DNA topoisomerase II-DNA complex (Top2-DNA complex (or Topo II-DNA complex))

The **DNA topoisomerase II-DNA complex** is a short-lived, covalent enzyme–DNA intermediate generated during the catalytic cycle of DNA topoisomerase II, an essential ATP-dependent enzyme that regulates DNA topology in eukaryotic cells[1][4][6]. Topoisomerase II solves topological problems in DNA by generating transient double-strand breaks, allowing passage of another DNA segment, and then religating the break using ATP hydrolysis[4][1][3]. Many anticancer agents—so-called "topoisomerase II poisons"—exploit this mechanism by stabilizing the otherwise transient covalent complex, preventing religation, and inducing cytotoxic DNA double-strand breaks[1][4][7]. This complex is not a discrete, stable protein but a pharmacologically critical intermediate formed in the presence of enzyme, DNA, and drug. Its stabilization is key to the mechanism of some major chemotherapeutic agents, notably etoposide and doxorubicin. **Note:** "DNA/Topoisomerase II complex" is not the standardized name of a gene/protein target but refers to a drug-stabilized complex of DNA and topoisomerase II enzyme; for strictly structured database purposes, the canonical target should be "DNA topoisomerase II" (with subforms "DNA topoisomerase II alpha" or "DNA topoisomerase II beta", as relevant)[1][4].

Other names

Topoisomerase II-DNA cleavage complexTop2-DNA covalent complexDNA-Topoisomerase II intermediateTopo II-DNA adduct

*Topoisomerase II poisons:* Drugs intercalate at the enzyme-DNA interface and stabilize the normally transient cleavage complex, thereby preventing DNA religation and resulting in double-strand DNA breaks and cell death[1][4][7]. *Catalytic inhibitors* (rare): Some agents reduce topoisomerase II's catalytic activity without stabilizing the cleavage complex.