RT Journal Article
SR Electronic
T1 Towards the Dual Click <sup>18</sup>F-labeling of Antibodies<strong/>
JF Journal of Nuclear Medicine
JO J Nucl Med
FD Society of Nuclear Medicine
SP 1144
OP 1144
VO 59
IS supplement 1
A1 Steen, Johanna
A1 Denk, Christoph
A1 Norregaard, Kamilla
A1 Jorgensen, Jesper
A1 Rossin, Raffaella
A1 Svatunek, Dennis
A1 Edem, Patricia
A1 Robillard, Marc
A1 Kjaer, Andreas
A1 Kristensen, Jesper
A1 Mikula, Hannes
A1 Herth, Matthias
YR 2018
UL http://jnm.snmjournals.org/content/59/supplement_1/1144.abstract
AB 1144Objectives: Monoclonal antibodies (mAbs) are promising targeting-vectors for cancer diagnosis using nuclear molecular imaging techniques e.g. positron emission tomography (PET) due to their high affinity and specificity. However, their slow pharmacokinetics requires the use of long-lived radioisotopes in order to image their target accumulation. This results in high absorbed radiation doses for patients and a low imaging contrast.1,2 A pretargeted imaging approach, in which the targeting step is separated from the imaging step, circumvents these limitations since it enables the use of a short-lived radioisotope. This is achievable by using bioorthogonal click chemistry.3,4 Herein, we describe a pretargeted tumor imaging approach based on the inverse electron-demand Diels-Alder [4+2] cycloaddition (IEDDA) between various 18F-labeled 1,2,4,5-tetrazines and a mAb modified with trans-cyclooctene (TCO) (Figure 1). The sensitivity of the tetrazine-scaffold towards the basic conditions required for direct 18F-fluorination encouraged the use of an indirect labeling strategy by which a small library of 18F-tetrazines could be accessible for pretargeted imaging using PET. Methods: [18F]Fluoride was produced via the (p,n)-reaction by bombardment of a [18O]H2O with a 11 MeV proton beam in a cyclotron. Analysis of 18F-fluorination reactions were performed by radio-HPLC and radio-TLC. Small animal PET/CT imaging was performed in naïve BALB/c mice for the preliminary biodistribution studies and in vivo stability assessments, and in nude BALB/c mice bearing tumor xenografts (LS174T) for the pretargeted tumor imaging experiments. Imaging was performed 1 h after tracer administration. Results: Tetrazine precursors bearing alkyne-moieties were synthesized and 18F-labeled with three different [18F]F-azide synthons via Cu-catalyzed azide-alkyne [3+2] cycloaddition (CuAAC) in non-decay corrected radiochemical yields between 2-22% for the CuAAC and 1-8% with regard to starting amount of [18F]F-. Promising candidates were selected based on biodistribution and stability for further evaluation in pretargeted experiments. For the pretargeted tumor imaging, TCO-functionalized CC49-mAbs targeting TAG-72 antigen were injected intravenously into tumor bearing mice 72 h prior to administration of high molar activity [18F]F-tetrazines. Preliminary results indicated a tumor uptake between 2-3% ID/g for the tetrazines evaluated until this date. Conclusions: By using the CuAAC as an indirect labeling approach a small library of 18F- labeled tetrazines was available. Evaluation in pretargeted experiments is still ongoing. Future work is to develop a group of second generation tetrazines with more favorable pharmacokinetic profiles. Acknowledgements: The authors greatly acknowledge the H2020 project Click-it for financial support and the technical staff at the Department of Clinical Physiology, Nuclear Medicine &amp; PET at Rigshospitalet, Denmark. References: 1. Rossin R. et al., Angew. Chem. Int. Ed. 2010; 49. 2. Keinänen O. et al., EJNMMI Res. 2017; 7:95. 3. Herth M. M. et al., Chem. Commun. 2013; 49. 4. Denk C. et al., Angew. Chem. Int. Ed. 2014; 53.