title: Non-Invasive Imaging of Amyloid Deposits in a Mouse Model of AGel Using99mTc-Modified Nanobodies and SPECT/CT.
abstract: Gelsolin amyloidosis (AGel), also known as familial amyloidosis, Finnish type (FAF), is an autosomal, dominant, incurable disease caused by a point mutation (G654A/T) in the gelsolin (GSN) gene. The mutation results in loss of a Ca2+-binding site in the second gelsolin domain. Subsequent incorrect folding exposes a cryptic furin cleavage site, leading to the formation of a 68-kDa C-terminal cleavage product (C68) in the trans-Golgi network. This C68 fragment is cleaved by membrane type 1-matrix metalloproteinase (MT1-MMP) during secretion into the extracellular environment, releasing 8- and 5-kDa amyloidogenic peptides. These peptides aggregate and cause disease-associated symptoms. We set out to investigate whether AGel-specific nanobodies could be used to monitor amyloidogenic gelsolin buildup.
  
  
  
  Three nanobodies (FAF Nb1-3) raised against the 8-kDa fragment were screened as AGel amyloid imaging agents in WT and AGel mice using99mTc-based single-photon emission computed tomography (SPECT)/X-ray tomography (CT), biodistribution analysis, and immunofluorescence (IF). The quantitative characteristics were analyzed in a follow-up study with a Nb11-expressing mouse model.
  
  
  
  All three nanobodies possess the characteristics desired for a99mTc-based SPECT/CT imaging agent, high specificity and a low background signal. FAF Nb1 was identified as the most potent, based on its superior signal-to-noise ratio and signal specificity. As a proof of concept, we implemented99mTc-FAF Nb1 in a follow-up study of the Nb11-expressing AGel mouse model. Using biodistribution analysis and immunofluorescence, we demonstrated the validity of the data acquired via99mTc-FAF Nb1 SPECT/CT.
  
  
  
  These findings demonstrate the potential of this nanobody as a non-invasive tool to image amyloidogenic gelsolin deposition and assess the therapeutic capacity of AGel therapeutics currently under development. We propose that this approach can be extended to other amyloid diseases, thereby contributing to the development of specific therapies.
authors.affiliation: Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University, Albert Baertsoenkaai 3, B-9000, Ghent, Belgium.
authors.forename: Adriaan
authors.initials: A
authors.lastname: Verhelle
authors.affiliation: Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University, Albert Baertsoenkaai 3, B-9000, Ghent, Belgium.
authors.forename: Wouter
authors.initials: W
authors.lastname: Van Overbeke
authors.affiliation: In Vivo Cellular and Molecular Imaging Laboratory, Vrije Universiteit Brussel, Brussels, Belgium.
authors.forename: Cindy
authors.initials: C
authors.lastname: Peleman
authors.affiliation: Department of Medical and Forensic Pathology, Faculty of Medicine and Health Sciences, Ghent University, Ghent, Belgium.
authors.forename: Rebecca
authors.initials: R
authors.lastname: De Smet
authors.affiliation: Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University, Albert Baertsoenkaai 3, B-9000, Ghent, Belgium.
authors.forename: Olivier
authors.initials: O
authors.lastname: Zwaenepoel
authors.affiliation: In Vivo Cellular and Molecular Imaging Laboratory, Vrije Universiteit Brussel, Brussels, Belgium.
authors.forename: Tony
authors.initials: T
authors.lastname: Lahoutte
authors.affiliation: Department of Medical and Forensic Pathology, Faculty of Medicine and Health Sciences, Ghent University, Ghent, Belgium.
authors.forename: Jo
authors.initials: J
authors.lastname: Van Dorpe
authors.affiliation: In Vivo Cellular and Molecular Imaging Laboratory, Vrije Universiteit Brussel, Brussels, Belgium.
authors.forename: Nick
authors.initials: N
authors.lastname: Devoogdt
authors.affiliation: Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University, Albert Baertsoenkaai 3, B-9000, Ghent, Belgium. jan.gettemans@ugent.be.
authors.forename: Jan
authors.initials: J
authors.lastname: Gettemans
mesh_terms: D000682:Amyloid / Q000378:metabolism*; D028226:Amyloidosis, Familial / Q000000981:diagnostic imaging*; D000818:Animals; D000918:Antibody Specificity / Q000276:immunology; D001665:Binding Sites; D004195:Disease Models, Animal; D005455:Fluorescent Antibody Technique; D018260:Gelsolin / Q000737:chemistry; D008810:Mice, Inbred C57BL; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D059629:Signal-To-Noise Ratio; D061905:Single-Domain Antibodies / Q000737:chemistry*; D013194:Staining and Labeling; D013667:Technetium / Q000737:chemistry*; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon; D014057:Tomography, X-Ray Computed
chemical_list: D000682:Amyloid; D018260:Gelsolin; D061905:Single-Domain Antibodies; D013667:Technetium
keywords: AGel; Gelsolin; Nanobody; SPECT; VHH