Human DNA Topoisomerase IIα-dependent DNA Cleavage and Yeast Cell Killing by Anthracycline Analogues

Anthracyclines are among the most clinically useful topoisomerase II poisons. A complete understanding of their molecular mechanism is thus fundamental for a rational design of novel agents. We evaluated four anthracycline analogues with respect to human topoisomerase IIα-dependent DNA cleaving activity, efficiency in killing yeast cells, and uptake and retention in yeast and compared the yeast system to tumor cell line models. The yeast JN394 top2–4 strain was used because it has a topoisomerase II ts gene mutation: enzyme activity is much less at 30°C than at 25°C and is completely lost at 35°C. Untransformed JN394 top2–4 cells were 33-fold more sensitive to idarubicin at 25°C than at 30°C, showing that topoisomerase II is the primary drug target. Overexpression of human topoisomerase IIα was toxic to yeast cells when the yeast enzyme was inactivated. Drug-dependent killing of yeast cells expressing low levels of the human α isoenzyme at 35°C showed that the analogues spanned a 3-log range of cytotoxic potency in yeast, as they did in tumor cells. However, the compounds were much less active against the yeast strain than mammalian tumor cell lines. Drug uptake was determined and found to be altered in yeast with respect to tumor cells. Although DNA cleavage stimulated by anthracyclines roughly correlated with cytotoxicity, the cleavage level:cytotoxicity ratios were different for the studied drugs. Thus, the results suggest that other drug-dependent molecular factors contribute to drug activity in addition to the cellular content of topoisomerase IIα and drug uptake.