BACKGROUND: Targeted protein degradation has emerged as one of the most promising approaches in drug discovery, but has been mainly limited to modulation of membrane and intracellular proteins. With the recent discovery of cell surface receptors (e.g., ASGPR) that can shuttle extracellular ligands into the lysosomal degradation pathway, there are now many opportunities for exploring extracellular drug targets. One such target is PCSK9, a serum protein which has a major role in cholesterol metabolism.

AIM: Here, we explore the potential for targeted degradation of PCSK9, which would represent a markedly different approach to the majority of peptide drug leads that act by inhibiting PCSK9 binding to its cognate receptor.

METHOD and RESULTS: We engineered bifunctional peptide-based degraders capable of binding to both ASGPR and PCSK9 by ligating tri-GalNAc (an ASGPR binder) to different sites of a cyclic PCSK9 inhibitory peptide via click chemistry. Their bifunctional binding activities to PCSK9 and ASGPR were characterized by SPR, and shown to have nanomolar binding affinities to either target. The in vivo activity of these degraders will be examined in the future.

CONCLUSION and SIGNIFICANCE:

As a result, we successfully engineered bifunctional peptides that have the potential for degrading PCSK9. This work well represents an example of engineering degraders based on peptide inhibitors and an application of extracellular targeted protein degradation on a clinically validated target.