Brief Communication : Nonspecific Inhibition of DNA Repair by Promoting and Nonpromoting Phorbol Esters 2

The effects of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) and its nonpromoting structural analogue, 4-O-methyl-12-O-tetradecanoylphorbol-13-acetate (Me-TPA), on N-acetoxy-2-acetylaminofluorene-elicited DNA repair and replicative DNA synthesis was measured in normal human fibroblasts. Both esters inhibited DNA repair synthesis, and Me-TPA was nearly as effective as TPA. In addition, TPA inhibited replicative DNA synthesis. These findings showed that inhibition of DNA repair synthesis may not be a major factor in the mechanisms of action of tumor promoters.