The topoisomerase II inhibitor voreloxin causes cell cycle arrest and apoptosis in myeloid leukemia cells and acts in synergy with cytarabine

Abstract

BackgroundTopoisomerase II is essential for the maintenance of DNA integrity and the survival of proliferating cells. Topoisomerase II poisons, including etoposide and doxorubicin, inhibit enzymemediated 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 anticancer 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. Design and MethodsPrimary 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. ResultsThe mean lethal dose 50% (LD50) (± standard deviation) of voreloxin for primary acute myeloid leukemia blasts was 2.30 mM (± 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. ConclusionsVoreloxin 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.Key words: voreloxin, topoisomerase II inhibitor, myeloid leukemia, synergism, cytarabine. cytarabine. Haematologica 2011;96(3):393-399. doi:10.3324/haematol.2010 This is an open-access paper. Citation: Walsby EJ, Coles SJ, Knapper S, and Burnett AK. The topoisomerase II inhibitor voreloxin causes cell cycle arrest and apoptosis in myeloid leukemia cells and acts in synergy with

A phase 1b/2 study of vosaroxin in combination with cytarabine in patients with relapsed or refractory acute myeloid leukemia

“…10 Importantly, due to the stability of the quinolone backbone, vosaroxin does not produce significant free radicals, 11 or the reactive oxygen species implicated in the cumulative cardiotoxicity seen with anthracyclines. 10 Additionally, vosaroxin is not a substrate for the P glycoprotein efflux pump, and its activity is independent of p53 family members; [11][12][13] it may, therefore, bypass some mechanisms of chemotherapy resistance. Consistent with this, single-agent activity has been noted in anthracycline-resistant populations, 13 including women whose ovarian cancer progressed on liposomal doxorubicin 14 and AML patients with refractory/relapsed disease.…”

Vosaroxin: a new valuable tool with the potential to replace anthracyclines in the treatment of AML?

“…Administration of a single intravenous (i.v.) dose of vosaroxin was shown to result in activation of caspase-3, a key mediator of apoptosis and its activity is independent of p53 [48]. The long tumor half-life observed (8 h) in non-clinical investigation [50] also supported an intermittent dosing schedule.…”

“…Preclinical studies have demonstrated effective synergy when vosaroxin was combined with cytarabine (Ara-C) [48,51]. Authors suggested this enhanced cytotoxicity is likely the result of cells exiting S phase with cytarabine-induced DNA damage and entering G2 phase, unable to repair these DNA DSB and sustaining further insult as a result of the action of vosaroxin.…”

“…The DNA DSB that result from exposure to vosaroxin are preferentially induced in actively replicating cells [22]. During the G2/M phases, when cells are dividing and topo IIa is at its greatest concentration, vosaroxin induces the greatest numbers of DSB and significant DNA fragmentation, leading to maximum cytotoxicity at this point of the cell cycle ( Figure 2) [22,48].…”

Enhancement of radiosensitivity by the novel anticancer quinolone derivative vosaroxin in preclinical glioblastoma models

“…Vosaroxin is a naphthyridine analog (Figure 1), structurally related to quinolone antibacterials, that exerts its anticancer activity exclusively by DNA intercalation and inhibition of topoisomerase II, leading to site-selective DNA double-strand breaks and apoptosis [26][27][28]. Vosaroxin is not a substrate for P-glycoprotein drug pumps, and can induce apoptosis independent of p53, thereby avoiding two common mechanisms of drug resistance [29].…”