Phase I Study of a Liposomal Carrier (CPX-351) Containing a Synergistic, Fixed Molar Ratio of Cytarabine (Ara-C) and Daunorubicin (DNR) in Advanced Leukemias

Background: CPX-351 is a liposomal formulation of Ara-C and DNR which fixes the synergistic 5:1 molar ratio found to enhance efficacy in both in vitro and in vivo preclinical leukemia models. CPX-351 overcomes the pharmacokinetic (PK) differences of each drug, enabling the maintenance of the 5:1 molar ratio for extended periods of time after IV administration and the delivery of this ratio to bone marrow. Preclinical data from in vitro models show that CPX-351 is actively internalized by leukemic cells within vacuoles and subsequently releases DNR intracellularly. A Phase I study was performed with CPX-351 in patients with acute myelogenous leukemia (AML), acute lymphocytic leukemia (ALL), and myelodysplastic syndrome (MDS).

Objectives:

1. to determine safety, tolerability, and pharmacokinetics of a 90 min IV infusion of CPX-351 given on days 1, 3, 5 to patients with advanced leukemia and MDS, and

2. to seek preliminary evidence of antitumor activity.

Methods: Patients with relapsed/refractory AML/ALL and MDS were eligible. A second induction course was permitted if the day 14 bone marrow showed evidence of antileukemic effect and persistent leukemia. Dosing started at 3 units/m² (1 u = 1 mg Ara-C and 0.44 mg DNR) using single patient cohorts and dose doublings. Three patient cohorts and 33% dose increments began after evidence of antileukemic activity and continued until limiting toxicities (DLTs) completed dose escalation. PK samples were collected after each dose.

Results: Forty-seven subjects received 69 courses of CPX-351: Male/Female = 31/16, median age = 62 years (range 23–81); 44 patients had AML and 3 patients had ALL; median number of prior regimens = 2 (1–7). Thirty-seven patients entered the escalation phase of the study and ten subjects, most in first relapse, were treated after completion of dose escalation to confirm safety. At 24 u/m² antileukemic effects were observed leading to increased cohort size to 3 and decreased escalation rate to 33%. The MTD and recommended Phase 2 dose was 101 u (101 mg Ara-C + 44 mg DNR)/m² after observing 3 DLTs (decreased LVEF, hypertensive crisis, prolonged aplasia) at 134 u/m². Adverse events data are available for 36 of 37 patients from the escalation phase of the study. Nonhematologic grade 3–5 toxicities occurring in more than one patient included: infections (58%), dyspnea (11%), fever (11%), hypophosphatemia (8%), hypokalemia (6%), renal failure (6%), skin rash (6%), headache (6%) hyperglycemia (6%) hypoxia (6%) and respiratory failure (6%). Mucositis of any grade was observed in 42% of patients with 3% having grade 3 mucositis. Diarrhea of grade 1 and 2 severity occurred in 39% of patients. Interim analysis of PK data demonstrates maintenance of the 5:1 molar ratio and detectable encapsulated drug persisting up to 24 hours. The average half-lives were 35 hr for total Ara-C and 23 hr for DNR, significantly longer than reported for the conventional drugs. Overall, 11 patients achieved CR/CRp. Among the 19 patients treated at the MTD, 5 of the 13 patients evaluable for response achieved CR. Six patients were treated above the MTD (134 u/m²) and 2 achieved CR. Median time to CR was 43 days.

Conclusions: The recommended phase 2 dose is 101 u/m². CPX-351 was well tolerated, with no unexpected toxicities noted up to the MTD. GI toxicities and mucositis were transient and nearly always of mild to moderate severity. Reduced LV function was observed in two patients both with substantial prior anthracycline exposure. CRs were observed in heavily pre-treated patients with relapsed/refractory AML. Future plans include a randomized Phase 2 study comparing CPX-351 versus Cytarabine + Daunorubicin (“7 + 3”) in older (>60 yo) subjects with previously untreated AML, and a phase 2 study in patients with AML in 1^st relapse.