this knowledge for the protection of individuals at risk. Considering the basic role played by chromosomal anomalies in oncogenesis, additional weight must be attributed to studies on anticlastogenicity. The employment of human cells in this kind of study dates back to 1969/70, while classical mammalian cell systems were used only later on. Various modes of application of both clastogens and anticlastogens (AC) were examined, but simultaneous addition to the cultures of both reagents was the most favored way. A wide spectrum of cytogenetic endpoints can be studied, but differences can be demonstrated with regard to efficacy of inhibitors on different types of cytogenetic changes, e.g., open breaks vs. rearrangements, but also vs. SCEs. Depending on their mode of influence on this spectrum, ACs can be arranged in various categories which are of practical importance, for instance, with regard to their oncogenic potential. A wide variety of factors was shown to influence AC action, e.g., time and mode of application of the test substances, physiologic and metabolic features of the cell types studied, type and mechanism of the clastogen used, etc. The addition of S9 mix can drastically change the patterns of efficacy of the ACs. The combined application of two or more ACs, as far as investigated, apparently neither potentiates nor even merely adds their effects.