Altered growth properties of normal human cells induced by phorbol 12,13-didecanoate.

The tumor promoter phorbol 12,13-didecanoate (PDD) significantly altered the growth properties of early passage normal human skin cells in vitro in culture medium supplemented with elevated concentrations of selected amino acids. Continuous treatment of cells with 10(-7) or 10(-8) M PDD resulted in a 5 to 10-fold increase in saturation density at early passages followed by a long-term two- to fourfold increase. The PDD-treated cultures remained in exponential growth at cell densities greater than 10-fold higher than the control cultures. Removal of PDD from the culture medium while the cells were at a high cell density resulted in a return to near-normal saturation density by the subsequent passage. Anchorage independent growth of normal human cells in methylcellulose was also promoted by PDD in a dose dependent manner, with prior subculturing in the presence of PDD being required for maximal colony formation. The structural analog 4 alpha-phorbol 12,13-didecanoate failed to elicit similar cellular responses.