An Orally Active Bradykinin B<sub>1</sub> Receptor Antagonist Engineered as a Bifunctional Chimera of Sunflower Trypsin Inhibitor

An orally active and metabolically stable peptide TIBA was successfully engineered as a chimera by fusing an analgesic bradykinin receptor antagonist peptide and the trypsin inhibitory loop of sunflower trypsin inhibitor-1. As a fusion cyclic peptide, the metabolically labile analgesic peptide is protected from degradation by exopeptidases as well as the endopeptidases, and its serum half-life extended from <5 min to >6 h as a chimera. Moreover, the chimera TIBA was also found to be orally active in an animal pain model using a hot plate assay.