Preclinical Validation of the Heparin-Reactive Peptide p5+14 as a Molecular Imaging Agent for Visceral Amyloidosis
Amyloid is a complex pathologic matrix comprised principally of para-crystalline protein fibrils and heparan sulfate proteoglycans. Systemic amyloidoses are rare (~3500 new cases per year in the US); thus, routine diagnosis is often challenging, and effective treatment options are limited, resulting in high morbidity and mortality rates. Glycosaminoglycans contribute inextricably to the formation of amyloid fibrils and foster the deposition of amyloid in tissues. Those present in amyloid deposits are biochemically and electrochemically distinct from glycosaminoglycans found in the plasma membrane and extracellular matrices of healthy tissues due to the presence of a high degree of heparin-like hypersulfation. We have exploited this unique property and evaluated heparin-reactive peptides, such as p5+14. Herein we show efficacious detection of murine systemic amyloid in vivo by using molecular imaging, and the specific targeting of the peptide to major forms of human amyloid in tissue sections. Furthermore, we have demonstrated that the peptide also binds synthetic amyloid fibrils that lack glycosaminoglycans implying that the dense anionic motif present on heparin is mimicked by the amyloid protein fibril itself. These biochemical and functional data support the translation of radiolabeled peptide p5+14 for the clinical imaging of amyloid in patients; thus, providing a novel technique for prognostication, patient stratification, and monitoring response to therapy.