In vivo kinetics of micronuclei induction by bifunctional alkylating antineoplastics

Abstract

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.

Different behavior of SCE‐eliciting lesions induced by low and high doses of busulfan

“…Our previous studies revealed atypical busulfan-dosedependent effects [Morales-Ramírez et al, 2004, 2006. Kinetic studies on the induction of micronuclei in murine peripheral blood erythrocytes indicate that exposure to a low dose of busulfan causes a maximal induction at 32 hr after exposure, and higher doses cause a maximal micronuclei induction at 48 hr after exposure; in addition, the micronuclei induction rate per dose is more than double for the higher dose (Fig.…”

“…The low (30 lmol/kg bw) and high (80 lmol/kg bw) doses of busulfan were selected from our previous in vivo studies in mice using micronuclei and single cell gel assays [Morales-Ramírez et al, 2004, 2006. These doses caused a differential response with both end points as can be seen in Figure 3.…”

“…Busulfan appears to exert its cytotoxic effects through genotoxic action; doses below 60 lmol/kg body weight do not reduce the frequency of polychromatic erythrocytes in mice, but do cause a slight increase in micronuclei; higher doses produce both an increase in micronuclei fre-quency and a decrease in the frequency of polychromatic erythrocytes [Morales-Ramírez et al, 2004]. Our earlier studies revealed atypical dose-dependent effects [MoralesRamírez et al, 2004[MoralesRamírez et al, , 2006 on the induction of micronuclei in murine peripheral blood erythrocytes over time.…”

“…These studies suggested that busulfan causes a transition from micronuclei induction by failed excision repair at low doses, to micronuclei induction by mismatch repair at higher doses, over a narrow dose range. Therefore, different lesions may be involved in micronuclei induction by low and high doses [Morales-Ramírez et al, 2004]. Moreover, the kinetics of busulfan-induced DNA-damage and repair in murine lymphocytes in vivo reveal a transition, in a small dose range, from early induction of comet-eliciting lesions and their repair, to the absence of comet induction.…”

Mecanismos de reparo de DNA envolvidos com lesões induzidas por agente alquilante (Nimustina) em células humanas e sua associação com a resistência de gliomas.

“…A droga TMZ é um agente alquilante que atua pela metilação das bases do DNA, sendo a lesão mais frequente, mutagênica e responsável pela indução da morte celular a metilação da MORALES-RAMIREZ et al, 2004).…”