A safety evaluation of omacetaxine mepesuccinate for the treatment of chronic myeloid leukemia.

INTRODUCTION: Therapy of chronic myeloid leukemia (CML) has been completely transformed by the development of tyrosine kinase inhibitors (TKIs). However, a subset of patients will fail TKI therapy due to resistance or intolerance. Omacetaxine mepesuccinate (OM), a protein translation inhibitor, is currently the only approved therapy that does not directly target the kinase domain. It has activity for CML patients irrespective of the phase or underlying kinase domain mutation status. AREAS COVERED: We searched the MEDLINE database for articles published in English on homoharringtonine or omacetaxine from 1970 to present. This article reviews the pharmacokinetics of OM and its clinical evolution for the treatment of CML pre- and post TKI development. Toxicity profile, drug administration and future directions are also discussed. EXPERT OPINION: OM represents a unique addition to the CML therapeutic armamentarium with its distinct mechanism of action and activity. The adverse event profile is manageable and with subcutaneous administration at the approved dose, cardiac toxicity is no longer a concern. The recent approval of home administration will facilitate access to this therapy and increase patient compliance. We conclude with specific scenarios where OM use should be considered in CP and AP-CML patients in the era of TKI therapy.

Pharmacokinetics and excretion of (14)C-omacetaxine in patients with advanced solid tumors.

Background Omacetaxine mepesuccinate is indicated in adults with chronic myeloid leukemia resistant and/or intolerant to ≥ 2 tyrosine kinase inhibitor treatments. This phase I study assessed the disposition, elimination, and safety of (14)C-omacetaxine in patients with solid tumors. Methods The study comprised a 7-days pharmacokinetic assessment followed by a treatment period of ≤ six 28-days cycles. A single subcutaneous dose of 1.25 mg/m(2) (14)C-omacetaxine was administered to six patients. Blood, urine, and feces were collected through 168 h or until radioactivity excreted within 24 h was <1 % of the dose. Total radioactivity (TRA) was measured in all matrices and concentrations of omacetaxine, 4'-desmethylhomoharringtonine (4'-DMHHT), and cephalotaxine were measured in plasma and urine. For each treatment cycle, patients received 1.25 mg/m(2) omacetaxine twice daily for 7 days. Results Mean TRA recovered was approximately 81 % of the dose, with approximately half of the radioactivity recovered in feces and half in urine. Approximately 20 % of the dose was excreted unchanged in urine; cephalotaxine (0.4 % of dose) and 4' DMHHT (9 %) were also present. Plasma concentrations of TRA were higher than the sum of omacetaxine and known metabolites, suggesting the presence of other (14)C-omacetaxine-derived compounds. Fatigue and anemia were common, consistent with the known toxicity profile of omacetaxine. Conclusion Renal and hepatic processes contribute to the elimination of (14)C-omacetaxine-derived radioactivity in cancer patients. In addition to omacetaxine and its known metabolites, other (14)C-omacetaxine-derived materials appear to be present in plasma and urine. Omacetaxine was adequately tolerated, with no new safety signals.

Metabolite profiling of 14C-omacetaxine mepesuccinate in plasma and excreta of cancer patients.

Omacetaxine mepesuccinate (hereafter referred to as omacetaxine) is a protein translation inhibitor approved by the US Food and Drug Administration for adult patients with chronic myeloid leukemia with resistance and/or intolerance to two or more tyrosine kinase inhibitors. The objective was to investigate the metabolite profile of omacetaxine in plasma, urine and faeces samples collected up to 72 h after a single 1.25-mg/m2 subcutaneous dose of 14C-omacetaxine in cancer patients. High-performance liquid chromatography mass spectrometry (MS) (high resolution) in combination with off-line radioactivity detection was used for metabolite identification. In total, six metabolites of omacetaxine were detected. The reactions represented were mepesuccinate ester hydrolysis, methyl ester hydrolysis, pyrocatechol conversion from the 1,3-dioxole ring. Unchanged omacetaxine was the most prominent omacetaxine-related compound in plasma. In urine, unchanged omacetaxine was also dominant, together with 4'-DMHHT. In feces very little unchanged omacetaxine was found and the pyrocatechol metabolite of omacetaxine, M534 and 4'-desmethyl homoharringtonine (4'-DMHHT) was the most abundant metabolites. Omacetaxine was extensively metabolized, with subsequent renal and hepatic elimination of the metabolites. The low levels of the metabolites found in plasma indicate that the metabolites are unlikely to contribute materially to the efficacy and/or toxicity of omacetaxine.

Omacetaxine mepesuccinate in chronic myeloid leukemia.

INTRODUCTION: Homoharringtonine (HHT) and other alkaloid esters were originally isolated from the Cephalotaxus evergreen tree and have been used in traditional Chinese medicine since the 1970s to treat a variety of malignancies. Although HHT was investigated for the treatment of chronic myeloid leukemia (CML) in the 1990s with good results, the advent of BCR-ABL1 tyrosine kinase inhibitors (TKIs) at that time rapidly established a new standard of care for CML. Omacetaxine mepesuccinate is a semisynthetic derivative of HHT with known clinical activity in relapsed or refractory CML following TKI therapy. AREAS COVERED: In this review, we summarize the biologic effects of HHT and its derivative, omacetaxine, in CML. Additionally, we analyze the concepts learned from the early trials using these drugs. Data from clinical trials resulting in drug approval are also reviewed. EXPERT OPINION: Omacetaxine has a clear role in the CML armamentarium for patients in chronic and accelerated phase who have failed or were intolerant to two or more TKIs.

Pharmacokinetic study of omacetaxine mepesuccinate administered subcutaneously to patients with advanced solid and hematologic tumors.

PURPOSE: Omacetaxine mepesuccinate is a first-in-class cephalotaxine demonstrating clinical activity in chronic myeloid leukemia. A subcutaneous (SC) formulation demonstrated efficacy and safety in phase 1/2 trials in patients previously treated with ≥1 tyrosine kinase inhibitor. This study assessed pharmacokinetics and safety of SC omacetaxine in patients with advanced cancers. METHODS: Omacetaxine 1.25 mg/m(2) SC was administered BID, days 1-14 every 28 days for 2 cycles, until disease progression or unacceptable toxicity. Blood and urine were collected to measure omacetaxine concentrations and inactive metabolites. Adverse events, including QT interval prolongation, were recorded. Tumor response was assessed at cycle 2 completion. RESULTS: Pharmacokinetic parameters were estimated from cycle 1, day 1 data in 21 patients with solid tumors or hematologic malignancies and cycle 1, day 11 data in 10 patients. Omacetaxine was rapidly absorbed, with mean peak plasma concentrations observed within 1 h, and widely distributed, as evidenced by an apparent volume of distribution of 126.8 L/m(2). Plasma concentration versus time data demonstrated biexponential decay; mean steady-state terminal half-life was 7 h. Concentrations of inactive metabolites 4'-DMHHT and cephalotaxine were approximately 10 % of omacetaxine and undetectable in most patients, respectively. Urinary excretion of unchanged omacetaxine accounted for <15 % of the dose. Grade 3/4 drug-related adverse events included thrombocytopenia (48 %) and neutropenia (33 %). Two grade 2 increases in QTc interval (>470 ms) were observed and were not correlated with omacetaxine plasma concentration. No objective responses were observed. CONCLUSIONS: Omacetaxine is well absorbed after SC administration. Therapeutic plasma concentrations were achieved with 1.25 mg/m(2) BID, supporting clinical development of this dose and schedule.

Omacetaxine mepesuccinate for the treatment of leukemia.

INTRODUCTION: Omacetaxine mepesuccinate, formerly known as homoharringtonine, is a first-in-class cephalotaxine that has experienced phases of increasing and waning interest since its first use in traditional Chinese medicine. With activity being reported in patients with chronic myeloid leukemia (CML) resistant to currently available tyrosine kinase inhibitors, renewed interest has recently been generated. AREAS COVERED: The development of omacetaxine mepesuccinate, with emphasis on synthesis and mode of administration, is addressed. An overview on current clinical results as a single agent or within combination regimens in patients with acute myeloid leukemia (AML) and CML is given. EXPERT OPINION: Omacetaxine mepesuccinate has a unique mode of action and appreciable activity in AML and CML with generally mild nonhematologic toxicity. In patients with AML, results indicate a role within combination regimens in selected, possibly elderly patient populations. In CML, patients with resistance to tyrosine kinase inhibitors, especially due to the T315I mutation, are the most intensively studied. Despite successful results in some patients, single-agent therapy with omacetaxine mepesuccinate has resulted in modest results. However, upfront combination with tyrosine kinase inhibitor represents an attractive option due their differing mechanisms of action.

Omacetaxine mepesuccinate--a semisynthetic formulation of the natural antitumoral alkaloid homoharringtonine, for chronic myelocytic leukemia and other myeloid malignancies.

Homoharringtonine (HHT), a natural alkaloid extracted from various Cephalotaxus species, exerts its antitumoral and anti-angiogenic activity through an inhibition of protein synthesis and the promotion of apoptosis. ChemGenex Pharmaceuticals Ltd, in collaboration with Stragen Group, is developing omacetaxine mepesuccinate, a semisynthetic formulation of HHT, as a potential treatment for chronic myelocytic leukemia (CML), myelodysplastic syndrome (MDS) and acute myelogenous leukemia (AML). In preclinical studies, omacetaxine mepesuccinate induced apoptosis in leukemia cell lines. Results from phase II clinical trials revealed omacetaxine mepesuccinate to be active in patients with CML that was resistant to tyrosine kinase inhibitor (TKI) therapy, including those patients who carry the BCR-ABL1T315I mutation, which is highly insensitive to the TKIs imatinib, nilotinib and dasatinib; the therapeutic was also generally well tolerated. Phase II and III clinical trials are underway to assess the activity of omacetaxine mepesuccinate, either alone or in combination with TKIs or other cytotoxic drugs, in patients with CML that is resistant to TKI therapy. Phase I and II clinical trials for omacetaxine mepesuccinate in the treatment of AML and MDS are also ongoing; intravenous, subcutaneous and oral formulations of the drug are being developed. Omacetaxine mepesuccinate appears to hold potential for the treatment of CML and, in particular, imatinib-resistant CML; the development of alternative formulations of the therapeutic further expands the potential for success in drug development.

Homoharringtonine for the treatment of chronic myelogenous leukemia.

BACKGROUND: The anticancer activity of the natural alkaloid homoharringtonine (HHT) was first recognized by Chinese investigators. HHT exerts its activity through inhibition of protein synthesis and promotion of apoptosis. METHODS: The authors reviewed the most relevant preclinical and clinical studies involving patients with chronic myelogenous leukemia (CML) receiving therapy with either natural HHT or omacetaxine mepesuccinate (Ceflatonin, Myelostat, CGX-653), a semisynthetic subcutaneously bioavailable form of HHT presently under development for the treatment of CML. RESULTS: Prior to the advent of the tyrosine kinase inhibitor (TKI) imatinib mesilate, controlled clinical studies established HHT as the most active therapy in CML after failure of IFN-a for patients who were not candidates for allogeneic stem cell transplantation. Preliminary results from Phase II studies suggest that omacetaxine mepesuccinate is active in patients with imatinib-resistant CML, including those carrying the T315I mutation, which renders imatinib and second-generation TKIs ineffective. CONCLUSION: These encouraging results have propelled the development of several Phase II/III trials both in Europe and in the US to further delineate the activity of omacetaxine mepesuccinate in patients with CML who are resistant to TKI therapy.

A phase I dose-finding and pharmacokinetic study of subcutaneous semisynthetic homoharringtonine (ssHHT) in patients with advanced acute myeloid leukaemia.

To determine the maximum-tolerated dose (MTD), dose-limiting toxicities and pharmacokinetic of semisynthetic homoharringtonine (ssHHT), given as a twice daily subcutaneous (s.c.) injections for 9 days, in patients with advanced acute leukaemia, 18 patients with advanced acute myeloid leukaemia were included in this sequential Bayesian phase I dose-finding trial. A starting dose of 0.5 mg m(-2) day(-1) was explored with subsequent dose escalations of 1, 3, 5 and 6 mg m(-2) day(-1). Myelosuppression was constant. The MTD was estimated as the dose level of 5 mg m(-2) day(-1) for 9 consecutive days by s.c. route. Dose-limiting toxicities were hyperglycaemia with hyperosmolar coma at 3 mg m(-2), and (i) one anasarque and haematemesis, (ii) one life-threatening pulmonary aspergillosis, (iii) one skin rash and (iv) one scalp pain at dose level of 5 mg m(-2) day(-1). The mean half-life of ssHHT was 11.01+/-3.4 h, the volume of distribution at steady state was 2+/-1.4 l kg(-1) and the plasma clearance was 11.6+/-10.4 l h(-1). Eleven of the 12 patients with circulating leukaemic cells had blood blast clearance, two achieved complete remission and one with blast crisis of CMML returned in chronic phase. The recommended daily dose of ssHHT on the 9-day schedule is 5 mg m(-2) day(-1).

Homoharringtonine: a new treatment option for myeloid leukemia.

HHT, one of the alkaloids from a Chinese natural plant, Cephalotaxus, has shown its potential in leukemia treatment. This compound demonstrated strong growth-inhibiting activities in vitro and in animal experiments, and obtained encouraging results in some clonal proliferative disease such as in chronic myeloid leukemia (CML) and in polycythemia vera. Evidences also confirmed HHT as an apoptosis inducer in tumor cell lines and fresh cells from cancer patients. The CR rate reported with HHT-based regimen in acute nonlymphocytic leukemia showed no statistic differences from that with DNR-based regimen, although the case number was limited. While used in clinical trial, the drug often cause noticeably cardiovascular disturbances if be given rapidly by intravenous infusion. Myelosuppression is the common complication in HHT-based chemotherapy. Although with the anti-growth activity in vitro and praisable achievement in acute and chronic myeloid leukemia treatment, the drug shows no beneficial effect in lymphocytic leukemia and solid tumors. The underlying mechanism for the discrepancy of efficacy keeps unknown. This review will present with the preclinical research data including the action mechanism, pharmacokinetics and drug resistance of HHT as well as the result from the clinical trial with HHT in China and the United States.

[Pharmacokinetics of harringtonine liposomes in rabbits].

After i.v. free harringtonine (FH) and harringtonine liposomes (HL) with high and low encapsulation percentage (En%) to rabbits, their blood concentrations were determined by reverse-phase HPLC. The blood concentration-time curves were shown to fit a two-compartments open model. FH: T1/2 alpha = 1.32 +/- 0.24, T1/2 beta = 32 +/- 6 min; Low En % HL: T1/2 alpha = 4.12 +/- 0.25, T1/2 beta = 106 +/- 5 min; High En % HL: T1/2 alpha = 9.4 +/- 1.2, T1/2 beta = 209 +/- 5 min.

[Distribution of harringtonine positively and negatively charged liposome in rat tissues].

Distribution of harringtonine positively and negatively charged liposome (HL(+), HL(-)) and harringtonine free drug (FH) in rat tissues were measured by HPLC. Their LD50 in mice were compared. The results showed that distribution of HL(+), HL(-), In vivo may be changed, that the amount of HL(+), HL(-) was increased in the liver, lung, and spleen and in these tissues it was 2-30-fold higher than that of HF after iv 2 h. HL(+), HL(-) may aid to permeate through the blood-brain, blood-testicle barrier, and to reduce acute lethal toxicity. Areas under the time curve of HL(+), HL(-) in brain and testis within 2 h were 2-4.5 times as much as those of HF. There were significant differences in the fate between negatively and positively charged liposomes in vivo.

Reversal of C1300 murine neuroblastoma multidrug resistance by cremophorEL, a solvent for cyclosporin A.

We previously developed a homoharringtonine resistant C-1300 neuroblastoma cell line with cross-resistance to adriamycin and increased levels of p-glycoprotein, and showed that drug resistance could be reversed in this cell line by cyclosporin A. The present study shows that cremophor EL, a parenteral vehicle for cyclosporin A, can also completely reverse this multidrug resistance in a clonogenic assay system. Cremophor EL incubated with resistant cells for up to six days did not reduce levels of p-glycoprotein. Intracellular homoharringtonine analysis using HPLC revealed increased drug accumulation in resistant cells treated with cremophor EL. The increased drug level was not due to blocking of drug efflux commonly seen in other multidrug resistant models. The data suggest that resistance modulation with cyclosporin A should be interpreted with caution when cremophor EL is a solvent. Our work suggests cremophor EL, a relatively nontoxic lipophylic solvent, may have a direct effect on membrane permeability, although other mechanisms cannot be ruled out.

Quantitation of homoharringtonine in plasma by high-performance liquid chromatography with amperometric detection.

A high-performance liquid chromatographic procedure was developed for the quantitation of homoharringtonine in plasma. Harringtonine was used as an internal standard, and 1 ml of sample was required. The single-step extraction with dichloromethane resulted in almost 100% recovery for homoharringtonine and harringtonine. Analysis was performed on a reversed-phase CN column with amperometric detection. Chromatography was completed in 12 min. At an oxidation potential of +1.0 V, the detection limit was 1 ng/ml at a signal-to-noise ratio of 2. The mean analytical recovery for homoharringtonine was 99.5%. The within-run precision and between-run precision were both less than 11%. The method is equally applicable for plasma or serum, and it has been demonstrated to be applicable for study of the pharmacokinetics of homoharringtonine in patients suffering from acute non-lymphocytic leukaemia.

Pharmacokinetics of homoharringtonine in dogs.

We studied the pharmacokinetics and distribution of homoharringtonine (HHT), an antitumor alkaloid, in anesthetized dogs using chromatographic and radiochemical techniques. Uniformly tritiated HHT was administered i.v. to five dogs at doses of 0.05 to 0.34 mg/kg, 200 microCi per animal. Unchanged HHT disappeared in a triphasic manner from the plasma with an initial plasma t1/2 of 9.4 +/- 4.2 min, an intermediary t1/2 of 1.4 +/- 0.5 h, and a terminal t1/2 of 40.6 +/- 4.6 h. The plasma clearance was 114.0 +/- 20.1 ml/kg-1 h-1 and the steady-state volume of distribution was 6.2 +/- 0.7 1/kg. In 72 h, 40.1% +/- 4.0% of the administered radioactivity was excreted in the urine, 17.8% +/- 2.7% of which was unchanged HHT. HHT was metabolized extensively to one major and two minor metabolites. Biliary excretion of total radioactivity was 14.4% in 5 h, 2% of which was HHT. HHT concentration in the CSF was highest 4 h after drug administration, about 40% of the concentration in the concurrent plasma. At autopsy 5 h after dosing, the highest percentage of HHT was in the liver (7.4%), followed by the small intestine (2.5%), stomach (1.0%), pancreas (0.8%), kidneys (0.8%), and lungs (0.7%). The heart, spleen, large intestine, and brain each retained less than 0.5%. However, 24 h after dosing, 4% of the HHT still remained in the liver, 1% in the small intestine, and less than 1% in the other organs. HHT seems to be extensively metabolized in dogs and partially retained in the body.