A Novel Radioimmune 99mTc-Labeled Tracer for Imaging Sphingosine 1-Phosphate Receptor 1 in Tumor Xenografts: An In Vitro and In Vivo Study.

Sphingosine-1-phosphate (S1P) is a phospholipid that regulates pleiotropic biological activities and exerts extracellular functions by binding to five specific G-protein-coupled receptors, S1P receptors (S1PR) 1-5. When activated by S1P, S1PR promote the proliferation and invasion of tumor cells by inducing the formation of new blood vessels. We developed and assessed a new monoclonal antibody imaging probe 99mTc-HYNIC-S1PR1mAb, to explore the feasibility of targeting the S1PR1 in vitro and in vivo. S1PR1mAb was prepared and followed by technetium-99m labeling with succinimidyl 6-hydraziniumnicotinate hydrochloride. Cell uptake and blocking studies were performed to investigate the binding specificity of 99mTc-HYNIC-S1PR1mAb in vitro. 99mTc-HYNIC-S1P1mAb was also tested in vivo in mice xenografted with SK-HEP-1 (high-expression of S1PR1) and MCF-7 (low-expression of S1PR1) using single-photon emission-computed tomography (SPECT). Ex vivo gamma counting of tissues from tumor-bearing mice was used to evaluate 99mTc-HYNIC-S1PR1mAb biodistribution. The biodistribution study results showed significantly higher uptake in SK-HEP-1 tumors than in MCF-7 tumors (P < 0.001). Reduced uptake of 99mTc-HYNIC-S1PR1mAb in SK-HEP-1 was observed in tumor-bearing nude mice pretreated with fingolimod, which binds competitively to the receptors, especially S1PR1. 99mTc-HYNIC-S1PR1mAb can be synthesized and specifically targeted to S1PR1 in vitro and in vivo, allowing S1PR1 expression assessment with SPECT imaging.

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.

Microwave assisted synthesis of Fe3O4 stabilized ZrO2 nanoparticles - Free radical scavenging, radiolabeling and biodistribution in rabbits.

AIMS: In vivo biodistribution of radio labeled ZrO2 nanoparticles is addressed for better imaging, therapy and diagnosis. Nanoparticles are synthesized by microwave assisted sol-gel technique using Fe3O4 as a stabilizer. Antioxidant assay, hemolytic activity in human blood and biodistribution in rabbits was explored to study the therapeutical as well as in vivo targeted diagnostic applications of as synthesized nanoparticles. MAIN METHODS: Fe3O4 stabilized zirconia nanoparticles are synthesized using microwave assisted sol-gel method. Microwave (MW) powers are varied in the range of 100 to 1000 W. As synthesized nanoparticles are evaluated using different characterizations such as X-ray diffractometer, scanning electron microscope, Raman spectroscopy, impedance analyzer, Vickers micro hardness indenter, FTIR, and UV-Vis spectroscopy. In vitro activity of synthesized nanoparticles is checked in freshly extracted human blood serum. To study biodistribution of Fe3O4 stabilized zirconia nanoparticles in rabbit, technetium-99 m was used for labeling purpose. The labeling efficacy and stability of labeled nanoparticles are also measured with instant thin layer chromatography (ITLC) method. Intravenous injection of 99mTc-Fe3O4 stabilized zirconia nanoparticles (0.2 ml), containing 110 MBq of radioactivity, is performed to study the biodistribution; nanoparticles are injected into the ear vein of animal (rabbit). KEY FINDINGS: Zirconia (ZrO2) nanoparticles (NPs) are stabilized using Fe3O4 that were prepared by means of microwave assisted sol-gel method. Crystallite size (~20 nm) agrees well with the values required to stabilize tetragonal zirconia (t-ZrO2). Volume shrinkage results in high value of hardness (~1369). Dielectric constant values, compatible for biomedical application, are observed for tetragonally stabilized samples. Low value of hemolytic response is observed for Fe3O4 stabilized ZrO2 NPs. 99mTc radio labeled ZrO2 NPs proved to be potential candidate to study biodistribution. Biodistribution studies show stability of radiolabeled NPs in the original suspension as well as in blood serum. CT scan of rabbit is performed for several times to check the biodistribution of NPs with time and survival of rabbit. Results suggest that these NPs can also be used as targeted nanoparticles as well as variants of drug payload carrier. SIGNIFICANCE: Results signify that Fe3O4 stabilized ZrO2 nanoparticles synthesized by microwave assisted sol-gel method may be considered as "all-rounder" nanoplatform and are safe enough to be used in diagnostic as well as therapeutic purposes.

Imaging Hydrogen Sulfide in Hypoxic Tissue with [99mTc]Tc-Gluconate.

Hydrogen sulfide (H2S) is the third gasotransmitter and is generated endogenously in hypoxic or inflammatory tissues and various cancers. We have recently demonstrated that endogenous H2S can be imaged with [99mTc]Tc-gluconate. In the present study, we detected H2S generated in hypoxic tissue, both in vitro and in vivo, using [99mTc]Tc-gluconate. In vitro uptake of [99mTc]Tc-gluconate was measured under hypoxic and normoxic conditions, using the colon carcinoma cell line CT26, and was higher in hypoxic cells than that in normoxic cells. An acute hindlimb ischemia-reperfusion model was established in BALB/c mice by exposing the animals to 3 h of ischemia and 3 h of reperfusion prior to in vivo imaging. [99mTc]Tc-gluconate (12.5 MBq) was intravenously injected through the tail vein, and uptake in the lower limb was analyzed by single-photon emission computed tomography/computed tomography (SPECT/CT). SPECT/CT images showed five times higher uptake in the ischemic limb than that in the normal limb. The standard uptake value (SUVmean) of the ischemic limb was 0.39 ± 0.03, while that of the normal limb was 0.07 ± 0.01. [99mTc]Tc-gluconate is a novel imaging agent that can be used both in vitro and in vivo for the detection of endogenous H2S generated in hypoxic tissue.

Beta Cell Imaging-From Pre-Clinical Validation to First in Man Testing.

There are presently no reliable ways to quantify human pancreatic beta cell mass (BCM) in vivo, which prevents an accurate understanding of the progressive beta cell loss in diabetes or following islet transplantation. Furthermore, the lack of beta cell imaging hampers the evaluation of the impact of new drugs aiming to prevent beta cell loss or to restore BCM in diabetes. We presently discuss the potential value of BCM determination as a cornerstone for individualized therapies in diabetes, describe the presently available probes for human BCM evaluation, and discuss our approach for the discovery of novel beta cell biomarkers, based on the determination of specific splice variants present in human beta cells. This has already led to the identification of DPP6 and FXYD2ga as two promising targets for human BCM imaging, and is followed by a discussion of potential safety issues, the role for radiochemistry in the improvement of BCM imaging, and concludes with an overview of the different steps from pre-clinical validation to a first-in-man trial for novel tracers.

Renal Handling of 99mTc-Labeled Antibody Fab Fragments with a Linkage Cleavable by Enzymes on Brush Border Membrane.

The high and persistent renal radioactivity levels after injection of radiolabeled low-molecular-weight polypeptides constitute a significant problem for their diagnostic and therapeutic applications, especially when they are labeled with metallic radionuclides. To improve the renal radioactivity levels of technetium-99m (99mTc)-labeled Fab fragments, a mercaptoacetyltriglycine (MAG3)-based new bifunctional chelating agent with a cleavable glycyl-phenylalanyl-lysine (GFK) linkage, MAG3-GFK-suc-TFP, was designed, synthesized, and evaluated. 99mTc-labeled Fab was obtained by reacting MAG3-GFK-Fab conjugate with 99mTc-glucarate. The GFK linkage remained stable in plasma but was cleaved by enzymes on the renal brush border membrane. The comparative biodistribution studies with indium-111 (111In)-labeled Fab using SCN-CHX-A″-DTPA showed that while both radiolabeled Fabs exhibited similar elimination rates from the blood, [99mTc]Tc-MAG3-GFK-Fab registered much lower renal radioactivity levels from 30 min post-injection onward due to the release and subsequent urinary excretion of [99mTc]Tc-MAG3-Gly. However, [99mTc]Tc-MAG3-GFK-Fab showed an increase in the intestinal radioactivity levels with the time that was not observed with 111In-labeled Fab. The analysis of the intestinal contents suggested the redistribution of [99mTc]Tc-MAG3-Gly to the intestine. The retrospective comparison of [99mTc]Tc-MAG3-GFK-Fab with the radiolabeled Fabs so far prepared under the identical concept suggested that some portion of [99mTc]Tc-MAG3-Gly was generated after the coated vesicle formation and they were excreted into the blood, and subsequently redistributed in the intestine via hepatobiliary excretion. In conclusion, MAG3-GFK-suc-TFP provided 99mTc-labeled Fabs that exhibit low renal radioactivity shortly after injection by the post-labeling procedure. The present study indicated that, contrary to our earlier proposal, the generation of the radiometabolites would proceed not only during the internalization process of the parental antibody fragments but also after coated vesicle formation. This study also showed that the intracellular behaviors of radiometabolites played crucial roles in the elimination rates and the routes of the radioactivity from the kidney.

Chromosome aberrations during in-vitro labeling of red blood cells with 99mTc: a study with cytokinesis block micronucleus assay in human peripheral blood lymphocytes.

Radiopharmaceuticals are special medicines composed by a radionuclide and a non-radioactive compound characterized by non-pharmacodynamic effects, low prevalence of side effects, and a possible risk of oncogenesis, since its administration to patients supposes a radiation dose to organism. Over these years, radiation damage induced by diagnosis radiopharmaceuticals has been evaluated, including the radiolabeled autologous cells, a group of radiopharmaceuticals where blood cells extracted from patients are labeled in-vitro and readministered for diagnosis. There is not a consensus about the possibility of increasement of risk for malignancies associated with the radiolabeled blood cells, so for a more accurate evaluation of the potential oncogenic risk related to the administration of [Tc]Tc labeled red blood cells, radiation dose received by the cells during the labeling process is studied by means of the cytokinesis-blocked micronucleus (CBMN) assay and a dose-response curve constructed by in-vitro external irradiation of blood samples. Our work enables to establish the range of activity to be added during the in-vitro labeling of red blood cells with [Tc]Tc pertechnetate to avoid radiation damage to cells. Activities recommended for blood volume determination and angiography do not increase the risk of malignancies, whilst activities of 370 MBq show chromosome aberrations in lymphocytes. Evaluation of the radiation damage related to the in-vitro labeling is recommended to estimate the potential oncogenic risk and minimize it.

Cardiac Scintigraphy With Technetium-99m-Labeled Bone-Seeking Tracers for Suspected Amyloidosis: JACC Review Topic of the Week.

Technetium-labeled cardiac scintigraphy (i.e., Tc-PYP scan) has been repurposed for the diagnosis of transthyretin amyloid cardiomyopathy (ATTR-CM). Validated in cohorts of patients with heart failure and echocardiographic and/or cardiac magnetic resonance imaging findings suggestive of cardiac amyloidosis, cardiac scintigraphy can confirm the diagnosis of ATTR-CM only when combined with blood and urine testing to exclude a monoclonal protein. Multisocietal guidelines support the nonbiopsy diagnosis of ATTR-CM using cardiac scintigraphy, yet emphasize its use in the appropriate clinical context and the crucial need to rule out light chain amyloid cardiomyopathy. Although increased awareness of ATTR-CM and the advent of effective therapy have led to rapid adoption of diagnostic scintigraphy, there is heterogeneity in adherence to consensus guidelines. This perspective outlines clinical scenarios wherein findings on technetium-labeled cardiac scintigraphy have been misinterpreted, reviews causes of false-negative and false-positive results, and provides strategies to avoid costly and potentially fatal misdiagnoses.

Lung aeration in experimental malaria-associated acute respiratory distress syndrome by SPECT/CT analysis.

Malaria-associated acute respiratory distress syndrome (ARDS) is an inflammatory disease causing alveolar-pulmonary barrier lesion and increased vascular permeability characterized by severe hypoxemia. Computed tomography (CT), among other imaging techniques, allows the morphological and quantitative identification of lung lesions during ARDS. This study aims to identify the onset of malaria-associated ARDS development in an experimental model by imaging diagnosis. Our results demonstrated that ARDS-developing mice presented decreased gaseous exchange and pulmonary insufficiency, as shown by the SPECT/CT technique. The pulmonary aeration disturbance in ARDS-developing mice on the 5th day post infection was characterized by aerated tissues decrease and nonaerated tissue accumulation, demonstrating increased vascular permeability and pleural effusion. The SPECT/CT technique allowed the early diagnosis in the experimental model, as well as the identification of the pulmonary aeration. Notwithstanding, despite the fact that this study contributes to better understand lung lesions during malaria-associated ARDS, further imaging studies are needed.

Single-Photon Emission Computed Tomography Imaging Using Formyl Peptide Receptor 1 Ligand Can Diagnose Aortic Aneurysms in a Mouse Model.

BACKGROUND: Our previous studies showed that neutrophil infiltration and activation plays an important role in the pathogenesis of abdominal aortic aneurysms (AAA). However, there is a lack of noninvasive, inflammatory cell-specific molecular imaging methods to provide early diagnosis of AAA formation. Formyl peptide receptor 1 (FPR1) is rapidly upregulated on neutrophils during inflammation. Therefore, it is hypothesized that the use of cinnamoyl-F-(D)L-F-(D)L-F-K (cFLFLF), a PEGylated peptide ligand that binds FPR1 on activated neutrophils, would permit accurate and noninvasive diagnosis of AAA via single-photon emission computed tomography (SPECT) imaging. MATERIALS AND METHODS: Male C57BL/6 (wild-type) mice were treated with topical elastase (0.4 U/mL type 1 porcine pancreatic elastase) or heat-inactivated elastase (control), and aortic diameter was measured by video micrometry. Comparative histology was performed on Day 14 to assess neutrophil infiltration in aortic tissue. We performed near-infrared fluorescence imaging using c-FLFLF-Cy7 probe on Days 7 and 14 postelastase treatment and measured fluorescence intensity ex vivo in excised aortic tissue. A separate group of animals were injected with 99mTc-c-FLFLF 2 h before SPECT imaging on Day 14 using a SPECT/computed tomography/positron emission tomography trimodal scanner. Coexpression of neutrophils with c-FLFLF was also performed on aortic tissue by immunostaining on Day 14. RESULTS: Aortic diameter was significantly increased in the elastase group compared with controls on Days 7 and 14. Simultaneously, a marked increase in neutrophil infiltration and elastin degradation as well as decrease in smooth muscle integrity were observed in aortic tissue after elastase treatment compared with controls. Moreover, a significant increase in fluorescence intensity of c-FLFLF-Cy7 imaging probe was also observed in elastase-treated mice on Day 7 (approximately twofold increase) and Day 14 (approximately 2.5-fold increase) compared with respective controls. SPECT imaging demonstrated a multifold increase in signal intensity for 99mTc-cFLFLF radiolabel probe in mice with AAA compared with controls on Day 14. Immunostaining of aortic tissue with c-FLFLF-Cy5 demonstrated a marked increase in coexpression with neutrophils in AAA compared with controls. CONCLUSIONS: cFLFLF, a novel FPR1 ligand, enables quantifiable, noninvasive diagnosis and progression of AAAs. Clinical application of this inflammatory, cell-specific molecular probe using SPECT imaging may permit early diagnosis of AAA formation, enabling targeted therapeutic interventions and preventing impending aortic rupture.

Superior Diagnostic Performance of the GLP-1 Receptor Agonist [Lys40(AhxHYNIC-[99mTc]/EDDA)NH2]-Exendin-4 over Conventional Imaging Modalities for Localization of Insulinoma.

PURPOSE: Insulinomas are the most common functioning neuroendocrine neoplasms of the pancreas, typically diagnosed due to characteristic symptoms. In the vast majority, the treatment is surgical and curative, requiring accurate localization of the tumour; conventional imaging, including somatostatin receptor molecular imaging, is negative in up to 10 % of cases. Recently, labelled glucagon-like peptide receptor (GLP-1R) analogues were introduced as a sensitive diagnostic method for localization of insulinomas. The aim of this study was to assess the diagnostic accuracy of a Tc-99m-labelled GLP-1R agonist [Lys40(AhxHYNIC-[99mTc]EDDA)NH2]-exendin-4 for localization of occult insulinoma. PROCEDURES: Eight patients (all females; age range 35-75 years) with biochemically proven insulinoma and with negative or inconclusive conventional imaging (consisting of somatostatin receptor scintigraphy, computed tomography, endoscopic ultrasound and magnetic resonance imaging) were enrolled. Whole-body single-photon emission tomography/computed tomography (SPECT/CT) imaging was performed 4 h post-injection of 740 MBq of [Lys40(AhxHYNIC-[99mTc]EDDA)NH2]-exendin-4. Surgical treatment was performed based on imaging findings. Histology of the removed lesions and biochemical and clinical symptom resolution was considered as the gold standard for analysis of the imaging results. RESULTS: Focal uptake of [Lys40(AhxHYNIC-[99mTc]EDDA)NH2]-exendin-4 was found in all patients, leading to successful removal of the offending lesion and complete biochemical and symptomatic resolution. Histological analysis confirmed insulinoma in all included patients. CONCLUSIONS: [Lys40(AhxHYNIC-[99mTc]EDDA)NH2]-exendin-4 SPECT/CT appears to be an excellent molecular imaging method for preoperative localization of an occult insulinoma, surpassing conventional imaging methods. If routinely available, it could be considered as a method of choice due to its favorable combination of imaging characteristics.

White blood cell labeling with Technetium-99m (99mTc) using red blood cell extracellular vesicles-mimetics.

BACKGROUND: Extracellular vesicles, have gained increasing attention for their application in drug delivery. Here, we developed a novel method for radiolabeling WBCs with 99mTc using RBC-derived extracellular vesicles -mimetics (EVMs), and monitored in vivo inflammation tracking of 99mTc-WBC using gamma camera in acute inflammation mouse model. METHODS: Engineered EVMs from RBCs were produced by a one-step extrusion method. RBC-EVMs were analyzed by NTA and TEM. Cells were labeled with 99mTc by using 99mTc-RBC-EVMs. Inflammation mice model was prepared and confirmed by 18F-FDG PET/CT. 99mTc-WBCs were injected in mice, and their biodistribution was analyzed by gamma camera. FINDING: The radiochemical purity of 99mTc-RBC-EVMs was 100%. The 99mTc-labeling did't affect the size and morphology. The 99mTc in the cytoplasm of RBC-EVMs was successfully confirmed by high angle annular dark field STEM (scanning transmission electron microscope). Cells were successfully labeled with 99mTc using 99mTc-RBC-EVMs, and the counts per minute was increased in dose- and time-dependent manners. The 18F-FDG PET/CT images confirmed establishment of acute inflammation (left mouse foot). 99mTc-WBCs showed higher uptake in the inflamed foot than non-inflamed foot. INTERPRETATION: This novel method for radiolabeling WBCs using RBC-EVMs. 99mTc labeling may be a feasible method to monitor the in vivo biodistribution of cells.

A novel delivery system for supraglottic atomization allows increased lung deposition rates of pulmonary surfactant in newborn piglets.

BACKGROUND: Earlier attempts to deliver effective lung doses of surfactant by aerosolization were unsuccessful, mostly because of technical shortcomings. We aimed at quantifying the lung deposition of poractant alfa with a new supraglottic delivery system for surfactant atomization in an experimental neonatal model. METHODS: The method involved six sedated 1-day-old piglets lying in the lateral decubitus, spontaneously breathing on nasal-mask continuous positive airway pressure (nCPAP). A pharyngeal cannula housing a multi-channel air-blasting atomization catheter was placed through the mouth with its tip above the glottis entrance. In all, 200 mg kg-1 of a 99mTc-surfactant mixture was atomized through the catheter synchronously with inspiration. Six intubated control piglets received an equal amount of intratracheally instilled 99mTc-surfactant mixture. The percentage of the 99mTc-surfactant mixture deposited in the lungs was estimated by scintigraphy. RESULTS: Median (range) deposition in the lungs was 40% (24-68%) after atomization and 87% (55-95%) after instillation (p < 0.001). Overall, almost 80% of the deposited surfactant was in the dependent lung. Effective atomization time (atomizer on) was 28 (17-52) min, yielding an output rate of 0.1-0.2 mL min-1. CONCLUSIONS: Without endotracheal intubation, in spontaneously breathing newborn piglets, this new supraglottic atomizer delivery system attained a median lung deposition of 40% of the nominal dose of surfactant.

99mTc-Labeled Native RBC Scintigraphy in Distinguishing Polysplenia From Abdominal Masses in a Patient With Situs Inversus Totalis.

A 39-year-old previously healthy woman presented possible hematuria. An ultrasound examination showed right adrenal mass and suggested pheochromocytoma. A Tc-HYNIC-TOC SPECT/CT was performed, which incidentally detected situs inversus totalis and suspicion of polysplenia without definite normal spleen in the right upper abdomen. In order to differentiate the polysplenia from other etiologies, a heat-damaged Tc RBC scintigraphy was performed. The images showed significant activity in the multiple soft tissue nodules in the posterior right abdomen, consistent with ectopic polysplenia.

SPECT/CT imaging of apoptosis in aortic aneurysm with radiolabeled duramycin.

The objective of this research was to estimate whether a [99mTc]duramycin probe can be used for apoptosis imaging in patients with aortic aneurysm (AA). Vascular smooth muscle cell (SMC) apoptosis has an important influence on AA development. Thus, non-invasive imaging of SMC apoptosis may be able to evaluate AA progress and risk stratification. SMCs were treated with hydrogen peroxide (H2O2; 200 µΜ) or culture medium as a control. Apoptosis was measured using flow cytometry and [99mTc]duramycin to detect the binding efficiency to apoptotic SMCs. C57/BL6 mice were administered angiotensin-II and beta-aminopropionitrile (BAPN) subcutaneously to establish an AA model, or saline for controls. Aortic specimens underwent pathological evaluation and their aortic diameters were measured after 6 weeks. Micro-SPECT/CT scanning of [99mTc]duramycin and 18F-FDG PET detection were performed. SMCs treated with H2O2 showed more apoptosis compared with the control group (67.2 ± 3.8% vs. 16.1 ± 0.6%, P < 0.01). The experimental group showed a high rate of AA formation (70%) compared with no AA formation in the control group. The average aorta diameter was higher and [99mTc]duramycin uptake at the AA site was higher in the experimental group compared with the control group. Compared with the normal aorta in the control group, AA in experiment group had more severe medial degeneration, elastic fiber reduction and fracture, and collagen degeneration. TUNEL staining verified the higher apoptosis rate at the AA site in experiment group compared with the control group (63.9 ± 3.7% in ascending AA, 66.4 ± 4.0% in thoracic AA, vs. 3.5 ± 0.3% in normal aorta, P < 0.01). [99mTc]Duramycin may be an effective probe to evaluate apoptosis in AA.

Left Ventricular Assist Device-Associated Gastrointestinal Bleeding: Recognition of an Iatrogenic Etiology on 99mTc-Tagged Red Blood Cell Scintigraphy.

99mTc-tagged red blood cell scintigraphy is the imaging modality of choice in the diagnosis of active gastrointestinal bleeding. Continuous-flow left ventricular assist devices are the state-of-the-art treatment for advanced heart failure, with gastrointestinal bleeding as the most common complication. Recognition of the distinctive imaging feature of continuous-flow left ventricular assist devices on scintigraphic images can aid diagnosis of gastrointestinal bleeding.

Non-cardiac uptake of technetium-99m pyrophosphate in transthyretin cardiac amyloidosis.

BACKGROUND: Technetium-based bone scintigraphy is rapidly becoming the most common non-invasive imaging tool in the diagnosis of Transthyretin cardiac amyloidosis (ATTR). Skeletal muscle uptake has been described with technetium-99m-3,3-diphosphono-1,2-propanodicarboxylic acid (TcDPD), and may account for masking of bony uptake. We sought to investigate skeletal muscle uptake of technetium-99m-pyrophosphate (TcPYP) in patients with ATTR. METHODS AND RESULTS: This was a retrospective analysis of 57 patients diagnosed with ATTR who underwent TcPYP scintigraphy. Cardiac uptake was assessed on whole-body planar imaging using a semiquantitative scale (grades 0 to 3) and on single-photon emission computed tomography (SPECT) with CT attenuation correction using total myocardial counts per voxel after a 3-hour incubation. Skeletal muscle (psoas and biceps), vertebral body, LV myocardium, and blood pool mean counts were calculated. In the cohort (age 78 ± 9 years, 77% male, and 30% hereditary ATTR), there was no visualized tracer uptake in skeletal muscle or soft tissue on qualitative SPECT assessment. Total and blood pool-corrected uptake in the muscle groups were significantly less than myocardium and bone (P < 0.001). Blood pool-corrected muscle uptake was not associated with semiquantitative grade 3 vs 2 uptake (psoas P = 0.66, biceps P = 0.13) or presence of hereditary ATTR (psoas P = 0.43, biceps P = 0.69). As bony uptake decreased, there was no corresponding increase in skeletal muscle uptake. CONCLUSIONS: In patients with ATTR cardiac amyloidosis, skeletal muscle uptake of TcPYP is minimal when assessed by qualitative and quantitative metrics, and is not significantly different in patients with grade 2 vs 3 semiquantitative uptake. The properties of this tracer may be different than TcDPD with respect to non-cardiac uptake.

Evaluation of 99mTc-sulfadiazine as Bacillus microorganisms infection imaging agent using animal model.

Bacterial infection is one of the vital sources of morbidity and mortality. The development of single photon emission computed tomography (SPECT) radiotracer agents using antibiotics, for targeting in-vivo bacteria, helps in antibiotic dose calibration, targeted infection therapy and reduction in mortality rate. The aim of this study was to appraised 99mTc-labeling sulfadiazine as a radiopharmaceutical for bacillus infections imaging. Radiolabeling of sulfadiazine with technetium-99m was carried out by subsequent addition of 1.5 mL aqueous solution of sulfadiazine (1mg/mL), 120µg stannous tartrate, gentistic acid as stabilizing agent and 185 MBq normal saline solution of 99mTcO4-1 (pertechnetate) at pH = 5. The reaction mixture was incubated for 40 min at room temperature with light stirring. The quality control analysis (ITLC-SG and paper chromatography analysis) revealed ~ 98% labeling yield. Biodistribution and scintigraphic study was carried using bacillus bacterial infection induced New Zealand white rabbits. Due to the ease of 99mTc-sulfadiazine conjugation method, high labeling efficiency, shelf stability (>95% up to 6h), blood serum stability (~90% up to 6h) and high uptake in the infected muscle (T/NT =2.21 at 1H), 99mTc-SDZ could be used as radiopharmaceutical of choice for further pre-clinical and clinical studies.

Preferential Cleavage of a Tripeptide Linkage by Enzymes on Renal Brush Border Membrane To Reduce Renal Radioactivity Levels of Radiolabeled Antibody Fragments.

The obstructive renal radioactivity after injection of antibody fragments/constructs labeled with metallic radionuclides would be improved by liberating a radiometal chelate of urinary excretion from the antibody molecules by enzymes on the renal brush border membrane (BBM). A tripeptide GFK sequence was newly evaluated as an enzyme-cleavable linkage and conjugated to a 99mTc chelate of an isonicotinic acid derivative of 2-picolylglycine (99mTc-IPG). 99mTc-IPG-glycine was liberated from 99mTc-IPG-GFK by the enzymes, while 99mTc-IPG-GK (where the tripeptide GFK was substituted with a dipeptide GK) did not. When injected into mice, 99mTc-IPG-GFK-conjugated Fab exhibited lower renal radioactivity levels than directly radioiodinated Fab shortly after injection without reducing the tumor radioactivity levels, due to a release and excretion of 99mTc-IPG-glycine by enzymes present on the renal BBM. These findings would provide insights to develop antibody fragments/constructs labeled with metallic radionuclides of the clinical relevance for improved renal radioactivity levels.

Lung uptake during 99mTc-hydroxymethylene diphosphonate scintigraphy in patient with TTR cardiac amyloidosis: An underestimated phenomenon.

BACKGROUND: Full body scintigraphy using bone tracers plays an important role in defining the type of amyloidosis and in diagnosing the heart involvement (cardiac amyloidosis, CA). No study has been conducted to explore lung retention (LR) in CA and its correlation to heart retention (HR).We evaluated LR in patients undergoing 99mTc-HMDP scintigraphy during evaluation for suspected CA. METHODS AND RESULTS: We enrolled 93 suspected CA patients. Patients underwent a complete diagnostic work up. After diagnostic process 82 patients resulted affected by certain CA (20 AL and 62 TTR), while 11 subjects showed left ventricular hypertrophy (LVH) not caused by CA. 99mTc-HMDP cardiac uptake was evaluated using the Perugini visual score while the modified Janssen score was used for LR estimation (grade 0 no uptake, grade 1 less than ribs, grade 2 more than ribs). RESULTS: 99mTc-HMDP LR was observed in 1/20 AL patient (5%), while 36/62 (58%) TTR patients showed LR with 29 grade 1 (47%) and 7 grade 2 (11%). No LR was observed in patients with LVH and no CA. LR was not evident in patients without HR, present in 1/3 (33%) of the patients with Perugini 1 HR and 11/24 (46%) and 26/36 (72%) of the patients showing respectively a Perugini 2 and a Perugini 3. CONCLUSION: 99mTc-HMDP scintigraphy shows LR in about 60% of TTR subjects, related to the grade of HR. In AL amyloidosis LR is less frequent than in TTR amyloidosis suggesting an aetiological tropism that seems comparable to the already known TTR related cardiac tropism.