Stimulation of DNA synthesis in calcium-deprived T51B liver cells by the tumor promoters phenobarbital, saccharin, and 12-O-tetradecanoylphorbol-13-acetate.

Extracellular calcium deprivation arrested the proliferative development of T51B rat liver cells in late G1 or S phases. These arrested cells initiated DNA synthesis within an hr after addition of calcium or a tumor promoter such as phorbol-12,13-didecanoate, phenobarbital, saccharin, or 12-O-tetradecanoylphorbol-13-acetate. Nonpromoting relatives of 12-O-tetradecanoylphorbol-13-acetate such as phorbol, 4-O-methyl-12-O-tetradecanoylphorbol-13-acetate, and 4 alpha-phorbol-12,13-didecanoate were unable significantly to induce the calcium-deprived cells to initiate DNA synthesis. It is suggested that an ability to elicit a prompt DNA-synthetic response from calcium-deprived cells might be a useful in vitro indicator of tumor-promoting potential.