Quantification of sulfur mustard-induced DNA interstrand cross-links and single-strand breaks in cultured human epidermal keratinocytes.

The induction of DNA interstrand cross-links and their repair has been studied in cultured human epidermal keratinocytes exposed to sulfur mustard, bis-(beta-chloroethyl)sulfide. Alkaline elution is the most sensitive method to determine the number of DNA interstrand cross-links quantitatively. However, in the case of sulfur mustard the reliability of these data will be less since sulfur mustard also induces DNA single-strand breaks (SSB) and/or alkali-labile sites (ALS). The frequency of SSB and/or ALS induced by sulfur mustard is determined immunochemically. Correction for the induction of SSB and/or ALS induced by sulfur mustard resulted in a substantial increase in the calculated number of cross-links. Our results indicate that per microM sulfur mustard approximately 0.05 SSB (and/or ALS)/10(9) Da of DNA and approximately 0.12 cross-links/10(9) Da of DNA were induced immediately after exposure. Most of the DNA interstrand cross-links are removed during the first 24 h post exposure, but a small number of lesions seem to be persistent. In cells exposed to sulfur mustard concentrations as low as 1 microM, repair seems to occur not at all.