Cancer cell uptake and distribution of oxanorbornane-based synthetic lipids and their prospects as novel drug delivery systems

Innovative developments in drug delivery technologies rely on our ability to tune the properties of supramolecular and macromolecular carriers through the chemical characteristics of individual components or building-blocks. In this regard, oxanorbornane-based synthetic lipids offer great promise as novel drug delivery systems (NDDS). As part of our efforts to develop them as vehicles for anticancer drugs, we have designed and synthesized a new derivative with a fluorescent tag (NBD) on the head group, and investigated its uptake and distribution in A549 cells. Addition of its DMSO solution to aqueous phase followed by extrusion generated solid lipid particles (SLPs), which were characterized by DLS, AFM and TEM techniques. Vesicles of this lipid in a co-assembled state with phosphatidylcholine (PC) and cholesterol were also prepared by thin-film hydration method. DLS data obtained from samples suspended in PBS showed that average size of SLPs is relatively smaller (∼56 nm) than that of vesicles (∼262 nm). The zeta potential of these particles was between −45 and −51 mV, which favor stable formulations. Confocal microscopic analysis of these aggregates after incubation with A549 cells showed that they get distributed predominantly in the cytosolic side. Concentration- and time-dependent flow cytometry analysis revealed that the uptake commences in the initial 5 min itself, and almost 90% of cells become NBD-positive in 2 h. There was an increase in uptake at higher concentration, indicative of passive diffusion. At the same time, a reduction in uptake at lower temperature (4 °C) compared to that at 37 °C pointed towards some contribution from active transport as well. Variation in uptake after pre-treatment with endocytosis inhibitors such as chlorpromazine and methyl-β-cyclodextrin suggested involvement of clathrin- and caveolae-mediated endocytic pathways. Cell viability and hemolytic assays further indicated that these nanocarriers have good safety profile.