As per the Food and Drug Administration (FDA) guidance Quality Considerations in Demonstrating Biosimilarity to a Reference Product, a biosimilar is defined as “a biological product that is highly similar to a reference biological product notwithstanding minor differences in clinically inactive components, and for which there are no clinically meaningful differences between the biological product and the reference product in terms of the safety, purity, and potency of the product.”

Clinical pharmacology studies are a critical part of demonstrating this ‘biosimilarity’, and provide the data for the biosimilarity in drug exposure between the biosimilar and the originator / reference product to confirm no clinically meaningful differences. These studies also include pharmacodynamic (PD) endpoints and pharmacometric analysis – which is the assessment of the clinical relevance of the PD endpoints. This clinical pharmacology data becomes an important point of justification for clinical extrapolation, and more critically is used to demonstrate immunogenic similarity.

Immunogenicity is the immune response to the biological product that may result in immune-mediated toxicity and / or lack of effectiveness. The importance of immunogenicity data is reinforced by the FDA’s regulations stating that “the goal of the immunogenicity assessment is to evaluate potential differences between the proposed product and the originator / reference product in the incidence and severity of human immune responses . . . Thus, establishing that there are no clinically meaningful differences in immune response between a proposed product and the reference product is a key element in the demonstration of biosimilarity.” The European Medicines Agency (EMA) regulations provide a similar focus, noting that “immunogenicity testing of the biosimilar and the reference products should be conducted within the comparability exercise by using the same assay format and sampling schedule. Assays should be performed with both the reference and biosimilar molecule in parallel (in a blinded fashion) to measure the immune response against the product that was received by each patient.”

Therefore, it is critical to collect, evaluate, and compare the safety and immunogenicity data from clinical pharmacology studies used in biosimilar development. Such data becomes even more critical when the originator or reference product is known to have the potential for immune-mediated toxicity.

Because this is a relatively new area of study, the guidance to address the unique challenges of bioanalytical assays supporting biosimilar development is limited. But, this area is also rapidly growing, and with an increasing need to address specific biosimilar requirements, recent attempts have been made to assess the critical assay performance characteristics for both PK and immunogenicity ADA assays to support biosimilar comparability studies.

PK Assays – An Agreed Upon Approach:

Industry consensus for this approach is to quantify both biosimilar and originator compounds equally using a single assay. During method development and validation, it will be demonstrated that only one drug (biosimilar or originator) can be used for standard curve and quality controls. All parameters to be tested are described in Marini et al. 2014 paper.

Immunogenicity (Tier 1-2-3 Assays & Neutralization Assays) – Divided Opinions:

In these type of assays, complexities reside in the fact that they are generally qualitative and nonquantitative, highly susceptible to drug interference, and sometimes difficult to set up in the presence of matrix (for cell-based assays in particular). These are some of the reasons why industry opinion seems to be divided between using one-assay vs. two-assay as the optimal approach.

I recently contributed to an eBook sponsored by Bioanalysis Zone titled “Bioanalysis for Biosimilars Development”, and in that you will see that we recommend use of a one-assay approach. While the biggest concern for using one assay to detect both anti-biosimilar and anti-originator ADA is that the ADAs may not be detected equally if only the biosimilar set of capture and detection reagent are used, the main advantage is that using one set of reagents can provide less inter-assay variability and is advantageous with blinded studies. To be able to effectively use the one assay approach, it is critical to demonstrate comparability in development and validation.

In a two-assay approach, some critical assay characteristics are likely to be different between the two validated assays, and this introduction of variability may reduce reliability. It makes comparison and interpretation of immunogenic data more challenging because two different assays are used, unless the following assay parameters are equivalent:

  • Cut point
  • Sensitivity
  • Drug tolerance
  • Accuracy and precision

Whether one or two assays are used for Immunogenicity (tier 1-2-3 & Neutralization assays), it is important to conduct a thorough evaluation to ensure the assay, or assays, can detect ADAs against the biosimilar and its originator equivalently.

The “Bioanalysis for Biosimilars Development” eBook noted above also includes case studies that show some of the most critical components to evaluate when developing and validating bioanalytical assays for biosimilar programs. You can find the details on those case studies here.

If you have a perspective on assay development and validation to support pre-clinical and clinical comparability studies for biosimilars that you’d like to share, please feel free to contact me. I’d also be happy to answer any questions, and discuss how BioAgilytix can provide the expertise needed to effectively support your biosimilars development program.