Stability of Freeze-Dried Protein Formulations: Contributions of Ice Nucleation Temperature and Residence Time in the Freeze-Concentrate

Quantification of Residual Water in Pharmaceutical Frozen Solutions Via 1H Solid-State NMR

Freezing is essential for the stability of biological drug substances and products, particularly in frozen solution formulations and during the primary drying of lyophilized preparations. However, the unfrozen segment within the frozen matrix can alter solute concentration, ionic strength, and stabilizer crystallization, posing risks of increased biophysical instability and faster chemical degradation. While quantifying the unfrozen water content is important for designing stable biopharmaceuticals, there is a lack of analytical techniques for in situ quantitative measurements. In this study, we introduce a 1H magic angle spinning NMR technique to identify the freezing point (Tice) and quantify mobile water content in frozen biologics, applying this method to analyze the freezing of a commercial high-concentration drug product, Dupixent®. Our results demonstrate that water freezing is influenced by buffer salt properties and formulation composition, including the presence of sugar cryoprotectants and protein concentration. Additionally, the 1H chemical shift can probe pH in the unfrozen phase, potentially predicting the microenvironmental acidity in the frozen state. Our proposed methodology provides fresh insights into the analysis of freeze-concentrated solutions, enhancing our understanding of the stability of frozen and lyophilized biopharmaceuticals.

Impact of secondary ice in a frozen NaCl freeze-concentrated solution on the extent of methylene blue aggregation

Freezing and lyophilization have been utilized for decades to stabilize pharmaceutical and food products. Freezing a solution that contains dissolved salt and/or organic matter produces pure primary ice crystal grains separated by freeze-concentrated solutions (FCS). The microscopic size of the primary ice crystals depends on the cooling conditions and the concentration of the solutes. It is generally accepted that primary ice crystals size influences the rate of sublimation and also can impact physico-chemical behaviour of the species in the FCS. This article, however, presents a case where the secondary ice formed inside the FCS plays a critical role. We microscoped the structures of ice-cast FCS with an environmental scanning electron microscope and applied the aggregation-sensitive spectroscopic probe methylene blue to determine how the microstructure affects the molecular arrangement. We show that slow cooling at -50 °C produces large salt crystals with a small specific surface, resulting in a high degree of molecular aggregation within the FCS. In contrast, fast liquid nitrogen cooling yields an ultrafine structure of salt crystals having a large specific surface area and, therefore, inducing smaller aggregation. The study highlights a critical role of secondary ice in solute aggregation and introduces methylene blue as a molecular probe to investigate freezing behaviour of aqueous systems with crystalline solute.

Multiple approaches to reduce reconstitution time of lyophilized drug products with high protein concentration

Background

Lyophilized drug products with high protein concentration often perform long reconstitution time, which is inconvenient for clinical use. The objective of this work is to achieve short reconstitution time with multiple and combined strategies.

Methods

Here, we describe the following approaches that lead to reduction of reconstitution time, including adding annealing step, decreasing headspace pressure, decreasing protein concentration with reducing diluent volume, increasing high surface-area-to-height ratio of the cakes, increasing frequency of swirling and diluent temperature.

Results

Among these strategies, reducing diluent volume to achieve high protein concentration and reducing headspace pressure show markedly reduction of reconstitution time. Moreover, we propose combined strategies to mitigate the reconstitution time, at the same time, to achieve same target dose in clinics.

Conclusions

Therefore, this paper provides insights on the application of multiple strategies to accelerate the reconstitution of lyophilized drug products with high concentration, and facilitates their widespread clinical application.

Solid-State NMR Spectroscopy to Probe State and Phase Transitions in Frozen Solutions

Freezing is commonly encountered during the processing and storage of biomacromolecule products. Therefore, understanding the phase and state transitions in pharmaceutical frozen solutions is crucial for the rational development of biopharmaceuticals. Solid-state nuclear magnetic resonance spectroscopy (ssNMR) was used to analyze solutions containing sodium phosphate buffer, histidine, and trehalose. Upon freezing, crystallization of disodium phosphate hydrogen dodecahydrate (Na2HPO4·12H2O, DPDH) and histidine was identified using 31P and 13C ssNMR, respectively, and confirmed by synchrotron X-ray diffractometry (SXRD). Using histidine as a molecular probe and based on the chemical shifts of atoms of interest, the pH of the freeze concentrate was measured. The unfrozen water content in freeze concentrates was quantified by 1H single pulse experiments. 13C-insensitive nuclei enhancement by polarization transfer (INEPT) and cross-polarization (CP) experiments were used as orthogonal tools to characterize the solutes in a "mobile" and a more "solid-like" state in the freeze-concentrated solutions, respectively. The above analyses were applied to a commercial monoclonal antibody (mAb) formulation of dupilumab. This work further establishes ssNMR spectroscopy as a highly capable biophysical tool to investigate the attributes of biopharmaceuticals and thereby provide insights into process optimization and formulation development.

Investigating freezing-induced acidity changes in citrate buffers

Citrate buffers are commonly utilized in the field of biomolecule stabilization. We investigate their applicability in the frozen state within a range of initial pHs (2.5 to 8.0) and concentrations (0.02 to 0.60 M). Citrate buffer solutions subjected to various cooling and heating temperatures are examined in terms of the freezing-induced acidity changes, revealing that citrate buffers acidify upon cooling. The acidity is assessed with sulfonephthalein molecular probes frozen in the samples. Optical cryomicroscopy combined with differential scanning calorimetry was employed to investigate the causes of the observed acidity changes. The buffers partly crystallize and partly vitrify in the ice matrix; these processes influence the resulting pH and allow designing the optimal storage temperatures in the frozen state. The freezing-induced acidification apparently depends on the buffer concentration; at each pH, we suggest pertinent concentration, at which freezing causes minimal acidification.

Impact of Controlled Ice Nucleation and Lyoprotectants on Nanoparticle Stability during Freeze-drying and upon Storage

The freezing step of the lyophilization process can impact nanoparticle stability due to increased particle concentration in the freeze-concentrate. Controlled ice nucleation is a technique to achieve uniform ice crystal formation between vials in the same batch and has attracted increasing attention in pharmaceutical industry. We investigated the impact of controlled ice nucleation on three types of nanoparticles: solid lipid nanoparticles (SLNs), polymeric nanoparticles (PNs), and liposomes. Freezing conditions with different ice nucleation temperatures or freezing rates were employed for freeze-drying all formulations. Both in-process stability and storage stability up to 6 months of all formulations were assessed. Compared with spontaneous ice nucleation, controlled ice nucleation did not cause significant differences in residual moisture and particle size of freeze-dried nanoparticles. The residence time in the freeze-concentrate was a more critical factor influencing the stability of nanoparticles than the ice nucleation temperature. Liposomes freeze-dried with sucrose showed particle size increase during storage regardless of freezing conditions. By replacing sucrose with trehalose, or adding trehalose as a second lyoprotectant, both the physical and chemical stability of freeze-dried liposomes improved. Trehalose was a preferable lyoprotectant than sucrose to better maintain the long-term stability of freeze-dried nanoparticles at room temperature or 40°C.

Large-Scale Freeze-Thaw of Protein Solutions: Study of the Relative Contributions of Freeze-Concentration and Ice Surface Area on Stability of Lactate Dehydrogenase

Although bulk biotherapeutics are often frozen during fill finish and shipping to improve their stability, they can undergo degradation leading to losses in biological activity during sub-optimal freeze-thaw (F/T) process. Except for a few small-scale studies, the relative contribution of various F/T stresses to the instability of proteins has not been addressed. Thus, the objective of this study was to determine the individual contributions of freeze-concentration, ice surface area, and processing time to protein destabilization at a practical manufacturing-scale. Lactate dehydrogenase (LDH) in histidine buffer solutions were frozen in 1L containers. The frozen solutions were sliced into representative samples and assessed for the ice specific surface area (SSA) and extent of solutes freeze-concentration. For the first time to our knowledge, ice SSA was measured in dried samples from large-volume protein solutions using volumetric nitrogen adsorption isotherms. SSA measurements of the freeze-dried cakes showed that the ice surface area increased with an increase in the freezing rate. The ice SSA was also impacted by the position of the sample within the container: samples closer to the active cooled surface of the container exhibited smaller ice surface area compared to ice-cored samples from the center of the bottle. The freeze-concentrate composition was determined by measuring LDH concentration in the ice-cored samples. The protein distributed more evenly throughout the frozen solution after fast freezing which also correlated with enhanced protein stability compared to slow freezing conditions. Overall, better protein stability parameters correlated with higher ice SSA and lower freeze-concentration extent which was achieved at a faster freezing rate. Thus, extended residence time of the protein at the freeze-concentrated microenvironment is the critical destabilizing factor during freezing of LDH in bulk histidine buffer system. This study expands the understanding of the relative contributions of freezing stresses which, coupled with the knowledge of cryoprotection mechanisms, is imperative to the development of optimized processes and formulations aiming stable frozen protein solutions.

Recent advances and persistent challenges in the design of freeze-drying process for monoclonal antibodies

Monoclonal antibodies constitute nowadays an important therapeutic class and the number of approved molecules for clinical uses continues to increase, achieving considerable part of the therapeutic market. Yet, the stability in solution of these biopharmaceuticals is often low. That's why freeze-drying has been and remains the method of choice to obtain monoclonal antibodies in the solid state and to improve their stability. The design of freeze-drying process and its optimization are still topical subjects of interest and the pharmaceutical industry is regularly challenged by the requirements of quality, safety and efficiency set by the regulatory authorities. These requirements imply a deep understanding of each step of the freeze-drying process, developing techniques to control the critical parameters and to monitor the quality of the intermediate and the final product. In addition to quality issues, the optimization of the freeze-drying process in order to reduce the cycle length is of great interest since freeze-drying is known to be an energy-expensive and time consuming process. In this review, we will present the recent literature dealing with the freeze-drying of monoclonal antibodies and focus on the process parameters and strategies used to improve the stability of these molecules and to optimize the FD process.

Recent Advances in Freeze-Drying: Variables, Cycle Optimization, and Innovative Techniques

Freeze-drying (FD) is the most substantial drying technique utilized in the pharmaceutical and biopharmaceutical industries. It is a drying process where the solvent is crystallized at low temperatures and then sublimed from the solid-state directly into the vapor phase. Although FD possesses several merits as its suitability for thermolabile materials and its ability to produce dry products with high-quality attributes, it is a complex and prolonged process that requires optimization of both; process and formulation variables. This review attains to disassemble freeze-drying complications through a detailed explanation of the lyophilization concept, stages, the factors influencing the process including controlled ice nucleation, and the modified and innovative freeze-drying technologies proposed in recent years to overcome the shortage of traditional freeze-drying. In addition, this work points out the quality by design (QbD), critical quality of attributes (CQAs), limitations, and drawbacks of lyophilization.HighlightsLyophilization is a propitious drying technique for thermolabile materials.Optimizing the lyophilization cycle requires controlling the process parameters.The formulation excipients and the dispersion medium play crucial roles in designing a successful process.Numerous approaches were developed to ameliorate the lyophilization performance.

Molecular Dynamics Modeling Based Investigation of the Effect of Freezing Rate on Lysozyme Stability

PURPOSE

The stability of protein drug products frozen during fill finish operations is greatly affected by the freezing rate applied. Non-optimal freezing rates may lead to the denaturation of protein's complex macromolecular conformation. However, limited work has been done to address the effect of different freezing rates on protein stability at nano-scale level.

METHODS

The stability of a model protein, lysozyme, was investigated at atomic and molecular scale under varying freezing rates and moving ice-water interface. Ice seeding approach was adopted to initiate ice formation in this present simulation.

RESULTS

The faster freezing rate (11-12 K/490 ns) applied resulted in overall smaller ice fraction within the simulation box with a larger freeze-concentrated liquid (FCL) region. Consequently, the faster freezing rate better maintained protein stability with less secondary structure deviations, higher hydration level and structural compactness, and less fluctuations at individual residues than observed following slow (5-6 K/490 ns) and medium (7-8 K/490 ns) freezing rates. The present study also identified the residues near and within helices 3, 6, 7, and 8 dominate the structural instability of the lysozyme at 247 K freezing temperature.

CONCLUSIONS

For the first time, ice formation in therapeutic protein solution was studied "non-isothermally" at different freezing rates using molecular dynamics simulations. Thus, a good understanding of freezing rates on protein instability was revealed by applying the developed computational model.

Stochastic ice nucleation governs the freezing process of biopharmaceuticals in vials

Biopharmaceuticals commonly require freezing to ensure the stability of the active pharmaceutical ingredients (APIs). At commercial scale, freezing is typically carried out over the course of days in pallets comprising tens of thousands of vials. The selected process conditions have to ensure both complete freezing in all vials and a satisfactory manufacturing throughput. Current process design, however, is mainly experimental, since no mechanistic understanding of pallet freezing and its underlying phenomena has been achieved so far. Within this work, we derive a mechanistic modeling framework and compare the model predictions with engineering run data from the Janssen COVID-19 vaccine. The model qualitatively reproduced all observed trends and reveals that stochastic ice nucleation governs both process duration and batch heterogeneity. Knowledge on the ice nucleation kinetics of the formulation to be frozen thus is required to identify suitable freezing process conditions. The findings of this work pave the way towards a more rational design of pallet freezing, from which a plethora of frozen drug products may benefit. For this reason, we provide open source access to the model in the form of a python package (Deck et al., 2021).

IMPACT OF ANNEALING AND CONTROLLED ICE NUCLEATION ON PROPERTIES OF A LYOPHILIZED 50 MG/ML MAB FORMULATION

We compared "ice-fog" controlled ice nucleation at -6 °C to annealing at the same temperature for a 50 mg/mL monoclonal antibody formulation, using shelf-ramp freezing as a control. Cake structure, drying time, reconstitution time, specific surface area, calculated cake resistance and size exclusion chromatography were all compared. Controlled nucleation resulted in the fastest reconstitution, shortest primary drying, lowest calculated cake resistance, lowest specific surface area and highest moisture content. There was no effect upon the results for size exclusion chromatography. Results for annealing were between those for controlled nucleation and shelf-ramp freezing. All results were consistent with "ice-fog" controlled nucleation at -6 °C having greater impact upon the ice crystal morphology than annealing at the same temperature for 3 hours.

Investigation of the Freezing Phenomenon in Vials Using an Infrared Camera

The freezing phenomenon has a dramatic impact on the quality of freeze-dried products. Several freezing models applied to solutions in vials have been proposed to predict the resulting product morphology and describe heat transfer mechanisms. However, there is a lack of detailed experimental observations of the freezing phenomenon in vials in the literature. Thus, the present work offers new experimental observations of the freezing phenomenon in vials by infrared (IR) thermography. IR imaging allowed each vial’s whole axial temperature profile to be collected during freezing, providing significant insights into the process. Spontaneous nucleation and vacuum-induced surface freezing (VISF), as a controlled nucleation technique, are investigated. Batches having vials in direct contact with the shelf (exchanging heat mainly through conduction) as well as suspended (exchanging heat mainly through natural convection and radiation) were tested. The study used three solutions: sucrose 5%, mannitol 5%, and dextran 10%. SEM images coupled with an automated image segmentation technique were also performed to examine possible correlations between the freezing observations and the resulting pore size distributions. IR thermography was found to be a promising tool for experimentally predicting the resulting product morphology in-line.

Enzymatic characterization of D-lactate dehydrogenase and application in alanine aminotransferase activity assay kit

D-lactate dehydrogenase (D-LDH) is widely used for the clinical detection of alanine aminotransferase (ALT) activity. It is a key enzyme in ALT detection kits, and its enzymatic properties directly determine sensitivity and accuracy of such kits. In this study, D-lactate dehydrogenase (WP_011543503, ldLDH) coding sequence derived from Lactobacillus delbrueckii was obtained from the NCBI database by gene mining. LdLDH was expressed and purified in Escherichia coli, and its enzyme activity, kinetic parameters, optimum temperature, and pH were characterized. Furthermore, stabilizers, including sugars, polyols, amino acids, certain salts, proteins, and polymers, were screened to improve stability of ldLDH during freeze-drying and storage. Finally, a kit based on ldLDH was tested to determine whether the enzyme had potential clinical applications. The results showed that ldLDH had a specific activity of 1,864 U/mg, K_m value of 1.34 mM, optimal reaction temperature of 55°C, and an optimal pH between 7.0 and 7.5. When sucrose or asparagine was used as a stabilizer, freeze-dried ldLDH remained stable at 37°C for > 2 months without significant loss of enzymatic activity. These results indicated that ldLDH possesses high activity and stability. Test results using the ALT assay kit prepared with ldLDH were consistent with those of commercial kits, with a relative deviation <5%. These results indicated that ldLDH met the primary requirements for ALT assays, laying a foundation for the development of new ALT kits with potential clinical applications.

Recommended Best Practices for Lyophilization Validation-2021 Part I: Process Design and Modeling

Abstract

This work describes lyophilization process validation and consists of two parts. Part I focuses on the process design and is described in the current paper, while part II is devoted to process qualification and continued process verification. The intent of these articles is to provide readers with recent updates on lyophilization validation in the light of community-based combined opinion on the process and reflect the industrial prospective. In this paper, the design space approach for process design is described in details, and examples from practice are provided. The approach shows the relationship between the process inputs; it is based on first principles and gives a thorough scientific understanding of process and product. The lyophilization process modeling and scale-up are also presented showing the impact of facility, equipment, and vial heat transfer coefficient. The case studies demonstrating the effect of batch sizes, fill volume, and dose strength to show the importance of modeling as well as the effect of controlled nucleation on product resistance are discussed.

Graphical abstract

Lyophilization Preserves the Intrinsic Cardioprotective Activity of Bioinspired Cell-Derived Nanovesicles

Recently, bioinspired cell-derived nanovesicles (CDNs) have gained much interest in the field of nanomedicine due to the preservation of biomolecular structure characteristics derived from their parent cells, which impart CDNs with unique properties in terms of binding and uptake by target cells and intrinsic biological activities. Although the production of CDNs can be easily and reproducibly achieved with any kind of cell culture, application of CDNs for therapeutic purposes has been greatly hampered by their physical and chemical instability during long-term storage in aqueous dispersion. In the present study, we conceived a lyophilization approach that would preserve critical characteristics regarding stability (vesicles' size and protein content), structural integrity, and biological activity of CDNs for enabling long-term storage in freeze-dried form. Compared to the lyoprotectant sucrose, trehalose-lyoprotected CDNs showed significantly higher glass transition temperature and lower residual moisture content. As assessed by ATR-FTIR and far-UV circular dichroism, lyophilization in the presence of the lyoprotectant effectively maintained the secondary structure of cellular proteins. After reconstitution, lyoprotected CDNs were efficiently associated with HeLa cells, CT26 cells, and bone marrow-derived macrophages at a rate comparable to the freshly prepared CDNs. In vivo, both lyoprotected and freshly prepared CDNs, for the first time ever reported, targeted the injured heart, and exerted intrinsic cardioprotective effects within 24 h, attributable to the antioxidant capacity of CDNs in a myocardial ischemia/reperfusion injury animal model. Taken together, these results pave the way for further development of CDNs as cell-based therapeutics stabilized by lyophilization that enabled long-term storage while preserving their activity.

Stabilizers and their interaction with formulation components in frozen and freeze-dried protein formulations

This review aims to provide an overview of the current knowledge on protein stabilization during freezing and freeze-drying in relation to stress conditions commonly encountered during these processes. The traditional as well as refined mechanisms by which excipients may stabilize proteins are presented. These stabilizers encompass a wide variety of compounds including sugars, sugar alcohols, amino acids, surfactants, buffers and polymers. The rational selection of excipients for use in frozen and freeze-dried protein formulations is presented. Lyophilized protein formulations are generally multicomponent systems, providing numerous possibilities of excipient-excipient and protein-excipient interactions. The interplay of different formulation components on the protein stability and excipient functionality in the frozen and freeze-dried systems are reviewed, with discussion of representative examples of such interactions.

Key factors governing the reconstitution time of high concentration lyophilized protein formulations

Lyophilized protein formulations containing highly concentrated proteins often have long and variable reconstitution times. Reconstitution time is dependent on a number of factors in a complex manner. Furthermore, factors influencing the reconstitution of partially crystalline cakes are reportedly different from those of amorphous cakes. The objectives of this work were to identify the key factors governing reconstitution and understand the mechanisms involved in reconstitution of both amorphous and partially crystalline cakes. Partial crystallinity in the final cake, larger pores and low "concentrated formulation viscosity" (i.e., viscosity near the surface of the dissolving cake) were identified as desirable characteristics for expediting reconstitution. Crystallinity and larger pores dramatically improved wettability and liquid penetration into partially crystalline cakes, ultimately resulting in well dispersed small pieces of partially dissolved cake. The smaller disintegrated cake pieces dissolved faster because of the increased surface area. The amorphous cakes exhibited poorer wettability than partially crystalline cakes. Moreover, the ability of the reconstitution fluid to penetrate the pores, and the resulting cake disintegration was much lower than that observed for partially crystalline cakes. In fact, for some of the amorphous cakes, the reconstitution fluid did not penetrate the cake at all. As a result, the undissolved intact cake or a large cake chunk floated on the reconstitution fluid amidst foam or bubbles generated during reconstitution. Dissolution of the floating cake appeared to proceed via gradual surface erosion where reconstitution time was found to be highly correlated with the viscosity near the surface of the dissolving cake solids. A higher viscosity prolonged reconstitution. Thus, both formulation and processing conditions can be tailored to achieve faster reconstitution. Including a crystallizable excipient proved to be beneficial. Incorporating an annealing step to facilitate crystallization of the crystallizable excipient and to promote larger pores was also found to be advantageous. A viscosity lowering excipient in the formulation could potentially be helpful but needs to be explored further.

Strengthening of Porcine Plasma Protein Superabsorbent Materials through a Solubilization-Freeze-Drying Process

The replacement of common acrylic derivatives by biodegradable materials in the formulation of superabsorbent materials would lessen the associated environmental impact. Moreover, the use of by-products or biowastes from the food industry that are usually discarded would promote a desired circular economy. The present study deals with the development of superabsorbent materials based on a by-product from the meat industry, namely plasma protein, focusing on the effects of a freeze-drying stage before blending with glycerol and eventual injection molding. More specifically, this freeze-drying stage is carried out either directly on the protein flour or after its solubilization in deionized water (10% w/w). Superabsorbent materials obtained after this solubilization-freeze-drying process display higher Young's modulus and tensile strength values, without affecting their water uptake capacity. As greater water uptake is commonly related to poorer mechanical properties, the proposed solubilization-freeze-drying process is a useful strategy for producing strengthened hydrophilic materials.

Influence of image analysis strategy, cooling rate, and sample volume on apparent protein cloud-point temperature determination

The protein cloud-point temperature (TCloud) is a known representative of protein-protein interaction strength and provides valuable information during the development and characterization of protein-based products, such as biopharmaceutics. A high-throughput low volume TCloud detection method was introduced in preceding work, where it was concluded that the extracted value is an apparent TCloud (TCloud,app). As an understanding of the apparent nature is imperative to facilitate inter-study data comparability, the current work was performed to systematically evaluate the influence of 3 image analysis strategies and 2 experimental parameters (sample volume and cooling rate) on TCloud,app detection of lysozyme. Different image analysis strategies showed that TCloud,app is detectable by means of total pixel intensity difference and the total number of white pixels, but the latter is also able to extract the ice nucleation temperature. Experimental parameter variation showed a TCloud,app depression for increasing cooling rates (0.1-0.5 °C/min), and larger sample volumes (5-24 μL). Exploratory thermographic data indicated this resulted from a temperature discrepancy between the measured temperature by the cryogenic device and the actual sample temperature. Literature validation confirmed that the discrepancy does not affect the relative inter-study comparability of the samples, regardless of the image analysis strategy or experimental parameters. Additionally, high measurement precision was demonstrated, as TCloud,app changes were detectable down to a sample volume of only 5 μL and for 0.1 °C/min cooling rate increments. This work explains the apparent nature of the TCloud detection method, showcases its detection precision, and broadens the applicability of the experimental setup.

Molecular Dynamics Simulation to Uncover the Mechanisms of Protein Instability During Freezing

Freezing is a common process applied in the pharmaceutical industry to store and transport biotherapeutics. Herewith, multi-scale molecular dynamics simulations of Lactate dehydrogenase (LDH) protein in phosphate buffer with/without ice formation performed to uncover the still poorly understood mechanisms and molecular details of protein destabilization upon freezing. Both fast and slow ice growing conditions were simulated at 243 K from one or two-side of the simulation box, respectively. The rate of ice formation at all-atom simulations was crucial to LDH stability, as faster freezing rates resulted in enhanced structural stability maintained by a higher number of intramolecular hydrogen bonds, less flexible protein's residues, lower solvent accessibility and greater structural compactness. Further, protein aggregation investigated by coarse-grained simulations was verified to be initiated by extended protein structures and retained by electrostatic interactions of the salt bridges between charged residues and hydrogen bonds between polar residues of the protein. Lastly, the study of free energy of dissociation through steered molecular dynamics simulation revealed LDH was destabilized by the solvation of the hydrophobic core and the loss of hydrophobic interactions. For the first time, experimentally validated molecular simulations revealed the detailed mechanisms of LDH destabilization upon ice formation and cryoconcentration of solutes.

Instability of therapeutic proteins - An overview of stresses, stabilization mechanisms and analytical techniques involved in lyophilized proteins

Solid-state is the preferred choice for storage of protein therapeutics to improve stability and preserve the biological activity by decreasing the physical and chemical degradation associated with liquid protein formulations. Lyophilization or freeze-drying is an effective drying method to overcome the instability problems of proteins. However, the processing steps (freezing, primary drying and secondary drying) involved in the lyophilization process can expose the proteins to various stress and harsh conditions, leading to denaturation, aggregation often a loss in activity of protein therapeutics. Stabilizers such as sugars and surfactants are often added to protect the proteins against physical stress associated with lyophilization process and storage conditions. Another way to curtail the degradation of proteins due to process related stress is by modification of the lyophilization process. Slow freezing, high nucleation temperature, decreasing the extent of supercooling, and annealing can minimize the formation of the interface (ice-water) by producing large ice crystals with less surface area, thereby preserving the native structure and stability of the proteins. Hence, a thorough understanding of formulation composition, lyophilization process parameters and the choice of analytical methods to characterize and monitor the protein instability is crucial for development of stable therapeutic protein products. This review provides an overview of various stress conditions that proteins might encounter during lyophilization process, mechanisms to improve the stability and analytical techniques to tackle the proteins instability during both freeze-drying and storage.

Evaluation of Predictors of Protein Relative Stability Obtained by Solid-State Hydrogen/Deuterium Exchange Monitored by FTIR

PURPOSE

Hydrogen/deuterium (H/D) exchange over a range of temperatures suggests a protein structural/mobility transition in the solid state below the system glass transition temperature (T_g). The purpose of this study was to determine whether solid-state protein stability correlates with the difference between storage temperature and apparent T_d where an abrupt change in mobility occurs, or alternatively, the extent of H/D exchange at a single temperature correlates directly to protein stability in lyophilized solids.

METHODS

Solid-state H/D exchange was monitored by FTIR spectroscopy to study the extent of exchange and the apparent transition temperature in both pure recombinant human serum albumin (rHSA) and rHSA formulated with sucrose or trehalose. H/D exchange of freeze-dried formulations at 11% RH and temperatures from 30 to 80°C was monitored. Protein stability against aggregation at 40°C/11% RH for 6 months was assessed by size exclusion chromatography (SEC).

RESULTS

Both sucrose and trehalose showed equivalent protection of protein secondary structure by FTIR. The rHSA:sucrose formulation showed superior long-term stability at 40°C by SEC over the trehalose formulation, but the apparent T_d determined from H/D exchange was much higher in the trehalose formulation. Instead, the extent of H/D exchange (X_∞) was lower in the sucrose formulation at the temperature of the stability studies (40°C) than found for the trehalose formulation, which was consistent with better stability in the sucrose formulation.

CONCLUSIONS

While apparent T_d did not correlate with protein stability for rHSA, the extent of H/D exchange, X_∞, did.

Preserving the Integrity of Liposomes Prepared by Ethanol Injection upon Freeze-Drying: Insights from Combined Molecular Dynamics Simulations and Experimental Data

The freeze-drying of complex formulations, such as liposomes, is challenging, particularly if dispersions contain residual organic solvents. This work aimed to investigate the effects of possible protectants, namely sucrose, trehalose and/or poly(vinyl pyrrolidone) (PVP), on the main features of the dried product using a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)-based liposomal dispersion prepared by ethanol injection and containing ethanol up to 6%, as a model. The interactions among vesicles and protectants were preliminary screened by Molecular Dynamics (MD) simulations, which have been proved useful in rationalizing the selection of protectant(s). The freeze-drying protocol was based on calorimetric results. Overall data suggested a stronger cryo-protectant effect of trehalose, compared with sucrose, due to stronger interactions with the DPPC bilayer and the formation of highly ordered clusters around the lipids. The effect further improved in the presence of PVP. Differently from the other tested protectants, the selected trehalose/PVP combination allows to preserve liposome size, even in the presence of 6% ethanol, as demonstrated by Nanoparticle Tracking Analysis (NTA). Nevertheless, it should be also underlined that cakes blew out at an ethanol concentration higher than 1% v/v, probably due to the poor cohesion within the cake and solvent vapour pressure upon sublimation.