Ice Recrystallization in a Solution of a Cryoprotector and Its Inhibition by a Protein: Synchrotron X-Ray Diffraction Study

Freeze-thaw of pharmaceutical solutions: counter-intuitive finding of an increase in mechanical stress between Tg" and Tg' in frozen sucrose/water mixtures

High-resolution synchrotron X-ray powder diffraction has been utilized to detect mechanical stresses in frozen solutions, via analysis of the profiles of the diffraction peaks of ice. Increase in the width of the peaks (peaks broadening) reflects disruption of the crystal lattice, with contributions including a decrease in the crystallite size and an increase in microstrain. Frozen sucrose solutions (5 and 10 % w/v) were frozen at 100K and then heated and annealed at -45°C (228 K) and -15°C (258 K), i.e. between the two apparent glass transition events in the freeze-concentrated solutions (Tg" and Tg'), and above the Tg', respectively. A decrease in microstrain and an increase in ice crystallite size were observed during annealing at -15°C (above the Tg'), which is consistent with Ostwald ripening of ice crystals. Unexpectedly, and for the first time, an opposite trend was observed during annealing at the lower temperature of -45°C, between Tg" and Tg'. To the best of our knowledge, this is the first report of an increased strain in the crystalline ice domains and of simultaneous size reduction during annealing of frozen aqueous solutions. Considering that the interaction with ice crystals may result in protein destabilization, the size and microstrain of ice crystallites can serve as markers of the freeze/thaw stresses on biopharmaceuticals. A practical implication is that a prolonged hold between Tg" and Tg' may increase stress imposed on protein molecules, i.e. a lower temperature is not always better for preserving biopolymers when freezing their aqueous solutions.

Excipient-Induced Lattice Disorder in Active Pharmaceutical Ingredient: Implications on Drug Product Continuous Manufacturing

Our previous work (Mol Pharm, 20 (2023) 3427) showed that crystalline excipients, specifically anhydrous dibasic calcium phosphate (DCPA), facilitated the dehydration of carbamazepine dihydrate (CBZDH) and the formation of an amorphous product phase during the mixing stage of continuous tablet manufacturing. Understanding the mechanism of this excipient-induced effect was the object of this study. Blending with DCPA for 15 min caused pronounced lattice disorder in CBZDH. This was evident from the 190% increase in the apparent lattice strain determined by the Williamson-Hall plot. The rapid dehydration was attributed to the increased reactivity of CBZDH caused by this lattice disorder. Lattice disorder in CBZDH was induced by a second method, cryomilling it with DCPA. The dehydration was accelerated in the milled sample. Annealing the cryomilled sample reversed the effect, thus confirming the effect of lattice disorder on the dehydration kinetics. The hardness of DCPA appeared to be responsible for the disordering effect. DCPA exhibited a similar effect in other hydrates, thereby revealing that the effect was not unique to CBZDH. However, its magnitude varied on a case-by-case basis. The high shear powder mixing was necessary for rapid and efficient powder mixing during continuous drug product manufacturing. The mechanical stress imposed on the CBZDH, and exacerbated by DCPA, caused this unexpected destabilization.

Phase transitions and mechanisms of cryoprotection of serum-/xeno-free media based on dextran and dimethyl sulfoxide

The development of serum-/xeno-free media may help avoid the drawbacks of using serum and its components, such as probable contamination, instability of composition, or difficulty in sterilization. The objectives of this research were to investigate the use of combinations of a permeating cryoprotective agent (Me₂SO) and non-permeating (polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, hydroxyethyl starch, dextran) polymers for cryopreservation of interstitial cells (ICs) of rat testis, and to propose the mechanism of cryoprotection of such compositions. In the course of this study, the best combination was 100 mg/ml dextran (M.m. 40 kDa) (Dex40) with 0.7 M Me₂SO in Ham's F12. The ICs were additionally cooled and warmed to different end temperatures (-30, -50, -50 and -196 °C) to determine which temperature intervals contributed most to the IC loss. Then, the cryoprotective action of this serum-/xeno-free medium was investigated in comparison with serum or albumin-containing media by differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). The results showed that the medium based on Dex40 did not decrease the amount of ice formed. However, it could undergo other phase separation and phase transformation to form glassy states. Potential cell-damaging physical processes such as eutectic crystallization/melting, recrystallization of NaCl and/or Me₂SO derivatives, found in serum-containing media and taking place in specific temperature intervals, were not observed in the Dex40 based media. This was in good correlation with indicators of cell survival. Additionally, the application of Dex40 allowed using Me₂SO in lower concentrations (0.7 M) than required for serum-containing media (1.4 M), which may decrease the toxicity of serum-/xeno-free media.

Impact of lyoprotectors on protein-protein separation in the solid state: Neutron- and X-ray-scattering investigation

BACKGROUND

Polyhydroxycompounds (PHC) are used as lyoprotectors to minimize aggregation of pharmaceutical proteins during freeze-drying and storage.

METHODS

Lysozyme/PHC mixtures with 1:1 and 1:3 (w/w) ratios are freeze-dried from either H₂O or D₂O solutions. Disaccharides (sucrose and trehalose), monosaccharide (glucose), and sugar alcohol (sorbitol) are used in the study. Small-angle neutron and X-ray scattering (SANS and SAXS) are applied to study protein-protein interaction in the freeze-dried samples.

RESULTS

Protein interaction peak in the freeze-dried mixtures has been detected by both SANS (D₂O-based samples only) and SAXS (both D₂O- and H₂O-based). In the 1:1 mixtures, protein separation distances are similar (center-of-mass distance of approx. 31 Å) between all lyoprotectors studied. Mixtures with a higher content of the disaccharides (1:3 ratio) have a higher separation distance of approx 40 Å. The higher separation could reduce protein-protein contacts and therefore be associated with less favourable aggregation conditions. In the 1:3 mixtures with glucose and sorbitol, complex SANS and SAXS/WAXS patterns are observed. The pattern for the glucose sample indicate two populations of lysozyme molecules, while the origin of multiple SAXS peaks in the lysozyme/sorbitol 1:3 mixture is uncertain.

CONCLUSIONS

Protein-protein separation distance is determined predominantly by the lyoprotector/protein weight ratio.

GENERAL SIGNIFICANCE

Use of SANS and SAXS improves understanding of mechanisms of protein stabilization by sugars in freeze-dried formulations, and provide a tool to verify hypothesis on relationship between protein/protein separation and aggregation propensity in the dried state.

The Role of Cyclodextrins against Interface-Induced Denaturation in Pharmaceutical Formulations: A Molecular Dynamics Approach

Protein-based pharmaceutical products are subject to a variety of environmental stressors, during both production and shelf-life. In order to preserve their structure, and, therefore, functionality, it is necessary to use excipients as stabilizing agents. Among the eligible stabilizers, cyclodextrins (CDs) have recently gained interest in the scientific community thanks to their properties. Here, a computational approach is proposed to clarify the role of β-cyclodextrin (βCD) and 2-hydroxypropyl-β-cyclodextrin (HPβCD) against granulocyte colony-stimulating (GCSF) factor denaturation at the air–water and ice–water interfaces, and also in bulk water at 300 or 260 K. Both traditional molecular dynamics (MD) simulations and enhanced sampling techniques (metadynamics, MetaD) are used to shed light on the underlying molecular mechanisms. Bulk simulations revealed that CDs were preferentially included within the surface hydration layer of GCSF, and even included some peptide residues in their hydrophobic cavity. HPβCD was able to stabilize the protein against surface-induced denaturation in proximity of the air–water interface, while βCD had a destabilizing effect. No remarkable conformational changes of GCSF, or noticeable effect of the CDs, were instead observed at the ice surface. GCSF seemed less stable at low temperature (260 K), which may be attributed to cold-denaturation effects. In this case, CDs did not significantly improve conformational stability. In general, the conformationally altered regions of GCSF seemed not to depend on the presence of excipients that only modulated the extent of destabilization with either a positive or a negative effect.

Dynamical in-situ observation of the lyophilization and vacuum-drying processes of a model biopharmaceutical system by an environmental scanning electron microscope

The paper discusses the real-time monitoring of the changing sample morphology during the entire lyophilization (freeze-drying) and vacuum-drying processes of model biopharmaceutical solutions by using an environmental scanning electron microscope (ESEM); the device's micromanipulators were used to study the interior of the samples in-situ without exposing the samples to atmospheric water vapor. The individual collapse temperatures (T_c) of the formulations, pure bovine serum albumin (BSA) and BSA/sucrose mixtures, ranged from -5 to -29 °C. We evaluated the impact of the freezing method (spontaneous freezing, controlled ice nucleation, and spray freezing) on the morphologies of the lyophiles at the constant drying temperature of -20 °C. The formulations with T_c above -20 °C resulted in the lyophiles' morphologies significantly dependent on the freezing method. We interpret the observations as an interplay of the freezing rates and directionalities, both of which markedly influence the morphologies of the frozen formulations, and, subsequently, the drying process and the mechanical stability of the freeze-dried cake. The formulation with T_c below -20 °C yielded a collapsed cake with features independent of the freezing method. The vacuum-drying produced a material with a smooth and pore-free surface, where deep cracks developed at the end of the process.

X-ray diffraction to probe the kinetics of ice recrystallization inhibition

Understanding the nucleation and growth of ice is crucial in fields ranging from infrastructure maintenance, to the environment, and to preserving biologics in the cold chain. Ice binding and antifreeze proteins are potent ice recrystallization inhibitors (IRI), and synthetic materials that mimic this function have emerged, which may find use in biotechnology. To evaluate IRI activity, optical microscopy tools are typically used to monitor ice grain size either by end-point measurements or as a function of time. However, these methods provide 2-dimensional information and image analysis is required to extract the data. Here we explore using wide angle X-ray scattering (WAXS/X-ray powder diffraction (XRD)) to interrogate 100's of ice crystals in 3-dimensions as a function of time. Due to the random organization of the ice crystals in the frozen sample, the number of orientations measured by XRD is proportional to the number of ice crystals, which can be measured as a function of time. This method was used to evaluate the activity for a panel of known IRI active compounds, and shows strong agreement with results obtained from cryo-microscopy, as well as being advantageous in that time-dependent ice growth is easily extracted. Diffraction analysis also confirmed, by comparing the obtained diffraction patterns of both ice binding and non-binding additives, that the observed hexagonal ice diffraction patterns obtained cannot be used to determine which crystal faces are being bound. This method may help in the discovery of new IRI active materials as well as enabling kinetic analysis of ice growth.

Interfacial Stress in the Development of Biologics: Fundamental Understanding, Current Practice, and Future Perspective

Biologic products encounter various types of interfacial stress during development, manufacturing, and clinical administration. When proteins come in contact with vapor-liquid, solid-liquid, and liquid-liquid surfaces, these interfaces can significantly impact the protein drug product quality attributes, including formation of visible particles, subvisible particles, or soluble aggregates, or changes in target protein concentration due to adsorption of the molecule to various interfaces. Protein aggregation at interfaces is often accompanied by changes in conformation, as proteins modify their higher order structure in response to interfacial stresses such as hydrophobicity, charge, and mechanical stress. Formation of aggregates may elicit immunogenicity concerns; therefore, it is important to minimize opportunities for aggregation by performing a systematic evaluation of interfacial stress throughout the product development cycle and to develop appropriate mitigation strategies. The purpose of this white paper is to provide an understanding of protein interfacial stability, explore methods to understand interfacial behavior of proteins, then describe current industry approaches to address interfacial stability concerns. Specifically, we will discuss interfacial stresses to which proteins are exposed from drug substance manufacture through clinical administration, as well as the analytical techniques used to evaluate the resulting impact on the stability of the protein. A high-level mechanistic understanding of the relationship between interfacial stress and aggregation will be introduced, as well as some novel techniques for measuring and better understanding the interfacial behavior of proteins. Finally, some best practices in the evaluation and minimization of interfacial stress will be recommended.

Identification of Plant Ice-binding Proteins Through Assessment of Ice-recrystallization Inhibition and Isolation Using Ice-affinity Purification

Ice-binding proteins (IBPs) belong to a family of stress-induced proteins that are synthesized by certain organisms exposed to subzero temperatures. In plants, freeze damage occurs when extracellular ice crystals grow, resulting in the rupture of plasma membranes and possible cell death. Adsorption of IBPs to ice crystals restricts further growth by a process known as ice-recrystallization inhibition (IRI), thereby reducing cellular damage. IBPs also demonstrate the ability to depress the freezing point of a solution below the equilibrium melting point, a property known as thermal hysteresis (TH) activity. These protective properties have raised interest in the identification of novel IBPs due to their potential use in industrial, medical and agricultural applications. This paper describes the identification of plant IBPs through 1) the induction and extraction of IBPs in plant tissue, 2) the screening of extracts for IRI activity, and 3) the isolation and purification of IBPs. Following the induction of IBPs by low temperature exposure, extracts are tested for IRI activity using a 'splat assay', which allows the observation of ice crystal growth using a standard light microscope. This assay requires a low protein concentration and generates results that are quickly obtained and easily interpreted, providing an initial screen for ice binding activity. IBPs can then be isolated from contaminating proteins by utilizing the property of IBPs to adsorb to ice, through a technique called 'ice-affinity purification'. Using cell lysates collected from plant extracts, an ice hemisphere can be slowly grown on a brass probe. This incorporates IBPs into the crystalline structure of the polycrystalline ice. Requiring no a priori biochemical or structural knowledge of the IBP, this method allows for recovery of active protein. Ice-purified protein fractions can be used for downstream applications including the identification of peptide sequences by mass spectrometry and the biochemical analysis of native proteins.

Freeze concentration-induced PLGA and polystyrene nanoparticle aggregation: Imaging and rational design of lyoprotection

Long-term storage of stable nanoparticulate systems is critical to the utilization of nanotechnology in biomedical applications. Freeze-drying or lyophilization is the most commonly used approach to preparing stable injectable nano formulations. A detailed understanding of the freezing stress on nanoparticles is essential to the successful preservation of original particle attributes and to the development of reliable lyophilization processes. However, visualization of the freezing process and the underlying mechanisms that result in particle aggregation remains challenging. Here, we show a clear causal relationship between the freeze-concentration event and particle aggregation by employing correlative imaging techniques, encompassing both real-time dynamic visualization and super-resolution imaging for frozen systems. Direct evidence was obtained to corroborate the particle isolation hypothesis. Moreover, ice-ice, ice-air and ice-container interfaces were identified as hotspots for generating freezing stress on susceptible nanoparticles. In light of these observations, sphere close packing models were explored. Based on the relationship between jammed particles and void fraction within a confined interfacial space, we are able to define the boundary condition of the minimal 'cryoprotectant to particle ratio' required for effective design space of particle isolation and cryoprotection. These findings clearly demonstrated the utility of visualization techniques and modeling in elucidating the mechanism of freezing stress and protection, providing guiding tools to the rational design of cryoprotectant containing nano formulations and processes.