Chemical biology tools for probing transcytosis at the blood-brain barrier.

Absorptive- and receptor-mediated transcytosis (AMT/RMT) are widely studied strategies to deliver therapeutics across the blood-brain barrier (BBB). However, an improved understanding of the mechanism surrounding trafficking is required that could promote delivery. Accordingly, we designed a flexible platform that merged AMT and RMT motifs on a single scaffold to probe various parameters (ligand, affinity, valency, position) in a screening campaign. During this process we adapted an BBB model to reliably rank transcytosis of the vehicle library. Our results demonstrate heightened uptake and trafficking for the shuttles, with a structure-activity relationship for transcytosis emerging. Notably, due to their small size, the majority of shuttles demonstrated increased permeation compared to transferrin, with the highest performing shuttle affording a 4.9-fold increase. Consequently, we have identified novel peptide conjugates that have the capacity to act as promising brain shuttles.