Ligand spatial presentation and density play important roles in signaling pathways mediated by cell receptors and are critical parameters when designing protein-conjugated therapeutic nanoparticles. Here, we harness lipid phase separation to spatially control the protein presentation on lipid vesicles. We use this system to improve the cytotoxicity of TNF-related apoptosis inducing ligand (TRAIL), a therapeutic anticancer protein. Vesicles with phase-separated TRAIL presentation induce more cell death in Jurkat cancer cells than vesicles with uniformly presented TRAIL, and cytotoxicity is dependent on TRAIL density. We assess this relationship in other cancer cell lines and demonstrate that phase-separated vesicles with TRAIL only enhance cytotoxicity through one TRAIL receptor, DR5, while another TRAIL receptor, DR4, is less sensitive to TRAIL density. This work demonstrates a rapid and accessible method to control protein conjugation and density on vesicles that can be adopted to other nanoparticle systems to improve receptor signaling by nanoparticles.

The addition of both cell-targeting moieties and polyethylene glycol (PEG) to nanoparticle (NP) drug delivery systems is a standard approach to improve the biodistribution, specificity, and uptake of therapeutic cargo. The spatial presentation of these molecules affects avidity of the NP to target cells in part through an interplay between the local ligand concentration and the steric hindrance imposed by PEG molecules. Here, we show that lipid phase separation in nanoparticles can modulate liposome avidity by changing the proximity of PEG and targeting protein molecules on a nanoparticle surface. Using lipid-anchored nickel-nitrilotriacetic acid (Ni-NTA) as a model ligand, we demonstrate that the attachment of lipid anchored Ni-NTA and PEG molecules to distinct lipid domains in nanoparticles can enhance liposome binding to cancer cells by increasing ligand clustering and reducing steric hindrance. We then use this technique to enhance the binding of RGD-modified liposomes, which can bind to integrins overexpressed on many cancer cells. These results demonstrate the potential of lipid phase separation to modulate the spatial presentation of targeting and shielding molecules on lipid nanocarriers, offering a powerful tool to enhance the efficacy of NP drug delivery systems.

The addition of both cell-targeting moieties and polyethylene glycol (PEG) to nanoparticle (NP) drug delivery systems is a standard approach to improve the biodistribution, specificity, and uptake of therapeutic cargo. The spatial presentation of these molecules affects avidity of the NP to target cells in part through an interplay between the local ligand concentration and the steric hindrance imposed by PEG molecules. Here, we show that lipid phase separation in nanoparticles can modulate liposome avidity by changing the proximity of PEG and targeting protein molecules on a nanoparticle surface. Using lipid-anchored nickelnitrilotriacetic acid (Ni-NTA) as a model ligand, we demonstrate that the attachment of lipid anchored Ni-NTA and PEG molecules to distinct lipid domains in nanoparticles can enhance liposome binding to cancer cells by increasing ligand clustering and reducing steric hindrance. We then use this technique to enhance the binding of RGD-modified liposomes, which can bind to integrins overexpressed on many cancer cells. These results demonstrate the potential of lipid phase separation to modulate the spatial presentation of targeting and shielding molecules on nanocarriers, offering a powerful tool to enhance the efficacy of NP drug delivery systems.

Ligand spatial presentation and density play important roles in many signaling pathways mediated by cell receptors and are critical parameters when designing protein-conjugated therapeutic nanoparticles. Currently, Janus particles are most often used to spatially control ligand conjugation, but the technological challenge of manufacturing Janus particles limits adoption for translational applications. Here, we demonstrate that lipid phase separation can be used to spatially control protein presentation onto lipid vesicles. We used this system to study the density dependence of TNF-related apoptosis inducing ligand (TRAIL), a model therapeutic protein that exhibits greater cytotoxicity to cancer cells when conjugated onto a vesicle surface than when administered as a soluble protein. Using assays for apoptosis and caspase activity, we show that phase separated TRAIL vesicles induced higher cytotoxicity to Jurkat cancer cells than uniformly-conjugated TRAIL vesicles, and enhanced cytotoxicity was dependent on the TRAIL domain density. We then assessed this relationship in other cancer cell lines and demonstrated that phase separated TRAIL vesicles only enhanced cytotoxicity through one TRAIL receptor, DR5, while another TRAIL receptor, DR4, was unaffected by the TRAIL density. These results indicate unique signaling requirements for each TRAIL receptor and how TRAIL therapy could be tailored depending on the relative levels of expression for cancer receptors of interest. Overall, this work demonstrates a readily adoptable method to control protein conjugation and density on bilayer vesicles that can be easily adopted to other therapeutic nanoparticle systems to improve receptor signaling of nanoparticles targeted to cancer and diseased cells.