Relationship of DNA repair phenotypes of human fibroblast and tumor strains to killing by N-methyl-N'-nitro-N-nitrosoguanidine.

Two DNA repair assays were used to group human cells. (a) The first assay, survival of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-treated adenovirus infecting cellular monolayers, was previously used to define the Mer phenotype of the strain. Strains that supported the growth of MNNG-treated viruses as well as did human fibroblasts were "Mer+"; those that gave rise to clearly less virus survival were "Mer-." (b) The second assay, data from which are presented in this paper, was that of post-MNNG colony-forming ability, and defined the Rem phenotype of the strain. Strains having post-MNNG colony-forming ability like that of human fibroblasts were "Rem+"; more sensitive strains were "Rem-". In all, 22 human cell strains were analyzed for their post-MNNG colony-forming ability. The most resistant strains (eight Mer+ Rem+ strains) had an average inactivation slope of 0.32 "lethal hit"/microM and were those fully able to repair O6-methylguanine (O6mGua) produced in their DNA by a 5 microM dose of MNNG. The most sensitive strains (9 Mer- Rem- strains) had an average inactivation slope of 7.0 "lethal hits"/microM, and were strains that failed to repair O6mGua. Five strains of intermediate sensitivity (Mer+ Rem-) had an average inactivation slope of 0.93 "lethal hit"/microM and were able to repair some labeled O6mGua produced by a 5 microM dose of labeled MNNG, but they repaired significantly less labeled O6mGua if pretreated with unlabeled MNNG. Representative strains from each group were treated with MNNG and assayed for ability: (a) to perform DNA repair synthesis (and DNA repair replication); (b) to support the growth of MNNG-treated adenoviruses; and (c) to restore control levels of tertiary structure to their DNA as assayed by nucleoid sedimentation. The results support the hypothesis that a lesion (both produced by agents that produce O6mGua and repaired by cell strains that repair O6mGua, but not by those that do not) is a lesion lethal to Mer- Rem- strains. This lesion may also initiate induction of excess DNA repair synthesis, the relaxed conformation of nucleoids, the reduced ability to repair MNNG-treated adenovirus, and sister chromatid exchanges as well.

Sensitivity of human cell strains having different abilities to repair O6-methylguanine in DNA to inactivation by alkylating agents including chloroethylnitrosoureas.

In order to investigate the mechanisms of cellular damage by alkylating agents, human fibroblasts and tumor cell strains having different sensitivities to killing by N-methyl-N'-nitro-N-nitrosoguanidine [and different abilities to repair O6-methylguanine ( O6mGua ) in their DNA] were treated with other alkylating agents. Methyl methanesulfonate, 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), 1-(2-hydroxyethyl)-3-(2-chloroethyl)-3-nitrosourea, and N-ethyl-N'-nitro-N-nitrosoguanidine gave rise to sensitivity differences, but the differences were less than those observed with N-methyl-N'-nitro-N-nitrosoguanidine. After treatment with UV light, the strains showed similar survival. The data show that the DNA repair mechanism(s) responsible for the differential survival of the strains after N-methyl-N'-nitro-N-nitrosoguanidine treatment probably play(s) a role in repairing DNA damage produced by methyl methanesulfonate, N-ethyl-N'-nitro-N-nitrosoguanidine, BCNU, and 1-(2-hydroxyethyl)-3-(2-chloroethyl)-3-nitrosourea but not that produced by UV. Furthermore, the results support the idea that a breakdown product of BCNU, that does not cause damage repairable by O6mGua repair mechanisms, contributes to the lethal effects due to BCNU-produced DNA-damage that is repairable by O6mGua repair mechanisms. The survival data, along with nucleoid sedimentation and adenovirus host-cell reactivation data, are consistent with the hypothesis that the lesion(s) lethal to tumor cells defective in O6mGua DNA repair are lesions in which DNA oxygen atoms are alkylated.

Lymphoblastoid lines and skin fibroblasts from patients with tuberous sclerosis are abnormally sensitive to ionizing radiation and to a radiomimetic chemical.

Lymphoblastoid lines, derived by transforming peripheral blood lymphocytes with Epstein-Barr virus, and skin fibroblast lines were established from two patients with tuberous sclerosis. The number of viable lymphoblastoid cells was determined by their ability to exclude the vital dye trypan blue after their irradiation with x-rays or 254 nm ultraviolet light. The growth of fibroblasts was determined by their ability to form colonies after treatment with the radiomimetic, DNA-damaging chemical N-methyl-N'-nitro-N-nitrosoguanidine. The tuberous sclerosis lymphoblastoid lines were hypersensitive to x-rays but had normal sensitivity to the ultraviolet radiation. The tuberous sclerosis fibroblast lines were hypersensitive to the N-methyl-N'-nitro-N-nitrosoguanidine. The hypersensitivity of tuberous sclerosis cells to x-rays and to N-methyl-N'-nitro-N-nitrosoguanidine is believed to reflect defective repair of DNA damaged by these agents and may provide the basis for in vitro, including prenatal, diagnostic tests for tuberous sclerosis.

Hypersensitivity to N-methyl-N'-nitro-N-nitrosoguanidine in fibroblasts from patients with Huntington disease, familial dysautonomia, and other primary neuronal degenerations.

Cells from patients with ataxia telangiectasia, a rare autosomal recessive disease characterized by primary neuronal degeneration, are abnormally sensitive to the DNA-damaging chemical N-methyl-N'-nitro-N-nitrosoguanidine. We have conducted experiments to determine whether more common primary neuronal degenerations also have a hypersensitivity to this radiomimetic chemical. Fibroblast strains from 13 control donors and from 13 patients with inherited primary neuronal degenerations were treated in vitro with the chemical, and the strains' sensitivity to the chemical was then determined by measuring their ability to divide and form colonies. Twelve of the 13 patient strains, including the 6 Huntington disease and the 4 familial dysautonomia strains, were abnormally sensitive. This hypersensitivity, which is believed to reflect defective repair of the chemically-induced DNA damage, might provide the basis for presymptomatic and prenatal diagnostic tests for these disorders and for elucidating their pathogenesis.