A Modular Platform for the Rapid Site-Specific Radiolabeling of Proteins with ¹⁸F Exemplified by Quantitative Positron Emission Tomography of Human Epidermal Growth Factor Receptor 2

Abstract

Receptor-specific proteins produced by genetic engineering are attractive as PET imaging agents, but labeling with conventional (18)F-based prosthetic groups is problematic due to long synthesis times, poor radiochemical yields, and low specific activities. Therefore, we developed a modular platform for the rapid preparation of water-soluble prosthetic groups capable of efficiently introducing (18)F into proteins. The utility of this platform is demonstrated by the thiol-specific prosthetic group, [(18)F]FPEGMA, which was used to produce site-specifically (18)F-labeled protein ((18)F-trastuzumab-ThioFab) in 82 min with a total radiochemical yield of 13 +/- 3% and a specific activity of 2.2 +/- 0.2 Ci/micromol. (18)F-trastuzumab-ThioFab retained the biological activity of native protein and was successfully validated in vivo with microPET imaging of Her2 expression in a xenograft tumor-bearing murine model modulated by the Hsp90 inhibitor, 17-(allylamino)-17-demethoxygeldanamycin.

Synthesis and Anticancer Activity of Glucosylated Podophyllotoxin Derivatives Linked via 4β-Triazole Rings

“…Compounds 10 and 11 were prepared in 70% yield by treatment of triethylene glycol and hexaethylene glycol with sodium hydride and propargyl bromide as previous described [29,30]. Fisher glycosylation of D-glucose with propargyl alcohols 9-11 in the presence of H 2 SO 4 -silica as a catalyst [31] provided the corresponding glycosides 12-17 as α/β mixtures.…”

Tissue Distribution Studies of Protein Therapeutics Using Molecular Probes: Molecular Imaging

“…As a possible alternative to Tc-99m, Ga-68 (half-life, 68 min) is a PET isotope produced in a convenient generator from Ge-68 (half-life, 9 months) that combines good imaging properties and a simple non-covalent point-ofuse labeling strategy applied to peptide reagents such as somatostatin analogs (60) and Affibodies (61). Generatorproduced Ga-68 was presumed to be much easier and cheaper to work with in the radiopharmacy setting than the cyclotron-produced F-18 (half-life, 110 min), which typically requires relatively complex covalent radiochemistry for labeling proteins and peptides (62)(63)(64). However, recent breakthroughs in non-covalent labeling with F-18 fluoride through chelated AlF complexes (65,66) challenge this presumption, and the longer half-life, excellent imaging properties, and wide availability of F18 fluoride could be powerful advantages.…”

Emerging Role of ImmunoPET in Receptor Targeted Cancer Therapy

“…Another class of fully orthogonal methods utilizes copper-I catalyzed 1,3-dipolar cycloaddition (CuAAC) to couple alkyne or azide decorated peptides with 18 F-fluorinated azides or alkynes [35,36]. The CuAAC reaction proceeds smoothly under mild conditions and provides high yields of 18 F-labeled peptides and proteins especially in the presence of copper-I stabilizing co-catalysts such as tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA) and bathophenantrolinedisulfonate (BPDS) [37].…”

“…Several thiol reactive 18 F-prosthetic groups developed for peptides were tested to label proteins but the yields were generally low mostly due to the low solubility of the lipophilic prosthetic groups in aqueous media [23][24][25][26][52][53][54]. Maleimide bearing prosthetic groups containing polyethylene glycol 18 FPEGMA [37] or 18 FBOM [26] were designed to improve water solubility and overall conjugation yield. Notably Fab fragments with engineered cysteines THIOFABs were modified site-specifically with 18 FPEGMA in good yields and high specific activity [37].…”

“…Maleimide bearing prosthetic groups containing polyethylene glycol 18 FPEGMA [37] or 18 FBOM [26] were designed to improve water solubility and overall conjugation yield. Notably Fab fragments with engineered cysteines THIOFABs were modified site-specifically with 18 FPEGMA in good yields and high specific activity [37].…”