Elevated Cellular Uptake of Succinimide- and Glucose-Modified Liposomes for Blood-Brain Barrier Transfer and Glioblastoma Therapy.

The uptake of four liposomal formulations was tested with the murine endothelial cell line bEnd.3 and the human glioblastoma cell line U-87 MG. All formulations were composed of DPPC, cholesterol, 5 mol% of mPEG (2000 Da, conjugated to DSPE), and the dye DiD. Three of the formulations had an additional PEG chain (nominally 5000 Da, conjugated to DSPE) with either succinimide (NHS), glucose (PEG-bound at C-6), or 4-aminophenyl ß-D-glucopyranoside (bound at C-1) as ligands at the distal end. Measuring the uptake kinetics at 1 h and 3 h for liposomal incubation concentrations of 100 µM, 500 µM, and 1000 µM, we calculated the liposomal uptake saturation S and the saturation half-time t1/2. We show that only succinimide has an elevated uptake in bEnd.3 cells, which makes it a very promising and so far largely unexplored candidate for BBB transfer and brain cancer therapies. Half-times are uniform at low concentrations but diversify for high concentrations for bEnd.3 cells. Contrary, U-87 MG cells show almost identical saturations for all three ligands, making a uniform uptake mechanism likely. Only mPEG liposomes stay at 60% of the saturation for ligand-coated liposomes. Half-times are diverse at low concentrations but unify at high concentrations for U-87 MG cells.

Increased Cellular Uptake of ApoE3- or c(RGD)-Modified Liposomes for Glioblastoma Therapy Depending on the Target Cells.

As effective treatment of glioblastoma is still an unmet need, targeted delivery systems for efficient treatment are of utmost interest. Therefore, in this paper, surface modifications with a small peptide c(RGD) or physiological protein (ApoE3) were investigated. Cellular uptake in murine endothelial cells (bEnd.3) and different glioma cells (human U-87 MG, rat F98) was tested to elucidate possible differences and to correlate the uptake to the receptor expression. Different liposomal formulations were measured at 1 and 3 h for three lipid incubation concentrations. We calculated the liposomal uptake saturation S and the saturation half-time t1/2. An up to 9.6-fold increased uptake for ApoE3-modified liposomes, primarily in tumor cells, was found. Contrarily, c(RGD) liposomes showed a stronger increase in uptake in endothelial cells (up to 40.5-fold). The uptake of modified liposomes revealed enormous differences in S and t1/2 when comparing different tumor cell lines. However, for ApoE3-modified liposomes, we proved comparable saturation values (~25,000) for F98 cells and U-87 MG cells despite a 6-fold lower expression of LRP1 in F98 cells and a 5-fold slower uptake rate. Our findings suggest that cellular uptake of surface-modified liposomes depends more on the target structure than the ligand type, with significant differences between cell types of different origins.