Subcutaneous Omacetaxine (OM) Treatment of Chronic Phase (CP) Chronic Myeloid Leukemia (CML) Patients Following Multiple Tyrosine Kinase Inhibitor (TKI) Failure

Multiple TKI failure is a growing problem in a subset of CML patients. Treatment with a third TKI after two have failed often yields poor results. New treatment options are needed for this patient population. OM is a first-in-class cetaxine with demonstrated activity as a single agent in CML. It inhibits the production of short-lived oncoproteins (such as Mcl-1) involved in cancer cell survival via a mechanism independent of Bcr-Abl binding. Several studies have suggested that OM has a favorable toxicity profile when given to patients with CML via the subcutaneous route. We explored OM efficacy and safety in a subset of patients who had received therapy with multiple prior approved TKI.

We analyzed a subset of adult CML-CP patients who had received two or more TKI (imatinib, dasatinib, nilotinib), from a combined interim dataset of two prospective Phase 2 studies (CML-202, for patients with the T315I kinase domain mutation, and CML-203, for patients with failure to ≥2 TKI) utilizing OM in the treatment adult patients with all phases of CML who had failed TKI. TKI failure was defined as no complete hematologic response (CHR) by 12 weeks (wk), no cytogenetic response by 6 months (mo), no major cytogenetic response (MCyR) by 12 mo, loss of CHR or MCyR, or progressive leukocytosis. The focus of this analysis was to assess the CHR and MCyR response rates as well as the overall safety of OM in these patients. Adverse events presented are Grade 3/4 events that occurred in ≥ 5% of patients (regardless of causality).

A total of 73 of the 93 CML-CP patients from these two studies had received two or more TKI prior to OM treatment. Median time from initial CML diagnosis to first dose of OM was 74.4 months. Mutations of any kind were seen in 48% of the patients, whereas 29% had no identified mutation and 23% had no available data on mutation status. Sixty (82%) of these 73 patients achieved or maintained (twelve patients were in CHR at study entry) a CHR and 17 (23%) achieved a MCyR (9 complete and 8 partial). The median duration of MCyR was 4.4+ months (range 1.2–14.1+). Median overall survival for patients treated with OM after failure of 2 or more TKI has not yet been reached [95% Confidence Interval (CI) 22.9, NA months] (Figure 1). Eleven patients had a treatment—emergent adverse event leading to death, and two deaths were probably related to study drug. Median progression-free survival was 11.1 months (95% CI 6.5, 13.8 months). Median follow-up time was 7.5 months for all patients with twenty-five patients remaining on study at the time of this data cut. A total of 36 of the 93 CP patients from these two studies had been treated with three or more TKI; 27 (75.0%) achieved or maintained a CHR and 7 (19.4%) achieved a MCyR (4 complete and 3 partial) on OM treatment. The median duration of MCyR in this group was 4.0+ months (range 1.2–11.5+) at the time of data cut-off. The primary Grade 3/4 adverse events in patients who received OM after failure of 2 or more TKI were hematologic, including thrombocytopenia (64%), neutropenia (48%) and anemia (40%) most commonly, followed by febrile neutropenia (12%), bone marrow failure (12%), pancytopenia (7%) and febrile bone marrow aplasia (6%). These events were dosing schedule dependent. Clinical sequelae were uncommon and managed with transient treatment interruptions and dose adjustments. Grade 3/4 non-hematologic adverse events were infrequent, with only fatigue (6%) occurring ≥5% of patients.

OM, through a mechanism of action independent of Bcr-Abl, may offer a clinically viable option for patients who have progressed on multiple TKI treatment.

Figure 1

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Overall Survival of CML-CP Adult Patients Treated with Omacetaxine Following ≥2 TKI Failure

Figure 1

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Overall Survival of CML-CP Adult Patients Treated with Omacetaxine Following ≥2 TKI Failure

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Off Label Use: The drug is currently in development and has an NDA submitted for use in TKI resistant CML. Cram: ChemGenex: Employment, Equity Ownership. Humphriss: ChemGenex: Employment, Equity Ownership. Benichou: ChemGenex: Consultancy, Equity Ownership. Craig: ChemGenex: Employment, Equity Ownership, Executive Management Level.