Sister chromatid exchanges in lymphocytes of early cases of nasopharyngeal carcinoma and in 100 healthy subjects

Sister chromatid exchange rate was studied in 12 early diagnosed cases of nasopharyngeal carcinoma and in their paired controls. Exchange frequencies were also analyzed in 100 healthy subjects distributed in four regions of Hunan Province and correlated to nationality, age and sex. The incidence of sister chromatid exchange was significantly higher in the cancer patients than in the normal controls. No correlation was found between the frequency of sister chromatid exchange and region, nationality, age or sex.

Evidence for a major premutagenic ethyldeoxythymidine-DNA adduct in an in vivo system: N-nitroso-N-ethylurea-treated Salmonella typhimurium

Mutagenesis induced by N-nitroso-N-ethylurea (NEU) was assayed in four strains of Salmonella typhimurium which are known to be reverted to histidine prototrophy by mutations at A-T base pairs and by extragenic suppression. NEU-induced revertants were characterized for the presence of extragenic suppressors by their sensitivities to the histidine analogue, thiazolealanine. In strains carrying the plasmid, pKM101, only a small percentage of the revertants was due to suppressors, indicating that NEU gives rise to a major premutagenic adenine or thymidine-DNA adduct. In strains without plasmid, mutagenesis was much less efficient and resulted mainly from suppressors. Apparently error-prone DNA-repair plays an important role in mutagenesis via the A or T-DNA adduct in the plasmid-containing strains. Ethylmethanesulfonate (EMS), a mutagen known to form ethyladenines but not ethylthymidines, induced mutagenesis that resulted mainly from suppressors in all strains, and there was little inter-strain difference in the sensitivity to EMS. Since NEU, but not EMS, forms ethylthymidines in appreciable yield, and only NEU induced high percentages of revertants with mutations at A-T base pairs, it appears that at least one ethylthymidine is a major premutagenic adduct in NEU-induced mutagenesis.

Mutagenesis by N-nitroso compounds in Salmonella typhimurium TA102 and TA104: evidence for premutagenic adenine or thymine DNA adducts

Mutagenesis induced by the N-nitroso compounds: N-nitrosomethylurea, N-nitrosoethylurea, N-nitrosodi-n-propylamine and N-nitrosopyrrolidine was measured in Salmonella typhimurium TA100, TA102 and TA104. TA100 detects damage mainly at G-C base pairs while TA102 and TA104 can detect damage at A-T base pairs. In general all strains were similarly sensitive, except that TA104 was much less sensitive to high doses of N-nitroso-N-methylurea. In TA104 a significant percentage of the revertants induced by all agents except NMU resulted from point mutations at A-T base pairs, indicating that adenine or thymine DNA adducts are important premutagenic adducts formed by certain N-nitroso compounds.