Solid Peptide Nanoparticles - Structural Characterization and Quantification of Cargo Encapsulation

Amphiphilic mPEG-Modified Oligo-Phenylalanine Nanoparticles Chemoenzymatically Synthesized via Papain

Amphiphilic mPEG-modified peptide nanoparticles were developed from oligo-phenylalanine (OPhe) nanoparticles (NPs) synthesized via papain. Tyndall effects indicate that OPhe NPs are amphiphobic. Addition of protein perturbants, sodium dodecyl sulfate (SDS), and urea, in the dispersion solution of OPhe NPs can significantly reduce the R _h,m value of NPs, from approximately 749.2 nm to about 200 nm. Therefore, the hydrophobic interaction and hydrogen bonding play major roles in maintaining the aggregation of OPhe NPs. Using the "grafting to" method, the methoxypolyethylene-modified OPhe NPs (mPEG-g-OPhe NPs) were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), ¹H NMR, electrospray ionization mass spectrometry (ESI-MS), and dynamic light scattering (DLS). The attenuated total reflectance (ATR) spectrum of OPhe NPs and mPEG-g-OPhe NPs demonstrate that the secondary structures of these NPs are mainly β-type. mPEG-g-OPhe NPs can self-aggregate into spherical micelles both in water and cyclohexane. Increasing the chain length of the mPEG moiety, the critical micellar concentrations of mPEG-g-OPhe NPs increased in water but decreased in cyclohexane. The light stability, thermal stability, hydrolysis stability, and encapsulation stability of curcumin were significantly promoted by encapsulation in the micelles formed by mPEG-g-OPhe NPs. The protective effects regularly varied with the variations in the mPEG chain length of mPEG-g-OPhe NPs.

Stimuli-Responsive Codelivery of Oligonucleotides and Drugs by Self-Assembled Peptide Nanoparticles

Ever more emerging combined treatments exploiting synergistic effects of drug combinations demand smart, responsive codelivery carriers to reveal their full potential. In this study, a multifunctional stimuli-responsive amphiphilic peptide was designed and synthesized to self-assemble into nanoparticles capable of co-bearing and -releasing hydrophobic drugs and antisense oligonucleotides for combined therapies. The rational design was based on a hydrophobic l-tryptophan-d-leucine repeating unit derived from a truncated sequence of gramicidin A (gT), to entrap hydrophobic cargo, which is combined with a hydrophilic moiety of histidines to provide electrostatic affinity to nucleotides. Stimuli-responsiveness was implemented by linking the hydrophobic and hydrophilic sequence through an artificial amino acid bearing a disulfide functional group (H3SSgT). Stimuli-responsive peptides self-assembled in spherical nanoparticles in sizes (100-200 nm) generally considered as preferable for drug delivery applications. Responsive peptide nanoparticles revealed notable nucleotide condensing abilities while maintaining the ability to load hydrophobic cargo. The disulfide cleavage site introduced in the peptide sequence induced responsiveness to physiological concentrations of reducing agent, serving to release the incorporated molecules. Furthermore, the peptide nanoparticles, singly loaded or coloaded with boron-dipyrromethene (BODIPY) and/or antisense oligonucleotides, were efficiently taken up by cells. Such amphiphilic peptides that led to noncytotoxic, reduction-responsive nanoparticles capable of codelivering hydrophobic and nucleic acid payloads simultaneously provide potential toward combined treatment strategies to exploit synergistic effects.

Electrospray loading and release of hydrophobic gramicidin in polyester microparticles

Gramicidin, a pentadecapeptide with well-known antimicrobial properties and recently identified therapeutic activity against different carcinomas, has been loaded by electrospraying in biodegradable and biocompatible poly(tetramethylene succinate).

Multicompartment micelle-structured peptide nanoparticles: a new biocompatible gene- and drug-delivery tool

Self-assembled, biodegradable materials that embed fragile, soluble, or insoluble compounds of therapeutic interest have potential use as drug delivery systems. The bead-forming peptide Ac-X3-gT can embed hydrophobic and hydrophilic payloads. Loaded peptide beads were internalized by human acute monocytic leukemia cell line (THP-1) macrophages, THP-1 monocytes, and hepatocellular carcinoma cells (Huh7). Furthermore, paclitaxel and doxorubicin coencapsulated in the peptide beads were delivered to THP-1 monocytes, causing a decrease in cell viability due to the activity of the anticancer drugs. In addition to the bead-forming peptide Ac-X3-gT, the use of a positively charged peptide analogue increased the RNA/DNA embedding efficiency to 99% by charge compensation and micellar complexation. Internalization of the resulting gene delivery systems by Huh7 cells led to specific gene silencing either by embedded small interfering RNA or by plasmid-encoding small hairpin RNA delivered in cells. The new class of purely peptidic material caused no measurable toxicity during in vitro experiments, thereby indicating potential use as a drug delivery system for multidrug delivery and gene therapy.

Delivery of membrane impermeable cargo into CHO cells by peptide nanoparticles targeted by a protein corona

Nanocarriers can fulfill essential functions in the stabilization and delivery of drugs: they prevent solubility issues and degradation, reduce side effects and modify the pharmacokinetic profile. However, particle based pharmaceuticals are complex and thus challenging to scale up. As formulation routines account for a large fraction of production costs, reducing complexity in the process of assembly, loading and functionalization of nanoparticles is desirable. Unlike existing approaches with similar goals, our protocol is designed to minimize usage of material and time. Prerequisite to this elegant one-step-procedure is the controlled phase-separation of a hydrophobic peptide to nanoparticles, inducing concurrent cargo-entrapment and association of a protein corona. We demonstrate the process by assembling Flutax-2 containing peptide nanoparticles functionalized with transferrin. Cellular uptake of the particles and cargo release depend on specific particle-cell interactions via transferrin receptor. These data indicate corona-mediated delivery of membrane impermeable cargo in vitro by a particulate delivery system entirely composed of amino acids.

From fibers to micelles using point-mutated amphiphilic peptides

Biocompatible, self-assembled nanostructures are attracting ever more attention, in particular in aqueous media for biomedical applications. Here, we present the successful, solid-phase peptide synthesis (SPPS) and characterization of short amino acid sequences with amphiphilic character with the aim of gaining insight into their self-assembled, supramolecular structures. The peptide design includes three parts: (a) a charged lysine part, (b) an acetylated lysine part, and (c) a constant hydrophobic rodlike helix, based on gramicidin A (gA). By stepwise replacement of free lysine (K) with acetylated lysine (X) we generated a library of a total of 10 peptides, Ac-X(8)-gA and K(m)X(8-m)-gA (m ranging from 0 to 8). By using point mutations, we adjusted the degree of acetylation (DA) and thus the overall amphiphilicity of the peptides, which led to a change in the secondary structure in the aqueous environment from a β-sheet to an α-helix. This transition generated a significant change in the morphology of the self-assembled structures from fibers to micelles. Two different regions were observed for the conformation of the hydrophilic part of the peptide: one region, a β-sheet-like secondary structure, inducing fiber formation (high DA), the other an α-helical-like secondary structure, generating micelle formation (moderate and low DA). The micellar structures depended on the degree of acetylation, which influenced their critical micelle concentration (cmc). These morphology regions were determined by a combination of circular dichroism, dynamic light scattering, surface tension, and transmission electron microscopy, which allowed us to correlate the generated supramolecular architectures with the fine changes obtained by means of the point mutation strategy.