Submit to Special Issue Submit Abstract to Special Issue Review for Pharmaceuticals Propose a Special Issue

Journal Menu

Journal Browser

Challenges in the Development of PET and SPECT Radiotracers: Innovative Ideas with Negative Outcomes

Print Special Issue Flyer
Special Issue Editors
Special Issue Information
Keywords
Benefits of Publishing in a Special Issue
Published Papers

A special issue of Pharmaceuticals (ISSN 1424-8247). This special issue belongs to the section "Radiopharmaceutical Sciences".

Deadline for manuscript submissions: 27 February 2026 | Viewed by 7793

Share This Special Issue

Special Issue Editors

Dr. Magali Toussaint

E-Mail Website
Guest Editor

Department of Neuroradiopharmaceuticals, Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden-Rossendorf, Research Site, Leipzig, Germany
Interests: brain tumours; PET/MRI; small animal imaging; radiotracer development

Dr. Barbara Wenzel

E-Mail Website
Guest Editor

Department of Neuroradiopharmaceuticals, Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden-Rossendorf, Research Site, Leipzig, Germany
Interests: radiotracer development; brain PET imaging; radiochemistry; Fluorine-18; HPLC

Special Issue Information

Dear Colleagues,

We are pleased to announce a Special Issue dedicated to the challenges and innovative efforts in the development of PET and SPECT radiotracers. This collection aims to highlight the complexities and hurdles in this field and the importance of "unsuccessful" endeavors for the advancement of radiopharmaceutical research.

With this Special Issue, we will provide a space to present substantial research with negative results in the field of radiotracer development and seek to emphasize innovative ideas that, despite their potential, have resulted in supposedly unpublishable outcomes. We believe that knowing what fails is as important as knowing what succeeds to support a comprehensive understanding, encourage methodological improvements and finally strengthen the scientific community.

Radiotracer development for PET and SPECT imaging involves numerous challenges in medicinal chemistry, radiolabeling, purification, stability, target selectivity, and in vivo pharmacokinetics. These obstacles can lead to unexpected negative results, which are often underreported but crucial for scientific progress and innovation.

Publishing such results is essential for advancing our collective knowledge and guiding future research. Moreover, it prevents duplications of efforts and contributes to a more reliable scientific literature. We therefore look forward to receiving your contributions in the fields of medicinal chemistry, radiochemistry, and in vitro and/or in vivo preclinical evaluation of newly developed or known PET and SPECT radiopharmaceuticals.

This Special Issue is open to original research articles, brief reports, and reviews.

Dr. Magali Toussaint
Dr. Barbara Wenzel
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Pharmaceuticals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2900 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

radiotracer development
positron emission tomography (PET)
single-photon emission computed tomography (SPECT)
negative results
diagnostic radiotracers
therapeutic radiopharmaceuticals
radiolabeling
automated synthesis and GMP
pre-clinical studies
medicinal chemistry

Benefits of Publishing in a Special Issue

Ease of navigation: Grouping papers by topic helps scholars navigate broad scope journals more efficiently.
Greater discoverability: Special Issues support the reach and impact of scientific research. Articles in Special Issues are more discoverable and cited more frequently.
Expansion of research network: Special Issues facilitate connections among authors, fostering scientific collaborations.
External promotion: Articles in Special Issues are often promoted through the journal's social media, increasing their visibility.
Reprint: MDPI Books provides the opportunity to republish successful Special Issues in book format, both online and in print.

Further information on MDPI's Special Issue policies can be found here.

Published Papers (6 papers)

Download All Papers

Order results

Result details

Show export options Show export options

Select all

Export citation of selected articles as:

Research

16 pages, 8366 KB

Open AccessArticle

FAPI Tracer en Vogue: Evaluating [⁶⁸Ga]Ga-DATA^5m.SA.FAPi for Molecular Imaging of Pulmonary Fibrosis

by Victoria Weissenböck, Michaela Schlederer, Latifa Bakiri, Johanna Schaffenrath, Erwin F. Wagner, Frank Rösch, Marcus Hacker, Lukas Kenner and Cécile Philippe

Pharmaceuticals 2026, 19(1), 34; https://doi.org/10.3390/ph19010034 - 23 Dec 2025

Viewed by 488

Abstract

Background/Objectives: Radiolabeled fibroblast activation protein inhibitors (FAPIs) are emerging as promising imaging agents assessing fibrotic diseases. This study evaluates [⁶⁸Ga]Ga-DATA^5m.SA.FAPi for imaging pulmonary fibrosis in two mouse models, bleomycin-induced (BLM) and a transgenic (fra-2^tg) model, both displaying characteristics of human pulmonary fibrotic diseases. Methods: In the BLM model, C57BL/6 mice were treated with bleomycin or isotonic sodium chloride (controls) for 4, 5, and 6 weeks, followed by [⁶⁸Ga]Ga-DATA^5m.SA.FAPi PET/CT scans. Fra-2^tg mice and wildtype (WT) littermates underwent at 7, 11, and 18/19 weeks of age a PET/CT scan. The selected timepoints correspond to early, middle, and late disease stages for each model. Imaging was complemented by ex vivo quantification, histological, and immunohistochemical (IHC) analyses. Results: In BLM mice, pulmonary [⁶⁸Ga]Ga-DATA^5m.SA.FAPi uptake showed a trend toward increase as early as 5 weeks of treatment compared with the controls, which was confirmed by ex vivo analysis (BLM: 3.31 ± 0.29%ID/g, n = 5; control: 1.61 ± 0.29%ID/g, n = 4; p = 0.0035). In fra-2^tg mice, no significant differences could be detected. IHC revealed elevated pulmonary FAP expression specifically at early (BLM) and mild (fra-2^tg) disease stages, whereas for BLM, tracer uptake was more pronounced at later stages. Conclusions: Our findings complement and extend observations from previous studies and support the potential of FAPI tracers as molecular imaging agents for pulmonary fibrosis. Full article

(This article belongs to the Special Issue Challenges in the Development of PET and SPECT Radiotracers: Innovative Ideas with Negative Outcomes)

► Show Figures

Graphical abstract

18 pages, 2608 KB

Open AccessArticle

Toward Brain Na_V1.8 Imaging with [¹¹C]Suzetrigine

by Ramya Tokala, Torben D. Pearson, Braeden A. Mair, Sarah Bricault, Rachel Wallace, Hsiao-Ying Wey, Jacob M. Hooker and So Jeong Lee

Pharmaceuticals 2025, 18(12), 1816; https://doi.org/10.3390/ph18121816 - 28 Nov 2025

Viewed by 1091

Abstract

Background/Objective: Acute and chronic pain affect millions of individuals, yet there are currently no molecular imaging tools to directly assess pain-related mechanisms in the central nervous system (CNS). The voltage-gated sodium channel Na_V1.8 plays a pivotal role in neuropathic pain by increasing the excitability of nociceptive neurons following nerve injury or inflammation. In this work, we aimed to develop a novel positron emission tomography (PET) imaging probe for Na_V1.8 to facilitate noninvasive quantification of this target in the CNS and thereby advance our understanding of pain neurobiology. Methods: We selected the compound suzetrigine, a U.S. FDA-approved, highly selective non-opioid Na_V1.8 inhibitor, as the first candidate for a Na_V1.8-targeted PET tracer. The compound was first assessed using in silico docking and CNS multiparameter optimization (MPO) analysis to evaluate target binding and predicted brain penetrability. Radiolabeling was accomplished by O-methylation with [¹¹C]methyl iodide to yield [¹¹C]suzetrigine without structural modification. The tracer was then evaluated using in vitro binding assays, including autoradiography and saturation binding on rat brain tissues, to determine binding parameters (K_D, B_max), and using in vivo PET imaging in rats to assess brain uptake, time–activity curves (TACs), and tracer behavior under baseline and pretreatment conditions. Pretreatment was performed with unlabeled suzetrigine, the P-glycoprotein (P-gp) inhibitor verapamil, and the heterologous Na_V1.8 inhibitor A-803467. Results: In silico docking demonstrated favorable binding of suzetrigine to the Na_V1.8 active site, and the calculated CNS MPO score (>3.5) suggested adequate brain penetration. Radiochemical synthesis of [¹¹C]suzetrigine via O-methylation yielded a high decay-corrected radiochemical yield (19.2 ± 2.7%, n = 3), excellent purity (>98%, n = 3), and moderate molar activity (62.9 ± 51.8 MBq/nmol, n = 3). Autoradiography on rat brain tissue confirmed saturable and selective binding of [¹¹C]suzetrigine to Na_V1.8. Saturation binding assays revealed a B_max = 93 fmol/mg and a K_D = 0.1 nM, supporting the imageability of Na_V1.8 in the brain using this tracer. In vivo PET imaging in rats demonstrated rapid and sufficient brain uptake but revealed unexpected tracer behavior: signal intensity markedly increased following pretreatment with either unlabeled suzetrigine or the P-gp inhibitor verapamil, and showed a slight increase after pretreatment with the heterologous Na_V1.8 inhibitor A-803467. Detailed analysis of PET images, TACs, and normalized area-under-curve (AUC) values indicated that these atypical uptake patterns were primarily attributable to P-gp-mediated effects, although additional factors may also contribute. Conclusions: [¹¹C]Suzetrigine exhibits high affinity, good brain uptake, and selective target engagement in vitro, supporting its potential as a first-in-class Na_V1.8-PET tracer. However, in vivo performance is confounded by P-gp-mediated efflux and possibly other mechanisms that limit accurate quantification of Na_V1.8 in the living brain. These findings underscore the critical role of efflux transporters in CNS radiotracer development and highlight the need for design strategies that mitigate P-gp interaction when targeting ion channels in the brain. Future studies will include imaging under constant P-gp inhibition, arterial blood sampling for radiometabolite analysis and full kinetic modeling, and evaluation in non-human primates to assess translational feasibility. Full article

(This article belongs to the Special Issue Challenges in the Development of PET and SPECT Radiotracers: Innovative Ideas with Negative Outcomes)

► Show Figures

Graphical abstract

28 pages, 3652 KB

Open AccessArticle

Preclinical Evaluation of Stable Integrin α_vβ₃-Specific [¹⁹⁸Au]Gold Nanoparticles for Tumor Therapy

by Güllü Davarci, Carmen Wängler, Klaus Eberhardt, Margaret Tulessin, Christopher Geppert, Ralf Schirrmacher, Gert Fricker, Carolin Mogler, Marc Pretze and Björn Wängler

Pharmaceuticals 2025, 18(11), 1670; https://doi.org/10.3390/ph18111670 - 4 Nov 2025

Viewed by 937

Abstract

Objectives: This paper reports the preclinical evaluation of stable tumor-specific gold nanoparticles (AuNPs) activated by neutron irradiation as a therapeutic option for the treatment of cancers characterized by high tumor angiogenesis. Methods: A selection of promising AuNPs with high avidity to α_vβ₃-expressing glioma (U-87 MG) cells (IC₅₀ = 82–104 nM) were chosen with different surface loading of Arg-Gly-Asp (RGD) peptides as tumor targeting vectors for integrin α_vβ₃, a target which is overexpressed in tissues displaying high tumor angiogenesis. Three different [¹⁹⁸Au]AuNPs were evaluated applying three injection methods, intravenous (i.v.), intraperitoneal (i.p.), and intratumoral (i.t.), each in a group of six U-87 MG xenograft–bearing mice (54 female athymic nude mice in total). Their biodistribution and tumor accumulation was assessed by in vivo imaging within 1–7 days after injection and 7 days after injection by ex vivo measurement. Results: The developed [¹⁹⁸Au]AuNPs exhibited suboptimal biodistribution by i.v. application (accumulation pattern tail > liver > spleen, no significant tumor accumulation) and by i.p. application (accumulation pattern spleen >> liver > pancreas, slight tumor accumulation of <0.3 %ID/g). However, an acceptable biodistribution by i.t. application was observed (5.5 %ID/g in liver, 4.9 %ID/g in spleen, and 3.0 %ID/g in tumor). Conclusions: Despite the very promising in vitro results, the in vivo evaluation suggests that the [¹⁹⁸Au]AuNPs represent a platform for the development of restricted therapeutic strategies. Full article

(This article belongs to the Special Issue Challenges in the Development of PET and SPECT Radiotracers: Innovative Ideas with Negative Outcomes)

► Show Figures

Graphical abstract

16 pages, 1894 KB

Open AccessArticle

In Vitro Characterization of the Published Glypican-3-Targeting Peptide TJ12P2 Reveals a Lack of Specificity and Potency

by Eva-Maria Burger, Charlice Hill, Robert Wodtke, Kristof Zarschler, Markus Laube, Cornelius K. Donat, Sandra Hauser, Klaus Kopka, Jens Pietzsch and Sven Stadlbauer

Pharmaceuticals 2025, 18(11), 1656; https://doi.org/10.3390/ph18111656 - 1 Nov 2025

Viewed by 808

Abstract

Background/Objectives: The cell surface proteoglycan glypican-3 (GPC3) is reportedly overexpressed in hepatocellular carcinoma (HCC) tissues, but not in benign liver tissues, rendering this protein a potential target for radionuclide theranostic approaches. Peptides are generally a promising class of targeting molecules for the development of radioligands because they combine straightforward synthetic access with favorable pharmacokinetics. Among the published peptides with disclosed structures, one of the most promising radioligands is [¹⁸F]AlF-NOTA-TJ12P2, which has a reported comparably high binding affinity to GPC3 and a high hydrophilicity. In this study, we aimed to design novel GPC3-targeting radioligands based on the TJ12P2 peptidic scaffold. Methods: Peptides were synthesized on solid phase using an Fmoc protecting group strategy. For comparative investigations, the reference nanobody HN3 was expressed in E. coli, isolated and subsequently modified with NODA-GA or SulfoCy3. The binding of native peptides, scrambled variants and reference nanobodies to GPC3 was investigated by surface plasmon resonance (SPR) interaction analysis, and fluorescently labeled versions of peptides and nanobodies were used for fluorescence microscopy in HepG2 (GPC3+) or SK Hep1 (GPC3−) cells. The chelator-bearing peptides were radiolabeled with gallium-67 and their stability towards radiolysis and in human serum was investigated. The binding of radiolabeled peptides and nanobodies to HepG2 cells was assessed in real-time ligand binding experiments. Results: The synthesized native peptides did not exhibit binding towards GPC3 in SPR interaction analyses, and the observed response was comparable to that of the scrambled variants at equal concentrations. Additionally, no binding to or uptake of the fluorescent constructs into cells was observed with fluorescence microscopy regardless of cellular GPC3 expression level. In real-time radioligand binding experiments, very fast association and dissociation of the gallium-67 labeled peptides to GPC3 positive HepG2 cells was observed, suggesting either extremely fast binding kinetics or unspecific binding of the peptides. Conclusions: Taken together, these findings suggest that the peptide TJ12P2 lacks specific binding to GPC3 in vitro and might not serve as a basis for the development of radioligands targeting GPC3. Full article

(This article belongs to the Special Issue Challenges in the Development of PET and SPECT Radiotracers: Innovative Ideas with Negative Outcomes)

► Show Figures

Figure 1

25 pages, 4259 KB

Open AccessEditor’s ChoiceArticle

Towards Dual-Tracer SPECT for Prostate Cancer Imaging Using [^99mTc]Tc-PSMA-I&S and [¹¹¹In]In-RM2

by Carolina Giammei, Theresa Balber, Veronika Felber, Thomas Dillinger, Jens Cardinale, Marie R. Brandt, Anna Stingeder, Markus Mitterhauser, Gerda Egger and Thomas L. Mindt

Pharmaceuticals 2025, 18(7), 1002; https://doi.org/10.3390/ph18071002 - 3 Jul 2025

Viewed by 2223

Abstract

Background/Objectives: Radiolabeled biomolecules specifically targeting overexpressed structures on tumor cells hold great potential for prostate cancer (PCa) imaging and therapy. Due to heterogeneous target expression, single radiopharmaceuticals may not detect or treat all lesions, while simultaneously applying two or more radiotracers potentially improves staging, stratification, and therapy of cancer patients. This study explores a dual-tracer SPECT approach using [¹¹¹In]In-RM2 (targeting the gastrin-releasing peptide receptor, GRPR) and [^99mTc]Tc-PSMA-I&S (targeting the prostate-specific membrane antigen, PSMA) as a proof of concept. To mimic heterogeneous tumor lesions in the same individual, we aimed to establish a dual xenograft mouse model for preclinical evaluation. Methods: CHO-K1 cells underwent lentiviral transduction for human GRPR or human PSMA overexpression. Six-to-eight-week-old female immunodeficient mice (NOD SCID) were subsequently inoculated with transduced CHO-K1 cells in both flanks, enabling a dual xenograft with similar target density and growth of both xenografts. Respective dual-isotope imaging and γ-counting protocols were established. Target expression was analyzed ex vivo by Western blotting. Results: In vitro studies showed similar target-specific binding and internalization of [¹¹¹In]In-RM2 and [^99mTc]Tc-PSMA-I&S in transduced CHO-K1 cells compared to reference lines PC-3 and LNCaP. However, in vivo imaging showed negligible tumor uptake in xenografts of the transduced cell lines. Ex vivo analysis indicated a loss of the respective biomarkers in the xenografts. Conclusions: Although the technical feasibility of a dual-tracer SPECT imaging approach using ¹¹¹In and ^99mTc has been demonstrated, the potential of [^99mTc]Tc-PSMA-I&S and [¹¹¹In]In-RM2 in a dual-tracer cocktail to improve PCa diagnosis could not be verified. The animal model, and in particular the transduced cell lines developed exclusively for this project, proved to be unsuitable for this purpose. The in/ex vivo experiments indicated that results from an in vitro model may not necessarily be successfully transferred to an in vivo setting. To assess the potential of this dual-tracer concept to improve PCa diagnosis, optimized in vivo models are needed. Nevertheless, our strategies address key challenges in dual-tracer applications, aiming to optimize future SPECT imaging approaches. Full article

(This article belongs to the Special Issue Challenges in the Development of PET and SPECT Radiotracers: Innovative Ideas with Negative Outcomes)

► Show Figures

Graphical abstract

14 pages, 3879 KB

Open AccessArticle

PET Imaging Expedites Detection of Aberration in the Humanization of an Annexin A1 Targeting Antibody

by Hailey A. Houson, Brian D. Wright, Solana R. Fernandez, Tim Buss, Sharon L. White, Brittany Cederstrom, James M. Omweri, Jonathan E. McConathy, Jan E. Schnitzer and Suzanne E. Lapi

Pharmaceuticals 2025, 18(3), 295; https://doi.org/10.3390/ph18030295 - 21 Feb 2025

Viewed by 1222

Abstract

Objectives: Annexin-A1 is a 37 kDa phospholipid-binding protein which is concentrated in a truncated 34 kDa form (AnnA1) in caveolae on the tumor vascular endothelial cell surface with expression in many tumor types. PRISM developed the monoclonal mouse antibody mAnnA1 against AnnA1 for evaluation of AnnA1 as a potential target for imaging and therapy in oncology. mAnnA1 was humanized to make hAnnA1 for translation to clinical studies. Both PRISM-produced mAnnA1 and cGMP contractor-produced hAnnA1 were investigated using noninvasive PET/CT imaging, and dosimetry was evaluated to enable clinical translation of this strategy and to investigate in vivo behavior of hAnnA1. Methods: Antibodies mAnnA1 and hAnnA1 (PRISM “hAnnA1-P” or contractor generated “hAnnA1-C”) were conjugated with the chelator deferoxamine and evaluated for immunoreactivity with ELISA. Conjugated antibodies were radiolabeled with zirconium-89. Naïve mice, rats, and non-human primates (NHP) were injected with [⁸⁹Zr]mAnnA1 or [⁸⁹Zr]hAnnA1 and imaged with PET/CT up to 10 days post injection. After imaging, mice and rats were euthanized and organs were collected, weighed, and radioactivity was quantified using a gamma counter. Dosimetry in mice and NHPs were calculated using OLINDA. Results: [⁸⁹Zr]mAnnA1 showed similar biodistribution to other antibodies with slow clearance through the liver. Transition to [⁸⁹Zr]hAnnA1-C during the dosimetry studies revealed substantial uptake in the spleen (130 ± 48% ID/g at day 5 post injection in female BALB/c), which was not observed with [⁸⁹Zr]mAnnA1 (5.6 ± 1.7% ID/g at day 7 PI). Further studies in multiple strains of mice showed variable elevated splenic uptake of [⁸⁹Zr]hAnnA1-C across mouse strains, with the highest uptake observed in female BALB/c mice (118.4 ± 23.1% ID/g) and the lowest uptake observed in male CD1 mice (34.7 ± 10.2% ID/g). Additionally, splenic uptake of hAnnA1-C was observed in Fischer rats (2.8 ± 0.6% ID/organ) and NHPs (1.6 ± 0.6% ID/organ), although at lower levels than what was observed in BALB/c mice (8.8 ± 1.8% ID/organ). Dosimetry results showed similar values between estimates based on mouse and NHP data, with the largest difference seen in the spleen (5.2 vs. 2.6 mSv/MBq in females respectively). Sequencing of hAnnA1-C revealed a frameshift mutation in the antibody sequence introduced during cGMP manufacture. Restoration of the antibody sequence by PRISM returned the antibody distribution into alignment with mAnnA1. Conclusions: An aberration introduced during cGMP production of hAnnA1-C resulted in increased splenic uptake and alteration of the biodistribution in mice. PET imaging enabled quantitative detection of the immunogenic behavior of hAnnA1, which led to detection of the sequence error. Restoration of the sequence resulted in an antibody which was non-immunogenic to mice. Full article

(This article belongs to the Special Issue Challenges in the Development of PET and SPECT Radiotracers: Innovative Ideas with Negative Outcomes)

► Show Figures

Journal Menu

Journal Browser

Challenges in the Development of PET and SPECT Radiotracers: Innovative Ideas with Negative Outcomes

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Benefits of Publishing in a Special Issue

Published Papers (6 papers)

Research

Further Information

Guidelines

MDPI Initiatives

Follow MDPI