Formulation Development for Hydrophobic Therapeutic Proteins

Diligent Design Enables Antibody-ASO Conjugates with Optimal Pharmacokinetic Properties

Antisense-oligonucleotides (ASOs) are a promising drug modality for the treatment of neurological disorders, but the currently established route of administration via intrathecal delivery is a major limitation to its broader clinical application. An attractive alternative is the conjugation of the ASO to an antibody that facilitates access to the central nervous system (CNS) after peripheral application and target engagement at the blood-brain barrier, followed by transcytosis. Here, we show that the diligent conjugate design of Brainshuttle-ASO conjugates is the key to generating promising delivery vehicles and thereby establishing design principles to create optimized molecules with drug-like properties. An innovative site-specific transglutaminase-based conjugation technology was chosen and optimized in a stepwise process to identify the best-suited conjugation site, tags, reaction conditions, and linker design. The overall conjugation performance was found to be specifically governed by the choice of buffer conditions and the structure of the linker. The combination of the peptide tags YRYRQ and RYESK was chosen, showing high conjugation fidelity. Elaborate conjugate analysis revealed that one leading differentiating factor was hydrophobicity. The increase of hydrophobicity by the ASO payload could be mitigated by the appropriate choice of conjugation site and the heavy chain position 297 proved to be the most optimal. Evaluating the properties of the linker suggested a short bicyclo[6.1.0]nonyne (BCN) unit as best suited with regards to conjugation performance and potency. Promising in vitro activity and in vivo pharmacokinetic behavior of optimized Brainshuttle-ASO conjugates, based on a microtubule-associated protein tau (MAPT) targeting oligonucleotide, suggest that such designs have the potential to serve as a blueprint for peripherally delivered ASO-based drugs for the CNS in the future.

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.

Heterogeneous and Surface-Catalyzed Amyloid Aggregation Monitored by Spatially Resolved Fluorescence and Single Molecule Microscopy

Amyloid aggregation is associated with many diseases and may also occur in therapeutic protein formulations. Addition of co-solutes is a key strategy to modulate the stability of proteins in pharmaceutical formulations and select inhibitors for drug design in the context of diseases. However, the heterogeneous nature of this multicomponent system in terms of structures and mechanisms poses a number of challenges for the analysis of the chemical reaction. Using insulin as protein system and polysorbate 80 as co-solute, we combine a spatially resolved fluorescence approach with single molecule microscopy and machine learning methods to kinetically disentangle the different contributions from multiple species within a single aggregation experiment. We link the presence of interfaces to the degree of heterogeneity of the aggregation kinetics and retrieve the rate constants and underlying mechanisms for single aggregation events. Importantly, we report that the mechanism of inhibition of the self-assembly process depends on the details of the growth pathways of otherwise macroscopically identical species. This information can only be accessed by the analysis of single aggregate events, suggesting our method as a general tool for a comprehensive physicochemical characterization of self-assembly reactions.

Accelerating therapeutic protein design

Protein structures provide for defined microenvironments that can support complex pharmacological functions, otherwise unachievable by small molecules. The advent of therapeutic proteins has thus greatly broadened the range of manageable disorders. Leveraging the knowledge and recent advances in de novo protein design methods has the prospect of revolutionizing how protein drugs are discovered and developed. This review lays out the main challenges facing therapeutic proteins discovery and development, and how present and future advancements of protein design can accelerate the protein drug pipelines.

Determination of Protein-Protein Interactions in a Mixture of Two Monoclonal Antibodies

The coformulation of monoclonal antibody (mAb) mixtures provides an attractive route to achieving therapeutic efficacy where the targeting of multiple epitopes is necessary. Controlling and predicting the behavior of such mixtures requires elucidating the molecular basis for the self- and cross-protein-protein interactions and how they depend on solution variables. While self-interactions are now beginning to be well understood, systematic studies of cross-interactions between mAbs in solution do not exist. Here, we have used static light scattering to measure the set of self- and cross-osmotic second virial coefficients in a solution containing a mixture of two mAbs, mAbA and mAbB, as a function of ionic strength and pH. mAbB exhibits strong association at a low ionic strength, which is attributed to an electrostatic attraction that is enhanced by the presence of a strong short-ranged attraction of nonelectrostatic origin. Under all solution conditions, the measured cross-interactions are intermediate self-interactions and follow similar patterns of behavior. There is a strong electrostatic attraction at higher pH values, reflecting the behavior of mAbB. Protein-protein interactions become more attractive with an increasing pH due to reducing the overall protein net charges, an effect that is attenuated with an increasing ionic strength due to the screening of electrostatic interactions. Under moderate ionic strength conditions, the reduced cross-virial coefficient, which reflects only the energetic contribution to protein-protein interactions, is given by a geometric average of the corresponding self-coefficients. We show the relationship can be rationalized using a patchy sphere model, where the interaction energy between sites i and j is given by the arithmetic mean of the i-i and j-j interactions. The geometric mean does not necessarily apply to all mAb mixtures and is expected to break down at a lower ionic strength due to the nonadditivity of electrostatic interactions.

Human Serum Albumin, a Suitable Candidate to Stabilize Freeze-Dried IgG in Combination with Trehalose: Central Composite Design

Freeze-dried immunoglobulin G (IgG) incorporating trehalose and human serum albumin (HSA) was statistically evaluated regarding the existence of synergism between additives on the stability profile. The levels of HSA (X₁) and trehalose (X₂) were independent variables. Aggregation following the process (Y₁), after 2 and 3 months at 40°C (Y₂) and (Y₃), respectively, along with the rate constant of aggregation (Y₄) were dependent variables. Aggregation and beta-sheet conformation were quantified through size-exclusion chromatography (SEC-HPLC) and Fourier transform infrared spectroscopy (FTIR). Central composite design (CCD) suggested the best formulation. The integrity and thermodynamic stability of optimized formulation were investigated through sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and differential scanning calorimetry (DSC). The calculated responses were Y₁, 0-0.90%; Y₂, 0.4-4.3%; Y₃, 2.10-13.46%; and Y₄, 0.16-0.69 1/month. The optimized formulation had 10 mg IgG, 86 mg trehalose, and 1 mg HSA with observed responses of Y₁, 0.01%; Y₂, 0.51%; Y₃, 3.08%; and Y₄, 0.33 1/month. The models were statistically well-fitted. The optimized formulation was amorphous during freeze-drying (FD), and no fragmentation was observed. Trehalose and HSA demonstrated statistical synergism. CCD was successfully employed to recommend the best ratio of stabilizers and achieve the maximum stabilization of IgG as a model freeze-dried antibody.

19F NMR as a Tool for Monitoring Individual Differentially Labeled Proteins in Complex Mixtures

The ability to monitor the behavior of individual proteins in complex mixtures has many potential uses, ranging from analysis of protein interactions in highly concentrated solutions, modeling biological fluids or the intracellular environment, to optimizing biopharmaceutical co-formulations. Differential labeling NMR approaches, which traditionally use ¹⁵N or ¹³C isotope incorporation during recombinant expression, are not always practical in cases when endogenous proteins are obtained from an organism, or where the expression system does not allow for efficient labeling, especially for larger proteins. This study proposes differential labeling of proteins by covalent attachment of ¹⁹F groups with distinct chemical shifts, giving each protein a unique spectral signature which can be monitored by ¹⁹F NMR without signal overlap, even in complex mixtures, and without any interfering signals from the buffer or other unlabeled components. Parameters, such as signal intensities, translational diffusion coefficients, and transverse relaxation rates, which report on the behavior of individual proteins in the mixture, can be recorded even for proteins as large as antibodies at a wide range of concentrations.

Quantitative Analysis of Peptide-Matrix Interactions in Lyophilized Solids Using Photolytic Labeling

Peptide-matrix interactions in lyophilized solids were explored using photolytic labeling with reversed phase high performance liquid chromatography (rp-HPLC) and mass spectrometric (MS) analysis. A model peptide (Ac-QELHKLQ-NHCH₃) derived from salmon calcitonin was first labeled with a heterobifunctional cross-linker NHS-diazirine (succinimidyl 4,4'-azipentanoate; SDA) at Lys5 in solution, with ∼100% conversion. The SDA labeled peptide was then formulated with the following excipients at a 1:400 molar ratio and lyophilized: sucrose, trehalose, mannitol, histidine, arginine, urea, and NaCl. The lyophilized samples and corresponding solution controls were exposed to UV at 365 nm to induce photolytic labeling, and the products were identified by MS and quantified with rp-HPLC or MS. Peptide-excipient adducts were detected in the lyophilized solids except the NaCl formulation. With the exception of the histidine formulation, peptide-excipient adducts were not detected in solution and the fractional conversion to peptide-water adducts in solution was significantly greater than in lyophilized solids, as expected. In lyophilized solids, the fractional conversion to peptide-water adducts was poorly correlated with bulk moisture content, suggesting that the local water content near the labeled lysine residue differs from the measured bulk average. In lyophilized solids, the fractional conversion to peptide-excipient adducts was assessed using MS extracted ion chromatograms (EIC); subject to the assumption of equal ionization efficiencies, the fractional conversion to excipient adducts varied with excipient type. The results demonstrate that the local environment near the lysine residue of the peptide in the lyophilized solids can be quantitatively probed with a photolytic labeling method.

Sensitivity of human pluripotent stem cells to insulin precipitation induced by peristaltic pump-based medium circulation: considerations on process development

Controlled large-scale production of human pluripotent stem cells (hPSCs) is indispensable for their envisioned clinical translation. Aiming at advanced process development in suspension culture, the sensitivity of hPSC media to continuous peristaltic pump-based circulation, a well-established technology extensively used in hydraulically-driven bioreactors, was investigated. Unexpectedly, conditioning of low protein media (i.e. E8 and TeSR-E8) in a peristaltic pump circuit induced severe viability loss of hPSCs cultured as aggregates in suspension. Optical, biochemical, and cytological analyses of the media revealed that the applied circulation mode resulted in the reduction of the growth hormone insulin by precipitation of micro-sized particles. Notably, in contrast to insulin depletion, individual withdrawal of other medium protein components (i.e. bFGF, TGFβ1 or transferrin) provoked minor reduction of hPSC viability, if any. Supplementation of the surfactant glycerol or the use of the insulin analogue Aspart did not overcome the issue of insulin precipitation. In contrast, the presence of bovine or human serum albumin (BSA or HSA, respectively) stabilized insulin rescuing its content, possibly by acting as molecular chaperone-like protein, ultimately supporting hPSC maintenance. This study highlights the potential and the requirement of media optimization for automated hPSC processing and has broad implications on media development and bioreactor-based technologies.

The Role of Protein Excipient in Driving Antibody Responses to Erythropoietin

Human serum albumin (HSA) is an excipient present in formulations of several recombinant protein products that are approved for clinical use. We investigated the relative contributions of HSA and HSA particles to the generation of antibody responses against recombinant human erythropoietin (rhEPO) and the excipient HSA itself. Protein samples were characterized before injection for quantities of monomeric proteins, soluble protein aggregates, and nano- and micron-sized particles. rhEPO, containing various concentrations of HSA particles, were injected three times a week for 8 weeks into mice. Hematocrits and the production of anti-rhEPO and anti-HSA antibodies were determined at various time points. Levels of antibodies against rhEPO in mice injected with HSA-containing rhEPO were higher than those in mice treated with HSA-free rhEPO. Mice injected with formulations that contained particles of HSA produced strong anti-HSA antibody responses; whereas these responses were greatly reduced when particle-free formulations were administered. In contrast, anti-rhEPO antibody responses were not affected by the presence of particles.

Unconventional microbial systems for the cost-efficient production of high-quality protein therapeutics

Both conventional and innovative biomedical approaches require cost-effective protein drugs with high therapeutic potency, improved bioavailability, biocompatibility, stability and pharmacokinetics. The growing longevity of the human population, the increasing incidence and prevalence of age-related diseases and the better comprehension of genetic-linked disorders prompt to develop natural and engineered drugs addressed to fulfill emerging therapeutic demands. Conventional microbial systems have been for long time exploited to produce biotherapeutics, competing with animal cells due to easier operation and lower process costs. However, both biological platforms exhibit important drawbacks (mainly associated to intracellular retention of the product, lack of post-translational modifications and conformational stresses), that cannot be overcome through further strain optimization merely due to physiological constraints. The metabolic diversity among microorganisms offers a spectrum of unconventional hosts, that, being able to bypass some of these weaknesses, are under progressive incorporation into production pipelines. In this review we describe the main biological traits and potentials of emerging bacterial, yeast, fungal and microalgae systems, by comparing selected leading species with well established conventional organisms with a long run in protein drug production.

Protein-excipient interactions: mechanisms and biophysical characterization applied to protein formulation development

The purpose of this review is to demonstrate the critical importance of understanding protein-excipient interactions as a key step in the rational design of formulations to stabilize and deliver protein-based therapeutic drugs and vaccines. Biophysical methods used to examine various molecular interactions between solutes and protein molecules are discussed with an emphasis on applications to pharmaceutical excipients in terms of their effects on protein stability. Key mechanisms of protein-excipient interactions such as electrostatic and cation-pi interactions, preferential hydration, dispersive forces, and hydrogen bonding are presented in the context of different physical states of the formulation such as frozen liquids, solutions, gels, freeze-dried solids and interfacial phenomenon. An overview of the different classes of pharmaceutical excipients used to formulate and stabilize protein therapeutic drugs is also presented along with the rationale for use in different dosage forms including practical pharmaceutical considerations. The utility of high throughput analytical methodologies to examine protein-excipient interactions is presented in terms of expanding formulation design space and accelerating experimental timelines.

Polymeric drug delivery systems for localized cancer chemotherapy

Cancer has become one of the most difficult health challenges of our time, accounting for millions of deaths yearly. Systemic chemotherapy is the most common therapeutic approach; however, considerable limitations exist including toxicities to healthy tissues and low achievable drug concentrations at tumor sites. More than 85% of human cancers are solid tumors, which can greatly benefit from localized delivery. This approach allows for high drug concentrations at the target site, lower systemic toxicity, and extended drug exposure which may be beneficial for cell cycle-specific drugs. Polymers have been widely considered in the development of localized delivery systems. This review focuses on both natural and synthetic biodegradable polymers that have been explored for localized chemotherapy, exploring their advantages, disadvantages, and clinical potential while citing examples of their use in pre-clinical development.

The molecular chaperone alpha-crystallin as an excipient in an insulin formulation

Purpose

To investigate insulin fibrillation under accelerated stress conditions in the presence of a novel excipient, the molecular chaperone α-crystallin, in comparison with common excipients.

Methods

To induce fibrillation, recombinant human insulin (0.58 mg ml⁻¹) formulations without excipient or with bovine α-crystallin (0.01–0.2 mg ml⁻¹), human serum albumin (1–5 mg ml⁻¹), sucrose (10–100 mg ml⁻¹) or polysorbate 80 (0.075–0.3 mg ml⁻¹) were subjected to stirring stress in a fluorescence well plate reader and formulation vials. Protein fibrillation was monitored by thioflavin T. The formulations were further characterized by size-exclusion chromatography, light obscuration, UV/Vis and circular dichroism spectroscopy.

Results

In both methods, insulin formed thioflavin T-binding species, most likely fibrils. Addition of α-crystallin in the well plate assay greatly improved insulin’s resistance to fibrillation, measured as a 6-fold increase in fibrillation lag time for the lowest and 26-fold for the highest concentration used, whereas all other excipients showed only a marginal increase in lag time. The stabilizing effect of α-crystallin was shown by all characterization techniques used.

Conclusions

The effect of α-crystallin on insulin’s physical stability outperforms that of commonly used excipients. α-Crystallin is proposed to bind specifically to pre-fibrillation species, thereby inhibiting fibrillation. This makes α-crystallin an interesting excipient for proteins with propensity to fibrillate.

Glycosylation of therapeutic proteins: an effective strategy to optimize efficacy

During their development and administration, protein-based drugs routinely display suboptimal therapeutic efficacies due to their poor physicochemical and pharmacological properties. These innate liabilities have driven the development of molecular strategies to improve the therapeutic behavior of protein drugs. Among the currently developed approaches, glycoengineering is one of the most promising, because it has been shown to simultaneously afford improvements in most of the parameters necessary for optimization of in vivo efficacy while allowing for targeting to the desired site of action. These include increased in vitro and in vivo molecular stability (due to reduced oxidation, cross-linking, pH-, chemical-, heating-, and freezing-induced unfolding/denaturation, precipitation, kinetic inactivation, and aggregation), as well as modulated pharmacodynamic responses (due to altered potencies from diminished in vitro enzymatic activities and altered receptor binding affinities) and improved pharmacokinetic profiles (due to altered absorption and distribution behaviors, longer circulation lifetimes, and decreased clearance rates). This article provides an account of the effects that glycosylation has on the therapeutic efficacy of protein drugs and describes the current understanding of the mechanisms by which glycosylation leads to such effects.

Monoclonal antibody interactions with micro- and nanoparticles: adsorption, aggregation, and accelerated stress studies

Therapeutic proteins are exposed to various wetted surfaces that could shed subvisible particles. In this work we measured the adsorption of a monoclonal antibody (mAb) to various microparticles, characterized the adsorbed mAb secondary structure, and determined the reversibility of adsorption. We also developed and used a front-face fluorescence quenching method to determine that the mAb tertiary structure was near-native when adsorbed to glass, cellulose, and silica. Initial adsorption to each of the materials tested was rapid. During incubation studies, exposure to the air-water interface was a significant cause of aggregation but acted independently of the effects of microparticles. Incubations with glass, cellulose, stainless steel, or Fe(2)O(3) microparticles gave very different results. Cellulose preferentially adsorbed aggregates from solution. Glass and Fe(2)O(3) adsorbed the mAb but did not cause aggregation. Adsorption to stainless steel microparticles was irreversible, and caused appearance of soluble aggregates upon incubation. The secondary structure of mAb adsorbed to glass and cellulose was near-native. We suggest that the protocol described in this work could be a useful preformulation stress screening tool to determine the sensitivity of a therapeutic protein to exposure to common surfaces encountered during processing and storage.

Effects of glycosylation on the stability of protein pharmaceuticals

In recent decades, protein-based therapeutics have substantially expanded the field of molecular pharmacology due to their outstanding potential for the treatment of disease. Unfortunately, protein pharmaceuticals display a series of intrinsic physical and chemical instability problems during their production, purification, storage, and delivery that can adversely impact their final therapeutic efficacies. This has prompted an intense search for generalized strategies to engineer the long-term stability of proteins during their pharmaceutical employment. Due to the well known effect that glycans have in increasing the overall stability of glycoproteins, rational manipulation of the glycosylation parameters through glycoengineering could become a promising approach to improve both the in vitro and in vivo stability of protein pharmaceuticals. The intent of this review is therefore to further the field of protein glycoengineering by increasing the general understanding of the mechanisms by which glycosylation improves the molecular stability of protein pharmaceuticals. This is achieved by presenting a survey of the different instabilities displayed by protein pharmaceuticals, by addressing which of these instabilities can be improved by glycosylation, and by discussing the possible mechanisms by which glycans induce these stabilization effects.