Methylene blue (MB) can be employed as a photo-activatable antimicrobial drug in photodynamic therapy (PDT) due to its ability to release oxygen free radicals upon photo-activation. However, its poor ability to penetrate bacterial cell walls and bacterial biofilms limits its antimicrobial activity. To overcome these limitations, we propose some formulations of MB based on different cationic liposomes. The liposome–MB systems were characterized using dynamic light scattering (DLS), zeta potential analysis and UV-visible spectroscopy. Their ability to penetrate inside the cytoplasm of E. coli, taken as a bacterial model for Gram-negative strains, was investigated through laser scanning confocal microscopy (CLSM) and compared to the penetration of naked MB. Then, MB-loaded liposomes were photo-activated and their antimicrobial activity was tested against E. coli, showing a strong improvement with respect to MB solutions. The liposomal formulations dramatically enhance MB penetration in bacterial biofilms and reduce the inflammatory response due to lipopolysaccharide exposure in mammalian cells. The observed antimicrobial and anti-inflammatory efficacies show a clear correlation with some structural features of the carriers, namely the size and the surface charge density. Overall, these results provide fundamental knowledge that enables the design of novel efficient PDT treatments, which potentially overcome the rising incidence of antibiotic resistance of bacterial strains.

A comparative study between two novel, highly water soluble, ruthenium(II) polypyridyl complexes, [Ru(phen)₂L′] and [Ru(phen)₂Cu(II)L′] (L and L‐Cu^II), containing the polyaazamacrocyclic unit 4,4′‐(2,5,8,11,14‐pentaaza[15])‐2,2′‐bipyridilophane (L′), is herein reported. L and L‐Cu^II interact with calf‐thymus DNA and efficiently cleave DNA plasmid when light‐activated. They also possess great penetration abilities and photo‐induced biological activities, evaluated on an A375 human melanoma cell line, with L‐Cu^II being the most effective. Our study highlights the key role of the Fenton active Cu^II center within the macrocycle framework, that would play a synergistic role with light activation in the formation of cytotoxic ROS species. Based on these results, an optimal design of Ru^II polypyridyl systems featuring specific Cu^II‐chelating polyamine units could represent a suitable strategy for the development of novel and effective photosensitizers in photodynamic therapy.

Here we report a family of bis-amide receptors for anion binding that contain carboxylic acid groups vicinal to the amide function. Deprotonation of the carboxylic acids decreases the acidity of amide NHs, switching on the anion binding ability of the deprotonated receptors with selectivity for fluoride complexation. The proposed systems represent a unique example of anionic receptors able to bind anions via H-bonding.

Herein, we report on the successful encapsulation into human H-ferritin of two highly charged Ru(II) polypyridyl complexes, [Ru(phen)₂L′]²⁺ (Ru1, with L′ = 4,4′-(2,5,8,11,14-pentaaza[15])-2,2′-bipyridilophane) and [Ru(phen)₂L′′]²⁺ (Ru2, with L′′ = 4,4′-bis-[methylen-(1,4,7,10-tetraazacyclododecane)]-2,2′-bipyridine). The resulting Ru(II)-ferritin nanocomposites are highly luminescent, display great stability in physiological conditions and preserve the native shell–core structure of the protein. Moreover, the singlet oxygen sensitizing properties of metal complexes, established by independent spectrophotometric and spectrofluorimetric measurements, are largely maintained also in their encapsulated form. Ru(II)-ferritin nanocomposites are exclusively internalized by cancer cells expressing the transferrin receptor 1 (TfR1) (i.e. HeLa and A2780 with respect to non-cancerous C2C12 myoblasts). Immunofluorescence analysis also reveals the co-localization of Ru1 and Ru2 with the TfR1 in the internal cellular compartments of HeLa and A2780 cells, highlighting the crucial role played by the receptor-mediated endocytosis of H-type ferritins exerted by TfR1. Finally, an MTT assay probed that light-activation effectively leads to a marked dose-dependent cytotoxic effect uniquely against cancer cells. This study underlines the potential of human H-ferritin as a valuable tool for the tumor-targeted delivery of sensitizing agents for photodynamic therapy.