Direct site-specific radiolabeling of an Affibody protein with 4-[18F]fluorobenzaldehyde via oxime chemistry.
ABSTRACT In this study, we introduce a methodology for preparing 18F-labeled Affibody protein, specifically 18F-Anti-HER2 dimeric Affibody (14 kDa), for in vivo imaging of HER2neu with positron emission tomography (PET).
We have used 4-[18F]fluorobenzaldehyde as a synthon to prepare 18F-Anti-HER2 Affibody. Aminooxy-functionalized Affibody (Anti-HER2-ONH2) was incubated with 4-[18F]fluorobenzaldehyde in ammonium acetate buffer at pH 4 in the presence of methanol at 70 degrees C for 15 min. The resulting 18F-labeled Affibody molecule was evaluated as a PET probe in xenograft models expressing HER2.
We have successfully prepared 18F-Anti-HER2 dimeric Affibody (14 kDa), N-(4-[18F]fluorobenzylidine)oxime-Anti-HER2 Affibody, [18F]FBO-Anti-HER2, in 26-30% radiochemical yields (decay corrected). High-contrast small-animal PET images with relatively moderate tumor uptake (1.79 +/- 0.40% ID/g) were observed for the 18F-Anti-HER2 Affibody.
Site-specific 18F-labeled Affibody against HER2 has been synthesized via chemoselective oxime formation between an aminooxy-functionalized Affibody and 18F-fluorobenzaldehyde. The results have implications for radiolabeling of other affibodies and macromolecules and should also be important for advancing Affibody imaging with PET.
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ABSTRACT: A rapid, single step, aqueous 18F-labeling method that proceeds under mild conditions to provide radiotracers in high radiochemical yield and at high specific activity represents a long-standing challenge. Arylboronates capture aqueous 18F-fluoride ion in buffered pH 2–3 at moderate temperature to provide a highly polar 18F-ArBF3− anion. Similarly, 19F-18F isotope exchange on a 19F-ArBF3− should create an 18F-ArBF3−. We hypothesized that this reaction would proceed in volumes that would be amenable to the high levels of 18F-activity used in clinical hospitals. In order to measure both radiochemical and chemical yields, along with specific activity, we linked an alkyne-19F-ArBF3− to rhodamine azide by standard click chemistry to afford a precursor Rh-19F-ArBF3−. This precursor was aliquoted in portions of 50 nmol and lyophilized for on-demand use. Using robotic manipulators in a hot cell, we combined >29.6 GBq (800 mCi) and 50 nmol of the Rh-19F-ArBF3− in aqueous dimethylformamide at buffered pH 2–3. Following mild heating (40 °C) for 10-15 min, the reaction was quenched and analyzed. We observed radiochemical yields of 50% and specific activities of nearly 555 GBq/µmol (15 Ci/µmol). Similar radiochemical yields and slightly lower specific activities were also obtained with ~400 mCi (n = 2). With radiochemical yields in the hundreds of millicuries and specific activities that are 3–10-fold higher than most radiotracers, this method is very attractive method for preparing clinically useful radiotracers. Moreover, the ability to produce tracers at extraordinarily high specific activities expands the distribution time window from production labs to distant positron emission tomography scanners. Copyright © 2012 John Wiley & Sons, Ltd.Journal of Labelled Compounds 12/2012; 55(14). DOI:10.1002/jlcr.2990
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ABSTRACT: Affibody molecules are small scaffold-based affinity proteins with promising properties as probes for radionuclide-based molecular imaging. However, a high reabsorption of radiolabeled Affibody molecules in kidneys is an issue. We have shown that the use of 125I-3-iodo-((4-hydroxyphenyl)ethyl)maleimide (IHPEM) for site-specific labeling of cysteine-containing Affibody molecules provides high tumor uptake but low radioactivity retention in kidneys. We hypothesized that the use of 4-iodophenethylmaleimide (IPEM) would further reduce renal retention of radioactivity because of higher lipophilicity of radiometabolites. An anti-human epidermal growth factor receptor type 2 (HER2) Affibody molecule (ZHER2:2395) was labeled using 125I-IPEM with an overall yield of 45±3 %. 125I-IPEM-ZHER2:2395 bound specifically to HER2-expressing human ovarian carcinoma cells (SKOV-3 cell line). In NMRI mice, the renal uptake of 125I-IPEM-ZHER2:2395 (24±2 and 5.7±0.3 % IA g−1at 1 and 4 h after injection, respectively) was significantly lower than uptake of 125I-IHPEM-ZHER2:2395 (50±8 and 12±2 % IA g−1at 1 and 4 h after injection, respectively). In conclusion, the use of a more lipophilic linker for the radioiodination of Affibody molecules reduces renal radioactivity.ChemistryOpen 04/2015; 9999. DOI:10.1002/open.201402097 · 2.94 Impact Factor