Abstract
Lipid nanoparticles are used widely as anticancer drug and gene delivery systems. Internalizing into the target cell is a prerequisite for the proper activity of many nanoparticulate drugs. We show here, that the lipid composition of a nanoparticle affects its ability to internalize into triple-negative breast cancer cells. The lipid headgroup had the greatest effect on enhancing cellular uptake compared to other segments of the molecule. Having a receptor-targeted headgroup induced the greatest increase in cellular uptake, followed by cationic amine headgroups, both being superior to neutral (zwitterion) phosphatidylcholine or to negatively-charged headgroups. The lipid tails also affected the magnitude of cellular uptake. Longer acyl chains facilitated greater liposomal cellular uptake compared to shorter tails, 18:0 > 16:0 > 14:0. When having the same lipid tail length, unsaturated lipids were superior to saturated ones, 18:1 > 18:0. Interestingly, liposomes composed of phospholipids having 14:0 or 12:0-carbon-long-tails, such as DMPC and DLPC, decreased cell viability in a concertation dependent manner, due to a destabilizing effect these lipids had on the cancer cell membrane. Contrarily, liposomes composed of phospholipids having longer carbon tails (16:0 and 18:0), such as DPPC and HSPC, enhanced cancer cell proliferation. This effect is attributed to the integration of the exogenous liposomal lipids into the cancer-cell membrane, supporting the proliferation process. Cholesterol is a common lipid additive in nanoscale formulations, rigidifying the membrane and stabilizing its structure. Liposomes composed of DMPC (14:0) showed increased cellular uptake when enriched with cholesterol, both by endocytosis and by fusion. Contrarily, the effect of cholesterol on HSPC (18:0) liposomal uptake was minimal. Furthermore, the concentration of nanoparticles in solution affected their cellular uptake. The higher the concentration of nanoparticles the greater the absolute number of nanoparticles taken up per cell. However, the efficiency of nanoparticle uptake, i.e. the percent of nanoparticles taken up by cells, decreased as the concentration of nanoparticles increased. This study demonstrates that tuning the lipid composition and concentration of nanoscale drug delivery systems can be leveraged to modulate their cellular uptake.