Abstract 5534: Liposome accumulation within leukemia engrafted bone marrow is significantly enhanced when the formulation contains cytarabine plus daunorubicin

Abstract

Abstract CPX-351 is a liposome formulation designed to deliver a synergistic, fixed ratio of cytarabine and daunorubicin in vivo. It has been shown to be highly efficacious against a variety of mouse leukemia models and encouraging evidence of anti-leukemic activity has been observed in clinical trials. In this report we investigate liposome biodistribution properties that may contribute to the enhanced efficacy of CPX-351. In order to model bone marrow leukemia development, we utilized the human leukemia CCRF-CEM tumor which has been shown to efficiently engraft to the bone marrow of SCID Rag2M mice. Liposomes were prepared in the presence or absence of cytarabine and daunorubicin to compare the plasma clearance and biodistribution to bone marrow, liver, lung, spleen and kidney following multiple treatments. The plasma clearance of empty liposomes and CPX-351 were similar in both leukemia and non-leukemia bearing mice. Both liposomal formulations had similar organ distribution profiles in the presence or absence of leukemia; however lipid delivery to the bone marrow was markedly augmented by the presence of encapsulated drug. Accumulation of CPX-351 lipid in the bone marrow was 20 to 50% higher than for empty liposomes and this phenomenon was further enhanced in leukemia bearing mice. Leukemia-laden bone marrow accumulated 75% more CPX-351 lipid than the empty liposomes on the first injection and accumulation increased an additional 20% with subsequent injections. We attribute the increased efficacy of CPX-351 over the free drug cocktail of cytarabine and daunorubicin to elevated exposure of the tumor tissue to chemotherapeutic agents. This increased exposure is not only due to the prolonged circulation of the drug in the liposomes, but also due to the increased bone marrow uptake of the liposomes when drugs are present. Additionally the lipid accumulation is further increased with successive treatments of the leukemia. The results suggest that the liposomal drugs alter either the bone marrow microenvironment or resident cell populations in a manner that facilitates subsequent uptake and/or retention of CPX-351. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5534.