Intercalating TOP2 Poisons Attenuate Topoisomerase Action at Higher Concentrations

Area of Science:

• Biochemistry
• Molecular Biology
• Pharmacology

Background:

• Topoisomerase II (TOP2) poisons are crucial anticancer agents that stabilize TOP2-DNA complexes.
• Anthracyclines, like doxorubicin, have additional TOP2-independent cytotoxic mechanisms.
• The dual action of anthracyclines as TOP2 poisons and inhibitors is not fully understood.

Purpose of the Study:

• To investigate the concentration-dependent effects of anthracyclines and mitoxantrone on TOP2-DNA covalent complexes.
• To identify TOP2 isoforms in human cardiomyocytes derived from induced pluripotent stem cells (iPSCs).
• To explore the implications of these findings for combination cancer therapy and anthracycline cardiotoxicity.

Main Methods:

• Utilized iPSC-derived human cardiomyocytes as a model system.
• Employed immunofluorescence to detect TOP2 isoforms and TOP2-DNA covalent complexes.
• Conducted in vitro DNA cleavage assays to assess drug interactions.

Main Results:

• Anthracyclines and mitoxantrone stabilize TOP2-DNA complexes less effectively than etoposide.
• At higher concentrations, these drugs suppress TOP2-DNA complex formation, acting as inhibitors.
• TOP2B was identified as the sole TOP2 isoform in iPSC-derived cardiomyocytes; doxorubicin did not induce TOP2-DNA complexes and inhibited etoposide-induced complexes.

Conclusions:

• Anthracyclines and mitoxantrone exhibit dual activity: TOP2 poisoning at low concentrations and TOP2 inhibition at high concentrations.
• TOP2B inhibition by anthracyclines may contribute to cardiotoxicity.
• Combination therapies using anthracyclines or mitoxantrone with etoposide may have reduced efficacy due to TOP2 inhibition.