Abstract: | Part of the radioactive DNA extracted from prelabelled L1210 cells exposed in vitro to ellipticine, 9-hvdroxyellipticine, 2-methyl-9-hydroxyellipticinium and 9-aminoellipticine, migrate more slowly into an alkaline sucrose gradient. These effects occur in less than one hr of exposure, and can be detected at drug concentrations which lie respectively around 1000, 20, 100 and 500 ng per ml whereas the drug concentrations which inhibit by 50 per cent the rate of the in vitro cell growth are 242, 3.9, 13 and 53 ng per ml. The DNA breaks become rapidly undetectable when the cells' exposure to the drugs is discontinued. |