Nanoparticles based on natural, engineered or synthetic proteins and polypeptides for drug delivery applications

Stimuli-sensitive polymer prodrug nanocarriers by reversible-deactivation radical polymerization

Polymer prodrugs are based on the covalent linkage of therapeutic molecules to a polymer structure which avoids the problems and limitations commonly encountered with traditional drug-loaded nanocarriers in which drugs are just physically entrapped (e.g., burst release, poor drug loadings). In the past few years, reversible-deactivation radical polymerization (RDRP) techniques have been extensively used to design tailor-made polymer prodrug nanocarriers. This synthesis strategy has received a lot of attention due to the possibility of fine tuning their structural parameters (e.g., polymer nature and macromolecular characteristics, linker nature, physico-chemical properties, functionalization, etc.), to achieve optimized drug delivery and therapeutic efficacy. In particular, adjusting the nature of the drug-polymer linker has enabled the easy synthesis of stimuli-responsive polymer prodrugs for efficient spatiotemporal drug release. In this context, this review article will give an overview of the different stimuli-sensitive polymer prodrug structures designed by RDRP techniques, with a strong focus on the synthesis strategies, the macromolecular architectures and in particular the drug-polymer linker, which governs the drug release kinetics and eventually the therapeutic effect. Their biological evaluations will also be discussed.

Polypeptide-Based Systems: From Synthesis to Application in Drug Delivery

Synthetic polypeptides are biocompatible and biodegradable macromolecules whose composition and architecture can vary over a wide range. Their unique ability to form secondary structures, as well as different pathways of modification and biofunctionalization due to the diversity of amino acids, provide variation in the physicochemical and biological properties of polypeptide-containing materials. In this review article, we summarize the advances in the synthesis of polypeptides and their copolymers and the application of these systems for drug delivery in the form of (nano)particles or hydrogels. The issues, such as the diversity of polypeptide-containing (nano)particle types, the methods for their preparation and drug loading, as well as the influence of physicochemical characteristics on stability, degradability, cellular uptake, cytotoxicity, hemolysis, and immunogenicity of polypeptide-containing nanoparticles and their drug formulations, are comprehensively discussed. Finally, recent advances in the development of certain drug nanoformulations for peptides, proteins, gene delivery, cancer therapy, and antimicrobial and anti-inflammatory systems are summarized.

Dual drug loaded polypeptide delivery systems for cancer therapy

The present study was aimed to prepare and examine in vitro novel dual-drug loaded delivery systems. Biodegradable nanoparticles based on poly(L-glutamic acid-co-D-phenylalanine) were used as nanocarriers for encapsulation of two drugs from the paclitaxel, irinotecan, and doxorubicin series. The developed delivery systems were characterised with hydrodynamic diameters less than 300 nm (PDI < 0.3). High encapsulation efficiencies (≥75%) were achieved for all single- and dual-drug formulations. The release studies showed faster release at acidic pH, with the release rate decreasing over time. The release patterns of the co-encapsulated forms of substances differed from those of the separately encapsulated drugs, suggesting differences in drug-polymer interactions. The joint action of encapsulated drugs was analysed using the colon cancer cells, both for the dual-drug delivery sytems and a mixture of single-drug formulations. The encapsulated forms of the drug combinations demonstrated comparable efficacy to the free forms, with the encapsulation enhancing solubility of the hydrophobic drug paclitaxel.

Essential oil encapsulation by electrospinning and electrospraying using food proteins: A review

Proteins are excellent polymeric materials for encapsulating essential oils (EOs) by electrospinning and electrospraying to protect these compounds and form nanomaterials with active properties. Proteins can encapsulate bioactive molecules by several mechanisms, including surface activity, absorption and stabilization mechanisms, amphiphilic nature, film-forming capacity, foaming, emulsification, and gelation, due to interactions among their functional groups. However, proteins have some limitations in encapsulating EOs by the electrohydrodynamic process. Their properties can be improved by using auxiliary polymers, increasing their charges by adding ionic salts or polyelectrolytes, denaturing their structure by heat, and exposure to specific pH conditions and ionic strength. This review addresses the main proteins used in electrospinning/electrospraying techniques, production methods, their interactions with EOs, bioactive properties, and applications in food matrices. Multivariate analysis associated with bibliometrics of metadata extracted from studies in Web of Science using the keywords electrospinning and essential oil (EO) were used as the search strategy.

Aqueous synthesis and self-assembly of bioactive and thermo-responsive HA-b-ELP bioconjugates

The design of synthetic (bio)macromolecules that combine biocompatibility, self-assembly and bioactivity properties at the molecular level is an intense field of research for biomedical applications such as (nano)medicine. In this contribution, we have designed and synthesized a library of bioactive and thermo-responsive bioconjugates from elastin-like polypeptides (ELPs) and hyaluronic acid (HA) in order to access bioactive self-assembled nanoparticles. These were prepared by a simple synthetic and purification strategy, compatible with the requirements for biological applications and industrial scale-up. A series of 9 HA-b-ELP bioconjugates with different compositions and block lengths was synthesized under aqueous conditions by strain-promoted azide-alkyne cycloaddition (SPAAC), avoiding the use of catalysts, co-reactants and organic solvents, and isolated by a simple centrifugation step. An extensive physico-chemical study was then performed on the whole library of bioconjugates in an attempt to establish structure-property relationships. In particular, the determination of the critical conditions for thermally driven self-assembly was carried out upon temperature (CMT) and concentration (CMC) gradients, leading to a phase diagram for each of these bioconjugates. These parameters and the size of nanoparticles were found to depend on the chemical composition of the bioconjugates, namely on the respective size of individual blocks. Understanding the mechanism underlying this dependency is a real asset for designing more effective experiments: with key criteria defined (e.g. concentration, temperature, salinity, and biological target), the composition of the best candidates can be rationalized. In particular, four of the bioconjugates (HA_4.6k-ELPn80 or n100 and HA_24k-ELPn80 or n100) were found to self-assemble into well-defined spherical core-shell nanoparticles, with a negative surface charge due to the HA block exposed at the surface, a hydrodynamic diameter between 40 and 200 nm under physiological conditions and a good stability over time at 37 °C. We therefore propose here a versatile and simple design of smart, controllable, and bioactive nanoparticles that present different behaviors depending on the diblocks' composition.

Coacervates: recent developments as nanostructure delivery platforms for therapeutic biomolecules

Coacervation is a liquid-liquid phase separation that can occur in solutions of macromolecules through self-assembly or electrostatic interactions. Recently, coacervates composed of biocompatible macromolecules have been actively investigated as nanostructure platforms to encapsulate and deliver biomolecules such as proteins, RNAs, and DNAs. One particular advantage of coacervates is that they are derived from aqueous solutions, unlike other nanoparticle delivery systems that often require organic solvents. In addition, coacervates achieve high loading while maintaining the viability of the cargo material. Here, we review recent developments in the applications of coacervates and their limitations in the delivery of therapeutic biomolecules. Important factors for coacervation include molecular structures of the polyelectrolytes, mixing ratio, the concentration of polyelectrolytes, and reaction conditions such as ionic strength, pH, and temperature. Various compositions of coacervates have been shown to deliver biomolecules in vitro and in vivo with encouraging activities. However, major hurdles remain for the systemic route of administration other than topical or local delivery. The scale-up of manufacturing methods suitable for preclinical and clinical evaluations remains to be addressed. We conclude with a few research directions to overcome current challenges, which may lead to successful translation into the clinic.

Heterogeneous Synthetic Vesicles toward Artificial Cells: Engineering Structure and Composition of Membranes for Multimodal Functionalities

The desire to develop artificial cells to imitate living cells in synthetic vesicle platforms has continuously increased over the past few decades. In particular, heterogeneous synthetic vesicles made from two or more building blocks have attracted attention for artificial cell applications based on their multifunctional modules with asymmetric structures. In addition to the traditional liposomes or polymersomes, polypeptides and proteins have recently been highlighted as potential building blocks to construct artificial cells owing to their specific biological functionalities. Incorporating one or more functionally folded, globular protein into synthetic vesicles enables more cell-like functions mediated by proteins. This Review highlights the recent research about synthetic vesicles toward artificial cell models, from traditional synthetic vesicles to protein-assembled vesicles with asymmetric structures. We aim to provide fundamental and practical insights into applying knowledge on molecular self-assembly to the bottom-up construction of artificial cell platforms with heterogeneous building blocks.

Characteristics and Stability Assessment of Therapeutic Methionine γ-lyase-Loaded Polyionic Vesicles

Pyridoxal 5'-phosphate-dependent methionine γ-lyase from Citrobacter freundii (MGL, EC 4.4.1.11) is studied as an antitumor enzyme and in combination with substrates as an antibacterial agent in enzyme pro-drug therapy. For the possibility of in vivo trials, two mutant forms, C115H MGL and V358Y MGL, were encapsulated into polyionic vesicles (PICsomes). Five pairs of polymers with the number of polymer chain units 20, 50, 70, 120, and 160 were synthesized. The effect of polymer length-PEGylated poly-l-aspartic acid and poly-l-lysine-on the degree of MGL incorporation into PICsomes and their size was investigated. Encapsulation of proteins in PICsomes is a rather new technique. Our data demonstrated that the length of the polymers and, therefore, the ratio of the hydrophobic and hydrophilic fragments most likely should be selected individually for each protein to be encapsulated. The efficiency of encapsulation of MGL mutant forms into PICsomes was up to 11%. The hydrodynamic diameter and surface potential of hollow and MGL-loaded PICsomes were evaluated by the dynamic light scattering method. The size and morphology of the PICsomes were determined by atomic force microscopy. The most acceptable for further in vivo studies were PICsomes₂₀ with a size of 57-64 nm, PICsomes₇₀ of 50-90 nm, and PICsomes₁₂₀ of 100-105 nm. The analysis of the steady-state parameters has demonstrated that both mutant forms retained their catalytic properties inside the nanoparticles. The release study of the enzymes from PICsomes revealed that about 50% of the enzymes remained encapsulated in PICsomes₇₀ and PICsomes₁₂₀ after 24 h. Based on the data obtained, the most promising for in vivo studies are PICsomes₇₀ and PICsomes_120.

New Insights Toward Nanostructured Drug Delivery of Plant-Derived Polyphenol Compounds: Cancer Treatment and Gene Expression Profiles

The increasing prevalence of cancer has led to the expansion of traditional medicine objectives for developing novel drug delivery systems. A wide range of plant-derived polyphenol bioactive substances have been investigated in order to explore anti-cancer effects of these natural compounds and to promote effective treatment of cancer through apoptosis induction. In this regard, plant-derived polyphenol compounds including curcumin, silibinin, quercetin, and resveratrol have been the subject of intense interest for anti-cancer applications due to their ability in regulating apoptotic genes. However, some limitations of pure polyphenol compounds, such as poor bioavailability, short-term stability, low-cellular uptake, and insufficient solubility, have restricted their efficiency. Nanoscale formulations of bioactive agents have provided a novel platform to address these limitations. This paper reviews recent advances in nanoformulation approaches of polyphenolic drugs, and their effects on improving the delivery of chemotherapy agents to cancer cells.

Toward Activatable Collagen Mimics: Combining DEPSI "Switch" Defects and Template-Guided Self-Organization to Control Collagen Mimetic Peptides

Collagen mimetic peptides (CMPs), which imitate various structural or functional features of natural collagen, constitute advanced models illuminating the folding aspects of the collagen triple helix (CTH) motif. In this study, the CMPs of repeating Gly-Pro-Pro (GPP) triplets are tethered to an organic scaffold based on a tris(2-aminoethyl) amine (TREN) derivative (TREN(sucOH)₃ ). These three templated peptide strands are further expanded via native chemical ligation to increase the number of GPP triplets and lead to a TREN(sucGPPGPPG(Ψ)SPGPPCPP[GPP]₄ )₃ construct. The incorporation of an ester switch segment, G(Ψ)S, as a positional O-acyl isopeptide (DEPSI) defect into the peptide strands allows the pH-controlled acceleration of CTH formation. The strand assembly process is monitored by circular dichroism (CD) spectroscopy. The results of pH jump experiments and thermal denaturation studies provide new insights into the contributions of structural DEPSI defects to the template-guided self-assembly of the CTH motif. While the organic scaffold drives the CTH formation, the switch defects act as temporary opponents and slow down the folding. CD spectroscopy data confirm that the switch defects contribute to the formation of a more stable CTH motif by enhancing the structural dynamics at the early stage of the folding process.

Refining the Design of Diblock Elastin-Like Polypeptides for Self-Assembly into Nanoparticles

Diblock copolymers based-on elastin-like polypeptide (ELP) have the potential to undergo specific phase transitions when thermally stimulated. This ability is especially suitable to form carriers, micellar structures for instance, for delivering active cargo molecules. Here, we report the design and study of an ELP diblock library based on ELP-[M1V3-i]-[I-j]. First, ELP-[M1V3-i]-[I-j] (i = 20, 40, 60; j = 20, 90) that showed a similar self-assembly propensity (unimer-to-aggregate transition) as their related monoblocks ELP-[M1V3-i] and ELP-[I-j]. By selectively oxidizing methionines of ELP-[M1V3-i] within the different diblocks structures, we have been able to access a thermal phase transition with three distinct regimes (unimers, micelles, aggregates) characteristic of well-defined ELP diblocks.

Self-assembly of supramolecular chemoenzymatic poly-l-phenylalanine

The self-assembly behavior of chemoenzymatic high molecular weight (ca. 30 000 Da) poly-l-phenylalanine (ePLP) and the nano-morphologies thereof are investigated.