Biodegradation of poly(amino acid)s: Evaluation methods and structure-to-function relationships

Influence of Selected Factors on the Adsorption Layer Structure of Polyamino Acids and Their Block Copolymers at the Solid-Aqueous Solution Interface

The adsorption mechanism of different polymers containing ionic polyamino acids monomers in the chain structure at the solid-liquid interface was investigated. Initially, the influence of molecular weight and solution pH on simple polyamino acids (poly(L-aspartic acid) and poly(L-lysine) binding was determined. Considering the obtained dependencies, the polymer adsorption layer conformation was proposed in the systems containing block copolymers (both diblock and symmetrical triblock) consisting of polypeptide as well as poly(ethylene glycol) fragments. The presented studies focused on the application of two experimental methods. The polymer adsorption was carried out using the batch method and the adsorbate concentration was determined spectrophotometrically. Then, the turbidimetric measurements were taken. The analysis of the obtained results showed that the adsorption process of block copolymers depends on two factors. Firstly, the solution pH determines both the nature of the interactions of the copolymer structural units with the solid surface and the conformation of the polypeptide chains. The second parameter influencing the adsorption layer structure is the ratio of the lengths of both blocks. Introducing a short PEG fragment into the polymer main chain may improve the polymer adsorption properties by increasing the number of interactions with the adsorbent surface.

Noncovalent PEGylation of protein and peptide therapeutics

Clinical applications of protein therapeutics-an advanced generation of drugs characterized by high biological specificity-are rapidly expanding. However, their development is often impeded by unfavorable pharmacokinetic profiles and largely relies on the use of drug delivery systems to prolong their in vivo half-life and suppress undesirable immunogenicity. Although a commercially established PEGylation technology based on protein conjugation with poly(ethylene glycol) (PEG)-protective steric shield resolves some of the challenges, the search for alternatives continues. Noncovalent PEGylation, which mainly relies on multivalent (cooperative) interactions and high affinity (host-guest) complexes formed between protein and PEG offers a number of potential advantages. Among them are dynamic or reversible protection of the protein with minimal loss of biological activity, drastically lower manufacturing costs, "mix-and-match" formulations approaches, and expanded scope of PEGylation targets. While a great number of innovative chemical approaches have been proposed in recent years, the ability to effectively control the stability of noncovalently assembled protein-PEG complexes under physiological conditions presents a serious challenge for the commercial development of the technology. In an attempt to identify critical factors affecting pharmacological behavior of noncovalently linked complexes, this Review follows a hierarchical analysis of various experimental techniques and resulting supramolecular architectures. The importance of in vivo administration routes, degradation patterns of PEGylating agents, and a multitude of potential exchange reactions with constituents of physiological compartments are highlighted. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Amino acid derived biopolymers: Recent advances and biomedical applications

Over the past few years, amino acids (AA) have emerged as promising biomaterials for the synthesis of functional polymers. Owing to the diversity of functional groups in amino acids, various polymerization methods may be used to make a wide range of well-defined functional amino-acid/peptide-based optically active polymers with varying polymer lengths, compositions, and designs. When incorporated with chirality and self-assembly, they offer a wide range of applications and are particularly appealing in the field of drug delivery, tissue engineering, and biosensing. There are several classes of these polymers that include polyamides (PA), polyesters (PE), poly(ester-amide)s (PEA)s, polyurethanes (PU)s, poly(depsipeptide)s (PDP)s, etc. They offer the ability to control functionality, conjugation, crosslinking, stimuli responsiveness, and tuneable mechanical/thermal properties. In this review, we present the recent advancements in the synthesis strategies for obtaining these amino acid-derived bio-macromolecules, their self-assembly properties, and the wealth of prevalent applications.

Bio-Inspired Amphiphilic Block-Copolymers Based on Synthetic Glycopolymer and Poly(Amino Acid) as Potential Drug Delivery Systems

In this work, a method to prepare hybrid amphiphilic block copolymers consisting of biocompatible synthetic glycopolymer with non-degradable backbone and biodegradable poly(amino acid) (PAA) was developed. The glycopolymer, poly(2-deoxy-2-methacrylamido-D-glucose) (PMAG), was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Two methods for modifying the terminal dithiobenzoate-group of PMAG was investigated to obtain the macroinitiator bearing a primary aliphatic amino group, which is required for ring-opening polymerization of N-carboxyanhydrides of hydrophobic α-amino acids. The synthesized amphiphilic block copolymers were carefully analyzed using a set of different physico-chemical methods to establish their composition and molecular weight. The developed amphiphilic copolymers tended to self-assemble in nanoparticles of different morphology that depended on the nature of the hydrophobic amino acid present in the copolymer. The hydrodynamic diameter, morphology, and cytotoxicity of polymer particles based on PMAG-b-PAA were evaluated using dynamic light scattering (DLS) and transmission electron microscopy (TEM), as well as CellTiter-Blue (CTB) assay, respectively. The redox-responsive properties of nanoparticles were evaluated in the presence of glutathione taken at different concentrations. Moreover, the encapsulation of paclitaxel into PMAG-b-PAA particles and their cytotoxicity on human lung carcinoma cells (A549) and human breast adenocarcinoma cells (MCF-7) were studied.

Investigation on the controlled synthesis and post-modification of poly-[(N-2-hydroxyethyl)-aspartamide]-based polymers

We report the controlled synthesis of PHEA-based polymers and enhanced the post-modification reactivity by reducing the intramolecular hydrogen bonding.

Preparation, Characterization, and Biological Evaluation of Poly(Glutamic Acid)-b-Polyphenylalanine Polymersomes

Different types of amphiphilic macromolecular structures have been developed within recent decades to prepare the polymer particles considered as drug delivery systems. In the present research the series of amphiphilic block-copolymers containing poly(glutamatic acid) as hydrophilic, and polyphenylalanine as hydrophobic blocks was synthesized and characterized. Molecular weights for homo- and copolymers were determined by gel-permeation chromatography (GPC) and amino acid analysis, respectively. The copolymers obtained were applied for preparation of polymer particles. The specific morphology of prepared polymerosomes was proved using transmission electron microscopy (TEM). The influence on particle size of polymer concentration and pH used for self-assembly, as well as on the length of hydrophobic and hydrophilic blocks of applied copolymers, was studied by dynamic light scattering (DLS). Depending on different experimental conditions, the formation of nanoparticles with sizes from 60 to 350 nm was observed. The surface of polymersomes was modified with model protein (enzyme). No loss in biocatalytic activity was detected. Additionally, the process of encapsulation of model dyes was developed and the possibility of intracellular delivery of the dye-loaded nanoparticles was proved. Thus, the nanoparticles discussed can be considered for the creation of modern drug delivery systems.

Amphiphilic triblock copolymers of methoxy-poly(ethylene glycol)-b-poly(L-lactide)-b-poly(L-lysine) for enhancement of osteoblast attachment and growth

Amphiphilic triblock copolymers of methoxy-poly(ethylene glycol)-poly(L-lactide)-poly(L-lysine) (MPEG-b-PLLA-b-PLL) (Mn=8540-22 240) were synthesized through the ring-opening polymerization of Nepsilon-(Z)-lysine-N-carboxyanhydrides (N(epsilon)-(Z)-Lys-NCA) using MPEG-b-PLLA-NH2 as a macroinitiator. The triblock copolymers and diblock precursors were characterized by 1H NMR, ATR-FTIR, and GPC. The chain lengths of each block could be controlled by varying the feed ratios of the monomers. The surface properties of films of PLLA modified by blending with the triblock copolymers were investigated by XPS and AFM and demonstrated an enrichment of PLL blocks on the surface of the PLLA film. No cytotoxicity was detected on a range of modified PLLA films arising from the incorporation of the triblock copolymers. The triblock copolymers MPEG-b-PLLA-b-PLL showed better surface properties in promoting osteoblast adhesion and proliferation compared with pure PLLA and PLLA modified with MPEG-b-PLLA diblock copolymers. This study demonstrated that the triblock copolymers containing free amino groups, which self-segregate on the surface of biodegradable polyesters, have potential for applications in cell delivery and tissue engineering.