The topoisomerase II inhibitor voreloxin causes cell cycle arrest and apoptosis in myeloid leukemia cells and acts in synergy with cytarabine.
BACKGROUND
Topoisomerase II is essential for the maintenance of DNA integrity and the survival of proliferating cells. Topoisomerase II poisons, including etoposide and doxorubicin, inhibit enzyme-mediated DNA ligation causing the accumulation of double-stranded breaks and have been front-line drugs for the treatment of leukemia for many years. Voreloxin is a first-in-class anti-cancer quinolone derivative that intercalates DNA and inhibits topoisomerase II. The efficacy and mechanisms of action of voreloxin in acute myeloid leukaemia were addressed in this study.


METHODS
Primary acute myeloid leukemia blasts (n = 88) and myeloid cell lines were used in vitro to study voreloxin through viability assays to assess cell killing and synergy with other drugs. Apoptosis and cell cycling were assessed by flow cytometry. DNA relaxation assays were utilized to determine that voreloxin was active on topoisomerase II.


RESULTS
The mean lethal dose 50% (LD(50)) (± standard deviation) of voreloxin for primary acute myeloid leukemia blasts was 2.30 μM (± 1.87). Synergy experiments between voreloxin and cytarabine identified synergism in 22 of 25 primary acute myeloid leukemia samples tested, with a mean combination index of 0.79. Apoptosis was shown to increase in a dose-dependent manner. Furthermore, voreloxin was active in the p53-null K562 cell line suggesting that the action of voreloxin is not affected by p53 status. The action of voreloxin on topoisomerase II was confirmed using a DNA relaxation assay.


CONCLUSIONS
Voreloxin may provide an interesting addition to the cache of drugs available for the treatment of acute myeloid leukemia, a disease with a poor long-term survival. In addition to its potent action as a single agent in dividing cells, the synergy we demonstrated between voreloxin and cytarabine recommends further investigation of this topoisomerase II inhibitor.
Cardiff Experimental Cancer Medicine Centre, Department of Haematology, School of Medicine, Cardiff University, Heath Park, Cardiff, UK. walsbyej@cf.ac.uk
Elisabeth J
EJ
Walsby
Steven J
SJ
Coles
Steven
S
Knapper
Alan K
AK
Burnett
D017209:Apoptosis / Q000187:drug effects*; D018929:Cell Culture Techniques; D002453:Cell Cycle / Q000187:drug effects*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects*; D003561:Cytarabine / Q000494:pharmacology / Q000627:therapeutic use; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005260:Female; D017353:Gene Deletion; D016158:Genes, p53; D006801:Humans; D007928:Lethal Dose 50; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy / Q000473:pathology; D008297:Male; D008875:Middle Aged; D022423:Myeloid Cells / Q000378:metabolism / Q000473:pathology; D009287:Naphthyridines / Q000494:pharmacology* / Q000627:therapeutic use; D013844:Thiazoles / Q000494:pharmacology* / Q000627:therapeutic use; D059005:Topoisomerase II Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use
D009287:Naphthyridines; D013844:Thiazoles; D059005:Topoisomerase II Inhibitors; D003561:Cytarabine; D004250:DNA Topoisomerases, Type II; C485113:vosaroxin