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Author: Fiona M Greer, Global Director, SGS Life Science Services, Wokingham, UK

Introduction

Since the first recombinant DNA-produced biologic, human insulin, was approved in 1982, the biotechnology industry has firmly established itself as a major source of new human therapeutic drugs. Now, many of these first generation products have reached, or are about to reach, patent expiry and this has led to the advent of “biosimilars” – legally approved versions of an existing branded biologic. These products are granted marketing approval on the basis of analytical, pre-clinical and clinical data which show they are highly similar to the original drug. Many countries have now established legal and regulatory pathways which allow manufacture of “copies” of a patent-expired biotherapeutic product molecule and many more are examining this new category of therapeutics.

The potential market for these products is forecast to be substantial; IMS Health estimates that US$64 billion in global biologics sales will be off-patent by 2015. Hence, there are many factors encouraging this emerging pharma sector, but undoubtedly a key driving factor is the universal need for more affordable medicines in both developed and developing economies.

The Challenge of Large Molecules

The exact structure of small synthetic molecule drugs and their impurities can be well defined chemically. This enables generic manufacturers to avoid full, costly clinical studies if they are able to establish that their product is “bioequivalent” in pharmacokinetic studies to the brand/listed drug. However, biologically-derived products are large, complex protein molecules, usually comprising of a mixture of closely related species which undergo “post-translational modifications” which influence the anticipated protein structure. In addition, the complexities of cellular expression and biomanufacturing make exact replication of the originator’s molecule nearly impossible – the process will certainly be different. So these are not simple generics. The fundamental difference with complex protein molecules is that they cannot be absolutely identical to the original. Instead, companies developing these “copies” must demonstrate that they are similar by performing a side-by-side comparison with a reference sample of the originator.

Regulatory Issues

The European Union (EU) established the first legal regulatory guidelines for “similar biological medicinal products” i.e. biosimilars (Original adopted documents:1,2,3). Subsequently, specific product annexes were published. Several of the original guidelines have been, or are in the process of being, revised. The first biosimilar molecule approved in Europe (April 2006) was Omnitrope, a version of somatropin. To date, the EU has approved 14 applications, all of which are versions of somatropin, epoetin or more recently, filgrastim. All guidelines plus current revision concept papers and drafts of new guidelines are available on the EMA Multidisciplinary: Biosimilars website4.

Meanwhile, in the United States, the Biologics Price Competition and Innovation Act (BPCIA) provides a new pathway for biosimilars – the 351(k) route of the Public Health Service (PHS) Act. This pathway also requires comparison of a biosimilar molecule to a single reference product which has been approved under the normal 351(a) route with reference to prior findings on safety, purity and potency. In contrast, one aspect of the legislation unique to the US is the provision for two levels of product –‘ Biosimilar’ and ‘Interchangeable Biosimilar’. In February 2012, the U.S. Food and Drug Administration (FDA) published three draft guidance documents to assist biosimilar developers: Scientific Considerations in Demonstrating Biosimilarity to a Reference Product5, Quality Considerations in Demonstrating Biosimilarity to a Reference Protein Product 6 and Biosimilars: Questions and Answers Regarding Implementation of the Biologics Price Competition and Innovation Act of 20097. Earlier this year, a fourth guidance, dealing with scientific meetings, was issued8.

Many other countries including Brazil, Australia, Turkey, Taiwan, India, Malaysia, Argentina, Mexico, Japan, Canada and South Africa have also established regulatory pathways and have licensed copies of biotech drugs. Some have modelled their guidelines on those of the EMA, requiring a comparative approach. However, others have produced their own versions, or use their standard drug authorisation process. If this process does not involve the scientific comparison against the original product, the term “non-comparable biologic” (NCB) is used to differentiate these from true biosimilars. Likewise, the World Health Organisation (WHO) adopted a “Guideline on Evaluation of Similar Biotherapeutic Products” in 2009.

Biosimilars products

To date, biosimilars accepted under current guidelines have been small to medium-sized proteins/glycoproteins. In contrast, monoclonal antibodies are considerably larger, at around 150,000 Daltons for an IgG. This class of drug has proved to be extremely successful, with the market forecast to reach nearly $58 billion by 2016. The “best sellers” such as Avastin, Herceptin, Humira, Remicade and Rituxin, which account for over half of all global revenues, are attractive targets for biosimilars. In April 2012, a South Korean company, Celltrion, filed the first application for a biosimilar mAb with the EMA. The product, CT-P13 is an infliximab and the patent for the original product, Remicade, expires in the EU in 2014. EMA has now authorised in June, two antibody products, Celltrions Remsima and Hospira's Inflectra.

Establishing Biosimilarity

The development pathway for a biosimilar is unlike that of a novel biotherapeutic. Undoubtedly there is an increased requirement for analytics - initially of batches of the originator, then subsequently the biosimilar and then head-to-head comparisons of the two. This enhanced analytical effort may be rewarded in the reduced requirement for clinical trials - generally a Phase II trial is not necessary. However, careful consideration must be given to planning of each phase of development. Many regulatory authorities throughout the world refer to a “step-by-step” approach to establishing biosimilarity.

Therefore, any manufacturer seeking to initiate a biosimilar development program requires comprehensive physicochemical (glyco) protein structural characterization. Initially, the aim is to determine the exact amino acid sequence of the target originator molecule. This is a critical step prior to cell lines and clones being selected and developed. Without doubt, sensitive sequencing techniques, particularly de-novo mass spectrometry sequencing will be required. In addition, post-translational modifications should be screened-for and assessment made of which may be potential “Critical Quality Attributes” or CQAs. Basically, it means establishing the goal-posts for the development of the biosimilar. The new EU Quality guidelines refer to this as determining the Quality Target Product Profile or QTPP. The next stage, once the biosimilar product is produced, is then to conduct studies to provide comparative data for the biosimilar side-by-side with the originator molecule. Assessment of primary and higher order structure requires a host of sophisticated analytical techniques. Various chromatographic, spectroscopic, and electrophoretic methods can be used to interrogate and compare on the basis of size, charge, and shape. One of the most important analytical techniques for biomolecule structural characterization is mass spectrometry (MS). Usually several different types of instruments are used in the detailed study of a glycoprotein so that the overall structure can be elucidated. A variety of so-called “soft” ionisation techniques can be utilised, including Electrospray Mass Spectrometry (ES-MS), on-line ES-MS (where the MS is coupled to an HPLC), Matrix Assisted Laser Desorption Ionisation Mass Spectrometry (MALDI-MS), and for derivatised carbohydrates, Gas Chromatography Mass Spectrometry (GC-MS). Apart from the ability to study non-protein modifications such as sulphation and phosphorylation, the other major strength of an MS approach is in the analysis of mixtures – this has obvious applications in the analysis of heterogeneous glycoforms. Depending on the molecule, non-routine techniques such as protein NMR and X-ray crystallography may also be utilized. In fact, a whole panel of methods should be employed, including orthogonal techniques to analyse particular quality attributes.

Once structural biosimilarity is established using physicochemical methods, biological functional, safety and clinical studies can all commence in a step-wise manner.

Conclusion

Biosimilar drugs are now available in many highly regulated markets with many more products, including ”blockbuster” monoclonal antibodies, in development. The legal and regulatory basis for authorization of these products is built on strong scientific and quality foundations coupled with appropriate clinical studies.

The initial requirement is for a stepwise head-to-head comparison against the reference product to establish “biosimilarity”. At the molecular level, the structural analysis of highly complicated glycoproteins requires a battery of analytical techniques, both chemical and instrumental. Current analytical science and instrumentation can certainly rise to the challenge of biosimilar comparability assessment.

References

  1. CHMP/437/04 Guideline on Similar Biological Medicinal Products. September 2005.
  2. CHMP/49348/05 Similar Biological Medicinal Products Containing Biotechnology-Derived Proteins as Active Substance: Quality Issues. February 2006.
  3. CHMP/42832/05 Guideline on Similar Biological Medicinal Products Containing Biotechnology-Derived Proteins as Active Substance: Nonclinical and Clinical Issues. February 2006.
  4. EMA Multidisciplinary:Biosimilars.
  5. Quality Considerations in Demonstrating Biosimilarity to a Reference Protein Product.
  6. Scientific Considerations in Demonstrating Biosimilarity to a Reference Product.
  7. Biosimilars: Questions and Answers Regarding Implementation of the Biologics Price Competition and Innovation Act of 2009.
  8. Guidance for Industry Formal Meetings Between the FDA and Biosimilar Biological Product Sponsors or Applicants.