Keita Masuda

Background/Objectives: Discriminating bacterial from mammalian membranes remains a central challenge in antibiotic design. Bacterial membranes are enriched in phosphatidylethanolamine (PE), a lipid normally absent from the outer leaflet of mammalian cells, providing a signature for selective molecular engagement. We report a compact covalent ligand, 6-dimethylamino-4-ketohexanoic acid (DMAX), which targets PE via Schiff base formation, leveraging its tertiary amine to facilitate the reaction and strengthen ionic binding with the phosphate group. Methods: The reactivity of DMAX and PE was evaluated by computational simulations, and their interaction was examined by spectroscopic analyses (NMR and FT-IR) and an artificial membrane assay. The targeting ability of DMAX for live bacteria was determined by microscopy study, and its applicability to therapeutic system was tested in vitro under washed conditions that mimic rapid in vivo clearance. Results: Spectrometric analyses revealed the selective covalent interaction of DMAX and PE, consistent with the simulated results. Fluorescently labeled DMAX selectively binds PE-enriched model membranes and efficiently recognizes Gram-negative bacteria while sparing mammalian cells. Conjugation of DMAX to Gemifloxacin (Gem) significantly enhanced antibiotic efficacy by 10-fold compared with free Gem, even after rapid drug clearance, while maintaining safety in mammalian cells. Conclusions: These results identify DMAX as an efficient and versatile PE-targeting platform, enabling selective membrane anchoring to advance precision antibiotic strategies.

Multi-arm star-shaped block copolymers with precisely tuned nano-architectures are promising candidates for drug delivery. Herein, we developed 4- and 6-arm star-shaped block copolymers consisting of poly(furfuryl glycidol) (PFG) as the core-forming segments and biocompatible poly(ethylene glycol) (PEG) as the shell-forming blocks. The polymerization degree of each block was controlled by adjusting the feeding ratio of a furfuryl glycidyl ether and ethylene oxide. The size of the series of block copolymers was found to be less than 10 nm in DMF. In water, the polymers showed sizes larger than 20 nm, which can be related to the association of the polymers. The star-shaped block copolymers effectively loaded maleimide-bearing model drugs in their core-forming segment with the Diels–Alder reaction. These drugs were rapidly released upon heating via a retro Diels–Alder step. When the star-shaped block copolymers were injected intravenously in mice, they showed prolonged blood circulation, with more than 80% of the injected dose remaining in the bloodstream at 6 h after intravenous injection. These results indicate the potential of the star-shaped PFG-PEG block copolymers as long-circulating nanocarriers.

Messenger RNA (mRNA) therapeutics have recently demonstrated high clinical potential with the accelerated approval of SARS-CoV-2 vaccines. For fulfilling the promise of unprecedented mRNA-based treatments, the development of safe and efficient carriers is still necessary to achieve effective delivery of mRNA. Herein, we prepared mRNA-loaded nanocarriers for enhanced in vivo delivery using biocompatible block copolymers having functional amino acid moieties for tunable interaction with mRNA. The block copolymers were based on flexible poly(ethylene glycol)-poly(glycerol) (PEG-PG) modified with glycine (Gly), leucine (Leu) or tyrosine (Tyr) via ester bonds to generate block catiomers. Moreover, the amino acids can be gradually detached from the block copolymers after ester bond hydrolyzation, avoiding cytotoxic effects. When mixed with mRNA, the block catiomers formed narrowly distributed polymeric micelles with high stability and enhanced delivery efficiency. Particularly, the micelles based on tyrosine-modified PEG-PG (PEG-PGTyr), which formed polyion complex (PIC) and π–π stacking with mRNA, displayed excellent stability against polyanions and promoted mRNA integrity in serum. The PEG-PGTyr-based micelles also increased the cellular uptake and the endosomal escape, promoting high protein expression both in vitro and in vivo. Furthermore, the PEG-PGTyr-based micelles significantly extended the half-life of the loaded mRNA after intravenous injection. Our results highlight the potential of PEG-PGTyr-based micelles as safe and effective carriers for mRNA, expediting the rational design of polymeric materials for enhanced mRNA delivery. Graphical abstract

The development of effective treatments against infectious diseases is an extensive and ongoing process due to the rapid adaptation of bacteria to antibiotic-based therapies. However, appropriately designed activity enhancers, including antibiotic delivery systems, can increase the effectiveness of current antibiotics, overcoming antimicrobial resistance and decreasing the chance of contributing to further bacterial resistance. The activity/delivery enhancers improve drug absorption, allow targeted antibiotic delivery, improve their tissue and biofilm penetration and reduce side effects. This review provides insights into various antibiotic activity enhancers, including polymer, lipid, and silver-based systems, designed to reduce the adverse effects of antibiotics and improve formulation stability and efficacy against multidrug-resistant bacteria.