Biomolecules known as peptides consist of amino acids connected through peptide bonds and display properties of high efficiency alongside low toxicity with strong specificity. Drug delivery research has seen a growing focus on peptide application in recent years. The distinctive characteristics of these molecules provide promising capabilities for targeted delivery and cell penetration while demonstrating environmental responsiveness and self-assembly abilities.
Definition and Advantages of Peptides
Peptides consist of multiple amino acids and display a wide variety of structures and functions that are highly specific. Peptides demonstrate superior biological activity while showing reduced toxicity levels when compared to small molecule drugs. Despite their high biological activity and lower toxicity, peptide drugs encounter drug delivery problems including their destruction by gastrointestinal enzymes alongside their brief half-lives and poor ability to penetrate cells. Structural modification techniques alongside nanotechnology and drug-device combinations present effective solutions to these delivery barriers while enhancing peptide drug stability and delivery performance.
Key Strategies for Peptides in Drug Delivery
Targeted peptides can specifically recognize and bind to specific cell surface receptors or molecules, enabling precise drug delivery.
Receptor-Mediated Targeting (e.g., RGD, NGR): RGD peptides target the integrin αvβ3 receptor, enhancing the selective delivery of anti-tumor drugs.
Ligand-Receptor Interaction (e.g., T7 Peptide): T7 peptides target transferrin receptors, improving blood-brain barrier penetration for neurodegenerative disease treatment.
Immuno-Targeting (e.g., PD-L1 Targeting Peptides): PD-L1-mediated delivery enhances the effectiveness of immunotherapy.
Cell penetrating peptides enable drugs to cross the cell membrane and enter the cytoplasm, which is crucial for drugs that need to act intracellularly, such as nucleic acid and protein drugs. CPPs enhance drug uptake through interactions with the cell membrane, promoting endocytosis or direct transmembrane transport, increasing intracellular drug concentration. CPP-based delivery systems are widely used for intracellular delivery of small molecules, proteins, peptides, and nucleic acids, showing significant potential in cancer, gene therapy, and vaccine fields.
Cationic CPPs (e.g., TAT, Penetratin): Enter cells through electrostatic interactions with the cell membrane.
Hydrophobic CPPs (e.g., TP10, C105Y): Promote transmembrane delivery through membrane fusion mechanisms.
Chimeric CPPs (e.g., Pep-1): Combine cationic and hydrophobic characteristics to enhance delivery efficiency.
Responsive peptides undergo structural or functional changes based on specific physiological environments (such as pH, temperature, enzyme concentrations), enabling controlled drug release.
pH-Responsive Peptides (e.g., His-modified peptides): Release drugs in the acidic tumor microenvironment.
Enzyme-Responsive Peptides (e.g., MMP-2 Recognition Peptides): Degrade specifically within tumor tissues expressing high levels of MMP-2 and release drugs.
Self-assembling peptides can form various nanostructures, such as nanoparticles, nanofibers, and nanotubes. These nanostructures not only enhance the stability of peptide drugs but also enable sustained drug release. Self-assembling peptides can form hydrogels that encapsulate drugs within a nanonetwork, providing sustained release and local delivery. Typical applications include:
Anti-tumor Drug Delivery (e.g., Doxorubicin-loaded peptide hydrogels).
Tissue Engineering and Regenerative Medicine (e.g., Growth factor-loaded peptide hydrogels promoting wound healing).
- Nanocarrier-Peptide Delivery Systems
Combining peptides with nanocarriers can improve drug stability, bioavailability, and targeting ability. This includes:
Liposome-Peptide Complex Systems: Liposomes can encapsulate hydrophilic or hydrophobic drugs, while peptides can enhance targeting, such as RGD-modified liposomes.
Polymeric Nanoparticle-Peptide Complex Systems: e.g., PLGA-peptide nanoparticles, suitable for long-lasting delivery.
Gold Nanoparticles (AuNPs) and Quantum Dots (QDs) combined with Peptide Delivery: Used for imaging and therapy integration.
Key Technologies in Peptide Drug Delivery Systems
End-Terminal Modification: Modifications like N-acetylation and C-amidation can extend the half-life of peptides in the body and improve their stability. For example, GLP-1 receptor agonists significantly prolong their plasma half-life by fusion with albumin.
Side Chain Modification: Replacing specific amino acids with modified ones can improve properties such as solubility and binding affinity of the peptide.
Backbone Modification: Altering the peptide backbone structure can make it more stable and resistant to enzymatic degradation.
PEGylation: Linking peptides with polyethylene glycol (PEG) can extend their half-life, improve bioavailability, and reduce immunogenicity.
Nanoparticles: Peptides can self-assemble into nanoparticles to encapsulate and deliver drugs. For example, elastin-like peptides (ELP) are temperature-responsive and can be used to prepare intelligent drug delivery systems.
Nanofibers: Peptide nanofibers possess good biocompatibility and mechanical properties, making them suitable for sustained and controlled drug release, such as in tissue engineering and regenerative medicine.
Nanovesicles: Peptide nanovesicles can encapsulate hydrophilic or hydrophobic drugs, enhancing the stability and bioavailability of the drugs.
Principle of Self-Assembly: Peptides spontaneously assemble into ordered nanostructures under specific conditions (such as pH, temperature, ion strength). These structures can serve as drug carriers for efficient drug delivery.
Types of Self-Assembling Peptides: Includes β-sheet peptides, α-helix peptides, and amphipathic peptides, each with different assembly behaviors and structural characteristics.
Applications of Self-Assembly: Self-assembled peptides can be used to prepare drug delivery systems, tissue engineering scaffolds, and biosensors.
- Drug-Device Combination Technology
Microneedles: Combining peptide drugs with microneedles allows for transdermal drug delivery, improving bioavailability and patient compliance.
Patches: Peptide drugs can be incorporated into patches for localized drug delivery, such as in the treatment of skin diseases or pain management.
Iontophoresis/Ultrasound: Using electrical fields or sound waves to increase the permeability of the skin or mucosa, facilitating the absorption of peptide drugs.
Future Prospects in Drug Delivery
Peptides have broad application prospects in drug delivery due to their unique structures and functions, offering significant advantages in targeted delivery, cell penetration, environmental responsiveness, and self-assembly. However, peptide drug delivery systems still face challenges such as high production costs, poor stability, and fast metabolism. Future research will focus on the following areas:
Development of Novel Peptide Modification Techniques: Introducing non-natural amino acids via chemical modification to extend peptide half-life and improve stability.
Synergistic Effect of Peptides with Other Delivery Systems: Exploring the synergy between peptides and systems like liposomes, nanoparticles, and hydrogels to develop more efficient drug delivery platforms.
Clinical Translation and Application: Promoting the clinical translation of peptide drug delivery systems to develop more clinically valuable peptide drugs, offering greater hope for patients.
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