The analyses we perform to investigate the structure of any biosimilar are understandably detailed and exacting. They are designed to cover all features of molecular structure, from the primary level through amino acid sequence investigations, examination of post translational modifications (including detailed investigations into glycosylation profiles) to investigations of secondary and tertiary structure (i.e. higher order structure (HOS)) and aggregation. These analyses are all encapsulated in the ICH Q6B guideline (1), which serves as a clear resource for the expectations of a full structural characterization study. This document is referenced by the EMA (2), FDA (3) PMDA (4) and UK MHRA (5) in their biosimilar guidelines, detailing their expectations in terms of what is required when taking the biosimilar pathway for bringing a drug to market.
The analyzes are designed to investigate rigorously the structure of the biosimilar in a comparative sense using side-by-side investigations with the innovator product i.e. comparability studies. It is likely that through the course of these investigations some minor differences will be found between biosimilar and innovator, despite the focus on achieving the defined quality target product profile.
The question is of course, how meaningful are these differences? This can only really be answered by a consideration of not only the structural data but by contextualizing it with functional and pharmacokinetic (PK) and pharmacodynamic (PD) data. Within the current regulatory landscape, robust and detailed analytical data, supported by PK and PD studies, can be used to provide evidence that comparative efficacy studies (CES) are not needed for PMDA (4), MHRA (5), FDA (6) or EMA (7) biosimilar product approval. Removal of the need for clinical trials will significantly reduce the time to market for the product in these territories, with all the associated cost savings and return on investment that brings.
In order to identify any true differences between biosimilar and innovator products, analysis of multiple batches must be performed. Without this dataset, there can be no determination of the shape of the design spaces for the products and thus no identification of the area of overlap of properties.
The requirement for structural and functional analysis of multiple batches of biosimilar and innovator is detailed in the regulatory documents mentioned above. All these same documents describe the need to analyze reference batches with different dates of manufacture (with different sites of manufacture also being examined if appropriate). The number of innovator batches required for a comparability study is not given a definite value either by the FDA or EMA. However, with the emphasis placed on analytical data to support CES waivers by both agencies, sufficient batches must be structurally characterized to give confidence and clarity of design space in which the proposed biosimilar should fit. For the EMA for example, at least 10 batches of innovator should be used with the preferred number being between 15 and 30 innovator batches.
On-going monitoring of innovator batches is considered beneficial to assess for any change in innovator profile over time (7). In this way, comparative analysis of innovator against biosimilar allows a clear assessment of how products compare as well as assessing the structural profile and any changes of the reference batch as it ages. Application of orthogonal techniques and state-of-the-art instrumentation for assessment of specific structural features is very important and again specifically mentioned in the guidelines (2,3,4,5), all with the notion of producing the most comprehensive analytical dataset possible.
The question that needs to be considered is, what is an acceptable level of “difference” between biosimilar and innovator? Whilst stressing the need to ensure any biosimilar is as closely matched to the innovator as possible, the regulatory guidelines recognize that differences between biosimilar and innovator may well exist, although the EMA and FDA take slightly different stances on this issue in their documentation (2,3). So, in order to understand the product as fully as possible and give meaning to any structural differences observed, it is important to assess samples from a functional standpoint.
Any minor structural differences that may be seen between biosimilar and innovator can then be contextualized in terms of impact (or hopefully lack thereof) on activity. To this end it is important that each bioassay is precisely relevant to the functional testing required, the characteristics of the bioassay are well understood and they are capable of detecting an effect on function that subtle structural differences may cause.
The importance of the structure and function relationship is something that we should be aware of as we work to develop these types of product. Whilst structural data may indicate “minor” differences in a product profile that could trigger changes in manufacturing or purification processes to eliminate this difference in the final product, it may be that biological assessment indicates that the structural change has no impact on product safety, quality or efficacy.
On the other hand, what could appear as a small structural difference could lead to a marked difference in a bioassay response. If bioassay data indicate that there are differences in functional characteristics between biosimilar and innovator, this can be related back to observed structural differences and processes can subsequently adapted to remove or improve this issue. Therefore, whilst analysis of molecular structure will allow firm structural conclusions to be drawn, this is just one aspect that needs to be considered in the larger picture of biosimilarity assessment. This interdependency of structural and functional data to build an overall picture of the product’s characteristics means good communications between groups working in these areas can be a significant benefit.
In addition, data from in vitro bioassays allow a complete assessment of different aspects of the product’s biological characteristics such as binding, signal transduction and activity to flesh out the data from the structural side. These biological data are potentially able to either confirm functional biosimilarity or to serve as a guide for modifications in the drug development process itself.
This combination and integration of structural and functional testing allows a detailed evaluation of the drug profile and delivers a clear demonstration of structure and function characteristics for both the innovator and biosimilar. Any claim of biosimilarity is derived from these data and with a comprehensive and well-structured analytical package designed and delivered, the potential for CES waiver and a more rapid route to market is significantly enhanced.
BioPharmaSpec scientists have provided data to support many global biosimilar development programs. Contact our scientists now to understand how we can use our protein characterization methods to accelerate the development of your molecule.
