Unresolved regulatory concerns
In separate presentations at the meeting, Dr. Kay described many of the nuances that define biosimilars, which go by different terminology in other countries, such as “follow-on biologic” in Japan, “subsequent-entry biological” in Canada, and “similar biological medicinal product” in the European Union. They are defined as a legitimate copy of an off-patent biopharmaceutical that has undergone rigorous analytical comparison and clinical assessment, in comparison to its reference product, and are approved by a regulatory agency according to a specific pathway for biosimilar evaluation. These differ from biomimetics, which are developed as a replica of a biopharmaceutical but have not been developed, assessed, or approved according to regulatory guidelines for biosimilars.
The FDA takes a “totality of the evidence” approach to establish biosimilarity. The biosimilar pathway for approval is different from the originator pathway by relying more on analytical and preclinical studies and less on the clinical pharmacology and clinical trial data to support biosimilarity.
However, the agency has not yet published final guidance for all steps in demonstrating biosimilarity, particularly for clinical pharmacology data. Draft guidance says the biosimilar must be analyzed and assigned to an assessment grade: not similar, similar, highly similar, and highly similar with fingerprintlike similarity.
During production, both originator and biosimilar biopharmaceuticals can have protein-folding variants, misfolding, aggregation, enzymatic cleavage, and degradation that can lead to inactivation of the protein or increased immunogenicity. Even so, most biosimilars are not identical to the originator because of post-translational modifications, but they do not matter as long as they are not clinically meaningful. Even originator products can drift over time because small changes in manufacturing processes can lead to gradual changes in the molecule, Dr. Kay said.
Extrapolation of indications from the originator to a biosimilar is another area of concern, Dr. Kay said. The FDA will consider the extrapolation of data from a clinical trial of a biosimilar conducted in one disease to support approval for additional indications for which the originator product is already licensed, but not across indications with different mechanisms of action, such as between rheumatoid arthritis and non-Hodgkin’s lymphoma for rituximab. But for which inflammatory diseases should a biosimilar be studied to provide adequate information for extrapolation of indications? Dr. Kay asked. This situation brings about questions of whether dermatologists would be comfortable using a biosimilar that has been studied for rheumatoid arthritis to treat psoriasis or gastroenterologists using a drug with data only from psoriatic arthritis to treat Crohn’s disease or ulcerative colitis.
Both the Coalition of State Rheumatology Organizations and the ACR oppose extrapolation of indications from the clinical trial data of a biosimilar in one disease to support approval of additional indications for which the originator product is already licensed, but Dr. Kay thought that “extrapolation of indications makes perfect sense” because it won’t be possible to review a biosimilar for indications not already approved for the originator and it’s natural to extrapolate to already approved indications once the protein is shown to function nearly identically to the originator.
Ideally, the nomenclature system for biosimilars should clearly identify each product to improve pharmacovigilance and to differentiate between products that have not been determined to be interchangeable, Dr. Kay said. In August, the FDA announced draft guidance proposing that all biopharmaceutical products (originator and biosimilars) would have a nonproprietary name that includes a suffix of four lowercase letters that is devoid of meaning. For example, all products that share a core name such as replicamab would be named replicamab-cznm, replicamab-hixf, and so on, Dr. Kay said. Some people have voiced concern that it would be better for names to have some meaning, such as using an abbreviated name for the developing company along with the nonproprietary name of the originator product, but others noted that method could be problematic when companies merge or are acquired by others.
Dr. Huffstutter disclosed relationships with Janssen, UCB, Lilly, Pfizer, Genentech, Bristol-Myers Squibb, and Celgene. Dr. Kay has received grant and research support from many pharmaceutical companies and has served as a consultant or on an advisory board for many pharmaceutical companies, including those developing biosimilars.