Peptide therapeutics account for 5% of the global pharmaceutical market and will continue to expand over the coming years. The increase in investment and research efforts in the peptide field, the maturity of peptide synthesis technology, and the success of biologics collectively contribute to the fast-growing market of peptide therapeutics.
Peptides are composed of the same building blocks–amino acids–as proteins and naturally form secondary structures such as alpha-helix and beta-sheets. The fundamental difference between proteins and peptides is the length of the amino acid chain. Although there is no specific cut-off number of amino acids for defining a peptide or a protein, it is traditionally considered that peptides consist of 2-50 amino acids. Depending on the size, most peptides do not form tertiary or quaternary structures like proteins do which further stabilize their integrity. As a result, chemical and physical stability becomes the main challenge for peptides to be directly used as therapeutics. Chemical modifications such as PEGylation and disulfide mimetics are often implemented in peptide therapeutics development to increase metabolic stability and bioavailability. It is therefore critical to ensure that the peptide maintains the secondary structure–the sole higher order structural determinant of its biological function and efficacy, during the development and formulation processes.