Antimicrobial resistance represents an increasing threat to public health and makes urgent the need for new-generation antimicrobials with novel modes of action and potent therapeutic activity. Endogenous antimicrobial peptides (AMPs) adopt a facial amphiphilic structure when in contact with bacterial membranes, by winding into alpha-helical or ß-sheet structures with positive charges and lipophilic groups arranged on opposite sides. This facial amphiphilicity allows AMPs to efficiently bind to the negatively charged bacterial membranes and penetrate into them leading to cell death. In the fight against antimicrobial resistance, the development of new antimicrobials able to reproduce the main structural feature of AMPs, like peptide amphiphiles (PAs), is a major strategy. Unfortunately, PAs prepared by joining hydrophobic chains of conventional head-tail surfactants to hydrophilic cationic peptides, cannot fulfill the facial amphiphilicity of AMPs. Facial amphiphilicity is typical of bile acids (BAs), cholesterol-derived steroid acids that are produced in mammals and other vertebrates. This project is aimed at creating unconventional PAs by joining the facial amphiphilic skeletons of BAs to peptides, thereby adding a facial amphiphilic structure to PAs. Lysine-based peptides are used in order to provide a positive charge to the PAs. Conjugation at different sites of the BA molecules, such as the terminal carboxylic group or the hydroxyl bearing carbons, is investigated. Incorporation of D-amino acids is also considered in order to obtain protease resistant BA-based PAs. Beside the synthesis, the project focuses on the self-assembly of the PAs, which is known to regulate their local concentration and activity at the bacterial membrane. The loading of carriers is also investigated, which is generally used to efficiently and safely deliver antibiotics to infections, thereby overcoming problems hindering the antimicrobial efficacy such as proteolysis or toxicity
- The synthesis of the BA-based PAs will provide antimicrobials with a facial amphiphilic structure, which is known to be fundamental for the activity of AMPs. The synthesis represents an interesting step forward in the preparation of antimicrobial PAs, that present a conventional head-tail structure of amphiphiles with a hydrophobic tail and a peptide polar head. We foresee that the facial structure will facilitate the bacterial membrane attack from the antimicrobial PAs thereby increasing their efficacy.
- The BA-based PAs provide antimicrobials with a particularly versatile molecular architecture, whose activity can be tuned and properly optimized by selecting different BA and for each of them: i) conjugation sites, ii) conjugation degree, iii) peptide residues.
- Within this general molecular platform, conventional methods can be used to prevent protease susceptibility, like the incorporation of D-amino acids in the peptide sequence.
- The project also tackles the delivery and controlled release of the antimicrobials, which is known to be a fundamental method to protect them from proteolysis, to prevent problems of toxicity and to provide a sustained or triggered antimicrobial release. In this respect, the project will analyze the loading of PAs on mixed micelles formed by natural BAs and thermo-responsive non-ionic PEO-PPO-PEO triblock copolymers or PEG-PCL diblock copolymers. Recently reported results from our group demonstrate that positively charged anticancer drugs can be conveniently loaded by this kind of mixed carriers, and be slowly released under physiological conditions. These results promote these carriers as potential candidates for a sustained release of antimicrobials, generally needed in the case of recurring biomaterials-related infections.
References for the whole project
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