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Novel PET Radiopharmaceuticals: Molecular Probes for Personalized Imaging, 2nd Edition

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Dear Colleagues,

We are glad to share with you that Volume I of this Special Issue (https://www.mdpi.com/journal/ijms/special_issues/molecular_probes) was a success, so we reopened this Special Issue as “Novel PET Radiopharmaceuticals: Molecular Probes for Personalized Imaging 2.0”:

The emerging role of novel radiopharmaceuticals for PET imaging allows for the opportunity to investigate and depict many diseases, enlarge the fields of application of PET/CT and PET/MRI from oncology to infectious diseases and neuro-oncology, and to evaluate neurodegenerative diseases.

For this reason, the accurate knowledge of the synthesis, availability, and in vivo biodistribution of these novel molecular probes is of utmost importance for physicians and professionals.

Beyond scientific papers focused on specific clinical settings, an accurate collection of PET tracers in a single volume is still missing; it is necessary to cover all aspects of these tracers in order to assess their biochemical peculiarities, diagnostic overlapping, and efficacy.

For these reasons, a monography with several chapters on the peculiar aspects of these molecular probes is needed.

Suitable topics include, but are not limited to, the synthesis, kinetics, biodistribution of PET radiopharmaceuticals, and their current applications.

Dr. Ferdinando F. Calabria
Guest Editor

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Research

18 pages, 10425 KiB

Open AccessArticle

Evaluation of Chelator-to-Antibody Ratio on Development of ⁸⁹Zr-iPET Tracer for Imaging of PD-L1 Expression on Tumor

by Shih-Chuan Tsai, Shiou-Shiow Farn, Wei-Lin Lo, Fang-Yu Ou Yang, Yong-Ching Kang, Liang-Cheng Chen, Kuo-Ting Chen, Jiunn-Wang Liao, Jui-Yin Kung, Jenn-Tzong Chen and Feng-Yun J. Huang

Int. J. Mol. Sci. 2023, 24(24), 17132; https://doi.org/10.3390/ijms242417132 - 5 Dec 2023

Cited by 1 | Viewed by 1598

Abstract

⁸⁹Zr-iPET has been widely used for preclinical and clinical immunotherapy studies to predict patient stratification or evaluate therapeutic efficacy. In this study, we prepared and evaluated ⁸⁹Zr-DFO-anti-PD-L1-mAb tracers with varying chelator-to-antibody ratios (CARs), including ⁸⁹Zr-DFO-anti-PD-L1-mAb_3X (tracer_3X), ⁸⁹Zr-DFO-anti-PD-L1-mAb_10X (tracer_10X), and ⁸⁹Zr-DFO-anti-PD-L1-mAb_20X (tracer_20X). The DFO-anti-PD-L1-mAb conjugates with varying CARs were prepared using a random conjugation method and then subjected to quality control. The conjugates were radiolabeled with ⁸⁹Zr and evaluated in a PD-L1-expressing CT26 tumor-bearing mouse model. Next, iPET imaging, biodistribution, pharmacokinetics, and ex vivo pathological and immunohistochemical examinations were conducted. LC–MS analysis revealed that DFO-anti-PD-L1-mAb conjugates were prepared with CARs ranging from 0.4 to 2.0. Radiochemical purity for all tracer groups was >99% after purification. The specific activity levels of tracer_3X, tracer_10X, and tracer_20X were 2.2 ± 0.6, 8.2 ± 0.6, and 10.5 ± 1.6 μCi/μg, respectively. ⁸⁹Zr-iPET imaging showed evident tumor uptake in all tracer groups and reached the maximum uptake value at 24 h postinjection (p.i.). Biodistribution data at 168 h p.i. revealed that the tumor-to-liver, tumor-to-muscle, and tumor-to-blood uptake ratios for tracer_3X, tracer_10X, and tracer_20X were 0.46 ± 0.14, 0.58 ± 0.33, and 1.54 ± 0.51; 4.7 ± 1.3, 7.1 ± 3.9, and 14.7 ± 1.1; and 13.1 ± 5.8, 19.4 ± 13.8, and 41.3 ± 10.6, respectively. Significant differences were observed between tracer_3X and tracer_20X in the aforementioned uptake ratios at 168 h p.i. The mean residence time and elimination half-life for tracer_3X, tracer_10X, and tracer_20X were 25.4 ± 4.9, 24.2 ± 6.1, and 25.8 ± 3.3 h and 11.8 ± 0.5, 11.1 ± 0.7, and 11.7 ± 0.6 h, respectively. No statistical differences were found between-tracer in the aforementioned pharmacokinetic parameters. In conclusion, ⁸⁹Zr-DFO-anti-PD-L1-mAb tracers with a CAR of 1.4–2.0 may be better at imaging PD-L1 expression in tumors than are traditional low-CAR ⁸⁹Zr-iPET tracers. Full article

(This article belongs to the Special Issue Novel PET Radiopharmaceuticals: Molecular Probes for Personalized Imaging, 2nd Edition)

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22 pages, 2321 KiB

Open AccessArticle

Preparation of N_In-Methyl-6-[¹⁸F]fluoro- and 5-Hydroxy-7-[¹⁸F]fluorotryptophans as Candidate PET-Tracers for Pathway-Specific Visualization of Tryptophan Metabolism

by Niklas Kolks, Felix Neumaier, Bernd Neumaier and Boris D. Zlatopolskiy

Int. J. Mol. Sci. 2023, 24(20), 15251; https://doi.org/10.3390/ijms242015251 - 17 Oct 2023

Cited by 1 | Viewed by 1253

Abstract

Tryptophan (Trp) is an essential proteinogenic amino acid and metabolic precursor for several signaling molecules that has been implicated in many physiological and pathological processes. Since the two main branches of Trp metabolism—serotonin biosynthesis and kynurenine pathway—are differently affected by a variety of neurological and neoplastic diseases, selective visualization of these pathways is of high clinical relevance. However, while positron emission tomography (PET) with existing probes can be used for non-invasive assessment of total Trp metabolism, optimal imaging agents for pathway-specific PET imaging are still lacking. In this work, we describe the preparation of two ¹⁸F-labeled Trp derivatives, N_In-methyl-6-[¹⁸F]fluorotryptophan (N_In-Me-6-[¹⁸F]FTrp) and 5-hydroxy-7-[¹⁸F]fluorotryptophan (5-HO-7-[¹⁸F]FTrp). We also report feasible synthetic routes for the preparation of the hitherto unknown boronate radiolabeling precursors and non-radioactive reference compounds. Under optimized conditions, alcohol-enhanced Cu-mediated radiofluorination of the respective precursors afforded N_In-Me-6-[¹⁸F]FTrp and 5-HO-7-[¹⁸F]FTrp as application-ready solutions in radiochemical yields of 45 ± 7% and 29 ± 4%, respectively. As such, our work provides access to two promising candidate probes for pathway-specific visualization of Trp metabolism in amounts sufficient for their preclinical evaluation. Full article

(This article belongs to the Special Issue Novel PET Radiopharmaceuticals: Molecular Probes for Personalized Imaging, 2nd Edition)

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