Infection Imaging Agent Research Articles

Radiosynthesis and Preclinical Evaluation of [99mTc]Tc-Tigecycline Radiopharmaceutical to Diagnose Bacterial Infections.

As a primary source of mortality and disability, bacterial infections continue to develop a severe threat to humanity. Nuclear medicine imaging (NMI) is known for its promising potential to diagnose deep-seated bacterial infections. This work aims to develop a new technetium-99m (99mTc) labeled tigecycline radiopharmaceutical as an infection imaging agent. Reduced 99mTc was used to make a coordinate complex with tigecycline at pH 7.7-7.9 at room temperature. Instantaneous thin-layer chromatography impregnated with silica gel (ITLC-SG) and ray detector equipped high-performance liquid chromatography (ray-HPLC) was performed to access the radiolabeling yield and radiochemical purity (RCP). More than 91% labeling efficiency was achieved after 25 min of mild shaking of the reaction mixture. The radiolabeled complex was found intact up to 4 h in saline. Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) infection-induced rats were used to record the biodistribution of the radiopharmaceutical and its target specificity; 2 h' post-injection biodistribution revealed a 2.39 ± 0.29 target/non-target (T/NT) ratio in the E. coli infection-induced animal model, while a 2.9 ± 0.31 T/NT value was recorded in the S. aureus bacterial infection-induced animal model. [99mTc]Tc-tigecycline scintigraphy was performed in healthy rabbits using a single photon emission computed tomography (SPECT) camera. Scintigrams showed normal kidney perfusion and excretion into the bladder. In conclusion, the newly developed [99mTc]Tc-tigecycline radiopharmaceutical could be considered to diagnose broad-spectrum bacterial infections.

68Ga Radiolabeling of NODASA-Functionalized Phage Display-Derived Peptides for Prospective Assessment as Tuberculosis-Specific PET Radiotracers.

This research presents the development of positron emission tomography (PET) radiotracers for detecting Mycobacterium tuberculosis (MTB) for the diagnosis and monitoring of tuberculosis. Two phage display-derived peptides with proven selective binding to MTB were identified for development into PET radiopharmaceuticals: H8 (linear peptide) and PH1 (cyclic peptide). We sought to functionalize H8/PH1 with NODASA, a bifunctional chelator that allows complexation of PET-compatible radiometals such as gallium-68. Herein, we report on the chelator functionalization, optimized radiosynthesis, and assessment of the radiopharmaceutical properties of [68Ga]Ga-NODASA-H8 and [68Ga]Ga-NODASA-PH1. Robust radiolabeling was achieved using the established routine method, indicating consistent production of a radiochemically pure product (RCP ≥ 99.6%). For respective [68Ga]Ga-NODASA-H8 and [68Ga]Ga-NODASA-PH1, relatively high levels of decay-corrected radiochemical yield (91.2% ± 2.3%, 86.7% ± 4.0%) and apparent molar activity (Am, 3.9 ± 0.8 and 34.0 ± 5.3 GBq/μmol) were reliably achieved within 42 min, suitable for imaging purposes. Notably, [68Ga]Ga-NODASA-PH1 remained stable in blood plasma for up to 2 h, while [68Ga]Ga-NODASA-H8 degraded within 30 min. For both 68Ga peptides, minimal whole-blood cell binding and plasma protein binding were observed, indicating a favorable pharmaceutical behavior. [68Ga]Ga-NODASA-PH1 is a promising candidate for further invitro/in vivo evaluation as a tuberculosis-specific infection imaging agent.

Exploring the potential of radiolabeled duramycin as an infection imaging probe.

The continuous pursuit of designing an ideal infection imaging agent is a crucial and ongoing endeavor in the field of biomedical research. Duramycin, an antimicrobial peptide exerts its antimicrobial action on bacteria by specific recognition of phosphatidylethanolamine (PE) moiety present on most bacterial membranes, particularly Escherichia coli (E. coli). E. coli membranes contain more than 60% PE. Therefore, duramycin is an attractive candidate for the formulation of probes for in situ visualization of E. coli driven focal infections. The aim of the present study is to develop 99m Tc labeled duramycin as a single-photon emission computed tomography (SPECT)-based agent to image such infections. Duramycin was successfully conjugated with a bifunctional chelator, hydrazinonicotinamide (HYNIC). PE specificity of HYNIC-duramycin was confirmed by a dye release assay on PE-containing model membranes. Radiolabeling of HYNIC-duramycin with 99m Tc was performed with consistently high radiochemical yield (>90%) and radiochemical purity (>90%). [99m Tc]Tc-HYNIC-duramycin retained its specificity for E. coli, in vitro. SPECT and biodistribution studies showed that the tracer could specifically identify E. coli driven infection at 3 h post injection. While 99m Tc-labeled duramycin is employed for monitoring early response to cancer therapy and cardiotoxicity, the current studies have confirmed, for the first time, the potential of utilizing 99m Tc labeled duramycin as an imaging agent for detecting bacteria. Its application in imaging PE-positive bacteria represents a novel and promising advancement.

Imaging of bacterial infection: Harnessing positron emission tomography and Cherenkov luminescence imaging with UBI-derived octapeptide.

Noninvasive imaging techniques for the early detection of infections are in high demand. In this study, we present the development of an infection imaging agent consisting of the antimicrobial peptide fragment UBI (31-38) conjugated to the chelator 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODAGA), which allows for labeling with the positron emitter Ga-68. The preclinical evaluation of [68 Ga]Ga-NODAGA-UBI (31-38) was conducted to investigate its potential for imaging bacterial infections caused by Staphylococcus aureus. The octapeptide derived from ubiquicidin, UBI (31-38), was synthesized and conjugated with the chelator NODAGA. The conjugate was then radiolabeled with Ga-68. The radiolabeling process and the stability of the radio formulation were confirmed through chromatography. The study included both in vitro evaluations using S. aureus and in vivo evaluations in an animal model of infection and inflammation. Positron emission tomography (PET) and Cherenkov luminescence imaging (CLI) were performed to visualize the targeted localization of the radio formulation at the site of infection. Ex vivo biodistribution studies were carried out to quantify the uptake of the radio formulation in different organs and tissues. Additionally, the uptake of [18 F]Fluorodeoxyglucose ([18 F] FDG) in the animal model was also studied for comparison. The [68 Ga]Ga-NODAGA-UBI (31-38) complex consistently exhibited high radiochemical purity (>90%) after formulation. The complex demonstrated stability in saline, phosphate-buffered saline, and human serum for up to 3 h. Notably, the complex displayed significantly higher uptake in S. aureus, which was inhibited in the presence of unconjugated UBI (29-41) peptide, confirming the specificity of the formulation for bacterial membranes. Bacterial imaging capability was also observed in PET and CLI images. Biodistribution results indicated a substantial target-to-nontarget ratio of approximately 4 at 1 h postinjection of the radio formulation. Conversely, the uptake of [18 F]FDG in the animal model did not allow for the discrimination of infected and inflamed sites. Our studies have demonstrated that [68 Ga]Ga-NODAGA-UBI (31-38) holds promise as a radiotracer for imaging bacterial infections caused by S. aureus.

A Team for Unique Molecular Imaging Based in South Africa

AbstractThis invited Team Profile was created by the Ebenhan Lab (Professor Thomas Ebenhan and Professor Jan Rijn Zeevaart) at the Preclinical Imaging Facility, Nuclear Medicine Research Infrastructure (NuMeRI) NPC, Pretoria (South Africa) in collaboration with Arno C. Gouws, Professor Hendrik G. Kruger, and Professor Tricia Naicker from the Catalysis and Peptide Research Unit at the University of KwaZulu Natal, Durban (South Africa); Professor Olivier Gheysens from the Department of Nuclear Medicine, Cliniques Universitaires Saint‐Luc and Institute of Clinical and Experimental Research, Université Catholique de Louvain, Brussels (Belgium); and ProfessorThavendran Govender from the Department of Chemistry, University of Zululand, KwaDlangezwa (South Africa). Researchers at these institutes have a 10‐year track record of joint publications. The review written by this collaboration provides a summary of the relevant antibiotic‐derived PET radiotracers, grouped either by radiotracer development for infection imaging, or radio‐antibiotic PET imaging for pharmacologic drug characterization. The review includes a critical, in‐depth evaluation, addressing the challenges and pitfalls of developing antibiotic‐derived PET radiotracers as infection imaging agents. “Antibiotic‐Derived Radiotracers for Positron Emission Tomography: Nuclear or ‘Unclear' Infection Imaging?”, A. C. Gouws, H. G. Kruger, O. Gheysens, J. R. Zeevaart, T. Govender, T. Naicker, T. Ebenhan, Angew. Chem. Int. Ed. 2022, e202204955.

A Team for Unique Molecular Imaging Based in South Africa.

This invited Team Profile was created by the Ebenhan Lab (Professor Thomas Ebenhan and Professor Jan Rijn Zeevaart) at the Preclinical Imaging Facility, Nuclear Medicine Research Infrastructure (NuMeRI) NPC, Pretoria (South Africa) in collaboration with Arno C. Gouws, Professor Hendrik G. Kruger, and Professor Tricia Naicker from the Catalysis and Peptide Research Unit at the University of KwaZulu Natal, Durban (South Africa); Professor Olivier Gheysens from the Department of Nuclear Medicine, Cliniques Universitaires Saint-Luc and Institute of Clinical and Experimental Research, Université Catholique de Louvain, Brussels (Belgium); and ProfessorThavendran Govender from the Department of Chemistry, University of Zululand, KwaDlangezwa (South Africa). Researchers at these institutes have a 10-year track record of joint publications. The review written by this collaboration provides a summary of the relevant antibiotic-derived PET radiotracers, grouped either by radiotracer development for infection imaging, or radio-antibiotic PET imaging for pharmacologic drug characterization. The review includes a critical, in-depth evaluation, addressing the challenges and pitfalls of developing antibiotic-derived PET radiotracers as infection imaging agents. "Antibiotic-Derived Radiotracers for Positron Emission Tomography: Nuclear or 'Unclear' Infection Imaging?", A. C. Gouws, H. G. Kruger, O. Gheysens, J. R. Zeevaart, T. Govender, T. Naicker, T. Ebenhan, Angew. Chem. Int. Ed. 2022, e202204955.

China’s radiopharmaceuticals on expressway: 2014–2021

AbstractThis review provides an essential overview on the progress of rapidly-developing China’s radiopharmaceuticals in recent years (2014–2021). Our discussion reflects on efforts to develop potential, preclinical, and in-clinical radiopharmaceuticals including the following areas: (1) brain imaging agents, (2) cardiovascular imaging agents, (3) infection and inflammation imaging agents, (4) tumor radiopharmaceuticals, and (5) boron delivery agents (a class of radiopharmaceutical prodrug) for neutron capture therapy. Especially, the progress in basic research, including new radiolabeling methodology, is highlighted from a standpoint of radiopharmaceutical chemistry. Meanwhile, we briefly reflect on the recent major events related to radiopharmaceuticals along with the distribution of major R&D forces (universities, institutions, facilities, and companies), clinical study status, and national regulatory supports. We conclude with a brief commentary on remaining limitations and emerging opportunities for China’s radiopharmaceuticals.

Radiolabeling and evaluation of a novel [99mTcN]2+ complex with deferoxamine dithiocarbamate as a potential agent for bacterial infection imaging

In order to find a 99mTc-labeled deferoxamine radiotracer for bacterial infection imaging, deferoxamine dithiocarbamate (DFODTC) was successfully synthesized and it was radiolabeled with [99mTcN]2+ core to prepare the 99mTcN(DFODTC)2 complex. 99mTcN(DFODTC)2 was obtained with high radiochemical purity without further purification. The complex was lipophilic and exhibited good in vitro stability. According to the result of bacterial binding study, the binding of 99mTcN(DFODTC)2 to bacteria was specific. Biodistribution in mice study indicated that 99mTcN(DFODTC)2 had a higher uptake in bacterial infection tissues than in turpentine-induced abscesses at 120 min after injection, which showed that the radiotracer could differentiate between bacterial infection and sterile inflammation. SPECT/CT images showed that there was a clear accumulation in infection sites, suggesting that 99mTcN(DFODTC)2 could be a potential bacterial infection imaging radiotracer.

SP-111 - Fluoroquinolone dithiocarbamate rhenium and technetium-99m complexes for potential infection imaging agents

SP-111 - Fluoroquinolone dithiocarbamate rhenium and technetium-99m complexes for potential infection imaging agents

Synthesis and Evaluation of Novel Norfloxacin Isonitrile 99mTc Complexes as Potential Bacterial Infection Imaging Agents.

To develop potential technetium-99m single-photon emission computed tomography (SPECT) imaging agents for bacterial infection imaging, the novel norfloxacin isonitrile derivatives CN4NF and CN5NF were synthesized and radiolabeled with a [99mTc][Tc(I)]+ core to obtain [99mTc]Tc-CN4NF and [99mTc]Tc-CN5NF. These compounds were produced in high radiolabeling yields and showed hydrophilicity and good stability in vitro. The bacterial binding assay indicated that [99mTc]Tc-CN4NF and [99mTc]Tc-CN5NF were specific to bacteria. Compared with [99mTc]Tc-CN4NF, biodistribution studies of [99mTc]Tc-CN5NF showed a higher uptake in bacteria-infected tissues than in turpentine-induced abscesses, indicating that [99mTc]Tc-CN5NF could distinguish bacterial infection from sterile inflammation. In addition, [99mTc]Tc-CN5NF had higher abscess/blood and abscess/muscle ratios. SPECT image of [99mTc]Tc-CN5NF showed that there was a clear accumulation in the infection site, suggesting that it could be a potential bacterial infection imaging radiotracer.

Design, Preparation, and Evaluation of a Novel 99mTcN Complex of Ciprofloxacin Xanthate as a Potential Bacterial Infection Imaging Agent.

In order to seek novel technetium-99m bacterial infection imaging agents, a ciprofloxacin xanthate (CPF2XT) was synthesized and radiolabeled with [99mTcN]2+ core to obtain the 99mTcN-CPF2XT complex, which exhibited high radiochemical purity, hydrophilicity, and good stability in vitro. The bacteria binding assay indicated that 99mTcN-CPF2XT had specificity to bacteria. A study of biodistribution in mice showed that 99mTcN-CPF2XT had a higher uptake in bacterial infection tissues than in turpentine-induced abscesses, indicating that it could distinguish bacterial infection from sterile inflammation. Compared to 99mTcN-CPFXDTC, the abscess/blood and abscess/muscle ratios of 99mTcN-CPF2XT were higher and the uptakes of 99mTcN-CPF2XT in the liver and lung were obviously decreased. The results suggested that 99mTcN-CPF2XT would be a potential bacterial infection imaging agent.

Maltotriose-based probes for fluorescence and photoacoustic imaging of bacterial infections

Currently, there are no non-invasive tools to accurately diagnose wound and surgical site infections before they become systemic or cause significant anatomical damage. Fluorescence and photoacoustic imaging are cost-effective imaging modalities that can be used to noninvasively diagnose bacterial infections when paired with a molecularly targeted infection imaging agent. Here, we develop a fluorescent derivative of maltotriose (Cy7-1-maltotriose), which is shown to be taken up in a variety of gram-positive and gram-negative bacterial strains in vitro. In vivo fluorescence and photoacoustic imaging studies highlight the ability of this probe to detect infection, assess infection burden, and visualize the effectiveness of antibiotic treatment in E. coli-induced myositis and a clinically relevant S. aureus wound infection murine model. In addition, we show that maltotriose is an ideal scaffold for infection imaging agents encompassing better pharmacokinetic properties and in vivo stability than other maltodextrins (e.g. maltohexose).

99mTc-radiolabeled Levofloxacin and micelles as infection and inflammation imaging agents

Easy and early detection of infection and inflammation is essential for early and effective treatment. In this study, PEGylated micelles were designed and both micelles and Levofloxacin were radiolabeled with 99mTcO4- to develop potential radiotracers for detection of infection/inflammation. Radiolabeling efficiency, in vitro stability and bacterial binding of 99mTc-Levofloxacin and 99mTc-micelles were compared. The aim of this study is to formulate and compare 99mTc-Levofloxacin and 99mTc-micelles as infection and inflammation agents having different mechanisms for the accumulation at infection and inflammation site. PEGylated micelles were designed with a particle size of 80 ± 0.7 nm and proper characterization properties. High radiolabeling efficiency was achieved for 99mTc-Levofloxacin (96%) and 99mTc-micelles (87%). The radiolabeling efficiency was remained stable with some insignificant alterations for both radiotracers at 25 °C for 24 h. Although in vitro bacterial binding of 99mTc-levofloxacine was higher than 99mTc-micelles, 99mTc-micelles may also be evaluated potential agent due to long circulation and passive accumulation mechanisms at infection/inflammation site. Both radiopharmaceutical agents exhibit potential results in design, characterization, radiolabeling efficiency and in vitro bacterial binding point of view.

Utility of Tc-99m-labeled levofloxacin as an infection-imaging agent in musculoskeletal infections

Utility of Tc-99m-labeled levofloxacin as an infection-imaging agent in musculoskeletal infections

In Vivo Microbial Targeting of 99mTc-Labeled Human β-Defensin-3 in a Rat Model of Infection.

Differentiation of infection from aseptic inflammation represents a major clinical issue. None of the commercially available compounds (labeled granulocytes, antigranulocyte antibodies, Ga-citrate, labeled immunoglobulin G, F-FDG) is capable of this differentiation, producing a nonnegligible false-positive rate. Recently, our group reported on a reliable labeling procedure of the antimicrobial peptide human β-defensin 3 (HBD-3) with Tc. The aim of this study was to evaluate in vivo Tc-HBD-3 uptake in a rat model of infection. Recombinant HBD-3 was radiolabeled with Tc. Radiolabeling yield and specific activity of the compound were calculated. Chromatographic behavior and biological activity of Tc-HBD-3 were also assessed. An experimental model involving Staphylococcus aureus-induced infection and carrageenan-induced aseptic inflammation was performed in 5 Wistar rats. Serial planar scintigraphic acquisitions were performed from 15 to 180 minutes after Tc-HBD-3 intravenous administration. Radiotracer uptake was evaluated qualitatively and semiquantitatively as a target-to-nontarget ratio. Radiolabeling yield of Tc-HBD-3 was 70% with a specific activity of 6 to 8 MBq/μg. A significant and progressive Tc-HBD-3 uptake was observed in the site of S. aureus-induced infection, with a maximum average target-to-nontarget ratio of 5.7-fold higher in the infection site compared with an inflammation site observed at 140 minutes. In vivo imaging with Tc-HBD-3 in a rat model of S. aureus-induced infection demonstrated favorable uptake in the infection site compared with sterile inflammation and background. These promising results, together with previous ex vivo uptake and toxicity assessment, suggest the potential of Tc-HBD-3 as a novel agent for specific infection imaging.

Research Progress of [68Ga]Citrate PET's Utility in Infection and Inflammation Imaging: a Review.

Imaging diagnosis of infection and inflammation has been challenging for many years. Infection imaging agents commonly used in nuclear medicine, such as [67Ga]citrate, 2-deoxy-2-[18F]fluoro-D-glucose([18F]FDG), and radionuclide-labeled leukocytes, have their own shortcomings. Identification of a tracer with considerable economic benefit, high specificity, and low radiation dose has become clinically urgent. In the twenty-first century, with the increasing availability of positron emission tomography (PET) devices and the commercialization of Ge-68/Ga-68 generators, the study of [68Ga]citrate applications for infection and inflammation has increased and shown good potential. In this report, the research progress that supports [68Ga]citrate PET's applications various infectious diseases and inflammation is reviewed.

99m Tc-Ceftizoxime: Synthesis, characterization and its use in diagnosis of diabetic foot osteomyelitis.

The diagnosis of diabetic foot osteomyelitis is crucial and challenging for the proper management of diabetic foot. 99m Tc labelled Ceftizoxime was used as a non-invasive diagnostic agent for diabetic foot osteomyelitis. Ceftizoxime [CFT], a third generation cephalosporin, was used in a simple and direct method for the synthesis of 99m TcO4 - labelled infection imaging agent with stannous chloride as reducing agent. Its radiochemical purity was checked by thin Layer chromatography. Partition co-efficient was measured with phosphate buffer and chloroform. The radiochemical complex was injected to control and infected animal model for 3hours in-vivo localization studied with the help of dual head gamma camera. The labelled complexes were injected to 5 patients of known type II diabetes mellitus suspected of diabetic foot osteomyelitis. All patients underwent dynamic and static 99m Tc-MDP and 99m Tc-CFT scans. The synthesized radio labelled complex was 98.8% pure, with hydrophilic character. When injected to animal model, at 120minutes, 49.3% was localized in foci of infection with 3.35% in liver and excretion through kidney. Human studies were interpreted as true or false positive and true or false negative based on bone histopathology/culture and clinical follow-up. We found that of 5 patients, 2 were true positive, 2 as true negative with no false positive or negative and 01 patient had soft tissue infection. This study showed that 99m Tc-CFT labelled complex could be used for detection of diabetic foot osteomyelitis; however, further confirmation of results with a larger patient population would be optimal.

Ciprofloxacin: from infection therapy to molecular imaging.

Diagnosis of deep-seated bacterial infection remains a serious medical challenge. The situation is becoming more severe with the increasing prevalence of bacteria that are resistant to multiple antibiotic classes. Early efforts to develop imaging agents for infection, such as technetium-99m (99mTc) labeled leukocytes, were encouraging, but they failed to differentiate between bacterial infection and sterile inflammation. Other diagnostic techniques, such as ultrasonography, magnetic resonance imaging, and computed tomography, also fail to distinguish between bacterial infection and sterile inflammation. In an attempt to bypass these problems, the potent, broad-spectrum antibiotic ciprofloxacin was labeled with 99mTc to image bacterial infection. Initial results were encouraging, but excitement declined when controversial results were reported. Subsequent radiolabeling of ciprofloxacin with 99mTc using tricarbonyl and nitrido core, fluorine and rhenium couldn't produce robust infection imaging agent and remained in discussion. The issue of developing a robust probe can be approached by reviewing the broad-spectrum activity of ciprofloxacin, labeling strategies, potential for imaging infection, and structure-activity (specificity) relationships. In this review we discuss ways to accelerate efforts to improve the specificity of ciprofloxacin-based imaging.

Gallium-68 labeled Ubiquicidin derived octapeptide as a potential infection imaging agent

IntroductionGallium-68 based infection imaging agents are in demand to detect infection foci with high spatial resolution and sensitivity. In this study, Ubiquicidin derived octapeptide, UBI (31–38) conjugated with macrocyclic chelator NOTA was radiolabeled with 68Ga to develop infection imaging agent. MethodsCircular dichroism (CD) spectroscopy was performed to study conformational changes in UBI (31–38) and its NOTA conjugate in a “membrane like environment”. Radiolabeling of NOTA-UBI (31–38) with 68Ga was optimized and quality control analysis was done by chromatography techniques. In vitro evaluation of 68Ga-NOTA-UBI (31–38) in S. aureus and preliminary biological evaluation in animal model of infection was studied. Initial clinical evaluation in three patients with suspected infection was carried out. Results68Ga-NOTA-UBI (31–38) was prepared in high radiochemical yields and high radiochemical purity. In vitro evaluation of 68Ga-NOTA-UBI (31–38) complex in S. aureus confirmed specificity of the agent for bacteria. Biodistribution studies with 68Ga-NOTA-UBI (31–38) revealed specific uptake of the complex in infected muscle compared to inflamed muscle with T/NT ratio of 3.24 ± 0.7 at 1 h post-injection. Initial clinical evaluation in two patients with histopathologically confirmed infective foci conducted after intravenous injection of 130–185 MBq of 68Ga-NOTA-UBI (31–38) and imaging at 45–60 min post-injection revealed specific uptake at the sites of infection and clearance from vital organs. No uptake of tracer was observed in suspected infection foci in one patient, which was proven to be aseptic and served as negative control. ConclusionThis is the first report on 68Ga labeled NOTA-UBI (31–38) fragment for prospective infection imaging.

Prospective of 68Ga Radionuclide Contribution to the Development of Imaging Agents for Infection and Inflammation.

During the last decade, the utilization of 68Ga for the development of imaging agents has increased considerably with the leading position in the oncology. The imaging of infection and inflammation is lagging despite strong unmet medical needs. This review presents the potential routes for the development of 68Ga-based agents for the imaging and quantification of infection and inflammation in various diseases and connection of the diagnosis to the treatment for the individualized patient management.