Pharmacokinetics, drug metabolism, and tissue distribution of CPX-351 in animals.

CPX-351, a liposomal encapsulation of cytarabine and daunorubicin at a synergistic 5:1 molar ratio, is indicated for adults with newly diagnosed, therapy-related acute myeloid leukemia or acute myeloid leukemia with myelodysplasia-related changes. In preclinical species, this article demonstrated (1) similar release of cytarabine and daunorubicin by CPX-351 in plasma; (2) similar patterns of metabolism of cytarabine and daunorubicin following administration of CPX-351 versus non-liposomal cytarabine/daunorubicin combination; (3) prolonged tissue exposure to CPX-351; (4) dramatically different tissue distribution of cytarabine and daunorubicin following administration of CPX-351 versus non-liposomal combination (tissue:plasma ratios generally <1 versus >1, respectively); and (5) dramatically lower unbound plasma and tissue concentrations of cytarabine and daunorubicin following administration of CPX-351 versus non-liposomal combination. Together, these results provide insight into the safety profile of CPX-351, as well as mechanisms that drive the improved efficacy observed for CPX-351 versus the conventional 7 + 3 cytarabine/daunorubicin regimen in clinical studies.