INHIBITION OF SALVAGE SYNTHESIS OF NUCLEIC-ACID BY ADENOSINE 3',5'-CYCLIC DECYLPHOSPHORAMIDATE IN MASTOCYTOMA P-815 CELLS

Constant exposure of mastocytoma P-815 cells to adenosine 3',5'-cyclic decylphosphoramidate (1), which is permeable to the cell membrane and resistant to the action of phosphodiesterase, caused a dose-dependent (1 to 50 muM) inhibition in the synthesis of DNA and cell proliferation. Pretreating the cells with compound 1 (20 muM, 4 h) caused considerable inhibition of the incorporation of [H-3]thymidine ([H-3]TdR) into [H-3]deoxythymidine 5'-triphosphate ([H-3]dTTP) and that of [C-14]hypoxanthine into nucleic acid, but not the synthesis of [C-14]dTTP from [(U-C)-C-14]aspartate. These results indicate that compound 1 preferentially inhibits the salvage synthesis of intracellular nucleotides and nucleic acids. Thymidine kinase, a key enzyme in salvage synthesis of nucleotides, was almost undetectable in cells pretreated with compound 1 at 20 muM for 4 h Or at 5 muM for 15 h. On the other hand, compound 1 activated partially purified cAMP-dependent protein kinase A from bovine heart. Judging from these observations, it is likely that compound 1 readily permeates the cell membrane, activates cAMP-dependent protein kinase, then inhibits the salvage synthesis of nucleotides and nucleic acids by inhibiting thymidine kinase, which results in the inhibition of cell growth.