Antibiotic resistance is one of the major threats to public health, with an increasing number of deaths annually and respiratory tract infections are considered a leading cause of global death, particularly in vulnerable populations. It is therefore extremely urgent to find new therapeutic strategies to overcome this problem and one of these is represented by the design of aerosolizable nanoformulations (NEs). In this work we designed NEs composed by a mixture of Rosmarinus officinalis and Thymus vulgaris essential oils aiming to obtain an active nanocarrier capable and useful to entrap different active compounds. The formulation, NEs-1, was deeply characterized in terms of dynamic light scattering, ζ-potential measurements, stability studies, antimicrobial activity and cytotoxicity. Our results showed that NEs-1 exhibited useful physico-chemical properties for nose-to lung applications, as well as significant biological activity. However, at the selected oil concentration, it induced cytotoxic effects on eukaryotic cells. We subsequently identified the optimum oil concentration, and the formulation was then optimized to obtain NEs-2, nanoemulsions with similar physico-chemical properties to NEs-1. NEs-2 was furthermore characterized by morphological analysis, in terms of resistance to nebulization process and stability in simulated biological fluid such as nasal and artificial sputum. Moreover, NEs-2 demonstrated the ability to slow down the growth of E. coli and K. pneumoniae, confirming its potential as a bioactive carrier with the aim of encapsulating antimicrobial molecules and increasing their effectiveness and reducing their adverse effects.

The rise of antimicrobial resistance and the global burden of cancer demand innovative therapeutic strategies. Frog skin secretions offer a rich source of bioactive peptides, some of which exhibit remarkable dual functionality—potent antimicrobial activity coupled with selective anticancer effects. This review highlights frog skin-derived peptides that bridge the gap between antimicrobial and anticancer therapeutics, emphasizing their structural diversity, mechanisms of action, and translational potential. A comprehensive literature search was conducted to identify peptides isolated from diverse anuran species, with emphasis on studies reporting structural features, activity against Gram-positive and Gram-negative bacteria, including multidrug resistant clinical isolates, anticancer effects, and underlying molecular mechanisms of cytotoxicity. Peptides such as dermaseptins, temporins, and brevinins disrupt microbial membranes while triggering apoptosis or necrosis in cancer cells. Key physicochemical characteristics, including net positive charge, amphipathicity, and α-helical conformation, contribute to their dual functionality. Recent advances in peptide engineering and delivery have improved stability, selectivity, and therapeutic efficacy, enhancing the clinical prospects of these naturally occurring bioactive molecules. Frog skin peptides represent promising candidates for the development of next-generation antimicrobial and anticancer therapeutics.

Antimicrobial peptides (AMPs) represent valid alternatives to conventional antibiotics primarily due to their mechanism of action, which consists of cytoplasmic membrane disruption. However, their clinical application is often limited by cytotoxicity at high concentrations and low intrinsic biostability. To address these limitations, various biochemical approaches have been explored. In recent years, the frog‐skin derived AMP Esc(1‐21) has been extensively characterized for its potent antimicrobial activity, especially against Gram‐negative bacteria, both in vitro and in vivo. In this study, we designed and synthesized novel Esc(1‐21) analogs in which a single isopeptide bond was introduced in place of a conventional peptide bond at specific positions within the sequence. The resulting five analogs were evaluated for their (i) chemical and structural properties, (ii) resistance to proteolytic degradation, (iii) antimicrobial and antibiofilm activities, (iv) hemolytic and cytotoxic effects, and (v) ability to perturb bacterial cytoplasmic membranes. Among these, Esc(1‐21)ε20 showed the most promising features, maintaining antimicrobial and antibiofilm activities comparable to those of the parent peptide while exhibiting lower cytotoxicity towards eukaryotic cells at higher concentrations and greater resistance to enzymatic degradation. These findings highlight Esc(1‐21)ε20 as an attractive lead candidate for the development of new antibiotic therapeutics.

The emergence of multidrug-resistant Pseudomonas aeruginosa strains is increasingly becoming a critical threat to global health. Among the resistance mechanisms, the MexAB–OprM efflux pump confers P. aeruginosa with an efficient method to export a broad spectrum of antibiotics. The antimicrobial peptide Esc (1-21)-1c was shown to downregulate this efflux system, though its mechanism of action has not been unveiled thus far. Here, we employed a combination of molecular modeling and experimental methods to investigate the precise peptide inhibitory mechanism. Functional proteomic experiments revealed the P. aeruginosa protein Q9I5H3, homologous to E. coli QseB, as a putative key target of Esc(1-21)-1c. Molecular docking predicted stable peptide–protein interactions, which were experimentally validated through fluorescence spectroscopy. Furthermore, electrophoretic mobility shift assays demonstrated that Q9I5H3 specifically binds the MexAB–OprM promoter and that Esc(1-21)-1c competitively inhibits this interaction in a dose-dependent manner. These findings reveal a previously uncharacterized regulatory pathway for efflux pump control and highlight Q9I5H3 as a promising therapeutic target against multidrug-resistant P. aeruginosa.