First-in-human infection imaging with 89Zr-labelled leukocytes and comparison of scan quality with [99mTc]Tc-HMPAO-labelled leukocytes.

Introduction: Nuclear medicine infection imaging is routinely performed with the use of leukocytes radiolabelled with technetium-99m hexamethylpropyleneamine oxime ([99mTc]Tc-HMPAO) and single-photon emission computed tomography (SPECT). Positron emission tomography (PET) is more sensitive than SPECT and results in higher-quality images. Zirconium-89 (89Zr) is a positron emitter with a half-life of 78.4 h, which translates to the biological half-life and slow biodistribution of intact cells and allows delayed PET imaging for more accurate biodistribution of the labelled leukocytes to infection foci. A first-in-human study with [89Zr]Zr-oxine-leukocytes in four healthy volunteers was reported in 2022. Our first-in-human study utilising the cell surface labelling approach aimed to image infection in patients with the use of 89Zr-labelled leukocytes, using p-isothiocyanatobenzyl-desferrioxamine B (Df-Bz-NCS) as a bifunctional chelating agent, and to compare the scan quality and biodistribution of [89Zr]Zr-Df-Bz-NCS-labelled leukocytes on PET images to SPECT images obtained with [99mTc]Tc-HMPAO-labelled leukocytes. Methods: Leukocytes were isolated from whole-blood samples of eight patients with clinically and/or radiologically confirmed infection. Isolated leukocytes were labelled with [99mTc]Tc-HMPAO according to standardised methods, and [89Zr]Zr-Df-Bz-NCS according to our previously published radiolabelling method. Whole-body SPECT imaging was performed 2 and 18 h post injection of [99mTc]Tc-HMPAO-labelled leukocytes, and whole-body PET/CT was performed 3 and 24 h post injection of [89Zr]Zr-Df-Bz-NCS-labelled leukocytes in seven patients. Results: Successful [89Zr]Zr-Df-Bz-NCS-leukocyte labelling was achieved. High labelling efficiencies were obtained (81.7% ± 3.6%; n = 8). A mean high viability of [89Zr]Zr-Df-Bz-NCS-labelled leukocytes was observed (88.98% ± 12.51%). The [89Zr]Zr-Df-Bz-NCS-leukocyte labelling efficiency was not significantly affected by the white blood cell count of the patient. The performance of [99mTc]Tc-HMPAO- and [89Zr]Zr-Df-Bz-NCS-labelled leukocytes, in terms of the ability to accurately detect infection, were similar in two out of seven patients, and [99mTc]Tc-HMPAO-labelled leukocytes outperformed [89Zr]Zr-Df-Bz-NCS-labelled leukocytes in one patient with femoral osteomyelitis. However, in two cases of pulmonary pathology, [89Zr]Zr-Df-Bz-NCS-labelled leukocytes demonstrated improved pathological uptake. No skeletal activity was observed in any of the patients imaged with [89Zr]Zr-Df-Bz-NCS-labelled leukocytes, illustrating the in vivo stability of the radiolabel. Discussion: Although the [89Zr]Zr-Df-Bz-NCS-leukocyte labelling aspect of this study was noteworthy, infection imaging did not yield convincingly positive results due to the pulmonary trapping of intravenously administered [89Zr]Zr-Df-Bz-NCS-labelled leukocytes.

Radiotracers for in situ infection imaging: Experimental considerations for in vitro microbial uptake of gallium-68-labeled siderophores.

In vitro screening of gallium-68(68Ga)-siderophores in pathogens relevant to infections is valuable for determining species specificity, their effect on cell viability, and potential clinical applications. As the recognition and internalization of siderophores relies on the presence of receptor- and/or siderophore-binding proteins, the level of uptake can vary between species. Here, we report in vitro uptake validation in Escherichia coli with its native siderophore, enterobactin (ENT) ([68Ga]Ga-ENT), considering different experimental factors. Compared with other reporting methods of uptake, '% Added dose/109 CFU/mL (% AD/109 CFU/mL),' considering the total viable count, showed a better comparison among microbial species. Later, in vitro screening with [68Ga]Ga-desferrioxamine B (DFO-B) showed high uptake by Staphylococcus aureus and S. epidermidis; moderate uptake by Pseudomonas aeruginosa; poor uptake by E. coli, Candida albicans, and Aspergillus fumigatus; and no uptake by Enterococcus faecalis and C. glabrata. Except for S. epidermidis, [68Ga]Ga-DFO-B did not reduce the cell viability.

Vasogenic Edema Covering the Brain Surface in a Case of Severe Meningoencephalitis Due to Varicella-Zoster Virus Infection.

Meningoencephalitis caused by varicella-zoster virus (VZV) is a serious condition requiring prompt antiviral treatments, but magnetic resonance imaging (MRI) findings are often normal, limiting early diagnostic utility. We report a case of severe VZV-associated meningoencephalitis characterized by diffuse T2 hyperintense lesions covering the brain surface on MRI, presumed to be vasogenic edema. An immunocompetent 78-year-old Japanese woman presented with a disturbance of consciousness preceded by seven days of headache. On admission, she was in a semi-coma with intermittent convulsive seizures and had a localized skin rash with blisters on her back. Brain MRI showed diffuse T2 hyperintensity on the brain surface with an elevated apparent diffusion coefficient and the marked gadolinium-contrast enhancement of the pia-arachnoid membrane and vessel walls. Polymerase chain reaction using cerebrospinal fluid revealed the presence of VZV, and then she was diagnosed with VZV-associated meningoencephalitis. Treatment with acyclovir and corticosteroids was initiated, leading to some clinical improvement; however, the patient developed acute non-occlusive mesenteric ischemia and died on the 10th day of hospitalization. The characteristic MRI findings observed in our patient may be useful in considering the pathogenesis and early diagnosis of this rare entity.

[68Ga]Ga-Schizokinen, a Potential Radiotracer for Selective Bacterial Infection Imaging.

Gallium-68-labeled siderophores as radiotracers have gained interest for the development of in situ infection-specific imaging diagnostics. Here, we report radiolabeling, in vitro screening, and in vivo pharmacokinetics (PK) of gallium-68-labeled schizokinen ([68Ga]Ga-SKN) as a new potential radiotracer for imaging bacterial infections. We radiolabeled SKN with ≥95% radiochemical purity. Our in vitro studies demonstrated its hydrophilic characteristics, neutral pH stability, and short-term stability in human serum and toward transchelation. In vitro uptake of [68Ga]Ga-SKN by Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and S. epidermidis, but no uptake by Candida glabrata, C. albicans, or Aspergillus fumigatus, demonstrated its specificity to bacterial species. Whole-body [68Ga]Ga-SKN positron emission tomography (PET) combined with computerized tomography (CT) in healthy mice showed rapid renal excretion with no or minimal organ uptake. The subsequent ex vivo biodistribution resembled this fast PK with rapid renal excretion with minimal blood retention and no major organ uptake and showed some dissociation of the tracer in the urine after 60 min postinjection. These findings warrant further evaluation of [68Ga]Ga-SKN as a bacteria-specific radiotracer for infection imaging.

18F-FDG PET CT in cardiac device infections - A Case series.

With the increasing number of interventional cardiology procedures, the number of cardiac device infections (including pacemakers, prosthetic valves, coronary and aortic stents) have also increased. These infections can cause significant morbidity and can even lead to mortality if not managed promptly. If suspected clinically the first-line imaging modality is Trans-Thoracic Echocardiography, while Transesophageal Echocardiography is also used in selected cases. The confirmation of a cardiac device infection is mostly done with the help of blood or pus culture. Even though Echocardiography is a very efficient technique for the evaluation of the heart, it cannot differentiate infection from thrombus or fibrosis. With the increasing availability of Positron Emission Tomography CT (PET CT) machines worldwide, the use of 18F-FDG PET CT for infection imaging has gained traction, especially for cardiac device infection. Most of the recent studies show a good diagnostic accuracy of 18F-FDG PET CT with many of the recent diagnostic and management guidelines now acknowledging its role, especially in equivocal cases. We present six such cases where 18F-FDG PET CT provided valuable information either for diagnosis, confirming the presence of infection, delineating extent, therapy response or sometimes even helping appropriate treatment decision making in patients with suspected cardiac device infection.

Recently developed radiopharmaceuticals for bacterial infection imaging.

BACKGROUND: Infection remains a major cause of morbidity and mortality, regardless of advances in antimicrobial therapy and improved knowledge of microorganisms. With the major global threat posed by antimicrobial resistance, fast and accurate diagnosis of infections, and the reliable identification of intractable infection, are becoming more crucial for effective treatment and the application of antibiotic stewardship. Molecular imaging with the use of nuclear medicine allows early detection and localisation of infection and inflammatory processes, as well as accurate monitoring of treatment response. There has been a continuous search for more specific radiopharmaceuticals to be utilised for infection imaging. This review summarises the most prominent discoveries in specifically bacterial infection imaging agents over the last five years, since 2019. MAIN BODY: Some promising new radiopharmaceuticals evaluated in patient studies are reported here, including radiolabelled bacterial siderophores like [68Ga]Ga-DFO-B, radiolabelled antimicrobial peptide/peptide fragments like [68Ga]Ga-NOTA-UBI29-41, and agents that target bacterial synthesis pathways (folic acid and peptidoglycan) like [11C]para-aminobenzoic acid and D-methyl-[11C]-methionine, with clinical trials underway for [18F]fluorodeoxy-sorbitol, as well as for 11C- and 18F-labelled trimethoprim. CONCLUSION: It is evident that a great deal of effort has gone into the development of new radiopharmaceuticals for infection imaging over the last few years, with remarkable progress in preclinical investigations. However, translation to clinical trials, and eventually clinical Nuclear Medicine practice, is apparently slow. It is the authors' opinion that a more structured and harmonised preclinical setting and well-designed clinical investigations are the key to reliably evaluate the true potential of the newly proposed infection imaging agents.

Synthesis and preclinical evaluation of novel 18F-vancomycin-based tracers for the detection of bacterial infections using positron emission tomography.

INTRODUCTION: Bacterial infections are a major problem in medicine, and the rapid and accurate detection of such infections is essential for optimal patient outcome. Bacterial infections can be diagnosed by nuclear imaging, but most currently available modalities are unable to discriminate infection from sterile inflammation. Bacteria-targeted positron emission tomography (PET) tracers have the potential to overcome this hurdle. In the present study, we compared three 18F-labelled PET tracers based on the clinically applied antibiotic vancomycin for targeted imaging of Gram-positive bacteria. METHODS: [18F]FB-NHS and [18F]BODIPY-FL-NHS were conjugated to vancomycin. The resulting conjugates, together with our previously developed [18F]PQ-VE1-vancomycin, were tested for stability, lipophilicity, selective binding to Gram-positive bacteria, antimicrobial activity and biodistribution. For the first time, the pharmacokinetic properties of all three tracers were compared in healthy animals to identify potential binding sites. RESULTS: [18F]FB-vancomycin, [18F]BODIPY-FL-vancomycin, and [18F]PQ-VE1-vancomycin were successfully synthesized with radiochemical yields of 11.7%, 2.6%, and 0.8%, respectively. [18F]FB-vancomycin exhibited poor in vitro and in vivo stability and, accordingly, no bacterial binding. In contrast, [18F]BODIPY-FL-vancomycin and [18F]PQ-VE1-vancomycin showed strong and specific binding to Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), which was outcompeted by unlabeled vancomycin only at concentrations exceeding clinically relevant vancomycin blood levels. Biodistribution showed renal clearance of [18F]PQ-VE1-vancomycin and [18F]BODIPY-FL-vancomycin with low non-specific accumulation in muscles, fat and bones. CONCLUSION: Here we present the synthesis and first evaluation of the vancomycin-based PET tracers [18F]BODIPY-FL-vancomycin and [18F]PQ-VE1-vancomycin for image-guided detection of Gram-positive bacteria. Our study paves the way towards real-time bacteria-targeted diagnosis of soft tissue and implant-associated infections that are oftentimes caused by Gram-positive bacteria, even after prophylactic treatment with vancomycin.

Expanding a peptide-covalent probe hybrid for PET imaging of S. aureus driven focal infections.

BACKGROUND: The urgent demand for innovative theranostic strategies to combat bacterial resistance to antibiotics is evident, with substantial implications for global health. Rapid diagnosis of life-threatening infections can expedite treatment, improving patient outcomes. Leveraging diagnostic modalities i.e., positron emission tomography (PET) and single photon emission computed tomography (SPECT) for detecting focal infections has yielded promising results. Augmenting the sensitivity of current PET and SPECT tracers could enable effective imaging of pathogenic bacteria, including drug-resistant strains.UBI (29-41), an antimicrobial peptide (AMP) fragment recognizes the S. aureus membrane through electrostatic binding. Radiolabeled UBI (29-41) is a promising SPECT and PET-based tracer for detecting focal infections. 2-APBA (2-acetyl-phenyl-boronic acid), a non-natural amino acid, specifically targets lysyl-phosphatidyl-glycerol (lysyl-PG) on the S. aureus membranes, particularly in AMP-resistant strains. We propose that combining UBI with 2-APBA could enhance the diagnostic potential of radiolabeled UBI. RESULTS: Present work aimed to compare the diagnostic potential of two radiolabeled peptides, namely UBI (29-41) and 2-APBA modified UBI (29-41), referred to as UBI and UBI-APBA. APBA modification imparted antibacterial activity to the initially non-bactericidal UBI against S. aureus by inducing a loss of membrane potential. The antibacterial activity demonstrated by UBI-APBA can be ascribed to the synergistic interaction of both UBI and UBI-APBA on the bacterial membrane. To enable PET imaging, we attached the chelator 1,4,7-triazacyclononane 1-glutaric acid 4,7-acetic acid (NODAGA) to the peptides for complexation with the positron emitter Gallium-68 (68Ga). Both NODAGA conjugates were radiolabeled with 68Ga with high radiochemical purity. The resultant 68Ga complexes were stable in phosphate-buffered saline and human serum. Uptake of these complexes was observed in S. aureus but not in mice splenocytes, indicating the selective nature of their interaction. Additionally, the APBA conjugate exhibited superior uptake in S. aureus while preserving the selectivity of the parent peptide. Furthermore, [68Ga]Ga-UBI-APBA demonstrated accumulation at the site of infection in rats, with an improved target-to-non-target ratio, as evidenced by ex-vivo biodistribution and PET imaging. CONCLUSIONS: Our findings suggest that linking UBI, as well as AMPs in general, with APBA shows promise as a strategy to augment the theranostic potential of these molecules.

Radiosynthesis and Bioevaluation of 99mTc-Labeled Isocyanide Ubiquicidin 29-41 Derivatives as Potential Agents for Bacterial Infection Imaging.

To develop a novel 99mTc-labeled ubiquicidin 29-41 derivative for bacterial infection single-photon emission computed tomography (SPECT) imaging with improved target-to-nontarget ratio and lower nontarget organ uptake, a series of isocyanide ubiquicidin 29-41 derivatives (CNnUBI 29-41, n = 5-9) with different carbon linkers were designed, synthesized and radiolabeled with the [99mTc]Tc(I)+ core, [99mTc][Tc(I)(CO)3(H2O)3]+ core and [99mTc][Tc(V)N]2+ core. All the complexes are hydrophilic, maintain good stability and specifically bind Staphylococcus aureus in vitro. The biodistribution in mice with bacterial infection and sterile inflammation demonstrated that [99mTc]Tc-CN5UBI 29-41 was able to distinguish bacterial infection from sterile inflammation, which had an improved abscess uptake and a greater target-to-nontarget ratio. SPECT imaging study of [99mTc]Tc-CN5UBI 29-41 in bacterial infection mice showed that there was a clear accumulation in the infection site, suggesting that this radiotracer could be a potential radiotracer for bacterial infection imaging.

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.

A fluorogenic micrococcal nuclease-based probe for fast detection and optical imaging of Staphylococcus aureus in prosthetic joint and fracture-related infections.

PURPOSE: Staphylococcus aureus is the most common and impactful multi-drug resistant pathogen implicated in (periprosthetic) joint infections (PJI) and fracture-related infections (FRI). Therefore, the present proof-of-principle study was aimed at the rapid detection of S. aureus in synovial fluids and biofilms on extracted osteosynthesis materials through bacteria-targeted fluorescence imaging with the 'smart-activatable' DNA-based AttoPolyT probe. This fluorogenic oligonucleotide probe yields large fluorescence increases upon cleavage by micrococcal nuclease, an enzyme secreted by S. aureus. METHODS: Synovial fluids from patients with suspected PJI and extracted osteosynthesis materials from trauma patients with suspected FRI were inspected for S. aureus nuclease activity with the AttoPolyT probe. Biofilms on osteosynthesis materials were imaged with the AttoPolyT probe and a vancomycin-IRDye800CW conjugate (vanco-800CW) specific for Gram-positive bacteria. RESULTS: 38 synovial fluid samples were collected and analyzed. Significantly higher fluorescence levels were measured for S. aureus-positive samples compared to, respectively, other Gram-positive bacterial pathogens (p < 0.0001), Gram-negative bacterial pathogens (p = 0.0038) and non-infected samples (p = 0.0030), allowing a diagnosis of S. aureus-associated PJI within 2 h. Importantly, S. aureus-associated biofilms on extracted osteosynthesis materials from patients with FRI were accurately imaged with the AttoPolyT probe, allowing their correct distinction from biofilms formed by other Gram-positive bacteria detected with vanco-800CW within 15 min. CONCLUSION: The present study highlights the potential clinical value of the AttoPolyT probe for fast and accurate detection of S. aureus infection in synovial fluids and biofilms on extracted osteosynthesis materials.

Imaging the Bacterial Cell Wall Using N-Acetyl Muramic Acid-Derived Positron Emission Tomography Radiotracers.

Imaging infections in patients is challenging using conventional methods, motivating the development of positron emission tomography (PET) radiotracers targeting bacteria-specific metabolic pathways. Numerous techniques have focused on the bacterial cell wall, although peptidoglycan-targeted PET tracers have been generally limited to the short-lived carbon-11 radioisotope (t1/2 = 20.4 min). In this article, we developed and tested new tools for infection imaging using an amino sugar component of peptidoglycan, namely, derivatives of N-acetyl muramic acid (NAM) labeled with the longer-lived fluorine-18 (t1/2 = 109.6 min) radioisotope. Muramic acid was reacted directly with 4-nitrophenyl 2-[18F]fluoropropionate ([18F]NFP) to afford the enantiomeric NAM derivatives (S)-[18F]FMA and (R)-[18F]FMA. Both diastereomers were easily isolated and showed robust accumulation by human pathogens in vitro and in vivo, including Staphylococcus aureus. These results form the basis for future clinical studies using fluorine-18-labeled NAM-derived PET radiotracers.

89Zr-leukocyte labelling for cell trafficking: in vitro and preclinical investigations.

BACKGROUND: The non-invasive imaging of leukocyte trafficking to assess inflammatory areas and monitor immunotherapy is currently generating great interest. There is a need to develop more robust cell labelling and imaging approaches to track living cells. Positron emission tomography (PET), a highly sensitive molecular imaging technique, allows precise signals to be produced from radiolabelled moieties. Here, we developed a novel leukocyte labelling approach with the PET radioisotope zirconium-89 (89Zr, half-life of 78.4 h). Experiments were carried out using human leukocytes, freshly isolated from whole human blood. RESULTS: The 89Zr-leukocyte labelling efficiency ranged from 46 to 87% after 30-60 min. Radioactivity concentrations of labelled cells were up to 0.28 MBq/1 million cells. Systemically administered 89Zr-labelled leukocytes produced high-contrast murine PET images at 1 h-5 days post injection. Murine biodistribution data showed that cells primarily distributed to the lung, liver, and spleen at 1 h post injection, and are then gradually trafficked to liver and spleen over 5 days. Histological analysis demonstrated that exogenously 89Zr-labelled human leukocytes were present in the lung, liver, and spleen at 1 h post injection. However, intravenously injected free [89Zr]Zr4+ ion showed retention only in the bone with no radioactivity in the lung at 5 days post injection, which implied good stability of radiolabelled leukocytes in vivo. CONCLUSIONS: Our study presents a stable and generic radiolabelling technique to track leukocytes with PET imaging and shows great potential for further applications in inflammatory cell and other types of cell trafficking studies.

Imaging-Selected Host Responses in the Context of Infections.

Recently developed molecular imaging approaches can be used to visualize specific host responses and pathology in a quest to image infections where few microbe-specific tracers have been developed and in recognition that host responses contribute to morbidity and mortality in their own right. Here we highlight several recent examples of these imaging approaches adapted for imaging infections. The early successes and new avenues described here encompass diverse imaging modalities and leverage diverse aspects of the host response to infection-including inflammation, tissue injury and healing, and key nutrients during host-pathogen interactions. Clearly, these approaches merit further preclinical and clinical study as they are complementary and orthogonal to the pathogen-focused imaging modalities currently under investigation.

Evaluating the Performance of Pathogen-Targeted Positron Emission Tomography Radiotracers in a Rat Model of Vertebral Discitis-Osteomyelitis.

BACKGROUND: Vertebral discitis-osteomyelitis (VDO) is a devastating infection of the spine that is challenging to distinguish from noninfectious mimics using computed tomography and magnetic resonance imaging. We and others have developed novel metabolism-targeted positron emission tomography (PET) radiotracers for detecting living Staphylococcus aureus and other bacteria in vivo, but their head-to-head performance in a well-validated VDO animal model has not been reported. METHODS: We compared the performance of several PET radiotracers in a rat model of VDO. [11C]PABA and [18F]FDS were assessed for their ability to distinguish S aureus, the most common non-tuberculous pathogen VDO, from Escherichia coli. RESULTS: In the rat S aureus VDO model, [11C]PABA could detect as few as 103 bacteria and exhibited the highest signal-to-background ratio, with a 20-fold increased signal in VDO compared to uninfected tissues. In a proof-of-concept experiment, detection of bacterial infection and discrimination between S aureus and E coli was possible using a combination of [11C]PABA and [18F]FDS. CONCLUSIONS: Our work reveals that several bacteria-targeted PET radiotracers had sufficient signal to background in a rat model of S aureus VDO to be potentially clinically useful. [11C]PABA was the most promising tracer investigated and warrants further investigation in human VDO.

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.

Preclinical evaluation of 2-[18F]fluorodeoxysorbitol as a tracer for targeted imaging of Enterobacterales infection.

Fluorine-18-fluorodeoxyglucose ([18F]FDG) positron emission tomography (18F-FDG-PET) is widely used for the detection of inflammatory and infectious diseases. Although this modality has proven to be a useful diagnostic tool, reliable distinction of bacterial infection from sterile inflammation or even from a malignancy remains challenging. Therefore, there is a need for bacteria-specific tracers for PET imaging that facilitate a reliable distinction of bacterial infection from other pathology. The present study was aimed at exploring the potential of 2-[18F]-fluorodeoxysorbitol ([18F]FDS) as a tracer for detection of Enterobacterales infections. Sorbitol is a sugar alcohol that is commonly metabolized by bacteria of the Enterobacterales order, but not by mammalian cells, which makes it an attractive candidate for targeted bacterial imaging. The latter is important in view of the serious clinical implications of infections caused by Enterobacterales. Here we demonstrate that sorbitol-based PET can be applied to detect a broad range of clinical bacterial isolates not only in vitro, but also in blood and ascites samples from patients suffering from Enterobacterales infections. Notably, the possible application of [18F]FDS is not limited to Enterobacterales since Pseudomonas aeruginosa and Corynebacterium jeikeium also showed substantial uptake of this tracer. We conclude that [18F]FDS is a promising tracer for PET-imaging of infections caused by a group of bacteria that can cause serious invasive disease.

Leukocyte Labeling with Tc-99m-HMPAO: The Role of Leucocyte Numbers and Medication on the Labeling Efficacy and Image Quality.

Objectives: The aim of this study is to evaluation of Tc-99m-hexamethylpropyleneamineoxime (HMPAO)-labeled leukocytes in terms of radiochemical, biochemical, and microbiological quality controls and to examine the effect of leukocyte numbers of the blood obtained from patients and the medications currently used by the patients on the radiochemical yields of Tc-99m-HMPAO-labeled leukocytes, and imaging quality was evaluated. Methods: Thirty paients were included in our study who applied to Istanbul University-Cerrahpasa, Cerrahpasa Faculty of Medicine, Department of Nuclear Medicine for Tc-99m-HMPAO-labeled leukocyte scintigraphy. Devices and chemicals used in the preparation of Tc-99m-HMPAO-labeled laukocytes were compared with other nuclear medicine clinics. Tc-99m-HMPAO-labeled leukocytes were evaluated in terms of radiochemical, biochemical, and microbiological quality controls. The effect of leukocyte numbers of the blood obtained from patients and the medications currently used by the patients on the radiochemical yields of Tc-99m-HMPAO-labeled leukocytes and imaging quality was evaluated. Results: The pH range of Tc-99m-HMPAO was 6-8 and the radiochemical purity was 90±2.04% (n=30), the radiochemical yield of Tc-99m-HMPAO-labeled leukocytes was 51±2.18% (n=30), the radiolabeling yield of Tc-99m-HMPAO-labeled leukocyte increased as the amount of white blood cell in the blood increased and whether the patients used any antibiotic, blood thinners, insulin and blood pressure medications did not affect the radiolabeling yield of Tc-99m-HMPAO-labeled leukocytes. The number of erythrocytes were removed at a rate of >99% in LPR by starch solution (6% HES; in the hemocytometric examination of Tc-99m-HMPAO-labeled leukocytes performed zeroth and 4th h, living/dead cell ratio was found 97.5% and the product was sterile. Conclusion: Tc-99m-HMPAO was labeled with leukocytes successfully, and Tc-99m-HMPAO-labeled leukocytes was safely injected to the patients as sterile without loss of vitality and aggregation.

Synthesis and Bioevaluation of Novel Technetium-99m-Labeled Complexes with Norfloxacin HYNIC Derivatives for Bacterial Infection Imaging.

To seek a novel 99mTc-labeled quinolone derivative for bacterial infection SPECT imaging that aims to lower nontarget organ uptake, a novel norfloxacin 6-hydrazinoicotinamide (HYNIC) derivative (HYNICNF) was designed and synthesized. It was radiolabeled with different coligands, such as tricine, trisodium triphenylphosphine-3,3',3″-trisulfonate (TPPTS), sodium triphenylphosphine-3-monosulfonate (TPPMS), and ethylenediamine-N,N'-diacetic acid (EDDA), to obtain three 99mTc-labeled norfloxacin HYNIC complexes, namely, [99mTc]Tc-tricine-TPPTS-HYNICNF, [99mTc]Tc-tricine-TPPMS-HYNICNF, and [99mTc]Tc-EDDA-HYNICNF. These complexes were purified (RCP > 95%) and evaluated in vitro and in vivo for targeting bacteria. All three complexes are hydrophilic, maintain good stability, and specifically bind Staphylococcus aureus in vitro. The biodistribution in mice with bacterial infection demonstrated that [99mTc]Tc-EDDA-HYNICNF showed a higher abscess uptake and lower nontarget organ uptake and was able to distinguish bacterial infection and sterile inflammation. Single photon emission computed tomography (SPECT) image study in bacterial infection mice showed there was a visible accumulation in the infection site, suggesting that [99mTc]Tc-EDDA-HYNICNF is a potential radiotracer for bacterial infection imaging.

A decade of ubiquicidin development for PET imaging of infection: A systematic review.

BACKGROUND: Ubiquicidin is a peptide fragment with selective binding to negatively charged bacterial cell membranes. Besides its earlier labelling with gamma emitting radionuclides, it has been labelled with Positron Emission Tomography (PET) radionuclides in the last decade for imaging infection and distinguishing infectious disease from sterile inflammation. This systematic review aims to evaluate the technology readiness level of PET based ubiquicidin radiopharmaceuticals. METHODS: Two independent researchers reviewed all articles and abstracts pertaining ubiquicidin and PET imaging that are currently available. Scopus, Google Scholar and PubMed/Medline were used in the search. Upon completion of the literature search all articles and abstracts were evaluated and duplicates were excluded. All non-PET articles as well as review articles without new data were deemed ineligible. RESULTS: From a total of 17 papers and 10 abstracts the studies were grouped into development, preclinical and clinical studies. Development was published in 15/17 (88%) publications and 6/10 (60%) abstracts, preclinical applications in 9/17 (53%) publications and 1/10 (10%) of abstracts. Finally, clinical studies made up 6/17 (35%) of full publications and 4/10 (40%) of the available abstracts. Development results were the most abundant. All the findings in the different areas of development of ubiquicidin as PET radiopharmaceutical are summarized in this paper. CONCLUSION: Labelling procedures are generally uncomplicated and relatively fast and there are indications of adequate product stability. The production of PET radiopharmaceuticals based on UBI will therefore not be a barrier for clinical introduction of this technology. Systematization and unification of criteria for preclinical imaging and larger clinical trials are needed to ensure the translation of this radiopharmaceutical into the clinic. Therefore a conclusion with regards to the clinical relevance of ubiquicidin based PET is not yet possible.