Biosimilar & Similarity Assessment
Biosimilar development requires a comprehensive evaluation of the similarity between a proposed biosimilar and its reference product. Because biologics are structurally complex and may exhibit inherent molecular heterogeneity, similarity assessment typically involves multiple analytical and functional attributes rather than reliance on a single test.
Protheragen provides integrated biosimilar and similarity assessment services to support the analytical and CMC aspects of biosimilar development. By combining physicochemical characterization, structural analysis, purity and heterogeneity assessment, and biological activity testing, the assessment can provide a comprehensive understanding of similarities and potential differences between the proposed biosimilar and reference product.
Overview of Biosimilar & Similarity Assessment
Biosimilar development follows a stepwise approach in which analytical characterization provides the foundation for demonstrating similarity between a proposed biosimilar and its reference product. The assessment considers relevant quality attributes that may influence molecular structure, physicochemical properties, biological activity, and overall product quality.
A comprehensive similarity assessment typically begins with extensive analytical characterization and progresses to functional evaluation based on the identified attributes and residual uncertainties. Orthogonal analytical methods can be used to evaluate structural and physicochemical characteristics, while biological assays provide complementary evidence regarding functional similarity.
The scope and depth of assessment can be tailored according to the molecular complexity, mechanism of action, available reference product information, development stage, and applicable regulatory expectations.
Fig.1 Building evidence for biosimilarity—comparison of data requirements for approval of a biosimilar versus an RP. (Mascarenhas-Melo, F., et al., 2024)
Our Services
Protheragen's upstream process development services cover key stages of mammalian cell culture process development, from media screening and culture optimization to bioreactor development and scale-up.
Reference Product Characterization
A well-characterized reference product provides the basis for establishing the target quality profile of a biosimilar.
Reference product characterization includes:
- Molecular identity
- Molecular weight
- Primary structure
- Higher-order structure
- Purity
- Aggregation
- Fragmentation
- Charge variants
- Glycosylation
- Post-translational modifications
- Physicochemical properties
- Biological activity
Multiple reference product lots may be evaluated where appropriate to understand natural product variability and establish a representative quality range.
Analytical Similarity Assessment
Analytical similarity assessment compares the proposed biosimilar with the reference product across a comprehensive set of relevant quality attributes.
The assessment covers:
- Primary structure
- Higher-order structure
- Molecular size
- Charge heterogeneity
- Purity
- Product-related variants
- Glycosylation
- Post-translational modifications
- Physicochemical properties
- Stability-related characteristics
The analytical strategy can combine orthogonal methods to provide complementary evidence and increase confidence in the overall similarity assessment.
Primary and Higher-Order Structure Similarity
Structural similarity is a fundamental component of biosimilar development.
Services can evaluate:
- Amino acid sequence
- Peptide mapping
- Molecular mass
- Terminal structures
- Disulfide bonds
- Secondary structure
- Tertiary structure
- Conformational characteristics
- Higher-order structural attributes
Comparative structural characterization helps determine whether the proposed biosimilar has a molecular structure consistent with the reference product.
Purity and Product-Related Variant Similarity
Purity and product-related variants can influence the quality and biological characteristics of therapeutic proteins.
Comparative assessments include:
- Monomer content
- Aggregates
- Fragments
- Charge variants
- Oxidized species
- Deamidated species
- Other product-related variants
- Process-related impurities
The distribution and levels of relevant variants can be compared between biosimilar and reference product samples to identify meaningful differences requiring further evaluation.
Glycosylation Similarity Assessment
Glycosylation is an important quality attribute for many biologic products and may influence biological activity, pharmacokinetics, immunogenicity, and product stability.
Glycosylation similarity assessment includes:
- N-glycan profiles
- Glycan composition
- Glycosylation site occupancy
- Sialylation
- Fucosylation
- High-mannose structures
- Other glycan-related attributes
Comparing glycosylation profiles between the biosimilar and reference product can provide important evidence regarding structural and functional similarity.
Physicochemical Similarity Assessment
Physicochemical characterization provides complementary evidence for evaluating biosimilarity.
Depending on the product, services can assess:
- Molecular weight
- Size distribution
- Charge profile
- Protein concentration
- pH
- Thermal stability
- Conformational properties
- Colloidal stability
- Other molecule-specific physicochemical characteristics
The analytical scope can be adjusted according to the molecular characteristics and known critical quality attributes of the reference product.
Biological and Functional Similarity Assessment
Analytical similarity alone may not fully establish that the proposed biosimilar has comparable biological properties. Functional studies therefore provide an important complementary component of the overall similarity assessment.
Depending on the mechanism of action, services include:
- Target binding
- Receptor binding
- Enzyme activity
- Cell-based functional assays
- Signal transduction
- Effector functions
- Relative potency
- Mechanism-of-action-related biological activities
Functional similarity can help determine whether observed molecular differences, if any, have a meaningful impact on biological function.
Stability and Degradation Profile Similarity
Comparative stability assessment can provide additional evidence regarding the behavior of the proposed biosimilar and reference product under relevant storage or stress conditions.
Services can evaluate:
- Aggregation
- Fragmentation
- Charge changes
- Oxidation
- Deamidation
- Structural changes
- Potency changes
- Degradation pathways
- Other stability-indicating attributes
Where appropriate, forced degradation and accelerated stability studies can be incorporated to compare degradation profiles and identify potential differences in product behavior.
Reference Product and Biosimilar Comparative Assessment
A scientifically robust similarity assessment requires appropriate characterization of both the proposed biosimilar and reference product.
| Attribute Category |
Biosimilar |
Reference Product |
Assessment Objective |
| Identity |
Molecular identity |
Reference identity |
Confirm molecular consistency |
| Primary Structure |
Sequence and peptide map |
Reference sequence and peptide map |
Assess structural similarity |
| Higher-Order Structure |
Conformation |
Reference conformation |
Evaluate structural comparability |
| Molecular Size |
Monomer, aggregates, fragments |
Reference profile |
Compare size-related variants |
| Charge |
Charge variants |
Reference charge profile |
Evaluate charge heterogeneity |
| Glycosylation |
Glycan profile |
Reference glycan profile |
Assess glycosylation similarity |
| Purity |
Product and process impurities |
Reference impurity profile |
Compare product quality |
| Physicochemical Properties |
Relevant physicochemical attributes |
Reference attributes |
Evaluate physicochemical similarity |
| Biological Function |
Binding and potency |
Reference activity |
Assess functional similarity |
| Stability |
Degradation profile |
Reference degradation profile |
Evaluate stability-related similarity |
This quality attribute-based framework allows multiple analytical results to be integrated into an overall assessment of product comparability.
Biosimilar Similarity Assessment Across Development
Similarity assessment evolves as the biosimilar program progresses. Early analytical characterization establishes an understanding of the reference product and informs the development target, while subsequent comparative studies generate increasingly comprehensive evidence supporting similarity.
- Early Biosimilar Development
Early studies focus on reference product characterization, identification of relevant quality attributes, and establishment of an analytical target profile.
- Analytical Similarity Development
The proposed biosimilar is extensively characterized against the reference product across structural, physicochemical, purity, and heterogeneity attributes.
- Functional Similarity Assessment
Relevant biological and functional assays are incorporated to evaluate whether the proposed biosimilar and reference product exhibit comparable biological activity.
- Stability and Degradation Assessment
Comparative stability and degradation studies provide additional information regarding molecular robustness and product behavior.
- Integrated Similarity Assessment
Results from multiple analytical and functional studies are integrated to establish an overall similarity conclusion and identify any remaining analytical uncertainties.
Risk-Based Similarity Assessment
Not all quality attributes carry the same potential impact on product quality or biological function. A risk-based strategy can therefore be used to prioritize analytical investigations according to:
- Molecular characteristics
- Mechanism of action
- Known critical quality attributes
- Product-related heterogeneity
- Manufacturing process knowledge
- Reference product variability
- Potential clinical relevance of differences
Attributes with higher potential impact can receive more comprehensive characterization and functional assessment, while lower-risk attributes can be evaluated using appropriately justified analytical approaches.
Why Choose Protheragen
- Comprehensive Analytical Coverage
Similarity studies can integrate structural, physicochemical, purity, heterogeneity, glycosylation, stability, and functional assessments.
- Reference Product-Focused Strategy
The analytical program can be designed around the characteristics and quality profile of the reference product to establish an appropriate basis for biosimilar assessment.
- Orthogonal Characterization
Complementary analytical techniques can be combined to provide multiple lines of evidence for key quality attributes.
The scope and depth of testing can be prioritized according to molecular characteristics, quality attributes, mechanism of action, and potential impact of observed differences.
Similarity assessment can be connected with product characterization, analytical development, stability research, process development, and comparability studies throughout the development lifecycle.
Biosimilar and similarity assessment provides a structured analytical framework for evaluating the relationship between a proposed biosimilar and its reference product. Comprehensive characterization across molecular structure, physicochemical properties, purity, heterogeneity, glycosylation, stability, and biological function can provide multiple complementary lines of evidence for similarity. By integrating analytical and functional studies within a risk-based, lifecycle-oriented strategy, Protheragen supports biosimilar developers in building robust product knowledge and generating CMC-relevant evidence for informed development and regulatory decision-making. For tailored biosimilar characterization and similarity assessment strategies aligned with your molecule, reference product, development stage, and CMC objectives, contact us to discuss your project requirements.
Reference
- Mascarenhas-Melo, F., et al. "An Overview of Biosimilars—Development, Quality, Regulatory Issues, and Management in Healthcare." Pharmaceuticals. 2024; 17(2):235.
