Collagen like peptide bioconjugates for targeted drug delivery applications
Date
2016
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Collagen is the most abundant protein in mammals, and there has been long-standing interest in understanding and controlling collagen assembly in the design of new materials. Collagen-like peptides (CLP), also known as collagen-mimetic peptides (CMP), are short synthetic peptides which mimic the triple helical conformation of native collagens. In the past few decades, collagen like peptides and their conjugated hybrids have become a new class of biomaterials that possesses unique structures and properties. In addition to traditional applications of using CLPs to decipher the role of different amino acid residues and tripeptide motifs in stabilizing the collagen triple helix and mimicking collagen fibril formation, with the introduction of specific interactions including electrostatic interactions, π-π stacking interaction and metal-ligand coordination, a variety of artificial collagen-like peptides with well-defined sequences have been designed to create higher order assemblies with specific biological functions. The CLPs have also been widely used as bioactive domains or physical cross-linkers to fabricate hydrogels, which have shown potential to improve cell adhesion, proliferation and ECM macromolecule production. Despite this widespread use, the utilization of CLPs as domains in stimuli responsive bioconjugates represents a relatively new area for the development of functional polymeric materials. ☐ In this work, a new class of thermoresponsive diblock conjugates, containing collagen-like peptides and a thermoresponsive polymer, namely poly(diethylene glycol methyl ether methacrylate) (PDEGMEMA), is introduced. The CLP domain maintains its triple helix conformation after conjugation with the polymer. The engineered LCST of these conjugates has enabled temperature-induced assembly under aqueous conditions, at physiologically relevant temperatures, into well-defined vesicles with diameters of approximately 50–200 nm. The formation of nanostructures was driven by the coil/globule conformational transition of the PDEGMEMA building block above its LCST with stabilization of the nanostructures by the hydrophilic CLP. To the best of our knowledge, this is the first report on such assembled nanostructures from collagen-like peptide containing copolymers. Due to the strong propensity for CLPs to bind to natural collagen via strand invasion processes, these nanosized vesicles may be used as drug carriers for targeted delivery. ☐ In addition to synthetic polymers, the collagen like peptide is then conjugated with a thermoresponsive elastin-like peptide (ELP). The resulting ELP-CLP diblock conjugates show a remarkable reduction in the inverse transition temperature of the ELP domain, attributed to the anchoring effect of the CLP triple helix. The lower transition temperature of the conjugate enables facile formation of well-defined vesicles at physiological temperature and the unexpected resolubilization of the vesicles at elevated temperatures upon unfolding of the CLP domain. Given the ability of CLPs to modify collagens, this work provides not only a simple and versatile avenue for controlling the inverse transition behavior of elastin-like peptides, but also suggest future opportunities for these thermoresponsive nanostructures in biologically relevant environments. ☐ In the last section, the potential of using the ELP-CLP nanoparticles as drug delivery vehicles for targeting collagen containing matrices is evaluated. A sustained release of clinically relevant amount of encapsulated modelled drug is achieved within three weeks, followed by a thermally controlled burst release. As expected, the ELP-CLP nanoparticles show strong retention on collagen substrate, via specific binding through collagen triple helix hybridization. Additionally, cell viability and proliferation studies using fibroblasts and chondrocytes suggest the nanoparticles are non-cytotoxic. Additionally, almost no TNF-α expression from macrophages is observed, suggesting that the nanoparticles do not initiate inflammatory response. Endowed with specific collagen binding, controlled thermoresponsiveness, excellent cytocompatibility, and non-immune responsiveness, we believe the ELP-CLP nanoparticles are promising candidates as drug delivery vehicles for targeting collagen containing matrices. ☐ Considering the critical role of collagens in extracellular matrix and the unique ability of the CLP to target native collagens, our work offers significant opportunities for the design of collagen-like peptides and their bioconjugates for targeted application in the biomedical arena.