Targeting glioma cells in vitro with ascorbate-conjugated pharmaceutical nanocarriers.

6-Ascorbate-PEG-1,2-distearoyl-sn-glycero-3-phosphoethanolamine (6-ascorbate-PEG-PE) was synthesized according to a two-step procedure: (1) activation of ascorbic acid with bromine, and (2) synthesis of 6-ascorbate-PEG-PE by reacting 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino (poly(ethylene glycol))-2000] with an excess of 6-Br-ascorbic acid. The 6-ascorbate-PEG-PE was recovered by precipitation in diethyl ether and purified by gel permeation chromatography. The analysis of the product by 1H NMR and UV-vis spectroscopy confirmed the identity of the conjugate. Liposomes and PEG-PE-based lipid-core micelles were prepared by thin film hydration technique incorporating 6-ascorbate-PEG-PE as targeting moiety. The targeting properties of the ascorbate-decorated nanosystems were tested by fluorescence-activated cell sorting (FACS) analysis and fluorescent microscopy on a panel of tumor cell lines preliminary selected for their ability to express the SVCT2 ascorbate transporter. Cell lines had been selected on the basis of the immunological properties assessed by FACS, which showed that two glioma cell lines, C6 and F98, and fibroblasts NIH/3T3 express plasma membrane-associated SVCT2 transporter for reduced ascorbic acid. Ascorbate-decorated pharmaceutical nanocarriers were endowed with selective targeting properties toward the SVCT2 transporter expressed in glioma cell models. This study shows that SVCT2 transporter for ascorbic acid expressed both in peculiar epithelial cells of the choroid plexus responsible for the filtering of vitamin C into the central nervous system (CNS) and, in some brain tumor cell lines, can be conceivably exploited as a potential target for delivery of drug-loaded pharmaceutical nanocarriers to the brain.