A temperature sensitive topoisomerase II allele confers temperature dependent drug resistance on amsacrine and etoposide: a genetic system for determining the targets of topoisomerase II inhibitors.
We have developed a simple system for determining the specific contribution of topoisomerase II targeting to the cytotoxic activity of a drug. We have constructed yeast strains that are permeable to anti-topoisomerase II drugs, carry a DNA repair mutation, rad52, and also have a temperature sensitive topoisomerase II mutation, top2-1. Strains carrying the top2-1 mutation have nearly normal topoisomerase II activity at 25 degrees C but less than 10% of wild type activity at 36 degrees C. We find that at a semi-permissive temperature (30 degrees C), there is sufficient topoisomerase II activity for viability; but since the topoisomerase II activity is greatly reduced, the cells are very resistant to anti-topoisomerase II drugs. Conversely, such cells are hypersensitive to the topoisomerase I inhibitor camptothecin. These results provide strong support for the model that drug stabilized DNA cleavage, rather than a lack of enzyme activity, is responsible for cell killing by eukaryotic anti-topoisomerase II agents. They also show that there is a minimum level of topoisomerase II activity in yeast that is consistent with viability but also allows a high degree of resistance to anti-topoisomerase II agents.
Division of Hematology/Oncology, Children's Hospital of Los Angeles, California 90027.
J L
JL
Nitiss
Y X
YX
Liu
Y
Y
Hsiung
D000483:Alleles; D000677:Amsacrine / Q000494:pharmacology*; D002166:Camptothecin / Q000494:pharmacology; D002455:Cell Division / Q000502:physiology; D004249:DNA Damage; D004260:DNA Repair; D004250:DNA Topoisomerases, Type II / Q000235:genetics*; D004351:Drug Resistance; D005047:Etoposide / Q000494:pharmacology*; D008954:Models, Biological; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology / Q000235:genetics; D012680:Sensitivity and Specificity; D013696:Temperature; D059005:Topoisomerase II Inhibitors
D059005:Topoisomerase II Inhibitors; D000677:Amsacrine; D005047:Etoposide; D004250:DNA Topoisomerases, Type II; D002166:Camptothecin