Functional Blood‐Brain Barrier Crossing by Biomimetic M13 Phage Vectors for Targeted Neuronal Delivery

The blood-brain barrier (BBB) is a highly selective gatekeeper. While providing essential protection against pathogens, BBB also poses a major challenge by restricting the delivery of systemically administered therapeutics. Consequently, there is a pressing need for innovative strategies that can efficiently and selectively target neuronal populations to treat diverse brain disorders. Nanomaterials enable transcellular transport across the endothelial layer; however, given the biomolecular corona paradigm, designing biomimetic hybrid nanoconstructs that preserve and leverage biological functionality within a complex physiological environment is more promising. Here, we investigated the potential of M13 bacteriophages as biocompatible and versatile nanovectors across the BBB. M13 phages exhibited: (i) a high cargo capacity within the main protein capsomer (here exploited for fluorescent labeling); (ii) offered genetic flexibility for ligand display; (iii) showed a natural propensity to efficiently cross the endothelial layer via specific intracellular pathways; (iv) maintained their structure and functionality intact. We also demonstrate that M13 phages engineered to target specific neuronal populations via single-domain antibody display retain their specificity after BBB translocation and in a protein- and cell-crowded environment. Overall, our results provide mechanistic insights emphasizing an unprecedented field of application for (engineered) M13 phages as biomimetic nanotools for targeting and delivery across the BBB.