Abstract A135: Evaluation of CPX‐351 (cytarabine:daunorubicin) liposome injection efficacy in acute lymphoblastic leukemia (ALL) xenograft models

CPX‐351 is a liposome formulation of cytarabine (Cyt) and daunorubicin (Daun) in which the ratio of the two drugs (5:1, mol:mol) maximizes synergy. The marked increase in efficacy observed for CPX‐351 vs the free drug cocktail is associated with passive targeting of the synergistic drug ratio to bone marrow where drug‐loaded liposomes are preferentially taken up by leukemia cells. Clinical testing of CPX‐351 to date has focused on acute myelogenous leukemia (AML), however significant antileukemic activity may also be achievable against ALL. Investigations were undertaken by the Pediatric Preclinical Testing Program (PPTP) of the NCI to provide evidence for CPX‐351 treatment‐related antileukemic activity against representative pediatric ALL xenograft models. The maximum tolerated dose (MTD) of CPX‐351 was established by i.v. dose escalation in non‐engrafted NOD/SCID mice with a q2dx3 schedule. Leukemia engraftment was established by i.v. inoculation of either ALL‐4 (B‐precursor) or ALL‐8 (T‐lineage) cells into NOD/SCID mice. Drug or vehicle buffer (control) treatment was initiated when the %huCD45+ cells in the peripheral blood was greater than 1% for each cohort. An experimental end‐point for each mouse was attained when either the %huCD45+ was greater‐than or equal to 25% (an event) or if the mouse reached day 42 without an event. Two measures of antitumor activity were used: 1) an objective response measure (ORM) modeled after the clinical setting; and 2) a time to event measure based on the median event‐free survival (EFS) of treated and control animals for each xenograft. Non‐engrafted NOD/SCID mice exhibited increased sensitivity to CPX‐351 with a corresponding MTD that was roughly 50% of that observed in immune competent mice. Treatment with CPX‐351, at a Cyt:Daun dose of 5 units/kg (5 mg/kg Cyt + 2.2 mg/kg Daun), was very effective and yielded objective responses in all evaluable leukemia‐bearing mice in both leukemia models. In the ALL‐4 model, treatment with CPX‐351 induced a median event‐free survival (EFS) of 31.0 days (6.8 days for control), which corresponded to a leukemia growth delay (LGD) of 24.2 days (p Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A135.