Biomimetic Camouflage Imparts Cell-Like Functions to Synthetic Particles

The therapeutic efficacy of systemic drug delivery vehicles is limited by their ability to evade the mononuclear phagocyte system, preferentially localize to the target tissue, and negotiate past the endothelial barrier. In order to create a delivery vehicle capable of all these functions, we developed a biomimetic functionalization of synthetic particles using membranes isolated from leukocytes. This new generation of injectable carriers, named LeukoLike Vectors (LLV), were produced by self-assembly of purified cell membranes around the surface of nanoporous silicon particles (NPS). LLV camouflage prevented opsonization and leveraged self-recognition mechanisms to delay phagocytic uptake in vitro. LLV interaction with surface receptors expressed on inflamed endothelium increased LLV binding and transport across the monolayer while avoiding the lysosomal pathway. Furthermore, LLV appeared sufficiently stable in vivo to enhance particle circulation time and improve tumoritropic accumulation. This bio-hybrid system opens exciting opportunities for the improvement of systemic drug delivery vectors. Introduction Biophysical barriers within the body provide protection by regulating the trafficking, exchange, and clearance of organic and inorganic exogenous agents. The vasculature, for example, functions as a semipermeable compartment populated by cells responsible for identifying and capturing potential hazards . Systemically administered drugs and particles, upon entering the blood, are marked as foreign bodies by opsonization and subsequently sequestered by the mononuclear phagocyte system. Provided they are able to avoid clearance, systemic agents must preferentially localize at the target tissue and efficiently negotiate past the endothelial barrier . The encapsulation of free drug into particle-based delivery vehicles can prolong drug half-life, improve site-specific targeting, reduce side-effects, and enhance therapeutic indices without requiring alterations to drug chemistry . Instead, physical and chemical properties of the vehicles themselves are modulated to confer new capabilities in vivo 9, . Optimization of particle size 11, , shape , and surface charge , for example, enhance passive tumor targeting via a mechanism known as enhanced permeation and retention (EPR) . Particle surface modification with polyethylene glycol (PEG) improves the biodistribution of chemotherapeutics , whereas bioconjugation of active targeting molecules enhances cell-specific chemotherapy delivery 17, . More recently, efforts have focused on the development of multistage vectors that decouple each of these functions in vivo . Based around a NanoPorous Silicon (NPS) platform 18, , these particles can carry a variety of cargo, navigate through blood flow 21, , recognize and bind specific endothelial targets , and protect therapeutic cargo for enhanced efficacy 25 . Particle-based drug delivery vehicles have yet to reach their full therapeutic potential . Avoidance of particle opsinization and non-specific clearance remains a challenge : The use of PEG does not avoid cumulative uptake by the mononuclear phagocyte system , and in fact, PEGylated liposomal doxorubicin (DOXIL) is thought to activate the human complement system. Nevertheless, transient enhancements in particle circulation time increase the probability of tumoritropic particle accumulation 30, , yielding higher therapeutic indices in tumors with fenestrated endothelium. Given the complexity of mass transport in vascular compartment, it is not surprising that “biomimetic camouflage” strategies are gaining popularity 32, . Virus-based carriers , targeted protocells , and bio-nano hybrid systems 37 have been proposed as potential strategies for overcoming vascular barriers to drug delivery. Here we describe an approach to transfer bioactive cellular components to the surface of synthetic particles in order to confer unique functions not otherwise attainable through current bioconjugation techniques. This new generation of injectable carriers, named Leukolike Vectors (LLV), are produced by camouflaging NPS particles with cellular membranes isolated from freshly harvested leukocytes. Using a combination of in vitro and in vivo experiments, we show that LLV are able to avoid opsonization, delay uptake by the mononuclear phagocyte system, preferentially bind inflamed endothelium, and facilitate chemotherapeutics transport across the endothelium while eluding the lysosomal pathway.