Epidemiological Study on Case Definition of Methicillin-Resistant Staphylococcus aureus Enteritis.

Background: Methicillin-resistant Staphylococcus aureus (MRSA) enteritis is a condition in which MRSA grows abnormally in the intestine after administration of antimicrobial agents, resulting in enteritis. Patients with MRSA detected in stool culture tests are often diagnosed with MSRA enteritis. However, uncertainty remains in the diagnostic criteria; therefore, we conducted epidemiological studies to define these cases. Patients and Methods: Patients who tested positive for MRSA by stool culture using selective media 48 h after admission to Kochi Medical School Hospital between April 1, 2012, and December 31, 2022, and did not meet the exclusion criteria were included. We defined MRSA enteritis (Group A) as cases that were responsive to treatment with vancomycin hydrochloride powder, had a Bristol Stool Scale of ≥ 5, and a stool frequency of at least three times per day; all others were MRSA carriers (Group B). Multivariate analysis was performed to risk factors associated with MRSA enteritis. Results: Groups A and B included 18 (25.4%) and 53 (74.6%) patients, respectively. Multivariate logistic regression analysis showed that a white blood cell count of > 10000/µL (odds ratio [OR], 5.50; 95% confidence interval [CI], 1.12-26.9), MRSA count of ≥ 2+ in stool cultures (OR, 8.91; 95% CI, 1.79-44.3), and meropenem administration within 1 month of stool specimen submission (OR, 7.47; 95% CI, 1.66-33.6) were risk factors of MRSA enteritis. Conclusion: The case definitions reviewed for MRSA enteritis may be useful as diagnostic criteria.

Synthesis and Biological Evaluation of a Novel Sugar-Conjugated Platinum(II) Complex Having a Tumor-Targeting Effect.

We designed and synthesized a novel platinum complex conjugated with 2-fluorinated 2-deoxyglucoside, named FGC-Pt, to capitalize on the Warburg effect and metabolic trapping properties of [18F]2-deoxy-2-fluoro-d-glucose ([18F]FDG). Then, we conducted comprehensive in vitro and in vivo studies to evaluate the effects of FGC-Pt. In vitro cytotoxicity assays using HeLa cells revealed that FGC-Pt exhibited concentration-dependent cytotoxicity, even though its cytotoxic effect was less pronounced than that of cisplatin. In the evaluation of in vivo biodistribution in mice, platinum concentration in tumors and major organs (muscle, bone, blood, liver, and kidney) and the ratio of platinum concentration in tumors to major organs following the tail vein injection of FGC-Pt and cisplatin suggest that FGC-Pt is more retained in tumors than in other organs and tends to accumulate in tumors more than cisplatin. Furthermore, an in vivo assessment of the antitumor effect conducted in A549 cell-bearing mice demonstrated that FGC-Pt possesses substantial potential as an antitumor agent. It exhibited a tumor growth-inhibitory effect comparable to that of cisplatin while inducing lower toxicity, as evidenced by lower weight loss after administration. Herein, we successfully produced a novel compound with a tumor-growth-inhibitory effect comparable to that of cisplatin and low toxicity.

Translational enhancement of target endogenous mRNA in mammalian cells using programmable RNA-binding pentatricopeptide repeat proteins.

Programmable protein scaffolds are invaluable in the development of genome engineering tools. The pentatricopeptide repeat (PPR) protein is an attractive platform for RNA manipulation because of its programmable RNA-binding selectivity, which is determined by the combination of amino acid species at three specific sites in the PPR motif. Translation is a key RNA regulatory step that determines the final gene expression level and is involved in various human diseases. In this study, designer PPR protein was used to develop a translational enhancement technique by fusion with the translation initiation factor eIF4G. The results showed that the PPR-eIF4G fusion protein could activate the translation of endogenous c-Myc and p53 mRNAs and control cell fate, indicating that PPR-based translational enhancement is a versatile technique applicable to various endogenous mRNAs in mammalian cells. In addition, the translational enhancement was dependent on both the target position and presence of eIF4G, suggesting the presence of an unknown translation activation mechanism.

Production and synthesis of a novel 191Pt-labeled platinum complex and evaluation of its biodistribution in healthy mice.

We previously reported that our sugar-conjugated platinum complex (cis-dichloro [(2-fluoro-α-d-glucopylanosidyl) propane-1,3-diamine] platinum: FGC-Pt) has low toxicity and tumor growth inhibitory effect comparable to that of cisplatin. We focused on radioactive Pt isotopes in order to analyze the kinetics of FGC-Pt using gamma-ray imaging techniques, assuming that FGC-Pt could be used for chemotherapy in the future. Therefore, in this study, we aimed to develop a non-invasive method to analyze the biodistribution of FGC-Pt using 191Pt-labeled FGC-Pt ([191Pt]FGC-Pt). 191Pt was produced via the (n,2n) reaction induced by accelerator neutrons. [191Pt]FGC-Pt was prepared using two different methods. In the first method, [191Pt]FGC-Pt (method A) was obtained through the accelerator neutron irradiation of FGC-Pt. In the second method, [191Pt]FGC-Pt (method B) was synthesized using [191Pt]K2PtCl4, which was obtained by the accelerator neutron irradiation of K2PtCl4. Highly purified [191Pt]FGC-Pt was obtained using the latter method, which suggests that the synthetic method using a 191Pt-labeled platinum reagent is suitable for the radioactivation of platinum complexes. We also aimed to investigate whether a significant correlation existed between the biodistribution of FGC-Pt and [191Pt]FGC-Pt in healthy mice 24 h after tail vein administration. FGC-Pt and [191Pt]FGC-Pt were similarly distributed in healthy mice, with a higher accumulation in the liver and kidney 24 h post injection. In addition, a significant correlation (p < 0.05, r = 0.92) between the 191Pt radioactivity concentration (%ID/g (gamma counter)) and platinum concentration (%ID/g (ICP-MS)) was observed in 13 organs. These results suggest that 191Pt-labeled compounds, synthesized using radioactive platinum reagents, can be used to confirm the biodistribution of platinum compounds. Our study on the biodistribution of [191Pt]FGC-Pt is expected to contribute to the development of novel platinum-based drugs in the future.

Effect of Water on Direct Radioiodination of Small Molecules/Peptides Using Copper-Mediated Iododeboronation in Water-Alcohol Solvent.

Direct radioiodination of peptides using copper-mediated iododeboronation is a promising radiosynthetic method for solving issues of classical direct radiolabeling, such as toxicity of the organotin precursor (iododestannylation) or formation of radio byproducts (by electrophilic iodination of a tyrosine residue). However, the parameters for optimizing the reaction conditions for various peptides are not completely understood. In particular, considering peptide solubility, the effects of water-containing solvents on labeling efficiency should be thoroughly investigated. Herein, we describe the effect of water on copper-mediated radioiododeboronation and the key factors for ensuring the successful radiolabeling of small molecules and peptides in water-organic solvents. 125I-labeled substrates containing peptides ([125I]m/p-IBTA) were obtained with high radiochemical conversions (RCCs: >95%) using an alcohol solvent, and a decrease in these RCCs was observed with increasing water content in the methanol solvent. Additionally, when using water-methanol solvents, a difference in RCC due to the substituent effect was also observed. However, the RCCs can be improved without the use of other additives by adjusting the copper catalyst and time of the labeling reaction or by utilizing substituent effects. This study contributes to the improvement of the design of boronic peptide precursors and radiolabeling protocols using copper-mediated iododeboronation.

First case of bacteremia caused by Cetobacterium somerae following necrotizing cholecystitis.

Cetobacterium somerae, a gram-negative anaerobic rod, first identified in the feces of children with autism, also colonize freshwater fish intestinal tract. However there have been no reports of human C. somerae infection. Here, we describe the first case of C. somerae bacteremia in a patient with necrotizing cholecystitis. A 72-year-old male presented to the emergency department with chills, vomiting, and fever and was diagnosed with acute necrotizing cholecystitis. An emergency cholecystectomy was performed and the following day, two sets of blood culture were positive for gram-negative bacilli. Identification of C. somerae from the biochemical profile was difficult but possible by mass spectrometry and 16s rRNA sequence.

Novel [ 111 In]In-BnDTPA-EphA2-230-1 Antibody for Single-Photon Emission Computed Tomography Imaging Tracer Targeting of EphA2.

Erythropoietin-producing hepatocellular receptor A2 (EphA2) is overexpressed in cancer cells and causes abnormal cell proliferation. Therefore, it has attracted attention as a target for diagnostic agents. In this study, the EphA2-230-1 monoclonal antibody (EphA2-230-1) was labeled with [111In]In and evaluated as an imaging tracer for single-photon emission computed tomography (SPECT) of EphA2. EphA2-230-1 was conjugated with 2-(4-isothiocyanatobenzyl)-diethylenetriaminepentaacetic acid (p-SCN-BnDTPA) and then labeled with [111In]In. [111In]In-BnDTPA-EphA2-230-1 was evaluated in cell-binding, biodistribution, and SPECT/computed tomography (CT) studies. The cellular uptake ratio of [111In]In-BnDTPA-EphA2-230-1 was 14.0 ± 2.1%/mg protein at 4 h in the cell-binding study. In the biodistribution study, a high uptake of [111In]In-BnDTPA-EphA2-230-1 was observed in tumor tissue (14.6 ± 3.2% injected dose/g at 72 h). The superior accumulation of [111In]In-BnDTPA-EphA2-230-1 in tumors was also confirmed using SPECT/CT. Therefore, [111In]In-BnDTPA-EphA2-230-1 has potential as a SPECT imaging tracer for EphA2.

Construction of a Versatile, Programmable RNA-Binding Protein Using Designer PPR Proteins and Its Application for Splicing Control in Mammalian Cells.

RNAs play many essential roles in gene expression and are involved in various human diseases. Although genome editing technologies have been established, the engineering of sequence-specific RNA-binding proteins that manipulate particular cellular RNA molecules is immature, in contrast to nucleotide-based RNA manipulation technology, such as siRNA- and RNA-targeting CRISPR/Cas. Here, we demonstrate a versatile RNA manipulation technology using pentatricopeptide-repeat (PPR)-motif-containing proteins. First, we developed a rapid construction and evaluation method for PPR-based designer sequence-specific RNA-binding proteins. This system has enabled the steady construction of dozens of functional designer PPR proteins targeting long 18 nt RNA, which targets a single specific RNA in the mammalian transcriptome. Furthermore, the cellular functionality of the designer PPR proteins was first demonstrated by the control of alternative splicing of either a reporter gene or an endogenous CHK1 mRNA. Our results present a versatile protein-based RNA manipulation technology using PPR proteins that facilitates the understanding of unknown RNA functions and the creation of gene circuits and has potential for use in future therapeutics.

U-to-C RNA editing by synthetic PPR-DYW proteins in bacteria and human culture cells.

Programmable RNA editing offers significant therapeutic potential for a wide range of genetic diseases. Currently, several deaminase enzymes, including ADAR and APOBEC, can perform programmable adenosine-to-inosine or cytidine-to-uridine RNA correction. However, enzymes to perform guanosine-to-adenosine and uridine-to-cytidine (U-to-C) editing are still lacking to complete the set of transition reactions. It is believed that the DYW:KP proteins, specific to seedless plants, catalyze the U-to-C reactions in mitochondria and chloroplasts. In this study, we designed seven DYW:KP domains based on consensus sequences and fused them to a designer RNA-binding pentatricopeptide repeat (PPR) domain. We show that three of these PPR-DYW:KP proteins edit targeted uridine to cytidine in bacteria and human cells. In addition, we show that these proteins have a 5' but not apparent 3' preference for neighboring nucleotides. Our results establish the DYW:KP aminase domain as a potential candidate for the development of a U-to-C editing tool in human cells.

Copper-mediated radioiodination and radiobromination via aryl boronic precursor and its application to 125I/77Br-labeled prostate-specific membrane antigen imaging probes.

Prostate-specific membrane antigen (PSMA), expressed in prostate cancer cells, is being investigated extensively worldwide as a target for imaging and therapy of prostate cancer. Various radioiodinated PSMA imaging probes have been developed, and their structure has a peptidomimetic urea-based skeleton as a pharmacophore. For direct radioiodination of molecules containing these peptidomimetic structures, prior studies performed radioiododestannylation or electrophilic radioiodination of tyrosine residues. However, although these radiolabeling methods are frequently used, there are some issues with precursor toxicity and by-product production. Therefore, it is required to investigate a radiolabeling method that can be used for the radiosynthesis of radioiodinated PSMA imaging probes with urea-based peptidomimetic structures. We recently reported that copper-mediated radioiodination via a boronic precursor is an effective method for directly labeling a peptide. This radiohalogenation method was expected to be an effective method for radiosynthesis of PSMA imaging probes with a peptidomimetic structure. In this study, to confirm that this labeling method applies to the synthesis of the PSMA imaging probe, we synthesized PSMA imaging probes labeled with 125I and 77Br ([125I]mIB-PS and [77Br]mBrB-PS) using a copper-mediated radiohalogenation via common boronic precursors and investigated optimal boronic precursor and labeling conditions. As a result, the radiochemical yields of [125I]mIB-PS and [77Br]mBrB-PS were improved to > 93% at room temperature by optimizing the structure of the boronic precursor. We demonstrate that copper-mediated nucleophilic radiochemistry using a boronic precursor is a promising radiosynthetic method of PSMA imaging probes. Although we focused on the synthesis of PSMA imaging probes, the results in this study will also be useful for the synthesis of various radioiodine or radiobromine-labeled bioactive molecules.

Development of novel radioiodinated exendin-4 derivatives targeting GLP-1 receptor for detection of ß-cell mass.

In subjects with type 2 diabetes mellitus (T2DM), pancreatic ß-cell mass decreases; however, it is unknown to what extent this decrease contributes to the pathophysiology of T2DM. Therefore, the development of a method for noninvasive detection of ß-cell mass is underway. We previously reported that glucagon-like peptide-1 receptor (GLP-1R) is a promising target molecule for ß-cell imaging. In this study, we attempted to develop a probe targeting GLP-1R for ß-cell imaging using single-photon emission computed tomography (SPECT). For this purpose, we selected exendin-4 as the lead compound and radiolabeled lysine at residue 12 in exendin-4 or additional lysine at the C-terminus using [123I]iodobenzoylation. To evaluate in vitro receptor specificity, binding assay was performed using dispersed mouse islet cells. Biodistribution study was performed in normal ddY mice. Ex vivo autoradiography was performed in transgenic mice expressing green fluorescent protein under control of the mouse insulin I gene promoter. Additionally, SPECT imaging was performed in normal ddY mice. The affinity of novel synthesized derivatives toward pancreatic ß-cells was not affected by iodobenzoylation. The derivatives accumulated in the pancreas after intravenous administration specifically via GLP-1R expressed on the pancreatic ß-cells. Extremely high signal-to-noise ratio was observed during evaluation of biodistribution of [123I]IB12-Ex4. SPECT images using normal mice showed that [123I]IB12-Ex4 accumulated in the pancreas with high contrast between the pancreas and background. These results indicate that [123I]IB12-Ex4 for SPECT is useful for clinical applications because of its preferable kinetics in vivo.

A Putative Single-Photon Emission CT Imaging Tracer for Erythropoietin-Producing Hepatocellular A2 Receptor.

Erythropoietin-producing hepatocellular (Eph) receptors are receptor tyrosine kinases involved in cell-cell contact. The EphA2 receptor is associated with cancer proliferation and migration. Therefore, EphA2 receptor imaging has the potential for cancer diagnosis. Here, we synthesized N-(5-((4-((4-ethylpiperazin-1-yl)methyl)-3-(trifluoromethyl)phenyl)carbamoyl)-2-methylphenyl)-5-[123I]iodonicotinamide ([123I]ETB) and evaluated it as an imaging tracer for single-photon emission computed tomography (SPECT) imaging of the EphA2 receptor. [123I]ETB was designed on the basis of ALW-II-41-27, an inhibitor of EphA2 receptor kinase. Nonradioactive ETB was also synthesized and has been shown to efficiently inhibit EphA2 receptor kinase activity in vitro (IC50: ETB, 90.2 ± 18.9 nM). A cell-binding assay demonstrated that [125I]ETB binds specifically to the EphA2 receptor. The ex vivo biodistribution study of [125I]ETB in U87MG tumor-bearing mice also revealed tumor uptake (2.2% ID/g at 240 min). In addition, [123I]ETB uptake in tumors was visualized via SPECT/CT imaging. On the basis of the above, [123I]ETB can be considered a potential SPECT imaging tracer for the EphA2 receptor.

Copper-mediated radioiodination reaction through aryl boronic acid or ester precursor and its application to direct radiolabeling of a cyclic peptide.

A copper-mediated radioiodination using aryl boronic precursors is attracting attention as a solution to oxidative iododestannylation and nickel-mediated radioiodination drawbacks. The copper-mediated radiolabeling method allows radioiodination at room temperature with stable aryl boronic precursors without preparing complex starting materials or reagents and can be performed in a reaction vessel exposed to air. This method has good potential in radiochemistry; however, studies on the scope of copper-mediated radioiodination through boronic precursors are insufficient. In particular, few reports have demonstrated the effect of protecting groups on radiolabeling efficiency. Therefore, the effect of the protecting group of aryl boronic acids on the copper-mediated radioiodination was investigated. In addition, this method, which does not require heating, is expected to be useful for direct radiolabeling of peptides. Thus, we attempted direct radioiodination of c(RGDyk) as an example. The resulting radioiodination method was well tolerated in various substrates and was unaffected by the pinacol ester-type protecting group. Also, c(RGDyk) was labeled with 125 I via copper-mediated radioiodination using an aryl boronic acid precursor. The reaction time and yield were improved, compared with the indirect method. Furthermore, the large difference in polarity between the boronic acid precursor and the radiolabeled compound facilitated purification.

Daptomycin for the successful treatment of postoperative methicillin-resistant Staphylococcus aureus empyema: a case report.

Empyema is typically treated using pleural space drainage and systemic treatment with antimicrobials, and specific antimicrobial agents in the case of methicillin-resistant Staphylococcus aureus (MRSA) infections. A 57-year-old man underwent segmental resection of the left lung owing to multiple lung metastases and developed MRSA-related empyema postoperatively. Although the patient received chest drainage and linezolid, the inflammation caused by the infection persisted. Consequently, linezolid was replaced by daptomycin, and his empyema was accordingly resolved. Our findings indicate that daptomycin could be an effective treatment for postoperative MRSA-related empyema.

Temperature-dependent fasciation mutants provide a link between mitochondrial RNA processing and lateral root morphogenesis.

Although mechanisms that activate organogenesis in plants are well established, much less is known about the subsequent fine-tuning of cell proliferation, which is crucial for creating properly structured and sized organs. Here we show, through analysis of temperature-dependent fasciation (TDF) mutants of Arabidopsis, root redifferentiation defective 1 (rrd1), rrd2, and root initiation defective 4 (rid4), that mitochondrial RNA processing is required for limiting cell division during early lateral root (LR) organogenesis. These mutants formed abnormally broadened (i.e. fasciated) LRs under high-temperature conditions due to extra cell division. All TDF proteins localized to mitochondria, where they were found to participate in RNA processing: RRD1 in mRNA deadenylation, and RRD2 and RID4 in mRNA editing. Further analysis suggested that LR fasciation in the TDF mutants is triggered by reactive oxygen species generation caused by defective mitochondrial respiration. Our findings provide novel clues for the physiological significance of mitochondrial activities in plant organogenesis.

Aicardi-Goutières syndrome-like encephalitis in mutant mice with constitutively active MDA5.

MDA5 is a cytoplasmic sensor of viral RNA, triggering type I interferon (IFN-I) production. Constitutively active MDA5 has been linked to autoimmune diseases such as systemic lupus erythematosus, Singleton-Merten syndrome (SMS) and Aicardi-Goutières syndrome (AGS), a genetically determined inflammatory encephalopathy. However, AGS research is challenging due to the lack of animal models. We previously reported lupus-like nephritis and SMS-like bone abnormalities in adult mice with constitutively active MDA5 (Ifih1G821S/+), and herein demonstrate that these mice also exhibit high lethality and spontaneous encephalitis with high IFN-I production during the early postnatal period. Increases in the number of microglia were observed in MDA5/MAVS signaling- and IFN-I-dependent manners. Furthermore, microglia showed an activated state with an increased phagocytic capability and reduced expression of neurotrophic factors. Although multiple auto-antibodies including lupus-related ones were detected in the sera of the mice as well as AGS patients, Ifih1G821S/+Rag2-/- mice also exhibited up-regulation of IFN-I, astrogliosis and microgliosis, indicating that auto-antibodies or lymphocytes are not required for the development of the encephalitis. The IFN-I signature without lymphocytic infiltration observed in Ifih1G821S/+ mice is a typical feature of AGS. Collectively, our results suggest that the Ifih1G821S/+ mice are a model recapitulating AGS and that microglia are a potential target for AGS therapy.

Synthesis of 18F-labeled streptozotocin derivatives and an in-vivo kinetics study using positron emission tomography.

Glucose transporter 2 (GLUT2) is involved in glucose uptake by hepatocytes, pancreatic beta cells, and absorptive cells in the intestine and proximal tubules in the kidney. Pancreatic GLUT2 also plays an important role in the mechanism of glucose-stimulated insulin secretion. In this study, novel Fluorine-18-labeled streptozotocin (STZ) derivatives were synthesized to serve as glycoside analogs for in-vivo GLUT2 imaging. Fluorine was introduced to hexyl groups at the 3'-positions of the compounds, and we aimed to synthesize compounds that were more stable than STZ. The nitroso derivatives exhibited relatively good stability during purification and purity analysis after radiosynthesis. We then evaluated the compounds in PET imaging and ex-vivo biodistribution studies. We observed high levels of radioactivity in the liver and kidney, which indicated accumulation in these organs within 5 min of administration. In contrast, the denitroso derivatives accumulated only in the kidney and bladder shortly after administration. Compounds with nitroso groups are thus expected to accumulate in GLUT2-expressing organs, and the presence of a nitroso group is essential for in-vivo GLUT2 imaging.

Identification of new pentatricopeptide repeat proteins, MREF1 and 2, involved in mitochondrial RNA editing, using computational target RNA prediction.

C-to-U RNA editing has been widely observed in mitochondrial and plastid RNAs in plants. The editing sites are known to be recognized by pentatricopeptide repeat (PPR) proteins, which belong to one of the largest protein families in vascular plants. PPR proteins are sequence-specific RNA-binding proteins that participate in various steps of organelle RNA metabolism, such as cleavage, stabilization, splicing, translation, and editing. Elucidating the underlying mechanisms of sequence-specific RNA recognition by PPR proteins expanded our understanding of the role of PPR proteins in plant organellar RNA editing and enabled the computational prediction of target RNA-editing sites for PPR proteins of interest. Combining computational prediction and experimental verification, we identified three new PPR proteins involved in mitochondrial RNA editing: At1g56570, known as PGN for RNA editing of nad6_leader_-73 and cox2_742, At4g04370 for RNA editing of nad5_242, and At2g41080 for atp1_1292. Therefore, At4g04370 and At2g41080 were designated as mitochondrial RNA-editing factor 1 (MREF1) and MREF2, respectively. This study supports the use of computational prediction in establishing connections between PPR proteins and specific RNA-editing sites, which are important for maintaining various physiological processes, such as plant development, embryogenesis, and biotic- and abiotic-stress responses.

Impact of repeated yearly vaccination on immune responses to influenza vaccine in an elderly population.

BACKGROUND: The effectiveness of repeated vaccination for seasonal influenza remains controversial. Here, we measured antibody responses to the influenza virus (A/H1N1, A/H3N2 and B) in a closed cohort of older participants vaccinated against influenza virus in each of 5 consecutive years. METHODS: One hundred and 11 volunteers aged >61 years were vaccinated subcutaneously with 1 dose (0.5 ml) of inactivated influenza vaccine as recommended by the World Health Organization from the 2005-2006 season through the 2009-2010 season. Hemagglutination inhibition (HI) antibody titers were determined. RESULTS: HI antibody titers against all 3 virus strains were significantly higher at 4 weeks after vaccination than at a time point prior to vaccination in each of the 5 seasons (P < .01); HI antibody titers were detected at the original prevaccination levels just prior to re-vaccination the following year. Sero-protection and HI antibody titers at 4 weeks after vaccination were similar against all influenza strains and during most of the 5 seasons evaluated. Vaccine strain changes were associated with specific immune responses in 9 of 12 (75%) intervals. CONCLUSIONS: Taken together, our results suggest that annual vaccination is necessary to maintain humoral immunity for the elderly population. Furthermore, our findings revealed that annual seasonal vaccination was not associated with reduced vaccine effectiveness, and that the reformation of the vaccine resulted in amplified immune responses among those undergoing yearly vaccination in the elderly population.

Initial Evaluation of AF78: a Rationally Designed Fluorine-18-Labelled PET Radiotracer Targeting Norepinephrine Transporter.

PURPOSE: Taking full advantage of positron emission tomography (PET) technology, fluorine-18-labelled radiotracers targeting norepinephrine transporter (NET) have potential applications in the diagnosis and assessment of cardiac sympathetic nerve conditions as well as the delineation of neuroendocrine tumours. However, to date, none have been used clinically. Drawbacks of currently reported radiotracers include suboptimal kinetics and challenging radiolabelling procedures. PROCEDURES: We developed a novel fluorine-18-labelled radiotracer targeting NET, AF78, with efficient one-step radiolabelling based on the phenethylguanidine structure. Radiosynthesis of AF78 was undertaken, followed by validation in cell uptake studies, autoradiography, and in vivo imaging in rats. RESULTS: [18F]AF78 was successfully synthesized with 27.9 ± 3.1 % radiochemical yield, > 97 % radiochemical purity and > 53.8 GBq/mmol molar activity. Cell uptake studies demonstrated essentially identical affinity for NET as norepinephrine and meta-iodobenzylgaunidine. Both ex vivo autoradiography and in vivo imaging in rats showed homogeneous and specific cardiac uptake. CONCLUSIONS: The new PET radiotracer [18F]AF78 demonstrated high affinity for NET and favourable biodistribution in rats. A structure-activity relationship between radiotracer structures and affinity for NET was revealed, which may serve as the basis for the further design of NET targeting radiotracers with favourable features.