Phase I and Pharmacokinetic Study of a Low-Clearance, Unilamellar Liposomal Formulation of Lurtotecan, a Topoisomerase 1 Inhibitor, in Patients with Advanced Leukemia

OSI-211 is a low-clearance, unilamellar liposomal formulation of a water-soluble camptothecin analogue, lurtotecan. OSI-211 has significant activity in severe combined immunodeficient mouse models of human leukemia. METHODS. This study was conducted to define the dose-limiting toxicities (DLT) and pharmacokinetics of OSI-211 in patients with refractory myeloid leukemias. Patients with refractory acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), or chronic myelogenous leukemia in blastic phase (CML-BP) were eligible. OSI-211 was given as an intravenous infusion over 30 minutes daily for 3 days. The starting dose was 1.5 mg/m² per day (4.5 mg/m² per course). The dose was escalated by 50% until Grade 2 toxicity was observed and then by 30-35% until the DLT was defined. Serial plasma and urine samples were collected, and drug levels were determined by high-performance liquid chromatography with fluorescence detection. RESULTS. Twenty patients (18 patients [90%] with AML, and 1 patient each [5%] with MDS and CML-BP) were treated. Mucositis and diarrhea were considered to be the DLTs. The maximum tolerated dose was 3.7 mg/m² per day. Fourteen of 18 evaluable patients (78%) with AML or MDS achieved transient bone marrow aplasia. The mean systemic clearance of lurtotecan in plasma was 0.946 ± 1.53 L/hour/m ². Urinary recovery of lurtotecan was 6.66% ± 5.26% (range, 1.05-18.4%). CONCLUSIONS. Liposomal encapsulation of lurtotecan altered its metabolism significantly. There was no evident correlation between exposure, as measured by plasma pharmacokinetics of lurtotecan, and clinical response or toxicities. OSI-211 merits further study in hematologic malignancies.