A peptide is usually considered to be any polymer of 40 or less amino acids. This means they are small biopharmaceuticals with less structural complexity than, for example, monoclonal antibodies. Peptide drugs can be chemically synthesized or recombinantly produced using a cell line such as E.coli. Peptide products may have a homogenous sequence, where all molecules in the product have an identical amino acid sequence, or they may be composed of peptides with heterogenous sequences. A heterogenous peptide product is a mixture of peptides with different sequences, such as glatiramer acetate.
Peptide Structure
Peptide products can have complex shapes that are highly dependent on the correct amino acid sequence. For this reason, peptides often present unique and difficult structural characterization challenges.
Linaclotide
One example of this would be the confirmation of the disulfide bridge structure in Linaclotide. Linaclotide is only 14 amino acids long but contains three disulfide bridges when it is correctly produced. The below schematic shows the 14 amino acids, using single letter code, and the positions of the three disulfide bonds.
Structural Characterization of Peptides
The regulators have seen a rapid increase in the number of applications submitted for peptide drug products driven mainly by the significant number of generic peptide product submissions. Characterization approaches differ significantly according to the peptide product being analyzed.
ICH guideline Q6A addresses the regulatory requirements for developing synthetic peptides of low molecular weight. Based on this guideline, identification testing should discriminate between compounds of closely related structures that are likely to be present. This would include identification of the molecules with mismatched (also known as scrambled
) disulfide bridges.
![Disulfides_Incorrect[1]](https://biopharmaspec.com/wp-content/uploads/2020/11/Disulfides_Incorrect1.svg "Disulfides_Incorrect[1]")
Identification tests should be specific for the drug substance. Therefore, identification by a single chromatographic retention time alone is not regarded as being specific. However, the use of two chromatographic procedures, where the separation is based on different principles or the use of a combination of tests into a single procedure, such as HPLC/UV diode array, HPLC/MS, or GC/MS is generally acceptable.
For peptide products with a single defined (homogenous) sequence, BioPharmaSpec has developed methods to provide in-depth information for the product and any product-related impurities.
For generics of heterogeneous peptide drug products (i.e. those that vary in amino acid length and sequence, such as glatiramer acetate), the requirement is to demonstrate that the active ingredients in the generic are comparable to the Reference Product. This type of analysis requires high-end analytical characterization and a comparability assessment using statistically significant data.
Characterizing your peptide product
Please contact our scientists if you would like to discuss appropriate characterization strategies for your peptide product.