THE ANTIPROLIFERATIVE EFFECT OF 8-CHLORO-ADENOSINE, AN ACTIVE METABOLITE OF 8-CHLORO-CYCLIC ADENOSINE-MONOPHOSPHATE, AND DISTURBANCES IN NUCLEIC-ACID SYNTHESIS AND CELL-CYCLE KINETICS

8-Chloro-adenosine, the dephosphorylated metabolite of the antineoplas tic agent 8-chloro-cyclic AMP, has been proposed to act on the regulat ory subunits of cyclic AMP-dependent protein kinase. 8-Chloro-adenosin e has a growth-inhibitory effect, the mechanism of which is unclear. W e investigated the effects of 8-chloro-cyclic AMP and 8-chloro-adenosi ne on nucleic acid synthesis and cell cycle kinetics in two human glio ma cell lines. These effects were compared to those of the cyclic AMP analogue 8-(4-chlorophenyl)-thio-cyclic AMP (8-CPTcAMP), which is less susceptible to dephosphorylation. Whereas 8-CPTcAMP almost completely inhibited RNA and DNA synthesis, both 8-chloro-adenosine and 8-chloro -cyclic AMP only partly inhibited synthesis of RNA and DNA at growth-i nhibitory concentrations, as demonstrated by using [5-H-3]-uridine and [C-14]thymidine incorporation. Therefore, the growth-inhibitory effec t of 8-chloro-cyclic AMP is not (or not completely) due to activation of cyclic AMP-dependent protein kinase nor to the inhibition of nuclei c acid synthesis. Flow cytometric analysis revealed that 8-chloro-cycl ic AMP and 8-chloro-adenosine probably block cell cycle progression at the G(2)M phase. The effects of 8-chloro-cyclic AMP on nucleic acid s ynthesis and cell cycle progression were largely prevented by adenosin e deaminase, which inactivates 8-chloro-adenosine. This indicates that the effects of 8-chloro-cyclic AMP were at least in part due to its m etabolite 8-chloro-adenosine. Incorporation of 8-chloro-adenosine into RNA and DNA might contribute to the disturbance of the cell cycle kin etics and growth-inhibitory effect of 8-chloro-adenosine. Copyright (C ) 1996 Elsevier Science Inc.