Kit-Like 18F-Labeling of Proteins: Synthesis of 4-(Di-tert-butyl[18F]fluorosilyl)benzenethiol (Si[18F]FA-SH) Labeled Rat Serum Albumin for Blood Pool Imaging with PET

Abstract

Radiosyntheses of ¹⁸F-radiopharmaceuticals for positron emission tomography (PET) normally require an extraordinarily high effort of technical equipment and specially trained personnel. We recently reported a novel method for the introduction of fluorine-18 into peptides for PET-imaging based on silicon-¹⁸F-chemistry (SiFA technique). We herewith introduce the first SiFA-based Kit-like radio-fluorination of a protein (rat serum albumin, RSA) and demonstrate its usefulness for in vivo imaging with μPET in normal rats as well as in a rat heterotropic transplanted heart model. As a labeling agent, we prepared 4-(di-tert-butyl[¹⁸F]fluorosilyl)benzenethiol (Si[¹⁸F]FA-SH) by simple isotopic exchange in 40−60% radiochemical yield (RCY) and coupled it directly to a Sulfo-SMCC derivatized RSA in an overall RCY of 12% within 20−30 min. The technically simple labeling procedure does not require any elaborated purification procedures and is a straightforward example of a successful application of Si−¹⁸F chemistry for in vivo imaging with PET.