Molecular pharmacology of DNA topoisomerase II drugs

Abstract

Topoisomerase II (TOP2) is an important anti-cancer drug target. This study demonstrates that proteasomal inhibition by MG132 or PS341 potentiates the effect of TOP2 poisons on cell growth inhibition. Mitoxantrone was potentiated the most. The presence of the proteasome inhibitor MG132 prolonged the half-life of drug-induced DNA-TOP2 complexes stabilised by mitoxantrone or etoposide. Genotoxicity was measured in K562 cells using in vitro micronucleus assays for combinations of a proteasome inhibitor (MG132 or PS341) and mitoxantrone and for each agent alone. Combinations that potentiated the cytotoxicity reduced the genotoxicity. This suggests that combining a proteasome inhibitor with a TOP2 drug has the potential to reduce late toxicities such as therapy related leukaemia. The genotoxicity of six TOP2 poisons was determined by high throughput in vitro micronucleus assays in three Nalm-6 cell lines with differing TOP2 levels. Lower genotoxicity was observed in TOP2B knock-out and TOP2A knock-down cells, suggesting both TOP2A and TOP2B have a role in genotoxicity triggered by TOP2 poisons