Nano-fenretinide demonstrates remarkable activity in acute promyeloid leukemia cells

Acute promyelocytic leukemia (APL) is characterized by rearrangements of the retinoic acid receptor, RARα, which makes all-trans retinoic acid (ATRA) highly effective in the treatment of this disease, inducing promyelocytes differentiation. Current therapy, based on ATRA in combination with arsenic trioxide, with or without chemotherapy, provides high rates of event-free survival and overall survival. However, a decline in the drug activity, due to increased ATRA metabolism and RARα mutations, is often observed over long-term treatments. Furthermore, dedifferentiation can occur providing relapse of the disease. In this study we evaluated fenretinide, a semisynthetic ATRA derivative, encapsulated in nanomicelles (nano-fenretinide) as an alternative treatment to ATRA in APL. Nano-fenretinide was prepared by fenretinide encapsulation in a self-assembling phospholipid mixture. Physico-chemical characterization was carried out by dinamic light scattering and spectrophotometry. The biological activity was evaluated by MTT assay, flow cytometry and confocal laser-scanning fluorescence microscopy. Nano-fenretinide induced apoptosis in acute promyelocytic leukemia cells (HL60) by an early increase of reactive oxygen species and a mitochondrial potential decrease. The fenretinide concentration that induced 90-100% decrease in cell viability was about 2.0 µM at 24 h, a concentration easily achievable in vivo when nano-fenretinide is administered by oral or intravenous route, as demonstrated in previous studies. Nano-fenretinide was effective, albeit at slightly higher concentrations, also in doxorubicin-resistant HL60 cells, while a comparison with TK6 lymphoblasts indicated a lack of toxicity on normal cells. The results indicate that nano-fenretinide can be considered an alternative therapy to ATRA in acute promyelocytic leukemia when decreased efficacy, resistance or recurrence of disease emerge after protracted treatments with ATRA.