title: NK314, a topoisomerase II inhibitor that specifically targets the alpha isoform.
abstract: Topoisomerase II (Top2) is a ubiquitous nuclear enzyme that relieves torsional stress in chromosomal DNA during various cellular processes. Agents that target Top2, involving etoposide, doxorubicin, and mitoxantrone, are among the most effective anticancer drugs used in the clinic. Mammalian cells possess two genetically distinct Top2 isoforms, both of which are the target of these agents. Top2alpha is essential for cell proliferation and is highly expressed in vigorously growing cells, whereas Top2beta is nonessential for growth and has recently been implicated in treatment-associated secondary malignancies, highlighting the validity of a Top2alpha-specific drug for future cancer treatment; however, no such agent has been hitherto reported. Here we show that NK314, a novel synthetic benzo[c]phenanthridine alkaloid, targets Top2alpha and not Top2beta in vivo. Unlike other Top2 inhibitors, NK314 induces Top2-DNA complexes and double-strand breaks (DSBs) in an alpha isoform-specific manner. Heterozygous disruption of the human TOP2alpha gene confers increased NK314 resistance, whereas TOP2beta homozygous knock-out cells display increased NK314 sensitivity, indicating that the alpha isoform is the cellular target. We further show that the absence of Top2beta does not alleviate NK314 hypersensitivity of cells deficient in non-homologous end-joining, a critical pathway for repairing Top2-mediated DSBs. Our results indicate that NK314 acts as a Top2alpha-specific poison in mammalian cells, with excellent potential as an efficacious and safe chemotherapeutic agent. We also suggest that a series of human knock-out cell lines are useful in assessing DNA damage and repair induced by potential topoisomerase-targeting agents.
authors.affiliation: International Graduate School of Arts and Sciences, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama, Japan.
authors.forename: Eriko
authors.initials: E
authors.lastname: Toyoda
authors.forename: Shigehide
authors.initials: S
authors.lastname: Kagaya
authors.forename: Ian G
authors.initials: IG
authors.lastname: Cowell
authors.forename: Aya
authors.initials: A
authors.lastname: Kurosawa
authors.forename: Keiichi
authors.initials: K
authors.lastname: Kamoshita
authors.forename: Kiyohiro
authors.initials: K
authors.lastname: Nishikawa
authors.forename: Susumu
authors.initials: S
authors.lastname: Iiizumi
authors.forename: Hideki
authors.initials: H
authors.lastname: Koyama
authors.forename: Caroline A
authors.initials: CA
authors.lastname: Austin
authors.forename: Noritaka
authors.initials: N
authors.lastname: Adachi
mesh_terms: D000951:Antigens, Neoplasm / Q000235:genetics / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology; D049109:Cell Proliferation / Q000187:drug effects*; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D019008:Drug Resistance, Neoplasm / Q000187:drug effects / Q000235:genetics; D004354:Drug Screening Assays, Antitumor / Q000379:methods; D004791:Enzyme Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D017353:Gene Deletion; D006367:HeLa Cells; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D009369:Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics; D010616:Phenanthrenes / Q000494:pharmacology* / Q000627:therapeutic use; D000075223:Poly-ADP-Ribose Binding Proteins; D059005:Topoisomerase II Inhibitors
chemical_list: D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D007527:Isoenzymes; C522060:NK314; D009363:Neoplasm Proteins; D010616:Phenanthrenes; D000075223:Poly-ADP-Ribose Binding Proteins; D059005:Topoisomerase II Inhibitors; D004250:DNA Topoisomerases, Type II; C000618811:TOP2A protein, human