Effect of Buffer Salts on Physical Stability of Lyophilized and Spray-Dried Protein Formulations Containing Bovine Serum Albumin and Trehalose

Effects of buffers on spray-freeze-dried/lyophilized high concentration protein formulations

Solid-state protein formulations are known to exhibit enhanced storage stability compared to their liquid dosage form counterparts. pH is one of the factors affecting the stability of protein formulations. The pH of protein formulations in the solution could be influenced by the buffer used, directly impacting their solid-state stability. During lyophilization, buffer components may interact with other formulation components present in the protein formulations, causing a pH shift. This study aimed to investigate the effects of phosphate buffer and amino acid buffers (such as histidine and/or arginine) on the physical properties and accelerated storage stability of spray freeze-dried or lyophilized protein formulations. A model protein, bovine serum albumin (BSA), was used to prepare high-concentration protein formulations. The formulations consisted of BSA, trehalose, and mannitol in an 80:15:5 ratio (w/w), respectively. Various buffers were utilized in the preparation of protein formulations, and the resultant solid formulations underwent screening via accelerated stability study using size exclusion chromatography (SEC). The combination of phosphate and arginine buffers resulted in increased monomer loss in the accelerated storage stability study. Additional characterizations, including solid-state Fourier transform infrared spectroscopy (ssFTIR) and powder X-ray diffraction (PXRD), were conducted. While these analyses did not definitively elucidate the mechanism behind the observed instability, their outcomes provide valuable insights for further investigation, highlighting the need for future research in this area.

Molecular mechanisms for stabilizing biologics in the solid state

Protein drugs exhibit challenges of biophysical and biochemical instability due to their structural complexity and rich dynamics. Solid-state biologics aim to enhance stability by increasing molecular rigidity within the formulation matrix, representing a primary category of drug products alongside sterile liquid formulations. Understanding the molecular mechanisms behind the stabilization and destabilization of protein drugs, influenced by formulation composition and drying processes, provides scientific rationale for drug product design. This review aims to elaborate on the two primary models of water-to-sugar substitution and matrix vitrification, respectively, via thermodynamic and kinetic stabilization. It offers an up-to-date review of experimental investigations into these hypotheses, specifically elucidating protein structure and protein-excipient interactions at the molecular level, molecular dynamics across a broad range of motion regimes, and microscopic attributes such as protein-sugar and protein-salt miscibility and microenvironmental acidity, in relevant liquid, frozen, and solid states, using advanced biophysical techniques for solid-state analysis. Moreover, we discuss how these mechanistic understandings facilitate the investigation and prediction of critical stability behaviors and enables the design of solid biological drug products.

Investigation of Protein Therapeutics in Frozen Conditions Using DNP MAS NMR: A Study on Pembrolizumab

The success of modern biopharmaceutical products depends on enhancing the stability of protein therapeutics. Freezing and thawing, which are common thermal stresses encountered throughout the lifecycle of drug substances, spanning protein production, formulation design, manufacturing, storage, and shipping, can impact this stability. Understanding the physicochemical and molecular behaviors of components in biological drug products at temperatures relevant to manufacturing and shipping is essential for assessing stability risks and determining appropriate storage conditions. This study focuses on the stability of high-concentration monoclonal antibody (mAb) pembrolizumab, the drug substance of Keytruda (Merck & Co., Inc., Rahway, NJ, United States), and its excipients in a frozen solution. By leveraging dynamic nuclear polarization (DNP), we achieve more than 100-fold signal enhancements in solid-state NMR (ssNMR), enabling efficient low-temperature (LT) analysis of pembrolizumab without isotopic enrichment. Through both ex situ and in situ ssNMR experiments conducted across a temperature range of 297 to 77 K, we provide insights into the stability of crystalline pembrolizumab under frozen conditions. Importantly, utilizing LT magic-angle spinning (MAS) probes allows us to study molecular dynamics in pembrolizumab from room temperature down to liquid nitrogen temperatures (<100 K). Our results demonstrate that valuable insights into protein conformation and dynamics, crystallinity, and the phase transformations of excipients during the freezing of the formulation matrix can be readily obtained for biological drug products. This study underscores the potential of LT-MAS ssNMR and DNP techniques for analyzing protein therapeutics and vaccines in frozen solutions.

Crucial aspects for maintaining rAAV stability

The storage of rAAV vectors for gene therapy applications is critical for ensuring a constant product quality and defined amount of medication at the time of administration. Therefore, we determined the influence of different storage conditions on the physicochemical and biological properties of rAAV8 and rAAV9 preparations. Particular attention was paid to short-term storage, which plays a crucial role in both the manufacturing process and in clinical applications. Additionally, we addressed the question, of viability of rAAV8 and rAAV9 when subjected to very low-temperature storage conditions (below -65 °C) or lyophilization. To determine the impact on rAAV vectors, various analyses were used, including the quantification of capsid and genome titers, as well as biopotency assessments, which are pivotal determinants in characterizing vector behavior and efficacy. Our data showed that freeze/thaw cycles hardly affected the functionality of rAAV9-aGAL vectors. In contrast, prolonged storage at room temperature for several days, resulted in a discernible decrease in biopotency despite consistent capsid and genome titers. When the storage temperature was further increased, the rAAV8-aGAL decay accelerated. For example, a short-term exposure of + 40 °C and more, led to a reduction in the physical viral titer and to an even faster decline in efficacy determined by biopotency. However, the addition of sucrose and sorbitol to the rAAV9-aGAL and rAAV9-GAA preparations reduced the temperature sensitivity of rAAV and improved its stability. Furthermore, exposure of rAAV9-aGAL to highly acidic conditions (pH 2.5) dramatically reduced its biopotency by 70% or more. Most interestingly, a long-term storage of rAAV9-aGAL and rAAV8-FVIII vectors over 12 and 36 months, respectively, demonstrated exceptional stability at storage temperatures below -65 °C. Also, lyophilization conserved functionality for at least 10 months. Our data showed how to maintain rAAV biopotency levels over the time without substantial loss. Storage at very low temperatures (below -65 °C) preserved its effectiveness over years. Overall, pH and temperature conditions during the manufacturing process, storage and clinical application are worth considering. Consistency in the rAAV capsid titer determination did not necessarily indicate the preservation of biopotency. In conclusion, our approach determined several options for maximizing rAAV stability.

In-situ biophysical characterization of high-concentration protein formulations using wNMR

High-concentration protein formulation is of paramount importance in patient-centric drug product development, but it also presents challenges due to the potential for enhanced aggregation and increased viscosity. The analysis of critical quality attributes often necessitates the transfer of samples from their primary containers together with sample dilution. Therefore, there is a demand for noninvasive, in situ biophysical methods to assess protein drug products directly in primary sterile containers, such as prefilled syringes, without dilution. In this study, we introduce a novel application of water proton nuclear magnetic resonance (wNMR) to evaluate the aggregation propensity of a high-concentration drug product, Dupixent® (dupilumab), under stress conditions. wNMR results demonstrate a concentration-dependent, reversible association of dupilumab in the commercial formulation, as well as irreversible aggregation when exposed to accelerated thermal stress, but gradually reversible aggregation when exposed to freeze and thaw cycles. Importantly, these results show a strong correlation with data obtained from established biophysical analytical tools widely used in the pharmaceutical industry. The application of wNMR represents a promising approach for in situ noninvasive analysis of high-concentration protein formulations directly in their primary containers, providing valuable insights for drug development and quality assessment.

Mechanism of Insoluble Aggregate Formation in a Reconstituted Solution of Spray-Dried Protein Powder

BACKGROUND

Spray-drying is considered a promising alternative drying method to lyophilization (freeze-drying) for therapeutic proteins. Particle counts in reconstituted solutions of dried solid dosage forms of biologic drug products are closely monitored to ensure product quality. We found that high levels of particles formed after reconstitution of protein powders that had been spray-dried under suboptimal conditions.

METHODS

Visible and subvisible particles were evaluated. Soluble proteins in solution before spray-drying and in the reconstituted solution of spray-dried powder were analyzed for their monomer content levels and melting temperatures. Insoluble particles were collected and analyzed by Fourier transform infrared microscopy (FTIR), and further analyzed with hydrogen-deuterium exchange (HDX).

RESULTS

Particles observed after reconstitution were shown not to be undissolved excipients. FTIR confirmed their identity as proteinaceous in nature. These particles were therefore considered to be insoluble protein aggregates, and HDX was applied to investigate the mechanism underlying aggregate formation. Heavy-chain complementarity-determining region 1 (CDR-1) in the aggregates showed significant protection by HDX, suggesting CDR-1 was critical for aggregate formation. In contrast, various regions became more conformationally dynamic globally, suggesting the aggregates have lost protein structural integrity and partially unfolded after spray-drying.

DISCUSSION

The spray-drying process could have disrupted the higher-order structure of proteins and exposed the hydrophobic residues in CDR-1 of the heavy chain, contributing to the formation of aggregate through hydrophobic interactions upon reconstitution of spray-dried powder. These results can contribute to efforts to design spray-dry resilient protein constructs and improve the robustness of the spray-drying process.

Radio Frequency - Assisted Ultrasonic Spray Freeze Drying for Pharmaceutical Protein Solids

This study examined physical stability of spray freeze dried (SFD) bovine serum albumin (BSA) solids produced using the radio frequency (RF)-assisted drying technique. BSA formulations were prepared with varying concentrations of trehalose and mannitol, using an excipient-free formulation as control. These formulations were produced using either traditional ultrasonic spray freeze drying (SFD) or RF-assisted ultrasonic spray freeze drying (RFSFD). The dried formulations were then characterized using Karl Fischer moisture content measurement, powder X-ray diffraction (PXRD), size exclusion chromatography (SEC), and solid-state hydrogen/deuterium exchange with mass spectrometry (ssHDX-MS). Moisture content did not have a good correlation with the physical stability of the formulations measured by SEC. ssHDX-MS metrics such as deconvoluted peak areas of the deuterated samples showed a satisfactory correlation (R2 = 0.914) with the SEC stability data. RFSFD improved the stability of formulations with 20 mg/ml of trehalose and no mannitol, and had similar stability with all other formulations as compared to SFD. This study demonstrated that RFSFD technique can significantly reduce the duration of primary drying cycle from 48.0 h to 27.5 h while maintaining or improving protein physical stability as compared to traditional lyophilization.

Molecular Mechanism of Antimicrobial Excipient-Induced Aggregation in Parenteral Formulations of Peptide Therapeutics

Antimicrobial preservatives are used as functional excipients in multidose formulations of biological therapeutics to destroy or inhibit the growth of microbial contaminants, which may be introduced by repeatedly administering doses. Antimicrobial agents can also induce the biophysical instability of proteins and peptides, which presents a challenge in optimizing the drug product formulation. Elucidating the structural basis for aggregation aids in understanding the underlying mechanism and can offer valuable knowledge and rationale for designing drug substances and drug products; however, this remains largely unexplored due to the lack of high-resolution characterization. In this work, we utilize solution nuclear magnetic resonance (NMR) as an advanced biophysical tool to study an acylated 31-residue peptide, acyl-peptide A, and its interaction with commonly used antimicrobial agents, benzyl alcohol and m-cresol. Our results suggest that acyl-peptide A forms soluble octamers in the aqueous solution, which tumble slowly due to an increased molecular weight as measured by diffusion ordered spectroscopy and ¹H relaxation measurement. The addition of benzyl alcohol does not induce aggregation of acyl-peptide A and has no chemical shift perturbation in ¹H-¹H NOESY spectra, suggesting no detectable interaction with the peptide. In contrast, the addition of 1% (w/v) m-cresol results in insoluble aggregates composed of 25% (w/w) peptides after a 24-hour incubation at room temperature as quantified by ¹H NMR. Interestingly, ¹H-¹³C heteronuclear single-quantum coherence and ¹H-¹H total correlation experiment spectroscopy have identified m-cresol and peptide interactions at specific residues, including Met, Lys, Glu, and Gln, suggesting that there may be a combination of hydrophobic, hydrogen bonding, and electrostatic interactions with m-cresol driving this phenomenon. These site-specific interactions have promoted the formation of higher-order oligomerization such as dimers and trimers of octamers, eventually resulting in insoluble aggregates. Our study has elucidated a structural basis of m-cresol-induced self-association that can inform the optimized design of drug substances and products. Moreover, it has demonstrated solution NMR as a high-resolution tool to investigate the structure and dynamics of biological drug products and provide an understanding of excipient-induced peptide and protein aggregation.