Comparison of the activity of phorbol 12-myristate 13-acetate and the diglyceride glycerol 1-myristate 2-acetate.

Diglycerides function as analogs of the phorbol ester tumor promoters. We compare here the activity of glycerol 1-myristate 2-acetate (GMA) with the corresponding phorbol 12-myristate 13-acetate (PMA). GMA inhibited phorbol ester binding to reconstituted protein kinase C, stimulated protein kinase C enzymatic activity, and, upon addition to intact 3T3 cells, inhibited [125I]EGF binding. Its potency was much less than that of PMA, however (2.9 X 10(4)-fold less for phorbol ester binding, greater than 1.2 X 10(5)-fold less for inhibition of EGF binding), and its activity on the intact cells was more transient. The marked difference in potency contrasts with the much smaller differences found previously for the corresponding pairs of dilaurate and dioleate derivatives.