Control of Peptide Aggregation and Fibrillation by Physical PEGylation

Impact of Confinement within a Hydrogel Mesh on Protein Thermodynamic Stability and Aggregation Kinetics

Though protein stability and aggregation have been well characterized in dilute solutions, the influence of a confining environment that exists (e.g., in intercellular and tissue spaces and therapeutic formulations) on the protein structure is largely unknown. Herein, the effects of confinement on stability and aggregation were explored for proteins of different sizes, stability, and hydrophobicity when encapsulated in hydrophilic poly(ethylene glycol) hydrogels. Denaturation curves show linear correlations between confinement size (mesh size) and thermodynamic stability, i.e., unfolding free energy and surface area accessible for solvation (represented by m-value). Two clusters of protein types are identifiable from these correlations; the clusters are defined by differences in protein stability, surface area, and aggregation propensity. Proteins with higher stability, larger surface area, and lower aggregation propensity (e.g., lysozyme and myoglobin) are less affected by the confinement imposed by mesh size than proteins with lower stability, smaller surface area, and higher aggregation propensity (e.g., growth hormone and aldehyde dehydrogenase). According to aggregation kinetics measured by thioflavin T fluorescence, confinement in smaller mesh sizes resulted in slower aggregation rates than that in larger mesh sizes. Compared to that in buffer solution, the confinement of a hydrophobic protein (e.g., human insulin) in the hydrogels accelerates protein aggregation. Conversely, the confinement of a hydrophilic protein (e.g., human amylin) in the hydrogels decelerates or prevents aggregation, with the rates of aggregation inversely proportional to mesh size. These findings provide new insights into protein conformational stability in confined microenvironments relevant to various cellular, tissue, and therapeutics scenarios.

Designing Formulation Strategies for Enhanced Stability of Therapeutic Peptides in Aqueous Solutions: A Review

Over the past few decades, there has been a tremendous increase in the utilization of therapeutic peptides. Therapeutic peptides are usually administered via the parenteral route, requiring an aqueous formulation. Unfortunately, peptides are often unstable in aqueous solutions, affecting stability and bioactivity. Although a stable and dry formulation for reconstitution might be designed, from a pharmaco-economic and practical convenience point of view, a peptide formulation in an aqueous liquid form is preferred. Designing formulation strategies that optimize peptide stability may improve bioavailability and increase therapeutic efficacy. This literature review provides an overview of various degradation pathways and formulation strategies to stabilize therapeutic peptides in aqueous solutions. First, we introduce the major peptide stability issues in liquid formulations and the degradation mechanisms. Then, we present a variety of known strategies to inhibit or slow down peptide degradation. Overall, the most practical approaches to peptide stabilization are pH optimization and selecting the appropriate type of buffer. Other practical strategies to reduce peptide degradation rates in solution are the application of co-solvency, air exclusion, viscosity enhancement, PEGylation, and using polyol excipients.

Retinal neuroprotection by controlled release of a VCP inhibitor from self-assembled nanoparticles

Mutations in rhodopsin lead to its misfolding resulting in autosomal dominant retinitis pigmentosa (adRP). Pharmacological inhibition of the ATP-driven chaperone valosin-containing protein (VCP), a molecular checkpoint for protein quality control, slows down retinal degeneration in animal models. However, poor water-solubility of VCP inhibitors poses a challenge to their clinical translation as intravitreal injections for retinal treatment. In order to enable the delivery of VCP inhibitors, we have developed and investigated two formulations for the VCP inhibitor ML240. Nanoformulations of ML240 were obtained by using amphiphilic polymers methoxy-poly (ethylene glycol)_5kDa-cholane (mPEG_5kDa-cholane) and methoxy-poly (ethylene glycol)_5kDa-cholesterol (mPEG_5kDa-cholesterol). Both formulations increased the water-solubility of ML240 by two orders of magnitude and prolonged the drug released over ten days. In addition, encapsulation of ML240 in mPEG_5kDa-cholane showed superior photoreceptor protection at lower drug concentrations, normalized rhodopsin localization, and alleviated inflammatory microglial responses in an ex vivo rat model of retinal degeneration. The study demonstrates the potential of VCP inhibitor nanoformulations to treat adRP, a pharmacologically orphan disease.

Glabrescione B delivery by self-assembling micelles efficiently inhibits tumor growth in preclinical models of Hedgehog-dependent medulloblastoma

Aberrant activation of the Hedgehog (Hh) pathway leads to the development of several tumors, including medulloblastoma (MB), the most common pediatric brain malignancy. Hh inhibitors acting on GLI1, the final effector of Hh signaling, offer a valuable opportunity to overcome the pitfalls of the existing therapies to treat Hh-driven cancers. In this study, the toxicity, delivery, biodistribution, and anticancer efficacy of Glabrescione B (GlaB), a selective GLI1 inhibitor, were investigated in preclinical models of Hh-dependent MB. To overcome its poor water solubility, GlaB was formulated with a self-assembling amphiphilic polymer forming micelles, called mPEG_5kDa-cholane. mPEG_5kDa-cholane/GlaB showed high drug loading and stability, low cytotoxicity, and long permanence in the bloodstream. We found that mPEG_5kDa-cholane efficiently enhanced the solubility of GlaB, thus avoiding the use of organic solvents. mPEG_5kDa-cholane/GlaB possesses favorable pharmacokinetics and negligible toxicity. Remarkably, GlaB encapsulated in mPEG_5kDa-cholane micelles was delivered through the blood-brain barrier and drastically inhibited tumor growth in both allograft and orthotopic models of Hh-dependent MB. Our findings reveal that mPEG_5kDa-cholane/GlaB is a good candidate for the treatment of Hh-driven tumors and provide relevant implications for the translation of GlaB into clinical practice.

Mechanistic Understanding From Molecular Dynamics Simulation in Pharmaceutical Research 1: Drug Delivery

In this review, we outline the growing role that molecular dynamics simulation is able to play as a design tool in drug delivery. We cover both the pharmaceutical and computational backgrounds, in a pedagogical fashion, as this review is designed to be equally accessible to pharmaceutical researchers interested in what this new computational tool is capable of and experts in molecular modeling who wish to pursue pharmaceutical applications as a context for their research. The field has become too broad for us to concisely describe all work that has been carried out; many comprehensive reviews on subtopics of this area are cited. We discuss the insight molecular dynamics modeling has provided in dissolution and solubility, however, the majority of the discussion is focused on nanomedicine: the development of nanoscale drug delivery vehicles. Here we focus on three areas where molecular dynamics modeling has had a particularly strong impact: (1) behavior in the bloodstream and protective polymer corona, (2) Drug loading and controlled release, and (3) Nanoparticle interaction with both model and biological membranes. We conclude with some thoughts on the role that molecular dynamics simulation can grow to play in the development of new drug delivery systems.

Williams G, Brocchini S, Awwad S. Injectables and Depots to Prolong Drug Action of Proteins and Peptides

Proteins and peptides have emerged in recent years to treat a wide range of multifaceted diseases such as cancer, diabetes and inflammation. The emergence of polypeptides has yielded advancements in the fields of biopharmaceutical production and formulation. Polypeptides often display poor pharmacokinetics, limited permeability across biological barriers, suboptimal biodistribution, and some proclivity for immunogenicity. Frequent administration of polypeptides is generally required to maintain adequate therapeutic levels, which can limit efficacy and compliance while increasing adverse reactions. Many strategies to increase the duration of action of therapeutic polypeptides have been described with many clinical products having been developed. This review describes approaches to optimise polypeptide delivery organised by the commonly used routes of administration. Future innovations in formulation may hold the key to the continued successful development of proteins and peptides with optimal clinical properties.

Physical PEGylation to Prevent Insulin Fibrillation

Insulin is one of the most marketed therapeutic proteins worldwide. However, its formulation suffers from fibrillation, which affects the long-term storage limiting the development of novel devices for sustained delivery including portable infusion devices. We have investigated the effect of physical PEGylation on structural and colloidal stability of insulin by using 2 PEGylating agents terminating with polycyclic hydrophobic moieties, cholane and cholesterol: mPEG_5kDa-cholane and mPEG_5kDa-cholesterol, respectively. Microcalorimetric analyses showed that mPEG_5kDa-cholane and mPEG_5kDa-cholesterol efficiently bind insulin with binding constants (Ka) of 3.98 10⁴ and 1.14 10⁵ M^-1, respectively. At room temperature, the 2 PEGylating agents yielded comparable structural stabilization of α-helix conformation and decreased dimerization of insulin. However, melting studies showed that mPEG_5kDa-cholesterol has superior stabilizing effect of the protein conformation than mPEG_5kDa-cholane. Furthermore, the fibrillation study showed that at a 1:1 and 1:5 insulin/polymer molar ratios, mPEG_5kDa-cholesterol delays insulin fibrillation 40% and 26% more efficiently, respectively, as compared to mPEG_5kDa-cholane which was confirmed by transmission electron microscopy imaging. Insulin was released from the mPEG_5kDa-cholane and mPEG_5kDa-cholesterol assemblies with comparable kinetic profiles. The physical PEGylation has a beneficial effect on the stabilization and shielding of the insulin structure into the monomeric form, which is not prone to fibrillation and aggregation.