Topoisomerase II inhibitors in AML: past, present, and future

Introduction: Topoisomerase II inhibitors have long been used in the frontline and as salvage therapy for AML, with daunorubicin and idarubicin being prototypical agents in this therapeutic class, classically in combination with nucleoside analogs, e.g. cytarabine. Most recently, several other compounds from this drug class have or are being investigated. Areas covered: The current paper reviews older and newer topoisomerase II inhibitors in clinical development for the treatment of AML. The authors discuss the clinical use of these agents, current trials involving them as well as their safety profile. Important side effects of these medications including therapy-related AML (t-AML) are also covered. Expert opinion: Topoisomerase II inhibitors have helped improve outcomes in AML. Recently, the FDA approved several agents including CPX-351 for the treatment of secondary and t-AML. CPX-351 may have applicability in other high-risk myeloid diseases. Future directions include a combination of these agents with other targeted therapies. Finally, the authors believe that small molecule inhibitors, such as venetoclax and possibly immunotherapy options could also be incorporated to our treatment paradigm in selected patients.

Advances in the drug therapies of acute myeloid leukemia (except acute wpromyelocytic leukemia)

Acute myeloid leukemia (AML) is a heterogeneous hematologic malignancy, characterized by the clonal expansion of myeloid blasts in the peripheral blood, bone marrow, and/or other tissues. The new drugs used for treating AML are facing a big challenge, and the candidates include cytotoxic drugs, targeted small-molecule inhibitors, and monoclonal antibodies. In recent years, active research has focused on several new agents for including them in the large antileukemic drug family. This review aims to introduce some of these new drugs and highlights new advances made in the old drugs, mainly in the last 5 years.

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

Purpose

Glioblastoma multiforme (GBM) is the most aggressive brain tumor. The activity of vosaroxin, a first-in-class anticancer quinolone derivative that intercalates DNA and inhibits topoisomerase II, was investigated in GBM preclinical models as a single agent and combined with radiotherapy (RT).

Results

Vosaroxin showed antitumor activity in clonogenic survival assays, with IC₅₀ of 10−100 nM, and demonstrated radiosensitization. Combined treatments exhibited significantly higher γH2Ax levels compared with controls. In xenograft models, vosaroxin reduced tumor growth and showed enhanced activity with RT; vosaroxin/RT combined was more effective than temozolomide/RT. Vosaroxin/RT triggered rapid and massive cell death with characteristics of necrosis. A minor proportion of treated cells underwent caspase-dependent apoptosis, in agreement with in vitro results. Vosaroxin/RT inhibited RT-induced autophagy, increasing necrosis. This was associated with increased recruitment of granulocytes, monocytes, and undifferentiated bone marrow–derived lymphoid cells. Pharmacokinetic analyses revealed adequate blood-brain penetration of vosaroxin. Vosaroxin/RT increased disease-free survival (DFS) and overall survival (OS) significantly compared with RT, vosaroxin alone, temozolomide, and temozolomide/RT in the U251-luciferase orthotopic model.

Materials and Methods

Cellular, molecular, and antiproliferative effects of vosaroxin alone or combined with RT were evaluated in 13 GBM cell lines. Tumor growth delay was determined in U87MG, U251, and T98G xenograft mouse models. (DFS) and (OS) were assessed in orthotopic intrabrain models using luciferase-transfected U251 cells by bioluminescence and magnetic resonance imaging.

Conclusions

Vosaroxin demonstrated significant activity in vitro and in vivo in GBM models, and showed additive/synergistic activity when combined with RT in O6-methylguanine methyltransferase-negative and -positive cell lines.

Therapies for acute myeloid leukemia: vosaroxin

Vosaroxin, a quinolone-derivative chemotherapeutic agent, was considered a promising drug for the treatment of acute myeloid leukemia (AML). Early-stage clinical trials with this agent led to a large randomized double-blind placebo-controlled study of vosaroxin in combination with intermediate-dose cytarabine for the treatment of relapsed or refractory AML. The study demonstrated better complete remission rates with vosaroxin, but there was no statistically significant overall survival benefit in the whole cohort. A subset analysis censoring patients who had undergone allogeneic stem cell transplantation, however, revealed a modest but statistically significant improvement in overall survival particularly among older patients. This article reviews the data available on vosaroxin including clinical trials in AML and offers an analysis of findings of these studies as well as the current status of vosaroxin.

Molecular and Pharmacologic Properties of the Anticancer Quinolone Derivative Vosaroxin: A New Therapeutic Agent for Acute Myeloid Leukemia

Vosaroxin is a first-in-class anticancer quinolone derivative that targets topoisomerase II and induces site-selective double-strand breaks in DNA, leading to tumor cell apoptosis. Vosaroxin has chemical and pharmacologic characteristics distinct from other topoisomerase II inhibitors due to its quinolone scaffold. The efficacy and safety of vosaroxin in combination with cytarabine were evaluated in patients with relapsed/refractory acute myeloid leukemia (AML) in a phase III, randomized, multicenter, double-blind, placebo-controlled study (VALOR). In this study, the addition of vosaroxin produced a 1.4-month improvement in median overall survival (OS; 7.5 months with vosaroxin/cytarabine vs. 6.1 months with placebo/cytarabine; hazard ratio [HR] 0.87, 95 % confidence interval [CI] 0.73−1.02; unstratified log-rank p\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$=$$\end{document}= 0.061; stratified log-rank p\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$=$$\end{document}=0.024), with the greatest OS benefit observed in patients ≥60 years of age (7.1 vs. 5.0 months; HR 0.75, 95 % CI 0.62−0.92; p\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$=$$\end{document}=0.003) and patients with early relapse (6.7 vs. 5.2 months; HR 0.77, 95 % CI 0.59−1.00; p\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$=$$\end{document}= 0.039), two AML patient groups that typically have poor prognosis. Here we review the chemical and pharmacologic properties of vosaroxin, how these properties are distinct from those of currently available topoisomerase II inhibitors, how they may contribute to the efficacy and safety profile observed in the VALOR trial, and the status of clinical development of vosaroxin for treatment of AML.

The preclinical discovery of vosaroxin for the treatment of acute myeloid leukemia

INTRODUCTION

Acute myeloid leukemia (AML) represents a disease with a very poor outcome and remains an area of significant unmet need necessitating novel therapeutic strategies. Among novel therapeutic agents, vosaroxin is a first-in-class anticancer quinolone derivative that targets topoisomerase II and induces site-selective double-strand breaks in DNA, leading to tumor cell apoptosis. Areas covered: Herein, the authors provide a comprehensive review of the preclinical development of vosaroxin. This includes coverage of vosaroxin's mechanism of action in addition to its pharmacology and of the main studies reported over the past few years with vosaroxin when used to treat adult AML. Expert opinion: Given that vosaroxin is associated with fewer potential side effects, it may be of benefit to elderly patients with relapsed/refractory AML and to those with additional comorbidities who have previously received an anthracycline and cytarabine combination. Furthermore, vosaroxin also was seen to be active in multidrug-resistant preclinical models. However, further studies have to be performed to better evaluate its place in the armamentarium against AML.

Vosaroxin in relapsed/refractory acute myeloid leukemia: efficacy and safety in the context of the current treatment landscape

Treatment for acute myeloid leukemia (AML) generally consists of a combination of cytarabine and an anthracycline. Although induction therapy leads to complete remission (CR) for most patients, refractoriness to chemotherapy or relapse after initial response is associated with poor outcomes. The 1-year survival rates after first relapse have been reported at 29%, declining to 11% at 5 years. Prognosis is particularly poor among older patients whose higher prevalence of unfavorable cytogenetics and high frequency of comorbidities diminish their ability to tolerate intensive chemotherapy. There is no standard of care for relapsed/refractory (R/R) AML, and no new therapies have shown consistently superior outcomes in this setting in over two decades. Vosaroxin is an anticancer quinolone derivative (AQD) that was evaluated in combination with cytarabine for the treatment of R/R AML in the randomized, double-blind, placebo-controlled, phase III VALOR study (n = 711). Compared with placebo/cytarabine, the vosaroxin/cytarabine regimen demonstrated favorable CR rates and survival in patients ⩾60 years of age, with toxicities similar to other AML regimens. Here we review outcomes of recent studies of commonly used chemotherapy regimens for the treatment of R/R AML and evaluate the results of the VALOR trial in the context of the current treatment landscape.

Metabolism and disposition of the anticancer quinolone derivative vosaroxin, a novel inhibitor of topoisomerase II

Background Vosaroxin is a first-in-class anticancer quinolone derivative that is being investigated for patients with relapsed or refractory acute myeloid leukemia (AML). The primary objective of this study was to quantitatively determine the pharmacokinetics of vosaroxin and its metabolites in patients with advanced solid tumors. Methods This mass balance study investigated the pharmacokinetics (distribution, metabolism, and excretion) of vosaroxin in cancer patients after a single dose of 60 mg/m^{2 14}C-vosaroxin, administered as short intravenous injection. Blood, urine and feces were collected over 168 h after injection or until recovered radioactivity over 24 h was less than 1% of the administered dose (whichever was earlier). Total radioactivity (TRA), vosaroxin and metabolites were studied in all matrices. Results Unchanged vosaroxin was the major species identified in plasma, urine, and feces. N-desmethylvosaroxin was the only circulating metabolite detected in plasma, accounting for <3% of the administered dose. However, in plasma, the combined vosaroxin + N-desmethylvosaroxin AUC_0-∞ was 21% lower than the TRA AUC_0-∞ , suggesting the possible formation of protein bound metabolites after 48 h when the concentration-time profiles diverged. The mean recovery of TRA in excreta was 81.3% of the total administered dose; 53.1% was excreted through feces and 28.2% through urine. Conclusions Unchanged vosaroxin was the major compound found in the excreta, although 10 minor metabolites were detected. The biotransformation reactions were demethylation, hydrogenation, decarboxylation and phase II conjugation including glucuronidation.

Targeting acute myeloid leukemia with TP53-independent vosaroxin

Vosaroxin is a quinolone compound that intercalates DNA and induces TP53-independent apoptosis, demonstrating activity against acute myeloid leukemia (AML) in Phase I-III trials. Here, we examine vosaroxin's mechanism of action and pharmacology, and we review its use in AML to date, focusing on details of individual clinical trials. Most recently, when combined with cytarabine in a randomized Phase III trial (VALOR), vosaroxin improved outcomes versus cytarabine alone for relapsed/refractory AML in patients older than 60 years and for patients in early relapse. We consider its continued role in the context of a multifaceted strategy against AML, including its current use in clinical trials. Prospective use will define its role in the evolving landscape of AML therapy.

Considerations and challenges for patients with refractory and relapsed acute myeloid leukaemia

Despite advances in understanding the complexities of acute myeloid leukaemia (AML), the treatment of refractory or relapsed AML (rrAML) remains a daunting clinical challenge. Numerous clinical trials have failed to identify new treatments or combinations of existing therapies that substantially improve outcomes and survival. This may be due, at least in part, to heterogeneity among study patients with respect to multiple inter-related factors that have been shown to affect treatment outcomes for patients with rrAML; such factors include age, cytogenetics, immunophenotypic changes, and (in the case of relapsed AML) duration of first complete remission, or if the patient has had a previous blood and marrow transplant (BMT). A clear understanding of disease characteristics and patient-related factors that influence treatment response, as well as expected outcomes with existing and emerging therapies, can aid clinicians in helping their patients navigate through this complex disease state.

Quantification of vosaroxin and its metabolites N-desmethylvosaroxin and O-desmethylvosaroxin in human plasma and urine using high-performance liquid chromatography-tandem mass spectrometry

Vosaroxin is a first-in-class anticancer quinolone derivative topoisomerase II inhibitor that is currently in development in combination with cytarabine for the treatment of acute myeloid leukemia (AML). To investigate vosaroxin pharmacokinetics (PK) in patients, liquid chromatography tandem mass spectrometry (LC-MS/MS) assays to quantify vosaroxin and the two metabolites N-desmethylvosaroxin and O-desmethylvosaroxin in human plasma and urine were developed and validated. Immediately after collection the samples were stored at -80°C. Prior to analysis, the plasma samples were subjected to protein precipitation and the urine samples were diluted. For both assays the reconstituted extracts were injected on a Symmetry Shield RP8 column and gradient elution was applied using 0.1% formic acid in water and acetonitrile-methanol (50:50, v/v). Analyses were performed with a triple quadruple mass spectrometer in positive-ion mode. A deuterated isotope of vosaroxin was used as internal standard for the quantification. The validated assays quantify vosaroxin and N-desmethylvosaroxin in the concentration range of 2-500ng/mL in plasma and urine. For O-desmethylvosaroxin the concentration range of 4-500ng/mL in plasma and urine was validated. Dilution integrity experiments show that samples can be diluted 25 fold in control matrix prior to analysis. The expanded concentration range for plasma and urine for vosaroxin and N-desmethylvosaroxin is therefore from 2 to 15,000ng/mL and in plasma for O-desmethylvosaroxin from 4 to 15,000ng/mL.

New drugs in acute myeloid leukemia

The standard therapy for acute myeloid leukemia (AML) has not changed meaningfully for the past four decades. Improvements in supportive care and modifications to the dose and schedule of existing agents have led to steady improvements in outcomes. However, developing new therapies for AML has been challenging. Although there have been advances in understanding the biology of AML, translating this knowledge to viable treatments has been slow. Active research is currently ongoing to address this important need and several promising drug candidates are currently in the pipeline. Here, we review some of the most advanced and promising compounds that are currently in clinical trials and may have the potential to be part of our future armamentarium. These drug candidates range from cytotoxic chemotherapies, targeted small-molecule inhibitors, and monoclonal antibodies.

Acute myeloid leukemia--major progress over four decades and glimpses into the future

In this Review, the progress in research and therapy of acute myeloid leukemia is detailed.

A "Double-Edged" Scaffold: Antitumor Power within the Antibacterial Quinolone

In the late 1980s, reports emerged describing experimental antibacterial quinolones having significant potency against eukaryotic Type II topoisomerases (topo II) and showing cytotoxic activity against tumor cell lines. As a result, several pharmaceutical companies initiated quinolone anticancer programs to explore the potential of this class in comparison to conventional human topo II inhibiting antitumor drugs such as doxorubicin and etoposide. In this review, we present a modern re-evaluation of the anticancer potential of the quinolone class in the context of today's predominantly pathway-based (rather than cytotoxicity-based) oncology drug R&D environment. The quinolone eukaryotic SAR is comprehensively discussed, contrasted with the corresponding prokaryotic data, and merged with recent structural biology information which is now beginning to help explain the basis for that SAR. Quinolone topo II inhibitors appear to be much less susceptible to efflux-mediated resistance, a current limitation of therapy with conventional agents. Recent advances in the biological understanding of human topo II isoforms suggest that significant progress might now be made in overcoming two other treatment-limiting disadvantages of conventional topo II inhibitors, namely cardiotoxicity and drug-induced secondary leukemias. We propose that quinolone class topo II inhibitors could have a useful future therapeutic role due to the continued need for effective topo II drugs in many cancer treatment settings, and due to the recent biological and structural advances which can now provide, for the first time, specific guidance for the design of a new class of inhibitors potentially superior to existing agents.

Iron(III)-binding of the anticancer agents doxorubicin and vosaroxin

The Fe(iii)-binding constant of vosaroxin, an anticancer quinolone derivative, has been determined spectrophotometrically and compared with the analogous Fe(iii) complex formed with doxorubicin. The in vivo metabolic stability and iron coordination properties of the quinolones compared to the anthracylines may provide significant benefit to cardiovascular safety. The mechanism of action of both molecules target the topoisomerase II enzyme. Both doxorubicin (Hdox, log βFeL3 = 33.41, pM = 17.0) and vosaroxin (Hvox, log βFeL3 = 33.80(3), pM = 15.9) bind iron(iii) with comparable strength; at physiological pH however, [Fe(vox)3] is the predominant species in contrast to a mixture of species observed for the Fe:dox system. Iron(iii) nitrate and gallium(iii) nitrate at a 1 : 3 ratio with vosaroxin formed stable tris(vosaroxacino)-iron(iii) and tris(vosaroxino)gallium(iii) complexes that were isolated and characterized. Their redox behavior was studied by CV, and their stereochemistry was further explored in temperature dependent (1)H NMR studies. The molecular pharmacology of their interaction with iron(iii) may be one possible differentiation in the safety profile of quinolones compared to anthracyclines in relation to cardiotoxicity.

Vosaroxin plus cytarabine versus placebo plus cytarabine in patients with first relapsed or refractory acute myeloid leukaemia (VALOR): a randomised, controlled, double-blind, multinational, phase 3 study

BACKGROUND

Safe and effective treatments are urgently needed for patients with relapsed or refractory acute myeloid leukaemia. We investigated the efficacy and safety of vosaroxin, a first-in-class anticancer quinolone derivative, plus cytarabine in patients with relapsed or refractory acute myeloid leukaemia.

METHODS

This phase 3, double-blind, placebo-controlled trial was undertaken at 101 international sites. Eligible patients with acute myeloid leukaemia were aged 18 years of age or older and had refractory disease or were in first relapse after one or two cycles of previous induction chemotherapy, including at least one cycle of anthracycline (or anthracenedione) plus cytarabine. Patients were randomly assigned 1:1 to vosaroxin (90 mg/m(2) intravenously on days 1 and 4 in a first cycle; 70 mg/m(2) in subsequent cycles) plus cytarabine (1 g/m(2) intravenously on days 1-5) or placebo plus cytarabine through a central interactive voice system with a permuted block procedure stratified by disease status, age, and geographical location. All participants were masked to treatment assignment. The primary efficacy endpoint was overall survival and the primary safety endpoint was 30-day and 60-day all-cause mortality. Efficacy analyses were done by intention to treat; safety analyses included all treated patients. This study is registered with ClinicalTrials.gov, number NCT01191801.

FINDINGS

Between Dec 17, 2010, and Sept 25, 2013, 711 patients were randomly assigned to vosaroxin plus cytarabine (n=356) or placebo plus cytarabine (n=355). At the final analysis, median overall survival was 7·5 months (95% CI 6·4-8·5) in the vosaroxin plus cytarabine group and 6·1 months (5·2-7·1) in the placebo plus cytarabine group (hazard ratio 0·87, 95% CI 0·73-1·02; unstratified log-rank p=0·061; stratified p=0·024). A higher proportion of patients achieved complete remission in the vosaroxin plus cytarabine group than in the placebo plus cytarabine group (107 [30%] of 356 patients vs 58 [16%] of 355 patients, p<0·0001). Early mortality was similar between treatment groups (30-day: 28 [8%] of 355 patients in the vosaroxin plus cytarabine group vs 23 [7%] of 350 in the placebo plus cytarabine group; 60-day: 70 [20%] vs 68 [19%]). Treatment-related deaths occurred at any time in 20 (6%) of 355 patients given vosaroxin plus cytarabine and in eight (2%) of 350 patients given placebo plus cytarabine. Treatment-related serious adverse events occurred in 116 (33%) and 58 (17%) patients in each group, respectively. Grade 3 or worse adverse events that were more frequent in the vosaroxin plus cytarabine group than in the placebo plus cytarabine group included febrile neutropenia (167 [47%] vs 117 [33%]), neutropenia (66 [19%] vs 49 [14%]), stomatitis (54 [15%] vs 10 [3%]), hypokalaemia (52 [15%] vs 21 [6%]), bacteraemia (43 [12%] vs 16 [5%]), sepsis (42 [12%] vs 18 [5%]), and pneumonia (39 [11%] vs 26 [7%]).

INTERPRETATION

Although there was no significant difference in the primary endpoint between groups, the prespecified secondary analysis stratified by randomisation factors suggests that the addition of vosaroxin to cytarabine might be of clinical benefit to some patients with relapsed or refractory acute myeloid leukaemia.

FUNDING

Sunesis Pharmaceuticals.

Vosaroxin is a novel topoisomerase-II inhibitor with efficacy in relapsed and refractory acute myeloid leukaemia

INTRODUCTION

Vosaroxin is a first-in-class anti-cancer quinolone that inhibits topoisomerase-II leading to cell cycle arrest and apoptosis. It has shown efficacy in a range of solid organ and haematopoietic tumours in vitro, and several clinical trials are underway or completed in the field of Acute Myeloid Leukaemia (AML). The treatment of relapsed and refractory AML is a clinical challenge, where long-term survival is rare without allogeneic haematopoietic stem cell transplantation.

AREAS COVERED

We review the data from the published clinical trials of vosaroxin, including the recently presented Phase III VALOR study. In combination with intermediate dose cytarabine, vosaroxin almost doubled complete response (CR) rates in relapsed and refractory AML compared with cytarabine alone, and prolonged median survival by 1.4 months.

EXPERT OPINION

Vosaroxin is a promising new agent in the treatment of AML, with the potential to improve CR rates in a high-risk group of patients with relapsed and refractory AML. However, higher CR rates have been associated with higher rates of treatment-related morbidity and mortality, especially in elderly/unfit patients. Maximising the potential of vosaroxin will therefore require the identification of patients most likely to benefit from vosaroxin-containing combination regimens.

Vosaroxin and vosaroxin plus low-dose Ara-C (LDAC) vs low-dose Ara-C alone in older patients with acute myeloid leukemia

The development of new treatments for older patients with acute myeloid leukemia is an active area, but has met with limited success. Vosaroxin, a quinolone-derived intercalating agent has several properties that could prove beneficial. Initial clinical studies showed it to be well-tolerated in older patients with relapsed/refractory disease. In vitro data suggested synergy with cytarabine (Ara-C). To evaluate vosaroxin, we performed 2 randomized comparisons within the "Pick a Winner" program. A total of 104 patients were randomized to vosaroxin vs low-dose Ara-C (LDAC) and 104 to vosaroxin + LDAC vs LDAC. When comparing vosaroxin with LDAC, neither response rate (complete recovery [CR]/complete recovery with incomplete count recovery [CRi], 26% vs 30%; odds ratio [OR], 1.16 (0.49-2.72); P = .7) nor 12-month survival (12% vs 31%; hazard ratio [HR], 1.94 [1.26-3.00]; P = .003) showed benefit for vosaroxin. Likewise, in the vosaroxin + LDAC vs LDAC comparison, neither response rate (CR/CRi, 38% vs 34%; OR, 0.83 [0.37-1.84]; P = .6) nor survival (33% vs 37%; HR, 1.30 [0.81-2.07]; P = .3) was improved. A major reason for this lack of benefit was excess early mortality in the vosaroxin + LDAC arm, most obviously in the second month following randomization. At its first interim analysis, the Data Monitoring and Ethics Committee recommended closure of the vosaroxin-containing trial arms because a clinically relevant benefit was unlikely.

REVEAL-1, a phase 2 dose regimen optimization study of vosaroxin in older poor-risk patients with previously untreated acute myeloid leukaemia

This phase 2 study (N = 116) evaluated single-agent vosaroxin, a first-in-class anticancer quinolone derivative, in patients ≥60 years of age with previously untreated unfavourable prognosis acute myeloid leukaemia. Dose regimen optimization was explored in sequential cohorts (A: 72 mg/m² d 1, 8, 15; B: 72 mg/m² d 1, 8; C: 72 mg/m² or 90 mg/m² d 1, 4). The primary endpoint was combined complete remission rate (complete remission [CR] plus CR with incomplete platelet recovery [CRp]). Common (>20%) grade ≥3 adverse events were thrombocytopenia, febrile neutropenia, anaemia, neutropenia, sepsis, pneumonia, stomatitis and hypokalaemia. Overall CR and CR/CRp rates were 29% and 32%; median overall survival (OS) was 7·0 months; 1-year OS was 34%. Schedule C (72 mg/m²) had the most favourable safety and efficacy profile, with faster haematological recovery (median 27 d) and lowest incidence of aggregate sepsis (24%) and 30-d (7%) and 60-d (17%) all-cause mortality; at this dose and schedule, CR and CR/CRp rates were 31% and 35%, median OS was 7·7 months and 1-year OS was 38%. Overall, vosaroxin resulted in low early mortality and an encouraging response rate; vosaroxin 72 mg/m² d 1, 4 is recommended for further study in this population. Registered at www.clinicaltrials.gov: #NCT00607997.

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

Vosaroxin is a first-in-class anticancer quinolone derivative that intercalates DNA and inhibits topoisomerase II. This study assessed the safety and tolerability of vosaroxin plus cytarabine in patients with relapsed/refractory acute myeloid leukemia. Escalating vosaroxin doses (10-minute infusion; 10-90 mg/m(2); days 1, 4) were given in combination with cytarabine on one of two schedules: schedule A (24-hour continuous intravenous infusion, 400 mg/m(2)/day, days 1-5) or schedule B (2-hour intravenous infusion, 1 g/m(2)/day, days 1-5). Following dose escalation, enrollment was expanded at the maximum tolerated dose. Of 110 patients enrolled, 108 received treatment. The maximum tolerated dose of vosaroxin was 80 mg/m(2) for schedule A (dose-limiting toxicities: grade 3 bowel obstruction and stomatitis) and was not reached for schedule B (recommended phase 2 dose: 90 mg/m(2)). In the efficacy population (all patients in first relapse or with primary refractory disease treated with vosaroxin 80-90 mg/m(2); n=69), the complete remission rate was 25% and the complete remission/complete remission with incomplete blood count recovery rate was 28%. The 30-day all-cause mortality rate was 2.5% among all patients treated at a dose of 80-90 mg/m(2). Based upon these results, a phase 3 trial of vosaroxin plus cytarabine was initiated in patients with relapsed/refractory acute myeloid leukemia. (Clinicaltrials.gov identifier: NCT00541866).

Pharmacokinetic evaluation of C-3 modified 1,8-naphthyridine-3-carboxamide derivatives with potent anticancer activity: lead finding

To develop naphthyridine derivatives as anticancer candidates, pharmacokinetic (PK) evaluations of 10 novel derivatives of 1,4-dihydro-4-oxo-1-proparagyl-1,8-naphthyridine-3-carboxamide, with potent anticancer activity were done using in vitro ADME (absorption, distribution, metabolism, excretion) and pharmacokinetic--pharmcodynamic (PK/PD) assays. Only derivatives 5, 6, 9 and 10 showed better metabolic stability, solubility, permeability, partition coefficient and cytochrome P450 (CYP) inhibition values. PK of derivatives 5, 6, 9 and 10 in rat showed comparable PK profile for derivative 5 (C0 = 6.98 µg/mL) and 6 (C0 = 6.61 µg/mL) with no detectable plasma levels for derivatives 9 and 10 at 5.0 mg/kg i.v. dose. PK/PD assay of derivatives 5 and 6 in tumor-bearing mice (TBM) showed comparable PK but tumor plasma index (TPI) of derivative 6 (4.02) was better than derivative 5 (2.50), suggesting better tumor uptake of derivative 6. Derivative 6, as lead compound, showed highest tumor growth inhibition (TGI) value of 33.6% in human ovary cancer xenograft model.

Bispyrimidines as potent histamine H(4) receptor ligands: delineation of structure-activity relationships and detailed H(4) receptor binding mode

The basic methylpiperazine moiety is considered a necessary substructure for high histamine H4 receptor (H4R) affinity. This moiety is however also the metabolic hot spot for various classes of H4R ligands (e.g., indolcarboxamides and pyrimidines). We set out to investigate whether mildly basic 2-aminopyrimidines in combination with the appropriate linker can serve as a replacement for the methylpiperazine moiety. In the series of 2-aminopyrimidines, the introduction of an additional 2-aminopyrimidine moiety in combination with the appropriate linker lead to bispyrimidines displaying pKi values for binding the human H4R up to 8.2. Furthermore, the methylpiperazine replacement results in compounds with improved metabolic properties. The attempt to transfer the knowledge generated in the class of bispyrimidines to the indolecarboxamides failed. Combining the derived structure-activity relationships with homology modeling leads to new detailed insights in the molecular aspects of ligand-H4R binding in general and the binding mode of the described bispyrimidines in specific.

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

INTRODUCTION

Despite significant advances in diagnosis and supportive care, the majority of patients diagnosed with acute myeloid leukemia (AML) ultimately die of their disease. Standard intensive induction treatment continues to comprise cytarabine and a topoisomerase II (topo II) poison, usually an anthracycline. Vosaroxin , a novel first-in-class quinolone derivative has been developed for use in the treatment of AML as a new-generation topo II inhibitor. It has shown promising activity as a monotherapy and also in combination with intermediate dose cytarabine (IDAC) in relapsed and refractory patient cohorts with minimal toxicity and good tolerability.

AREAS COVERED

The authors discuss the mechanism of action of vosaroxin, the pharmacokinetics, safety and tolerability, preclinical and clinical trial results available as well as areas of ongoing research.

EXPERT OPINION

Vosaroxin has shown efficacy as a novel cytotoxic agent, and despite a similar mechanism of action has significant advantages over anthracyclines. It evades common resistance pathways of p53 and P-glycoprotein (P- gp) and does not appear to generate significant reactive oxygen species (ROS) associated with these agents. Should future investigation confirm its efficacy and advantageous safety profile, vosaroxin could potentially replace older generation topoisomerase poisons in the treatment of AML and other malignant conditions.

Vosaroxin : a novel antineoplastic quinolone

INTRODUCTION

The antineoplastic quinolone derivative vosaroxin (SNS-595, Sunesis, South San Francisco, CA, USA) was first described in 2002. It represents a novel class of anticancer drugs and is currently in a Phase III clinical trial for relapsed and refractory acute myeloid leukemia (AML). AML is the most common form of acute leukemia in adults and is increasing in incidence due to the aging of the American population. Despite advances in diagnosis, prognostic prediction, and treatment in younger age groups, there has been little improvement in survival among patients over 60 years of age, who make up the majority of those affected.

AREAS COVERED

The development of vosaroxin, its mechanism of action, pharmacology, and metabolism, and the preclinical and clinical data to date will be covered.

EXPERT OPINION

Despite its structural dissimilarity, vosaroxin has mechanisms of action similar to the anthracyclines and anthracenediones already in use for the treatment of AML. However, unlike these agents, vosaroxin is not a P-gp substrate, appears to be unaffected by overexpression of P-gp or TP53 mutations, and may be useful in the treatment of AML, especially in the elderly.

A phase Ib study of vosaroxin, an anticancer quinolone derivative, in patients with relapsed or refractory acute leukemia

This study of vosaroxin evaluated dose-limiting toxicity (DLT), maximum-tolerated dose (MTD), pharmacokinetics (PK), clinical activity and pharmacodynamics in relapsed/refractory leukemia. Dosing was weekly (days 1, 8 and 15) or twice weekly (days 1, 4, 8 and 11). Seventy-three treated patients had a median age of 65 years, 85% had acute myeloid leukemia and 78% had refractory disease. Weekly schedule: 42 patients received 18-90 mg/m(2); MTD was 72 mg/m(2). Twice-weekly schedule: 31 patients received 9-50 mg/m(2); MTD was 40 mg/m(2). DLT was stomatitis; primary non-hematologic toxicity was reversible gastrointestinal symptoms and febrile neutropenia. Thirty-day all-cause mortality was 11%. Five patients had complete or incomplete remissions; median duration was 3.1 months. A morphologic leukemia-free state (bone marrow blast reduction to <5%) occurred in 11 additional patients. Antileukemic activity was associated with total dose or weekly time above 1 μmol/l plasma vosaroxin concentration (P<0.05). Vosaroxin exposure was dose proportional over 9-90 mg/m(2). The average terminal half-life was ~25 h and clearance was non-renal. No induction or inhibition of vosaroxin metabolism was evident. Vosaroxin-induced DNA damage was detected as increased intracellular γH2AX. Vosaroxin had an acceptable safety profile, linear PK and encouraging clinical activity in relapsed/refractory leukemia.

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.

DESIGN AND 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.

Voreloxin, a first-in-class anticancer quinolone derivative, acts synergistically with cytarabine in vitro and induces bone marrow aplasia in vivo

Main purpose

Voreloxin is a first-in-class anticancer quinolone derivative that intercalates DNA and inhibits topoisomerase II, inducing site-selective DNA damage. Voreloxin is in clinical studies, as a single agent and in combination with cytarabine, for the treatment of acute myeloid leukemia (AML). The preclinical studies reported here were performed to investigate the activity of voreloxin alone and in combination with cytarabine, in support of the clinical program.

Research questions

Is single agent voreloxin active in preclinical models of AML? Does the combination of voreloxin and cytarabine enhance the activity of either agent alone?

Methods

Inhibition of proliferation was studied in three cancer cell lines: HL-60 (acute promyelocytic leukemia), MV4-11 (AML), and CCRF-CEM (Acute lymphoblastic leukemia). Combination index (CI) analysis established the effect of the drugs in combination. A mouse model of bone marrow ablation was used to investigate in vivo efficacy of the drugs alone and in combination. Peripheral white blood cell and platelet counts were followed to assess marrow impact and recovery.

Results

Voreloxin and cytarabine alone and in combination exhibited cytotoxic activity in human leukemia cell lines and in vivo. The two drugs had additive or synergistic activity in vitro and supra-additive activity in vivo. Bone marrow ablation was accompanied by reductions in peripheral white blood cells and platelets that were reversible within 1 week, consistent with the AML treatment paradigm.

Conclusions

These data support ongoing clinical evaluation of voreloxin both alone and in combination with cytarabine for the treatment of AML.