Chronic myeloid leukemia (CML) patients with the BCR-ABL T315I mutation do not benefit from therapy with currently approved tyrosine kinase inhibitors. Omacetaxine mepesuccinate is a protein synthesis inhibitor that has demonstrated activity in cells harboring the T315I mutation. This phase 2 trial assessed the efficacy of omacetaxine in CML patients with T315I and tyrosine kinase inhibitor failure. Patients received subcutaneous omacetaxine 1.25 mg/m 2 twice daily, days 1-14, every 28 days until hematologic response or a maximum of 6 cycles, and then days 1-7 every 28 days as maintenance. Results for patients treated in chronic phase are reported here. Patients (n ‫؍‬ 62) received a median of 7 (range, 1-41) cycles. Complete hematologic response was achieved in 48 patients (77%; 95% lower confidence limit, 65%); median response duration was 9.1 months. Fourteen patients (23%; 95% lower confidence limit, 13%) achieved major cytogenetic response, including complete cytogenetic response in 10 (16%). Median progression free-survival was 7.7 months. Grade 3/4 hematologic toxicity included thrombocytopenia (76%), neutropenia (44%), and anemia (39%) and was typically manageable by dose reduction. Nonhematologic adverse events were mostly grade 1/2 and included infection (42%), diarrhea (40%), and nausea (34%). Omacetaxine may provide a safe and effective treatment for CML patients with T315I mutation. This study is registered at www.clinicaltrials.gov as NCT00375219. (Blood. 2012;120(13):2573-2580)

Omacetaxine mepesuccinate (omacetaxine) is a first-in-class cephalotaxine with a unique mode of action, independent of BCR-ABL, that has shown promising activity in patients with chronic myeloid leukemia (CML). This multicenter, noncomparative, open-label phase 2 study evaluated the efficacy and safety of subcutaneous omacetaxine in CML patients with resistance or intolerance to two or more tyrosine kinase inhibitors (TKIs); results in patients in chronic phase are reported here. Patients received subcutaneous omacetaxine 1.25 mg/m2 twice daily days 1–14 every 28 days until hematologic response (up to a maximum of six cycles), then days 1–7 every 28 days as maintenance. Primary endpoints were rates of hematologic response lasting >8 weeks and major cytogenetic response (MCyR). Forty-six patients were enrolled: all had received imatinib, 83% had received dasatinib, and 57% nilotinib. A median 4.5 cycles of omacetaxine were administered (range, 1–36). Hematologic response was achieved or maintained in 31 patients (67%); median response duration was 7.0 months. Ten patients (22%) achieved MCyR, including 2 (4%) complete cytogenetic responses. Median progression-free survival was 7.0 months [95% confidence interval (CI), 5.9–8.9 months], and overall survival was 30.1 months (95% CI, 20.3 months—not reached). Grade 3/4 hematologic toxicity included thrombocytopenia (54%), neutropenia (48%), and anemia (33%). Nonhematologic adverse events were predominantly grade 1/2 and included diarrhea (44%), nausea (30%), fatigue (24%), pyrexia (20%), headache (20%), and asthenia (20%). Subcutaneous omacetaxine may offer clinical benefit to patients with chronic-phase CML with resistance or intolerance to multiple TKI therapies.

Introduction-Omacetaxine mepesuccinate (omacetaxine) is a first-in-class cephalotaxine that has demonstrated efficacy in CML. In this analysis we evaluated omacetaxine in CML patients with resistance or intolerance to 2 or more tyrosine kinase inhibitors (TKIs).

PurposeOmacetaxine 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.MethodsOmacetaxine 1.25 mg/m2 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.ResultsPharmacokinetic 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/m2. 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.ConclusionsOmacetaxine is well absorbed after SC administration. Therapeutic plasma concentrations were achieved with 1.25 mg/m2 BID, supporting clinical development of this dose and schedule.

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