Effect of dibutyryl cAMP on cell cycle progression of rat brain tumor cells in vitro.

Autoradiographic and flow microfluorometry analyses have been applied to a study of perturbed cell kinetics in 9L rat brain tumor cells treated with dibutyryl cyclic AMP and theophylline alone and in combination in vitro. At a concentration of 1 mM each, cell growth ceased shortly after the administration of these drugs. The results indicate that cells in S and G2 phase at the time of drug administration can undergo mitosis even though a considerable prolongation of G2 phase was apparent. However, cells in G1 at the time of drug administration was arrested in that phase, whereas those cells in S or G2 were able to complete one mitosis before becoming arrested in the G1 phase. This blocking effect was reversible, and cells resumed proliferation at a normal rate shortly after the removal of these drugs.