DNA-DAMAGE INDUCED BY CHLORO-4-(DICHLOROMETHYL)-5-HYDROXY-2[5H]-FURANONE (MX) IN HL-60 CELLS AND PURIFIED DNA IN-VITRO

Chlorinated tap water often contains chloro-4-(dichloromethyl)-5-hydro xy-2[5H]-furanone (MX), which is a potent directly acting bacterial mu tagen. We have investigated the induction of DNA damage by MX in a pro myelocytic human leukaemia cell line (HL-60 cells). Exposure of HL-60 cells to 100-300 mu M MX resulted in increased levels of DNA single-st rand breaks and/or alkali-labile sites (SSBs) as detected by alkaline filter elution. When adding inhibitors of DNA break repair (AraC plus hydroxyurea), increased levels of DNA SSBs were observed at very low c oncentrations (1-3 mu M) of MX, as observed by both alkaline filter el ution and the single-cell gel electrophoresis assay. Increased DNA SSB s could also be observed if DNA repair inhibitors were added immediate ly after exposure to 10 mu M MX, indicating that low concentrations of MX cause a relatively stable modification of DNA that may be recogniz ed and incised by DNA repair enzyme activities. Further studies with D NA break repair inhibitors indicated that HL-60 cells exposed to 10 mu M MX for 1 h repaired 50% of their initial DNA damage during a 2-h pe riod and the repair appeared to be complete at 22 h. Analysis of MX-tr eated DNA by sequencing methods indicated that MX preferentially react s with guanines in DNA.