title: A novel mechanism of cell killing by anti-topoisomerase II bisdioxopiperazines.
abstract: Bisdioxopiperazines are a unique class of topoisomerase II inhibitors that lock topoisomerase II at a point in the enzyme reaction cycle where the enzyme forms a closed clamp around DNA. We examined cell killing by ICRF-187 and ICRF-193 in yeast cells expressing human topoisomerase II alpha (htop-IIalpha). Expression of htop-IIalpha in yeast cells sensitizes them to both ICRF-187 and ICRF-193, compared with cells expressing yeast topoisomerase II. ICRF-193 is still able to exert growth inhibition in the presence of genes encoding both ICRF-193-resistant and ICRF-193-sensitive htop-IIalpha enzymes, indicating that sensitivity to bisdioxopiperazines is dominant. Killing by ICRF-193 occurs more rapidly, than the killing in yeast cells due to a temperature-sensitive yeast topoisomerase II incubated at the non-permissive temperature. These results are reminiscent of a top-II poison such as etoposide. However, the killing caused by ICRF-193 and ICRF-187 is not enhanced by mutations in the RAD52 pathway. The levels of drug-induced DNA cleavage observed with htop-IIalpha in vitro is insufficient to explain the sensitivity induced by this enzyme in yeast cells. Finally, arrest of cells in G(1) does not protect cells from ICRF-193 lethality, a result inconsistent with killing mechanisms due to catalytic inhibition of top-II or stabilization of a cleavable complex. We suggest that the observed pattern of cell killing is most consistent with a poisoning of htop-II by ICRF-193 by a novel mechanism. The accumulation of closed clamp conformations of htop-II induced by ICRF-193 that are trapped on DNA might interfere with transcription, or other DNA metabolic processes, resulting in cell death.
authors.affiliation: Molecular Pharmacology Department, St. Jude Children's Research Hospital, Memphis, Tennessee 38018, USA.
authors.forename: L H
authors.initials: LH
authors.lastname: Jensen
authors.forename: K C
authors.initials: KC
authors.lastname: Nitiss
authors.forename: A
authors.initials: A
authors.lastname: Rose
authors.forename: J
authors.initials: J
authors.lastname: Dong
authors.forename: J
authors.initials: J
authors.lastname: Zhou
authors.forename: T
authors.initials: T
authors.lastname: Hu
authors.forename: N
authors.initials: N
authors.lastname: Osheroff
authors.forename: P B
authors.initials: PB
authors.lastname: Jensen
authors.forename: M
authors.initials: M
authors.lastname: Sehested
authors.forename: J L
authors.initials: JL
authors.lastname: Nitiss
mesh_terms: D000483:Alleles; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism; D054659:Diketopiperazines; D004305:Dose-Response Relationship, Drug; D004352:Drug Resistance, Microbial; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005799:Genes, Dominant; D006801:Humans; D008826:Microbial Sensitivity Tests; D016296:Mutagenesis; D010879:Piperazines / Q000494:pharmacology*; D011487:Protein Conformation; D011929:Razoxane / Q000494:pharmacology*; D012441:Saccharomyces cerevisiae / Q000187:drug effects; D013997:Time Factors; D059005:Topoisomerase II Inhibitors; D014461:Ultracentrifugation
chemical_list: D000970:Antineoplastic Agents; D054659:Diketopiperazines; D004791:Enzyme Inhibitors; D010879:Piperazines; D059005:Topoisomerase II Inhibitors; C070899:4,4'-(1,2-dimethyl-1,2-ethanediyl)bis-2,6-piperazinedione; D011929:Razoxane; D004250:DNA Topoisomerases, Type II