Genotoxicity kinetics in murine normoblasts as an approach for the in vivo action of difluorodeoxycytidine

In vivo kinetics of the genotoxic and cytotoxic activities of cladribine and clofarabine

The aim of the present in vivo study was to determine the kinetics of the genotoxic and cytotoxic activities of cladribine and clofarabine in mouse normoblasts using flow cytometry. Mice in groups of five were treated with cladribine or clofarabine. Blood samples were obtained from the mouse tails before treatment and every 8 hr posttreatment for 72 hr. These samples were cytometrically scored for micronucleated reticulocytes (RETs), and the percentage of RETs was determined. The results showed that clofarabine and cladribine have early cytotoxic effects that are related to the genotoxic effects reported in previous studies; the drugs have both complex long-lasting genotoxic and cytotoxic kinetic activity, with similar profiles that suggest a relationship between the genotoxic and cytotoxic parameters. The initial genotoxkinetics timing of clofarabine is equivalent to those of difluorodeoxycytidine, likely because both agents inhibit DNA polymerase. Clofarabine shows a higher genotoxic and cytotoxic efficiency than cladribine, in agreement with previous results.

In vivo Characterization of the Radiosensitizing Effect of a Very Low Dose of BrdU in Murine Cells Exposed to Low-Dose Radiation

The aim of the present study was to characterize the in vivo radiosensitizing effect of a very low dose of bromodeoxyuridine (BrdU) in mice exposed to low-dose radiation by establishing the following: (1) the radiosensitizing effect during DNA synthesis using single-cell gel electrophoresis (SCGE) in murine bone marrow cells, and (2) the number and timing of the mechanisms of genotoxicity and cytotoxicity, as well as the correlation of both end points, using flow cytometry analysis of the kinetics of micronucleus induction in reticulocytes. Groups of mice received intraperitoneal injections of 0.125 mg/g of BrdU 24 h prior to irradiation with 0.5 Gy of ⁶⁰ Co gamma rays. DNA breaks measured using SCGE were determined at 30 min after exposure to radiation. The kinetics of micronucleated reticulocyte (MN-RET) induction was determined every 8 h after irradiation up to 72 h. The results from both experimental models indicated that low-level BrdU incorporation into DNA increased the sensitivity to 0.5 Gy of radiation, particularly in the S phase. The formation of micronuclei by gamma rays was produced at three different times using two main mechanisms. In the BrdU-substituted cells, the second mechanism was associated with a high cytotoxic effect that was absent in the irradiated BrdU-unsubstituted cells. The third mechanism, in which micronucleus formation was increased in irradiated substituted cells compared with the irradiated nonsubstituted control cells, was also related to an increase in cytotoxicity. Environ. Mol. Mutagen. 60:534-545, 2019. © 2019 Wiley Periodicals, Inc.