Asialoglycoprotein receptor-targeted liposomes loaded with a norcantharimide derivative for hepatocyte-selective targeting
In order to overcome the shortcomings associated with the clinical application of norcantharidin (NCTD), including intense irritation and a short half-life, and to obtain a hepatocyte-selective liposome system with high encapsulation efficiency (EE) and low leakage, we synthesized a C14 alkyl chain norcantharimide derivative of NCTD (2-tetradecylhexahydro-1H-4,7-epoxyisoindole-1,3(2H)-dione, N-14NCTDA). Asialoglycoprotein receptor-targeted, galactosylated liposomes loaded with N-14NCTDA (GAL-Lipo) were prepared by the lipid film hydration method. GAL-Lipo with a satisfactory particle size of approximately 120 nm has a higher encapsulation efficiency of more than 98.0%, which is markedly increased compared with NCTD loaded liposomes (EE% = 47.6%). In addition, GAL-Lipo remained stable for at least 1 month at 4 °C. In cytotoxicity assays, GAL-Lipo demonstrated stronger cytotoxicity effects (IC50 = 24.58 μmol L−1) on Hep G2 cells than free N-14NCTDA (100 μmol/L) and conventional liposomes (Con-Lipo, 39.49 μmol/L) without the GAL modification. GAL-Lipo can continuously accumulate in Hep G2 cells and be internalized into cells via two pathways, namely caveolin-dependent endocytosis and clathrin-dependent asialoglycoprotein receptors (ASGP-R) mediated endocytosis and produces considerably more significant cellular apoptosis. The results of vivo toxicity studies showed that GAL-Lipo dramatically reduced renal toxicity. In addition, GAL-Lipo has a markedly improved pharmacokinetic profile in vivo and a longer circulation time (AUC = 6.700 ± 2.964 mg L−1 h, t1/2z = 1.347 ± 0.519 h) than Con-Lipo (AUC = 2.319 ± 0.121 mg L−1 h, t1/2z = 0.413 ± 0.238 h). In conclusion, N-14NCTDA with an ideal logP is a better alternative for the treatment of primary hepatic carcinoma. GAL-Lipo offers an attractive strategy to specifically target hepatocytes via caveolin-dependent and clathrin-dependent asialoglycoprotein receptor-mediated endocytosis resulting in higher anticancer activity and fewer side-effects.