Analysis of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced DNA damage in tumor cell strains from Japanese patients and demonstration of MNNG hypersensitivity of Mer xenografts in athymic nude mice.

Abstract

Among 15 human tumor cell strains from Japanese patients, one strain derived from a patient with thyroid cancer showed inability to support the growth of adenovirus 5 treated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). When plated on this Mer- strain, adenovirus 5 showed 3-4 times higher sensitivity to MNNG-induced killing than when plated on any of the other 14 Mer+ tumor cell strains. Biochemical analysis showed that the Mer- strain was defective in demethylation repair of O6-methylguanine produced by MNNG treatment. The sensitivities of 12 of the 15 human tumor strains, including the Mer- strain, to MNNG were compared by measuring their colony-forming abilities. All the strains tested showed the Rem- phenotype (having higher sensitivity to MNNG-produced cell killing than normal fibroblasts). The differential killing effects of MNNG on Mer- and Mer+ tumor cells under in vivo conditions were tested using the Mer+ HeLa S3 strain and its Mer- variant. Mer+ cells and Mer- cells were implanted subcutaneously into the left and right flanks, respectively, of 10 nude mice and the next day, MNNG solution (0.25 ml at 1 mg/ml) was injected into the implantation sites of eight mice. Mer- tumor cells in six of eight treated mice showed no growth and those in the other two mice did grow, but regressed after approximately 3 weeks. In contrast, Mer+ tumor cells continued to grow in all the eight mice treated, indicating that Mer- tumor cells may be selectively inactivated by suitable therapeutic regimens with appropriate methylating drugs.