Preclinical characterisation of gallium-68 labeled ferrichrome siderophore stereoisomers for PET imaging applications

BACKGROUND

Siderophores are small iron-binding molecules produced by microorganisms to facilitate iron acquisition from the environment. Radiolabelled siderophores offer a promising solution for infection imaging, as they can specifically target the pathophysiological mechanisms of pathogens. Gallium-68 can replace the iron in siderophores, enabling molecular imaging with positron emission tomography (PET). Stereospecific interactions play a crucial role in the recognition of receptors, transporters, and iron utilisation. Furthermore, these interactions have an impact on the host environment, affecting pharmacokinetics and biodistribution. This study examines the influence of siderophore stereoisomerism on imaging properties, with a focus on ferrirubin (FR) and ferrirhodin (FRH), two cis-trans isomeric siderophores of the ferrichrome type.

RESULTS

Tested siderophores were labelled with gallium-68 with high radiochemical purity. The resulting complexes differed in their in vitro characteristics. [68Ga]Ga-FRH showed less hydrophilic properties and higher protein binding values than [68Ga]Ga-FR. The stability studies confirmed the high radiochemical stability of both [68Ga]Ga-siderophores in all examined media. Both siderophores were found to be taken up by S. aureus, K. pneumoniae and P. aeruginosa with similar efficacy. The biodistribution tested in normal mice showed rapid renal clearance with low blood pool retention and fast clearance from examined organs for [68Ga]Ga-FR, whereas [68Ga]Ga-FRH showed moderate retention in blood, resulting in slower pharmacokinetics. PET/CT imaging of mice injected with [68Ga]Ga-FR and [68Ga]Ga-FRH confirmed findings from ex vivo biodistribution studies. In a mouse model of S. aureus myositis, both radiolabeled siderophores showed radiotracer accumulation at the site of infection.

CONCLUSIONS

The 68Ga-complexes of stereoisomers ferrirubin and ferrirhodin revealed different pharmacokinetic profiles. In vitro uptake was not affected by isomerism. Both compounds had uptake with the same bacterial culture with similar efficacy. PET/CT imaging showed that the [68Ga]Ga-complexes accumulate at the site of S. aureus infection, highlighting the potential of [68Ga]Ga-FR as a promising tool for infection imaging. In contrast, retention of the radioactivity in the blood was observed for [68Ga]Ga-FRH. In conclusion, the stereoisomerism of potential radiotracers should be considered, as even minor structural differences can influence their pharmacokinetics and, consequently, the results of PET imaging.

The Development and Validation of Radiopharmaceuticals Targeting Bacterial Infection

The International Atomic Energy Agency organized a technical meeting at its headquarters in Vienna, Austria, in 2022 that included 17 experts representing 12 countries, whose research spanned the development and use of radiolabeled agents for imaging infection. The meeting focused largely on bacterial pathogens. The group discussed and evaluated the advantages and disadvantages of several radiopharmaceuticals, as well as the science driving various imaging approaches. The main objective was to understand why few infection-targeted radiotracers are used in clinical practice despite the urgent need to better characterize bacterial infections. This article summarizes the resulting consensus, at least among the included scientists and countries, on the current status of radiopharmaceutical development for infection imaging. Also included are opinions and recommendations regarding current research standards in this area. This and future International Atomic Energy Agency-sponsored collaborations will advance the goal of providing the medical community with innovative, practical tools for the specific image-based diagnosis of infection.

Radiotracer Development for Fungal-Specific Imaging: Past, Present, and Future

Invasive fungal infections have become a major challenge for public health, mainly due to the growing numbers of immunocompromised patients, with high morbidity and mortality. Currently, conventional imaging modalities such as computed tomography and magnetic resonance imaging contribute largely to the noninvasive diagnosis and treatment evaluation of those infections. These techniques, however, often fall short when a fast, noninvasive and specific diagnosis of fungal infection is necessary. Molecular imaging, especially using nuclear medicine-based techniques, aims to develop fungal-specific radiotracers that can be tested in preclinical models and eventually translated to human applications. In the last few decades, multiple radioligands have been developed and tested as potential fungal-specific tracers. These include radiolabeled peptides, antifungal drugs, siderophores, fungal-specific antibodies, and sugars. In this review, we provide an overview of the pros and cons of the available radiotracers. We also address the future prospects of fungal-specific imaging.

[68Ga]Ga-Ornibactin for Burkholderia cepacia complex Infection Imaging Using Positron Emission Tomography

Bacteria from the Burkholderia cepacia complex are generally considered to be non-pathogenic to the healthy population. However, some of these species may cause serious nosocomial infections in immunocompromised patients; as such, it is essential to diagnose these infections rapidly so that adequate treatment can be initiated. We report here the use of a radiolabeled siderophore, ornibactin (ORNB), for positron emission tomography imaging. We successfully radiolabeled ORNB with gallium-68 with high radiochemical purity and proved that the resulting complex has optimal in vitro characteristics. In mice, the complex did not show excessive accumulation in organs and was excreted in the urine. We demonstrated that the [⁶⁸Ga]Ga-ORNB complex accumulates at the site of Burkholderia multivorans infection, including pneumonia, in two animal infection models. These results suggest that [⁶⁸Ga]Ga-ORNB is a promising tool for the diagnosis, monitoring, and evaluation of the therapeutic response to B. cepacia complex infection.

Preparation, In Vitro Affinity, and In Vivo Biodistribution of Receptor-Specific 68Ga-Labeled Peptides Targeting Vascular Endothelial Growth Factor Receptors

As angiogenesis plays a key role in tumor growth and metastasis, the angiogenic process has attracted scientific interest as a target for diagnostic and therapeutic agents. Factors influencing angiogenesis include the vascular endothelial growth factor (VEGF) family and the two associated receptor types (VEGFR-1 and VEGFR-2). VEGFR-1/-2 detection and quantification in cancer lesions are essential for tumor process management. As a result of the advantageous pharmacokinetics and image contrast, peptides radiolabeled with PET emitters have become interesting tools for the visualization of VEGFR-1/-2-positive tumors. In this study, we prepared ⁶⁸Ga-labeled peptides containing 15 (peptide 1) and 23 (peptide 2) amino acids as new PET tracers for tumor angiogenic process imaging.

METHODS

The peptides were conjugated with NODAGA-tris(t-Bu ester) and subsequently radiolabeled with [⁶⁸Ga]Ga-chloride. The prepared [⁶⁸Ga]Ga-NODAGA-peptide 1 and [⁶⁸Ga]Ga-NODAGA-peptide 2 were tested for radiochemical purity and saline/plasma stability. Consequently, the binding affinity toward VEGFRs was assessed in vitro on human glioblastoma and kidney carcinoma cells. The found peptide receptor affinity was compared with the calculated values in the PROtein binDIng enerGY prediction (PRODIGY) server. Finally, the biodistribution study was performed on BALB/c female mice to reveal the basic pharmacokinetic behavior of radiopeptides.

RESULTS

The in vitro affinity testing of [⁶⁸Ga]Ga-NODAGA-peptides 1 and 2 showed retained receptor binding as characterized by equilibrium dissociation constant (K_D) values in the range of 0.5-1.2 μM and inhibitory concentration 50% (IC₅₀) values in the range of 3.0-5.6 μM. Better binding properties of peptide 2 to VEGFR-1/-2 were found in the PRODIGY server. The biodistribution study on mice showed remarkable accumulation of both peptides in the kidneys and urinary bladder with a short half-life after intravenous application. The in vitro plasma stability of [⁶⁸Ga]Ga-NODAGA-peptide 2 was superior to that of [⁶⁸Ga]Ga-NODAGA-peptide 1.

CONCLUSIONS

The obtained results demonstrated a high radiolabeling yield with no need for purification and preserved binding potency of ⁶⁸Ga-labeled peptides 1 and 2 toward VEGFRs in cancer cells. The peptide-receptor protein interaction assessed in protein-peptide docking determined the strongest interaction of peptide 2 with domain 2 of VEGFR-2 in addition to a more acceptable plasma stability (t_1/2 = 120 min) than that for peptide 1. We found both radiolabeled peptides very potent in their receptor binding, which makes them suitable imaging agents. The rapid transition of the radiopeptides into the urinary tract indicates suitable pharmacokinetic characteristics.

Modulating the pharmacokinetic profile of Actinium-225-labeled macropa-derived radioconjugates by dual targeting of PSMA and albumin

Rationale: Small ²²⁵Ac-labeled prostate-specific membrane antigen (PSMA)-targeted radioconjugates have been described for targeted alpha therapy of metastatic castration-resistant prostate cancer. Transient binding to serum albumin as a highly abundant, inherent transport protein represents a commonly applied strategy to modulate the tissue distribution profile of such low-molecular-weight radiotherapeutics and to enhance radioactivity uptake into tumor lesions with the ultimate objective of improved therapeutic outcome.

Methods: Two ligands mcp-M-alb-PSMA and mcp-D-alb-PSMA were synthesized by combining a macropa-derived chelator with either one or two lysine-ureido-glutamate-based PSMA- and 4-(p-iodophenyl)butyrate albumin-binding entities using multistep peptide-coupling chemistry. Both compounds were labeled with [²²⁵Ac]Ac³⁺ under mild conditions and their reversible binding to serum albumin was analyzed by an ultrafiltration assay as well as microscale thermophoresis measurements. Saturation binding studies and clonogenic survival assays using PSMA-expressing LNCaP cells were performed to evaluate PSMA-mediated cell binding and to assess the cytotoxic potency of the novel radioconjugates [²²⁵Ac]Ac-mcp-M-alb-PSMA and [²²⁵Ac]Ac-mcp-D-alb-PSMA, respectively. Biodistributions of both ²²⁵Ac-radioconjugates were investigated using LNCaP tumor-bearing SCID mice. Histological examinations of selected organs were performed to analyze the occurrence of necrosis using H&E staining, DNA damage via γH2AX staining and proliferation via Ki67 expression in the tissue samples.

Results: Enhanced binding to serum components in general and to human serum albumin in particular was revealed for [²²⁵Ac]Ac-mcp-M-alb-PSMA and [²²⁵Ac]Ac-mcp-D-alb-PSMA, respectively. Moreover, the novel derivatives are highly potent PSMA ligands as their K_D values in the nanomolar range (23.38 and 11.56 nM) are comparable to the reference radioconjugates [²²⁵Ac]Ac-mcp-M-PSMA (30.83 nM) and [²²⁵Ac]Ac-mcp-D-PSMA (10.20 nM) without albumin binders. The clonogenic activity of LNCaP cells after treatment with the ²²⁵Ac-labeled ligands was affected in a dose- and time-dependent manner, whereas the bivalent radioconjugate [²²⁵Ac]Ac-mcp-D-alb-PSMA has a stronger impact on the clonogenic cell survival than its monovalent counterpart [²²⁵Ac]Ac-mcp-M-alb-PSMA. Biodistribution studies performed in LNCaP tumor xenografts showed prolonged blood circulation times for both albumin-binding radioconjugates and a substantially increased tumor uptake (46.04 ± 7.77 %ID/g for [²²⁵Ac]Ac-mcp-M-alb-PSMA at 128 h p.i. and 153.48 ± 37.76 %ID/g at 168 h p.i. for [²²⁵Ac]Ac-mcp-D-alb-PSMA) with favorable tumor-to-background ratios. Consequently, a clear histological indication of DNA damage was discovered in the tumor tissues, whereas DNA double-strand break formation in kidney and liver sections was less pronounced.

Conclusion: The modification of the PSMA-based ²²⁵Ac-radioconjugates with one or two albumin-binding entities resulted in an improved radiopharmacological behavior including a greatly enhanced tumor accumulation combined with a rather low uptake in most non-targeted organs combined with a high excretion via the kidneys.

Desferrioxamine B-Mediated Pre-Clinical In Vivo Imaging of Infection by the Mold Fungus Aspergillus fumigatus

Fungal infections are a serious threat, especially for immunocompromised patients. Early and reliable diagnosis is crucial to treat such infections. The bacterially produced siderophore desferrioxamine B (DFO-B) is utilized by a variety of microorganisms for iron acquisition, while mammalian cells lack the uptake of DFO-B chelates. DFO-B is clinically approved for a variety of long-term chelation therapies. Recently, DFO-B-complexed gallium-68 ([68Ga]Ga-DFO-B) was shown to enable molecular imaging of bacterial infections by positron emission tomography (PET). Here, we demonstrate that [68Ga]Ga-DFO-B can also be used for the preclinical molecular imaging of pulmonary infection caused by the fungal pathogen Aspergillus fumigatus in a rat aspergillosis model. Moreover, by combining in vitro uptake studies and the chemical modification of DFO-B, we show that the cellular transport efficacy of ferrioxamine-type siderophores is impacted by the charge of the molecule and, consequently, the environmental pH. The chemical derivatization has potential implications for its diagnostic use and characterizes transport features of ferrioxamine-type siderophores.

Antifungal Siderophore Conjugates for Theranostic Applications in Invasive Pulmonary Aspergillosis Using Low-Molecular TAFC Scaffolds

Invasive pulmonary aspergillosis (IPA) is a life-threatening form of fungal infection, primarily in immunocompromised patients and associated with significant mortality. Diagnostic procedures are often invasive and/or time consuming and existing antifungals can be constrained by dose-limiting toxicity and drug interaction. In this study, we modified triacetylfusarinine C (TAFC), the main siderophore produced by the opportunistic pathogen Aspergillus fumigatus (A. fumigatus), with antifungal molecules to perform antifungal susceptibility tests and molecular imaging. A variation of small organic molecules (eflornithine, fludioxonil, thiomersal, fluoroorotic acid (FOA), cyanine 5 (Cy5) with antifungal activity were coupled to diacetylfusarinine C (DAFC), resulting in a "Trojan horse" to deliver antifungal compounds specifically into A. fumigatus hyphae by the major facilitator transporter MirB. Radioactive labeling with gallium-68 allowed us to perform in vitro characterization (distribution coefficient, stability, uptake assay) as well as biodistribution experiments and PET/CT imaging in an IPA rat infection model. Compounds chelated with stable gallium were used for antifungal susceptibility tests. [Ga]DAFC-fludioxonil, -FOA, and -Cy5 revealed a MirB-dependent active uptake with fungal growth inhibition at 16 µg/mL after 24 h. Visualization of an A. fumigatus infection in lungs of a rat was possible with gallium-68-labeled compounds using PET/CT. Heterogeneous biodistribution patterns revealed the immense influence of the antifungal moiety conjugated to DAFC. Overall, novel antifungal siderophore conjugates with promising fungal growth inhibition and the possibility to perform PET imaging combine both therapeutic and diagnostic potential in a theranostic compound for IPA caused by A. fumigatus.

Towards Targeted Alpha Therapy with Actinium-225: Chelators for Mild Condition Radiolabeling and Targeting PSMA-A Proof of Concept Study

Currently, targeted alpha therapy is one of the most investigated topics in radiopharmaceutical cancer management. Especially, the alpha emitter 225Ac has excellent nuclear properties and is gaining increasing popularity for the treatment of various tumor entities. We herein report on the synthesis of two universal 225Ac-chelators for mild condition radiolabeling and binding to conjugate molecules of pharmacological interest via the copper-mediated click chemistry. A convenient radiolabeling procedure was investigated as well as the complex stability proved for both chelators and two PSMA (prostate-specific membrane antigen)-targeting model radioconjugates. Studies regarding affinity and cell survival were performed on LNCaP cells followed by biodistribution studies, which were performed using LNCaP tumor-bearing mice. High efficiency radiolabeling for all conjugates was demonstrated. Cell binding studies revealed a fourfold lower cell affinity for the PSMA radioconjugate with one targeting motif compared to the radioconjugate owing two targeting motifs. Additionally, these differences were verified by in vitro cell survival evaluation and biodistribution studies, both showing a higher cell killing efficiency for the same dose, a higher tumor uptake (15%ID/g) and a rapid whole body clearance after 24 h. The synthesized chelators will overcome obstacles of lacking stability and worse labeling needs regarding 225Ac complexation using the DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid) chelator. Moreover, the universal functionalization expands the coverage of these chelators in combination with any sensitive bio(macro)molecule, thus improving treatment of any addressable tumor target.

Preclinical evaluation of anti-VEGFR2 monoclonal antibody ramucirumab labelled with zirconium-89 for tumour imaging

The key factors participating in angiogenesis include vascular endothelial growth factor (VEGF) and its receptors (VEGFRs), particularly VEGFR2. Angiogenesis suppression comprises the blocking of the VEGFR2 binding site by the monoclonal antibody ramucirumab (RAM). Our study focused on RAM radiolabelling with zirconium-89 along with subsequent in vitro and in vivo biological evaluation. RAM was conjugated with the bifunctional chelator p-SCN-Bn-deferoxamine (DFO) and subsequently radiolabelled with [⁸⁹ Zr]Zr-oxalate. The binding affinity of [⁸⁹ Zr]Zr-DFO-RAM to VEGFR2 was tested in vitro on prostate (PC-3) and ovary adenocarcinoma (SK-OV-3) cell lines. The positron emission tomography/computed tomography (PET/CT) imaging and ex vivo biodistribution experiments were performed in PC-3 and SK-OV-3 xenografted mice. The in vitro experiments revealed the preserved binding affinity of [⁸⁹ Zr]Zr-DFO-RAM to VEGFR2. The obtained ex vivo biodistribution data showed the uptake in PC-3 and SK-OV-3 tumours at about 8.7 ± 0.2 and 12.1 ± 1.6%ID/g, respectively. The tumour-to-muscle ratio for 1, 3 and 6 days post injection was 3.9, 5.5 and 5.12 for PC-3 and 6.0, 8.0 and 8.82 for SK-OV-3 tumours, respectively. PET/CT images showed high radioactivity accumulation in the tumours starting already on the first day after tracer administration. The obtained results proved the potency of [⁸⁹ Zr]Zr-DFO-RAM to target and image VEGFR2-positive tumours in vivo.

Head-To-Head Comparison of Biological Behavior of Biocompatible Polymers Poly(Ethylene Oxide), Poly(2-Ethyl-2-Oxazoline) and Poly[N-(2-Hydroxypropyl)Methacrylamide] as Coating Materials for Hydroxyapatite Nanoparticles in Animal Solid Tumor Model

Nanoparticles (NPs) represent an emerging platform for diagnosis and treatment of various diseases such as cancer, where they can take advantage of enhanced permeability and retention (EPR) effect for solid tumor accumulation. To improve their colloidal stability, prolong their blood circulation time and avoid premature entrapment into reticuloendothelial system, coating with hydrophilic biocompatible polymers is often essential. Most studies, however, employ just one type of coating polymer. The main purpose of this study is to head-to-head compare biological behavior of three leading polymers commonly used as “stealth” coating materials for biocompatibilization of NPs poly(ethylene oxide), poly(2-ethyl-2-oxazoline) and poly[N-(2-hydroxypropyl)methacrylamide] in an in vivo animal solid tumor model. We used radiolabeled biodegradable hydroxyapatite NPs as a model nanoparticle core within this study and we anchored the polymers to the NPs core by hydroxybisphosphonate end groups. The general suitability of polymers for coating of NPs intended for solid tumor accumulation is that poly(2-ethyl-2-oxazoline) and poly(ethylene oxide) gave comparably similar very good results, while poly[N-(2-hydroxypropyl)methacrylamide] was significantly worse. We did not observe a strong effect of molecular weight of the coating polymers on tumor and organ accumulation, blood circulation time, biodistribution and biodegradation of the NPs.

68Ga-labelled desferrioxamine-B for bacterial infection imaging

Purpose

With the increase of especially hospital-acquired infections, timely and accurate diagnosis of bacterial infections is crucial for effective patient care. Molecular imaging has the potential for specific and sensitive detection of infections. Siderophores are iron-specific chelators recognized by specific bacterial transporters, representing one of few fundamental differences between bacterial and mammalian cells. Replacing iron by gallium-68 without loss of bioactivity is possible allowing molecular imaging by positron emission tomography (PET). Here, we report on the preclinical evaluation of the clinically used siderophore, desferrioxamine-B (Desferal®, DFO-B), radiolabelled with ⁶⁸Ga for imaging of bacterial infections.

Methods

In vitro characterization of [⁶⁸Ga]Ga-DFO-B included partition coefficient, protein binding and stability determination. Specific uptake of [⁶⁸Ga]Ga-DFO-B was tested in vitro in different microbial cultures. In vivo biodistribution was studied in healthy mice and dosimetric estimation for human setting performed. PET/CT imaging was carried out in animal infection models, representing the most common pathogens.

Results

DFO-B was labelled with ⁶⁸Ga with high radiochemical purity and displayed hydrophilic properties, low protein binding and high stability in human serum and PBS. The high in vitro uptake of [⁶⁸Ga]Ga-DFO-B in selected strains of Pseudomonas aeruginosa, Staphylococcus aureus and Streptococcus agalactiae could be blocked with an excess of iron-DFO-B. [⁶⁸Ga]Ga-DFO-B showed rapid renal excretion and minimal retention in blood and other organs in healthy mice. Estimated human absorbed dose was 0.02 mSv/MBq. PET/CT images of animal infection models displayed high and specific accumulation of [⁶⁸Ga]Ga-DFO-B in both P. aeruginosa and S. aureus infections with excellent image contrast. No uptake was found in sterile inflammation, heat-inactivated P. aeruginosa or S. aureus and Escherichia coli lacking DFO-B transporters.

Conclusion

DFO-B can be easily radiolabelled with ⁶⁸Ga and displayed suitable in vitro characteristics and excellent pharmacokinetics in mice. The high and specific uptake of [⁶⁸Ga]Ga-DFO-B by P. aeruginosa and S. aureus was confirmed both in vitro and in vivo, proving the potential of [⁶⁸Ga]Ga-DFO-B for specific imaging of bacterial infections. As DFO-B is used in clinic for many years and the estimated radiation dose is lower than for other ⁶⁸Ga-labelled radiopharmaceuticals, we believe that [⁶⁸Ga]Ga-DFO-B has a great potential for clinical translation.

Electronic supplementary material

The online version of this article (10.1007/s00259-020-04948-y) contains supplementary material, which is available to authorized users.

Siderophore-Based Molecular Imaging of Fungal and Bacterial Infections-Current Status and Future Perspectives

Invasive fungal infections such as aspergillosis are life-threatening diseases mainly affecting immuno-compromised patients. The diagnosis of fungal infections is difficult, lacking specificity and sensitivity. This review covers findings on the preclinical use of siderophores for the molecular imaging of infections. Siderophores are low molecular mass chelators produced by bacteria and fungi to scavenge the essential metal iron. Replacing iron in siderophores by radionuclides such as gallium-68 allowed the targeted imaging of infection by positron emission tomography (PET). The proof of principle was the imaging of pulmonary Aspergillus fumigatus infection using [68Ga]Ga-triacetylfusarinine C. Recently, this approach was expanded to imaging of bacterial infections, i.e., with Pseudomonas aeruginosa. Moreover, the conjugation of siderophores and fluorescent dyes enabled the generation of hybrid imaging compounds, allowing the combination of PET and optical imaging. Nevertheless, the high potential of these imaging probes still awaits translation into clinics.

Modifying the Siderophore Triacetylfusarinine C for Molecular Imaging of Fungal Infection

Purpose

Aspergillus fumigatus produces the siderophore triacetylfusarinine C (TAFC) for iron acquisition which is essential for its virulence. Therefore, TAFC is a specific marker for invasive aspergillosis. We have shown previously that positron emission tomography (PET) imaging with [⁶⁸Ga]TAFC exhibited excellent targeting properties in an A. fumigatus rat infection model. In this study, we aimed to prepare TAFC analogs modifying fusarinine C (FSC) by acylation with different carbon chain lengths as well as with charged substituents and investigated the influence of introduced substituents on preservation of TAFC characteristics in vitro and in vivo.

Procedures

Fifteen TAFC derivatives were prepared and labeled with gallium-68. In vitro uptake assays were carried out in A. fumigatus under iron-replete as well as iron-depleted conditions and distribution coefficient was determined. Based on these assays, three compounds, [⁶⁸Ga]tripropanoyl(FSC) ([⁶⁸Ga]TPFC), [⁶⁸Ga]diacetylbutanoyl(FSC) ([⁶⁸Ga]DABuFC), and [⁶⁸Ga]trisuccinyl(FSC) ([⁶⁸Ga]FSC(suc)₃), with high, medium, and low in vitro uptake in fungal cultures, were selected for further evaluation. Stability and protein binding were evaluated and in vivo imaging performed in the A. fumigatus rat infection model.

Results

In vitro uptake studies using A. fumigatus revealed specific uptake of mono- and trisubstituted TAFC derivatives at RT. Lipophilicities as expressed by logD were 0.34 to − 3.80. The selected compounds displayed low protein binding and were stable in PBS and serum. Biodistribution and image contrast in PET/X-ray computed tomography of [⁶⁸Ga]TPFC and [⁶⁸Ga]DABuFC were comparable to [⁶⁸Ga]TAFC, whereas no uptake in the infected region was observed with [⁶⁸Ga]FSC(suc)₃.

Conclusions

Our studies show the possibility to modify TAFC without losing its properties and specific recognition by A. fumigatus. This opens also new ways for multimodality imaging or theranostics of fungal infection by introducing functionalities such as fluorescent dyes or antifungal moieties.

Hybrid Imaging Agents for Pretargeting Applications Based on Fusarinine C-Proof of Concept

Hybrid imaging combining the beneficial properties of radioactivity and optical imaging within one imaging probe has gained increasing interest in radiopharmaceutical research. In this study, we modified the macrocyclic gallium-68 chelator fusarinine C (FSC) by conjugating a fluorescent moiety and tetrazine (Tz) moieties. The resulting hybrid imaging agents were used for pretargeting applications utilizing click reactions with a trans-cyclooctene (TCO) tagged targeting vector for a proof of principle both in vitro and in vivo. Starting from FSC, the fluorophores Sulfocyanine-5, Sulfocyanine-7, or IRDye800CW were conjugated, followed by introduction of one or two Tz motifs, resulting in mono and dimeric Tz conjugates. Evaluation included fluorescence microscopy, binding studies, logD, protein binding, in vivo biodistribution, µPET (micro-positron emission tomography), and optical imaging (OI) studies. 68Ga-labeled conjugates showed suitable hydrophilicity, high stability, and specific targeting properties towards Rituximab-TCO pre-treated CD20 expressing Raji cells. Biodistribution studies showed fast clearance and low accumulation in non-targeted organs for both SulfoCy5- and IRDye800CW-conjugates. In an alendronate-TCO based bone targeting model the dimeric IRDye800CW-conjugate resulted in specific targeting using PET and OI, superior to the monomer. This proof of concept study showed that the preparation of FSC-Tz hybrid imaging agents for pretargeting applications is feasible, making such compounds suitable for hybrid imaging applications.

Hybrid Imaging of Aspergillus fumigatus Pulmonary Infection with Fluorescent, 68Ga-Labelled Siderophores

Aspergillus fumigatus (A. fumigatus) is a human pathogen causing severe invasive fungal infections, lacking sensitive and selective diagnostic tools. A. fumigatus secretes the siderophore desferri-triacetylfusarinine C (TAFC) to acquire iron from the human host. TAFC can be labelled with gallium-68 to perform positron emission tomography (PET/CT) scans. Here, we aimed to chemically modify TAFC with fluorescent dyes to combine PET/CT with optical imaging for hybrid imaging applications. Starting from ferric diacetylfusarinine C ([Fe]DAFC), different fluorescent dyes were conjugated (Cy5, SulfoCy5, SulfoCy7, IRDye 800CW, ATTO700) and labelled with gallium-68 for in vitro and in vivo characterisation. Uptake assays, growth assays and live-cell imaging as well as biodistribution, PET/CT and ex vivo optical imaging in an infection model was performed. Novel fluorophore conjugates were recognized by the fungal TAFC transporter MirB and could be utilized as iron source. Fluorescence microscopy showed partial accumulation into hyphae. µPET/CT scans of an invasive pulmonary aspergillosis (IPA) rat model revealed diverse biodistribution patterns for each fluorophore. [68Ga]Ga-DAFC-Cy5/SufloCy7 and -IRDye 800CW lead to a visualization of the infected region of the lung. Optical imaging of ex vivo lungs corresponded to PET images with high contrast of infection versus non-infected areas. Although fluorophores had a decisive influence on targeting and pharmacokinetics, these siderophores have potential as a hybrid imaging compounds combining PET/CT with optical imaging applications.

Comparison of 68Ga-labeled RGD mono- and multimers based on a clickable siderophore-based scaffold

Cyclic pentapeptides containing the amino acid sequence arginine-glycine-aspartic (RGD) have been widely applied to target α_vβ₃ integrin, which is upregulated in various tumors during tumor-induced angiogenesis. Multimeric cyclic RGD peptides have been reported to be advantageous over monomeric counterparts for angiogenesis imaging. Here, we prepared mono-, di-, and trimeric cyclic arginine-glycine-aspartic-D-phenylalanine-lysine (c (RGDfK)) derivatives by conjugation with the natural chelator fusarinine C (FSC) using click chemistry based on copper (I)-catalyzed azide-alkyne cycloaddition (CuAAC). The α_vβ₃ binding properties of ⁶⁸Ga-labeled mono-, di-, and trimeric c(RGDfK) peptides were evaluated in vitro as well as in vivo and compared with the references monomeric [⁶⁸Ga]GaNODAGA-c(RGDfK) and trimeric [⁶⁸Ga]GaFSC(suc-c(RGDfK))₃. All ⁶⁸Ga-labeled c(RGDfK) peptides displayed hydrophilicity (logD = -2.96 to -3.80), low protein binding and were stable in phosphate buffered-saline (PBS) and serum up to 2 h. In vitro internalization assays with human melanoma M21 (α_vβ₃-positive) and M21-L (α_vβ₃-negative) cell lines showed specific uptake of all derivatives and increased in the series: mono- < di- < trimeric peptide. The highest tumor uptake, tumor-to-background ratios, and image contrast were found for the dimeric [⁶⁸Ga]GaMAFC(c(RGDfK)aza)₂. In conclusion, we developed a novel strategy for direct, straight forward preparation of mono-, di-, and trimeric c(RGDfK) conjugates based on the FSC scaffold. Interestingly, the best α_vβ₃ imaging properties were found for the dimeric [⁶⁸Ga]GaMAFC(c(RGDfK)aza)₂.

Preclinical Evaluation of Radiolabeled Peptides for PET Imaging of Glioblastoma Multiforme

In this study, we have compared four ⁶⁸Ga-labeled peptides (three Arg-Gly-Asp (RGD) peptides and substance-P) with two ¹⁸F-tracers clinically approved for tumor imaging. We have studied in vitro and in vivo characteristics of selected radiolabeled tracers in a glioblastoma multiforme tumor model. The in vitro part of the study was mainly focused on the evaluation of radiotracers stability under various conditions. We have also determined in vivo stability of studied ⁶⁸Ga-radiotracers by analysis of murine urine collected at various time points after injection. The in vivo behavior of tested ⁶⁸Ga-peptides was evaluated through ex vivo biodistribution studies and PET/CT imaging. The obtained data were compared with clinically used ¹⁸F-tracers. ⁶⁸Ga-RGD peptides showed better imaging properties compared to ¹⁸F-tracers, i.e., higher tumor/background ratios and no accumulation in non-target organs except for excretory organs.

On-cartridge preparation and evaluation of 68Ga-, 89Zr- and 64Cu-precursors for cell radiolabelling

INTRODUCTION

Indium-111 when formulated as indium-111 oxine remains the gold standard for long term cell tracking, whereas radiometals for improved PET applications still have to be established. We here describe the on-cartridge formation of gallium-68, zirconium-89 and copper-64 complexes in small volumes suitable for cell labelling, including labelling of red blood cells (RBC) and white blood cells (WBC) and their biological evaluation in vivo.

METHODS

Small volumes (1-2 mL) of tracers (oxine, tropolone) were directly prepared on an anion exchange cartridge (Sep-Pak QMA). Cells were radiolabelled and the labelling efficiency and efflux were evaluated. The in vivo biodistribution of copper-64-labelled WBC using [⁶⁴Cu][Cu(oxinate)₂] and [⁶⁴Cu][Cu(tropolonate)₂] was monitored in an infection and inflammation animal model using BALB/c mice.

RESULTS

On-cartridge concentration of gallium-68, zirconium-89 and copper-64 enabled formation of oxine and tropolone tracers in small volumes with good yields (≥50%) and quality (extraction ≥90%). Prepared tracers radiolabelled the RBC comparable to indium-111 tracers and in vivo biodistribution of copper-64 labelled WBC showed clear accumulation of cells at the site of infection and inflammation.

CONCLUSIONS

This on-cartridge preparation method enables simple formation of various PET tracers for cell radiolabelling. Zirconium-89 and copper-64 tracers radiolabelled cells with sufficient stability. Due to their longer half-life this approach could be promising for routine applications where longer evaluation periods for cell tracking are needed.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

This novel approach for on-cartridge concentration and preparation of oxine and tropolone precursors with different positron emitters, in small volume and suitable pH, offers a versatile tool towards cell labelling for preclinical and clinical PET applications.

Early and Non-invasive Diagnosis of Aspergillosis Revealed by Infection Kinetics Monitored in a Rat Model

Background:Aspergillus fumigatus is a ubiquitous saprophytic airborne fungus responsible for more than one million deaths every year. The siderophores of A. fumigatus represent important virulence factors that contribute to the microbiome-metabolome dialog in a host. From a diagnostic point of view, the monitoring of Aspergillus secondary metabolites in urine of a host is promising due to the non-invasiveness, rapidity, sensitivity, and potential for standardization.

Methods: Using a model of experimental aspergillosis in immunocompromised Lewis rats, the fungal siderophores ferricrocin (FC) and triacetylfusarinine C (TAFC) were monitored in rat urine before and after lung inoculation with A. fumigatus conidia. Molecular biomarkers in high-dose (HD) and low-dose (LD) infection models were separated using high performance liquid chromatography (HPLC) and were detected by mass spectrometry (MS). In the current work, we corroborated the in vivo MS infection kinetics data with micro-positron emission tomography/computed tomography (μPET/CT) kinetics utilizing ⁶⁸Ga-labeled TAFC.

Results: In the HD model, the initial FC signal reflecting aspergillosis appeared as early as 4 h post-infection. The results from seven biological replicates showed exponentially increasing metabolite profiles over time. In A. fumigatus, TAFC was found to be a less produced biomarker that exhibited a kinetic profile identical to that of FC. The amount of siderophores contributed by the inoculating conidia was negligible and undetectable in the HD and LD models, respectively. In the μPET/CT scans, the first detectable signal in HD model was recorded 48 h post-infection. Regarding the MS assay, among nine biological replicates in the LD model, three animals did not develop any infection, while one animal experienced an exponential increase of metabolites and died on day 6 post-infection. All remaining animals had constant or random FC levels and exhibited few or no symptoms to the experiment termination. In the LD model, the TAFC concentration was not statistically significant, while the μPET/CT scan was positive as early as 6 days post-infection.

Conclusion: Siderophore detection in rat urine by MS represents an early and non-invasive tool for diagnosing aspergillosis caused by A. fumigatus. μPET/CT imaging further determines the infection location in vivo and allows the visualization of the infection progression over time.

Lasioglossins LLIII affect the morphogenesis of Candida albicans and reduces the duration of experimental vaginal candidiasis in mice

Lasioglossins are a group of peptides with identified antimicrobial activity. The inhibitory effects of two synthetic lasioglossin derivatives, LLIII and D-isomeric variant LLIII-D, on morphological changes in Candida albicans in vitro and the effect of local administration of LLIII during experimental murine candidiasis were investigated. C. albicans blastoconidia were grown in the presence of lasioglossin LLIII or LLIII-D at concentrations of 11.5 μM and 21 μM, respectively, for 1, 2 and 3 days and their viability determined by flow cytometry using eosin Y staining. Morphological changes were examined by light and fluorescent microscopy. The Candida-inhibitory effect of daily intravaginal administration of 0.7 or 1.4 μg of LLIII was assessed in mice with experimentally-induced vaginal candidiasis. LLIII and LLIII-D lasioglossins exhibited candidacidal activity in vitro (>76% after 24 hr and >84% after 48 hr of incubation). After 72 hr incubation of Candida with low concentration of lasioglossins, an increase in viability was detected, probably due to a Candida antimicrobial peptides evasion strategy. Furthermore, lasioglossins inhibited temperature-induced morphotype changes toward hyphae and pseudohyphae with sporadic occurrence of atypical cells with two or enlarged nuclei, suggesting interference with mitosis or cytokinesis. Local application of LLIII reduced the duration of experimental candidiasis with no evidence of adverse effects. Lasioglossin LLIII is a promising candidate for development as an antimicrobial drug for treating the vaginal candidiasis.

In Vitro and In Vivo Comparison of Selected Ga-68 and Zr-89 Labelled Siderophores

Purpose

Some [⁶⁸Ga]siderophores show promise in specific and sensitive imaging of infection. Here, we compare the in vitro and in vivo behaviour of selected Ga-68 and Zr-89 labelled siderophores.

Procedures

Radiolabelling was performed in HEPES or sodium acetate buffer systems. Radiochemical purity of labelled siderophores was determined using chromatography. Partition coefficients, in vitro stability and protein binding affinities were determined. Ex vivo biodistribution and animal imaging was studied in mice.

Results

Certain differences among studied siderophores were observed in labelling efficiency. Protein binding and stability tests showed highest stabilities and lowest protein binding affinities for Ga-68 and [⁸⁹Zr]triacetylfusarinine C (TAFC). All studied Ga-68 and [⁸⁹Zr]siderophores exhibited a similar biodistribution and pharmacokinetics in mice with the exception of [⁸⁹Zr]ferrioxamine E (FOXE).

Conclusions

Zr-89 and [⁶⁸Ga]siderophores showed analogous in vitro and in vivo behaviour. Tested [⁸⁹Zr]siderophores could be applied for longitudinal positron emission tomography (PET) studies of fungal infections and especially TAFC for the development of novel bioconjugates.

Electronic supplementary material

The online version of this article (doi:10.1007/s11307-015-0897-6) contains supplementary material, which is available to authorized users.

Comparison of Ga-68-Labeled Fusarinine C-Based Multivalent RGD Conjugates and [(68)Ga]NODAGA-RGD-In Vivo Imaging Studies in Human Xenograft Tumors

PURPOSE

Multimeric arginine-glycine-aspartic acid (RGD) peptides have advantages for imaging integrin αvβ3 expression. Here, we compared the in vitro and in vivo behavior of three different Ga-68-labeled multimeric Fusarinine C-RGD (FSC-RGD) conjugates, whereby RGD was coupled directly, via a succinic acid or PEG linker (FSC(RGDfE)3, FSC(succ-RGD)3, FSC(Mal-RGD)3). The positron emission tomography/X-ray computed tomography (PET/CT) imaging properties were further compared using [(68)Ga]FSC(succ-RGD)3 with the monomeric [(68)Ga]NODAGA-RGD in a murine tumor model.

PROCEDURE

FSC-RGD conjugates were labeled with Ga-68, and stability properties were studied. For in vitro characterization, the partition coefficient, integrin αvβ3 binding affinity, and cell uptake were determined. To characterize the in vivo properties, biodistribution studies and microPET/CT were carried out using mice bearing either human M21/M21-L melanoma or human U87MG glioblastoma tumor xenografts.

RESULTS

All FSC-RGD conjugates were quantitatively labeled with Ga-68 within 10 min at RT. The [(68)Ga]FSC-RGD conjugates exhibited high stability and hydrophilic character, with only minor differences between the different conjugates. In vitro and in vivo studies showed enhanced integrin αvβ3 binding affinity, receptor-selective tumor uptake, and rapid renal excretion resulting in good imaging properties.

CONCLUSIONS

The type of linker between FSC and RGD had no pronounced effect on targeting properties of [(68)Ga]FSC-RGD trimers. In particular, [(68)Ga]FSC(succ-RGD)3 exhibited improved properties compared to [(68)Ga]NODAGA-RGD, making it an alternative for imaging integrin αvβ3 expression.

Developing Targeted Hybrid Imaging Probes by Chelator Scaffolding

Positron emission tomography (PET) as well as optical imaging (OI) with peptide receptor targeting probes have proven their value for oncological applications but also show restrictions depending on the clinical field of interest. Therefore, the combination of both methods, particularly in a single molecule, could improve versatility in clinical routine. This proof of principle study aims to show that a chelator, Fusarinine C (FSC), can be utilized as scaffold for novel dimeric dual-modality imaging agents. Two targeting vectors (a minigastrin analogue (MG11) targeting cholecystokinin-2 receptor overexpression (CCK2R) or integrin α_Vβ₃ targeting cyclic pentapeptides (RGD)) and a near-infrared fluorophore (Sulfo-Cyanine7) were conjugated to FSC. The probes were efficiently labeled with gallium-68 and in vitro experiments including determination of logD, stability, protein binding, cell binding, internalization, and biodistribution studies as well as in vivo micro-PET/CT and optical imaging in U-87MG α_Vβ₃- and A431-CCK2R expressing tumor xenografted mice were carried out. Novel bioconjugates showed high receptor affinity and highly specific targeting properties at both receptors. Ex vivo biodistribution and micro-PET/CT imaging studies revealed specific tumor uptake accompanied by slow blood clearance and retention in nontargeted tissues (spleen, liver, and kidneys) leading to visualization of tumors at early (30 to 120 min p.i.). Excellent contrast in corresponding optical imaging studies was achieved especially at delayed time points (24 to 72 h p.i.). Our findings show the proof of principle of chelator scaffolding for hybrid imaging agents and demonstrate FSC being a suitable bifunctional chelator for this approach. Improvements to fine-tune pharmacokinetics are needed to translate this into a clinical setting.

Siderophores for molecular imaging applications

This review covers publications on siderophores applied for molecular imaging applications, mainly for radionuclide-based imaging. Siderophores are low molecular weight chelators produced by bacteria and fungi to scavenge essential iron. Research on these molecules has a continuing history over the past 50 years. Many biomedical applications have been developed, most prominently the use of the siderophore desferrioxamine (DFO) to tackle iron overload related diseases. Recent research described the upregulation of siderophore production and transport systems during infection. Replacing iron in siderophores by radionuclides, the most prominent Ga-68 for PET, opens approaches for targeted imaging of infection; the proof of principle has been reported for fungal infections using ⁶⁸Ga-triacetylfusarinine C (TAFC). Additionally, fluorescent siderophores and therapeutic conjugates have been described and may be translated to optical imaging and theranostic applications. Siderophores have also been applied as bifunctional chelators, initially DFO as chelator for Ga-67 and more recently for Zr-89 where it has become the standard chelator in Immuno-PET. Improved DFO constructs and bifunctional chelators based on cyclic siderophores have recently been developed for Ga-68 and Zr-89 and show promising properties for radiopharmaceutical development in PET. A huge potential from basic biomedical research on siderophores still awaits to be utilized for clinical and translational imaging.

18th European Symposium on Radiopharmacy and Radiopharmaceuticals

OP03 Selective extraction of medically-related radionuclides from proton-irradiated thorium targets

V. Radchenko, J.W. Engle, C. Roy, J. Griswold, M.F. Nortier, E.R. Birnbaum, M. Brugh, S. Mirzadeh, K. D. John, M.E. Fassbender

OP04 Comparison of [68Ga]FSC(succ-RGD)3 and [68Ga]NODAGA-RGD for PET imaging of αvβ3 integrin expression

Chuangyan Zhai, Gerben M. Franssen, Milos Petrik, Peter Laverman, Clemens Decristoforo

OP05 A new NPY-Y1R targeting peptide for breast cancer PET imaging

Ait-Mohand Samia, Dumulon-Perreault Véronique, Guérin Brigitte

OP06 The influence of multivalency on CCK 2 receptor targeting

D. Summer, A. Kroess, C. Rangger, H. Haas, P. Laverman, F. Gerben, E. von Guggenberg, C.Decristoforo

OP07 SPECT Imaging of αvβ3 Expression by [99mTc(N)PNP43]- Bifunctional Chimeric RGD Peptide not Cross-Reacting with αvβ5

Cristina Bolzati, Nicola Salvarese, Fiorenzo Refosco, Laura Meléndez-Alafort, Debora Carpanese, Antonio Rosato, Michele Saviano, Annarita Del Gatto, Daniela Comegna, Laura Zaccaro

OP09 New dienophiles for the inverse-electron-demand Diels-Alder reaction and for pretargeted PET imaging

Emilie Billaud, Muneer Ahamed, Frederik Cleeren, Elnaz Shahbazali, Tim Noël, Volker Hessel, Alfons Verbruggen and Guy Bormans

OP10 New complexing agent for Al18F-labelling of heat-sensitive biomolecules: Synthesis and preclinical evaluation of Al18F-RESCA1-HAS

Cleeren F, Lecina J, Koole M, Verbruggen A and Bormans G

OP11 A novel versatile precursor efficient for F-18 radiolabelling via click-chemistry

B. Lugatoa, S. Stucchia, E.A. Turollaa, L. Giulianoa, S.Toddea, P. Ferraboschib

OP12 A general applicable method to quantify unidentified UV impurities in radiopharmaceuticals

R.P. Klok, M.P.J. Mooijer, N.H. Hendrikse, A.D. Windhorst

OP13 Development of [¹⁸F]Fluoro-C-glycosides to radiolabel peptides

Collet C., Petry N., Chrétien F., Karcher G., Pellegrini-Moïse N., Lamandé-Langle S.

OP14 A Microfluidic Approach for the 68Ga-labeling of PSMAHBED-CC and NODAGA-RGD

Sarah Pfaff, Cecile Philippe, Markus Mitterhauser, Marcus Hacker, Wolfgang Wadsak

OP16 Surprising reactivity of astatine in the nucleophilic substitution of aryliodonium salts: application to the radiolabeling of antibodies

François Guérard, Yong-Sok Lee, Sébastien Gouard, Kwamena Baidoo, Cyrille Alliot, Michel Chérel, Martin W. Brechbiel, Jean-François Gestin

OP17 ⁶⁴Cu-NOTA-pertuzumab F(ab')₂ fragments, a second-generation probe for PET imaging of the response of HER2-positive breast cancer to trastuzumab (Herceptin)

Lam K, Chan C, Reilly RM

OP18 Development of radiohalogenated analogues of a avb6-specific peptide for high LET particle emitter targeted radionuclide therapy of cancer

Salomé Paillas, John Marshall, Jean-Pierre Pouget, Jane Sosabowski

OP19 Ligand Specific Efficiency (LSE) as a guide in tracer optimization

Emmanuelle Briard, Yves P. Auberson, John Reilly, Mark Healy, David Sykes

OP23 The radiosynthesis of an 18F-labeled triglyceride, developed to visualize and quantify brown adipose tissue activity

Andreas Paulus, Wouter van Marken Lichtenbelt,Felix Mottaghy, Matthias Bauwens

OP24 Influence of the fluorescent dye on the tumor targeting properties of dual-labeled HBED-CC based PSMA inhibitors

Baranski, Ann-Christin, Schäfer, Martin, Bauder-Wüst, Ulrike, Haberkorn, Uwe, Eder, Matthias, Kopka, Klaus

OP25 [18F]MEL050 as a melanin PET tracer : fully automated radiosynthesis and evaluation for the detection of pigmented melanoma in mice pulmonary metastases

Chaussard M, Hosten B, Vignal N, Tsoupko-Sitnikov V, Hernio N, Hontonnou F, Merlet P, Poyet JL, Sarda-Mantel L, Rizzo-Padoin N

OP26 Design and Preclinical Evaluation of Novel Radiofluorinated PSMA Targeting Ligands Based on PSMA-617

J. Cardinale, M. Schäfer, M. Benešová, U. Bauder-Wüst, O. Seibert, F. Giesel, U. Haberkorn, M. Eder, K. Kopka

OP27 A novel radiolabeled peptide for PET imaging of prostate cancer: 64Cu-DOTHA2-PEG-RM26

Mansour Nematallah, Paquette Michel, Ait-Mohand Samia, Dumulon-Perreault Véronique, Lecomte Roger, Guérin Brigitte

OP29 Biodistribution of [¹⁸F]Amylovis®, a new radiotracer PET imaging of β-amyloid plaques

Fernandez-Maza L, Rivera-Marrero S, Prats Capote A, Parrado-Gallego A, Fernandez-Gomez I, Balcerzyk M, Sablon-Carrazana M, Perera-Pintado A, Merceron-Martinez D, Acosta-Medina E, Rodriguez-Tanty C

OP30 Synthesis and preclinical evaluation of [11C]-BA1 PET tracer for the imaging of CSF-1R

Bala Attili, Muneer Ahamed, Guy Bormans

OP31 In vivo imaging of the MCHR1 in the ventricular system via [18F]FE@SNAP

C. Philippe, M. Zeilinger, T. Scherer, C. Fürnsinn, M. Dumanic, W. Wadsak, M. Hacker, M. Mitterhauser

OP32 Synthesis of the first carbon-11 labelled P2Y12 receptor antagonist for imaging the anti-inflammatory phenotype of activated microglia

B. Janssen, D.J. Vugts, G.T. Molenaar, U. Funke, P.S. Kruijer, F. Dollé, G. Bormans, A.A. Lammertsma, A.D. Windhorst

OP33 Radiosynthesis of a selective HDAC6 inhibitor [11C]KB631 and in vitro and ex vivo evaluation

Koen Vermeulen, Muneer Ahamed, Michael Schnekenburger, Mathy Froeyen, Dag Erlend Olberg, Marc Diederich, Guy Bormansa

OP34 Improving metabolic stability of fluorine-18 labelled verapamil analogues

Raaphorst RM, Luurtsema G, Lammertsma AA, Elsinga PH, Windhorst AD

OP36 Development of a novel PET tracer for the activin receptor-like kinase 5

Lonneke Rotteveel, Uta Funke, Peter ten Dijke, Harm Jan Bogaard, Adriaan A. Lammertsma, Albert D. Windhorst

OP37 SPECT imaging and biodistribution studies of 111In-EGF-Au-PEG nanoparticles in vivo

Lei Song, Sarah Able, Nadia Falzone, Veerle Kersemans, Katherine Vallis

OP38 Melanoma targeting with [99mTc(N)(PNP3)]-labeled NAPamide derivatives: preliminary pharmacological studies

Davide Carta, Nicola Salvarese, Wiebke Sihver, Feng Gao, Hans Jürgen Pietzsch, Barbara Biondi, Paolo Ruzza, Fiorenzo Refosco, Cristina Bolzati

OP39 [⁶⁸Ga]NODAGA-RGD: cGMP synthesis and data from a phase I clinical study

Roland Haubner, Armin Finkensted, Armin Stegmair, Christine Rangger, Clemens Decristoforo, Heinz Zoller, Irene J. Virgolin

OP44 Implementation of a GMP-grade radiopharmacy facility in Maastricht

Ivo Pooters, Maartje Lotz, Roel Wierts, Felix Mottaghy, Matthias Bauwens

OP45 Setting up a GMP production of a new radiopharmaceutical

Forsback, Sarita, Bergman Jörgen, Kivelä Riikka

OP48 In vitro and in vivo evaluation of 68-gallium labeled Fe3O4-DPD nanoparticles as potential PET/MRI imaging agents

M. Karageorgou, M. Radović, C. Tsoukalas, B. Antic, M. Gazouli, M. Paravatou-Petsotas, S. Xanthopouls, M. Calamiotou, D. Stamopoulos, S. Vranješ-Durić, P. Bouziotis

OP49 Fast PET imaging of inflammation using 68Ga-citrate with Fe-containing salts of hydroxy acids

A. S. Lunev, A. A. Larenkov, K.A. Petrosova, O. E. Klementyeva, G. E. Kodina

PP01 Installation and validation of 11C-methionine synthesis

Kvernenes, O.H., Adamsen, T.C.H.

PP02 Fully automated synthesis of 68Ga-labelled peptides using the IBA Synthera® and Synthera® Extension modules

René Martin, Sebastian Weidlich, Anna-Maria Zerges, Cristiana Gameiro, Neva Lazarova, Marco Müllera

PP03 GMP compliant production of ¹⁵O-labeled water using IBA 18 MeV proton cyclotron

Gert Luurtsema, Michèl de Vries, Michel Ghyoot, Gina van der Woude, Rolf Zijlma, Rudi Dierckx, Hendrikus H. Boersma, Philip H. Elsinga

PP04 In vitro Nuclear Imaging Potential of New Subphthalocyanine and Zinc Phthalocyanine

Fatma Yurt Lambrecht, Ozge Er, Mine Ince, Cıgır Biray Avci, Cumhur Gunduz, Fatma Aslihan Sarı

PP05 Synthesis, Photodynamic Therapy Efficacy and Nuclear Imaging Potential of Zinc Phthalocyanines

Kasim Ocakoglu, Ozge Er, Onur Alp Ersoz, Fatma Yurt Lambrecht, Mine Ince, Cagla Kayabasi, Cumhur Gunduz

PP06 Radio-U(H)PLC – the Search on the Optimal Flow Cell for the γ-Detector

Torsten Kniess, Sebastian Meister, Steffen Fischer, Jörg Steinbach

PP07 Radiolabeling, characterization & biodistribution study of cysteine and its derivatives with Tc99m

Rabia Ashfaq, Saeed Iqbal, Atiq-ur-Rehman, Irfan ullah Khan

PP08 Radiolabelling of poly (lactic-co.glycolic acid) (PLGA) nanoparticles with 99mTC

R Iglesias-Jerez, Cayero-Otero, L. Martín-Banderas, A. Perera-Pintado, I. Borrego-Dorado

PP09 Development of [¹⁸F]PD-410 as a non-peptidic PET radiotracer for gastrin releasing peptide receptors

Ines Farinha-Antunes, Chantal Kwizera, Enza Lacivita, Ermelinda Lucente, Mauro Niso, Paola De Giorgio, Roberto Perrone, Nicola A. Colabufo, Philip H. Elsinga, Marcello Leopoldo

PP10 An improved nucleophilic synthesis of 2-(3,4-dimethoxyphenyl)-6-(2-[18F]fluoroethoxy) benzothiazole ([18F]FEDMBT), potential diagnostic agent for breast cancer imaging by PET

V.V. Vaulina, O.S. Fedorova, V.V. Orlovskaja, С.L. Chen, G.Y. Li, F.C. Meng, R.S. Liu, H.E. Wang, R.N. Krasikova

PP11 Internal radiation dose assessment of radiopharmaceuticals prepared with accelerator-produced 99mTc

Laura Meléndez-Alafort, Mohamed Abozeid, Guillermina Ferro-Flores, Anna Negri, Michele Bello, Nikolay Uzunov, Martha Paiusco, Juan Esposito, Antonio Rosato

PP12 A specialized five-compartmental model software for pharmacokinetic parameters calculation

Laura Meléndez-Alafort, Cristina Bolzati, Guillermina Ferro-Flores, Nicola Salvarese, Debora Carpanese, Mohamed Abozeid, Antonio Rosato, Nikolay Uzunov

PP13 Molecular imaging of the pharmacokinetic behavior of low molecular weight ¹⁸F-labeled PEtOx in comparison to ⁸⁹Zr-labeled PEtOx

Palmieri L, Verbrugghen T, Glassner M, Hoogenboom R, Staelens S, Wyffels L

PP14 Towards nucleophilic synthesis of the α-[18F]fluoropropyl-L-dihydroxyphenylalanine

V. V. Orlovskaja, O. F. Kuznetsova, O. S. Fedorova, V. I. Maleev, Yu. N. Belokon, A. Geolchanyan, A. S. Saghyan, L. Mu, R. Schibli, S. M. Ametamey, R. N. Krasikova

PP15 A convenient one-pot synthesis of [18F]clofarabine

Revunov, Evgeny, Malmquist, Jonas, Johnström, Peter, Van Valkenburgh, Juno, Steele, Dalton, Halldin, Christer, Schou, Magnus

PP16 BODIPY-estradiol conjugates as multi-modality tumor imaging agents

Samira Osati,Michel Paquette,Simon Beaudoin,Hasrat Ali,Brigitte Guerin, Jeffrey V. Leyton, Johan E. van Lier

PP17 Easy and high yielding synthesis of 68Ga-labelled HBED-PSMA and DOTA-PSMA by using a Modular-Lab Eazy automatic synthesizer

Di Iorio V, Iori M, Donati C, Lanzetta V, Capponi PC, Rubagotti S, Dreger T, Kunkel F, Asti M

PP18 Synthesis and evaluation of fusarinine C-based octadentate bifunctional chelators for zirconium-89 labelling

Chuangyan Zhai, Christine Rangger, Dominik Summer, Hubertus Haas, Clemens Decristoforo

PP19 Fully automated production of [18F]NaF using a re-configuring FDG synthesis module.

Suphansa Kijprayoon, Ananya Ruangma, Suthatip Ngokpol, Samart Tuamputsha

PP20 Extension of the Carbon-11 Small Labeling Agents Toolbox and Conjugate Addition

Ulrike Filp, Anna Pees, Carlotta Taddei, Aleksandra Pekošak, Antony D. Gee, Alex J. Poot, Albert D. Windhorst

PP21 In vitro studies on BBB penetration of pramipexole encapsulated theranostic liposomes for the therapy of Parkinson’s disease

Mine Silindir Gunay, A. Yekta Ozer, Suna Erdogan, Ipek Baysal, Denis Guilloteau, Sylvie Chalon

PP22 Factors affecting tumor uptake of 99mTc-HYNIC-VEGF165

Filippo Galli, Marco Artico, Samanta Taurone, Enrica Bianchi, Bruce D. Weintraub, Mariusz Skudlinski, Alberto Signore

PP23 Rhenium-188: a suitable radioisotope for targeted radiotherapy

Nicolas Lepareur, Nicolas Noiret, François Hindré, Franck Lacœuille, Eric Benoist, Etienne Garin

PP24 Preparation of a broad palette of 68Ga radiopharmaceuticals for clinical applications

Trejo-Ballado F, Zamora-Romo E, Manrique-Arias JC, Gama-Romero HM, Contreras-Castañon G, Tecuapetla-Chantes RG, Avila-Rodriguez MA

PP25 68Ga-peptide preparation with the use of two 68Ge/68Ga-generators

H. Kvaternik, D. Hausberger, C. Zink, B. Rumpf, R. M. Aigner

PP26 Assay of HEPES in 68Ga-peptides by HPLC

H. Kvaternik, D. Hausberger, B. Rumpf, R. M. Aigner

PP27 Preparation, in vitro and in vivo evaluation of a 99mTc(I)-Diethyl Ester (S,S)-Ethylenediamine- N,N´-DI-2-(3-Cyclohexyl) Propionic acid as a target-specific radiopharmaceutical

Drina Janković, Mladen Lakić, Aleksandar Savić, Slavica Ristić, Nadežda Nikolić, Aleksandar Vukadinović, Tibor J. Sabo, Sanja Vranješ-Đurić

PP28 90Y-labeled magnetite nanoparticles for possible application in cancer therapy

S. Vranješ-Đurić, M. Radović, D. Janković, N. Nikolić, G. F. Goya, P. Calatayud, V. Spasojević, B. Antić

PP29 Simplified automation of the GMP production of 68Ga-labelled peptides

David Goblet, Cristiana Gameiro, Neva Lazarova

PP30 Combining commercial production of multi-products in a GMP environment with Clinical & R&D activities

Cristiana Gameiro, Ian Oxley, Antero Abrunhosa, Vasko Kramer, Maria Vosjan, Arnold Spaans

PP31 ⁹⁹mTc(CO)3-labeling and Comparative In-Vivo Evaluation of Two Clicked cRGDfK Peptide Derivatives

Kusum Vats, Drishty Satpati, Haladhar D Sarma, Sharmila Banerjee

PP32 Application of AnaLig resin for 99mTc separation from molybdenum excess

Wojdowska W., Pawlak D.W., Parus L. J., Garnuszek P., Mikołajczak R.

PP33 Constraints for selection of suitable precursor for one-step automated synthesis of [18F]FECNT, the dopamine transporter ligand

Pijarowska-Kruszyna J, Jaron A, Kachniarz A, Malkowski B, Garnuszek P, Mikolajczak R

PP34 Gamma scintigraphy studies with 99mTc- amoxicillin sodium in bacterially infected and sterile inflamed rats

Derya Ilem-Ozdemir, Oya Caglayan-Orumlu, Makbule Asikoglu

PP35 Preparation of 99mTc- Amoxicillin Sodium Lyophilized Kit

Derya Ilem-Ozdemir, Oya Caglayan-Orumlu, Makbule Asikoglu

PP36 Outfits of Tracerlan FXC-PRO for 11C-Labeling

Arponen Eveliina, Helin Semi, Saarinen Timo, Vauhkala Simo, Kokkomäki Esa, Lehikoinen Pertti

PP37 Microfluidic synthesis of ω-[18F]fluoro-1-alkynes

Mariarosaria De Simone, Giancarlo Pascali, Ludovica Carzoli, Mauro Quaglierini, Mauro Telleschi, Piero A. Salvadori

PP38 Automated 18F-flumazenil production using chemically resistant disposable cassettes

Phoebe Lam, Martina Aistleitner, Reinhard Eichinger, Christoph Artner

PP39 The effect of the eluent solutions (TBAHCO3, Kryptand K2.2.2) on the radiochemical yields of 18F-Fluoromethylcholine

Surendra Nakka, Hemantha Kumara MC, Al-Qahtani Mohammed

PP40 [68Ga]Radiolabeling of short peptide that has a PET imaging potentials

Al-Qahtani, Mohammed, Al-Malki, Yousif

PP41 Is validation of radiochemical purity analysis in a public hospital in a developing country possible?

N Mambilima, SM Rubow

PP42 Improved automated radiosynthesis of [18F]FEPPA

N. Berroterán-Infante, M. Hacker, M. Mitterhauser, W. Wadsak

PP43 Synthesis and initial evaluation of Al18F-RESCA1-TATE for somatostatin receptor imaging with PET

Uta Funke, Frederik Cleeren, Joan Lecina, Rodrigo Gallardo, Alfons M. Verbruggen, Guy Bormans

PP44 Radiolabeling and SPECT/CT imaging of different polymer-decorated zein nanoparticles for oral administration

Rocío Ramos-Membrive, Ana Brotons, Gemma Quincoces, Laura Inchaurraga, Inés Luis de Redín, Verónica Morán, Berta García-García, Juan Manuel Irache, Iván Peñuelas

PP45 An analysis of the quality of 68Ga-DOTANOC radiolabelling over a 3 year period

Trabelsi, M., Cooper M.S.

PP46 In vivo biodistribution of adult human mesenchymal stem cells I (MSCS-ah) labeled with 99MTC-HMPAO administered via intravenous and intra-articular in animal model. Preliminary results

Alejandra Abella, Teodomiro Fuente, Antonio Jesús Montellano, Teresa Martínez, Ruben Rabadan, Luis Meseguer-Olmo

PP47 Synthesis of [¹⁸F]F-exendin-4 with high specific activity

Lehtiniemi P, Yim C, Mikkola K, Nuutila P, Solin O

PP48 Experimental radionuclide therapy with 177Lu-labelled cyclic minigastrin and human dosimetry estimations

von Guggenberg E, Rangger C, Mair C, Balogh L, Pöstényi Z, Pawlak D, Mikołajczak R

PP49 Synthesis of radiopharmaceuticals for cell radiolabelling using anion exchange column

Socan A, Kolenc Peitl P, Krošelj M, Rangger C, Decristoforo C

PP50 [68Ga]peptide production on commercial synthesiser mAIO

Collet C., Remy S., Didier R,Vergote T.,Karcher G., Véran N.

PP51 Dry kit formulation for efficient radiolabeling of 68Ga-PSMA

D. Pawlak, M. Maurin, P. Garnuszek, U. Karczmarczyk, R. Mikołajczak

PP52 Development of an experimental method using Cs-131 to evaluate radiobiological effects of internalized Auger-electron emitters

Pil Fredericia, Gregory Severin, Torsten Groesser, Ulli Köster, Mikael Jensen

PP53 Preclinical comparative evaluation of NOTA/NODAGA/DOTA CYCLO-RGD peptides labelled with Ga-68

R. Leonte, F. D. Puicea, A. Raicu, E. A. Min, R. Serban, G. Manda, D. Niculae

PP54 Synthesizer- and Kit-based preparation of prostate cancer imaging agent 68Ga-RM2

Marion Zerna, Hanno Schieferstein, Andre Müller, Mathias Berndt

PP55 Synthesis of pancreatic beta cell-specific [18F]fluoro-exendin-4 via strain-promoted aza-dibenzocyclooctyne/azide cycloaddition

Cheng-Bin Yim, Kirsi Mikkola, Pirjo Nuutila, Olof Solin

PP56 Automated systems for radiopharmacy

D. Seifert, J. Ráliš, O. Lebeda

PP57 Simple, suitable for everyday routine use quality control method to assess radionuclidic purity of cyclotron-produced 99mTc

Svetlana V. Selivanova, Helena Senta, Éric Lavallée, Lyne Caouette, Éric Turcotte, Roger Lecomte

PP58 Effective dose estimation using Monte Carlo simulation for patients undergoing radioiodine therapy

Marina Zdraveska Kochovska, Emilija Janjevik Ivanovska, Vesna Spasic Jokic

PP59 Chemical analysis of the rituximab radioimmunoconjugates in lyophilized formulations intended for oncological applications

Darinka Gjorgieva Ackova, Katarina Smilkov, Petre Makreski, Trajče Stafilov, Emilija Janevik-Ivanovska

PP61 The need and benefits of established radiopharmacy in developing African countries

Aschalew Alemu, Joel Munene Muchira, David Mwanza Wanjeh, Emilija Janevik-Ivanovska

PP62 University Master Program of Radiopharmacy – step forward for Good Radiopharmacy Education

Emilija Janevik-Ivanovska, Zoran Zdravev, Uday Bhonsle, Osso Júnior João Alberto, Adriano Duatti, Bistra Angelovska, Zdenka Stojanovska, Zorica Arsova Sarafinovska, Darko Bosnakovski, Darinka Gorgieva-Ackova, Katarina Smilkov, Elena Drakalska, Meera Venkatesh, Rubin Gulaboski

PP63 Synthesis and preclinical validations of a novel 18F-labelled RGD peptide prepared by ligation of a 2-cyanobenzothiazole with 1,2-aminothiol to image angiogenesis.

Didier J. Colin, James A. H. Inkster, Stéphane Germain, Yann Seimbille

Influence of a novel, versatile bifunctional chelator on theranostic properties of a minigastrin analogue

Background

6-[Bis(carboxymethyl)amino]-1,4-bis(carboxymethyl)-6-methyl-1,4-diazepane (AAZTA ) is a promising chelator with potential advantages over 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) for radiopharmaceutical applications. Its mesocyclic structure enables fast radiolabelling under mild conditions with trivalent metals including not only ⁶⁸Ga for positron emission tomography (PET) but also ¹⁷⁷Lu and ¹¹¹In for single-photon emission computed tomography (SPECT) and radionuclide therapy. Here, we describe the evaluation of a bifunctional AAZTA derivative conjugated to a model minigastrin derivative as a potential theranostic agent.

Methods

An AAZTA derivative with an aliphatic C₉ chain as linker was coupled to a minigastrin, namely [AAZTA⁰, D-Glu¹, desGlu^2–6]-minigastrin (AAZTA-MG), and labelled with ⁶⁸Ga, ¹⁷⁷Lu and ¹¹¹In. The characterisation in vitro included stability studies in different media and determination of logD (octanol/PBS). Affinity determination (IC₅₀) and cell uptake studies were performed in A431-CCK2R cells expressing the human CCK2 receptor. μPET/CT and ex vivo biodistribution studies were performed in CCK2 tumour xenograft-bearing nude mice and normal mice.

Results

AAZTA-MG showed high radiochemical yields for ⁶⁸Ga (>95 %), ¹⁷⁷Lu (>98 %) and ¹¹¹In (>98 %). The logD value of −3.7 for both [⁶⁸Ga]- and [¹⁷⁷Lu]-AAZTA-MG indicates a highly hydrophilic character. Stability tests showed overall high stability in solution with some degradation in human plasma for [⁶⁸Ga]- and transchelation towards DTPA for and [¹⁷⁷Lu]-AAZTA-MG. An IC₅₀ value of 10.0 nM was determined, which indicates a high affinity for the CCK2 receptor. Specific cell uptake after 60 min was >7.5 % for [⁶⁸Ga]-AAZTA-MG and >9.5 % for [¹⁷⁷Lu]-AAZTA-MG, comparable to other DOTA-MG-analogues. μPET/CT studies in CCK2 receptor tumour xenografted mice not only revealed high selective accumulation in A431-CCK2R positive tumours of ⁶⁸Ga-labelled AAZTA-MG (1.5 % ID/g in 1 h post injection) but also higher blood levels as corresponding DOTA-analogues. The ¹¹¹In-labelled peptide had a tumour uptake of 1.7 % ID/g. Biodistribution in normal mice with the [¹⁷⁷Lu]-AAZTA-MG showed a considerable uptake in intestine (7.3 % ID/g) and liver (1.5 % ID/g).

Conclusion

Overall, AAZTA showed interesting properties as bifunctional chelator for peptides providing mild radiolabelling conditions for both ⁶⁸Ga and trivalent metals having advantages over the currently used chelator DOTA. Studies are ongoing to further investigate in vivo targeting properties and stability issues and the influence of spacer length on biodistribution of AAZTA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-015-0154-7) contains supplementary material, which is available to authorized users.

Methods for assessment of keel bone damage in poultry

Keel bone damage (KBD) is a critical issue facing the laying hen industry today as a result of the likely pain leading to compromised welfare and the potential for reduced productivity. Recent reports suggest that damage, while highly variable and likely dependent on a host of factors, extends to all systems (including battery cages, furnished cages, and non-cage systems), genetic lines, and management styles. Despite the extent of the problem, the research community remains uncertain as to the causes and influencing factors of KBD. Although progress has been made investigating these factors, the overall effort is hindered by several issues related to the assessment of KBD, including quality and variation in the methods used between research groups. These issues prevent effective comparison of studies, as well as difficulties in identifying the presence of damage leading to poor accuracy and reliability. The current manuscript seeks to resolve these issues by offering precise definitions for types of KBD, reviewing methods for assessment, and providing recommendations that can improve the accuracy and reliability of those assessments.

Novel Bifunctional Cyclic Chelator for (89)Zr Labeling-Radiolabeling and Targeting Properties of RGD Conjugates

Within the last years (89)Zr has attracted considerable attention as long-lived radionuclide for positron emission tomography (PET) applications. So far desferrioxamine B (DFO) has been mainly used as bifunctional chelating system. Fusarinine C (FSC), having complexing properties comparable to DFO, was expected to be an alternative with potentially higher stability due to its cyclic structure. In this study, as proof of principle, various FSC-RGD conjugates targeting αvß3 integrins were synthesized using different conjugation strategies and labeled with (89)Zr. In vitro stability, biodistribution, and microPET/CT imaging were evaluated using [(89)Zr]FSC-RGD conjugates or [(89)Zr]triacetylfusarinine C (TAFC). Quantitative (89)Zr labeling was achieved within 90 min at room temperature. The distribution coefficients of the different radioligands indicate hydrophilic character. Compared to [(89)Zr]DFO, [(89)Zr]FSC derivatives showed excellent in vitro stability and resistance against transchelation in phosphate buffered saline (PBS), ethylenediaminetetraacetic acid solution (EDTA), and human serum for up to 7 days. Cell binding studies and biodistribution as well as microPET/CT imaging experiments showed efficient receptor-specific targeting of [(89)Zr]FSC-RGD conjugates. No bone uptake was observed analyzing PET images indicating high in vivo stability. These findings indicate that FSC is a highly promising chelator for the development of (89)Zr-based PET imaging agents.

Selected ⁶⁸Ga-siderophores versus ⁶⁸Ga-colloid and ⁶⁸Ga-citrate: biodistribution and small animal imaging in mice

BACKGROUND

(68)Ga-triacetylfusarinine C (TAFC) and (68)Ga-ferrioxamine E (FOXE) show great potential to be used as highly sensitive and selective tracers for Aspergillus infection imaging. Here we report on a comparison of the ex vivo biodistribution and small animal imaging of (68)Ga-TAFC and (68)Ga-FOXE versus (68)Ga-colloid and (68)Ga-citrate as unspecific control in mice.

METHODS

The radiochemical purity of tested (68)Ga labelled tracers was determined by RP-HPLC or ITLC-SG. Ex vivo biodistribution was studied in normal DBA/2 mice 30 min and 90 min p.i. Static and dynamic imaging were performed using µPET/CT.

RESULTS

(68)Ga-TAFC and (68)Ga-FOXE showed rapid renal excretion and low blood values even 90 min p.i. (68)Ga-TAFC showed almost no retention in other organs while (68)Ga-FOXE displayed some uptake in gastrointestinal tract. (68)Ga-colloid and (68)Ga-citrate revealed significantly different ex vivo biodistribution. (68)Ga-colloid showed pronounced radioactivity retention in the liver, while (68)Ga-citrate displayed high blood values and significant retention of radioactivity in highly perfused organs.

CONCLUSIONS

From the results, both (68)Ga-TAFC and (68)Ga-FOXE have excellent and significantly different in vivo behaviour compared to (68)Ga-colloid and (68)Ga-citrate. (68)Ga-TAFC in particular confirmed its great potential use as a specific tracer for Aspergillus infection imaging.

In vitro and in vivo evaluation of selected 68Ga-siderophores for infection imaging

Introduction

Siderophores are low-molecular-mass iron chelators serving as iron transporters for almost all bacteria, fungi and some plants. Iron is an essential element for majority of organisms and plays an important role in virulence of pathogenic organisms. ⁶⁸Ga is a positron emitter with complexing properties comparable to those of Fe(III) and readily available from a generator. Initial studies with ⁶⁸Ga-triacetylfusarinine C (TAFC) showed excellent targeting properties in a rat infection model. We report here on the in vitro and in vivo evaluation of other siderophores radiolabelled with ⁶⁸Ga as potential radiopharmaceuticals for infection imaging.

Methods

⁶⁸Ga labelling was performed using acetate buffer. Stability, log P and protein binding values were determined. In vitro uptake was tested using iron-deficient and iron-sufficient Aspergillus fumigatus (A.f.) cultures. Biodistribution of ⁶⁸Ga-siderophores was studied in Balb/c mice.

Results

Significant differences among studied siderophores were observed in labelling efficiency, stability and protein binding. Uptake in A.f. cultures was highly dependent on iron load and type of the siderophore. In mice, ⁶⁸Ga-TAFC and ⁶⁸Ga-ferrioxamine E (FOXE) showed rapid renal excretion and low blood values even at a short period after injection; in contrast, ⁶⁸Ga-ferricrocin and ⁶⁸Ga-ferrichrome revealed high retention in blood and ⁶⁸Ga-fusarinine C showed very high kidney retention.

Conclusions

Some of the studied siderophores bind ⁶⁸Ga with high affinity and stability, especially ⁶⁸Ga-TAFC and ⁶⁸Ga-FOXE. Low values of protein binding, high and specific uptake in A.f., and excellent in vivo biodistribution make them favourable agents for Aspergillus infection imaging.

68Ga-siderophores for PET imaging of invasive pulmonary aspergillosis: proof of principle

The diagnosis of invasive pulmonary aspergillosis (IPA) is difficult and lacks specificity and sensitivity. In the pathophysiology of Aspergillus fumigatus, iron plays an essential role as a nutrient during infection. A. fumigatus uses a specific and highly efficient iron uptake mechanism based on iron-complexing ferric ion Fe(III) siderophores, which are a requirement for A. fumigatus virulence. We aimed to evaluate the potential of siderophores radiolabeled with (68)Ga, a positron emitter with complexing properties comparable to those of Fe(III), as a radiopharmaceutical for imaging IPA.

METHODS

(68)Ga radiolabeling of the A. fumigatus siderophores desferri-triacetylfusarinine C (TAFC) and desferri-ferricrocin (FC) was performed at high specific activity. Stability, protein binding, and log P values were determined. In vitro uptake in A. fumigatus cultures was tested under varying conditions. Biodistribution was studied in healthy noninfected BALB/c mice, and uptake was studied in a model of A. fumigatus infection using immunosuppressed Lewis rats.

RESULTS

High-specific-activity (68)Ga labeling could be achieved, and resulting complexes were stable in serum, toward diethylenetriaminepentaacetic acid and Fe(III) challenge. Both siderophores showed hydrophilic properties ((68)Ga-TAFC, log P = -2.59; (68)Ga-FC, log P = -3.17) with low values of protein binding for (68)Ga-TAFC (<2%). Uptake of both siderophores was highly dependent on the mycelial iron load and could be blocked with an excess (10 microM) of siderophore or NaN(3), indicating specific, energy-dependent uptake. In noninfected mice, (68)Ga-TAFC showed rapid renal excretion and low blood values (1.6 +/- 0.37 percentage injected dose per gram [%ID/g] at 30 min); in urine only intact (68)Ga-TAFC was detected. In contrast, (68)Ga-FC revealed high retention in blood (16.1 +/- 1.07 %ID/g at 90 min) and rapid metabolism. In the rat IPA model, lung uptake of (68)Ga-TAFC was dependent on the severity of infection, with less than 0.04 %ID/g in control rats (n = 5) and 0.29 +/- 0.11 %ID/g in mildly infected (n = 3) and 0.95 +/- 0.37 %ID/g in severely infected (n = 4) rats. PET showed focal accumulation in infected lung tissue.

CONCLUSION

Both siderophores bound (68)Ga with high affinity, and (68)Ga-TAFC, especially, showed high stability. (68)Ga-TAFC displayed highly selective accumulation by A. fumigatus subspecies in vitro and in vivo. The high and specific uptake by A. fumigatus proves the potential of (68)Ga-labeled siderophores for the specific detection of A. fumigatus during infection. They hold promise as new PET agents for IPA.

Preparation and the kinetic stability of hyaluronan radiolabeled with 111In, 125I and 14C

Three different procedures for the labeling of hyaluronan (HA) with (111)In, (125)I and (14)C radionuclides were compared, and the kinetic stability of radiolabeled HA under different conditions (saline, artificial gastric juice and plasma) was established. Modification of HA structure with bifunctional chelating agents (DTPA) or with the prosthetic group (tyramine or tyrosine) was essential prior (111)In and (125)I labeling. These chemical labeling techniques were fast, simple and inexpensive, and labeled agents with a high specific activity were obtained. The only disadvantage of these methods was the occurrence of unknown functional groups in the HA molecule requiring further characterization of the compound. Conversely, HA labeling with (14)C by biotechnological synthesis was found to be rather expensive and time-consuming process. Although, the final product (14)C-HA was identical to natural HA its low specific activity presents certain limitation for its application in biological experiments. Stability studies showed that (14)C-HA and (125)I-Tm-HA were stable in all studied mediums. In the case of (125)I-Trs-HA, stability slightly decreased in rat plasma and in artificial gastric juice with increasing time. The least stable was (111)In-DTPA-HA, which degraded completely after 48h in artificial gastric juice. Kinetic stability studies may provide primary information concerning the properties of radiolabeled HA in vitro, which is essential for the use and explanation of its behavior in biological experiments.

A Bilinear Programming Approach for Multiagent Planning

Multiagent planning and coordination problems are common and known to be computationally hard. We show that a wide range of two-agent problems can be formulated as bilinear programs. We present a successive approximation algorithm that significantly outperforms the coverage set algorithm, which is the state-of-the-art method for this class of multiagent problems. Because the algorithm is formulated for bilinear programs, it is more general and simpler to implement. The new algorithm can be terminated at any time and-unlike the coverage set algorithm-it facilitates the derivation of a useful online performance bound. It is also much more efficient, on average reducing the computation time of the optimal solution by about four orders of magnitude. Finally, we introduce an automatic dimensionality reduction method that improves the effectiveness of the algorithm, extending its applicability to new domains and providing a new way to analyze a subclass of bilinear programs.

Whole-body CT trauma imaging with adapted and optimized CT angiography of the craniocervical vessels: do we need an extra screening examination?

BACKGROUND AND PURPOSE

Blunt carotid and vertebral artery injury (BCVI) is rare but potentially devastating. The objective of our study was to prospectively evaluate the usefulness of a dedicated and optimized CT angiography (CTA) protocol of the craniocervical vessels as part of a whole-body CT work-up of patients with multiple trauma in a population of patients with blunt trauma.

MATERIAL AND METHODS

From February 2006 to July 2007, a total of 368 consecutive patients with trauma were evaluated. All examinations were performed on a 16-row multisection CT (MSCT) scanner. CTA was performed from the level of the T2 vertebra to the roof of the lateral ventricles with 40 mL of iodinated contrast agent. Images were reconstructed with use of the angiography and bone window settings to evaluate vessels and bones.

RESULTS

Of all eligible patients imaged, 100 had injuries to the head and neck including 35 skull base fractures (9.5%), 24 maxillofacial (6.5%), and 11 cervical spine fractures (3%). CTA was diagnostic in all patients. BCVI was diagnosed in 6 cases (6 lesions of the internal carotid artery, 3 lesions of the vertebral artery); among them were 2 who did not meet the screening criteria. No patient with negative results on CTA subsequently had development of neurologic deficits suspicious for BCVI.

CONCLUSION

This study confirms that optimized craniocervical CTA can be easily integrated into a whole-body CT protocol for patients with multiple trauma. No additional screening technique is necessary to identify clinically relevant vascular injuries. Earlier recognition enables earlier treatment and may decrease mortality and morbidity rates of these rare but potentially devastating injuries.