title: From Unorthodox to Established: The Current Status of (18)F-Trifluoroborate- and (18)F-SiFA-Based Radiopharmaceuticals in PET Nuclear Imaging.
abstract: Unorthodox (18)F-labeling strategies not employing the formation of a carbon-(18)F bond are seldom found in radiochemistry. Historically, the formation of a boron- or silicon-(18)F bond has been introduced very early on into the repertoire of labeling chemistries, but is without translation into any clinical radiotracer besides inorganic B[(18)F]F4(-) for brain tumor diagnosis. For many decades these labeling methodologies were forgotten and have just recently been revived by a handful of researchers thinking outside the box. When breaking with established paradigms such as the inability to obtain labeled compounds of high specific activity via isotopic exchange or performing radiofluorination in aqueous media, the research community often reacts skeptically. In 2005 and 2006, two novel labeling methodologies were introduced into radiochemistry for positron emission tomography (PET) tracer development: RBF3(-) labeling reported by Perrin et al. and the SiFA methodology by Schirrmacher, Jurkschat, and Waengler et al. which is based on isotopic exchange (IE). Both labeling methodologies have been complemented by other noncanonical strategies to introduce (18)F into biomolecules of diagnostic importance, thus profoundly enriching the landscape of (18)F radiolabeling. B- and Si-based labeling strategies finally revealed that IE is a viable alternative to established and traditional radiochemistry with the advantage of simplifying both the labeling effort as well as the necessary purification of the radiotracer. Hence IE will be the focus of this contribution over other noncanonical labeling methods. Peptides for tumor imaging especially lend themselves favorably toward one-step labeling via IE, but small molecules have been described as well, taking advantage of these new approaches, and have been used successfully for brain imaging. This Review gives an account of both radiochemistries centered on boron and silicon, describing the very beginnings of their basic research, the path that led to optimization of their chemistries, and the first encouraging preclinical results paving the way to their clinical use. This side by side approach will give the reader the opportunity to follow the development of a new basic discovery into a clinically applicable radiotracer including all the hurdles that have had to be overcome.
authors.affiliation: Division of Oncological Imaging, Department of Oncology, University of Alberta , 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Canada.
authors.forename: Vadim
authors.initials: V
authors.lastname: Bernard-Gauthier
authors.affiliation: Division of Oncological Imaging, Department of Oncology, University of Alberta , 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Canada.
authors.forename: Justin J
authors.initials: JJ
authors.lastname: Bailey
authors.affiliation: Laboratory of Molecular Imaging and Nanomedicine, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health , 9000 Rockville Pike, Bethesda, Maryland 20892, United States.
authors.forename: Zhibo
authors.initials: Z
authors.lastname: Liu
authors.forename: Björn
authors.initials: B
authors.lastname: Wängler
authors.forename: Carmen
authors.initials: C
authors.lastname: Wängler
authors.affiliation: Department of Chemistry and Chemical Biology, Technical University of Dortmund , 44227 Dortmund, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Jurkschat
authors.affiliation: Department of Chemistry, University of British Columbia , 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada.
authors.forename: David M
authors.initials: DM
authors.lastname: Perrin
authors.affiliation: Division of Oncological Imaging, Department of Oncology, University of Alberta , 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Canada.
authors.forename: Ralf
authors.initials: R
authors.lastname: Schirrmacher
mesh_terms: D000818:Animals; D001881:Borates / Q000737:chemistry*; D005459:Fluorides / Q000737:chemistry; D005462:Fluorine Radioisotopes / Q000737:chemistry*; D006801:Humans; D010455:Peptides / Q000737:chemistry; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals / Q000737:chemistry*; D012825:Silicon / Q000737:chemistry*; D054852:Small Molecule Libraries / Q000737:chemistry
chemical_list: D001881:Borates; D005462:Fluorine Radioisotopes; D010455:Peptides; D019275:Radiopharmaceuticals; D054852:Small Molecule Libraries; D005459:Fluorides; D012825:Silicon