DEVELOPING BIOSIMILARS AND BIOBETTERS
Unlike small-molecule, chemically synthesized drugs, biobetters and biosimilars are biologically derived products. Subtle
structural differences may result from each manufacturing process used to produce the biologic drug substance that may result
in different properties. Throughout the development process for biosimilars and biobetters, the question of whether structural
changes will occur to the molecule during the manufacturing process, and the potential impact of such changes must be considered.
A more potent pharmacodynamic effect on the target could result in greater efficacy; however, this same change for another
molecule could result in an unwanted exaggerated pharmacological effect leading to greater toxicities. The challenge with
developing biosimilars and biobetters has been that typical analytical procedures used to evaluate the similarity of chemically
produced compounds are not adequate to assess the similarity of biologics.
There is not a clear regulatory pathway in evaluating the similarity of a biosimilar or biobetter to an originator. As with
novel biologics, a case-by-case approach is required, which takes into consideration the weight of evidence. The weight of
evidence is evaluated from data derived from standard toxicity studies, analytical and biological in vitro assays, the pharmacological properties of the drug, the biology associated with the mechanism of action or potential actions,
the intended patient population, the disposition of the drug, and any known published clinical information. Although biobetters
are regulated as innovator biologics, the pathway for regulatory approval of a biobetter can be reduced by evaluation of the
known published data available for the originator product and evaluation of other biologics within the same drug class. This
information can be used to streamline the drug development process by designing a well thought out development strategy upfront
that includes all aspects of the drug development process from production, to a pharmacokinetic comparability study in a non-good
laboratory practice (non-GLP) animal model, to a phase III clinical trial.
To reduce the time associated with the drug-development process, many sponsors in the biosimilar/biobetter market partner
with contract research organizations (CROs) and contract manufacturing organizations (CMOs) to reduce costs and timelines
to submission of the BLA. Sponsors are relying on the expertise and experience of the contract laboratory to expedite development
through their ability to start a study quickly, start studies in parallel based on availability of drug, produce a high quality
report for regulatory submission, and develop and validate the key assays required throughout the development stages. A range
of services will need to be evaluated from either single or multiple CROs depending upon the expertise and experience, range
of services the CRO/CMO provide to the sponsor, and timelines for development. A typical package to support a biosimilar would
include nonclinical support of both the in vitro assays and animal model toxicology studies. The in vitro pharmacodynamic studies would be designed on a case-by-case basis to specifically characterize and compare the biological
activity of the biosimilar/biobetter to the originator reference product. The in vitro assays should be conducted first or in parallel to the animal studies. If the studies are run in parallel, there is an obvious
risk if results lead to any potential differences observed.
An issue that may arise early in development is the availability of the biosimilar/biobetter drug. Engineering lots of material
may be used for assay development; however, GMP lots are required to validate the in vitro assays. It is also acceptable for the reference product to be used for method development and validation and for the biosimilar/biobetter
to be bridged into the assay once available. Typically, 5–10 lots of reference product need to be evaluated from different
manufacturing countries based on origin of regulatory submission. For example, in the case of Rituxan, both the US version
and EU version (Mabthera) need to be evaluated.
When comparing the biosimilar/biobetter drug to the reference products, it is imperative that an actual concentration is
determined. Typically, a nominal concentration is given in the product insert of the reference article, but obtaining the
actual concentration is key to minimizing variability in the various assays developed for biological activity assessment,
and pharmacokinetic and immunogenicity evaluation. Reagent procurement should be considered before development of the in vitro assays. For example, immunogenicity assays require a positive control antidrug antibody, which may not be commercially available.
If thought about in advance and in the context of the program, an early PK animal study can be used to procure this reagent,
thereby minimizing animal usage.
The in vitro pharmacodynamic assays should include binding to the target antigen, which can be conducted via flow cytometry or other techniques,
binding to all Fc? receptors, FcRn and complement, Fab functions such as neutralization, receptor activation or blockade,
and ADCC and CDC assays. The development and validation of the in vitro pharmacodynamic assays can be complex. Thought should be given to the use of the assays to demonstrate similarity and the
utility of use in the manufacturing GMP phase of the program in which assays are required to demonstrate similarity between
lot release. Before the animal model studies, bioanalysis and immunogenicity assay development and validation are required.
Bioanalysis can be evaluated using enzyme-linked immunosorbent assay (ELISA) or Meso Scale Discovery (MSD)techniques to obtain
accurate concentrations of both the reference product and the biosimilar/biobetter. If the reference product is used to create
the standard curve, then experiments should be conducted to show that both drugs give accurate concentrations against the
reference and biosimilar/biobetter standard curves. Immunogenicity assays are qualitative and can also be developed with ELISA
or MSD technology. The anticipated drug concentration in the nonclinical and clinical study samples should be evaluated when
developing both the bioanalysis and immunogenicity assays, because the sensitivities of the assays need to be sufficient to
obtain accurate data. Drug levels in study samples also need to be considered as they can interfere with immunogenicity assays
and produce false negative results. Therefore, acid dissociation methods should be considered for drugs administered at high
concentrations. The animal model studies often include a pharmacokinetic/pharmacodynamic non-GLP study for an initial assessment
of comparability followed by an investigational new drug application-enabling GLP study designed with an emphasis on safety
and pharmacokinetic, pharmacodynamic, and immunogenicity comparability.
To characterize the biosimilar or biobetter structure, the following analyses need to be conducted: protein quantity and purity
analysis, amino acid sequence analysis, glycosylation analysis, physiochemical property characterization, and aggregation
analysis. There are various techniques to assess the structure of the proteins that include but are not limited to sodium
dodecyl sulfate-polyacrylamide gel electrophoresis (SDS–PAGE), high-performance liquid chromatography (HPLC), high performance
anion-exchange chromatography with pulsed amperometric detection (HPAEC), ion-exchange high-performance liquid chromatography
(IEX–HPL), mass spectrometry/mass spectrometry (MS/MS), matrix assisted laser desorption ionization–in source decay (MALDI–ISD),
matrix assisted laser desorption ionization (MALDI), MS mass spectrometry (MS), and gas chromatography–mass spectrometry (GC–MS).
Functional characterization of the drug includes cell-based assays to compare the reference biologic to the biosimilar or
biobetter. The assays are designed based on the mechanism of action of the drug in question and may include potency/biological
activity testing, ADCC, complement-dependent cytotoxicity (CDC), and flow cytometry binding assays. It is imperative that
viral testing be included on each lot batch release and that stability testing be conducted throughout the program.