Induction of dark keratinocytes by 12-O-tetradecanoyl-phorbol-13-acetate and mezerein as an indicator of tumor-promoting efficiency

In a 1980 study by Klein-Szanto, Major, and Slaga, the tumor-promoting effects of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and mezerein (MZ) were compared by examining their ability to induce dark keratinocytes in mouse skin. TPA was found to induce significantly more dark cells than MZ, with a maximum of 21% increase in the basal layer of the skin 24 hours after a single application of 4 µg of TPA. Both TPA and MZ increased the labeling indices, indicating enhanced cell proliferation. The study, which used 141 mice and observed effects up to 144 hours post-treatment, concluded that the production of dark cells is an important early event in tumor promotion and that TPA is approximately 50 times more effective as a tumor promoter than MZ.