Intracellular uptake of 7-con-o-methylnogarol and adriamycin by cells in culture and its relationship to cell survival.

7-con-O-Methylnogarol (7-OMEN) is a new anthracycline antitumor agent with significant activity in vivo against murine P388 and L1210 leukemia (140% increase in life span) and B16 melanoma (114% increase in life span). We report here the complex relationship that exists between intracellular drug concentration and killing of Chinese hamster ovary (CHO), B16, and L1210 cells in culture by 7-OMEN and Adriamycin. The uptake of 7-OMEN and Adriamycin by CHO, B16, and L1210 cells was proportional to the extracellular concentration (/¿g/mlmedium) of the drug. At similar concentrations, CHO and B16 cells accumulated more 7-OMEN than Adriamycin. Based on intracellular concentration in CHO cells, Adriamycin was more lethal [lethal dose for 90% of the cells (LD90), 0.02 /ig/106 cells] than was 7-OMEN (LDso, 0.1 H9/106 cells). However, based on concentration in CHO cells extracellular 7OMEN was more lethal (LD90, 0.6 jug/ml) than was Adriamycin (LD90, 2.5 /ig/ml). This was probably due to the very low level of uptake of Adriamycin by CHO cells. For both 7-OMEN and Adriamycin, cell kill increased with increasing intracellular concentration. In contrast to the linear relationship between intracellular concentration and cell kill with Adriamycin, a biphasic relationship was seen with 7OMEN. For 7-OMEN, cell kill was proportional to intracellular concentration up to approximately 0.04 ¿ig/106cells. Further increase in intracellular concentration did not result in propor tional increase in cell kill. Exponentially growing cells not only accumulated more 7OMEN than did plateau-phase cells but were also inherently more sensitive to the drug. This latter conclusion was based on the observation that, even at similar intracellular concentra tion, more exponentially growing than plateau-phase cells were killed. Fluorescence microscopy showed that 7-OMEN accumu lated predominantly in the cytoplasm, whereas Adriamycin accumulated in the nucleus. The significance of this observa tion to the mode of action of these drugs is discussed.