DNA repair synthesis of cultured human cells as a rapid bioassay for chemical carcinogens

The feasibility of detection of carcinogenic chemicals using DNA repair synthesis of cultured human fibroblasts as measured by an unscheduled 3 HTdR incorporation has been explored. Of 64 chemicals tested, 29 were proximate or ultimate carcinogens, 15 were precarcinogens that required metabolic activation, 16 were non‐oncogenic compounds and 4 were of unknown carcinogenicity. All directly acting carcinogens triggered a DNA repair synthesis, whereas no unscheduled 3 HTdR incorporation was observed following the application of the 16 non‐oncogenic compounds. As a rule, the precarcinogens (without metabolic activation) do not elicit DNA repair synthesis. However, longer exposures and higher concentrations of the precarcinogens 2‐AAF, aflatoxin B 1 and sterigmatocystin gave unscheduled 3 HTdR uptake. The results suggest the suitability of using repair synthesis as endpoint, and cultured human cells as subjects in a prescreening programme for chemical carcinogens.