Published on 29/11/2025

Assay Transfers During Bridges: Bias and Correction

Assay transfers are a fundamental aspect in the development and commercialization of biosimilars, particularly during bridging studies aimed at ensuring analytical comparability. This article provides a comprehensive, step-by-step guide on understanding the concepts of biosimilar analytical comparability, including CQA mapping, fingerprint analytics, process drift monitoring, and equivalence testing. It targets pharma professionals engaged in clinical operations, regulatory affairs, and medical affairs across the US, UK, and EU, in adherence to applicable regulatory frameworks such as those set by FDA and EMA.

Understanding Biosimilar Analytical Comparability

Biosimilar analytical comparability refers to the assessment of the similarity between a proposed biosimilar and its reference product. The goal is to ensure that any differences observed in quality attributes do not translate into significant differences in safety or efficacy. The process involves rigorous testing to establish that the biosimilar performs similarly to the reference product concerning its clinical performance. The foundation of this analytical comparability rests on the Critical Quality Attributes (CQA) mapping.

Critical Quality Attributes are defined as physical, chemical, biological, or microbiological properties or characteristics that must be controlled to ensure the intended quality of a product. Properly mapping these attributes is essential to establish equivalence in the context of regulatory approval.

To effectively perform CQA mapping, it is essential to identify the most relevant attributes for both the biosimilar and reference product, ensuring that each characteristic contributes to the overall function of the biological product. This mapping should begin with a thorough understanding of the reference product’s Specifications and Quality Target Product Profile (QTPP).

CQA Mapping in Biosimilar Development

A well-structured CQA mapping strategy enables a systematic assessment of potential quality differences between the biosimilar and the reference product. This process can be broken down into several key steps:

• Identify Key Quality Attributes: Begin by analyzing the reference product, considering its manufacturing process and performance standards.
• Develop a Comparative Analysis: Compare the identified attributes with those of the biosimilar to pin down any variances that may arise during the manufacturing process.
• Establish Acceptance Criteria: Based on the comparative analysis, define the acceptance criteria that will be used to evaluate the biosimilar against the reference product.
• Link to Clinical Outcomes: Tie these CQAs back to clinical outcomes to substantiate why these attributes are critical.

The significance of CQA mapping cannot be understated, as it forms the bedrock for further analytical assessments, including equivalence testing, which will be discussed further.

Fingerprint Analytics: A Tool for Equivalence Testing

Fingerprint analytics is a sophisticated method employed in the assessment of biosimilar products. It involves the use of specific tests and methodologies that provide a detailed qualitative and quantitative analysis of the biosimilar’s quality attributes. The results from fingerprint analytics can be used to generate a “fingerprint” of the biosimilar versus that of the reference product, hence the name.

This approach is crucial when conducting equivalence testing since it facilitates the identification of any residual differences across the biosimilar and its reference. Fingerprint analytics is particularly beneficial for biosimilars following the Q5E comparability guideline established by the WHO.

The fingerprinting process typically consists of the following stages:

• Selection of Analytical Techniques: Choose suitable methodologies such as mass spectrometry or high-performance liquid chromatography (HPLC) to perform the fingerprint analysis.
• Sample Collection: Collect and prepare samples appropriately for analysis to minimize any external factors that could skew results.
• Data Analysis: Utilize advanced statistical tools to interpret the data generated from the analytic techniques.
• Establish Consistency: Verify that the biosimilar consistently matches the fingerprint of the reference product across all attributes.

Employing such techniques personifies a leading-edge method for ensuring biosimilar analytical comparability, thereby reinforcing the confidence of regulatory bodies in the equivalence of biosimilars to their reference products.

Process Drift Monitoring: Ensuring Quality Throughout the Lifecycle

Monitoring process drift is essential to maintaining the integrity of manufactured biosimilars over time. As manufacturing processes scale or evolve, variances may emerge that could impede the product’s quality attributes. Understanding how to monitor process drift involves several critical steps:

• Establish a Baseline: Document initial production characteristics and establish a baseline for all critical processes and attributes.
• Implement Regular Surveillance: Set up routine monitoring protocols to assess the process’ consistency, enabling early detection of divergence in product quality.
• Utilize Statistical Process Control (SPC): Employ SPC techniques to continually assess the performance of the manufacturing process against the established baseline. This serves as a critical step for process improvement and risk management.
• Perform Root Cause Analysis: In the event of deviations, conduct thorough investigations to identify underlying causes and rectify them promptly.

These monitoring strategies form an indispensable part of a holistic Quality Management System (QMS) for the lifecycle of a biosimilar product. Such actions not only facilitate maintaining compliance with regulatory bodies such as the EMA but also contribute to the overall quality assurance of biosimilars.

Bridging Justifications and Documentation for Equivalence Testing

To substantiate the data supporting equivalence testing, robust bridging justifications must be detailed within regulatory submissions. Bridging studies validate the connection between the biosimilar and the reference product by establishing that they are comparable in terms of the specified quality attributes. Important elements of bridging justifications include:

• Comparative Studies: Provide comprehensive data from comparative analyses, including CQA mapping and fingerprint analysis.
• Statistical Validity: Ensure statistical methods employed in equivalence testing are sound and yield reliable data.
• Regulatory Alignment: Align bridging justifications with guidance from relevant regulatory authorities including the FDA, EMA, and PIC/S.
• Comprehensive Documentation: Ensure that all methodology, findings, and rationale for conclusions are documented meticulously within submission dossiers.

Developing a PPQ CPV Strategy for Biosimilars

A robust Product Performance Qualification (PPQ) and Continued Process Verification (CPV) strategy is crucial for biosimilar developers. This strategy facilitates the real-time monitoring of critical attributes during and after manufacturing while also ensuring that product quality meets the established specifications. The development of an effective PPQ CPV strategy entails the following:

• Defining Critical Quality Attributes: Clearly delineate the CQAs that must be monitored throughout production cycles.
• Data Collection Strategy: Develop robust systems for data collection, ensuring that relevant metrics are recorded consistently.
• Trend Analysis: Periodically assess the collected data to identify trends and ensure continued compliance with defined specifications.
• Feedback Mechanisms: Establish mechanisms enabling feedback regarding product performance to inform further improvements in manufacturing processes.

Success in creating a viable PPQ CPV strategy ultimately contributes to higher levels of confidence for both manufacturers and regulators in the quality and equivalence of biosimilars.

Conclusion

Assay transfers during bridging studies are pivotal to the biosimilar development process, ensuring that analytical comparability is established convincingly. Through meticulous CQA mapping, the application of fingerprint analytics, monitoring process drift, and comprehensive bridging justifications, companies can successfully navigate the complexities involved in demonstrating equivalence between biosimilars and their reference products.

Implementing these strategies offers a pathway for manufacturers to comply with regulatory expectations while supporting effective product development. With a focus on robust methodologies and adherence to guidelines issued by authorities such as the FDA and EMA, organizations can efficiently manage the intricacies of biosimilar analytical comparability, ultimately facilitating patient access to safe and effective therapies.