Particle Elasticity and Tumor Cell Uptake

Nanoparticles (NPs) are increasingly applied for the delivery of therapeutics for diseases such as cancer. Previously, the intrinsic properties of NPs, for instance particle size and shape, have known to influence NP’s biological interactions during the delivery process. Recently, particle rigidity has also been reported to affect NPs’ bio-distribution and interactions with healthy and cancerous cells. However, the role of NP rigidity in their interactions with brain glioma tumor cells has not been explored before and may present an opportunity to improve the NP-based treatments for brain cancer.<br/><br/>Here we investigate the role of NP mechanics on their uptake by glioma cells, using nano-liposomes with varying elasticity levels. To prepare liposomes with varying elasticity, we applied a method that we have recently developed [1]. Briefly, we rehydrated a dried lipid film of DOPC/PEG-PE with either 0, 10, or 30% poly(ethylene glycol) diacrylate (PEGDA) solutions and 1 v/v% photo-initiator. 10 and 30% of PEGDA polymer were selected due to the significant increase of the elastic modulus of the hydrogel (0.1 to 4 MPa) examined by the compression test. The resultant mixtures of the lipids, PEGDA solution, and photo-initiator were extruded through a porous membrane with a pore size of 100 nm, followed by UV exposure to photo-crosslink the PEGDA polymers inside the liposomes. A fluorescent molecule, naphtho 2,3-a pyrene (NAP), was incorporated into the membrane of the liposomes to enable their tracking. These liposomes with cores of 0, 10, and 30% PEGDA gel were used as soft, intermediate, and hard NPs, respectively. We then investigated the cellular uptake of those gel-filled nano-liposomes by human glioblastoma cells, U87, <i>in vitro</i>. The qualitative and quantitative cellular uptake investigations were carried out by confocal imaging and flow cytometry (FACS analysis), respectively.<br/><br/>Our results showed that the inclusion of PEGDA hydrogel in liposomal lumen did not have an impact on their size distribution as all three liposome groups (with 0, 10, and 30% PEGDA) had a similar particle size within 114 to119 nm with PDI &lt;0.14 based on dynamic light scattering data. Similarly, all these liposomes had similar zeta potential (-1.9 to -2.7 mV) further confirming their surface similarities. After a 6 hour incubation of different liposomes with U87 cells, confocal images showed that they were up-taken by cells and accumulated inside the cytoplasm. While FACS analysis revealed that there were no significant differences in uptake between liposomes with 10% and 30% gel core after 1- and 9-hour incubation periods, the liposomes with a PEGDA hydrogel core had a significantly higher uptake compared to the liposomes without a gel core. Specifically, liposomes with 10% and 30% gel cores had about 2.5 and 2 times higher uptake by U87 compared to liposomes with no gel after 9 hours incubation. This result suggests that U87 are more partial to uptake NPs with a supporting structural core than their softer counterparts. This study may facilitate the development and improvement of delivery carriers for brain cancer treatment in the future.<br/><br/><b>References:</b><br/>[1] F. Mirab, et al., <i>2019 41st Annual International Conference of the IEEE (EMBC),</i> 2019, pp. 3935-3938.