A series of experiments evaluated the antileukemic effect of an agent which elevates cellular cyclic adenosine 3':5'-monophosphate levels by inhibiting phosphodiesterase. When ad ministered alone, theophylline had only modest antileukemic effects, but it had synergistic effects when administered with 1,3-bis(2-chloroethyl)-1 -nitrosourea. This synergism produced an improved therapeutic index in...

A series of experiments evaluated the antileukemic effect of an agent which elevates cellular cyclic adenosine 3':5'-monophosphate levels by phosphate levels by inhibiting phosphodiesterase. When administered alone, theophylline had only modest antileukemic effects, but it had synergistic effects when administered with 1,3-bis(2-chloroethyl)-1-nitrosourea. This synergism produced an improved th...

Attempts were made to provide proof for the occurrence of cyclic 3',5'-adenosine monophosphate in healthy and crown gall tissues of Vicia faba. Although our purified extracts gave positive readings in the Gilman binding assay for cyclic AMP, they were not digested by a specific cyclic 3',5'-adenosine monophosphate phosphodiesterase from beef heart. The extracts were digested, however, by a part...

The adenine nucleotides, 5'-AMP and 3',5'-cyclic AMP block L cells in the S-phase of the cell cycle. The intracellular level of cyclic AMP is reduced after incubation of cells with 5'-AMP, and rates of uridine transport are increased after incubation with either 5'-AMP or cyclic AMP. On the contrary, cyclic AMP levels are increased and uridine transport decreased in cells treated with an inhibi...