Cell-Penetrating Peptides: A Powerful Tool for Targeted Drug Delivery

An insight into cell-penetrating peptides: perspectives on design, optimization, and targeting in drug delivery systems

The authors carried out a comprehensive review of the application of peptides known as cell-penetrating peptides (CPPs) in various drug delivery systems (DDS), with the prospect of achieving novel solutions and ideas to overcome the challenges of DDS, by making them more able to penetrate cells and biological membranes. A conceptual search was conducted in relevant literature databases (Scopus, PubMed, Web of Science, and Google Scholar) up to 1 April 2025 using keywords such as drug delivery systems, cell-penetrating peptides, CPPs, complexes, conjugates, nanoparticles, dendrimers, exosomes, liquid crystalline, liposomes, micelles, nanospheres and lipid nanoparticles. The studies demonstrate that the antimicrobial effect of drugs, including curcumin, gentamicin, and antifungal drugs like imidazoacridinone derivatives, can be enhanced when they are conjugated or complexed with CPPs. CPPs possess positive charges, which make them suitable for gene therapy applications by facilitating the delivery of plasmids and siRNAs with negative charges in modern delivery systems. Medicinal formulations containing CPPs in combination with liquid crystals or nanostructured lipid carriers (NLCs) increase drugs penetration to the skin. Additionally, several investigations showed that CPPs could have a positive impact on the pharmacokinetic and pharmacodynamic of chemotherapy agents, reducing their side effects. CPPs have significant potential in enhancing penetration, bioavailability, targeting, and optimization of DDS. By using computer modeling and designing CPPs with more desirable features and conducting more clinical studies, new methods for treating diseases and better formulations can be achieved.

Advance in peptide-based drug development: delivery platforms, therapeutics and vaccines

The successful approval of peptide-based drugs can be attributed to a collaborative effort across multiple disciplines. The integration of novel drug design and synthesis techniques, display library technology, delivery systems, bioengineering advancements, and artificial intelligence have significantly expedited the development of groundbreaking peptide-based drugs, effectively addressing the obstacles associated with their character, such as the rapid clearance and degradation, necessitating subcutaneous injection leading to increasing patient discomfort, and ultimately advancing translational research efforts. Peptides are presently employed in the management and diagnosis of a diverse array of medical conditions, such as diabetes mellitus, weight loss, oncology, and rare diseases, and are additionally garnering interest in facilitating targeted drug delivery platforms and the advancement of peptide-based vaccines. This paper provides an overview of the present market and clinical trial progress of peptide-based therapeutics, delivery platforms, and vaccines. It examines the key areas of research in peptide-based drug development through a literature analysis and emphasizes the structural modification principles of peptide-based drugs, as well as the recent advancements in screening, design, and delivery technologies. The accelerated advancement in the development of novel peptide-based therapeutics, including peptide-drug complexes, new peptide-based vaccines, and innovative peptide-based diagnostic reagents, has the potential to promote the era of precise customization of disease therapeutic schedule.

Applications of cell penetrating peptide-based drug delivery system in immunotherapy

Cell penetrating peptides (CPPs) are usually positive charged peptides and have good cell membrane permeability. Meanwhile, CPPs are facile to synthesize, and can be functionalized to satisfy different demands, such as cyclization, incorporating unnatural amino acids, and lipid conjugation. These properties have made them as efficient drug-delivery tools to deliver therapeutic molecules to cells and tissues in a nontoxic manner, including small molecules, DNA, siRNA, therapeutic proteins and other various nanoparticles. However, the poor serum stability and low tumor targeting ability also hindered their broad application. Besides, inappropriate chemical modification can lead to membrane disruption and nonspecific toxicity. In this paper, we first reviewed recent advances in the CPP applications for cancer therapy via covalent or non-covalent manners. We carefully analyzed the advantages and disadvantages of each CPP modifications for drug delivery. Then, we concluded the recent progress of their clinical trials for different diseases. Finally, we discussed the challenges and opportunities CPPs met to translate into clinical applications. This review presented a new insight into CPPs for drug delivery, which could provide advice on the design of clinically effective systemic delivery systems using CPPs.

Diversity-oriented synthesis of second generation guanidinium-rich transporters toward cell-selective penetration

Cell-penetrating peptides (CPPs) hold significant promise for intracellular delivery of various cargo molecules such as therapeutics. However, the lack of selectivity remains a critical challenge and limits the clinical application of CPPs. Using an automated peptide synthesizer, we generated a diversity-oriented library of 256 peptidomimetics containing four modified peptoid guanidine-bearing monomers incorporated alternatively with four α-amino acids. These α-amino acids were chosen to enhance lipophilic interactions with the cell membrane (Phe, 2Nal) or to bear pH-sensitive properties (His), which could enhance cancer cell selectivity. The synthesized library exhibits selective internalization, with an average selectivity index (SI) of 1.49 for HeLa cells in comparison to non-cancerous HEK293 cells. Compounds 155 and 187, containing three His residues and either Phe or 2Nal, show high cellular uptake in HeLa cells (64.6% and 75.7%, respectively) and possess an SI of 2.7 and 2.9, respectively, at the tested dose of 5 μM. Altogether, these findings highlight the use of diversity-oriented library synthesis to identify cell-permeable candidates as well as their potential for targeted cellular delivery and enhanced specificity.

Spotlight on HIV-derived TAT peptide as a molecular shuttle in drug delivery

HIV-derived TAT peptide, with a high penetration rate into cells and its nonimmunogenic and minimally toxic nature, is an attractive tool for enhancing the biodistribution of drugs and their systemic administration. Despite the presence of numerous promising preclinical investigations illustrating its capability to specifically target distinct tissues and deliver a diverse range of pharmacological agents, the efficacy of various clinical trials incorporating TAT has been impeded by several considerable obstacles. Hence, there is much need for an in-depth investigation concerning the application of TAT in drug delivery mechanisms. In this review, we have elucidated the structure of TAT and its utility in the proficient delivery of various types of bioactive molecules.

Investigating the impact of thiol reactivity and disulfide formation on cellular uptake of cell-permeable peptides

Cell-penetrating peptides (CPPs) have been explored as versatile tools to transport various molecules into cells. The uptake mechanism of CPPs is still not clearly understood and most probably depends on several factors like the nature of the CPP itself, the attached cargo, the investigated cell system, and other experimental conditions, such as temperature and concentration. One of the first steps of internalization involves the interaction of CPPs with negatively charged molecules present at the outer layer of the cell membrane. Recently, thiol-mediated uptake has been found to support the effective translocation of sulfhydryl-bearing substances that would actually not be cell-permeable. Within this work, we aimed to understand the relevance of thiol reactivity for the uptake mechanism of cysteine-containing CPPs that we have developed previously in our group. Therefore, we compared the two peptides, sC18-Cys and CaaX-1, in their single reduced and dimeric disulfide versions. Cytotoxicity, intracellular accumulation, and impact on the internalization process of the disulfides were investigated in HeLa cells. Both disulfide CPPs demonstrated significantly stronger cytotoxic effects and membrane activity compared with their reduced counterparts. Notably, thiol-mediated uptake could be excluded as a main driver for translocation, showing that peptides like CaaX-1 are most likely taken up by other mechanisms.

Identifying Cell-Penetrating Peptides for Effectively Delivering Antimicrobial Molecules into Streptococcus suis

Cell-penetrating peptides (CPPs) are promising carriers to effectively transport antisense oligonucleotides (ASOs), including peptide nucleic acids (PNAs), into bacterial cells to combat multidrug-resistant bacterial infections, demonstrating significant therapeutic potential. Streptococcus suis, a Gram-positive bacterium, is a major bacterial pathogen in pigs and an emerging zoonotic pathogen. In this study, through the combination of super-resolution structured illumination microscopy (SR-SIM), flow cytometry analysis, and toxicity analysis assays, we investigated the suitability of four CPPs for delivering PNAs into S. suis cells: HIV-1 TAT efficiently penetrated S. suis cells with low toxicity against S. suis; (RXR)4XB had high penetration efficiency with inherent toxicity against S. suis; (KFF)3K showed lower penetration efficiency than HIV-1 TAT and (RXR)4XB; K8 failed to penetrate S. suis cells. HIV-1 TAT-conjugated PNA specific for the essential gyrase A subunit gene (TAT-anti-gyrA PNA) effectively inhibited the growth of S. suis. TAT-anti-gyrA PNA exhibited a significant bactericidal effect on serotypes 2, 4, 5, 7, and 9 strains of S. suis, which are known to cause human infections. Our study demonstrates the potential of CPP-ASO conjugates as new antimicrobial compounds for combating S. suis infections. Furthermore, our findings demonstrate that applying SR-SIM and flow cytometry analysis provides a convenient, intuitive, and cost-effective approach to identifying suitable CPPs for delivering cargo molecules into bacterial cells.