Bioactive Cyclization Optimizes the Affinity of a Proprotein Convertase Subtilisin/Kexin Type 9 (PCSK9) Peptide Inhibitor

Peptides
are regarded as promising next-generation therapeutics.
However, an analysis of over 1000 bioactive peptide candidates suggests
that many have underdeveloped affinities and could benefit from cyclization
using a bridging linker sequence. Until now, the primary focus has
been on the use of inert peptide linkers. Here, we show that affinity
can be significantly improved by enriching the linker with functional
amino acids. We engineered a peptide inhibitor of PCSK9, a target
for clinical management of hypercholesterolemia, to demonstrate this
concept. Cyclization linker optimization from library screening produced
a cyclic peptide with ∼100-fold improved activity over the
parent peptide and efficiently restored low-density lipoprotein (LDL)
receptor levels and cleared extracellular LDL. The linker forms favorable
interactions with PCSK9 as evidenced by thermodynamics, structure–activity
relationship (SAR), NMR, and molecular dynamics (MD) studies. This
PCSK9 inhibitor is one of many peptides that could benefit from bioactive
cyclization, a strategy that is amenable to broad application in pharmaceutical
design.