Stress Tolerance of Antibody-Poly(Amino Acid) Complexes for Improving the Stability of High Concentration Antibody Formulations

Development of a drying method for proteins based on protein-hyaluronic acid precipitation

This study aims to develop a new method to dry proteins based on protein-hyaluronic acid (HA) precipitation and apply the precipitation-redissolution technique to develop highly concentrated protein formulations. Lysozyme was used as a model protein and HA with various molecular weights (MW) were investigated. Under low ionic strength, low-MW HA (e.g., MW: around 5 K) did not induce lysozyme precipitation. Conversely, high-MW HA (e.g., MW: approximately from 40 K to 1.5 M) precipitated more than 90 % of lysozyme. The dried lysozyme-HA precipitates had moisture levels between 4 % and 5 %. The lysozyme-HA precipitates could be redissolved using PBS (pH 7.4, ionic strength: ∼ 163 mM). The viscosity of the reconstituted solution was dependent on HA MW, e.g., 4 cP for HA40K, and 155 cP for HA1.5 M, suggesting low-MW HA might be a proper excipient for highly concentrated solution formulations for subcutaneous/intraocular injection and high-MW HA may fit for other applications. The tertiary structure of lysozyme after the precipitation-redissolution steps had no significant difference from that of the original lysozyme as confirmed by fluorescence spectroscopy. The denaturation temperature of lysozyme after the precipitation-redissolution steps and that of the original lysozyme were close, indicating they possessed similar thermal stability. The accelerated stability study revealed that lysozyme stored in the dry precipitates was more physically stable than that in the buffer solution. Overall, this new drying technique is suitable for drying proteins and exhibits several benefits such as minimum energy consumption, cost effectiveness, high production yield, and mild processing conditions. In addition, the precipitation-redissolution technique proposed in this study can potentially be used to develop highly concentrated formulations, especially for proteins experiencing poor stability in the liquid state.

Reversible protein complexes as a promising avenue for the development of high concentration formulations of biologics

High concentration formulations have become an important pre-requisite in the development of biological drugs, particularly in the case of subcutaneous administration where limited injection volume negatively affects the administered dose. In this study, we propose to develop high concentration formulations of biologics using a reversible protein-polyelectrolyte complex (RPC) approach. First, the versatility of RPC was assessed using different complexing agents and formats of therapeutic proteins, to define the optimal conditions for complexation and dissociation of the complex. The stability of the protein was investigated before and after complexation, as well as upon a 4-week storage period at various temperatures. Subsequently, two approaches were selected to develop high concentration RPC formulations: first, using up-concentrated RPC suspensions in aqueous buffers, and second, by generating spray-dried RPC and further resuspension in non-aqueous solvents. Results showed that the RPC concept is applicable to a wide range of therapeutic protein formats and the complexation-dissociation process did not affect the stability of the proteins. High concentration formulations up to 200 mg/mL could be achieved by up-concentrating RPC suspensions in aqueous buffers and RPC suspensions in non-aqueous solvents were concentrated up to 250 mg/mL. Although optimization is needed, our data suggests that RPC may be a promising avenue to achieve high concentration formulations of biologics for subcutaneous administration.

Polyelectrolyte Influence on Beta-Hairpin Peptide Stability: A Simulation Study

Assemblies of proteins and charged macromolecules (polyelectrolytes) find important applications as pharmaceutical formulations, biocatalysts, and cell-contacting substrates. A key question is how the polymer component influences the structure and function of the protein. The present paper addresses the influence of charged polymers on the thermal stability of two model beta-hairpin-forming peptides through an all-atom, replica exchange molecular dynamics simulation. The (negatively charged) peptides consist of the terminal 16 amino acids of the B1 domain of Protein G (GB1) and a variant with three of the GB1 residues substituted with tryptophan (Tryptophan Zipper 4, or TZ4). A (cationic) lysine polymer is seen to thermally stabilize TZ4 and destabilize GB1, while a (also cationic) chitosan polymer slightly stabilizes GB1 but has essentially no effect on TZ4. Free energy profiles reveal folded and unfolded conformations to be separated by kinetic barriers generally acting in the direction of the thermodynamically favored state. Through application of an Ising-like statistical mechanical model, a mechanism is proposed based on competition between (indirect) entropic stabilization of folded versus unfolded states and (direct) competition for hydrogen-bonding and hydrophobic interactions. These findings have important implications to the design of polyelectrolyte-based materials for biomedical and biotechnological applications.

Fluorescence enables high throughput screening of polyelectrolyte–protein binding affinities

Förster resonance energy transfer (FRET) in combination with high throughput controlled radical polymerisation allows quick identification of polymers that can bind strongly to enzymes such as glucose oxidase.

Solubility Parameters of Amino Acids on Liquid-Liquid Phase Separation and Aggregation of Proteins

The solution properties of amino acids determine the folding, aggregation, and liquid–liquid phase separation (LLPS) behaviors of proteins. Various indices of amino acids, such as solubility, hydropathy, and conformational parameter, describe the behaviors of protein folding and solubility both in vitro and in vivo. However, understanding the propensity of LLPS and aggregation is difficult due to the multiple interactions among different amino acids. Here, the solubilities of aromatic amino acids (SAs) were investigated in solution containing 20 types of amino acids as amino acid solvents. The parameters of SAs in amino acid solvents (PSASs) were varied and dependent on the type of the solvent. Specifically, Tyr and Trp had the highest positive values while Glu and Asp had the lowest. The PSAS values represent soluble and insoluble interactions, which collectively are the driving force underlying the formation of droplets and aggregates. Interestingly, the PSAS of a soluble solvent reflected the affinity between amino acids and aromatic rings, while that of an insoluble solvent reflected the affinity between amino acids and water. These findings suggest that the PSAS can distinguish amino acids that contribute to droplet and aggregate formation, and provide a deeper understanding of LLPS and aggregation of proteins.

Glass-like protein condensate for the long-term storage of proteins

Long-term storage of proteins at ambient temperature is required for applications in pharmaceutics and biotechnology. Lyophilization is a versatile approach for stabilizing proteins at ambient temperature, although its freezing and drying processes negatively affect the protein structure. In this study, we show a glass-like protein condensate (GLPC) as a new method for protein stabilization at ambient temperature. Various protein types, including immunoglobulin G, gamma globulin, albumin, and chymotrypsin, formed a glassy state during ultracentrifugation and natural drying, while proteins that tend to crystalize, such as hen egg-white lysozyme, did not. The GLPCs were characterized by a transparent solid state, similar to a dry glass ball. Importantly, the GLPCs were dissolved easily in saline solution at a physiological concentration, thereby retaining their native structures and functions. The GLPCs preserved their native structures even after 1 year of incubation at ambient temperature. These results provide a framework for the development of protein preservation methods at ambient temperature other than lyophilization.

Hybrid chemoenzymatic heterogeneous catalyst prepared in one step from zeolite nanocrystals and enzyme-polyelectrolyte complexes

The combination of inorganic heterogeneous catalysts and enzymes, in so-called hybrid chemoenzymatic heterogeneous catalysts (HCEHCs), is an attractive strategy to effectively run chemoenzymatic reactions. Yet, the preparation of such bifunctional materials remains challenging because both the inorganic and the biological moieties must be integrated in the same solid, while preserving their intrinsic activity. Combining an enzyme and a zeolite, for example, is complicated because the pores of the zeolite are too small to accommodate the enzyme and a covalent anchorage on the surface is often ineffective. Herein, we developed a new pathway to prepare a nanostructured hybrid catalyst built from glucose oxidase and TS-1 zeolite. Such hybrid material can catalyse the in situ biocatalytic formation of H₂O₂, which is subsequently used by the zeolite to trigger the epoxidation of allylic alcohol. Starting from an enzymatic solution and a suspension of zeolite nanocrystals, the hybrid catalyst is obtained in one step, using a continuous spray drying method. While enzymes are expectedly unable to resist the conditions used in spray drying (temperature, shear stress, etc.), we leverage on the preparation of "enzyme-polyelectrolyte complexes" (EPCs) to increase the enzyme stability. Interestingly, the use of EPCs also prevents enzyme leaching and appears to stabilize the enzyme against pH changes. We show that the one-pot preparation by spray drying gives access to hybrid chemoenzymatic heterogeneous catalysts with unprecedented performance in the targeted chemoenzymatic reaction. The bifunctional catalyst performs much better than the two catalysts operating as separate entities. We anticipate that this strategy could be used as an adaptable method to prepare other types of multifunctional materials starting from a library of functional nanobuilding blocks and biomolecules.

Strategies in the delivery of Cas9 ribonucleoprotein for CRISPR/Cas9 genome editing

CRISPR/Cas9 genome editing has gained rapidly increasing attentions in recent years, however, the translation of this biotechnology into therapy has been hindered by efficient delivery of CRISPR/Cas9 materials into target cells. Direct delivery of CRISPR/Cas9 system as a ribonucleoprotein (RNP) complex consisting of Cas9 protein and single guide RNA (sgRNA) has emerged as a powerful and widespread method for genome editing due to its advantages of transient genome editing and reduced off-target effects. In this review, we summarized the current Cas9 RNP delivery systems including physical approaches and synthetic carriers. The mechanisms and beneficial roles of these strategies in intracellular Cas9 RNP delivery were reviewed. Examples in the development of stimuli-responsive and targeted carriers for RNP delivery are highlighted. Finally, the challenges of current Cas9 RNP delivery systems and perspectives in rational design of next generation materials for this promising field will be discussed.

Synthesis of Zwitterionic and Trehalose Polymers with Variable Degradation Rates and Stabilization of Insulin

Polymers that stabilize biomolecules are important as excipients in protein formulation. Herein, we describe a class of degradable polymers that have tunable degradation rates depending on the polymer backbone and can stabilize proteins to aggregation. Specifically, zwitterion- and trehalose-substituted polycaprolactone, polyvalerolactone, polycarbonate, and polylactide were prepared and characterized with regards to their hydrolytic degradation and ability to stabilize insulin to mechanical agitation during heat. Ring-opening polymerization (ROP) of allyl-substituted monomers was performed by using organocatalysis, resulting in well-defined alkene-substituted polymers with good control over molecular weight and dispersity. The polymers were then modified by using photocatalyzed thiol-ene reactions to install protein-stabilizing carboxybetaine and trehalose side chains. The resulting polymers were water-soluble and exhibited a wide range of half-lives, from 12 h to more than 3 months. The polymers maintained the ability to stabilize the therapeutic protein insulin from activity loss due to aggregation, demonstrating their potential as degradable excipients for protein formulation.

Protein-Polyelectrolyte Complexes and Micellar Assemblies

In this review, we highlight the recent progress in our understanding of the structure, properties and applications of protein-polyelectrolyte complexes in both bulk and micellar assemblies. Protein-polyelectrolyte complexes form the basis of the genetic code, enable facile protein purification, and have emerged as enterprising candidates for simulating protocellular environments and as efficient enzymatic bioreactors. Such complexes undergo self-assembly in bulk due to a combined influence of electrostatic interactions and entropy gains from counterion release. Diversifying the self-assembly by incorporation of block polyelectrolytes has further enabled fabrication of protein-polyelectrolyte complex micelles that are multifunctional carriers for therapeutic targeted delivery of proteins such as enzymes and antibodies. We discuss research efforts focused on the structure, properties and applications of protein-polyelectrolyte complexes in both bulk and micellar assemblies, along with the influences of amphoteric nature of proteins accompanying patchy distribution of charges leading to unique phenomena including multiple complexation windows and complexation on the wrong side of the isoelectric point.

Effect of additives on liquid droplet of protein-polyelectrolyte complex for high-concentration formulations

Liquid droplets of protein-polyelectrolyte complexes (PPCs) have been developed as a new candidate for stabilization and concentration of protein drugs. However, it remains unclear whether additives affect the precipitation and redissolution yields of PPCs. In the present study, we investigated the PPC formation of human immunoglobulin G (IgG) and poly-L-glutamic acid (polyE) in the presence of various additives that have diverse effects, such as protein stabilization. Alcohols, including ethanol, successfully increased the PPC precipitation yield to over 90%, and the PPCs formed were completely redissolved at physiological ionic strength. However, poly(ethylene glycol), sugars, and amino acids did not improve the precipitation and redissolution yields of PPCs over those observed when no additives were included. Circular dichroism spectrometry showed that the secondary structure of polyE as well as electrostatic interactions play important roles in increasing the PPC precipitation yield when ethanol is used as an additive. The maximum concentration of IgG reached 100 mg/ml with the use of ethanol, which was 15% higher efficiency of the protein yield after precipitation and redissolution than that in the absence of additives. Thus, the addition of a small amount of ethanol is effective for the concentration and stabilization of precipitated PPCs containing IgG formulations.

Liquid Droplet of Protein-Polyelectrolyte Complex for High-Concentration Formulations

The formulation of high-concentration protein solutions is a challenging issue for achieving subcutaneous administration. Previously, we developed a method of precipitation-redissolution using polyelectrolyte as a precipitant to produce protein solutions at high concentrations. However, the redissolution yield of proteins was insufficient. This study aims to optimize the solution conditions for practical applications by combining IgG and poly-l-(glutamic acid) (polyE). A systematic analysis of solution pH and polyE size conditions revealed that an acidic condition favors precipitation, whereas neutral pH values are more effective for the redissolution. We find that the optimal size for polyE ranged from 15,000 to 50,000. This slight modification in the procedure in comparison with previous studies increased the precipitation and redissolution yields to nearly 100%, without irreversible protein denaturation. The fully reversible IgG-polyE complex formed as a droplet structure, which is similar to a condensate of liquid-liquid phase separation. The droplet structure plays an indispensable role in the salt-induced, redissolved state, which is pertinent to the new application that takes advantage of the methods to produce highly concentrated protein solutions.

Viscosity Control of Protein Solution by Small Solutes: A Review

Viscosity of protein solution is one of the most troublesome issues for the high-concentration formulation of protein drugs. In this review, we summarize the practical methods that suppress the viscosity of protein solution using small molecular additives. The small amount of salts decreases the viscosity that results from electrostatic repulsion and attraction. The chaotrope suppresses the hydrophobic attraction and cluster formation, which can lower the solution viscosity. Arginine hydrochloride (ArgHCl) also suppresses the solution viscosity due to the hydrophobic and aromatic interactions between protein molecules. The small molecular additives are the simplest resolution of the high viscosity of protein solution as well as understanding of the primary cause in complex phenomena of protein interactions.

Substituted Polyesters by Thiol-Ene Modification: Rapid Diversification for Therapeutic Protein Stabilization

Many proteins, especially those used as therapeutics, are unstable to storage and shipping temperatures, leading to increased costs in research and industry. Therefore, the design and synthesis of novel stabilizers is an important area of investigation. Herein we report new degradable polymers that stabilize proteins to environmental stressors such as refrigeration and elevated temperature. Specifically, polycaprolactones with different pendant groups were synthesized and surveyed for their ability to stabilize an important therapeutic protein to storage and shipping conditions. Ring-opening polymerization (ROP) of an allyl-substituted caprolactone monomer was carried out using the organocatalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) to yield a well-defined, alkene-substituted degradable polymer, which was used as a common backbone to control for the degree of polymerization. Relevant side chains such as trehalose, lactose, glucose, carboxybetaine, and oligo(ethylene glycol) were installed via postpolymerization thiol-ene reactions. These degradable polymers were then employed as excipients for the stabilization of the therapeutic protein granulocyte colony-stimulating factor (G-CSF) against storage at 4 °C and shipping temperatures of 60 °C. The best stabilization was observed using the trehalose- and zwitterion- substituted polyesters. Both the trehalose- and carboxybetaine-substituted pCL were further investigated with regard to molecular weight dependence, and it was found that the molecular weight was minimally important for stabilization to refrigeration, but critical for G-CSF stabilization at elevated temperatures. Both high performing zwitterionic and trehalose polyesters were also degraded, and the polymers and degradation products were shown to be noncytotoxic. This work provides potential biocompatible polymers for stabilization of the important therapeutic G-CSF, as well as a general platform for the future discovery of new polymeric protein stabilizers.