Ketoboronate as a Minimal Covalent-Reversible Tag for Targeted Lysosomal Degradation of Extracellular and Membrane Proteins

Extracellular and
membrane-associated proteins play essential
roles
in nearly all our body’s biochemical processes and are implicated
in cancer, autoimmune disorders, and neurodegenerative diseases. Consequently,
a selective and universally applicable technique for the degradation
of these proteins in disease-relevant conditions could significantly
improve human health prospects. Lysosome-targeting chimeras (LYTACs)
are bifunctional degraders comprising of an antibody conjugated with
a cell–surface receptor ligand that enables cargo lysosome
shuttling and degradation. Herein, we demonstrate that conjugation
of antibodies with a small ketoboronate-based, lysine-reactive, covalent-reversible
uptake tag (KB) enables the internalization of plasma membrane and
extracellular proteins, directing them to lysosomal degradation via
receptor-mediated endocytosis. Chemoproteomic target deconvolution
revealed that reversible modification of lysine residues on the transferrin
receptor protein 1 (TFRC) and HLA class I histocompatibility antigen
A, B and C (HLA-ABC) enabled efficient uptake and lysosomal targeting
through both clathrin-dependent and -independent mechanisms. KB-antibody
conjugates (KB-TACs) efficiently degrade the epidermal growth factor
receptor (EGFR), vascular endothelial growth factor A (VEGFA) and
epidermal growth factor receptor 2 (HER2) in cancer cells. Furthermore,
we showed KB-TTZ degrades HER2 in vivo in BT-474 tumor xenografts,
with a significant reduction in tumor volumes compared to TTZ and
vehicle treatments. Altogether, the KB tag represents a versatile,
minimal-size chemical unit to functionalize therapeutic antibodies
for targeted protein degradation through dual receptor-mediated endocytosis
and lysosomal delivery.