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Induction of endogenous xenotropic type-C virus from Kirsten sarcoma-virus-transformed BALB/c (K-BALB) mouse cells was inhibited by short-term exposure to L-beta-3,4-dihydroxyphenylalanine (L-dopa) methyl ester. Partially synchronized cells cultured for 1-4 h with 0.8-1.6 mM L-dopa methyl ester and subsequently induced with 5-iododeoxyuridine (IdUrd), cycloheximide and histidinol showed inhibition of virus activation. Incorporation of thymidine, uridine and leucine was measured at the end of the drug treatment and during the subsequent induction period. L-dopa methyl ester had a pronounced effect on DNA synthesis, reducing it by more than 85% during a 4-h incubation period, whereas RNA and protein synthesis remained largely unaffected. Removal of the drug and replacement with fresh medium did not reverse DNA synthesis or virus activation during the subsequent induction interval. L-dopa methyl ester was also shown to potentially function as an analogue of tyrosine in this cell system. These results suggest that inhibition of virus induction may be caused by inhibiting the normal progressing of cells through the S phase of the cell cycle.

Eight food dyes or commercial color mixtures certified for use in the United States were tested for their ability to transform in vitro a serial line of Fischer rat embryo cells previously reported to be a sensitive indicator of chemicals having carcinogenic potential. Malignant cell transformation was induced by a commercial mixture (G2024) of two of these dyes (Blue 1 and Yellow 5) and by Blue 2, Green 3 (one of two experiments) and Red 4. Food dyes Blue 1, Red 3, Yellow 5 and Yellow 6 did not induce cell transformation. One to 1.5 mg of each dye was injected into suckling LVG or Graffi hamsters which were monitored for tumor induction and/or death over a 330-day period. None of the non-transforming dyes (Blue 1, Red 3, Yellow 5, Yellow 6) or Green 3 induced a significant increase in tumor (mostly lymphoma) incidence or animal mortality. Three of the transforming dyes (Blue 2, Green 2024, Red 4) did increase tumor incidence and/or mortality in at least one strain of hamster. We conclude the the in vitro assay suggested that certain food dyes were carcinogens and that in vivo studies in hamsters supported this interpretation.

The potential carcinogenicity of 3 azabenz(a)anthracenes was determined in vitro. The 3 compounds tested were 1-, 2-, and 9-azabenz(a)anthracene. The initial assay was chemical carcinogen-induced enhancement of anchorage-independent survival of Rauscher leukemia virus-infected Fischer rat embryo cells, 2FR(4)50 (2FR4). Cells treated with 2- and 9-azabenz(a)anthracene showed dose-dependent increased survival. After continued subculturing, the surviving cells from 2- and 9-azabenz(a)anthracene-treated cultures displayed morphological transformation and ability to grow in semi-solid medium. Mock-treated controls and I-azabenz(a)anthracene-treated cultures did not show either of these properties. These data suggest that certain azabenz(a)anthracenes are potential carcinogens.