RT Journal Article SR Electronic T1 Human Recombinant Apolipoprotein E-Enriched Liposomes Can Mimic Low-Density Lipoproteins as Carriers for the Site-Specific Delivery of Antitumor Agents JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 445 OP 455 DO 10.1124/mol.52.3.445 VO 52 IS 3 A1 Patrick C. N. Rensen A1 Raymond M. Schiffelers A1 A. Jenny Versluis A1 Martin K. Bijsterbosch A1 Marly E. M. J. Van Kuijk-Meuwissen A1 Theo J. C. Van Berkel YR 1997 UL http://molpharm.aspetjournals.org/content/52/3/445.abstract AB Progressive hypocholesterolemia is a feature associated with a number of cancers of different origin, and it is caused by the high expression of low-density lipoprotein (LDL) receptors (LDLrs) on many tumor cell types. Selective delivery of chemotherapeutics using LDL as a carrier has therefore been proposed, but the endogenous nature of LDL hampers its pharmaceutical application. In the current study, we explored the possibility of synthesizing liposomes that mimic LDL from commercially available lipids and proteins. Small unilamellar liposomes were created (28.9 ± 0.9 nm) and complexed with 5.8 ± 0.7 molecules of human recombinant apolipoprotein E (apoE). On intravenous injection into rats, the liposomes retained their aqueous core, structural integrity, and the majority of the preassociated apoE. [3H]Cholesteryl oleate-labeled apoE-enriched liposomes showed a relatively long serum half-life (>5 hr), and a low uptake by cells of the reticuloendothelial system was observed (<0.8% of the injected dose at 30 min after injection). Pretreatment of rats with 17α-ethinyl estradiol, which induces the expression of the LDLr on the liver and adrenals, led to a 2.5-fold accelerated serum clearance (t½ = 123 ± 10 min) and a selectively increased uptake of liposomes by the liver (2.0-fold) and adrenals (3.8-fold). The liver association of the liposomes was coupled to the lysosomal uptake route, similarly as for LDL. In vitro studies using B16 melanoma cells showed that the liposomes bound exclusively to the LDLr via their apoE moiety (90,000 liposomes/cell), with a 14-fold higher affinity (Kd = 0.77 ± 0.09 nm) than LDL itself. Because of their favorable properties, we anticipate that these apoE-enriched liposomes are advantageous compared with native LDL in the development of a selective LDLr-targeted antitumor therapy.