According to the EMEA “A biosimilar medicine is a medicine which is similar to a biological medicine that has already been authorised (the “biological reference medicine). (1) According to the US Price Competition and Innovation Act 2009, “A biosimilar is a biological product that is highly similar to the reference product, not withstanding minor differences in clinically inactive components, and for which there are no clinically meaningful differences between the biological product in terms of the safety, purity and potency. This Act also addresses the complexity of biologics as large complex molecules whose manufacture typically exhibits at least minor degrees of structural and functional variability.(2) A well defined regulatory pathway was created in Europe since 2005. To date, products such as somatropin, epoetin and, filgrastim have been approved as biosimilars. Indeed, Reuters reports that biosimilars are becoming a commercial reality for Novartis. Revenue from generic enoxaparin, a biosimilar of Sanofi-Aventis’ anticoagulant Lovenox, was valued at $292 million in 3Q10 and the product is on track to achieve blockbuster status, with annual sales above $1 billion. In the USA, it remains to be established how biosimilars will be regulated, though a legal pathway has been established. Progress is similarly underway in Japan and elsewhere. In the US, in March of this year, President Barack Obama signed the broad-based healthcare reform package into law and this was the foundation for the legal basis of biosimilars. The base approach is to be consistent across EU and US remits and the biological products will need to show that they are biosimilar to a reference product. For the purpose of this discussion, the experience in Europe will mostly be used, since the CHMP has more experience to date in this area. Although no biosimilar mAbs have been approved to date in Europe, a concept paper has been issued by EMEA on this subject.(3)
Biosimilar applications can be submitted to authorities, once the original medicine is no longer within the period of data protection. They are required to undergo scientific evaluation to assess efficacy, quality and safety. Whilst biosimilar applicants can make reference to the biological reference medicine, they do need to illustrate similarity via studies. Nevertheless, the package required for submission is less than that required for a full marketing authorisation application. It is not considered possible to produce identical biological products using manufacturing processes and the process for generics cannot be applied for biotech products. Required studies include additional clinical and non-clinical data to demonstrate equivalent safety and efficacy profiles to the originator product and a combination of physico-chemical and biological data. Such studies involve comparison of the quality and the consistency of the medicinal product and of the manufacturing process. Aggregates can form during manufacture, on storage or during reconstitution and are often associated with Mabs due to their high concentrations for therapy and the immunoglobulins that tend to aggregate. For this reason, appropriate formulation studies need to be performed to find an optimal formulation that is stable with respect to formation of particulates at release and during storage. Mabs by their nature are significantly larger than other biotech medicines. However, monoclonals are also being included for biosimilar applications. The EMA Concept paper underpins this. (4) Most of the therapeutic antibodies are humanized or human Immunoglobulins (IgGs) and are produced as recombinant glycoproteins in eukaryotic cells. Although IgGs glycans comprise of only about 3% of the total mass of the molecule they are involved in essential immune effector functions. However, they may also be allergenic, immunogenic and accelerate the plasmatic clearance of the linked antibody. For this reason, the glyco-variants have to be identified, controlled and limited for therapeutic uses. “Glycosylation depends on multiple factors like production system, selected clonal population, manufacturing process and may be genetically or chemically engineered.”(5) The glycosylation patterns observed for the current approved therapeutic antibodies produced in mammalian cell lines, classical and state-of-the-art analytical methods used for the characterization of glycoforms and the expected benefits of manipulating the carbohydrate components of antibodies by bio- or chemical engineering as well as the expected advantages of alternative biotechnological production systems developed for new generation of therapeutic antibodies and Fc-fusion proteins should be considered. Their primary structure must be compared to the reference product. Techniques such as MS-MS, C and N terminal sequencing, amino acid analysis and gene sequencing can underpin such characterisation. Techniques such as circular dichroism (CD), Fourier transform infra-red spectroscopy (FTIR) and micro-calorimetry have been used to differentiate between structures. Studies are also conducted to compare the safety and efficacy of the medicines. These studies should demonstrate that there are no meaningful differences between the biosimilar and the biological reference medicines in terms of safety or efficacy.
Whilst physico-chemical and biological studies can support applications, there remains the requirement to illustrate clinical safety. The safety of biosimilars should discount any toxicity in terms of immunogenicity, pharmacokinetics and pharmacodynamic effects. The CHMP nonclinical and clinical comparability guideline, stresses the need for in-vivo nonclinical studies. However, species specificity can be a barrier, as can the size and length of the study and also immunogenicity. Mostly monkeys are the preferred species to obtain nonclinical data and to provide the initial assurance that the biosimilar is safe to enter clinical trial in humans. The value of transgenic species must be considered since they are not validated models and in addition the value of nonclinical studies with regards to toxicity testing. For biosimilars, the value of nonclinical studies should also be considered and emphasis should be placed on knowledge of the toxicity associated with mechanism of action and unspecific toxicity, based in impurities. In-vitro studies should be utilised over animal studies in general. The level of glycosylation affects the Fc effector function i.e. the Fc region of the immunoglobulin from binding to the target receptors. For this reason, in-vitro potency assays are often used, which enable a comparison of the reference against the biosimilar as a functional level. However, for Mabs this is further complicated, since antibodies can bind not only to the target epitope but also with immune cells and complement. Changes in conformation of the protein can affect receptor affinity and expose epitopes. This can affect immunogenicity and lead to cell destruction or cytotoxicity. Immunogenicity monitoring does not differ from the reference production to the biosimilar product.(6) Comparative safety studies are required and it is not acceptable to use historical or literature based data. Changed glycosylation patterns can affect bioactivity such as defucosylation. The CHMP requests in-vitro and in-vivo studies, including receptor bind and cell based assays. Other considerations are the level of deamidation, oxidation and C terminal lysine processing. Variants can also be detected via SDS PAGE (sodium dodecyl sulphate polyacrylamide gel electrophoresis) SE-HPLC (size exclusion high performance chromatography) and analytical ultra-filtration. The challenge is to understand the significance of any differences between the reference medicine and the biosimilar. However, according to CHMP any difference in amino acid sequence or primary structure means that a protein must be treated as a different entity and therefore is not biosimilar. Mutagenicity, animal reproduction and carcinogenicity studies tend not to be required. Regulators are also concerned that despite understanding structure function activity, that physico-chemical and biological studies may not be sufficient to demonstrate safety and efficacy. For this reason, often Phase I studies are carried out on manufacturing scale batches and formulation. The phase I studies tend to be carried out in healthy volunteers, though sometimes ethical considerations must be considered as for Mabs where PK comparison of single treatments may not be appropriate. Therefore, phase III may only be possible in these instances. The EU CHMP Guideline should be considered in this context.(7)
In addition, the reference product should be sourced from the EU, if the biosimilar application is for submission in Europe. The FDA has still to define the level of flexibility in this context and if they will allow the use of non US reference products in pivotal clinical trials. When it comes to efficacy, the CHMP nonclinical and clinical guideline should also be considered. For biosimilars, it is important to note that the emphasis is on providing evidence for therapeutic equivalence, through understanding the structure, impurity profile and biological, nonclinical and clinical properties, along with an understanding of impact on the safety and efficacy. The three main classes of biosimilars approved in Europe to date are the human growth hormone (HGH), erythropoietin (EPO), and granulocyte colony stimulating factor (G-CSF). For biosimilars such as somatropin, epoetin and G-CSF all the indications were approved as for the reference product. For MAbs, this is more complicated, since there needs to be an understanding of the mechanism of action, the therapeutic effect may depend on blocking the target receptor, interference with downstream signaling and eliciting an immune response. Also, tools such as pharmacodynamic markers and clinical endpoints for the assessment of safety and efficacy in target population need further development. Short-term efficacy studies with surrogate clinical endpoints can support this. Placebo trials are not ethical, therefore the focus is on non-inferiority or equivalence trials. Two products are never 100% equivalent and the ICH E9 addresses this point. (8) ICH E9 states “this margin is the largest difference that can be judged as being clinically acceptable and should be smaller than differences observed in superiority trials of the active comparator.” So where a Mab is demonstrated to have similar physico-chemical and biological properties, similar invivo and in-vitro effects, the efficacy is almost certain to be similar to that of the reference product. It will be interesting to see if the FDA will permit the extrapolation of indications where comparable safety and efficacy of the biosimilar product to the reference product is demonstrated in for example one or two sensitive patient populations. Biosimilar medicines are manufactured following the same quality standards as for all other medicines.
The relationship between the structural characteristics of the protein and its functions, as well as the ability to demonstrate structural similarity between the follow on protein and the reference product are predictors of clinical comparability and as such, many companies will have to pursue more intensive clinical studies until the level of scientific understanding and technology advances to support such understanding. The choice of reference standards to be used from pre-clinical to clinical stages, differences in method of manufacturing including cell line, purification processes, in-process controls, analytical methods and specifications for in-vitro comparability, immunogenicity test methods and validation and comparative pharmacology and toxicology studies including species selection and scope of studies, first in human trials Phase I for comparative assessment of safety, tolerability and PK/PD profile will all play a part in supporting biosimilar applications.
References
- EMEA. Doc. Ref. EMEA/74562/2006 Rev. 1. London, 22 October 2008.
- Woodcock J. Assessing the Impact of a Safe and Equitable Biosimilar Policy in the United States. Statement before the Subcommittee on Health Committee On Energy and Commerce United States House of Representatives, May 2, 2007.
- Committee for Medicinal Products for Human Use (CHMP). Concept Paper on the development of a guideline on similar biological medicinal products containing monoclonal antibodies. European Medicines Agency (EMEA); October 22, 2009.
- CHMP Concept Paper on Development of a Guideline on similar biological medicinal products containing Monoclonal Antibodies (EMEA/CHMP/BMWP/632613/2009 EMA) October 2009
- Beck A, Wagner-Rousset E, Bussat MC, LokteffM, Klinguer-Hamour C, Haeuw JF, Goetsch L, Wurch T, Van Dorsselaer A, Corvaia N. Trends in glycosylation, glycoanalysis and glycoengineering of therapeutic antibodies and Fc-fusion proteins. Curr Pharm Biotechnol 2008 Dec;9(6):482-501.
- Immunogenicity Assessment of Biotechnology-derived Therapeutic Proteins (CHMP/BMWP/14327/06) effective April 2008, and Concept Paper on Immunogenicity Assessment of Monoclonal Antibodies Intended for In Vitro Chemical Use (EMEA/CHMP/BMWP/114720/2009), Committee for Medicinal Products for human use (CMPH), European Medicines Agency., CHMP/437/04, October 2005.
- CHMP Guideline on Similar Biological Medicinal Products containing Biotechnology-Derived Proteins as Active Substances Nonclinical and Clinical Issues (CHMP/42832/05) effective June 2006.
- ICH E9, Statistical Principles for Clinical Trials.