Site-Specific Molecular Engineering of Nanobody–Glucoside Conjugates for Enhanced Brain Tumor Targeting

Nanobodies play an increasingly prominent role in cancer imaging and therapy. However, their <i>in vivo</i> efficacy is often constrained by inadequate tumor penetration and rapid clearance from the bloodstream, particularly in brain tumors due to the intractable blood-brain barrier (BBB). Glycosylation is a favorable strategy for modulating the biological functions of nanobodies, including permeability and pharmacokinetics, but it also leads to heterogeneous glycan structures, which affect the targeting ability, stability, and quality of nanobodies. Here, we describe a post-translational modification strategy to produce precisely engineered and homogeneous nanobody-glucoside conjugates for effective BBB penetration and brain tumor targeting. Specifically, we employ an enzymatic method and click chemistry to functionalize nanobodies with glucoside and poly(ethylene glycol) (PEG), facilitating efficient transcytosis into the brain via glucose transporter-1 (GLUT1). Furthermore, we rationally select a near-infrared (NIR) fluorophore for labeling to maintain the metabolic pathway and biodistribution of nanobodies and assess their potency in two tumor models. The resulting nanobody-glucoside conjugates demonstrate a remarkable increase in BBB penetration and brain tumor accumulation, which are ∼2.9-fold higher in the transgenic mouse model and ∼5.7-fold higher in the orthotopic glioma model compared to unmodified nanobodies. This study provides a promising approach for the production of nanobody therapeutic agents for central nervous system (CNS) delivery.