Analytical challenges in biotherapeutics development

Biotherapeutics have transformed modern drug development, but their increasing complexity introduces significant analytical challenges. Unlike synthetic molecules, these therapies are inherently variable and require advanced analytical strategies to ensure consistent quality, safety, and performance throughout development and manufacturing.

Analytical testing has further emerged as a cornerstone of biotherapeutics development in recent years. This is largely driven by the rapid growth of biologics and advanced therapies, along with the increasing complexity of these modern drug modalities. Biotherapeutics are medicines derived from living organisms and include a wide range of products such as recombinant protein therapeutics, biological peptides, monoclonal antibodies, biosimilars, viral vectors, and advanced therapy medicinal products (ATMPs), including both cell and gene therapies. When compared to synthetic molecule drugs, the difference becomes clear quite quickly.

Synthetic molecules, often mistakenly synonymized with small molecule drugs (i.e. based on physical size), are chemically synthesized and usually have a well-defined and consistent structure. Biotherapeutics, on the other hand, are far less uniform. Because they are produced in living cells, variability is inherent to these products. Differences can appear in post-translational modifications, folding behaviour, and even biological activity. For that reason, it is often not accurate to describe a biotherapeutic as a single molecule. In practice, it is better referred to as a population of closely related variants rather than one exact product. Each of these variants contributes, in some way, to the overall performance of the product.

This is where analytical testing requires a more comprehensive and integrated approach. A single analytical technique is not sufficient on its own. In practice, multiple orthogonal methods are required to properly assess identity, purity, potency, and stability. Synthetic molecules can often be characterized using a more limited set of techniques, but this is rarely the case for biotherapeutics. Their complexity means that a broader and more integrated analytical approach is needed. Structural, physicochemical, and functional data have to be evaluated together to provide a complete understanding of the product. The situation becomes even more complex when considering how quickly therapeutic modalities are evolving.

Monoclonal antibodies still represent a large proportion of biotherapeutics, but newer approaches such as multi-specific antibodies, antibody-drug conjugates (ADCs) and nanobodies  are increasingly being developed. Gene therapies, RNA-based treatments, and engineered cell products each introduce their own analytical challenges, and traditional methods may not always fully address these requirements. Because of this, fields such as characterization and CMC analytical testing of biological molecules have become highly specialized disciplines, requiring technical expertise to ensure product quality and safety. The same applies to cell therapy and viral vector analytical testing, where analytical requirements are often more complex and less standardized. These areas require not only advanced analytical technologies, but also a strong combined knowledge of both biological systems and regulatory expectations¹,².

Protein therapeutics and biological peptides

Protein therapeutics, such as monoclonal antibodies and recombinant enzymes, are well-established within biopharmaceutical development. Even so, they require advanced analytical approaches. A large part of this comes from their structural heterogeneity, but also from how sensitive they are to environmental conditions during manufacturing and storage. Post-translational modifications (PTMs) are one of the main contributors to this complexity. These changes occur naturally during the biosynthesis process, and can have substantial impact on product quality. For example, changes in glycosylation patterns can affect stability, biological activity, and in some cases immunogenicity. For that reason, PTMs cannot be treated as negligible differences; they must be thoroughly described and monitored to maintain consistency across batches and throughout the product lifecycle. Glycosylation is one of the most important PTMs, affecting protein folding, stability, and bioactivity. Variability in glycan structures is influenced by the host cell system and manufacturing conditions, hence comprehensive characterization is required to ensure consistency and comparability.

Higher-order structure (HOS) is another aspect that cannot be ignored when looking at protein function. Even relatively small structural changes can sometimes lead to noticeable differences in how a protein performs. Because of that, techniques such as fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry, circular dichroism, nuclear magnetic resonance (NMR), and mass spectrometry are often used to examine structural stability and confirm that the protein maintains its expected conformation. Protein stability introduces additional considerations in analytical evaluation. Proteins are quite sensitive to their surroundings, and even small environmental changes can affect their structure. Temperature shifts, variations in pH, or mechanical stress during handling can all play a role. In some cases, these changes lead to aggregation or fragmentation; in others, the protein may partially unfold. Some of these changes may impact product quality and therefore require careful analytical monitoring. Aggregation is a well-known example, as it has been linked to increased immunogenicity. Because of this, it is typically monitored closely, e.g. by size-exclusion chromatography, during both development and routine analytical testing^3,4.

Cell therapies

Analytical testing of cell therapeutics is often seen as one of the more technically demanding aspects, surpassing the complexity of more traditional biotherapeutic testing. Unlike protein-based products, the therapeutic here itself consists of living cells. These cells do not behave in a fixed way. Their properties can shift over time and may also depend on the surrounding environment, which requires careful characterization. Potency is one of the main challenges. It is not always straightforward to define, and measuring it requires careful method development. In cell therapies, potency is usually linked to biological activity, for example immune response, cytokine production, or regenerative effects. These are not always captured using standard biochemical assays. Because of this, more relevant approaches are used, often based on cell-based assays. Even then, developing such assays and maintaining reproducibility over time requires careful optimization.

Batch variability is also a common concern in cell therapy products. The final product can be influenced by several factors, including donor material, expansion conditions, and different steps in the manufacturing process. Because of this, analytical testing usually needs to look at more than one aspect. Identity, purity, and functional performance are typically assessed together to ensure that the product behaves in a consistent way. When looking at cell identity, flow cytometry is usually the method of choice. It allows researchers to examine surface markers and get a sense of the phenotypic profile of the cells. Purity is handled separately and focuses on undesired or contaminating populations. However, safety is often more complex. This becomes especially important for genetically modified therapies, where additional risks may be involved. One of the concerns that often comes up is insertional mutagenesis. Because this cannot be ruled out completely, genetic stability needs to be carefully assessed throughout development, requiring well-designed analytical strategies^5,6.

Viral vectors and gene therapies

Viral vectors are widely used in gene therapy, mainly for delivering genetic material into target cells. Common types include adeno-associated viruses (AAV) and lentiviral vectors. As these systems have a direct influence on how the therapy effectively performs,they need to be studied carefully during development. Their role is not only linked to efficacy. Safety is also a concern, which means profound analytical evaluation cannot be overlooked.

A key aspect is how to measure the actual number of functional particles. Not every viral particle carries the intended genetic payload. Some are empty capsids, and these do not contribute to the therapeutic effect. Because of this, simply measuring total particle count is not enough. What matters more is the balance between full and empty capsids, and that ratio needs to be controlled carefully. The choice of analytical method usually depends on what needs to be measured. Techniques such as qPCR, digital PCR, and analytical ultracentrifugation are often used when looking at vector concentration or composition. They can provide useful insights, although none of them gives a complete picture on its own.

Genome integrity also needs to be checked as part of development. This involves making sure the expected genetic sequence is present and that no unintended changes have occurred. Sequencing methods are usually used for this purpose, especially when there is a need to look for rearrangements in the vector genome. Potency requires careful evaluation using appropriate analytical methods. It is not only about whether the vector enters the target cell. The more important question is whether the gene is actually expressed in a way that produces the intended biological effect. Because of this, cell-based assays are commonly used, even though they tend to show higher variability and it often requires an experienced partner to properly standardize⁷.

Structural characterization

Structural characterization gives insight into how a biotherapeutic behaves and whether it will perform its intended biological function as expected. It focuses on the relationship between molecular features and function, which is important for maintaining consistent product quality across batches. Primary structure refers to the amino acid sequence and is typically examined early in the analytical process. Peptide mapping and mass spectrometry are commonly applied to evaluate this. Through these methods, it becomes possible to detect sequence variations, truncations, or chemical changes that may arise during production. This aspect becomes especially important in biosimilar comparability studies, where maintaining close similarity to the reference product is a key requirement. Beyond the sequence itself, higher-order structure also needs attention. This includes how the protein folds into secondary and tertiary forms. These structural features influence biological behaviour, so even small changes can have an impact. Methods such as circular dichroism, FTIR, and NMR are often used to assess whether the structure remains intact.

Post-translational modifications add another layer of complexity. Glycosylation is a common example, and it can influence stability, folding, as well as interactions with the immune system. These modifications are not always consistent, which means they need closer examination during analysis. Methods such as LC-MS and capillary electrophoresis are often used to assess glycan patterns and their associated variation⁹.

Functional and potency attributes

Functional characterization deals with how the product behaves in a biological setting. It gives an indication of how the therapy is expected to perform in a clinical setting and its overall effectiveness in treating the target disease. Potency is evaluated using assays that reflect how the product functions, but matching the potency assay to the mechanism of action requires careful alignment. For monoclonal antibodies, binding or cell-based methods are commonly applied. With more complex therapies, including cell or gene-based products, behaviour can be less predictable. Several biological steps may be involved, which can introduce variability in the assay outcome.

As an example, functional testing plays an important role in biosimilar development. This step is meant to show that the product behaves similarly to the reference. If differences appear, they must be understood and supported with relevant data. Developing potency assays in this context requires a well-structured analytical approach. Some assays are sensitive to small changes in conditions, and that can affect result consistency. In such cases, methods may require adjustment, along with statistical support, to keep performance reliable over time¹⁰.

Advanced characterization techniques

Advanced analytical technologies are indispensable for analytical testing of protein therapeutics, as well as in biologics characterization work. For instance, liquid chromatography–High Resolution mass spectrometry (LC-HRMS) is widely applied in analytical workflows and supports detailed analysis of primary structure, post-translational modifications, and impurities. Peptide mapping with LC-HRMS helps identify sequence variants and modifications, while offering a detailed view of molecular structure. Glycosylation analysis makes use of chromatographic separation together with mass spectrometry to examine glycan structures and their distribution across the product. For monoclonal antibodies, differences in glycosylation patterns can influence effector function, and this continues to be an important consideration during analysis.      

Impurity profiling is another important part of analytical testing. Process-related impurities, including host cell proteins (HCPs), host cell DNA, and residual solvents, need to be identified and kept under control. Analytical approaches such as ELISA for HCP detection and qPCR for DNA quantification are often used for this purpose¹¹.

Analytical challenges in advanced therapies (ATMPs)

Advanced therapies, including cell and gene-based treatments, are increasingly gaining attention. These modalities introduce additional complexity into the development process from an analytical standpoint. Conventional approaches do not always match their specific requirements in real-life situations, and this becomes more noticeable as these therapies continue to evolve over time. ATMP analytical testing requires specialized approaches due to the unique challenges associated with living cells and viral vectors.

Cell therapy analytics

Analytical testing of cell therapeutics covers identity, purity, potency, and safety, with each area presenting its own challenges. Identity testing helps confirm that the intended cell population is present. Methods such as flow cytometry or molecular-based approaches are often used to characterize cell surface markers and phenotypic features. Purity assessment looks at whether any unwanted or contaminating cell types are present within the product. Potency requires particularly well-designed analytical approaches. In this context, cell therapies differ from conventional pharmaceuticals, where simpler assays often suffice. In many cases, they rely on functional tests linked to complex biological activity. These assays can show variability, so they need careful development and validation, particularly when consistent results are expected across different stages. Safety evaluation covers several aspects, including the presence of adventitious agents, genetic stability, and potential tumorigenicity. These considerations become more important for genetically modified cell therapies, where long-term effects need to be understood and continuously monitored¹³.

Viral vector characterization

Viral vector characterization plays an important role in gene therapy development and involves several analytical considerations. Quantifying viral particles is necessary for determining dose. Methods such as qPCR or digital PCR are widely used to estimate vector genome copies with a high level of sensitivity. Capsid characterization plays a role in the analysis, particularly when looking at the proportion of full and empty capsids. Analytical ultracentrifugation and chromatography can be used to assess capsid composition. Genome integrity calls for evaluation to confirm that the therapeutic gene has been correctly packaged and remains stable, whereas sequencing-based methods are used to examine vector genome structure in detail.

Stability testing and regulatory expectations

Stability testing and regulatory expectations are strongly connected in biotherapeutics development. Stability data help define product shelf-life and are also used within regulatory submissions to show that product quality remains consistent over time.

Stability studies in biologics development: accelerated, ASAP and long-term approaches

Stability testing helps build an understanding of how biotherapeutic products degrade and supports the determination of shelf-life. Accelerated stability studies expose products to stressed conditions (typically 40°C/75% RH), which makes it possible to observe degradation pathways more quickly. These studies give an early view of how the product behaves under less favorable conditions. The Accelerated Stability Assessment Program (ASAP) relies on predictive modeling to estimate long-term stability using short-term data. This approach proves useful during early stages of development, particularly in situations where long-term data are not yet available. Long-term stability studies are carried out under ICH recommended storage conditions. The data generated from these studies contribute to regulatory submissions and also support shelf-life, as they show how the product performs over time.

Regulatory expectations (EMA & FDA)

Regulatory agencies, including the European Medicines Agency (EMA) and the United States Food and Drug Administration (FDA), ask for detailed analytical data as part of product approval. Validation of analytical methods, comparability, and stability data all contribute to understanding how the product performs over time. ICH Q2(R2) and Q14 are used as references during analytical method-validation and development, with approaches that rely on both scientific understanding and risk assessment. Analytical data are included within the Chemistry, Manufacturing, and Controls (CMC) dossier. These data are then reviewed as part of the regulatory process¹⁴.

Analytical method development considerations

Early in development, analytical methods take on a more exploratory role and help build an initial understanding of product structure and function. At this point, the emphasis is on collecting enough information to guide the next stages of development and support decision-making. With continued development, these methods are refined and later validated so they can support regulatory submissions, as well as routine quality control activities. This follows the lifecycle concept described in ICH Q14, where analytical methods are updated as product knowledge expands. Risk-based approaches, such as Design of Experiments (DoE), are also used to improve method performance and define acceptable operating ranges. In practice, this helps make development more efficient and supports a clearer scientific basis for method control¹².

Frequently asked questions on biotherapeutics analytical testing

How are biologics analytically characterized?

Biologics are characterized using a comprehensive combination of analytical techniques. This can include structural analysis, physicochemical testing, and functional assays. Tools such as mass spectrometry, chromatography, and bioassays are commonly used to build a more complete picture of product quality and therapeutic performance.

What analytical challenges exist for ATMPs?

ATMPs come with a different set of challenges compared to conventional products. Variability between batches, the need for complex potency assays, and safety-related concerns all require more advanced and specialized analytical approaches.

How are biosimilars analytically compared to reference products?

Biosimilars are evaluated in comparability studies that examine multiple aspects of the product. Structural analysis, functional testing, and stability evaluation are all considered as part of this process. The expectation is that the biosimilar performs in a way that is highly similar to the reference product.

References

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