QNpt-22 nanoaggregate decouples hydrophobicity from toxicity, achieving potent antibacterial efficacy

Developing effective membrane-active antimicrobial peptide-mimicking macromolecules faces a critical activity-toxicity trade-off. While increased hydrophobicity enhances bactericidal potency by disrupting bacterial membranes, it often leads to elevated host-cell toxicity and reduced selectivity, as hydrophobic moieties indiscriminately interact with both bacterial and mammalian lipid membranes. Current antimicrobial strategies struggle with this inherent challenge, limiting the therapeutic window and potential for systemic administration. This research addresses this fundamental gap by introducing a novel design principle to overcome the non-selective nature of highly hydrophobic antimicrobial agents.

Researchers engineered maleimide-based cationic macromolecules with varying hydrophobic alkyl chain lengths (decyl to docosyl). They investigated how increasing alkyl chain length influenced nanoaggregation and its effect on selectivity and toxicity. The optimized stable nanoaggregate, QNpt-22 (bearing a docosyl chain), was then thoroughly characterized. Its antibacterial activity was assessed against stationary-phase bacteria and preformed biofilms in vitro. Host-cell toxicity was evaluated against zwitterionic mammalian membranes. For in vivo assessment, QNpt-22 was tested for biocompatibility across multiple routes of administration in mice and its therapeutic efficacy was demonstrated in an Acinetobacter baumannii superficial skin infection model.

The study found that increasing the alkyl chain length in the designed macromolecules promoted nanoaggregation. Specifically, the macromolecule with the longest chain (docosyl), designated QNpt-22, underwent a structural transition. In this transition, nonselective hydrophobic segments were effectively masked within a stable aggregate core, while cationic functionalities remained surface-exposed. This topological segregation significantly diminished nonspecific interactions with zwitterionic mammalian membranes, leading to significantly lower toxicity compared to non-aggregated hydrophobic counterparts. The optimized QNpt-22 nanoaggregate exhibited potent antibacterial activity, including the eradication of stationary-phase bacteria and preformed biofilms, which are major challenges for conventional antibiotics. Furthermore, in preclinical models, the nanoaggregate demonstrated excellent biocompatibility across multiple routes of administration in mice.

QNpt-22 displayed significant therapeutic efficacy in an Acinetobacter baumannii superficial skin infection model, highlighting its potential for in vivo application. These findings establish that spatial segregation of hydrophobic domains via nanoaggregation is a robust strategy to achieve selectivity.