CMC regulatory challenges during peptide development
Samrat Sisodia, vice president RA and QA at Palatin Technologies spoke at the 2024 TIDES Oligonucleotide & Peptide Therapeutics Conference in Boston in May about peptide development and where regulatory focus needs to be directed.
Peptide development
Sisodia delved into the variable definition of a peptide. He explained that some people class a peptide between 40 amino acid chains, and others between fifty and sixty. However, the US Food and Drug Administration (FDA) considers any alpha amino acid polymer composed of forty or fewer amino acids to be a peptide, not a protein.
Peptides play an incredibly important role as they are short acting, targeted and they are used for multiple purposes, he continued. This characteristic makes peptide development and regulatory landscape a desirable space for exploration.
Synthesis
Sisodia described three ways of synthesizing a peptide: Solid Phase, Solution Phase, and a combination of both.
Within Solid Phase Peptide Synthesis (SPPS), the peptide is constructed on resins attached to solid support. This method is well suited to large-scale production and simplifies purification because it does not require column purification, although it is not ideal for large peptides and requires specialized resins and equipment.
In solution phase synthesis, fully protected peptide segments are prepared separately and then condensed in organic solvents to form larger polypeptides. While this is suitable for smaller peptides, it requires complex purification and structural analysis.
Using a hybrid approach, however, is helpful to eliminate some of the bad tendencies or impurities that accumulate through each of these methods. Smaller peptide segments are initially synthesized using SPPS on solid-phase resins which Sisodia explained is efficient for production of longer peptides and provides scalability for large scale production.
Structural elucidation
Whichever method of synthesis is chosen, developers must be aware that immunogenicity is a core concern agency have when they evaluate the peptide and its primary structure.
FDA guidance explains that, in some circumstances, peptide-related impurities may create the potential for differences in immunogenicity or may otherwise affect the safety or effectiveness of a peptide drug product.
Sisodia said a secondary structure evaluation is also essential when trying to define controls over peptides. Some of the techniques used to identify secondary structure include Circular Dichroism (CD) or Fourier transform infrared (FTIRs). These methods help to define the secondary structure and provide controls that would render increased precision.
There could also be a need to express the higher structure evaluation during the drug review process.
Purification
Peptide purification poses several challenges, especially during large-scale production. Sisodia highlighted peptide purification requires a delicate balance between achieving high purity and maintaining yield.
The FDA is focusing on eliminating aggregates. Peptides may form aggregates due to hydrophobic interactions or improper folding. They have their own biological reactivity and can invoke allergic reactions and therefore, data should demonstrate the proposed generic synthetic peptide does not increase the aggregation tendency, or the nature of the aggregates formed.
Further things to consider are ensuring high recovery rates are achieved while also maintaining purity to guarantee protein capture is efficient and stable.
Control strategies
Control strategies must be put in place during peptide synthesis to ensure there are no unknown impurities within the final product. Sisodia said the control of resins, amino acids, derivatives and reagents and solvents are critical in this process.
Furthermore, in-process strategies are equally important as a clear understanding must be demonstrated of what kind of impurity build up could happen and how such accumulation of impurities will not be carried from one stage to the other.
Generic drugs
Generic peptides undergo extensive characterisation. It is required to do multiple analysis to confirm primary, secondary, and higher order structures.
They require a full understanding of development to demonstrate sameness of higher order structures between generic and RLD peptides.
Given the current state of technology for peptide synthesis and characterization, the FDA believes it is now possible for an ANDA applicant to demonstrate that the active ingredient in a proposed generic synthetic peptide drug product (proposed generic synthetic peptide) is the “same” as the active ingredient in a previously approved peptide of rDNA origin.
Sisodia states that these pathways need to be understood as it is required that every new peptide-related impurity be characterised, and a justification be provided as to how this will not affect the safety of the proposed generic synthetic peptide or its effectiveness.
