Discovery of cyclic peptide inhibitors of a serine protease

Cyclic peptides possess unique properties, such as a small molecular weight, high binding affinity and specificity, and ease of synthesis and modification, that make them ideal for the development of novel therapeutic molecules. Indeed, in the last decade, an increasing number of peptide-based drugs have been approved by the US Food and Drug Administration. To accelerate the discovery of cyclic peptide-based binders, we recently developed a combinatorial technology. In this project, we assessed the efficacy of our novel platform to rapidly isolate cyclic peptide inhibitors of a serine protease. The identity of selected peptides was initially revealed by DNA sequencing and the binding affinities readily determined using recombinantly expressed peptide fusions. Best cyclic peptide inhibitors were further chemically synthesized via solid phase peptide synthesis. Peptide cyclisation was achieved through cysteine oxidation using a buffer containing DMSO. Next, cyclic peptides were purified by RP HPLC and their molecular weights assessed by mass spectrometry. Finally, the inhibitory potency of isolated peptides was determined using a colorimetric assay. Best isolated cyclic peptide inhibitor showed picomolar inhibitory activity and affinity.