title: Pretreatment of normal human fibroblasts and human colon carcinoma cells with MNNG allows chloroethylnitrosourea to produce DNA interstrand crosslinks not observed in cells treated with chloroethylnitrosourea alone.
abstract: Chloroethylnitrosoureas (CNU) are antitumor agents which produce DNA interstrand crosslinks. We have proposed that crosslinks are produced in DNA via monoadduct formation at the guanine-O6 position, followed by a delayed reaction with the opposite DNA strand. Human cells are known to differ in their capacity to repair the O6-methylguanine lesion. One example of this repair capacity is the ability of cells to reactivate adenovirus which has been damaged by in vitro treatment with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Cells that repair the virus are designated Mer+ and deficient cells Mer-. In a recent report, we showed a clear correlation between CNU-induced DNA interstrand crosslinking and the Mer phenotype. Mer- cells produced consistently higher levels of interstrand crosslinks than did Mer+ cells. In the present study we have measured the CNU-induced DNA interstrand crosslinking in IMR-90 normal human fibroblasts (Mer+), HT-29 human colon carcinoma cells (Mer+), and VA-13 SV-40 transformed human cells (Mer-) following pretreatment with MNNG. Cells were treated for 1 h with MNNG, then for an additional 1 h with CNU. Comparable levels of CNU-induced DNA interstrand crosslinking were observed in all cell lines. This crosslinking has been previously undetected in the IMR-90 and HT-29 cells. Cytotoxicity studies showed that MNNG pretreatment greatly enhanced the killing of IMR-90 and HT-29 cells by CNU, however, in VA-13 cells the increase in cell kill was smaller. These data suggest that in Mer+ cells a DNA repair system may remove chloroethyl monoadducts before the lethal DNA interstrand crosslinks can form. However, pretreatment of cells with MNNG may saturate this repair system rendering it inoperable.
mesh_terms: D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D003110:Colonic Neoplasms / Q000235:genetics*; D004247:DNA / Q000378:metabolism*; D005038:Ethylnitrosourea / Q000031:analogs & derivatives / Q000494:pharmacology*; D005260:Female; D005347:Fibroblasts / Q000187:drug effects*; D006801:Humans; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology*; D009607:Nitrosourea Compounds / Q000494:pharmacology*; D011247:Pregnancy; D013997:Time Factors
chemical_list: D009607:Nitrosourea Compounds; D008769:Methylnitronitrosoguanidine; C017139:1-(2-chloroethyl)-1-nitrosourea; D004247:DNA; D005038:Ethylnitrosourea