Cynthia A. Challener is a contributing editor to Pharmaceutical Technology.

Cynthia A. Challener

Biopharmaceutical manufacturing involves a series of complex unit operations linked together to provide high-purity, biologic actives with specified physicochemical and pharmacokinetic properties. The development of commercial-scale processes that consistently provide high-quality product that meets those specifications requires extensive examination of numerous process variables and potential process variations. Conducting the required number of studies on the commercial scale is not practical; scale-down models are therefore employed to determine optimum conditions for downstream separation processes, including chromatography and viral clearance steps. Qualification that such models provide results truly representative of commercial-scale processes becomes necessary as molecules move closer to commercialization.

A scale-down model is a bench-scale process designed to predict the results that will be obtained when the process is run at commercial scale. Unlike initial processes that are used during the discovery and early development phases to produce material for characterization, efficacy, safety, and other studies, scale-down models are intended to aid in optimization and characterization of the process that will be implemented for manufacture of large quantities of a biologic once the product has been approved.

	While process simulations are an ideal surrogate, given the complexity and inaccuracy of many theoretical models, there often remains no substitute for a physical scaled-down model, according to Adam J. Meizinger, a process engineer in Genzyme’s Purification, Manufacturing Science, and Technology Laboratory.

	Scale-down models are used in the development of nearly every unit operation in the overall biopharmaceutical manufacturing process, including both upstream and downstream steps, and separation and filtrations steps, such as chromatography and viral filtration processes. A scaled-down chromatography process, for instance, is designed considering the residence time, flow rate, and column bed height of the large-scale process. Additional parameters that are considered include buffer preparation and feed stream. “The ideal model behaves identically to the scaled-up process such that the results obtained in the lab exactly predict the results that will be obtained in the manufacturing plant,” says Paul Jorjorian, director of global technology transfer for Patheon. Because they are models, however, such a situation does not occur. The goal, therefore, is to mimic the commercial-scale process as closely as possible.

The quality-by-design (QbD) approach to process development requires characterization of the impacts of different process parameters on product critical quality attributes (CQAs), which in turn necessitates considerable experimentation, according to Meizinger. “While the consideration of up-front risk assessments, access to general scientific understanding, and the use of design-of-experiment (DoE) methodology minimizes the required number of runs and maximizes the informational output, it is impractical to conduct such characterization experiments at full scale. Qualified scaled-down models are instrumental for conducting such characterization work, as well as for viral clearance studies, continuous process improvement, and for conducting impromptu investigations in support of large-scale operations, such as when deviations occur,” he adds.


	While ideal scaled-down models correlate exactly with their large-scale counterpart processes, generally a perfect match is not achieved between the bench and commercial scales, and therefore, model processes are not perfectly scalable. The causes, according to Jorjorian, may not relate directly to the process, but can be attributed to small, nuanced differences that still have an impact on the results at different scales. “The issues are often unavoidable and thus must be addressed by developing correction factors and/or transfer functions that enable the accurate prediction of the behavior of manufacturing processes,” explains Jorjorian. “It is important, however, to minimize the need for correction factors and transfer functions, and for those that are required, provide thorough justification and clearly demonstrate their suitability,” he adds.

	Another aspect of scale-down models that can create issues when predicting large-scale behavior is the fact that models are qualified at the center point of the process design space. “This approach can lead to discrepancies in predicted and actual results when the model is applied to the entire design space,” Jorjorian observes. He adds that timing and planning of modeling runs is also important and can negatively influence results if not done effectively. For example, it is important to use the same feed used for production runs in scale-down modeling runs; therefore, modeling runs must be scheduled when the feed is available. In many cases, that isn’t possible, and the feed may need to be frozen, which introduces a new variable that can impact the reliability of the model.

	Specifically for chromatography operations, some key considerations in developing scaled-down models are minimizing the differences in the extra-column volume, which varies considerably with scale, contending with increasing wall effects inherent in small-diameter chromatography columns, and accounting for differences in detector-specific path lengths and the associated non-linearity of detector output, according to Meizinger. He also notes that some steps (e.g., gas overlays for intermediate holds) may be challenging to implement as part of scaled-down model development, and mixing dynamics and heat transfer often remain different between scales. “The impact of these differences must be carefully assessed for their resulting impact on scaled-down model performance,” he says.

	Scale-down modeling of membrane chromatography processes can also be difficult, according to Jorjorian. The reason often relates to the designs used for small- and large-scale membranes; they are often different, with large-scale membranes having added flutes or pleats or other features that affect their performance such that it is difficult to develop bench-scale processes that can reliably predict production-scale outcomes.

There is nothing new about the use of bench-scale process models during the development of biopharmaceutical manufacturing processes. What has become an important trend in process development is the need to demonstrate that scaled-down models truly represent their large-scale counterparts. “It has only recently become standard practice to demonstrate that scaled-down models provide results that are statistically equivalent to those obtained from commercial-scale versions of the same processes,” states Meizinger.

	Often during earlier stages of development, even through Phase I clinical trials, scale-down models of downstream biopharmaceutical processes are generally not formal, qualified models. “For these models, the basis for use of each model and the rationale for why it is expected to be representative of the process at large scale are documented,” notes Jorjorian. As a molecule progresses toward commercialization, however, formal, qualified models are required. The ability of the model to predict results at large-scale must be demonstrated by performing at least triplicate runs. The use of any correction factors and/or transfer functions must also be justified and their application demonstrated to provide robust results.

	Qualification of most models for chromatographic separations is fairly straightforward, according to Jorjorian. “There is a lot of documentation and analyses to complete, so in essence, qualification of scale-down models is often an exercise in coordination, rather than presenting a substantial technical challenge,” he observes. Meizinger agrees that the use of statistical equivalence for testing quality attributes and process performance indicators between scales is generally not an issue. “Demonstration of both individual unit and linked unit output (recovery, product quality attributes, product purity, chromatographic profiles/transition analysis, etc.) comparability between small and large scales remains both practical and accepted,” he states.

Qualification of scale-down models can be challenging, however, when very small column sizes are involved. There is significant interest in using high-throughput approaches for scale-down modeling to speed up development times. There are, however, technical issues that arise due to the different behaviors observed in very large and very small columns, such as the wall effects mentioned previously. 

	“It is definitely more challenging to establish robust scale-down models using high-throughput methodologies because typically transfer functions and correction factors are required. As a result, it is more difficult to adequately demonstrate the scalability of the models to the level required for qualification,” Jorjorian says. He adds that there is a lot of effort being devoted to overcoming these issues to enable high-throughput modeling of downstream bioprocesses.

	A few groups are also investigating the application of first principles calculations to the scale-down modeling of both upstream and downstream unit operations, and particularly for chromatography, for which there is significant understanding of separation behaviors and existing mathematical models. “This approach to scale-down modeling is in the earliest phases and largely limited to large pharmaceutical companies and university research groups with the resources and computing power required,” Jorjorian says.


	“Despite the limitations of existing scale-down modeling methods, the use of scaled-down models is recommended wherever possible, including for process characterization, viral clearance studies, continuous improvement, manufacturing-related investigations, evaluation of changes in raw materials, and so on, barring only validation efforts and clinical trial/commercial manufacturing requirements for performance of large-scale runs,” asserts Meizinger. “Today, scaled-down models serve as efficient and cost-effective representations of full-scale processes. While the inability to demonstrate equivalence between scaled-down and large-scale operations is often inevitable for some metrics, further understanding of these scale-related differences, particularly through the development/refinement of associated engineering models, promises to continuously improve the accuracy and utility of scaled-down models,” he states.

Articles

Scale-down modeling accelerates the development of downstream biopharma manufacturing processes.

Small-Scale Modeling Boosts Downstream Development

The ultimate goal in pharmaceutical manufacturing is to achieve complex syntheses in high yields with high selectivities in as few steps as possible, and to meet quality requirements. Many reagents considered hazardous due to their extremely high reactivity and/or toxicity can often be used in processes that meet these criteria. In the past, however, the safe handling of such materials and the design of safe processes using them have been a challenge. Advances in engineering control and reactor/process technologies combined with greater understanding of the underlying fundamental physical and chemical behaviors of hazardous reagents are leading to their increasing use for pharmaceutical production.


	Reagents are typically classified as hazardous if they are highly unstable and/or react violently under specific conditions, such as exposure to oxygen or moisture in the air or when combined with other reactive species. Explosive compounds and substances that are sensitive to shock, friction, and heat are examples of unstable, hazardous reagents. Reactions that produce or use these compounds as raw materials, as well as highly energetic processes, require precise and careful control of the process conditions, including the use of inert blanketing gases, selection of the appropriate order and rate of addition, and maintenance of suitable reaction temperatures. Some toxic reagents also fall into the hazardous reagent category, such as extremely strong acids and bases and other corrosive materials.

	Key examples of hazardous processes that have applicability for the synthesis of pharmaceutical intermediates and APIs include:

	Of these technologies, halogenations, nitrations, and azide-based reactions are the most commonly performed hazardous reaction processes, according to Thierry Durand, R&D director at Novasep Synthesis. “These reactions are the most prevalent because they provide access to a large variety of functionalized aromatics and heterocycles that are present in many APIs,” he notes.


	Although the natural reaction to the concept of hazardous reagent chemistry is to assume that such processes will be more complex, costly, and lead to complex mixtures of products, the opposite is often true. Hazardous reagents often allow the synthesis of desired compounds in fewer steps than more conventional reagents. In addition, the reactions often proceed more rapidly with higher yields and greater selectivities than can be achieved using multi-step routes with less reactive materials. “Overall, the use of hazardous reagents often leads to more cost-effective processes that provide purer products, and in fact as many as 10 of the 12 principles of green chemistry (1) can be fulfilled for these transformations,” Durand asserts. He adds that careful evaluation can lead to the development of short and elegant synthetic routes using hazardous chemistry that have reduced environmental impacts.

	Realization of these benefits within the pharmaceutical industry is leading to greater interest in hazardous chemistry routes, particularly for the production of non-regulated raw materials and intermediates. Durand does note, however, that cGMP requirements are becoming more common for starting materials and earlier intermediates in overall synthetic schemes for APIs than even a few years ago, which can be a challenge to using hazardous chemistry for some pharmaceutical companies.

	“Regulatory and supply chain risk management by pharmaceutical manufacturers requires alignment of the technologies used by multiple partners in their supply networks, often to the most standard technologies. Because specialized technical expertise is necessary for safe operations using hazardous reagents, many contract manufacturers do not have extensive capabilities in this chemistry. Some pharmaceutical companies therefore choose not to take advantage of the benefits offered by this technology,” he explains. On a positive note, however, there are many examples of the use of azide chemistry in the final steps of API syntheses. In addition, recently developed azide building blocks are now used to perform click chemistry to modify a large variety of biomolecules.


	Novasep has been using hazardous reagents for more than 135 years and in that time uncovered many examples where hazardous chemistry offers significant advantages over more conventional synthetic methods. For instance, a recent process for the reduction of a hydroxy ester using a standard ester-reducing agent that originally involved five steps--including protection and deprotection of the hydroxyl group and provided the desired product in 59% yield--was replaced with a two-step route that proceeded via direct amide formation and gaseous diborane reduction (no protection/deprotection required) in 81% yield. Production costs were reduced by 60%, and the reaction using hazardous reagents proceeded with much higher atom efficiency, a lower E-factor, and the use of less solvent.

	In a second recent example, a multistep Grignard/carboxylation process was replaced with a one-step carbonylation reaction. The customer required conversion of an aryl chloride bearing a keto substituent to an aromatic ester. The original process involved three steps, including protection of the keto functionality. The new process developed by Novasep involved Pd-mediated carbonylation and provided the desired product in quantitative yield without any need for a protection step. In this case, raw material consumption was reduced by 50% due to the high atom efficiency of the transformation and reduced solvent use.


	Realization of such dramatic benefits does require extensive experience with hazardous reagent chemistry. Not all processes that at first glance may appear to be suitable for replacement with hazardous chemistry are appropriate. “It is necessary to consider not only the chemistry involved, but also the process conditions and controls required to ensure process safety and performance. A process must be feasible, safe, and economically advantageous,” observes Durand.

	Novasep proposals are based on a careful evaluation of different options, including hazardous chemistry, because it is considered a standard tool in the company’s synthetic tool box and therefore not a negative criterion. “Alignment with customer timelines and cost expectations are the key drivers when determining the optimum synthetic route. Hazardous processes, even after taking into account necessary process safety measures, are often highly competitive solutions,” Durand says.

	Equally important has been an increase in customer awareness with respect to the advantages of hazardous chemistry. They also have a greater understanding of the risks associated with hazardous processes and the advanced safety measures that are available today, according to Durand. “Novasep actively participates in symposia and webinars about hazardous chemistry in order to educate pharmaceutical companies about the state-of-the-art technologies that are being implemented. We believe that sharing information with our customers and the hazardous chemistry community is critical to increasing the perception that hazardous chemistry is safe when properly conducted,” he comments.

	Durand also stresses that there is a significant internal commitment at Novasep surrounding its hazardous chemistry operations. Procedures for all operations are detailed, and extensive training of both employees and contractors is performed to ensure a high level of expertise within the company. Continuity of that expertise is also maintained by identifying future internal experts in anticipation of their career development.


	Hazardous chemistry can only be conducted safely if the process can be effectively monitored and controlled. Reactor and other engineering safety control technologies continue to advance and help address some of these concerns. The most exciting developments, however, have been related to process analytical technology (PAT), according to Durand. He points to ReactIR (Mettler Toledo), a real-time, in situ mid-infrared-based system designed for monitoring the progression of solution-phase reactions and determining the gas-phase concentrations of key reagents (e.g., HN

 concentration). The system also provides specific information about a reaction’s initiation, conversion, intermediates, and endpoint, and is therefore an important new PAT tool. “The development of MRT (micro reaction technology) has contributed to further reductions in the level of risk associated with hazardous processes (extremely efficient control of exotherms and minimization of reaction volumes/quantities) and also helped to decrease somewhat the psychological barriers to using these highly beneficial chemical technologies,” Durand states.

, Oxford University Press (New York, 1998) p.30.

Hazardous reagents can prove to be faster, simpler, cheaper, and greener.

Hazardous Reagents for Higher Yields

Materials science, while often associated with industries other than bio/pharmaceuticals, also plays a significant role in the production of drug substances and formulated products, from reactor and purification equipment design to catalyst technology, the selection of polymorphs, the development of new drug-delivery technologies, and the choice of materials for medical devices. A selection of developments in nanocatalysis for API synthesis and nanoparticle technologies for more effective API delivery is discussed here.


	Many types of nanocatalysts have been developed and investigated as mediators of complex synthetic organic transformations. They are attractive because nanoparticles have different properties from their bulk counterparts, including high surface areas. Their electronic, optical, and magnetic properties are often vastly different from bulk materials, and consequently their reactivities are different on many levels. Synthetic chemists have sought to use these different behaviors to prepare highly stable nanocatalysts with high activities and selectivities. Magnetic nanocatalysts are of particular interest in organic synthesis because they can often be readily recovered and reused, while the separation of non-magnetic nanocatalysts that are also non-supported can be problematic.

	Audrey H. Moores at McGill University in Canada focuses on the synthesis of novel magnetic, reusable metal nanocatalysts for coupling, hydrogenation, C-H activation, and oxidation. Robust, inexpensive, amphiphilic polymer-stabilized Fe(0) nanoparticle (Fe NP) catalysts developed by Moores are highly efficient for the hydrogenation of alkenes, alkynes, aromatic imines, and in ethanol or water in a flow reactor. Aliphatic amines and aldehydes, ketones, esters, arenes, and nitro and aryl halide groups are not affected (1). Nanocatalysts comprising Fe

 particles surrounded by nitrogen-doped graphene layers have also been shown by Matthias Beller of the Liebniz Institute for Catalysis and the University of Rostock in Germany to mediate the hydrogenation of structurally diverse and functionalized nitroarenes to anilines and the one-pot reductive amination of carbonyl compounds with nitroarenes (2). His group prepared more than 40 amines useful as building blocks for pharmaceuticals and other fine/specialty chemicals.

	Moores has also shown that patches of palladium nanoparticles deposited on colloidal cellulose nanocrystallite (CNC) nanowhiskers catalyze the enantioselective hydrogenation of prochiral ketones in water at room temperature and 4 bar H

, achieving an enantiomeric excess of 65% with 100% conversion (3). Meanwhile, researchers at Birjand University and Payame Noor University in Iran deposited ionic liquids (ILs) on magnetic nanoparticles to overcome their limited recyclability (4). This approach led to increased activity of the ILs and their reduced consumption, and the heterogeneous nanoparticles were recoverable. The researchers suggest that the nanoparticle-stabilized ILs can be used as solvents, catalysts, or for the extraction of specific compounds that form bonds with the ILs. 


	A large number of small-molecule drug candidates under development today have poor solubility, and thus reduced bioavailability. In many cases, formulation strategies and drug delivery technologies can overcome this issue. Nanoparticles in particular can increase the stability of APIs, protect them against degradation, and enhance their bioavailability by increasing their solubilization, enhancing their permeability, reducing their rate of metabolism, and/or improving their transport. 

	While biodegradable polymers are often selected for the formation of nanoparticles, some researchers have focused on the use of lipids due to their greater physiologic similarity. Solid lipid nanoparticles (SLNs) also offer site-specific targeting, with high adhesion to the gut wall, which is an ideal location for the absorption of release APIs (5). In addition, both lipophilic and hydrophilic drugs can be incorporated into SLNs without the need to use organic solvents. It is important, however, to select an appropriate lipid for a given API to obtain crystalline SLNs with uniformly dispersed API and suitable lipophilicity for improved drug solubility. In some cases, biodegradable polymers may be used as surfactants to stabilize SLNs or as a surface coating to increase the biodistribution of APIs. Other excipients may also be used in SLN formulations, including non-polymeric nonioninc surfactants, cosolvents, and antioxidants.


	As the potency of many drugs-particularly oncology APIs-increases, there is significant need for technologies that enable their targeted delivery to the site of action to minimize the unwanted side effects common with systemic delivery. Many researchers are turning to nanotechnology to achieve that goal. Careful design of nanoparticle properties, typically through modification of their surface properties, can enable their binding to specific components within the body and influence their API release behaviors.

	Two examples of the use of nanotechnology for targeted drug delivery come from Southern California-based universities. In the first example, scientists from the California NanoSystems Institute at UCLA developed a nanoparticle delivery system for the antibiotic moxifloxacin that vastly improves the drug’s effectiveness against pneumonic tularemia, a type of pneumonia caused by inhalation of the bacterium 

, which is highly infectious and designated as a top-tier bioterrorism agent (6), survives and multiplies within macrophages, particularly those in the liver, spleen, and lung. Jeffrey Zink and colleagues designed mesoporous silica nanoparticles that are readily taken up by macrophages. The nanoparticles are soaked overnight in a solution of the API, which is adsorbed in the pores. The pores are then blocked with nanovalves that are designed to degrade in the acidic environment of the macrophages. As a result, the drug is not distributed systemically, but only once it enters the macrophages. The approach allows for significantly more API to reach the site of infection without the side effects typically observed when moxifloxacin is administered freely into the blood stream (6). The researchers found that in mice given a lethal dose of 

, the nanoparticle-delivered moxifloxacin caused few side effects and was more effective at reducing the number of bacteria in the lungs than a dose of freely injected moxifloxacin two to four times greater.

	Researchers at the University of California, San Diego Jacobs School of Engineering, led by Liangfang Zhang, have taken a different approach to targeted delivery using nanotechnology. In their case, nanoparticles formed of a biodegradable polymer were coated with fragments of human platelet membranes, which preferentially bind to damaged blood vessels and certain pathogens, such as Methicillin-resistant 

 (MRSA) bacteria, and protect the nanoparticles from attack by the immune system (7). Unlike synthetic platelet mimics, the platelet membrane fragments possess the complete set of surface receptors, antigens, and proteins naturally present on platelet membranes. Once the platelet fragments bind to the desired site, the polymeric core degrades and is safely metabolized by the body, releasing the drug at the site of action. When nanoparticles loaded with docetaxel, a drug used to prevent scar tissue formation in the lining of damaged blood vessels, were administered to rats afflicted with injured arteries, the loaded nanoparticles were observed to selectively bind to the damaged sites of arteries and heal them (7). 

	Nanoparticles loaded with vancomycin at one-sixth the clinical dose and injected into mice systemically infected with MRSA bacteria resulted in up to a one-thousand-fold reduction of the bacterial counts than those in mice treated with the clinical dose of vancomycin alone (7).


	A third approach to nanoparticle-based delivery of APIs relies on the use of nanoparticles formed from natural biomolecules. Silk fibroin (SF) has attracted particular attention due to its excellent biocompatibility, biodegradability, and low immunogenicity combined with a high binding capacity for many types of drugs, good controlled release properties, and ease of preparation (8). SF is an alternative to biodegradable polymers, such as poly (lactic acid) (PLA), poly (ε-caprolactone) (PCL), and poly (glycolic acid) (PGA) because protein-based nanoparticles bear functional groups that are naturally designed to interact with cells and cause biological responses. SF in particular is widely used as a biomaterial and is well characterized and understood. Studies of SF nanoparticle systems have shown that its biodegradation rate is influenced by its crystallinity, molecular weight, and degree of crosslinking. However, while numerous methods for the fabrication of nanoparticles have been developed, there is significant variation in the structure of SF obtained from different species and even individuals, and thus interest in genetically recombinant SF-based nanoparticles is increasing. Surface modifications are also required to improve the delivery specificity (8).

	A nanoparticle-based formulation of the drug ormeloxifene (ORM) for the treatment of pancreatic cancer is under development by researchers at the Department of Pharmaceutical Sciences and the Center for Cancer Research at the University of Tennessee Health Science Center in order to enable tumor-specific targeted delivery (9). The ORM was readily encapsulated in poly(lactic-co-glycolic acid) nanoparticles that were then subjected to antibody/aptamer conjugation to achieve tumor-specific targeting. Cellular uptake and internalization studies with the 100-nm-diameter particles confirmed that they did not undergo lysosomal degradation and survived to allow efficient endosomal release. Treatment of a xenograft mice model resulted in increased animal survival and suppressed pancreatic tumor growth (9).

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	8. Y. Li et al., 

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	9. S.C. Chauhan et al., 

Nanoscale catalysts and engineered nanoparticles show promise for API synthesis and delivery.

Nanoparticles Demonstrate Potential for Small-Molecule Pharmaceuticals


	When referring to this article, please cite it as C. Challener, "Going Small to Achieve Success on the Commercial Scale," 

Scale-down modeling is instrumental in supporting the development of downstream biopharma manufacturing processes.

Going Small to Achieve Commercial-Scale Success

:
	When referring to this article, please cite it as C. Challener, “Faster, Cheaper, and Greener," 

Hazardous reagents can simplify processes and provide higher yields and purities.

Faster, Cheaper, and Greener


	Although just a few decades old, the biopharmaceutical industry has evolved significantly since its inception. Many candidate biologics today-antibodies and antibody fragments, highly potent antibody-drug conjugates (ADCs), virus-like particles, cell- and gene-based therapies, etc.-are different from the first simple, recombinant proteins. Manufacturers have been continuously challenged to develop analytical methods for timely and accurate determination of the chemical, physical, and therapeutic properties of these different actives, as well as potential contaminants throughout the production process, from raw material selection to process analysis, formulation development, and release testing. 

	The introduction of biosimilars and the move toward continuous processing are creating the need for more rapid and sensitive analytical techniques. The advent of quality by design (QbD) has further increased the importance of analytical methods/technologies within a manufacturing environment, according to Fiona Greer, global director of biopharma services development at SGS Life Science Services.

	Newer versions of traditional methodologies, such as capillary isoelectric focusing (cIEF) versus IEF gels, peptide mapping with liquid chromatography-tandem mass spectrometry (LC/MS/MS), and high-performance LC (HPLC) are available today. Notably, mass spectrometry-based methods and next-generation sequencing technologies are addressing the need for greater sensitivity in less time. Automation and high-throughput technologies are also having an impact. As the industry introduces more complex and increasingly potent molecular formats with novel, highly potent product-related impurities, however, ongoing advances will be required.


	For product characterization, the most appropriate techniques will depend on the class of molecule: protein, glycoprotein, pegylated, ADC, vaccine, etc. “Improvements in biopharmaceutical mass spectrometry in the past 10 years-in sensitivity, dynamic range, resolution, mass accuracy, and user-friendliness-have dramatically improved our ability to get detailed protein molecular information,” says Byron Kneller, director of analytical/formulation development with CMC Biologics.

	The continued development and deployment of LC/MS-based applications are having a significant impact on both the characterization and quality testing of biopharmaceuticals, particularly for recombinant proteins and monoclonal antibodies, agrees Mike Garrett, senior director of global marketing for BioReliance. “While in the past these methods were reserved for early research into the structure of these molecules, today, methods are being developed that bring this technology closer to the quality control lab,” he observes. Access to more sensitive and detailed characterization data is allowing manufacturers to better understand and more carefully control the molecular structures of their products during the manufacturing process. Garrett also notes that LC/MS has enabled finer control of bioprocess optimization, allowing for correlation of process changes to both molecular structure and yield.

	Some of the most recent advances in product characterization techniques have, according to Greer, been developed in response to challenges encountered with biotherapeutic products and their post-translational modifications (PTMs). Glycosylation analysis in particular has been advanced significantly with the advent of high-resolution mass spectrometry and the use of hydrophilic interaction liquid chromatography (HILIC) columns for glycans. “Introduction of the quadrupole orthogonal acceleration time-of-flight (Q-ToF) geometry and the increased resolving power of MS now allow the direct determination of the monoisotopic mass of antibody heavy chains including modifications such as deamidation,” Greer explains. Kneller adds that current-generation Q-ToF and Orbitrap instruments allow for high-resolution intact mass and peptide mapping measurements for both characterization and process-development support, and current software continues to make data processing easier and faster.

	State-of-the-art MS instruments with markedly increased sensitivity are also providing profound insights into the impurity profiles of biotherapeutics and allowing the identification of previously unknown host-cell contaminants, according to Harald Wegele, head of analytical development and quality control in Europe for Roche. “Sensitive assessment of specific host-cell proteins (HCPs) and other contaminants provides crucial guidance for the development of impurity depleting process steps, which ultimately helps to warrant a maximum of product safety,” he states. Additional developments such as sequential window acquisition of all theoretical mass spectra (SWATH) and parallel reaction monitoring are improving the quantitative assessment of process-related impurities.

	Greer also expects wider adoption of numerous other MS-based analytical techniques, including ion mobility-MS, capillary electrophoresis-MS (CE-MS), and hydrogen-deuterium exchange-MS (HDX-MS). Wegele adds that size-exclusion chromatography (SEC) coupled to native MS already provides-particularly for novel antibody formats like bispecifics-a fast and easy means for gaining unachieved levels of information on, for example, the size-variant distribution of biotherapeutic, as early as at the onset of clinical development. He also points to 2D-HPLC as providing a convenient and accurate method for characterizing single product peaks, side products, and excipients.


	There is tremendous pressure on biopharmaceutical companies to get products to the market more quickly and at lower cost without compromising safety. Manufacturers are consequently looking for alternatives to conventional cell-based analytical methods. Newer personalized treatments such as cell-based therapies, in fact, require more rapid release testing because they do not have long-term stability and must be administered to patients soon after they are produced. Manufacturers are also moving to continuous processing, which requires process analytical technology (PAT) that provides real-time process monitoring data.

	Several newer testing methods have been developed and are in the process of being implemented by the biopharmaceutical industry, largely in cooperation with regulatory agencies such as FDA. Improvements in real-time, quantitative polymerase chain reaction (qPCR)-based methods have allowed for broader detection of known potential contaminants with improved speed and accuracy, according to Garrett. Newer nucleic acid detection technologies, such as next-generation sequencing, are also being applied to the quality control testing lab. “Importantly, these technologies will allow manufacturers to test their biopharmaceutical products for both known and unknown adventitious contaminants,” Garrett says.

	Advances in bioassays have also made potency testing easier, faster, and more reproducible, according to Kneller. “The broader availability of reporter-gene assays (e.g., for antibody-dependent cell-mediated cytotoxicity [ADCC]) testing has decreased the difficulty of implementing some potency assays, while access to soluble enzyme-linked immunosorbent assay (ELISA) formats and ready-to-use analytical cell banks has decreased both the time needed for potency assays and assay variability,” he explains. Wegele adds that novel LC-, cell-, and surface plasmon resonance (SPR)-based assay formats are facilitating the assessment of the impact of PTMs on antibody/bispecific antibody Fc (crystallizable fragment) effector functionality, including pharamacokinetic (PK) properties (e.g., via FcRn [neonatal Fc receptor] affinity chromatography). The Fc region of a therapeutic antibody interacts with receptors on various types of cells and is involved in immune-mediated effector functions, such as ADCC and complement-dependent cytotoxicity (CDC). It is therefore potentially important in determining drug safety and efficacy and must be fully characterized.

	Advances in chromatography methods are also enabling more rapid analyses, according to Kneller. “The increased use of ultra high-pressure liquid chromatography (UHPLC) systems and sub-2 µm columns has enabled more rapid, higher-resolution chromatographic assays, which has decreased testing time for many release methods,” he comments.


	Implementation of high-throughput (HTP) methods and expanding use of automation are additional avenues the biopharmaceutical industry is pursuing to achieve more rapid testing. The challenge has been to reduce testing times without loss of accuracy, precision, specificity, sensitivity, and robustness. Several successes have been achieved to date, however.

	Microfluidic capillary electrophoresis (MCE) has, according to Wegele, become a central pillar for product quality analytics during clone selection and bioprocess development due to its ease of sample preparation, robustness, and unrivaled high-throughput capability. “This HTP method is indispensable for meeting the steadily growing demand for the shortest possible sample turnover time and enhanced time efficiency in present-day biologics development,” he says.

	Automated high-throughput quantification of process-related impurities (e.g., HCPs and Protein A), titer, and fermentation broth supplements such as insulin, LongR3, etc., via electrochemiluminescence immunoassay (ECLIA) is also now used at Roche to support process development, process characterization/process validation studies, manufacturing, and in-process control/release testing, according to Wegele. “This technology is high-throughput-compatible and greatly reduces hands-on time. As a result, it enables novel insights for bioprocess development in near real-time and facilitates the assessment of process-related impurities depletion,” he says.

	Higher-throughput screens for formulation development coupled with the use of design-of-experiment (DoE) tools have also enabled faster, more comprehensive screening of many formulation conditions and excipients and decreased the time required for formulation optimization, according to Kneller. Often, combinations of light-scattering, intrinsic and extrinsic fluorescence, and calorimetry are used to rapidly deliver information on protein stability in many excipient combinations.


	Recent years have seen growing interest in newer types of biologic actives. Significant numbers of antibody-based treatments have been commercialized, and many more, including those based on antibody fragments and ADCs, are in advanced stages of development. Successful initial studies with cell- and gene-based therapies are attracting interest in these therapies, many of which are now in clinical trials. While many of the analyses required to characterize these different classes of biologic drug substances are the same, their characterization does in many cases require different analytical techniques.

	For newer antibody formats, both Garrett and Wegele note that LC/MS is a relatively fast method for gaining high levels of information on the size-variant distribution of biotherapeutics at early development stages. CE is also providing deeper insights into the structure of these molecules, according to Garrett. “Use of these techniques has led to numerous improvements in the manufacturing of antibodies and antibody fragments, particularly when considering the variables that can now be investigated and controlled as part of the manufacturing development process,” he asserts.

	For cell-based therapies, Garrett notes that the development and adoption of rapid, molecular-based testing methods for both process and product safety will enable cell therapy products to be manufactured in the timeframes necessary to both manipulate patient-derived cells and then deliver them safely. The development of methods for assessing the safety of the viral backbones used to produce gene therapies has also kept pace with their advancement into the clinic. “Virology-based tests have been refined such that they now provide information on the specific properties and quality of vector backbones, which is crucial for ensuring the safety of these advanced therapeutics,” Garrett states. He also notes that molecular methods such as next-generation sequencing are being employed to investigate the identity, purity, and stability of virus-based gene therapies.


	Full analytical characterization of branded biotherapeutics and potential biosimilar products is fundamental to the development of biosimilars, and the pathway for analytical method development for biosimilars is somewhat different from that of novel biotherapeutics, according to Jun Lu, director of analytical development for Catalent Pharma Solutions. “Both release and characterization methods are required at the very early stage of biosimilar development, because the reference product from multiple lots must be extensively characterized to establish the target product profile,” he says. More specifically, analytics are essential to defining the critical quality attributes (CQAs) that form the quality target product profile (QTPP).

	Demonstration of similarities between the biosimilar and reference product through side-by-side comparison (i.e., physical, biological, and chemical characterization) is required before progressing into the clinic, according to Greer. Matching of the amino acid sequence and PTMs of the reference product determined by using LC/MS/MS and other protein characterization methods must be performed as a clone selection criterion, because upstream and downstream development has minimal impacts on changing these CQAs, adds Lu.

	Use of orthogonal methods for biosimilar assessment is also emphasized by regulators, because subtle differences between a biosimilar and the reference product may be difficult to detect using only one analytical method. FDA in particular has introduced the concept of “fingerprint-like” analyses, according to Greer. “This approach entails the use of a carefully selected portfolio of characterization techniques for primary and higher-order structure, together with biological and potency assays producing data that, when combined, add up to more than the sum of the parts,” she says.

	For instance, Lu notes that for analysis of high-molecular-weight (HMW) species, which present a high-risk safety concern, supplementing SEC with analytical ultracentrifugation (AUC) is strongly recommended. For the determination of higher-order structure, a combination of at least two techniques from a list including circular dichroism (CD), Fourier-transform infrared (FTIR), differential scanning calorimetry (DSC), and HDX-MS can be used to potentially elucidate any detailed structure differences. Garrett adds that advanced cell-based potency assays are important for determining whether the 

 effects of biosimilars are similar to the originator molecule. Greer observes, however, that the link between higher order structure and biological activity remains to be explored. She does note, though, that several techniques are emerging from research backgrounds to address these questions, such as HDX-MS and 2D-nuclear magnetic resonance (NMR) imaging.

	Statistical analysis of analytical data for the determination of biosimilarity is also required by FDA to ensure confidence in the data. One consequence, according to Lu, has been the replacement of imaging methods such as sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and IEF gels with CE-SDS and cIEF, respectively, which allows greater analysis of the data output.


	Despite the numerous advances in MS, CE, next-generation sequencing, and other rapid assays, further developments are still needed. Adoption of many new analytical technologies takes time given the need for extensive confirmation and validation of performance. Many of these newer methods are gaining acceptance further down the development pathway and closer to quality control, but are not yet widely used. Regulators are, however, starting to explore the potential advantages these technologies can provide, according to Garrett.

	One specific issue for Kneller is HCP quantitation, which for early clinical work is typically performed using commercially-available ELISA kits, but then requires transition to costly custom assays later in development. “This transition can be difficult if kits do not provide adequate coverage of all HCPs potentially present in the product. Orthogonal approaches to HCP quantitation (e.g., mass spectrometry) are not yet feasible or widely-adopted, however,” he notes. Wegele points to the need for tools that enable the assessment of the criticality (e.g., safety, immunogenicity, PK, potency) of various product-related impurities/CQAs (e.g., HMW species, dimers, fragments, PTMs, charge variants, etc.) to identify control strategies that make sense and do not lead to excess testing burdens.

	Reed Harris, senior staff scientist in Pharma Technical Development at Genentech, would like to see more effective methods for identifying the causes of excipient degradation, which may be due to trace-level impurities that are below current detection capabilities. He also points to the need for better resolution of higher-molecular-weight species using SEC. SEC aggregate resolution is needed because there is growing evidence that antibody aggregates are not as immunogenic as originally believed, and further work is necessary to establish the true patient risks for different aggregate types. “Current SEC columns resolve monomers from dimers, but do not resolve different dimer types or multimers such as trimers, tetramers, etc., very effectively,” he says. Furthermore, he notes that while CE-SDS is an advance over SDS-PAGE, further improvements are needed. The presence of SDS makes it difficult to analyze CE-SDS peaks with mass spectrometry, and therefore, most peak assignments are performed by spiking forms prepared using other methods into samples, which is time consuming.

	Particle analysis is another issue for Wegele. He notes that currently available methods are mostly insufficient for precise and robust assessment of subvisible particles, particularly translucent proteinaceous particles and particles with diameters less than approximately 2 μm. Roche has developed a modified light-obscuration sensor that monitors the signal width rather than length, leading to improved detection of very small subvisible particles, reduction of artifacts during the analysis of low concentrations of translucent protein particles, and higher counting accuracy compared to flow imaging microscopy and standard light obscuration measurements.
	Other ongoing needs, according to Wegele, include replacement of cell-based potency assays with novel, cell-free assay formats in the quality control environment; methods for the evaluation of the impact of combined administration of biotherapeutics; and more automated testing solutions to cope with the steadily increasing sample load of ever more complex biologics and next-generation biologics, which are often highly potent therapeutics with novel, highly potent product-related impurities. “It is important to address novel and critical product-related side products (e.g., immune-cell-activating side products acting at the crossroads of immunology and oncology) to ensure maximum patient safety and guarantee efficacy,” he asserts.

	Finally, Harris notes that the industry is struggling to balance the needs for comprehensive testing, including testing to account for unexpected events, and more rapid product development. “Risk-based (i.e., QbD) test strategies will lead to a reduced set of tests, but it is also necessary to include tests that detect variation outside of process models. The two approaches present a fundamental conflict,” he states.

	Indeed, biopharmaceutical manufacturers remain challenged to increase the speed and accuracy of product development while still ensuring safety in the face of more rigorous regulatory scrutiny, novel biologic molecules, and evolving manufacturing strategies. “All of these factors are adding complexity to analytical testing programs,” Garrett concludes.


	Pharmaceutical Technology Europe
	Vol. 28, No. 3
	Page: 16-20


	When referring to this article, please cite it as C. Challener, “Emerging Analytical Technologies Advance Biopharma Development,” 

Time and sensitivity are essential for analytical technologies in all phases of biopharma development.