ABSTRACT
BACKGROUND: Busulfan (BUS) is a highly toxic antineoplastic bifunctional-alkylating agent and has a narrow therapeutic window. Our previous study revealed a narrow dose-range of BUS, which causes a sudden dose-dependent transition from early- to late-expressing micronucleus induction and from a non-cytotoxic to a cytotoxic effect. In the present study, the kinetics of DNA-damaged cell induction by BUS and its dose-effect relationship were established. METHODS: This was achieved by using the kinetics of DNA-damaged cell induction, determined by the comet assay in murine peripheral blood leukocytes of mice, after the intraperitoneal exposure to 16, 30, 45, 60 or 80 micromol/kg of BUS. RESULTS: Doses of 15 or 30 micromol/kg of BUS were able to increase DNA-damaged cell frequency, but doses of 45 micromol/kg body weight or higher caused a sudden drop in this frequency. CONCLUSIONS: This suggests that higher doses cause lesions that inhibit the expression of damage as comets, i.e., DNA-protein or interstrand crosslinks. The latter could be explained by sudden monoadduct-to-crosslink transformation due to a DNA conformational change induced by monoadduct accumulation that facilitates crosslink formation. This narrow dose-dependent transition could contribute to the narrow therapeutic window of BUS.
Subject(s)
Busulfan/pharmacokinetics , Busulfan/toxicity , DNA Damage/drug effects , Animals , Apoptosis/drug effects , Busulfan/administration & dosage , Dose-Response Relationship, Drug , Gene Expression/drug effects , Kinetics , Leukocytes/cytology , Leukocytes/drug effects , Male , Mice , Mice, Inbred BALB CABSTRACT
The aim of the present study was to determine in vivo the kinetics of micronucleated polychromatic erythrocyte (MN-PCE) induction in mice, as an approach for studying the mechanism of micronuclei induction by mitomycin C, cis-diamine dichloroplatinum, busulfan and bis-chloroethylnitrosourea, bifuctional alkylating antineoplastic agents having different patterns of crosslink induction. The kinetics of MN-PCE induction was established by scoring the frequency of MN-PCE in 2000 PCE in peripheral blood, for periods of 8 or 10 h after acute treatment and up to 80 h, with different doses of the agent. The kinetics of MN-PCE induction and particularly the times of maximal induction by different bifunctional alkylating agents were compared with the kinetics previously obtained for ethylnitrosourea, methylnitrosourea and 6-mercaptopurine, agents that cause MN-PCE mainly in the first, second and third divisions after exposure, respectively. The results obtained in the present study allow us to conclude that: (i) bifunctional alkylating agents have very different efficiencies of genotoxic and cytotoxic action; (ii) all assayed bifunctional alkylating agents induced micronuclei during the first cell division, owing to the mistaken repair of primary lesions, e.g. excision; (iii) busulfan and bis-chloroethylnitrosourea showed an additional late mechanism of micronuclei induction, which is expressed at the third division and seems to be related to the mismatch repair process.
