Detection of sites of infection in mice using 99mTc-labeled PN(2)S-PEG conjugated to UBI and 99mTc-UBI: a comparative biodistribution study

Current developments and prospects of the antibiotic delivery systems

Antibiotics have remained the cornerstone for the treatment of bacterial infections ever since their discovery in the twentieth century. The uproar over antibiotic resistance among bacteria arising from genome plasticity and biofilm development has rendered current antibiotic therapies ineffective, urging the development of innovative therapeutic approaches. The development of antibiotic resistance among bacteria has further heightened the clinical failure of antibiotic therapy, which is often linked to its low bioavailability, side effects, and poor penetration and accumulation at the site of infection. In this review, we highlight the potential use of siderophores, antibodies, cell-penetrating peptides, antimicrobial peptides, bacteriophages, and nanoparticles to smuggle antibiotics across impermeable biological membranes to achieve therapeutically relevant concentrations of antibiotics and combat antimicrobial resistance (AMR). We will discuss the general mechanisms via which each delivery system functions and how it can be tailored to deliver antibiotics against the paradigm of mechanisms underlying antibiotic resistance.

Peptide derived from plant defensins: A promising 68Ga radiolabelled agent for diagnostic of infection foci in PET

The development of new radiopharmaceuticals for the detection of hidden infection foci has great relevance for early detection and the selection of the correct treatment, particularly in immunosuppressed patients. In that sense, the labelling of antimicrobial peptides (AMPs) that are capable of binding specifically to the pathogenic microorganism which causes the infection, should provide a sufficiently specific agent, able to distinguish an infection from a sterile inflammation. Defensins are particularly interesting molecules with antimicrobial activity, the EcgDf1 defensin was identified from the genome of a Uruguayan native plant, Erythrina crista-galli, the 'Ceibo' tree. Our group has previously reported a synthetic biologically active short analogue EcgDf21 (ERFTGGHCRGFRRRCFCTKHC) successfully labelled with 99mTc. Herein we present a shorter analogue which also preserves the γ-core domain, as a pharmacophore for a potential infection detection agent. This peptide was derivatized with the bifunctional chelating agent 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) through a lysine linker in the amino-terminal group (NOTA-KGHCRGFRRRC) and radiolabelled with 68Ga ([68Ga]Ga-NOTA-K-EcgDf1(10)). The [68Ga]Ga-NOTA-K-EcgDf1(10) labelling procedure rendered a product with high radiochemical purity and stability in the labelling milieu. The Log P value indicated that the complex has a hydrophilic behaviour, confirmed by the biodistribution profile. The [68Ga]Ga-NOTA-K-EcgDf1(10) complex demonstrated specific binding to cultures of Candida albicans and Aspergillus niger. Its biodistribution showed renal elimination and low accumulation in the rest of the body. It was possible to successfully differentiate sterile inflammation from infection by PET images in nude mice with a target/non-target ratio of 3.3 for C. albicans and 3.7 for A. niger, respectively.

Biodistribution of Native and Nanoformulated Innate Defense Regulator Peptide 1002

Innate defense regulator-1002 (IDR-1002) is a synthetic peptide with promising immunomodulatory and antibiofilm properties. An appreciable body of work exists around its mechanism of action at the cellular and molecular level, along with its efficacy across several infection and inflammation models. However, little is known about its absorption, distribution, and excretion in live organisms. Here, we performed a comprehensive biodistribution assessment with a gallium-67 radiolabeled derivative of IDR-1002 using nuclear tracing techniques. Various dose levels of the radiotracer (2-40 mg/kg) were administered into the blood, peritoneal cavity, and subcutaneous tissue, or instilled into the lungs. The peptide was well tolerated at all subcutaneous and intraperitoneal doses, although higher levels were associated with delayed absorption kinetics and precipitation of the peptide within the tissues. Low intratracheal doses were rapidly absorbed systemically, and small increases in the dose level were lethal. Intravenous doses were rapidly cleared from the blood at lower levels, and upon escalation, were toxic with a high proportion of the dose accumulating within the lung tissue. To improve biocompatibility and prolong its circulation within the blood, IDR-1002 was further formulated onto high molecular weight hyperbranched polyglycerol (HPG) polymers. Constructs prepared at 5:1 and 10:1 peptide-to-polymer ratios were colloidally stable, maintained the biological profile of the peptide payload and helped reduce red blood cell lysis. The 5:1 construct circulated well in the blood, but higher peptide loading was associated with rapid clearance by the reticuloendothelial system. Many peptides face pharmacokinetic and biocompatibility challenges, but formulations such as those with HPG have the potential to overcome these limitations.

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.

[99m Tc]Tc-HYNIC-EcgDf21: A defensin short analogue with potential application in infection foci imaging

Opportunistic infections are a problem of great relevance in public health and the precise detection and localization of infection in the early stages of the disease is of great importance for patient management as well as cost containment. Our proposal seeks to contribute to developing a new agent that meets the needs of diagnosis and follow-up of fungal and bacterial infections, focused on the design of a radiotracer with the potential for recognition of hidden infection foci. Defensins are plant antimicrobial peptides that not only show activity against plant pathogens but also against human ones. A short analogue of EcgDf1 defensin, EcgDf21d (NH₂ -ERFTGGHCRGFRRRCFCTKHC-COOH), was labelled through the formation of a ^99m Tc-HYNIC complex which was assessed for physicochemical and biological behaviour both in vitro and in vivo. The [^99m Tc]Tc-HYNIC-EcgDf21 labelling procedure rendered a single product with remarkably high RCP and stability in the labelling milieu. The Log p value indicated that [^99m Tc]Tc-HYNIC-EcgDf21 has a hydrophilic behaviour, confirmed by the biodistribution profiles. The optimal uptake value was obtained for Candida albicans infection model reaching a lesion/muscle ratio of 3, this correlates with in vitro binding studies, and the lesion can be definitely observed in the scintigraphic images.

Microbiota in vivo imaging approaches to study host-microbe interactions in preclinical and clinical setting

In vivo imaging in preclinical and clinical settings can enhance knowledge of the host-microbiome interactions. Imaging techniques are a crucial node between findings at the molecular level and clinical implementation in diagnostics and therapeutics. The purpose of this study was to review existing knowledge on the microbiota in the field of in vivo imaging and provide guidance for future research, emphasizing the critical role that molecular imaging plays in increasing understanding of the host-microbe interaction. Preclinical microbiota animal models lay the foundation for the clinical translatability of novel microbiota-based therapeutics. Adopting animal models in which factors such as host genetic landscape, microbiota profile, and diet can be controlled enables investigating how the microbiota contributes to immunological dysregulation and inflammatory disorders. Current preclinical imaging of gut microbiota relies on models where the bacteria can be isolated, labelled, and re-administered. In vivo, optical imaging, ultrasound and magnetic resonance imaging define the bacteria's biodistribution in preclinical models, whereas nuclear imaging investigates bacterial metabolic activity. For the clinical investigation of microbe-host interactions, molecular nuclear imaging is increasingly becoming a promising approach. Future microbiota research should develop selective imaging probes to investigate in vivo microbiota profiles and individual strains of specific microbes. Preclinical knowledge can be translated into the molecular imaging field with great opportunities for studying the microbiome.

Biodistribution and Toxicity of Innate Defense Regulator 1018 (IDR-1018)

Innate defense regulators (IDRs) are synthetic host-defense peptides (HDPs) with broad-spectrum anti-infective properties, including immunomodulatory, anti-biofilm and direct antimicrobial activities. A lack of pharmacokinetic data about these peptides hinders their development and makes it challenging to fully understand how they work in vivo since their mechanism of action is dependent on tissue concentrations of the peptide. Here, we set out to define in detail the pharmacokinetics of a well-characterized IDR molecule, IDR-1018. To make the peptide traceable, it was radiolabeled with the long-lived gamma-emitting isotope gallium-67. After a series of bench-top characterizations, the radiotracer was administered to healthy mice intravenously (IV) or subcutaneously (SQ) at various dose levels (2.5-13 mg/kg). Nuclear imaging and ex-vivo biodistributions were used to quantify organ and tissue uptake of the radiotracer over time. When administered as an IV bolus, the distribution profile of the radiotracer changed as the dose was escalated. At 2.5 mg/kg, the peptide was well-tolerated, poorly circulated in the blood and was cleared predominately by the reticuloendothelial system. Higher doses (7 and 13 mg/kg) as an IV bolus were almost immediately lethal due to respiratory arrest; significant lung uptake of the radiotracer was observed from nuclear scans of these animals, and histological examination found extensive damage to the pulmonary vasculature and alveoli. When administered SQ at a dose of 3 mg/kg, radiolabeled IDR-1018 was rapidly absorbed from the site of injection and predominately cleared renally. Apart from the SQ injection site, no other tissue had a concentration above the minimum inhibitory concentration that would enable this peptide to exert direct antimicrobial effects against most pathogenic bacteria. Tissue concentrations were sufficient however to disrupt microbial biofilms and alter the host immune response. Overall, this study demonstrated that the administration of synthetic IDR peptide in vivo is best suited to local administration which avoids some of the issues associated with peptide toxicity that are observed when administered systemically by IV injection, an issue that will have to be addressed through formulation.

Oxidized phospholipids affect small intestine neuromuscular transmission and serotonergic pathways in juvenile mice

BACKGROUND

Oxidized phospholipid derivatives (OxPAPCs) act as bacterial lipopolysaccharide (LPS)-like damage-associated molecular patterns. OxPAPCs dose-dependently exert pro- or anti-inflammatory effects by interacting with several cellular receptors, mainly Toll-like receptors 2 and 4. It is currently unknown whether OxPAPCs may affect enteric nervous system (ENS) functional and structural integrity.

METHODS

Juvenile (3 weeks old) male C57Bl/6 mice were treated intraperitoneally with OxPAPCs, twice daily for 3 days. Changes in small intestinal contractility were evaluated by isometric neuromuscular responses to receptor and non-receptor-mediated stimuli. Alterations in ENS integrity and serotonergic pathways were assessed by real-time PCR and confocal immunofluorescence microscopy in longitudinal muscle-myenteric plexus whole-mount preparations (LMMPs). Tissue levels of serotonin (5-HT), tryptophan, and kynurenine were measured by HPLC coupled to UV/fluorescent detection.

KEY RESULTS

OxPAPC treatment induced enteric gliosis, loss of myenteric plexus neurons, and excitatory hypercontractility, and reduced nitrergic neurotransmission with no changes in nNOS⁺ neurons. Interestingly, these changes were associated with a higher functional response to 5-HT, altered immunoreactivity of 5-HT receptors and serotonin transporter (SERT) together with a marked decrease in 5-HT levels, shifting tryptophan metabolism toward kynurenine production.

CONCLUSIONS AND INFERENCES

OxPAPC treatment disrupted structural and functional integrity of the ENS, affecting serotoninergic tone and 5-HT tissue levels toward a higher kynurenine content during adolescence, suggesting that changes in intestinal lipid metabolism toward oxidation can affect serotoninergic pathways, potentially increasing the risk of developing functional gastrointestinal disorders during critical stages of development.

Recent Progress in the Molecular Imaging of Tumor-Treating Bacteria

Bacterial cancer therapy (BCT) approaches have been extensively investigated because bacteria can show unique features of strong tropism for cancer, proliferation inside tumors, and antitumor immunity, while bacteria are also possible agents for drug delivery. Despite the rapidly increasing number of preclinical studies using BCT to overcome the limitations of conventional cancer treatments, very few BCT studies have advanced to clinical trials. In patients undergoing BCT, the precise localization and quantification of bacterial density in different body locations is important; however, most clinical trials have used subjective clinical signs and invasive sampling to confirm bacterial colonization. There is therefore a need to improve the visualization of bacterial densities using noninvasive and repetitive in vivo imaging techniques that can facilitate the clinical translation of BCT. In vivo optical imaging techniques using bioluminescence and fluorescence, which are extensively employed to image the therapeutic process of BCT in small animal research, are hard to apply to the human body because of their low penetrative power. Thus, new imaging techniques need to be developed for clinical trials. In this review, we provide an overview of the various in vivo bacteria-specific imaging techniques available for visualizing tumor-treating bacteria in BCT studies.

In Vitro and In Vivo Evaluation of 99mTc-Polymyxin B for Specific Targeting of Gram-Bacteria

Background: Infectious diseases are one of the main causes of morbidity and mortality worldwide. Nuclear molecular imaging would be of great help to non-invasively discriminate between septic and sterile inflammation through available radiopharmaceuticals, as none is currently available for clinical practice. Here, we describe the radiolabeling procedure and in vitro and in vivo studies of ^99mTc-polymyxin B sulfate (PMB) as a new single photon emission imaging agent for the characterization of infections due to Gram-negative bacteria. Results: Labeling efficiency was 97 ± 2% with an average molar activity of 29.5 ± 0.6 MBq/nmol. The product was highly stable in saline and serum up to 6 h. In vitro binding assay showed significant displaceable binding to Gram-negative bacteria but not to Gram-positive controls. In mice, ^99mTc-HYNIC-PMB was mainly taken up by liver and kidneys. Targeting studies confirmed the specificity of ^99mTc-HYNIC-PMB obtained in vitro, showing significantly higher T/B ratios for Gram-negative bacteria than Gram-positive controls. Conclusions: In vitro and in vivo results suggest that ^99mTc-HYNIC-PMB has a potential for in vivo identification of Gram-negative bacteria in patients with infections of unknown etiology. However, further investigations are needed to deeply understand the mechanism of action and behavior of ^99mTc-HYNIC-PMB in other animal models and in humans.

Molecular imaging of microbiota-gut-brain axis: searching for the right targeted probe for the right target and disease

The highly bidirectional dialogue between the gut and the brain is markedly stimulated and influenced by the microbiome through integrated neuroendocrine, neurological and immunological processes. Gut microbiota itself communicate with the host producing hormonal intermediates, metabolites, proteins, and toxins responsible for a variety of biochemical and functional inputs, thereby shaping host homeostasis. Indeed, a dysregulated microbiota-gut-brain axis might be the origin of many neuroimmune-mediated disorders, e.g. autism, multiple sclerosis, depression, Alzheimer's and Parkinson's disease, which appear months or even years prior to a diagnosis, corroborating the theory that the pathological process is spread from the gut to the brain. A much deeper comprehension of how commensal microbe can be manipulated to interfere with disease progression is crucial for developing new strategies to diagnose and treat diseases. In recent years, the potential of positron-emission-tomography (PET) in the field of bacteria detection has gained attention. The uptake of several PET tracers has been evaluated to investigate infection pathophysiology, e.g. sterile or pathogen-mediated infection, monitoring of progression, or as a surrogate endpoint in clinical trials. In this minireview, we briefly describe the role of microbiome-gut-brain axis in health and disease and we discuss the imaging modalities and agents that could be applied to study the dynamic interactions between microbiome, gut and brain. These are key aspects in understanding the biochemical lexicon underpinning the microbiome-host crosstalk that would enable the development of diagnostics and therapeutics by targeting the human microbiota.

[99m Tc-HYNIC/EDDA]-MccJ25 antimicrobial peptide analog as a potential radiotracer for detection of infection

Bacterial infections are a serious risk to human health, and therefore techniques for early detection of infectious foci need to be further developed to begin treatment quickly and achieve better results. Antimicrobial peptides labeled with gamma-emission radio nuclides are important diagnostic radiotracers in nuclear medicine. This study was conducted to evaluate the potential of a ^99m Tc-labeled MicrocinJ25 (MccJ25) antimicrobial peptide analog for early detection of infection. For this purpose, a HYNIC conjugated cyclic peptide derivative based on the primary structure of MccJ25 peptide was prepared and labeled by ^99m Tc with tricine and EDDA as coligands. The [^99m Tc-HYNIC/EDDA]-MccJ25 peptide analog showed high radiochemical purity (˃90% (n = 5)) which was stable up to 24 hr after labeling. The radiotracer showed specific uptake to the Escherichia coli (E. coli) bacterial (40.45 ± 5.21%) at 1 hr incubation. High kidneys uptake of radioactivity (4.71 ± 0.84% and 3.76 ± 0.45% ID/g at 1 and 4 hr after injection respectively) demonstrates that most of the whole body clearance was proceeded via the urinary system. Significant radioactivity uptake (1.71 ± 0.34%ID/g) was observed in thigh muscle of mouse with E. coli induced infection at 1 hr after injection. In the blocking test, due to the significant decrease of radioactivity uptake in the infection site (0.62 ± 0.21%ID/g after 1 hr), the specificity of infection uptake was reviled. Despite the high activity of the bladder due to urinary excretion, the infected area was somewhat visible. Hence, the results indicate the potential of this new radiotracer to be used as a diagnostic agent in E. coli infections.

Pathogen-Specific Polymeric Antimicrobials with Significant Membrane Disruption and Enhanced Photodynamic Damage To Inhibit Highly Opportunistic Bacteria

Highly pathogenic Gram-negative bacteria and their drug resistance are a severe public health threat with high mortality. Gram-negative bacteria are hard to kill due to the complex cell envelopes with low permeability and extra defense mechanisms. It is challenging to treat them with current strategies, mainly including antibiotics, peptides, polymers, and some hybrid materials, which still face the issue of drug resistance, limited antibacterial selectivity, and severe side effects. Together with precise bacteria targeting, synergistic therapeutic modalities, including physical membrane damage and photodynamic eradication, are promising to combat Gram-negative bacteria. Herein, pathogen-specific polymeric antimicrobials were formulated from amphiphilic block copolymers, poly(butyl methacrylate)- b-poly(2-(dimethylamino) ethyl methacrylate- co-eosin)- b-ubiquicidin, PBMA- b-P(DMAEMA- co-EoS)-UBI, in which pathogen-targeting peptide ubiquicidin (UBI) was tethered in the hydrophilic chain terminal, and Eosin-Y was copolymerized in the hydrophilic block. The micelles could selectively adhere to bacteria instead of mammalian cells, inserting into the bacteria membrane to induce physical membrane damage and out-diffusion of intracellular milieu. Furthermore, significant in situ generation of reactive oxygen species was observed upon light irradiation, achieving further photodynamic eradication. Broad-spectrum bacterial inhibition was demonstrated for the polymeric antimicrobials, especially highly opportunistic Gram-negative bacteria, such as Pseudomona aeruginosa ( P. aeruginosa) based on the synergy of physical destruction and photodynamic therapy, without detectable resistance. In vivo P. aeruginosa-infected knife injury model and burn model both proved good potency of bacteria eradication and promoted wound healing, which was comparable with commercial antibiotics, yet no risk of drug resistance. It is promising to hurdle the infection and resistance suffered from highly opportunistic bacteria.

Comparison of 99mTc-UBI 29-41, 99mTc-ciprofloxacin, 99mTc-ciprofloxacin dithiocarbamate and 111In-biotin for targeting experimental Staphylococcus aureus and Escherichia coli foreign-body infections: an ex-vivo study

BACKGROUND

Diagnosis of implant-associated infection is challenging. Several radiopharmaceuticals have been described but direct comparisons are limited. Here we compared in vitro and in an animal model 99mTc-UBI, 99mTc-ciprofloxacin, 99mTcN-CiproCS2 and 111In-DTPA-biotin for targeting E. coli (ATCC 25922) and S. aureus (ATCC 43335).

METHODS

Stability controls were performed with the labelled radiopharmaceuticals during 6 hours in saline and serum. The in vitro binding to viable or killed bacteria was evaluated at 37 °C and 4 °C. For in vivo studies, Teflon cages were subcutaneously implanted in mice, followed by percutaneous infection. Biodistribution of i.v. injected radiolabelled radiopharmaceuticals were evaluated during 24 h in cages and dissected tissues.

RESULTS

Labelling efficiency of all radiopharmaceuticals ranged between 94% and 98%, with high stability both in saline and in human serum. In vitro binding assays displayed a rapid but poor bacterial binding for all tested agents. Similar binding kinetic occurred also with heat-killed and ethanol-killed bacteria. In the tissue cage model, infection was detected at different time points: 99mTc-UBI and 99mTcN-CiproCS2 showed higher infected cage/sterile cage ratio at 24 hours for both E. coli and S. aureus; 99mTc-Ciprofloxacin at 24 hours for both E. coli and at 4 hours for S. aureus; 111In-DTPA-biotin accumulates faster in both E. coli and S. aureus infected cages.

CONCLUSIONS

99mTc-UBI, 99mTcN-CiproCS2 showed poor in vitro binding but good in vivo binding to E. coli only. 111In-DTPA-biotin showed poor in vitro binding but good in vivo binding to S. aureus and poor to E. coli. 99mTc-Ciprofloxacin showed poor in vitro binding but good in vivo binding to all tested bacteria. The mechanism of accumulation in infected sites remains to be elucidated.

Technetium-99m based small molecule radiopharmaceuticals and radiotracers targeting inflammation and infection

^99mTc-labeled antibiotics, antifungal drugs, antimicrobial peptides and COX-2 inhibitors are comprehensively reviewed.

99mTc-Labeled Ubiquicidin Accumulation in a Retained Surgical Gauze

A 31-year-old woman underwent Tc-labeled UBI scanning for diagnosis of possible prosthesis infection evaluation in our department. The scan showed an area of increased tracer uptake in the mid-lateral portion of the left thigh. This was proven to be due to a retained surgical gauze in her left thigh.

Polymer therapeutics in surgery: the next frontier

Polymer therapeutics is a successful branch of nanomedicine, which is now established in several facets of everyday practice. However, to our knowledge, no literature regarding the application of the underpinning principles, general safety, and potential of this versatile class to the perioperative patient has been published. This study provides an overview of polymer therapeutics applied to clinical surgery, including the evolution of this demand‐oriented scientific field, cutting‐edge concepts, its implications, and limitations, illustrated by products already in clinical use and promising ones in development. In particular, the effect of design of polymer therapeutics on biophysical and biochemical properties, the potential for targeted delivery, smart release, and safety are addressed. Emphasis is made on principles, giving examples in salient areas of demand in current surgical practice. Exposure of the practising surgeon to this versatile class is crucial to evaluate and maximise the benefits that this established field presents and to attract a new generation of clinician–scientists with the necessary knowledge mix to drive highly successful innovation.

Functional Imaging in Diagnostic of Orthopedic Implant-Associated Infections

Surgeries’ sterile conditions and perioperative antibiotic therapies decrease implant associated infections rates significantly. However, up to 10% of orthopedic devices still fail due to infections. An implant infection generates a high socio-economic burden. An early diagnosis of an infection would significantly improve patients’ outcomes. There are numerous clinical tests to diagnose infections. The “Gold Standard” is a microbiological culture, which requires an invasive sampling and lasts up to several weeks. None of the existing tests in clinics alone is sufficient for a conclusive diagnosis of an infection. Meanwhile, there are functional imaging modalities, which hold the promise of a non-invasive, quick, and specific infection diagnostic. This review focuses on orthopedic implant-associated infections, their pathogenicity, diagnosis and functional imaging.

(99m)Tc-labeled ubiquicidin scintigraphy: a promising method in hip prosthesis infection diagnosis

AIM

Hip prosthesis implantation has witnessed a significant increase in recent years. Despite the advantages of this surgical procedure, it has some complications, the most serious of which is prosthetic infection. This study was conducted to investigate the feasibility of 99mTc-UBI scintigraphy in detection of infectious foci in painful hip prosthesis. UBI (Ubiquicidin 29-41) is an antimicrobial peptide fragment with the ability to target the bacterial colony directly.

PATIENTS, METHODS

34 patients, aged 20-79 years, with painful hip prosthesis were included. 99mTc-UBI scan and three phase bone scan were performed and two nuclear medicine specialists interpreted the UBI scans with and without bone scan results at hand. Both qualitative and semi-quantitative methods were used to interpret the 30 minute post injection images. The patients were actively followed up. According to the surgical findings, microbiological culture and active follow up, final diagnosis was made.

RESULTS

24 negative and 10 positive UBI scans were recorded. The sensitivity, specificity, negative and positive predictive values and accuracy of the study were all 100%. Bone scan did not have any influence on UBI interpretation. We were able to achieve excellent differentiation between infected and non-infected prostheses with a cut off value of 1.8 for target to non target (T/NT) ratio. No adverse effects were noticed following UBI scan.

CONCLUSION

Based on the findings, the authors believe that 99mTc-UBI scintigraphy, with its high sensitivity and specificity, provides the physician with an excellent tool for differentiating infection from aseptic loosening of hip prostheses. Using this radiopharmaceutical, it is possible to obtain highly accurate results only 30 minutes after the beginning of the study.

99mTc-Novobiocin: a~novel radiotracer for infection imaging

The radiosynthesis of 99mTc-Novobiocin (99mTc-NBN) complex and its suitability as a radiotracer for infection imaging was assessed. The radiochemical purity (RCP) of the 99mTc-NBN complex was determined using radio-TLC and radioactive HPLC and biodistribution was studied in artificially infected (A.I.) rats and rabbit, using single well gamma counter (SWGRC) interface with scalar count rate meter (SCRM) and Gamma Camera (γ-CM). The maximum RCP observed for the preparation having 2 mg of NBN, 111 MBq of sodium pertechnetate (Na99mTcO4) and 125 μL of SnF2 (1 μg/μL in 0.01 N HCl) at a pH 5.6 was 98.97±0.40% and remained stable >90% up to 120 min. The activity of the 99mTc-NBN in the infected muscle (TI) was significantly increased from 6.50±0.15 to 19.00±0.17% and decreased in the inflamed muscle (TII), normal muscle (NT), blood, liver, spleen, stomach and intestine within 120 min. The TI/NT and TII/NT ratios were 7.60±1.08 and 1.60±1.14. The Whole Body Static (WBS) images of A.I. rabbit were obtained at 30, 40, 50 and 60 min after the I.V. administration of 111 MBq of 99mTc-NBN to the A.I. rabbit. The stability in saline and serum, higher TI/NT, lower TII/NT ratios and WBS images confirmed the feasibility of the 99mTc-NBN complex as an infection imaging agent.

Radiosynthesis and biodistribution of (99m)Tc-rifampicin: a novel radiotracer for in-vivo infection imaging

(99m)Tc-rifampicin ((99m)Tc-RMP) a new radioantibiotic complex was synthesized specifically for the infection localization caused by methicillin-resistant Staphylococcus aureus (MRSA). The in-vitro radiochemical purity (RCP) yield, in-vivo biodistribution behavior in artificially infected rats (AIT) and scintigraphic accuracy in artificially infected rabbit (AIB) of the (99m)Tc-RMP complex was investigated using different concentration of the RMP, sodium pertechnetate (Na(99m)TcO(4)), stannous chloride dihydrate (SnCl(2) x 2H(2)O) at different pH ranges 5-6. The best RCP yield observed at 30, 60, 90 and 120 min after labeling was; 98.95+/-0.20, 98.15+/-0.24, 96.50+/-0.27 and 91.55+/-0.22%, respectively, using 1.5 mg RMP, 175 microL of SnCl(2) x 2H(2)O (1 microg/microL in 0.01 N HCl), 3 mCi of Na(99m)TcO(4), at pH 5.6. Initially in the infected muscle (INM) of the AIT the activity was lower but after 90 min it went up to 18.35+/-0.20% from 5.95+/-0.25%. The activity in the inflamed muscle (IMM), normal (NM) muscle, blood, liver and spleen was initially high that decreased with time. The ratios of the INM/NM and IMM/NM were 7.34+/-0.74 and 1.20+/-0.85, respectively. The whole body static (WBS) imaging of the MRSA infected rabbit confirmed the usefulness of the (99m)Tc-RMP as a precise radiotracer for MRSA infection imaging. On the basis of in-vitro RCP, in-vivo biodistribution and scintigraphic precision, we recommend the (99m)Tc-RMP complex prepared aseptically for in-vivo assessment of MRSA infection.