Systèmes vésiculaires colloïdaux pour la vectorisation de la 1-β-D-arabinofuranosylcytosine

Despite its rapid degradation and fast elimination in vivo, 1-β-D-arabinofuranosylcytosine (ara-C) is the main anticancer agent used in the treatment of acute myeloid leukemia (AML). The encapsulation of this drug into nanocarriers such as liposomes has been shown to improve its stability, pharmacokinetic profile and, consequently, the treatment efficacy. The purpose of this doctoral work was to develop two nanocarriers employing phospholipids, cholesterol and poly(ethylene glycol) (PEG) to encapsulate ara-C, with the ultimate goal of developing more efficient treatments for AML. The first formulation relied on Spherulites®, which are multilamellar vesicles possessing high entrapment yields due to their fabrication method. In a second part, pH-sensitive immunoliposomes were optimized to target specifically the leukemia cells and promote the release of the loaded ara-C at the desired intracellular site. Both formulations required a small diameter, stability in the presence of biological fluids and long circulation time properties when injected intravenously.   An optimized formulation of Spherulites® was developed. It was composed of Phospholipon 90G, Solutol HS15 and cholesterol. The vesicles (300 nm) were able to accommodate PEG-lipid derivatives at their surface without altering their concentric lamellar shape and their in vitro stability. The PEGylated Spherulites® were loaded with ara-C and injected intravenously into rats. The surface-modified vesicles exhibited longer circulation times compared to uncoated Spherulites®. However, most of the loaded-drug was cleared from the systemic circulation very rapidly, reflecting rapid leakage of ara-C from the vesicles.  The pH-sensitive immunoliposomes (~150 nm) were obtained by including a terminally-alkylated copolymer made of dioctadecyl, N-isopropylacrylamide (NIPAM) and methacrylic acid in the liposome bilayer. The whole monoclonal antibody anti-CD33 or its Fab’ fragment were grafted on liposomes to target leukemic cells. In vitro assays revealed that this formulation was really specific for the various CD33+ leukemic cell lines, stable in presence of blood proteins, and able to promote the intracellular release of an encapsulated fluorescent probe as well as ara-C. In vivo studies in naïve Balb/c and immunodeprimed (SCID) mice inoculated with HL60 cells confirmed that the anti-CD33 Fab’ targeted formulation possessed pharmacokinetic and biodistribution profiles similar to those of the non-targeted liposomes. The encapsulation of ara-C in this formulation improved substantially its circulation time after intravenous injection. However, although ara-C-loaded immunoliposomes were able to prolong the survival of leukemic mice compared to the free drug, the addition of pH-sensitive polymer did not add any benefit to the formulation.  Although these formulations require some optimization, the first part of this work pointed out that Spherulites® could be used to deliver anticancer agents provided that leakage is reduced in vivo. On the other hand, the data obtained with the targeted immunoliposomes suggest that these carriers could be beneficial in the treatment of AML.

Keyphrases: N-isopropylacrylamide, Anticorps monoclonal, ara-C, Acute myeloid leukemia, pH-sensitive immunoliposomes, Controlled release, Monoclonal antibody, CD33 receptor, Fab’ fragments, Pharmacokinetic, Spherulites®