Combinatorial Synthesis of and high-throughput protein release from polymer film and nanoparticle libraries

Polyanhydrides are a class of biomaterials with excellent biocompatibility and drug delivery capabilities. While they have been studied extensively with conventional one-sample-at-a-time synthesis techniques, a more recent high-throughput approach has been developed enabling the synthesis and testing of large libraries of polyanhydrides(1). This will facilitate more efficient optimization and design process of these biomaterials for drug and vaccine delivery applications. The method in this work describes the combinatorial synthesis of biodegradable polyanhydride film and nanoparticle libraries and the high-throughput detection of protein release from these libraries. In this robotically operated method (Figure 1), linear actuators and syringe pumps are controlled by LabVIEW, which enables a hands-free automated protocol, eliminating user error. Furthermore, this method enables the rapid fabrication of micro-scale polymer libraries, reducing the batch size while resulting in the creation of multivariant polymer systems. This combinatorial approach to polymer synthesis facilitates the synthesis of up to 15 different polymers in an equivalent amount of time it would take to synthesize one polymer conventionally. In addition, the combinatorial polymer library can be fabricated into blank or protein-loaded geometries including films or nanoparticles upon dissolution of the polymer library in a solvent and precipitation into a non-solvent (for nanoparticles) or by vacuum drying (for films). Upon loading a fluorochrome-conjugated protein into the polymer libraries, protein release kinetics can be assessed at high-throughput using a fluorescence-based detection method (Figures 2 and 3) as described previously(1). This combinatorial platform has been validated with conventional methods(2) and the polyanhydride film and nanoparticle libraries have been characterized with (1)H NMR and FTIR. The libraries have been screened for protein release kinetics, stability and antigenicity; in vitro cellular toxicity, cytokine production, surface marker expression, adhesion, proliferation and differentiation; and in vivo biodistribution and mucoadhesion(1-11). The combinatorial method developed herein enables high-throughput polymer synthesis and fabrication of protein-loaded nanoparticle and film libraries, which can, in turn, be screened in vitro and in vivo for optimization of biomaterial performance.

High-throughput synthesis of carbohydrates and functionalization of polyanhydride nanoparticles

Transdisciplinary approaches involving areas such as material design, nanotechnology, chemistry, and immunology have to be utilized to rationally design efficacious vaccines carriers. Nanoparticle-based platforms can prolong the persistence of vaccine antigens, which could improve vaccine immunogenicity. Several biodegradable polymers have been studied as vaccine delivery vehicles(1); in particular, polyanhydride particles have demonstrated the ability to provide sustained release of stable protein antigens and to activate antigen presenting cells and modulate immune responses. The molecular design of these vaccine carriers needs to integrate the rational selection of polymer properties as well as the incorporation of appropriate targeting agents. High throughput automated fabrication of targeting ligands and functionalized particles is a powerful tool that will enhance the ability to study a wide range of properties and will lead to the design of reproducible vaccine delivery devices. The addition of targeting ligands capable of being recognized by specific receptors on immune cells has been shown to modulate and tailor immune responses. C-type lectin receptors (CLRs) are pattern recognition receptors (PRRs) that recognize carbohydrates present on the surface of pathogens. The stimulation of immune cells via CLRs allows for enhanced internalization of antigen and subsequent presentation for further T cell activation. Therefore, carbohydrate molecules play an important role in the study of immune responses; however, the use of these biomolecules often suffers from the lack of availability of structurally well-defined and pure carbohydrates. An automation platform based on iterative solution-phase reactions can enable rapid and controlled synthesis of these synthetically challenging molecules using significantly lower building block quantities than traditional solid-phase methods. Herein we report a protocol for the automated solution-phase synthesis of oligosaccharides such as mannose-based targeting ligands with fluorous solid-phase extraction for intermediate purification. After development of automated methods to make the carbohydrate-based targeting agent, we describe methods for their attachment on the surface of polyanhydride nanoparticles employing an automated robotic set up operated by LabVIEW as previously described. Surface functionalization with carbohydrates has shown efficacy in targeting CLRs and increasing the throughput of the fabrication method to unearth the complexities associated with a multi-parametric system will be of great value (Figure 1a).

Harvesting murine alveolar macrophages and evaluating cellular activation induced by polyanhydride nanoparticles

Biodegradable nanoparticles have emerged as a versatile platform for the design and implementation of new intranasal vaccines against respiratory infectious diseases. Specifically, polyanhydride nanoparticles composed of the aliphatic sebacic acid (SA), the aromatic 1,6-bis(p-carboxyphenoxy)hexane (CPH), or the amphiphilic 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane (CPTEG) display unique bulk and surface erosion kinetics and can be exploited to slowly release functional biomolecules (e.g., protein antigens, immunoglobulins, etc.) in vivo. These nanoparticles also possess intrinsic adjuvant activity, making them an excellent choice for a vaccine delivery platform. In order to elucidate the mechanisms governing the activation of innate immunity following intranasal mucosal vaccination, one must evaluate the molecular and cellular responses of the antigen presenting cells (APCs) responsible for initiating immune responses. Dendritic cells are the principal APCs found in conducting airways, while alveolar macrophages (AMɸ) predominate in the lung parenchyma. AMɸ are highly efficient in clearing the lungs of microbial pathogens and cell debris. In addition, this cell type plays a valuable role in the transport of microbial antigens to the draining lymph nodes, which is an important first step in the initiation of an adaptive immune response. AMɸ also express elevated levels of innate pattern recognition and scavenger receptors, secrete pro-inflammatory mediators, and prime naïve T cells. A relatively pure population of AMɸ (e.g., greater than 80%) can easily be obtained via lung lavage for study in the laboratory. Resident AMɸ harvested from immune competent animals provide a representative phenotype of the macrophages that will encounter the particle-based vaccine in vivo. Herein, we describe the protocols used to harvest and culture AMɸ from mice and examine the activation phenotype of the macrophages following treatment with polyanhydride nanoparticles in vitro.

Tailoring the immune response by targeting C-type lectin receptors on alveolar macrophages using "pathogen-like" amphiphilic polyanhydride nanoparticles

C-type lectin receptors (CLRs) offer unique advantages for tailoring immune responses. Engagement of CLRs regulates antigen presenting cell (APC) activation and promotes delivery of antigens to specific intracellular compartments inside APCs for efficient processing and presentation. In these studies, we have designed an approach for targeted antigen delivery by decorating the surface of polyanhydride nanoparticles with specific carbohydrates to provide pathogen-like properties. Two conserved carbohydrate structures often found on the surface of respiratory pathogens, galactose and di-mannose, were used to functionalize the surface of polyanhydride nanoparticles and target CLRs on alveolar macrophages (AMϕ), a principle respiratory tract APC. Co-culture of functionalized nanoparticles with AMϕ significantly increased cell surface expression of MHC I and II, CD86, CD40 and the CLR CIRE over non-functionalized nanoparticles. Di-mannose and galactose functionalization also enhanced the expression of the macrophage mannose receptor (MMR) and the macrophage galactose lectin, respectively. This enhanced AMϕ activation phenotype was found to be dependent upon nanoparticle internalization. Functionalization also promoted increased AMϕ production of the pro-inflammatory cytokines IL-1β, IL-6 and TNF-α. Additional studies demonstrated the requirement of the MMR for the enhanced cellular uptake and activation provided by the di-mannose functionalized nanoparticles. Together, these data indicate that targeted engagement of MMR and other CLRs is a viable strategy for enhancing the intrinsic adjuvant properties of nanovaccine adjuvants and promoting robust pulmonary immunity.