Health Law Daily New interpretation of ‘protein’ and ‘chemically synthesized polypeptide’ proposed for biological products
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Wednesday, December 12, 2018

New interpretation of ‘protein’ and ‘chemically synthesized polypeptide’ proposed for biological products

By Laura Lefkow, J.D.

The FDA seeks comment on its proposal to amend the definition of "biological product" in the Public Health Service (PHS) Act to include the FDA’s interpretation of "protein" and "chemically synthesized polypeptide." Under the proposed rule, "protein" would mean any alpha amino acid polymer with a specific, defined sequence that is greater than 40 amino acids in size. A "chemically synthesized polypeptide" would mean any alpha amino acid polymer that is made entirely by chemical synthesis and is between 41 and 99 amino acids in size. The purpose of the change is to clarify whether certain products are regulated as drugs or biological products, and to conform the definition to the statutory definition enacted in the Biologics Price Competition and Innovation (BPCI) Act of 2009. Comments are due by February 25, 2019 (Proposed rule, 83 FR 63817, December 12, 2018).

The FDA has authority under Section 351 of the PHS Act and the Federal Food, Drug, and Cosmetic (FDCC) Act to amend its regulations to ensure that biological products are safe, pure, potent, and manufactured in accordance with current good practices. The majority of therapeutic biological products have been licensed under Section 351, but some protein products have been approved under Section 505 of the FD&C Act. The BPCI Act requires that marketing applications for biological products must now be submitted under Section 351 of the PHS Act, subject to certain exceptions during a 10-year transition period ending March 23, 2020. The BCPI Act amended the PHS Act to abbreviate the licensure pathway in Section 351(k) for biological products shown to be biosimilar to, or interchangeable with, an FDA-licensed biological reference product. By providing its interpretation of "protein" and "chemically synthesized polypeptide" the FDA can create a scientifically reasonable, bright-line rule and thereby clarify the statutory framework under which such products are regulated.

Proposal. After extensively reviewing the scientific literature and analyzing current regulatory practice, the FDA proposes a size-based cutoff for distinguishing peptides from proteins. The Agency concluded that apart from size there is not a precise set of structural or functional attributes that define a protein so as to clearly distinguish it from a peptide. Peptides generally refer to small, simple amino acids chains, while protein refers to larger, more complex chains. The proposed amendment to 21 C.F.R. 600 would amend biological product to be defined as a virus, therapeutic serum, toxin, antitoxin, vaccine, blood, blood component or derivative, allergenic product, protein (except any chemically synthesized polypeptide), or analogous product, or arsphenamine or derivative of arsphenamine (or any other trivalent organic arsenic compound), applicable to the prevention, treatment, or cure of a disease or condition of human beings.

A protein will be any alpha amino acid polymer with a specific, defined sequence that is greater than 40 amino acids in size. A chemically synthesized polypeptide is also defined as any alpha amino acid polymer that is made entirely by chemical synthesis and is greater than 40 amino acids but less than 100 amino acids in size.

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