Differential growth inhibition in two human carcinoma cell lines by cyclic adenosine 5'-monophosphate analogs

The inhibition of cell replication in two human carcinoma cell lines by various cyclic AMP analogs was explored. In all instances, the addition of the cyclic nucleotide phosphodiesterase inhibitor 1-methyl-3-isoburylxanthine resulted in synergistic growth inhibition by the analogs. A correlation was found between an analog's ability to inhibit growth and its ability to activate protein kinase. A differential effect of the breakdown product 8-bromo-AMP (8-BrAMP) on cell replication in the two cell lines was observed; i.e., one cell type was extremely sensitive to inhibition by 8-BrAMP and the growth inhibition could not be reversed by uridine, whereas the other cell type was less sensitive to 8-BrAMP and the growth inhibition was significantly reversed by uridine.