Mutagenesis in cultured human diploid cells. IV. Induction of 8-azaguanine resistant mutations by phloxine, a mutagenic red dye.

Disodium 9-(3',4',5',6'-tetrachloro-o-carboxyphenyl)-6-hydroxy-2,4,5,7-tetrabromo-3-isoxanthone (phloxine), a red dye used as a food additive, was tested for its activity to induce 8-azaguanine (8AG) resistant mutations in cultured human embryonic cells. Phloxine had a severe cytotoxic effect on the cells at concentrations of 1 to 10 mug/ml. At concentrations of more than 30 mug/ml of phloxine no further decrease in cell survival was found. This cytotoxic effect of phloxine was not dependent on the duration of treatment. After treatment with phloxine for 2 h division of cells in normal medium was inhibited for 120 h. When cells were treated with phloxine at various concentrations for 2 h, cultured in normal medium for 48 h, and then selected with 30 mug/ml of 8AG, an increase in the induced mutation frequency was found. This increase in mutation frequency was dependent on the concentration of phloxine used as a mutagen and treatment with 100 mug/ml of phloxine increased the frequency to six times that in untreated cultures.