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Quantitative Imaging of Liver Fibrosis and Fibrogenesis

Final Report Summary - LIVERFIBROSISIMAGING (Quantitative Imaging of Liver Fibrosis and Fibrogenesis)

The progression of liver fibrosis towards cirrhosis and its complications of liver decompensation and primary liver cancer development has emerged as the most relevant “hard endpoint” for patients with chronic liver diseases. Currently, there are no proven therapies that either prevent fibrosis progression or induce its reversal. One major reason for the slow development of antifibrotic therapies is the lack of sensitive and exact tools to quantify liver fibrosis and especially its progression (fibrogenesis).
This project aimed at the development of such tools by focusing on the design, synthesis and preclinical validation of imaging constructs that target and thus quantify either collagen, the major protein class of scar tissue (fibrosis), or cells that drive fibrosis progression (fibrogenesis).
Four different target structures were identified for the development of these imaging constructs. For fibrogenesis, the αvβ6-integrin is uniquely expressed on fibrogenic biliary cells (activated cholangiocytes), which are a major driving force of the fibrosis progression. Another target, the PDGF-β receptor, is unique to activated hepatic stellate cells and myofibroblasts, the major extracellular matrix producing cells in liver fibrosis. The third target structure of fibrogenesis is fibroblast activation protein (FAP), which is also expressed on activated activated hepatic stellate cells. Finally, triple helical collagen type I, the main extracellular matrix protein was chosen to quantify liver fibrosis.
To all of these targets a broad range of peptides and small molecules was synthesized to which a near infrared (NIR) dye and/or a radiochelator was attached, with numerous variations of the linkers in regard to chemical properties and spacing. Recently, several dual-labeled NIR-radioimaging agents were produced that permit rapid translation into the clinic after preclinical evaluation by NIR (and PET) -imaging. Here the NIR dye allows for high throughput in vitro and in vivo assessment of binding sensitivities specificities to the target molecule, while the isotope loaded radiochelator permits PET imaging potentially also in patients. Enrichment of the imaging agents in the liver was correlated to the degree of fibrosis and liver parameters of fibrogenesis in several complementary mouse models of liver fibrosis. More than $0 imaging constructs were synthesized and optimized. Three lead molecules showed good to excellent enrichment in fibrotic livers and signal to noise ratios, including a peptidomimetic, and especially cyclic peptides and small molecules. These are currently further investigated in vivo. Their development towards clinical tools is planned in a proof-of-concept follow up project.