DNA topoisomerase II–DNA cleavable complex (Topo II–DNA CC)

The DNA topoisomerase II–DNA cleavable complex is a transient intermediate formed during the catalytic cycle of topoisomerase II enzymes, which are essential for managing DNA topology during replication, transcription, and chromosome segregation (StatPearls: NBK557455). Under normal physiological conditions, the enzyme creates a double-strand break, passes a second DNA duplex through the gap, and rapidly religates the broken strands to maintain genomic integrity. However, certain chemotherapeutic agents, known as topoisomerase II poisons, bind to and stabilize this covalent complex, effectively preventing the religation step (PubMed: 23875711). This stabilization transforms an essential enzyme into a potent cellular toxin by generating persistent, protein-blocked double-strand breaks throughout the genome. When replication forks or transcription machinery encounter these stabilized complexes, they trigger irreversible DNA damage responses and apoptotic pathways, leading to programmed cell death. This mechanism is widely exploited in oncology to treat various malignancies, including leukemias, lymphomas, and solid tumors. Despite its clinical efficacy, targeting this complex carries significant risks, such as dose-limiting cardiotoxicity and the potential for developing secondary leukemias due to drug-induced genomic instability (PubMed: 15064704).

Other names

Topoisomerase II-DNA covalent complexTopo II-DNA cleavage complexDNA topoisomerase 2-DNA complexTopo II-DNA adduct

Topoisomerase II poisons act by binding to and stabilizing the covalent DNA-enzyme intermediate, known as the cleavable complex. This prevents the religation of the DNA double-strand break, leading to the accumulation of permanent DNA lesions that trigger cell cycle arrest and apoptosis (PubMed: 12672480).