Synergistic Effect of Mutagens and Incorporated DNA in Vitro

Abstract

Purified calf thymus DNA was incorporated, to saturation limits, into cultured hamster embryo cells. The cells were then exposed to carcinogenic and noncarcinogenic diepoxides and aromatic hydrocarbons. All tested cultures converted to permanent cell lines, exhibiting loss of contact inhibition. Tumors were not induced in compatible animals inoculated with converted cells. Control cultures (untreated, DNA-treated only, and chemical agent-treated only) failed to convert and degenerated. The incorporated, inactive DNA may have competed against cellular DNA for limited amounts of intracellular substances required for repairing genetic damage caused by the chemical agents. By analogy, massive invasion of buccopharyngeal epithelium by DNA viruses concurrently with exposure to environmental mutagens might act as cofactors to potentiate carcinogenesis in the human buccal cavity and oropharynx.