Quantitative Laser Diffraction for Quantification of Protein Aggregates: Comparison With Resonant Mass Measurement,Nanoparticle Tracking Analysis,Flow Imaging,and Light Obscuration

In the past, analysis of micron-sized (>1.0 μm) aggregates of therapeutic proteins has been limited to light obscuration (LO), and appropriate quantitative methods of evaluating protein aggregates need to be developed. Recently, novel methods with enhanced reliability and sensitivity, such as nanoparticle tracking analysis (NTA), resonant mass measurement (RMM), and flow imaging (FI), have emerged. We have found that quantitative laser diffraction (qLD) is also effective for quantitative evaluation of protein aggregates over a wide size range. However, the different detection principles of the methods potentially lead to inconsistencies in results. This study aimed to compare particle size distributions and concentrations of protein aggregates using the orthogonal methods. Protein aggregates were generated by stirring an immunoglobulin solution. Serial dilutions of the aggregates stock were analyzed by RMM, FI, and qLD to obtain the particle size distribution and concentration using each method. In addition, size distribution of a protein aggregates solution was compared by RMM, NTA, FI, LO, and qLD. Both particle size distribution and concentration were in good agreement between RMM and qLD (0.3-2 μm) and between FI and qLD (2-20 μm). Thus, we concluded that qLD enables covering of the overlapping particle size range between RMM and FI.     

Optimization of Infrared Microscopy to Assess Secondary Structure of Insulin Molecules Within Individual Subvisible Particles in Aqueous Formulations

The analysis of subvisible particles is currently challenging but pivotal to the understanding and control of the quality of protein therapeutics. While a range of characterization methods is available for subvisible particles, information on the protein conformation in a particle—considered a possible parameter in eliciting unwanted immunogenicity of protein therapeutics—is especially challenging in the lower micrometer range using existing analytical technologies. Using 6 different protein particle populations, we show that transmission Fourier transform infrared (FTIR) microscopy can determine protein secondary structure in single particles down to 10 μm. The analytical setup presented here is able to immobilize protein particles and obtain transmission FTIR spectra on individual protein particles in their intact aqueous environment. Spectra of dried particles, on the other hand, were found to occasionally differ from spectra of particles in aqueous environment. In summary, using the analytical setup described in this study, transmission FTIR microscopy uniquely provides information on single protein particles in particle populations in their aqueous environment without interference from the background protein solution.     

The Strengths of Total Holographic Video Microscopy in Detecting Sub-Visible Protein Particles in Biopharmaceuticals: A Comparison to Flow Imaging and Resonant Mass Measurement

Determination of subvisible particle (SVP) content in biopharmaceuticals is a prerequisite to ensure the quality of liquid biopharmaceutical products. Here, we present a comparison of the recently introduced holographic video microscopy (total holographic characterization, THC) with two orthogonal and well-established analytical technologies: micro flow imaging (MFI) and resonant mass measurement (RMM). The capabilities of the THC were investigated under conditions commonly applied in drug product development. Three different antibody products were used at different concentrations and formulations to cover a wide range of realistic use-cases. The comparison was particularly focused on protein aggregates to investigate the applicability of THC to this critical class of particles in drug product development. Protein concentrations up to 100 mg/ml were investigated covering a broad range of viscosity and refractive indices, both important parameters in particle detection. The comparison reveals that THC is highly sensitive to detect protein aggregates in a size range from 0.5 µm to 10 µm. THC shows a significant superiority to FI and RMM in detecting heterogenous protein aggregates which often appear as transparent and porous particles. Additionally, THC needs very small sample amount of about 30 µl and short measurement times, making it applicable for early development stages and high-throughput approaches. These results show that THC is a valuable supplement to the existing particle characterization method portfolio in drug product development.     

Collaborative Study for Analysis of Subvisible Particles Using Flow Imaging and Light Obscuration: Experiences in Japanese Biopharmaceutical Consortium

The evaluation of subvisible particles, including protein aggregates, in therapeutic protein products has been of great interest for both pharmaceutical manufacturers and regulatory agencies. To date, the flow imaging (FI) method has emerged as a powerful tool instead of light obscuration (LO) due to the fact that (1) protein aggregates contain highly transparent particles and thereby escape detection by LO and (2) FI provides detailed morphological characteristics of subvisible particles. However, the FI method has not yet been standardized nor listed in any compendium. In an attempt to assess the applicability of the standardization of the FI method, we conducted a collaborative study using FI and LO instruments in a Japanese biopharmaceutical consortium. Three types of subvisible particle preparations were shared across 12 laboratories and analyzed for their sizes and counts. The results were compared between the methods (FI and LO), inter-laboratories, and inter-instruments (Micro Flow Imaging and FlowCam). We clarified the marked difference between the detectability of FI and LO when counting highly transparent protein aggregates in the preparations. Although FlowCam provided a relatively higher number of particles compared with MFI, consistent results were obtained using the instrument from the same manufacturer in all 3 samples.     

Rapid Quantification of Protein Particles in High-Concentration Antibody Formulations

Current technologies for monitoring the subvisible particles that may be generated during fill-finish operations for protein formulations are cumbersome. Measurement times are generally too long for real-time analysis, and the high protein concentrations that are characteristic of many antibody products interfere with common optical techniques for particle analysis. To rapidly monitor protein particle levels in high-concentration protein solutions, we developed a fluorescence-based method that uses extrinsic fluorescent dyes such as 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid that are sensitive to the presence of aggregated protein. To test the method, antibody formulations containing various concentrations of protein particles were generated by application of various mechanical and freeze-thaw stresses. After addition of fluorescent dyes, fluorescence intensities were measured and compared to fluorescence intensities in particle-free formulations. The differences in fluorescence intensities were linearly proportional to protein particle levels, which for calibration purposes were measured offline by fluid imaging microscopy and protein assays. Protein particle levels could be measured without requiring sample dilution, even in high-concentration (e.g., 40 mg/mL) antibody formulations.     

A Platform for Preparing Homogeneous Proteinaceous Subvisible Particles With Distinct Morphologies

Regulatory authorities and scientific communities are increasingly attentive to the known and universal presence of small particulates in biological drug products. The underlying concern is that these particulates may cause unwanted formation of antidrug antibodies in patients. Pharmacological studies, however, have to date not succeeded in unambiguously identifying risk-prone particle properties. This lack of success may be partly due to a lack of available, well-defined, homogenous particle material. Protein particles arising from stress of protein drug products are by nature often highly heterogeneous in size, morphology, and structure of the constituent protein in the particles. Here, we present simple and pharmaceutically relevant stress conditions to produce 8 different highly homogenous micrometer-sized protein particles from human insulin, representing very different morphologies and conformation of the constituent protein molecules in the particles generated. Insulin's self-association patterns were varied by formulation approaches to create diverse starting materials. The resulting collection of homogenous particles underlines that the particle formation is not necessarily a random process but a consequence of formulation and specific stress condition. Owing to the inherent homogenicity of these populations, the particle materials can act as a standard platform for further studies on insulin subvisible particles in drug products.     

The Coulter Principle for Analysis of Subvisible Particles in Protein Formulations

The Coulter principle can be used for analysis of subvisible particles in protein formulations. The approach has several advantages including: an orthogonal operating principle, high sensitivity, ability to detect very small particles, excellent reproducibility, and high-resolution size information. This minireview discusses some of the important considerations that must be taken into account when utilizing the Coulter principle for subvisible particle analysis in protein formulations.     

A Risk- and Science-Based Approach to the Acceptance Sampling Plan Inspection of Protein Parenteral Products

The requirement for visual inspection of pharmaceuticals has been a compendial expectation for over a century, with some advancement of visible particle control strategies in recent years. Current philosophies include a 100% inspection and an Acceptance Sampling Plan inspection. The particles found during these inspections are normally categorized simply by particle size (visible vs. subvisible), particle source (intrinsic vs. extrinsic) and particle type (inherent vs. extraneous). We believe that a more risk- and science-based approach is attainable, which is grounded in forensic data, toxicological/medical opinions and prior knowledge. We have provided an outline for how to determine patient safety impact of visible particles found in parenteral products and potential actions that could be taken within the quality system regarding lot disposition. We believe this approach focuses efforts on patient safety risks, enhances the use of prior knowledge and improves consistency in how particle observations are handled.     

Stability of lyophilized sucrose formulations of an IgG1: subvisible particle formation

Eight lyophilized formulations of a IgG1 monoclonal antibody (MAb) were prepared containing increasing levels of sucrose. In addition, three of the formulations had sorbitol added at a level of 5% w/w relative to sucrose. The samples were stored for up to 4 weeks at 40°C, which is well below the T_g. Upon reconstitution, the levels of subvisible particles were measured using microflow imaging (MFI). The formulation containing no sucrose contained exceedingly high levels of subvisible particles, accounting for as much as 25% of the weight of the protein. Addition of sucrose markedly decreased the number of subvisible particles, with the maximal sucrose:protein weight ratio being 2:1 (the highest level tested). Addition of sorbitol further decreased subvisible particle levels, even for formulations where the sucrose:protein ratio was relatively high. This suggests that even small amounts of a plasticizer like sorbitol can improve the storage stability of a lyophilized antibody formulation, probably by dampening β-relaxations within the amorphous glass.     

折光率对微流成像法检测蛋白制剂不溶性微粒的影响

目的：蛋白制剂中不溶性微粒的含量是衡量样品质量的重要指标之一,为了更为准确地检测不溶性微粒的含量和粒径,本研究探讨了溶液折光率对于微流成像系统检测不溶性微粒的影响。方法：本研究以牛血清白蛋白（BSA）为例,通过常见的外界刺激条件（冷冻-解冻）制备高浓度的蛋白质不溶性微粒,并将此微粒稀释至不同折光率的溶液（由PEG1000、海藻糖制备）中,利用微流成像系统检测不溶性微粒的含量。结果：当溶液的折光率接近蛋白质不溶性微粒折光率时,利用微流成像技术检测的不溶性微粒含量低于实际的微粒含量。此外,随着溶液折光率的增加,采用微流成像技术检测出的不溶性微粒的粒径也随之减小。结论：蛋白质溶液的折光率发生改变,会影响利用微流成像技术检测不溶性微粒的准确性。因此,利用微流成像技术检测蛋白制剂中不溶性微粒时,需要考虑到制剂处方的折光率对于检测不溶性微粒的影响,必要时可以采用稀释的方法降低折光率对蛋白质颗粒的屏蔽作用。     

Light Obscuration Measurements of Highly Viscous Solutions: Sample Pressurization Overcomes Underestimation of Subvisible Particle Counts

Light obscuration (LO) is the current standard technique for subvisible particle analysis in the quality control of parenterally administered drugs, including therapeutic proteins. Some of those, however, exhibit high viscosities due to high protein concentrations, which can lead to false results by LO measurements. In this study, we show that elevated sample viscosities, from about 9 cP, lead to an underestimation of subvisible particle concentrations, which is easily overlooked when considering reported data alone. We evaluated a solution to this problem, which is the application of sample pressurization during analysis. The results show that this is an elegant way to restore the reliability of LO analysis of highly viscous products without the necessity of additional sample preparation.     

Unmasking Translucent Protein Particles by Improved Micro-Flow Imaging™ Algorithms

Micro-flow imaging (MFI™) is an increasingly important technique for the characterization of subvisible particles during the development of biopharmaceutical products. Protein particles are highly variable in size, appearance, and translucency posing challenges to optical detection techniques. We have developed a set of standard statistical tests applicable for routine evaluation of MFI™ particle dataset quality. The tests evaluate the spatial randomness of particles using nearest neighbor and quadrat analysis. Using case studies of stressed antibody samples, we demonstrate how the tests uncover fragmentation artifacts and uneven detector sensitivity for translucent particles. To improve the detection of translucent particles, a new local pixel intensity variance particle detection algorithm has been developed. The improved algorithm significantly decreases fragmentation artifacts, and also increases sensitivity toward translucent particles in general. Our results highlight current limitations and the potential for improvements in the optical detection techniques for subvisible protein aggregates. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:107–114, 2014     

Deep Convolutional Neural Network Analysis of Flow Imaging Microscopy Data to Classify Subvisible Particles in Protein Formulations

Flow-imaging microscopy (FIM) is commonly used to characterize subvisible particles in therapeutic protein formulations. Although pharmaceutical companies often collect large repositories of FIM images of protein therapeutic products, current state-of-the-art methods for analyzing these images rely on low-dimensional lists of “morphological features” to characterize particles that ignore much of the information encoded in the existing image databases. Deep convolutional neural networks (sometimes referred to as “CNNs or ConvNets”) have demonstrated the ability to extract predictive information from raw macroscopic image data without requiring the selection or specification of “morphological features” in a variety of tasks. However, the inherent heterogeneity of protein therapeutics and optical phenomena associated with subvisible FIM particle measurements introduces new challenges regarding the application of ConvNets to FIM image analysis. We demonstrate a supervised learning technique leveraging ConvNets to extract information from raw images in order to predict the process conditions or stress states (freeze-thawing, mechanical shaking, etc.) that produced a variety of different protein particles. We demonstrate that our new classifier, in combination with a “data pooling” strategy, can nearly perfectly differentiate between protein formulations in a variety of scenarios of relevance to protein therapeutics quality control and process monitoring using as few as 20 particles imaged via FIM.     

Critical Evaluation of Microfluidic Resistive Pulse Sensing for Quantification and Sizing of Nanometer- and Micrometer-Sized Particles in Biopharmaceutical Products

The objective was to evaluate performance, strengths, and limitations of the microfluidic resistive pulse sensing (MRPS) technique for the characterization of particles in the size range from about 50 to 2000 nm. MRPS, resonant mass measurement (RMM), nanoparticle tracking analysis (NTA) and dynamic light scattering were compared for the analysis of nanometer-sized polystyrene (PS) beads, liposomes, bacteria, and protein aggregates. An electrical conductivity of at least 3 mS/cm (equivalent to 25 mM NaCl) was determined as a key requirement for reliable analysis with MRPS. Particle size distributions of PS beads determined by MRPS, NTA, and RMM correlated well. However, counting precision varied significantly among the techniques and was best for RMM followed by MRPS and NTA. As determined by measuring single and mixed PS bead populations, MRPS showed the highest peak resolution for sizing. RMM and MRPS were superior over dynamic light scattering and NTA for the characterization of stressed protein samples. Finally, MRPS proved to be the only analytical technique able to characterize both bacteria and liposomes. In conclusion, MRPS is an orthogonal technique alongside other established techniques for a comprehensive analysis of a samples particle size distribution and particle concentration.     

Applying Pattern Recognition as a Robust Approach for Silicone Oil Droplet Identification in Flow-Microscopy Images of Protein Formulations

Discrimination between potentially immunogenic protein aggregates and harmless pharmaceutical components, like silicone oil, is critical for drug development. Flow imaging techniques allow to measure and, in principle, classify subvisible particles in protein therapeutics. However, automated approaches for silicone oil discrimination are still lacking robustness in terms of accuracy and transferability. In this work, we present an image-based filter that can reliably identify silicone oil particles in protein therapeutics across a wide range of parenteral products. A two-step classification approach is designed for automated silicone oil droplet discrimination, based on particle images generated with a flow imaging instrument. Distinct from previously published methods, our novel image-based filter is trained using silicone oil droplet images only and is, thus, independent of the type of protein samples imaged. Benchmarked against alternative approaches, the proposed filter showed best overall performance in categorizing silicone oil and non-oil particles taken from a variety of protein solutions. Excellent accuracy was observed particularly for higher resolution images. The image-based filter can successfully distinguish silicone oil particles with high accuracy in protein solutions not used for creating the filter, showcasing its high transferability and potential for wide applicability in biopharmaceutical studies.     

The use of flow cytometry for the detection of subvisible particles in therapeutic protein formulations

The amount, identity, and size distribution of particles in parenteral therapeutic protein formulations are of immense interest due to potential safety and efficacy-related implications. In this communication, we describe the use of a flow cytometer equipped with forward- and side-scattering as well as fluorescence detectors, to determine the number of subvisible particles in monoclonal antibody formulations. The method appears to detect particles of size 1 μ and larger, requiring relatively small sample volumes to estimate subvisible particle counts. Additionally, it facilitates differentiation of proteinaceous particles after staining with a fluorescent hydrophobic dye. The method is expected to be particularly well suited for pharmaceutical development, because it provides increased throughput due to the use of a 96-well autosampler.     

Flow Imaging: Moving Toward Best Practices for Subvisible Particle Quantitation in Protein Products

The potential impact of subvisible particles (SVPs) in protein therapeutic products has received a great deal of attention recently. As a result, new analytical methods have emerged to characterize and quantify SVPs. Among these, flow imaging (also called flow microscopy) has been widely employed. As we have used both FlowCAM® and Micro-Flow Imaging? in a variety of development projects, we wished to share our experiences and observations, with the intention of fostering a discussion that will lead to best practices for the use of flow imaging to quantify SVP levels in biopharmaceuticals. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:1133–1134, 2013     

Effects of Product Handling Parameters on Particle Levels in a Commercial Factor VIII Product: Impacts and Mitigation

To reduce the risk of immunogenicity that may be caused by therapeutic protein products, it is important to properly characterize subvisible particles and to develop strategies to reduce the levels of particles delivered to patients. In the present study, by using state-of-the-art methods to quantify particle levels, we found that the factor VIII product, Kogenate FS, contained relatively high levels of protein particles and silicone oil droplets, the vast majority of which were submicron in size. In a test of effects of product mishandling, the Kogenate FS vial was shaken instead of swirled during reconstitution. Levels of silicone oil droplets and protein particles were increased. In contrast, these levels were greatly reduced by 2 mitigation strategies tested, using a nonsiliconized syringe for the diluent container or using submicron pore size syringe filters during simulated infusion. Thus, to avoid potential adverse effects due to mishandling-induced increases in particle levels, it is important to educate end-users about proper product handling. Furthermore, effective particle mitigation and reduction strategies should be developed for factor VIII, and other therapeutic protein products. Such efforts could lead to clinically useful approaches to reduce the levels of particles delivered to patients and to an associated reduction in adverse immunogenicity.     

Imaging Flow Cytometry for Sizing and Counting of Subvisible Particles in Biotherapeutics

Imaging flow cytometry (IFC), a technique originally designed for cellular imaging, is featured by the parallel acquisition in brightfield (BF), fluorescence (FL), and side scattering channels. Introduced to the field of subvisible particle analysis in biopharmaceuticals roughly ten years ago, it has the potential to yield additional information, e.g., on particle origin. Here, we present an extensive, systematic development of masks for IFC image analysis to optimize the accuracy of size determination of polystyrene beads and pharmaceutically relevant particles (protein, silicone oil) in BF and FL channels. Based on the developed masks, particle sizing and counting by IFC are compared to flow imaging microscopy (FIM). Mask verification based on fluorescent polystyrene particles revealed good agreement between sizes obtained from IFC and FIM. In the evaluation of counting accuracy, IFC reported lower concentrations for polystyrene particle standards than FIM. For the analysis of fluorescently stained silicone oil and protein particles however, IFC FL imaging reported higher particle concentrations in the low micrometer size range. Overall, we identified IFC as suitable tool to generate supportive data for particle characterization purposes or trouble shooting activities, but not as routine quantitative technique, e.g., for subvisible particle analysis during drug product development or quality control.     

Analyzing Subvisible Particles in Protein Drug Products: a Comparison of Dynamic Light Scattering (DLS) and Resonant Mass Measurement (RMM)

Aggregation is common in protein drug manufacture, and while the effects of protein particulates are under investigation, many techniques applicable for their characterization have been recently developed. Among the methods available to characterize and quantify protein aggregates, none is applicable over the full size range and different methods often give conflicting results. The studies presented here compare two such methods: dynamic light scattering (DLS) and resonant mass measurement (RMM). The performance of each method was first characterized using polystyrene particle size standards (20, 60, 100, 200, 400, and 1,000 nm) over a range of concentrations. Standard particles were measured both singly and in binary mixtures containing 20 nm particles at a fixed concentration (10¹⁴ particles/mL) and various concentrations of one of the other particle sizes (i.e., 60, 100, 200, 400, or 1,000 nm). DLS and RMM were then used to detect unknown aggregate content in stressed samples of IgG. Both instruments were shown to have a working range that depends on particle size and concentration. In binary mixtures and polydisperse solutions, DLS was able to resolve two species in a manner dependent on both concentration and particle size. RMM was able to resolve particles above 200 nm (150 nm for protein) at concentrations below 10⁹ particles/mL. In addition, dilution was evaluated as a technique to confirm and quantify the number of particles in solution.