Insulin is a disulfide bridged peptide dimer (comprised of A- and B-chains) which regulates the absorption of carbohydrates, especially glucose, from the blood into various tissues and cells.
Various Insulin analogs have been developed, including longer acting forms such as Glargine and Detemir. Glargine differs from Insulin in that the A-chain has a glycine substituted for asparagine at Asn21 and two arginines added to the carboxy terminal of the B chain. In Detemir, a fatty acid (myristic acid) is bound to Lys29 towards the C-terminus of the B-chain. These longer acting insulin analogs are designed to form complexes in vivo which leads to the slow release of the active insulin analog monomer.
Fast acting analogs are also available on the market and these include Insulin aspart and Insulin lispro. In Insulin aspart, amino acid B28 (normally proline) is substituted with an aspartic acid residue. Insulin lispro has a lysine at residue 28 and a proline at residue 29 in the B-chain.
Mixed products containing combinations of the above drugs are also available.
Biosimilar Characterization Considerations
The EMA and US FDA Biosimilar guidelines covering analytical considerations recommend the application of extensive state-of-the-art characterization studies. These studies should incorporate multiple batches of the biosimilar/generic and the reference medicinal product (RMP), in order to demonstrate that the quality of the biosimilar is comparable to the RMP.
- Primary (de novo) Amino Acid Sequence
- Amino Acid Composition
- Terminal Amino Acid Sequence
- Peptide Map
- Disulfide Bridges
- Secondary and Tertiary Structure
Product Specific Technical Considerations
Particular attention should be paid to the following structural elements which are important and challenging when analyzing Insulin and analogs:
- Disulfide bridges
- Product-related impurities
- Oligomerization and oligomerized state
- Analysis of truncated forms and other modified forms