Optimization of a pretargeted strategy for the PET imaging of colorectal carcinoma via the modulation of radioligand pharmacokinetics Journal Article
| Authors: | Zeglis, B. M.; Brand, C.; Abdel-Atti, D.; Carnazza, K. E.; Cook, B. E.; Carlin, S.; Reiner, T.; Lewis, J. S. |
| Article Title: | Optimization of a pretargeted strategy for the PET imaging of colorectal carcinoma via the modulation of radioligand pharmacokinetics |
| Abstract: | Pretargeted PET imaging has emerged as an effective strategy for merging the exquisite selectivity of antibody-based targeting vectors with the rapid pharmacokinetics of radiolabeled small molecules. We previously reported the development of a strategy for the pretargeted PET imaging of colorectal cancer based on the bioorthogonal inverse electron demand Diels-Alder reaction between a tetrazine-bearing radioligand and a transcyclooctene-modified huA33 immunoconjugate. Although this method effectively delineated tumor tissue, its clinical potential was limited by the somewhat sluggish clearance of the radioligand through the gastrointestinal tract. Herein, we report the development and in vivo validation of a pretargeted strategy for the PET imaging of colorectal carcinoma with dramatically improved pharmacokinetics. Two novel tetrazine constructs, Tz-PEG7-NOTA and Tz-SarAr, were synthesized, characterized, and radiolabeled with 64Cu in high yield (>90%) and radiochemical purity (>99%). PET imaging and biodistribution experiments in healthy mice revealed that although 64Cu-Tz-PEG7-NOTA is cleared via both the gastrointestinal and urinary tracts, 64Cu-Tz-SarAr is rapidly excreted by the renal system alone. On this basis, 64Cu-Tz-SarAr was selected for further in vivo evaluation. To this end, mice bearing A33 antigen-expressing SW1222 human colorectal carcinoma xenografts were administered huA33-TCO, and the immunoconjugate was given 24 h to accumulate at the tumor and clear from the blood, after which 64Cu-Tz-SarAr was administered via intravenous tail vein injection. PET imaging and biodistribution experiments revealed specific uptake of the radiotracer in the tumor at early time points (5.6 ± 0.7 %ID/g at 1 h p.i.), high tumor-tobackground activity ratios, and rapid elimination of unclicked radioligand. Importantly, experiments with longer antibody accumulation intervals (48 and 120 h) yielded slight decreases in tumoral uptake but also concomitant increases in tumorto- blood activity concentration ratios. This new strategy offers dosimetric benefits as well, yielding a total effective dose of 0.041 rem/mCi, far below the doses produced by directly labeled 64Cu-NOTA-huA33 (0.133 rem/mCi) and 89Zr-DFO-huA33 (1.54 rem/mCi). Ultimately, this pretargeted PET imaging strategy boasts a dramatically improved pharmacokinetic profile compared to our first generation system and is capable of clearly delineating tumor tissue with high image contrast at only a fraction of the radiation dose created by directly labeled radioimmunoconjugates. © 2015 American Chemical Society. |
| Keywords: | positron emission tomography; colorectal cancer; pet; click chemistry; hua33; pretargeting; transcyclooctene; tetrazine; inverse electron demand diels-alder reaction |
| Journal Title: | Molecular Pharmaceutics |
| Volume: | 12 |
| Issue: | 10 |
| ISSN: | 1543-8384 |
| Publisher: | American Chemical Society |
| Date Published: | 2015-10-05 |
| Start Page: | 3575 |
| End Page: | 3587 |
| Language: | English |
| DOI: | 10.1021/acs.molpharmaceut.5b00294 |
| PROVIDER: | scopus |
| PMCID: | PMC4696756 |
| PUBMED: | 26287993 |
| DOI/URL: | |
| Notes: | Article -- Export Date: 2 November 2016 -- Source: Scopus |
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