Potent Cyclic Peptide Inhibitors of FXIIa Discovered by mRNA Display with Genetic Code Reprogramming

The
contact system comprises a series of serine proteases that
mediate procoagulant and proinflammatory activities via the intrinsic pathway of coagulation and the kallikrein–kinin
system, respectively. Inhibition of Factor XIIa (FXIIa), an initiator
of the contact system, has been demonstrated to lead to thrombo-protection
and anti-inflammatory effects in animal models and serves as a potentially
safer target for the development of antithrombotics. Herein, we describe
the use of the Randomised Nonstandard Peptide Integrated Discovery
(RaPID) mRNA display technology to identify a series of potent and
selective cyclic peptide inhibitors of FXIIa. Cyclic peptides were
evaluated in vitro, and three lead compounds exhibited
significant prolongation of aPTT, a reduction in thrombin generation,
and an inhibition of bradykinin formation. We also describe our efforts
to identify the critical residues for binding FXIIa through alanine
scanning, analogue generation, and via in
silico methods to predict the binding mode of our lead cyclic
peptide inhibitors.