Liposomal-all-trans-retinoic acid in treatment of acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) characterized by the translocation t(15;17) is uniquely sensitive to the differentiation-inducing effects of all-trans-retinoic acid (ATRA). All-trans-retinoic acid therapy induces complete clinical remissions (CRs) in most of patients with APL. However, chronic daily oral administration of ATRA results in accelerated metabolism of ATRA, leading to a progressive decline in plasma drug concentrations. These lower drug levels are associated with relapses and resistance to oral ATRA in patients with APL; thus the use of ATRA as a single agent is precluded. Liposomal ATRA (Lipo-ATRA) was designed to maintain high and stable plasma concentrations and to further improve the outcome of the APL disease by overcoming the development of ATRA resistance. Liposomal ATRA was shown to circumvent accelerated drug metabolism in the liver of rats in an animal model. In a phase I clinical study, intravenous (i.v.) administration of lipo-ATRA was shown to produce a significantly better pharmacokinetic profile than oral ATRA (non-liposomal) and to maintain higher and sustained plasma drug concentrations, with a similar side effects. More importantly, lipo-ATRA as a single agent induces PCR-negative molecular remissions in a high proportion of newly diagnosed patients with APL and maintain remissions up to 15-17 months or longer. In this review, we discuss the pharmacological features of lipo-ATRA and the molecular remissions induced by lipo-ATRA in newly diagnosed patients with APL or patients previously treated with ATRA or chemotherapy, and the possible impact of lipo-ATRA on the outcome of APL.