How similar is similar enough?
The analyses are designed to investigate rigorously the structure of the biosimilar in a comparative sense using side-by-side investigations with the innovator product. 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 contextualizing it with functional data. Indeed, this contextualization brings meaning to both structural and functional data sets and, with the current regulatory landscape, the need for robust structural and functional data has never been greater.
How many batches should I test?
The first point to consider is that true differences can only be identified following the analysis of multiple batches of biosimilar and innovator. Without this, 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. Whilst all these same documents describe the need to analyze reference batches with different dates of manufacture (and different sites of manufacture should also be examined if appropriate), only the FDA has given a numerical indication of the minimum number reference batches that should be assessed (although this is not a fixed value). So comparative analysis of several batches of innovator against several batches of biosimilar will allow a fair assessment of how products compare as well as assessing the structural profile and any changes of the reference batch as it ages. Also, application of orthogonal techniques for assessment of specific structural features helps build a robust dataset.
I observe some structural differences- what do they actually mean?
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 difference stances on this issue in their documentation (2,3). So, in order to understand the product as fully as possible and contextualize any structural differences observed, it is important to assess samples from a functional standpoint. Do any of the observed minor structural differences between the biosimilar and innovator impact 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.
Integrating structural and functional analytics for faster development
The importance of the structure and function relationship is something that we should be aware of as we work to develop biosimilars. Whilst structural data may indicate “minor” differences in a product profile that could trigger changes being made to the manufacturing or purification processes to eliminate this difference in the final product, it may be that biological assessment indicates that there is no impact on 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 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 is a significant benefit.
We also require data from in vitro bioassays to 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, from which the best picture of any claim to biosimilarity can come.