title: ADAPT, a Novel Scaffold Protein-Based Probe for Radionuclide Imaging of Molecular Targets That Are Expressed in Disseminated Cancers.
abstract: Small engineered scaffold proteins have attracted attention as probes for radionuclide-based molecular imaging. One class of these imaging probes, termed ABD-Derived Affinity Proteins (ADAPT), has been created using the albumin-binding domain (ABD) of streptococcal protein G as a stable protein scaffold. In this study, we report the development of a clinical lead probe termed ADAPT6 that binds HER2, an oncoprotein overexpressed in many breast cancers that serves as a theranostic biomarker for several approved targeting therapies. Surface-exposed amino acids of ABD were randomized to create a combinatorial library enabling selection of high-affinity binders to various proteins. Furthermore, ABD was engineered to enable rapid purification, to eradicate its binding to albumin, and to enable rapid blood clearance. Incorporation of a unique cysteine allowed site-specific conjugation to a maleimido derivative of a DOTA chelator, enabling radionuclide labeling, ¹¹¹In for SPECT imaging and ⁶⁸Ga for PET imaging. Pharmacologic studies in mice demonstrated that the fully engineered molecule (111)In/⁶⁸Ga-DOTA-(HE)3-ADAPT6 was specifically bound and taken up by HER2-expressing tumors, with a high tumor-to-normal tissue ratio in xenograft models of human cancer. Unbound tracer underwent rapid renal clearance followed by high renal reabsorption. HER2-expressing xenografts were visualized by gamma-camera or PET at 1 hour after infusion. PET experiments demonstrated feasibility for discrimination of xenografts with high or low HER2 expression. Our results offer a preclinical proof of concept for the use of ADAPT probes for noninvasive in vivo imaging.
authors: Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
authors: Javad
authors: J
authors: Garousi
authors: Department of Protein Technology, KTH Royal Institute of Technology, Stockholm, Sweden.
authors: Sarah
authors: S
authors: Lindbo
authors: Department of Protein Technology, KTH Royal Institute of Technology, Stockholm, Sweden.
authors: Johan
authors: J
authors: Nilvebrant
authors: Department of Protein Technology, KTH Royal Institute of Technology, Stockholm, Sweden.
authors: Mikael
authors: M
authors: Åstrand
authors: Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
authors: Jos
authors: J
authors: Buijs
authors: Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
authors: Mattias
authors: M
authors: Sandström
authors: Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
authors: Hadis
authors: H
authors: Honarvar
authors: Preclinical PET Platform, Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden.
authors: Anna
authors: A
authors: Orlova
authors: Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden. vadimir.tolmachev@igp.uu.se.
authors: Vladimir
authors: V
authors: Tolmachev
authors: Department of Protein Technology, KTH Royal Institute of Technology, Stockholm, Sweden.
authors: Sophia
authors: S
authors: Hober
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D004195:Disease Models, Animal; D005260:Female; D015870:Gene Expression; D064593:Heterografts; D006801:Humans; D007553:Isotope Labeling; D051379:Mice; D057054:Molecular Imaging; D009362:Neoplasm Metastasis; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs / Q000235:genetics*; D011506:Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D011877:Radionuclide Imaging; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D002352:Carrier Proteins; D011506:Proteins; D018719:Erb-b2 Receptor Tyrosine Kinases