Radiotracers used for the scintigraphic detection of infection and inflammation

Biodistribution of radiolabeled alpha-amanitin in mice: An Investigation

Mushroom poisonings caused by Amanita phalloides are the leading cause of mushroom-related deaths worldwide. Alpha-Amanitin (α-AMA), a toxic substance present in these mushrooms, is responsible for the resulting hepatotoxicity and nephrotoxicity. The objective of our study was to determine the distribution of α-AMA in Balb/c mice by labeling with Iodine-131. Mice were injected with a toxic dose (1.4 mg/kg) of α-AMA labeled with Iodine-131. The mice were sacrificed at the 1st, 2nd, 4th, 8th, 24th, and 48th hours under anesthesia. The organs of the mice were removed, and their biodistribution was assessed in all experiments. The percent injected dose per gram (ID/g %) value for kidney, liver, lung, and heart tissues at 1st hour were 1.59 ± 0.07, 1.25 ± 0.33, 3.67 ± 0.80 and 1.07 ± 0.01 respectively. This study provides insights into the potential long-term effects of α-AMA accumulation in specific organs. Additionally, this study has generated essential data that can be used to demonstrate the impact of antidotes on the biological distribution of α-AMA in future toxicity models.

In vivo behavior of technetium-99m labeled ibuprofen in infection and inflamation animal models

OBJECTIVE

The objective of this study was to develop radiolabeled ibuprofen (99mTc-ibu) for imaging and discrimination of inflammation and infection and compare its biodistribution in two different animal models.

SIGNIFICANCE

The development of radiolabeled ibuprofen as an imaging agent for inflammation and infection may have significant clinical implications for the diagnosis and management of various inflammatory and infectious diseases. This study provides a promising approach to the detection of sterile infections.

METHODS

Ibuprofen was radiolabeled with 99mTc using the stannous chloride method with a yield of 99.05 ± 0.83% (n = 5). The in vivo biological behavior of radiolabeled ibuprofen was determined in Wistar albino rat models of sterile inflammation and bacterial infection with Staphylococcus aureus gram-positive bacteria. Biodistribution studies were carried out at different time points, and the results were compared between the two animal models.

RESULTS

The uptake of 99mTc-ibu in sterile inflammation sites at all time points was higher than that in the infection sites. This suggests that 99mTc-ibu can be used to discriminate between sterile inflammation and bacterial infection.

CONCLUSIONS

The results of this study suggest that the detection of sterile infections with 99mTc-ibu is possible and highly encouraging.

Inflammation scintigraphy imaging through a novel antimicrobial peptide labeled with technetium-99m in an animal model

PURPOSE

Antimicrobial peptides (AMPs), due to their biological properties, have great potential for radiopharmaceutical development. In this research, a new antimicrobial peptide, derived from a 21-residue antimicrobial peptide microcinJ25 (MccJ25), was utilized to diagnose inflamed sites in mice bodies after labeling with [^99mTc]Tc.

MATERIALS AND METHODS

An antimicrobial peptide derivative was connected with an efficient chelator, hydrazinonicotinamide, and then labeled with [^99mTc]Tc. The binding of labeled microcinJ25 conjugate to lymphocyte was investigated in vitro. Turpentine oil-induced inflammation uptake and tissue distribution were assessed through the animal pattern. Detector scanning was done through scintigraphy post injection of [^99mTc]Tc-radiopeptide within different time points.

RESULTS

High radiochemical purity (>98%) was obtained for [^99mTc]Tc-radiopeptide. Lymphocyte binding assessment showed specific cell binding. Binding Inhibition was observed when additional unlabeled conjugate was used. In in vivo biological distribution studies, the uptake for inflamed tissue was 1.52 ± 0.12%ID/g. The inflammation site was visualized by scintigraphy imaging at 1 up to 2 hours.

CONCLUSION

Based on our results this new designed [^99mTc]Tc-radiopeptide was able to detect inflammation sites early and with high resolution, and could be considered a promising diagnostic candidate in inflammatory diseases.

125I–Amoxicillin preparation as a guide tracer for inflammation detection

The objective of this study is to label Amoxicillin with radioactive iodine (125I-AC) via direct electrophilic substitution to act as a promising tracer for inflammation imaging. The highest labeling yield of 80% was achieved after studying all the parameters affecting the labeling reaction using Iodogen (IG) as an oxidizing agent. Molecular Modeling Structure was done using MOE program to predict the suitable 125I position. The product structure was established by a cold iodination reaction using Iodine-127. Biological evaluation of (125I-AC) was carried out using groups of inflamed mice with different exogenous agents such as E.Coli and Turpentine oil. The (125I-AC) shows an in vitro stability of about 97% after 24 h.While doing in vivo studies over 4 h, the tracer stability of 99% was observed.

ACR Appropriateness Criteria® Infective Endocarditis

Infective endocarditis can involve a normal, abnormal, or prosthetic cardiac valve. The diagnosis is typically made clinically with persistently positive blood cultures, characteristic signs and symptoms, and echocardiographic evidence of valvular vegetations or valvular complications such as abscess, dehiscence, or new regurgitation. Imaging plays an important role in the initial diagnosis of infective endocarditis, identifying complications, prognostication, and informing the next steps in therapy. This document outlines the initial imaging appropriateness of a patient with suspected infective endocarditis and for additional imaging in a patient with known or suspected infective endocarditis. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

[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.

Rodent Leukocyte Isolation and Radiolabeling for Inflammation Imaging Study

Purpose

The objective of this study was to describe to develop methods of rodent leukocyte isolation and radiolabeling for in vivo inflammation imaging.

Methods

Thigh muscle inflammation was induced by injection of collagenase. Blood was collected from the jugular vein and separated by Histopaque. The collected cells were incubated in a 37 °C CO₂ incubator for 1~2 h. After incubation, ^99mTc-HMPAO and ¹⁸F-FDG were used to treat leukocytes followed by incubation for 30 min. ^99mTc-HMPAO and ¹⁸F-FDG labeled autologous leukocytes were injected into the tail veins of rats. The images were then acquired at various time points. Image-based lesion to normal muscle ratio was compared.

Results

After Histopaque separation, the proportion of lymphocytes was higher than that of other cell types. After CO₂ incubation, the collected leukocytes were viable, while room temperature exposed leukocytes without CO₂ incubation were non-viable. Granulocytes, especially, were more quickly influenced by various conditions than the mononuclear cells. Labeling efficiencies of ^99mTc-HMPAO and ¹⁸F-FDG were 4.00 ± 2.06 and 1.8%, respectively. ^99mTc-HMPAO- and ¹⁸F-FDG-labeled leukocytes targeted well the inflamed lesion. ^99mTc-HMPAO-labeled leukocytes, but not ¹⁸F-FDG-labeled leukocytes, were found in the abdomen activity.

Conclusion

Inflamed lesions of rats were well visualized using autologous radiolabeled leukocytes. This method might provide good information for understanding inflammatory diseases.

Analysis of Cell Fraction of ⁹⁹mTc-HMPAO Radiolabeled Leukocytes

PURPOSE

99mTc-HMPAO radiolabeled autologous leukocyte scintigraphy is routinely used clinically for infection imaging. Leukocytes are mostly separated via sedimentation. It is unknown whether leukocytes are clearly separated by sedimentation or selectively labeled. Therefore, in this study, the blood cell numbers were investigated after leukocyte radiolabeling to identify the cells strongly radiolabeled by 99mTc-HMPAO.

METHODS

This study was performed with leftover blood samples of the patients who underwent 99mTc-HMPAO scintigraphy at Chonbuk National University Hospital (2018-2019). The blood of 22 patients was drawn for 99mTc-HMPAO scintigraphy. WBCs were separated via conventional sedimentation at our clinic and radiolabeled. The concentration of cell components was determined using an automatic hematology analyzer. The cells in the final sample injectate sample were separated using Histopaque and counted with a dose calibrator.

RESULTS

The average numbers of RBCs, WBCs, and PLTs in the final injection sample were 79 ± 33, 23.26 ± 11.95, and 229.5 ± 206.57 x 103/μL, respectively. The PLT number was almost 10-fold the number of WBCs. The number of RBCs was nearly 3-fold higher than WBCs [RBC/WBC ratio = 4.67 ± 3.58, and PLT/WBC ratio = 10.65 ± 12.46]. Following Histopaque separation, the activity of each layer showed 99mTc-HMPAO labeling of WBC > RBC > PLT in order. The total activity/cell numbers of WBCs, RBCs and PLTs were 0.016 ± 0.010, 0.005 ± 0.005 and 0.003 ± 0.002, respectively (p > 0.05).

CONCLUSION

Although the numbers of RBCs and PLTs were highly increased after sedimentation, their individual cellular activity was lower than that of WBCs. 99mTc-HMPAO was more selective to WBCs than RBCs or PLTs. In conclusion, a higher number of WBCs were radiolabeled compared with RBCs and PLTs.

Multimodal Molecular Imaging of the Tumour Microenvironment

The tumour microenvironment (TME) surrounding tumour cells is a highly dynamic and heterogeneous composition of immune cells, fibroblasts, precursor cells, endothelial cells, signalling molecules and extracellular matrix (ECM) components. Due to the heterogeneity and the constant crosstalk between the TME and the tumour cells, the components of the TME are important prognostic parameters in cancer and determine the response to novel immunotherapies. To improve the characterization of the TME, novel non-invasive imaging paradigms targeting the complexity of the TME are urgently needed.The characterization of the TME by molecular imaging will (1) support early diagnosis and disease follow-up, (2) guide (stereotactic) biopsy sampling, (3) highlight the dynamic changes during disease pathogenesis in a non-invasive manner, (4) help monitor existing therapies, (5) support the development of novel TME-targeting therapies and (6) aid stratification of patients, according to the cellular composition of their tumours in correlation to their therapy response.This chapter will summarize the most recent developments and applications of molecular imaging paradigms beyond FDG for the characterization of the dynamic molecular and cellular changes in the TME.

Pathogen-Specific Bacterial Imaging in Nuclear Medicine

When serious infections are suspected, patients are often treated empirically with broad-spectrum antibiotics while awaiting results that provide information on the bacterial class and species causing the infection, as well as drug susceptibilities. For deep-seated infections, these traditional diagnostic techniques often rely on tissue biopsies to obtain clinical samples which can be expensive, dangerous, and has the potential of sampling bias. Moreover, these procedures and results can take several days and may not always provide reliable information. This combination of time and effort required for proper antibiotic selection has become a barrier leading to indiscriminate broad-spectrum antibiotic use. Exposure to nosocomial infections and indiscriminate use of broad-spectrum antibiotics are responsible for promoting bacterial drug-resistance leading to substantial morbidity and mortality, especially in hospitalized and immunosuppressed patients. Therefore, early diagnosis of infection and targeted antibiotic treatments are urgently needed to reduce morbidity and mortality caused by bacterial infections worldwide. Reliable pathogen-specific bacterial imaging techniques have the potential to provide early diagnosis and guide antibiotic treatments.

Detection of bacterial infection by a technetium-99m-labeled peptidoglycan aptamer

Nuclear medicine clinicians are still waiting for the optimal scintigraphic imaging agents capable of distinguishing between infection and inflammation, and between fungal and bacterial infections. Aptamers have several properties that make them suitable for molecular imaging. In the present study, a peptidoglycan aptamer (Antibac1) was labeled with ^99mTc and evaluated by biodistribution studies and scintigraphic imaging in infection-bearing mice. Labeling with ^99mTc was performed by the direct method and the complex stability was evaluated in saline, plasma and in the molar excess of cysteine. The biodistribution and scintigraphic imaging studies with the ^99mTc-Antibac1 were carried out in two different experimental infection models: Bacterial-infected mice (S. aureus) and fungal-infected mice (C. albicans). A ^99mTc radiolabeled library, consisting of oligonucleotides with random sequences, was used as a control for both models. Radiolabeling yields were superior to 90% and ^99mTc-Antibac1 was highly stable in presence of saline, plasma, and cysteine up to 6h. Scintigraphic images of S. aureus infected mice at 1.5 and 3.0h after ^99mTc-Antibac1 injection showed target to non-target ratios of 4.7±0.9 and 4.6±0.1, respectively. These values were statistically higher than those achieved for the ^99mTc-library at the same time frames (1.6±0.4 and 1.7±0.4, respectively). Noteworthy, ^99mTc-Antibac1 and ^99mTc-library showed similar low target to non-target ratios in the fungal-infected model: 2.0±0.3 and 2.0±0.6for ^99mTc-Antibac1 and 2.1±0.3 and 1.9 ± 0.6 for ^99mTc-library, at the same times. These findings suggest that the ^99mTc-Antibac1 is a feasible imaging probe to identify a bacterial infection focus. In addition, this radiolabeled aptamer seems to be suitable in distinguishing between bacterial and fungal infection.

(1→3)-β-D-glucan aptamers labeled with technetium-99m: Biodistribution and imaging in experimental models of bacterial and fungal infection

INTRODUCTION

Acid nucleic aptamers are RNA or DNA oligonucleotides capable of binding to a target molecule with high affinity and selectivity. These molecules are promising tools in nuclear medicine. Many aptamers have been used as targeting molecule of radiopharmaceuticals in preclinical studies. (1→3)-β-D-glucans are the main structural cell wall components of fungi and some bacteria. In the present study two radiolabeled (1→3)-β-D-glucan aptamers (seq6 and seq30) were evaluated to identity infectious foci caused by fungal or bacterial cells.

METHODS

Aptamer labeling with ^99mTc was performed by the direct method and biodistribution studies were accomplished in Swiss mice (n=6) infected in the right thigh muscle with Staphylococcus aureus or Candida albicans. A ^99mTc radiolabeled library consisting of oligonucleotides with random sequences was used as control.

RESULTS

There was a higher uptake of ^99mTc radiolabeled aptamers in the infected thigh than in the left thigh muscle (non-infected) in the S. aureus infected animals. The target/non-target ratios were 3.17±0.22 for seq6 and 2.66±0.10 for seq30. These ratios were statistically higher than the value (1.54±0.05) found for the radiolabeled library (control). With regard to biodistribution, no statistical difference was verified between aptamers and control uptakes in the infection foci in the C. albicans infected animals. The target/non-target ratios were 1.53±0.03, 1.64±0.12 and 1.08±0.02 for radiolabeled library, seq6 and seq30, respectively. Scintigraphic imaging of infected foci using radiolabeled aptamers was possible only for S. aureus infected mice.

CONCLUSIONS

Seq6 and seq30 aptamers proved to be inefficient for diagnosis of C. albicans infection. Nevertheless, their applicability for diagnosis of S. aureus and other bacterial infections by scintigraphy should be further explored.

Synthesis and antimicrobial evaluation of two peptide LyeTx I derivatives modified with the chelating agent HYNIC for radiolabeling with technetium-99m

Background

Current diagnostic methods and imaging techniques are not able to differentiate septic and aseptic inflammation. Thus, reliable methods are sought to provide this distinction and scintigraphic imaging is an interesting option, since it is based on physiological changes. In this context, radiolabeled antimicrobial peptides have been investigated as they accumulate in infectious sites instead of aseptic inflammation. The peptide LyeTx I, from the venom of Lycosa erythrognatha, has potent antimicrobial activity. Therefore, this study aimed to synthesize LyeTx I derivatives with the chelating compound HYNIC, to evaluate their antimicrobial activity and to radiolabel them with ^99mTc.

Methods

Two LyeTx I derivatives, HYNIC-LyeTx I (N-terminal modification) and LyeTx I-K-HYNIC (C-terminal modification), were synthesized by Fmoc strategy and purified by RP-HPLC. The purified products were assessed by RP-HPLC and MALDI-ToF-MS analysis. Microbiological assays were performed against S. aureus (ATCC® 6538) and E. coli (ATCC® 10536) in liquid medium to calculate the MIC. The radiolabeling procedure of LyeTx I-K-HYNIC with ^99mTc was performed in the presence of co-ligands (tricine and EDDA) and reducing agent (SnCl₂^.2H₂O), and standardized taking into account the amount of peptide, reducing agent, pH and heating. Radiochemical purity analysis was performed by thin-layer chromatography on silica gel strips and the radiolabeled compound was assessed by RP-HPLC and radioactivity measurement of the collected fractions. Data were analyzed by ANOVA, followed by Tukey test (p-values < 0.05).

Results

Both LyeTx I derivatives were suitably synthesized and purified, as shown by RP-HPLC and MALDI-ToF-MS analysis. The microbiological test showed that HYNIC-LyeTx I (N-terminal modification) did not inhibit bacterial growth, whereas LyeTx I-K-HYNIC (C-terminal modification) showed a MIC of 5.05 μmol^.L⁻¹ (S. aureus) and 10.10 μmol^.L⁻¹ (E. coli). Thus, only the latter was radiolabeled with ^99mTc. The radiochemical purity analysis of LyeTx I-K-HYNIC-^99mTc showed that the optimal radiolabeling conditions (10 μg of LyeTx I-K-HYNIC; 250 μg of SnCl₂^.2H₂O; pH = 7; heating for 15 min) yielded a radiochemical purity of 87 ± 1 % (n = 3). However, RP-HPLC data suggested ^99mTc transchelation from LyeTx I-K-HYNIC to the co-ligands (tricine and EDDA).

Conclusions

The binding of HYNIC to the N-terminal portion of LyeTx I seems to affect its activity against bacteria. Nevertheless, the radiolabeling of the C-terminal derivative, LyeTx I-K-HYNIC, must be better investigated to optimize the radiolabeled compound, in order to use it as a specific imaging agent to distinguish septic and aseptic inflammation.