RT Journal Article SR Electronic T1 Intercalating TOP2 poisons attenuate topoisomerase action at higher concentrations JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP mol.119.117259 DO 10.1124/mol.119.117259 A1 Mandeep Atwal A1 Rebecca L Swan A1 Chloe Rowe A1 Ka C Lee A1 David C Lee A1 Lyle Armstrong A1 Ian G Cowell A1 Caroline A Austin YR 2019 UL http://molpharm.aspetjournals.org/content/early/2019/08/09/mol.119.117259.abstract AB TOP2 poisons are effective cytotoxic anticancer agents that stabilise the normally transient TOP2-DNA covalent complexes formed during the enzyme reaction cycle. These drugs include etoposide, mitoxantrone and the anthracyclines, doxorubicin and epirubicin. Anthracyclines also exert cell-killing activity via TOP2-independent mechanisms including DNA adduct formation, redox activity and lipid peroxidation. Here we show that anthracyclines and another intercalating TOP2 poison mitoxantrone stabilise TOP2-DNA covalent complexes less efficiently than etoposide and at higher concentrations they suppress the formation of TOP2-DNA covalent complexes, thus behaving as TOP2 poisons at low concentration and inhibitors at high concentration. We employed iPSC-derived human cardiomyocytes as a model to study anthracycline induced damage in cardiac cells. We demonstrated for the first-time using immunofluorescence the presence of TOP2B as the only TOP2 isoform in iPSC derived cardiomyocytes. In these cells etoposide robustly induced TOP2B-covalent complexes, but we could not detect doxorubicin-induced TOP2- DNA complexes, and doxorubicin supressed etoposide-induced TOP2-DNA complexes. In vitro, etoposide-stabilised DNA cleavage was attenuated by doxorubicin, epirubicin or mitoxantrone. Clinical use of anthracyclines is associated with cardiotoxicity. The observations in this study have potentially important clinical consequences regarding the effectiveness of anticancer treatment regimens when TOP2 targeting drugs are used in combination. These observations suggest that inhibition of TOP2B activity rather than DNA damage resulting from TOP2 poisoning may play a role in doxorubicin cardiotoxicity.SIGNIFICANCE STATEMENT We show that anthracyclines and mitoxantrone act as TOP2 poisons at low concentration but attenuate TOP2 activity at higher concentration, both in cells and in in vitro cleavage experiments. Inhibition of type II topoisomerases suppresses the action of other drugs that poison TOP2. Thus, combinations containing anthracyclines or mitoxantrone and etoposide, may reduce the activity of etoposide as a TOP2 poison and thus reduce the efficacy of drug combinations.