Mechanistic Study on Flumequine Hepatocarcinogenicity Focusing on DNA Damage in Mice

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In order to elucidate the tumor-initiating potential of flumequine (FL) in the liver, male C3H mice were given dietary administration of 4000 ppm FL throughout the study or for 2 weeks at the initiation stage, and then received 2 intraperitoneal injections of D-galactosamine (Gal) at weeks 2 and 5, with or without 500 ppm phenobarbital (PB) in their drinking water for 13 weeks to provide tumor-promoting effects. Hepatocellular foci were observed in 2 out of 8 and 6 out of 7 animals in the FL/PB + Gal and FL/FL + Gal groups, respectively. In addition, in an alkaline single-cell gel electrophoresis (comet) assay that was performed using adult, infant, or partial hepatectomized male ddY mice to evaluate the potential of FL at 500 mg/kg or less, to act as a DNA damaging agent. FL induced dose-dependent DNA damage in the stomach, colon, and urinary bladder of adult mice at 3 h but not at 24 h after its administration. Similarly, DNA damage was noted in the regenerating liver and the livers of infant mice at the 3 h time point. Furthermore, in in vitro assays that were conducted to investigate the potential of FL to inhibit eukaryotic topoisomerase II, which is responsible for the double-strand DNA breakage reaction as well as bacterial gyrase, inhibitory effects of FL on topoisomerase II were high relative to the influence on bacterial gyrase. The results of our studies thus strongly suggest that FL has initiating potential in the livers of mice that is attributable to its induction of DNA strand breaks.