Synthetic peptides are universal molecules. They themselves can be used as therapeutics for a variety of diseases. When used in combination with other drugs, they can be used to reduce side effects and increase the efficiency of treatment. A major limitation to the use of peptides in therapy is their vulnerability to protease degradation. In recent years, however, researchers have been able to reduce this vulnerability by introducing modifications into the peptide backbone or by binding to other molecules. These modifications to the backbone include unnatural amino acids (including D-amino acids), chemical functionalities, cyclization, and PEGylation (attachment of PEG groups). These drastic changes reduce the likelihood that proteases will recognize bioactive peptides and prolong their half-life in patient plasma.
In recent years, the increased robustness of synthetic peptides has led to renewed interest in peptide-based therapies. Most peptides are used as bioactive agents for specific pathologies (eg anticancer peptides) or as imaging agents for diagnostic purposes. But peptides can also act as structurants. They do this by driving the self-assembly of molecular structures and thus can be used as efficient delivery systems. But while therapeutic peptides are becoming longer, more complex, and more difficult to produce, scientists studying peptide-based delivery systems are increasingly striving for simplicity. In recent years, numerous studies have been published describing simple and creative delivery systems driven and organized around short and ultrashort peptides. This trend can be explained by lowering the cost of peptide production and increasing the value of conventional therapies.
Synthetic peptides, especially small and ultrasmall peptides, are increasingly becoming smart drug delivery agents. Their ability to self-assemble and to be easily combined and modified has aroused interest in the scientific community. Therefore, they are currently being developed to increase the effectiveness of conventional therapeutics while reducing their overall adverse effects in humans.
Over the past decade, scientists have been working to improve the stability and specificity of synthetic peptides. In this case, the most exciting discoveries were made in anticancer therapy. In-depth study and modification of these molecules has shown us that peptides can be conjugated with cleavable PEG groups to increase their stability and reduce their rapid elimination from the organism. It also showed us that these peptides can self-assemble, thereby enhancing tissue penetration. Furthermore, sophisticated smart drug delivery systems can contain cleavable PEG groups, cell-penetrating peptides, and anticancer drugs within liposomes. Some of these systems have been tested in vivo using mouse models with encouraging results. Their promising results suggest that synthetic peptides will continue to drive the discovery of more efficient delivery systems.