Effects of 4-aminopyrazolo(3, 4- d)pyrimidine in combination with guanine on nucleic acid and protein synthesis by Ehrlich ascites cells in culture : Biochemical and cytochemical analyses

Abstract

Quantitative microspectrophotometric and microinterferometric analyses in combination with biochemical methods were used to examine the effects of 4-aminopyrazolo(3,4- d)pyrimidine (APP, 5 × 10 −6 M) in combination with guanine (2 × 10 −4 M) on the synthesis of DNA, RNA, and protein in asynchronously growing Ehrlich ascites cells in culture. Exposure to such concentrations of APP + guanine resulted in a nonlethal inhibition of cell multiplication. Pulse-labeling with 14C-thymidine, 14C-uridine and 14C-1-leucine in the presence of APP + guanine revealed an exponential decline in the per cell rate of DNA synthesis, while the per cell rate of RNA synthesis, as adjudged by 14C-uridine incorporation, was not significantly inhibited, and the per cell rate protein synthesis was inhibited only ca 50 per cent. Determination of the cellular content of DNA, RNA, and protein by cytochemical population analyses revealed an accumulation of cells in G1 or early S-phase in APP + guanine-treated cultures. These viable, but non-dividing cells continued to incorporate 14C-uridine and 14C-leucine, but there was no net increase in either RNA or protein per cell; thus continued synthesis must be limited to RNA and protein which is constantly in the process of degradation and resynthesis. It suggested that APP + guanine exerts its inhibitory effect by interference with the synthesis and pool sizes of intracellular purine nucleotides.