Fig. 10. Effect of drugs on ribonuclease-mediated cytotoxicity. The effect of G88R RNase A and ONC inhibition of cellular DNA synthesis was measured in the presence of NH₄Cl (20 mM), monensin (10 µM) and brefeldin A (10 µM). K-562 cells were pre-incubated with each drug for 2 hours at 37°C and then with G88R RNase A (circles) and ONC (squares). Open symbols represent control samples without drug treatment; filled symbols represent samples pre-incubated with drugs. Each point represents the percentage of [methyl-³H]thymidine incorporated compared with a PBS control (with or without drug) and is the mean (±s.e.) of at least three separate experiments with triplicate samples.