PT  - JOURNAL ARTICLE
AU  - Louise M. Winn
AU  - Perry M. Kim
AU  - Jac A. Nickoloff
TI  - Oxidative Stress-Induced Homologous Recombination As a Novel Mechanism for Phenytoin-Initiated Toxicity
AID  - 10.1124/jpet.103.052639
DP  - 2003 Aug 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 523--527
VI  - 306
IP  - 2
4099  - http://jpet.aspetjournals.org/content/306/2/523.short
4100  - http://jpet.aspetjournals.org/content/306/2/523.full
SO  - J Pharmacol Exp Ther2003 Aug 01; 306
AB  - Although the mechanism(s) of phenytoin-initiated toxicity is unknown, phenytoin can be enzymatically bioactivated to a reactive intermediate leading to increased formation of reactive oxygen species, which can damage essential macromolecules, including DNA. The oxidation of DNA can induce DNA double-strand breaks (DSBs), which may be repaired through homologous recombination. Increased levels of DSBs may induce hyper-recombination, leading to deleterious genetic changes. We hypothesize that these genetic changes mediate phenytoin-initiated toxicity. To investigate this hypothesis we used a Chinese hamster ovary cell line containing a neo direct repeat recombination substrate to determine whether phenytoin-initiated DNA oxidation increases homologous recombination. Cells were treated with 0 to 800 μM phenytoin for 5 or 24 h, and homologous recombination frequencies and recombinant product structures were determined. Phenytoin-initiated DNA oxidation was determined by measuring the formation of 8-hydroxy-2′-deoxyguanosine. We demonstrate that phenytoin increases both DNA oxidation and homologous recombination in a concentration- and time-dependent manner. All recombination products analyzed arose via gene conversion without associated crossover. Our data demonstrate that phenytoin-initiated DNA damage can induce homologous recombination, which may be a novel mechanism mediating phenytoin-initiated toxicity. The American Society for Pharmacology and Experimental Therapeutics