Frozen-state storage stability of a monoclonal antibody: aggregation is impacted by freezing rate and solute distribution

Directional freezing and thawing of biologics in drug substance bottles

Biological drug substance (DS) is typically stored frozen to increase stability. However, freezing and thawing (F/T) of DS can impact product quality and therefore F/T processes need to be controlled. Because active F/T systems for DS bottles are lacking, freezing is often performed uncontrolled in conventional freezers, and thawing at ambient temperature or using water baths. In this study, we evaluated a novel device for F/T of DS in bottles, which can be operated in conventional freezers, generating a directed air stream around bottles. We characterized the F/T geometry and process performance in comparison to passive F/T using temperature mapping and analysis of concentration gradients. The device was able to better control the F/T process by inducing directional bottom-up F/T. As a result, it reduced cryo-concentration during freezing as well as ice mound formation. However, freezing with the device was dependent on freezer performance, i.e. prolonged process times in a highly loaded freezer were accompanied by increased cryo-concentrations. Thawing was faster compared to without the device, but had no impact on concentration gradients and was slower compared to thawing in a water bath. High-performance freezers might be required to fully exploit the potential of directional freezing with this device and allow F/T process harmonization and scaling across sites.

Characterization of Freezing Processes in Drug Substance Bottles by Ice Core Sampling

Freezing of biological drug substance (DS) is a critical unit operation that may impact product quality, potentially leading to protein aggregation and sub-visible particle formation. Cryo-concentration has been identified as a critical parameter to impact protein stability during freezing and should therefore be minimized. The macroscopic cryo-concentration, in the following only referred to as cryo-concentration, is majorly influenced by the freezing rate, which is in turn impacted by product independent process parameters such as the DS container, its size and fill level, and the freezing equipment. (At-scale) process characterization studies are crucial to understand and optimize freezing processes. However, evaluating cryo-concentration requires sampling of the frozen bulk, which is typically performed by cutting the ice block into pieces for subsequent analysis. Also, the large amount of product requirement for these studies is a major limitation. In this study, we report the development of a simple methodology for experimental characterization of frozen DS in bottles at relevant scale using a surrogate solution. The novel ice core sampling technique identifies the axial ice core in the center to be indicative for cryo-concentration, which was measured by osmolality, and concentrations of histidine and polysorbate 80 (PS80), whereas osmolality revealed to be a sensitive read-out. Finally, we exemplify the suitability of the method to study cryo-concentration in DS bottles by comparing cryo-concentrations from different freezing protocols (-80°C vs -40°C). Prolonged stress times during freezing correlated to a higher extent of cryo-concentration quantified by osmolality in the axial center of a 2 L DS bottle.

Freeze-Induced Phase Transition and Local Pressure in a Phospholipid/Water System: Novel Insights Were Obtained from a Time/Temperature Resolved Synchrotron X-ray Diffraction Study

Water-to-ice transformation results in a 10% increase in volume, which can have a significant impact on biopharmaceuticals during freeze-thaw cycles due to the mechanical stresses imparted by the growing ice crystals. Whether these stresses would contribute to the destabilization of biopharmaceuticals depends on both the magnitude of the stress and sensitivity of a particular system to pressure and sheer stresses. To address the gap of the "magnitude" question, a phospholipid, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), is evaluated as a probe to detect and quantify the freeze-induced pressure. DPPC can form several phases under elevated pressure, and therefore, the detection of a high-pressure DPPC phase during freezing would be indicative of a freeze-induced pressure increase. In this study, the phase behavior of DPPC/water suspensions, which also contain the ice nucleation agent silver iodide, is monitored by synchrotron small/wide-angle X-ray scattering during the freeze-thaw transition. Cooling the suspensions leads to heterogeneous ice nucleation at approximately -7 °C, followed by a phase transition of DPPC between -11 and -40 °C. In this temperature range, the initial gel phase of DPPC, Lβ', gradually converts to a second phase, tentatively identified as a high-pressure Gel III phase. The Lβ'-to-Gel III phase transition continues during an isothermal hold at -40 °C; a second (homogeneous) ice nucleation event of water confined in the interlamellar space is detected by differential scanning calorimetry (DSC) at the same temperature. The extent of the phase transition depends on the DPPC concentration, with a lower DPPC concentration (and therefore a higher ice fraction), resulting in a higher degree of Lβ'-to-Gel III conversion. By comparing the data from this study with the literature data on the pressure/temperature Lβ'/Gel III phase boundary and the lamellar lattice constant of the Lβ' phase, the freeze-induced pressure is estimated to be approximately 0.2-2.6 kbar. The study introduces DPPC as a probe to detect a pressure increase during freezing, therefore addressing the gap between a theoretical possibility of protein destabilization by freeze-induced pressure and the current lack of methods to detect freeze-induced pressure. In addition, the observation of a freeze-induced phase transition in a phospholipid can improve the mechanistic understanding of factors that could disrupt the structure of lipid-based biopharmaceuticals, such as liposomes and mRNA vaccines, during freezing and thawing.

Application of Formulation Principles to Stability Issues Encountered During Processing, Manufacturing, and Storage of Drug Substance and Drug Product Protein Therapeutics

The field of formulation and stabilization of protein therapeutics has become rather extensive. However, most of the focus has been on stabilization of the final drug product. Yet, proteins experience stress and degradation through the manufacturing process, starting with fermentaition. This review describes how formulation principles can be applied to stabilize biopharmaceutical proteins during bioprocessing and manufacturing, considering each unit operation involved in prepration of the drug substance. In addition, the impact of the container on stabilty is discussed as well.

From cell factories to patients: Stability challenges in biopharmaceuticals manufacturing and administration with mitigation strategies

Active ingredients of biopharmaceuticals consist of a wide array of biomolecular structures, including those of enzymes, monoclonal antibodies, nucleic acids, and recombinant proteins. Recently, these molecules have dominated the pharmaceutical industry owing to their safety and efficacy. However, their manufacturing is hindered by high cost, inadequate batch-to-batch equivalence, inherent instability, and other quality issues. This article is an up-to-date review of the challenges encountered during different stages of biopharmaceutical production and mitigation of problems arising during their development, formulation, manufacturing, and administration. It is a broad overview discussion of stability issues encountered during product life cycle i.e., upstream processing (aggregation, solubility, host cell proteins, color change), downstream bioprocessing (aggregation, fragmentation), formulation, manufacturing, and delivery to patients.

Understanding and controlling the molecular mechanisms of protein aggregation in mAb therapeutics

In antibody development and manufacturing, protein aggregation is a common challenge that can lead to serious efficacy and safety issues. To mitigate this problem, it is important to investigate its molecular origins. This review discusses (1) our current molecular understanding and theoretical models of antibody aggregation, (2) how various stress conditions related to antibody upstream and downstream bioprocesses can trigger aggregation, and (3) current mitigation strategies employed towards inhibiting aggregation. We discuss the relevance of the aggregation phenomenon in the context of novel antibody modalities and highlight how in silico approaches can be exploited to mitigate it.

Use of capillary-mediated vitrification to produce thermostable, single-use antibody conjugates as immunoassay reagents

The performance of enzyme-linked immunoassays is directly dependent on the storage, handling, and long-term stability of the critical reagents used in the assay. Currently, antibody reagents are routinely stored as concentrated, multi-use, frozen aliquots. This practice results in material waste, adds complexity to laboratory workflows, and can compromise reagents via cross-contamination and freeze-thaw damage. While refrigeration or freezing can slow down many degradation processes, the freezing process itself can have damaging effects, including introduction of aggregation and microheterogeneity. To address these challenges, we evaluated the application of capillary-mediated vitrification (CMV) as a tool for storing antibody reagents in a thermostable, single-use format. CMV is a novel biopreservation method that enables vitrification of biological materials without freezing. Using an anti-human IgG-alkaline phosphatase conjugate as a model system, we prepared CMV-stabilized aliquots which were stored in a single-use format at temperatures ranging from 25 to 55 °C for up to 3 months. Each stabilized aliquot contained enough antibody to perform a single assay run. We evaluated the assay performance and functional stability of the CMV-stabilized reagents using a plate-based ELISA. Assays run using the CMV stabilized reagents exhibited good linearity and precision that was comparable to results obtained with a frozen control. Throughout the stability study, the maximum signal and EC50s observed for ELISAs run using CMV-stabilized reagents were generally consistent with those obtained using a frozen control. These results indicate that the CMV process has the potential to improve both reagent stability and long-term assay performance, while also reducing reagent waste and simplifying assay workflows.

Succinate Buffer in Biologics Products: Real-world Formulation Considerations, Processing Risks and Mitigation Strategies

The succinic acid/succinate system has an excellent buffering capacity at acidic pH values (4.5-6.0), promising to be a buffer of choice for biologics having slightly acidic to basic isoelectric points (pI 6 - 9). However, its prevalence in drug products is limited due to the propensity (risk) of its components to crystallize during freezing and the consequent shift in the pH which might affect the product stability. Most of these previous assessments have been performed under operational conditions that do not simulate typical drug product processing conditions. In this work, we have characterized the physicochemical behavior of succinate formulations under representative pharmaceutical conditions. Our results indicate that the pH increases by ∼ 1.2 units in 25 mM and 250 mM succinate buffers at pharmaceutically relevant freezing conditions. X-ray diffractometry studies revealed selective crystallization of monosodium succinate, which is posed as the causative mechanism. This salt crystallization was not observed in the presence of 2% w/v sucrose, suggesting that this pH shift can be mitigated by including sucrose in the formulation. Additionally, three monoclonal antibodies (mAbs) that represent different IgG subtypes and span a range of pIs (5.9 - 8.8) were formulated with succinate and sucrose and subjected to freeze-thaw, frozen storage and lyophilization. No detrimental impact on quality attributes (QA) such as high molecular weight (HMW) species, turbidity, alteration in protein concentration and sub-visible particles, was observed of any of the mAbs tested. Lastly, drug formulations lyophilized in succinate buffer with sucrose demonstrated acceptable QA profiles upon accelerated kinetic storage stability, supporting the use of succinate buffers in mAb drug products.

Raman Marker Bands for Secondary Structure Changes of Frozen Therapeutic Monoclonal Antibody Formulations During Thawing

In this work we use Raman spectroscopy for protein characterization in the frozen state. We investigate the behavior of frozen therapeutic monoclonal antibody IgG1 formulation upon thawing by Raman spectroscopy. Secondary and tertiary structure of the protein in three different mab formulations in the frozen state are followed through observation of marker bands for α-helix, β-sheet and random coil. We identify the tyrosine intensity ratio I₈₅₆/I₈₃₀ as a marker for mab aggregation. Upon fast cooling (40 °C/min) to -80 °C we observe a significant increase of random coil and α -helical structures, while this is not the case for slower cooling (20 °C/min) to -80 °C. Most changes in the protein's secondary structure are observed in the course of thawing in the range up to -20 °C, when passing through the glass transitions and cold-crystallization of the two types of freeze-concentrated solutions formed through macro- and microcryoconcentration. An increase of protein concentration and the addition of mannitol suppress secondary structural changes but do no impact on aggregation.

The effect of mAb and excipient cryoconcentration on long-term frozen storage stability – Part 1: Higher molecular weight species and subvisible particle formation

Cryoconcentration upon large-scale freezing of monoclonal antibody (mAb) solutions leads to regions of different ratios of low molecular weight excipients, like buffer species or sugars, to protein. This study focused on the impact of the buffer species to mAb ratio on aggregate formation after frozen storage at −80 °C, −20 °C, and − 10 °C after 6 weeks, 6 months, and 12 months. An optimised sample preparation was established to measure T_g′ of samples with different mAb to histidine ratios via differential scanning calorimetry (DSC). After storage higher molecular weight species (HMWS) and subvisible particles (SVPs) were detected using size-exclusion chromatography (SEC) and FlowCam, respectively. For all samples, sigmoidal curves in DSC thermograms allowed to precisely determine T_g′ in formulations without glass forming sugars. Storage below T_g′ did not lead to mAb aggregation. Above T_g′, at −20 °C and − 10 °C, small changes in mAb and buffer concentration markedly impacted stability. Samples with lower mAb concentration showed increased formation of HMWS. In contrast, higher concentrated samples led to more SVPs. A shift in the mAb to histidine ratio towards mAb significantly increased overall stability. Cryoconcentration upon large-scale freezing affects mAb stability, although relative changes compared to the initial concentration are small. Storage below T_g′ completely prevents mAb aggregation and particle formation.

The effect of mAb and excipient cryoconcentration on long-term frozen storage stability – part 2: Aggregate formation and oxidation

We examined the impact of monoclonal antibody (mAb) and buffer concentration, mimicking the cryoconcentration found upon freezing in a 2 L bottle, on mAb stability during frozen storage. Upon cryoconcentration, larger protein molecules and small excipient molecules freeze-concentrate differently, resulting in different protein to stabiliser ratios within a container. Understanding the impact of these shifted ratios on protein stability is essential. For two mAbs a set of samples with constant mAb (5 mg/mL) or buffer concentration (medium histidine/adipic acid) was prepared and stored for 6 months at −10 °C. Stability was evaluated via size-exclusion chromatography, flow imaging microscopy, UV/Vis spectroscopy at 350 nm, and protein A chromatography. Dynamic light scattering was used to determine k_D values. Soluble aggregate levels were unaffected by mAb concentration, but increased with histidine concentration. No trend in optical density could be identified. In contrast, increasing mAb or buffer concentration facilitated the formation of subvisible particles. A trend towards attractive protein-protein interactions was seen with higher ionic strength. MAb oxidation levels were negatively affected by increasing histidine concentration, but became less with higher mAb concentration. Small changes in mAb and buffer composition had a significant impact on stability during six-month frozen storage. Thus, preventing cryoconcentration effects in larger freezing containers may improve long-term stability.

An ACE2-Based Decoy Inhibitor Effectively Neutralizes SARS-CoV-2 Omicron BA.5 Variant

The recently circulating SARS-CoV-2 Omicron BA.5 is rampaging the world with elevated transmissibility compared to the original SARS-CoV-2 strain. Immune escape of BA.5 was observed after treatment with many monoclonal antibodies, calling for broad-spectrum, immune-escape-evading therapeutics. In retrospect, we previously reported Kansetin as an ACE2 mimetic and a protein antagonist against SARS-CoV-2, which proved potent neutralization bioactivity on the Reference, Alpha, Beta, Delta, and Omicron strains of SARS-CoV-2. Since BA.5 is expected to rely on the interaction of the Spike complex with human ACE2 for cell entry, we reasonably assumed the lasting efficacy of the ACE2-mimicking Kansetin for neutralizing the new SARS-CoV-2 variant. The investigation was accordingly performed on in vitro Kansetin-Spike binding affinity by SPR and cell infection inhibition ability with pseudovirus and live virus assays. As a result, Kansetin showed dissociation constant K_D and half inhibition concentration IC₅₀ at the nanomolar to picomolar level, featuring a competent inhibition effect against the BA.5 sublineage. Conclusively, Kansetin is expected to be a promising therapeutic option against BA.5 and future SARS-CoV-2 sublineages.

Direct Binding of Bovine IgG-Containing Immune Complexes to Human Monocytes and Their Putative Role in Innate Immune Training

Bovine milk IgG (bIgG) was shown to bind to and neutralize the human respiratory synovial virus (RSV). In animal models, adding bIgG prevented experimental RSV infection and increased the number of activated T cells. This enhanced activation of RSV-specific T cells may be explained by receptor-mediated uptake and antigen presentation after binding of bIgG-RSV immune complexes (ICs) with FcγRs (primarily CD32) on human immune cells. This indirect effect of bIgG ICs on activation of RSV-specific T cells was confirmed previously in human T cell cultures. However, the direct binding of ICs to antigen-presenting cells has not been addressed. As bovine IgG can induce innate immune training, we hypothesized that this effect could be caused more efficiently by ICs. Therefore, we characterized the expression of CD16, CD32, and CD64 on (peripheral blood mononuclear cells (PBMCs), determined the optimal conditions to form ICs of bIgG with the RSV preF protein, and demonstrated the direct binding of these ICs to human CD14⁺ monocytes. Similarly, bIgG complexed with a murine anti-bIgG mAb also bound efficiently to the monocytes. To evaluate whether the ICs could induce innate immune training more efficiently than bIgG itself, the resulted ICs, as well as bIgG, were used in an in vitro innate immune training model. Training with the ICs containing bIgG and RSV preF protein-but not the bIgG alone-induced significantly higher TNF-α production upon LPS and R848 stimulation. However, the preF protein itself nonsignificantly increased cytokine production as well. This may be explained by its tropism to the insulin-like growth factor receptor 1 (IGFR1), as IGF has been reported to induce innate immune training. Even so, these data suggest a role for IgG-containing ICs in inducing innate immune training after re-exposure to pathogens. However, as ICs of bIgG with a mouse anti-bIgG mAb did not induce this effect, further research is needed to confirm the putative role of bIgG ICs in enhancing innate immune responses in vivo.

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.

Environmental factors modulating protein conformations and their role in protein aggregation diseases

The adverse physiological conditions have been long known to impact protein synthesis, folding and functionality. Major physiological factors such as the effect of pH, temperature, salt and pressure are extensively studied for their impact on protein structure and homeostasis. However, in the current scenario, the environmental risk factors (pollutants) have gained impetus in research because of their increasing concentrations in the environment and strong epidemiologic link with protein aggregation disorders. Here, we review the physiological and environmental risk factors for their impact on protein conformational changes, misfolding, aggregation, and associated pathological conditions, especially environmental risk factors associated pathologies.

Evaluation of Two Novel Scale-Down Devices for Testing Monoclonal Antibody Aggregation During Large-Scale Freezing

There is a need for representative small volume devices that reflect monoclonal antibody (mAb) aggregation during freezing and thawing (FT) in large containers. We characterised two novel devices that aim to mimic the stress in rectangular 2 L bottles. The first scale-down device (SDD) consists of a 125 mL bottle surrounded by a 3D printed cover that manipulates heat exchange. The second device, a micro scale-down device (mSDD), adapts cooling and heating of 10 mL vials to extend stress time. MAb aggregation upon repeated FT was evaluated considering formation of higher molecular weight species, subvisible particles, and the increase in hydrodynamic radius, polydispersity index, and optical density at 350 nm. Three different mAb solutions were processed. Both an unshielded 125 mL bottle and the SDD can be used to predict aggregation during FT in 2 L bottles. In specific cases the unshielded 125 mL bottle underestimates whereas the SDD slightly overestimates soluble aggregate formation. The mSDD increases aggregation compared to 10 mL vials but is less representative than the SDD. Ultimately, both SDDs enable characterisation of protein sensitivity to large-scale FT with two orders of magnitude less volume and are superior to simply using smaller bottles.

Development and Application of a Mechanistic Cooling and Freezing Model of the Spin Freezing Step within the Framework of Continuous Freeze-Drying

During the spin freezing step of a recently developed continuous spin freeze-drying technology, glass vials are rapidly spun along their longitudinal axis. The aqueous drug formulation subsequently spreads over the inner vial wall, while a cold gas flow is used for cooling and freezing the product. In this work, a mechanistic model was developed describing the energy transfer during each phase of spin freezing in order to predict the vial and product temperature change over time. The uncertainty in the model input parameters was included via uncertainty analysis, while global sensitivity analysis was used to assign the uncertainty in the model output to the different sources of uncertainty in the model input. The model was verified, and the prediction interval corresponded to the vial temperature profiles obtained from experimental data, within the limits of the uncertainty interval. The uncertainty in the model prediction was mainly explained (>96% of uncertainty) by the uncertainty in the heat transfer coefficient, the gas temperature measurement, and the equilibrium temperature. The developed model was also applied in order to set and control a desired vial temperature profile during spin freezing. Applying this model in-line to a continuous freeze-drying process may alleviate some of the disadvantages related to batch freeze-drying, where control over the freezing step is generally poor.

Scaling Down Large-Scale Thawing of Monoclonal Antibody Solutions: 3D Temperature Profiles, Changes in Concentration, and Density Gradients

PURPOSE

Scale-down devices (SDD) are designed to simulate large-scale thawing of protein drug substance, but require only a fraction of the material. To evaluate the performance of a new SDD that aims to predict thawing in large-scale 2 L bottles, we characterised 3D temperature profiles and changes in concentration and density in comparison to 125 mL and 2 L bottles. Differences in diffusion between a monoclonal antibody (mAb) and histidine buffer after thawing were examined.

METHODS

Temperature profiles at six distinct positions were recorded with type T thermocouples. Size-exclusion chromatography allowed quantification of mAb and histidine. Polysorbate 80 was quantified using a fluorescent dye assay. In addition, the solution's density at different locations in bottles and the SDD was identified.

RESULTS

The temperature profiles in the SDD and the large-scale 2 L bottle during thawing were similar. Significant concentration gradients were detected in the 2 L bottle leading to marked density gradients. The SDD slightly overestimated the dilution in the top region and the maximum concentrations at the bottom. Fast diffusion resulted in rapid equilibration of histidine.

CONCLUSION

The innovative SDD allows a realistic characterisation and helps to understand thawing processes of mAb solutions in large-scale 2 L bottles. Only a fraction of material is needed to gain insights into the thawing behaviour that is associated with several possible detrimental limitations.

Electrostatic and Covalent Assemblies of Anionic Hydrogel-Coated Gold Nanoshells for Detection of Dry Eye Biomarkers in Human Tears

Although dry eye is highly prevalent, many challenges exist in diagnosing the symptom and related diseases. For this reason, anionic hydrogel-coated gold nanoshells (AuNSs) were used in the development of a label-free biosensor for detection of high isoelectric point tear biomarkers associated with dry eye. A custom, aldehyde-functionalized oligo(ethylene glycol)acrylate (Al-OEGA) was included in the hydrogel coating to enhance protein recognition through the formation of dynamic covalent (DC) imine bonds with solvent-accessible lysine residues present on the surface of select tear proteins. Our results demonstrated that hydrogel-coated AuNSs, composed of monomers that form ionic and DC bonds with select tear proteins, greatly enhance protein recognition due to changes in the maximum localized surface plasmon resonance wavelength exhibited by AuNSs in noncompetitive and competitive environments. Validation of the developed biosensor in commercially available pooled human tears revealed the potential for clinical translation to establish a method for dry eye diagnosis.

Raman spectroscopy as a process analytical technology to investigate biopharmaceutical freeze concentration processes

Freezing processes are a well-established unit operation in the biopharmaceutical industry to increase the shelf-life of protein-based drugs. While freezing reduces degradation reaction rates, it may also exert stresses such as freeze concentration. Macroscopic freeze concentration in large-scale freezing processes has been described thoroughly by examination of frozen bulk material, but the transient process leading to such freeze concentration profiles has not been monitored yet for biopharmaceutical solutions. In this study, Raman spectroscopy as a process analytical technology is demonstrated for model formulations containing monoclonal antibodies (mAbs) or bovine serum albumin (BSA) in varying concentrations of sucrose and buffer salts. Therefore, a Raman probe was immersed into a bulk volume at different heights, monitoring the freeze concentration in the liquid phase during the freezing processes. Partial least square regression models were used to quantitatively discriminate between the protein and excipients simultaneously. The freeze concentration profiles were dependend on freezing temperature and formulation with freeze concentrations up to 2.4-fold. Convection currents at the bottom of the freezing container were observed with a maximum height of 1 mm. Furthermore, freeze concentration was correlated with the sucrose concentration in a formulation. Analysis of the freeze concentration slope indicated diffusion from the bottom to the top of the container. In summary, Raman spectroscopy is a valuable tool for process validation of freeze concentration simulations and to overcome scale-dependent challenges.

Effect of multiple freeze-thaw cycles on the detection of anti-SARS-CoV-2 IgG antibodies

Several studies have investigated the effect of repeated freeze–thaw (F/T) cycles on RNA detection for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). However, no data are available regarding the effect of repeated F/T cycles on SARS-CoV-2 antibody detection in serum. We investigated the effect of multiple F/T cycles on anti-SARS-CoV-2 IgG detection using an ELISA test targeting the nucleocapsid antibodies. Ten positive and 1 negative SARS-CoV-2 IgG sera from 11 participants, in replicates of 5, were subjected to a total of 16 F/T cycles and stored at 4 °C until tested by ELISA. Statistical analysis was performed to test for F/T cycle effect. None of the 10 positive sera became negative after 16 F/T cycles. There was no significant difference in the OD average reading between the first and last F/T cycles, except for one serum with a minimal decline in the OD. The random effect linear regression of log (OD) on the number of cycles showed no significant trend, with a slope consistent with zero (B=−0.0001; 95 % CI −0.0008; 0.0006; P-value=0.781). These results suggest that multiple F/T cycles had no effect on the ability of the ELISA assay to detect SARS-CoV-2 IgG antibodies.

Impact of freeze-thaw processes on monoclonal antibody platform process development

Freezing of cell culture supernatant (CCS) is a standard procedure in process development of monoclonal antibody (mAb) platform processes as up- and downstream development are usually separated. In the manufacturing process of mAb, however, freezing is avoided, which poses the question of comparability and transferability from process development to manufacturing. In this case study, mAb CCS from Chinese hamster ovary (CHO) cells is frozen and thawed in a novel active freezing device and subsequently captured by protein A chromatography. Critical quality attributes such as host cell protein (HCP) concentration and soluble mAb dimer shares have been monitored throughout the case study. Furthermore, cryo-concentration of individual proteins was investigated. The main factors that drive cryo-concentration are diffusion and natural convection. Natural convection in freezing processes was found to increase at warmer freezing temperatures and thus slower freezing, leading to higher concentration gradients from top to bottom of a freezing chamber. The freeze concentration was dependent on protein size and correlated to diffusivity, where smaller proteins are exposed to higher cryo-concentration. Our results suggest that as a result of freezing processes, large particles based on mAb and specific host cell proteins (HCPs) expressing a certain affinity to mAbs are formed that have to be removed before purification. This leads to a significant improvement in HCP reduction by the protein A step, when compared with reference samples, where twice as much HCP remained in the eluate. Furthermore, HCP and mAb dimer concentrations in protein A eluate were dependent on the freezing temperature. As a conclusion, CCS should be frozen as rapidly as possible during process development to minimize issues of transferability from process development to manufacturing.

Temperature Based Process Characterization of Pharmaceutical Freeze-Thaw Operations

In biopharmaceutical production processes, freeze-thaw operations are used to ensure product integrity during long hold times, but they also introduce additional stresses such as freeze concentration gradients that might lead to a loss of protein activity. Process characterization of freeze-thaw operations at different scales should be conducted with attention to freezing time and boundary effects to ensure the product stability throughout the process and process development. Currently, process characterization often relies on one or very few temperature probes that detect freezing times based on raw temperature, which is largely influenced by freezing-point depression in case of concentrated solutions. A method to detect freezing based on the second derivative of temperature measurements from Fiber-Bragg-Grating sensors is presented to overcome this issue. The applicability of the method is demonstrated by process characterization of a novel small-scale freeze-thaw device with minimized boundary effects using freezing times of purified water and concentrated formulations. Freezing times varied from 35 to 81 min for temperatures between −60 and −20°C and impacted freeze concentration profiles. Furthermore, freezing time estimations based on the Plank equation revealed model limitations due to start-up temperature gradients, that can be corrected by an empirically extended Plank model. As a hypothesis, we conclude that freezing temperature, from a freeze concentration view, is less important in containers with small characteristic freezing distances such as freeze bags. Using a 2D-resolved temperature profile, a shift of the last point to freeze position from top to bottom of a container was observed when freezing above −30°C.

Optical cryomicroscopy and differential scanning calorimetry of buffer solutions containing cryoprotectants

In the pharmaceutical industry, cryoprotectants are added to buffer formulations to protect the active pharmaceutical ingredient from freeze- and thaw damage. We investigated the freezing and thawing of aqueous sodium citrate buffer with various cryoprotectants, specifically amino acids (cysteine, histidine, arginine, proline and lysine), disaccharides (trehalose and sucrose), polyhydric alcohols (glycerol and mannitol) and surfactants (polysorbate 20 and polysorbate 80). Hereby, we employed optical cryomicroscopy in combination with differential scanning calorimetry in the temperature range to -80 °C. The effect of cryoprotectants on the morphology of the ice crystals, the glass transition temperature and the initial melting temperature is presented. Some of the cryoprotectants have a significant impact on ice crystal size. Disaccharides restrict ice crystal growth, whereas surfactants and glycerol allow ice crystals to increase in size. Cysteine and mannitol cause dehydration after thawing. Either one or two glass transition temperatures were detected, where arginine, surfactants, glycerol, proline and lysine suppress the second, implying a uniform freeze-concentrated solution. The initial melting temperature of pure buffer solution can be shifted up by adding mannitol, both disaccharides and both surfactants; but down by glycerol, proline and lysine.

The effect of temperature on the stability of PCSK-9 monoclonal antibody: an experimental study

BACKGROUND

PCSK9 monoclonal antibody lowers plasma PCSK9 and LDL-cholesterol levels. The manufacturers recommend drug storage at 2-8 °C, and not above 25 °C. This study aimed to investigate drug stability at various temperatures that this drug could be exposed to during medication handling and transportation in tropical countries.

METHODS

Alirocumab and evolocumab were tested in 3 study conditions: room temperature (RT), cooler device with cold pack, and freeze-thaw for 9 and 18 h. Heated drugs were used as negative control. Free plasma PCSK9 levels from 9 hyperlipidemia subjects were measured with ELISA.

RESULTS

Average subject age was 49.2 ± 18.4 years. Percent PCSK9 inhibition significantly declined in heated drugs compared to baseline. Average RT during the study period was 30.4 ±2.6 °C. Change in percent PCSK9 inhibition of PCSK9 mAb at RT from baseline was - 5.8 ± 4.4% (P = 0.005) and - 11.0 ± 8.9% (P = 0.006) for alirocumab at 9 h and 18 h, and - 9.7 ± 11.8% (P = 0.04) and - 15.1 ± 14.3% (P = 0.01) for evolocumab at 9 and 18 h, respectively. In contrast, there were no significant changes in percent PCSK9 inhibition from baseline when PCSK9 mAb was stored in a cooler. In freeze-thaw condition, changes in percent PCSK9 inhibition from baseline to 9 and 18 h were - 5.2 ± 2.9% (P = 0.001) and - 2.6 ± 4.9% (P = 0.16) for alirocumab, and - 1.8 ± 4.2% (P = 0.24) and 0.4 ± 6.1% (P = 0.83) for evolocumab.

CONCLUSION

Proper drug storage according to manufacturer's recommendation is essential. Drug storage at RT in tropical climate for longer than 9 h significantly decreased drug efficacy; however, storage in a cooler device with cold pack for up to 18 h is safe.

Antibody stability: A key to performance - Analysis, influences and improvement

An antibody's stability greatly influences its performance (i.e. its specificity and affinity). Thus, stability is a major issue for researchers and manufacturers, especially with the increasing use of antibodies in therapeutics, diagnostics and rapid analytical platforms. Here we review antibody stability under five headings: (i) measurement techniques; (ii) stability issues in expression and production (expression, proteolysis, aggregation); (iii) effects of antibody format and engineering on stability and (iv) formulation, drying and storage conditions. We consider more than 100 sources, including patents, and conclude with (v) recommendations to promote antibody stability.

Cryoconcentration and 3D Temperature Profiles During Freezing of mAb Solutions in Large-Scale PET Bottles and a Novel Scale-Down Device

PURPOSE

Small-scale models that simulate large-scale freezing of bulk drug substance of biopharmaceuticals are highly needed to define freezing and formulation parameters based on process understanding. We evaluated a novel scale-down device (SDD), which is based on a specially designed insulation cover, with respect to changes in concentration after freezing, referred to as cryoconcentration, and 3D temperature profiles. Furthermore, the effect of the initial monoclonal antibody (mAb) concentration on cryoconcentration was addressed.

METHODS

2 L and 125 mL bottles were utilized. Temperatures were mapped using type T thermocouples. Frozen blocks were cut and mAb and histidine concentrations were analysed by HPLC. In addition, concentration- and temperature-dependent viscosities were measured.

RESULTS

3D freezing profiles in the SDD were comparable to large-scale bottles. The SDD accurately predicted cryoconcentration of both mAb and histidine of large-scale freezing. Concentric changes in concentration were evident as well as an unforeseen diluted core at the last point to freeze. At low initial mAb concentration cryoconcentration was substantial, while high initial mAb concentration suppressed cryoconcentration almost completely.

CONCLUSION

The novel SDD gives detailed insights into large-scale freezing of mAb solutions using only a fraction of the simulated volume. It is a promising material- and cost-saving tool to understand large-scale freezing processes.

Considerations on Protein Stability During Freezing and Its Impact on the Freeze-Drying Cycle: A Design Space Approach

Freezing is widely used during the manufacturing process of protein-based therapeutics, but it may result in undesired loss of biological activity. Many variables come into play during freezing that could adversely affect protein stability, creating a complex landscape of interrelated effects. The current approach to the selection of freezing conditions is however nonsystematic, resulting in poor process control. Here we show how mathematical models, and a design space approach, can guide the selection of the optimal freezing protocol, focusing on protein stability. Two opposite scenarios are identified, suggesting that the ice-water interface is the dominant cause of denaturation for proteins with high bulk stability, while the duration of the freezing process itself is the key parameter to be controlled for proteins that are susceptible to cold denaturation. Experimental data for lactate dehydrogenase and myoglobin as model proteins support the model results, with a slow freezing rate being optimal for lactate dehydrogenase and the opposite being true for myoglobin. A possible application of the calculated design space to the freezing and freeze-drying of biopharmaceuticals is finally described, and some considerations on process efficiency are discussed as well.

Inhomogeneous Distribution of Components in Solid Protein Pharmaceuticals: Origins, Consequences, Analysis, and Resolutions

Successful development of stable solid protein formulations usually requires the addition of one or several excipients to achieve optimal stability. In these products, there is a potential risk of an inhomogeneous distribution of the various ingredients, specifically the ratio of protein and stabilizer may vary. Such inhomogeneity can be detrimental for stability but is mostly neglected in literature. In the past, it was challenging to analyze inhomogeneous component distribution, but recent advances in analytical techniques have revealed new options to investigate this phenomenon. This paper aims to review fundamental aspects of the inhomogeneous distribution of components of freeze-dried and spray-dried protein formulations. Four key topics will be presented and discussed, including the sources of component inhomogeneity, its consequences on protein stability, the analytical methods to reveal component inhomogeneity, and possible solutions to prevent or mitigate inhomogeneity.

A phase diagram-based toolbox to assess the impact of freeze/thaw ramps on the phase behavior of proteins

The influence of process parameters during freeze/thaw (FT) operations is essential for the preservation of the protein stability/activity during production and storage processes in the biopharmaceutical industry. Process parameters, such as FT ramps, the final storage time and temperature, affect the occurring FT stress onto the target protein in different ways. FT stress includes cold denaturation, freeze concentration, and ice crystal formation which can result in protein aggregation. To visualize the impact of variations in FT ramps, descriptors such as solubility, phase behavior and crystal morphology were evaluated. The phase diagram-based toolbox in combination with an HTS-compatible cryo-device allowed the identification of suitable ramping schemes during FT operations. It could be clearly shown that rapid operations are needed above the glass transition temperature of the target protein to circumvent precipitation during FT cycles. Finally, a stability index is introduced which allows ranking of the systems investigated.

Characterizing and Minimizing Aggregation and Particle Formation of Three Recombinant Fusion-Protein Bulk Antigens for Use in a Candidate Trivalent Rotavirus Vaccine

In a companion paper, the structural integrity, conformational stability, and degradation mechanisms of 3 recombinant fusion-protein antigens comprising a non-replicating rotavirus (NRRV) vaccine candidate (currently being evaluated in early-stage clinical trials) are described. In this work, we focus on the aggregation propensity of the 3 NRRV antigens coupled to formulation development studies to identify common frozen bulk candidate formulations. The P2-VP8-P[8] antigen was most susceptible to shaking and freeze-thaw-induced aggregation and particle formation. Each NRRV antigen formed aggregates with structurally altered protein (with exposed apolar regions and intermolecular β-sheet) and dimers containing a non-native disulfide bond. From excipient screening studies with P2-VP8-P[8], sugars or polyols (e.g., sucrose, trehalose, mannitol, sorbitol) and various detergents (e.g., Pluronic F-68, polysorbate 20 and 80, PEG-3350) were identified as stabilizers against aggregation. By combining promising additives, candidate bulk formulations were optimized to not only minimize agitation-induced aggregation, but also particle formation due to freeze-thaw stress of P2-VP8-P[8] antigen. Owing to limited material availability, stabilization of the P2-VP8-P[4] and P2-VP8-P[6] was confirmed with the lead candidate P2-VP8-P[8] formulations. The optimization of these bulk NRRV candidate formulations is discussed in the context of subsequent drug product formulations in the presence of aluminum adjuvants.

Science and art of protein formulation development

Protein pharmaceuticals have become a significant class of marketed drug products and are expected to grow steadily over the next decade. Development of a commercial protein product is, however, a rather complex process. A critical step in this process is formulation development, enabling the final product configuration. A number of challenges still exist in the formulation development process. This review is intended to discuss these challenges, to illustrate the basic formulation development processes, and to compare the options and strategies in practical formulation development.

An Evaluation of the Delivery of Medicines Using Drones

This study tests the impact of drone transportation on the quality of a medicine. Modelling the critical process parameters of drone flight, the effects of temperature and vibration on insulin were investigated using the pharmacopoeia methods. The medicine, Actrapid, (3.5 mg/mL of insulin), was flown by a quad-rotor drone. Insulin stored between −20 and 40 °C for 30 mins, and subjected to vibration (0–40 Hz, 25 °C, 30 mins) passed the pharmacopeia tests. Dynamic light scattering identified the active tetrameric and hexameric forms of insulin post testing. Vibration frequencies during drone flight were between 0.1 and 3.4 Hz. There was no evidence of visible insulin aggregates following the drone transportation. The differences in UV absorbance readings between flown Actrapid and controls were insignificant (p = 0.89). No adverse impact of drone transport on insulin was observed. This study provides supporting evidence that drone transportation of medicinal products containing insulin is feasible. The authors recommend that when considering the drone delivery of medicines five tests need to be applied. These tests must determine the safe flight time and range, the quality of the medicine post flight, the onboard conditions experienced by the medicine, the security of the drone supply chain and the effect of drone failure on both the medicine and the environment.

Distribution of Protein Content and Number of Aggregates in Monoclonal Antibody Formulation After Large-Scale Freezing

Cryoconcentration of an in-house IgG₁ and number of aggregates in a formulation containing trehalose were determined in dependence on freezing protocol and volume. Morphology changes of ice crystals depending on cooling rates were captured by optical cryomicroscopy (OCM) images. UV-Vis and affinity chromatography (ALC) was used to determine protein content and size-exclusion chromatography (SEC) for detection of aggregates. Cooling to - 80°C rather than - 20°C is beneficial in avoiding hot spots of high protein concentration. An upscaling of 250 ml to 2 L bottles results in an up to fourfold increase of macroscopic cryoconcentration. There is no direct correlation between number of aggregates and macroscopic cryoconcentration. Aggregate formation of that specific mAb is not caused by macroscopic cryoconcentration but can be directly linked to microscopic cryoconcentration in between the ice dendrites. Slower cooling with set-point and storage temperatures below T_g' has proven to be advantageous for the prevention of aggregate formation. We reveal that the subcooling prior to freezing plays a key role in avoiding aggregates. The lower the solution is supercooled the more likely aggregates form. As a consequence, we suggest controlled initiation of the freezing process to avoid large supercooling.

Phase-Field Modeling of Freeze Concentration of Protein Solutions

Bulk solutions of therapeutic proteins are often frozen for long-term storage. During the freezing process, proteins in liquid solution redistribute and segregate in the interstitial space between ice crystals. This is due to solute exclusion from ice crystals, higher viscosity of the concentrated solution, and space confinement between crystals. Such segregation may have a negative impact on the native conformation of protein molecules. To better understand the mechanisms, we developed a phase-field model to describe the growth of ice crystals and the dynamics of freeze concentration at the mesoscale based on mean field approximation of solute concentration and the underlying heat, mass and momentum transport phenomena. The model focuses on evolution of the interfaces between liquid solution and ice crystals, and the degree of solute concentration due to partition, diffusive, and convective effects. The growth of crystals is driven by cooling of the bulk solution, but suppressed by a higher solute concentration due to increase of solution viscosity, decrease of freezing point, and the release of latent heat. The results demonstrate the interplay of solute exclusion, space confinement, heat transfer, coalescence of crystals, and the dynamic formation of narrow gaps between crystals and Plateau border areas along with correlations of thermophysical properties in the supercooled regime.

Label-Free Detection of Tear Biomarkers Using Hydrogel-Coated Gold Nanoshells in a Localized Surface Plasmon Resonance-Based Biosensor

The dependence of the localized surface plasmon resonance (LSPR) of noble-metal nanomaterials on refractive index makes LSPR a useful, label-free signal transduction strategy for biosensing. In particular, by decorating gold nanomaterials with molecular recognition agents, analytes of interest can be trapped near the surface, resulting in an increased refractive index surrounding the nanomaterial, and, consequently, a red shift in the LSPR wavelength. Ionic poly( N-isopropylacrylamide- co-methacrylic acid) (PNM) hydrogels were used as protein receptors because PNM nanogels exhibit a large increase in refractive index upon protein binding. Specifically, PNM hydrogels were synthesized on the surface of silica gold nanoshells (AuNSs). This composite material (AuNS@PNM) was used to detect changes in the concentration of two protein biomarkers of chronic dry eye: lysozyme and lactoferrin. Both of these proteins have high isoelectric points, resulting in electrostatic attraction between the negatively charged PNM hydrogels and positively charged proteins. Upon binding lysozyme or lactoferrin, AuNS@PNM exhibits large, concentration-dependent red shifts in LSPR wavelength, which enabled the detection of clinically relevant concentration changes of both biomarkers in human tears. The LSPR-based biosensor described herein has potential utility as an affordable screening tool for chronic dry eye and associated conditions.

Structural Characterization and Formulation Development of a Trivalent Equine Encephalitis Virus-Like Particle Vaccine Candidate

The zoonotic equine encephalitis viruses (EEVs) can cause debilitating and life-threatening disease, leading to ongoing vaccine development efforts for an effective virus-like particle (VLP) vaccine based on 3 strains of EEV (Eastern, Western, and Venezuelan or EEE, WEE and VEE VLPs, respectively). In this work, transmission electron microscopy and light scattering studies showed enveloped, spherical, and ∼70 nm sized VLPs. Biophysical studies demonstrated optimal VLP physical stability in the pH range of 7.5-8.5 and at temperatures below ∼50°C. Interestingly, the individual stability profiles differed notably between the 3 VLPs. Numerous pharmaceutical excipients were screened for their VLP stabilizing effects against thermal stress. Sucrose, sorbitol, sodium chloride, and pluronic F-68 were identified as promising stabilizers and the concentrations and combinations of these additives were optimized. Candidate monovalent VLP bulk formulations were incubated at temperatures ranging from -80°C to 40°C to establish freeze-thaw, long-term (2°C-8°C) and accelerated stability trends. Good VLP stability profiles were observed at each storage temperature, except for a distinct instability observed at -20°C. The interaction of monovalent and trivalent VLP formulations with aluminum adjuvants was examined, both in terms of antigen adsorption and desorption over time. The implications of these findings on future vaccine formulation development of EEV VLPs are discussed.

Impact of Buffer, Protein Concentration and Sucrose Addition on the Aggregation and Particle Formation during Freezing and Thawing

Purpose

This study addresses the effect of freezing and thawing on a therapeutic monoclonal antibody (mAb) solution and the corresponding buffer formulation. Particle formation, crystallization behaviour, morphology changes and cryo-concentration effects were studied after varying the freezing and thawing rates, buffer formulation and protein concentration. The impact of undergoing multiple freeze/thaw (FT)-cycles at controlled and uncontrolled temperature rates on mAb solutions was investigated in terms of particle formation.

Methods

Physicochemical characteristics were analysed by Differential Scanning Calorimetry whereas morphology changes are visualized by cryomicroscopy measurements. Micro Flow Imaging, Archimedes and Dynamic Light Scattering were used to investigate particle formation.

Results

Data retrieved in the present study emphasizes the damage caused by multiple FT-cyles and the need for sucrose as a cryoprotectant preventing cold-crystallization specifically at high protein concentrations. Low protein concentrations cause an increase of micron particle formation. Low freezing rates lead to a decreased particle number with increased particle diameter.

Conclusion

The overall goal of this research is to gain a better understanding of the freezing and thawing behaviour of mAb solutions with the ultimate aim to optimize this process step by reducing the unwanted particle formation, which also includes protein aggregates.

Charged poly(N-isopropylacrylamide) nanogels for use as differential protein receptors in a turbidimetric sensor array

Due to the high cost and environmental instability of antibodies, there is precedent for developing synthetic molecular recognition agents for use in diagnostic sensors. While these materials typically have lower specificity than antibodies, their cross-reactivity makes them excellent candidates for use in differential sensing routines. In the current work, we design a set of charge-containing poly(N-isopropylacrylamide) (PNIPAM) nanogels for use as differential protein receptors in a turbidimetric sensor array. Specifically, NIPAM was copolymerized with methacrylic acid and modified via carbodiimide coupling to introduce sulfate, guanidinium, secondary amine, or primary amine groups. Modification of the ionizable groups in the network changed the physicochemical and protein binding properties of the nanogels. For high affinity protein-polymer interactions, turbidity of the nanogel solution increased, while for low affinity interactions minimal change in turbidity was observed. Thus, relative turbidity was used as input for multivariate analysis. Turbidimetric assays were performed in two buffers of different pH (i.e., 7.4 and 5.5), but comparable ionic strength, in order to improve differentiation. Using both buffers, it was possible to achieve 100% classification accuracy of eleven model protein biomarkers with as few as two of the nanogel receptors. Additionally, it was possible to detect changes in lysozyme concentration in a simulated tear fluid using the turbidimetric sensor array.

Improving Heat Transfer at the Bottom of Vials for Consistent Freeze Drying with Unidirectional Structured Ice

The quality of lyophilized products is dependent of the ice structure formed during the freezing step. Herein, we evaluate the importance of the air gap at the bottom of lyophilization vials for consistent nucleation, ice structure, and cake appearance. The bottom of lyophilization vials was modified by attaching a rectified aluminum disc with an adhesive material. Freezing was studied for normal and converted vials, with different volumes of solution, varying initial solution temperature (from 5°C to 20°C) and shelf temperature (from -20°C to -40°C). The impact of the air gap on the overall heat transfer was interpreted with the assistance of a computational fluid dynamics model. Converted vials caused nucleation at the bottom and decreased the nucleation time up to one order of magnitude. The formation of ice crystals unidirectionally structured from bottom to top lead to a honeycomb-structured cake after lyophilization of a solution with 4% mannitol. The primary drying time was reduced by approximately 35%. Converted vials that were frozen radially instead of bottom-up showed similar improvements compared with normal vials but very poor cake quality. Overall, the curvature of the bottom of glass vials presents a considerable threat to consistency by delaying nucleation and causing radial ice growth. Rectifying the vials bottom with an adhesive material revealed to be a relatively simple alternative to overcome this inconsistency.

Practical Considerations for Determination of Glass Transition Temperature of a Maximally Freeze Concentrated Solution

Glass transition temperature is a unique thermal characteristic of amorphous systems and is associated with changes in physical properties such as heat capacity, viscosity, electrical resistance, and molecular mobility. Glass transition temperature for amorphous solids is referred as (T g), whereas for maximally freeze concentrated solution, the notation is (T g'). This article is focused on the factors affecting determination of T g' for application to lyophilization process design and frozen storage stability. Also, this review provides a perspective on use of various types of solutes in protein formulation and their effect on T g'. Although various analytical techniques are used for determination of T g' based on the changes in physical properties associated with glass transition, the differential scanning calorimetry (DSC) is the most commonly used technique. In this article, an overview of DSC technique is provided along with brief discussion on the alternate analytical techniques for T g' determination. Additionally, challenges associated with T g' determination, using DSC for protein formulations, are discussed. The purpose of this review is to provide a practical industry perspective on determination of T g' for protein formulations as it relates to design and development of lyophilization process and/or for frozen storage; however, a comprehensive review of glass transition temperature (T g, T g'), in general, is outside the scope of this work.

Forced degradation studies of biopharmaceuticals: Selection of stress conditions

Stability studies under stress conditions or forced degradation studies play an important role in different phases of development and production of biopharmaceuticals and biological products. These studies are mostly applicable to selection of suitable candidates and formulation developments, comparability studies, elucidation of possible degradation pathways and identification of degradation products, as well as, development of stability indicating methods. Despite the integral part of these studies in biopharmaceutical industry, there is no well-established protocol for the selection of stress conditions, timing of stress testing and required extent of degradation. Therefore, due to the present gap in the stability studies guidelines, it is the responsibility of researchers working in academia and biopharmaceutical industry to set up forced degradation experiments that could fulfill all the expectations from the stability studies of biopharmaceuticals under stress conditions. Concerning the importance of the function of desired stress conditions in forced degradation studies, the present review aims to provide a practical summary of the applicable stress conditions in forced degradation studies of biopharmaceuticals according to the papers published in a time period of 1992-2015 giving detailed information about the experimental conditions utilized to induce required stresses.