@article{ChenWernerLapaetal.2018, author = {Chen, Xinyu and Werner, Rudolf A. and Lapa, Constantin and Nose, Naoko and Hirano, Mitsuru and Javadi, Mehrbod S. and Robinson, Simon and Higuchi, Takahiro}, title = {Subcellular storage and release mode of the novel \(^{18}\)F-labeled sympathetic nerve PET tracer LMI1195}, series = {EJNMMI Research}, volume = {8}, journal = {EJNMMI Research}, number = {12}, issn = {2191-219X}, doi = {10.1186/s13550-018-0365-9}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-167081}, year = {2018}, abstract = {Background: \(^{18}\)F-N-[3-bromo-4-(3-fluoro-propoxy)-benzyl]-guanidine (\(^{18}\)F-LMI1195) is a new class of PET tracer designed for sympathetic nervous imaging of the heart. The favorable image quality with high and specific neural uptake has been previously demonstrated in animals and humans, but intracellular behavior is not yet fully understood. The aim of the present study is to verify whether it is taken up in storage vesicles and released in company with vesicle turnover. Results: Both vesicle-rich (PC12) and vesicle-poor (SK-N-SH) norepinephrine-expressing cell lines were used for in vitro tracer uptake studies. After 2 h of \(^{18}\)F-LMI1195 preloading into both cell lines, effects of stimulants for storage vesicle turnover (high concentration KCl (100 mM) or reserpine treatment) were measured at 10, 20, and 30 min. \(^{131}\)I-meta-iodobenzylguanidine (\(^{131}\)I-MIBG) served as a reference. Both high concentration KCl and reserpine enhanced \(^{18}\)F-LMI1195 washout from PC12 cells, while tracer retention remained stable in the SK-N-SH cells. After 30 min of treatment, 18F-LMI1195 releasing index (percentage of tracer released from cells) from vesicle-rich PC12 cells achieved significant differences compared to cells without treatment condition. In contrast, such effect could not be observed using vesicle-poor SK-N-SH cell lines. Similar tracer kinetics after KCl or reserpine treatment were also observed using 131I-MIBG. In case of KCl exposure, Ca\(^{2+}\)-free buffer with the calcium chelator, ethylenediaminetetracetic acid (EDTA), could suppress the tracer washout from PC12 cells. This finding is consistent with the tracer release being mediated by Ca\(^{2+}\) influx resulting from membrane depolarization. Conclusions: Analogous to \(^{131}\)I-MIBG, the current in vitro tracer uptake study confirmed that \(^{131}\)F-LMI1195 is also stored in vesicles in PC12 cells and released along with vesicle turnover. Understanding the basic kinetics of \(^{18}\)FLMI1195 at a subcellular level is important for the design of clinical imaging protocols and imaging interpretation.}, subject = {Positronen-Emissions-Tomografie}, language = {en} } @article{NoseNogamiKoshinoetal.2021, author = {Nose, Naoko and Nogami, Suguru and Koshino, Kazuhiro and Chen, Xinyu and Werner, Rudolf A. and Kashima, Soki and Rowe, Steven P. and Lapa, Constantin and Fukuchi, Kazuki and Higuchi, Takahiro}, title = {[18F]FDG-labelled stem cell PET imaging in different route of administrations and multiple animal species}, series = {Scientific Reports}, volume = {11}, journal = {Scientific Reports}, number = {1}, doi = {10.1038/s41598-021-90383-4}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-260590}, year = {2021}, abstract = {Stem cell therapy holds great promise for tissue regeneration and cancer treatment, although its efficacy is still inconclusive and requires further understanding and optimization of the procedures. Non-invasive cell tracking can provide an important opportunity to monitor in vivo cell distribution in living subjects. Here, using a combination of positron emission tomography (PET) and in vitro 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) direct cell labelling, the feasibility of engrafted stem cell monitoring was tested in multiple animal species. Human mesenchymal stem cells (MSCs) were incubated with phosphate-buffered saline containing [18F]FDG for in vitro cell radiolabelling. The pre-labelled MSCs were administrated via peripheral vein in a mouse (n=1), rats (n=4), rabbits (n=4) and non-human primates (n=3), via carotid artery in rats (n=4) and non-human primates (n=3), and via intra-myocardial injection in rats (n=5). PET imaging was started 10 min after cell administration using a dedicated small animal PET system for a mouse and rats. A clinical PET system was used for the imaging of rabbits and non-human primates. After MSC administration via peripheral vein, PET imaging revealed intense radiotracer signal from the lung in all tested animal species including mouse, rat, rabbit, and non-human primate, suggesting administrated MSCs were trapped in the lung tissue. Furthermore, the distribution of the PET signal significantly differed based on the route of cell administration. Administration via carotid artery showed the highest activity in the head, and intra-myocardial injection increased signal from the heart. In vitro [18F]FDG MSC pre-labelling for PET imaging is feasible and allows non-invasive visualization of initial cell distribution after different routes of cell administration in multiple animal models. Those results highlight the potential use of that imaging approach for the understanding and optimization of stem cell therapy in translational research.}, language = {en} } @article{JanssenHoffmannKannoetal.2020, author = {Janssen, Jan P. and Hoffmann, Jan V. and Kanno, Takayuki and Nose, Naoko and Grunz, Jan-Peter and Onoguchi, Masahisa and Chen, Xinyu and Lapa, Constantin and Buck, Andreas K. and Higuchi, Takahiro}, title = {Capabilities of multi-pinhole SPECT with two stationary detectors for in vivo rat imaging}, series = {Scientific Reports}, volume = {10}, journal = {Scientific Reports}, doi = {10.1038/s41598-020-75696-0}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-230616}, year = {2020}, abstract = {We aimed to investigate the image quality of the U-SPECT5/CT E-Class a micro single-photon emission computed tomography (SPECT) system with two large stationary detectors for visualization of rat hearts and bones using clinically available \(^{99m}\)Tc-labelled tracers. Sensitivity, spatial resolution, uniformity and contrast-to-noise ratio (CNR) of the small-animal SPECT scanner were investigated in phantom studies using an ultra-high-resolution rat and mouse multi-pinhole collimator (UHR-RM). Point source, hot-rod, and uniform phantoms with \(^{99m}\)Tc-solution were scanned for high-count performance assessment and count levels equal to animal scans, respectively. Reconstruction was performed using the similarity-regulated ordered-subsets expectation maximization (SROSEM) algorithm with Gaussian smoothing. Rats were injected with similar to 100 MBq [\(^{99m}\)TcTc-MIBI or similar to 150 MBq [\(^{99m}\)Tc]Tc-HMDP and received multi-frame micro-SPECT imaging after tracer distribution. Animal scans were reconstructed for three different acquisition times and post-processed with different sized Gaussian filters. Following reconstruction, CNR was calculated and image quality evaluated by three independent readers on a five-point scale from 1="very poor" to 5="very good". Point source sensitivity was 567 cps/MBq and radioactive rods as small as 1.2 mm were resolved with the UHR-RM collimator. Collimator-dependent uniformity was 55.5\%. Phantom CNR improved with increasing rod size, filter size and activity concentration. Left ventricle and bone structures were successfully visualized in rat experiments. Image quality was strongly affected by the extent of post-filtering, whereas scan time did not have substantial influence on visual assessment. Good image quality was achieved for resolution range greater than 1.8 mm in bone and 2.8 mm in heart. The recently introduced small animal SPECT system with two stationary detectors and UHR-RM collimator is capable to provide excellent image quality in heart and bone scans in a rat using standardized reconstruction parameters and appropriate post-filtering. However, there are still challenges in achieving maximum system resolution in the sub-millimeter range with in vivo settings under limited injection dose and acquisition time.}, language = {en} } @article{ChenWernerKoshinoetal.2022, author = {Chen, Xinyu and Werner, Rudolf A. and Koshino, Kazuhiro and Nose, Naoko and M{\"u}hlig, Saskia and Rowe, Steven P. and Pomper, Martin G. and Lapa, Constantin and Decker, Michael and Higuchi, Takahiro}, title = {Molecular Imaging-Derived Biomarker of Cardiac Nerve Integrity - Introducing High NET Affinity PET Probe \(^{18}\)F-AF78}, series = {Theranostics}, volume = {12}, journal = {Theranostics}, number = {9}, doi = {10.7150/thno.63205}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-300685}, pages = {4446 -- 4458}, year = {2022}, abstract = {Background: Radiolabeled agents that are substrates for the norepinephrine transporter (NET) can be used to quantify cardiac sympathetic nervous conditions and have been demonstrated to identify high-risk congestive heart failure (HF) patients prone to arrhythmic events. We aimed to fully characterize the kinetic profile of the novel \(^{18}\)F-labeled NET probe AF78 for PET imaging of the cardiac sympathetic nervous system (SNS) among various species. Methods: \(^{18}\)F-AF78 was compared to norepinephrine (NE) and established SNS radiotracers by employing in vitro cell assays, followed by an in vivo PET imaging approach with healthy rats, rabbits and nonhuman primates (NHPs). Additionally, chase protocols were performed in NHPs with NET inhibitor desipramine (DMI) and the NE releasing stimulator tyramine (TYR) to investigate retention kinetics in cardiac SNS. Results: Relative to other SNS radiotracers, 18F-AF78 showed higher transport affinity via NET in a cell-based competitive uptake assay (IC\(^{50}\) 0.42 ± 0.14 µM), almost identical to that of NE (IC\(^{50}\), 0.50 ± 0.16 µM, n.s.). In rabbits and NHPs, initial cardiac uptake was significantly reduced by NET inhibition. Furthermore, cardiac tracer retention was not affected by a DMI chase protocol but was markedly reduced by intermittent TYR chase, thereby suggesting that \(^{18}\)F-AF78 is stored and can be released via the synaptic vesicular turnover process. Computational modeling hypothesized the formation of a T-shaped π-π stacking at the binding site, suggesting a rationale for the high affinity of \(^{18}\)F-AF78. Conclusion: \(^{18}\)F-AF78 demonstrated high in vitro NET affinity and advantageous in vivo radiotracer kinetics across various species, indicating that \(^{18}\)F-AF78 is an SNS imaging agent with strong potential to guide specific interventions in cardiovascular medicine.}, language = {en} } @article{WernerWakabayashiChenetal.2019, author = {Werner, Rudolf A. and Wakabayashi, Hiroshi and Chen, Xinyu and Hayakawa, Nobuyuki and Lapa, Constantin and Rowe, Steven P. and Javadi, Mehrbod S. and Robinson, Simon and Higuchi, Takahiro}, title = {Ventricular distribution pattern of the novel sympathetic nerve PET radiotracer \(^{18}\)F-LMI1195 in Rabbit Hearts}, series = {Scientific Reports}, volume = {9}, journal = {Scientific Reports}, doi = {10.1038/s41598-019-53596-2}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-202707}, pages = {17026}, year = {2019}, abstract = {We aimed to determine a detailed regional ventricular distribution pattern of the novel cardiac nerve PET radiotracer \(^{18}\)F-LMI1195 in healthy rabbits. Ex-vivo high resolution autoradiographic imaging was conducted to identify accurate ventricular distribution of \(^{18}\)F-LMI1195. In healthy rabbits, \(^{18}\)F-LMI1195 was administered followed by the reference perfusion marker \(^{201}\)Tl for a dual-radiotracer analysis. After 20 min of \(^{18}\)F-LMI1195 distribution time, the rabbits were euthanized, the hearts were extracted, frozen, and cut into 20-μm short axis slices. Subsequently, the short axis sections were exposed to a phosphor imaging plate to determine \(^{18}\)F-LMI1195 distribution (exposure for 3 h). After complete \(^{18}\)F decay, sections were re-exposed to determine 201Tl distribution (exposure for 7 days). For quantitative analysis, segmental regions of Interest (ROIs) were divided into four left ventricular (LV) and a right ventricular (RV) segment on mid-ventricular short axis sections. Subendocardial, mid-portion, and subepicardial ROIs were placed on the LV lateral wall. \(^{18}\)F-LMI1195 distribution was almost homogeneous throughout the LV wall without any significant differences in all four LV ROIs (anterior, posterior, septal and lateral wall, 99 ± 2, 94 ± 5, 94 ± 4 and 97 ± 3\%LV, respectively, n.s.). Subepicardial \(^{201}\)Tl uptake was significantly lower compared to the subendocardial portion (subendocardial, mid-portion, and subepicardial activity: 90 ± 3, 96 ± 2 and *80 ± 5\%LV, respectively, *p < 0.01 vs. mid-portion). This was in contradistinction to the transmural wall profile of \(^{18}\)F-LMI1195 (90 ± 4, 96 ± 5 and 84 ± 4\%LV, n.s.). A slight but significant discrepant transmural radiotracer distribution pattern of \(^{201}\)Tl in comparison to \(^{18}\)F-LMI1195 may be a reflection of physiological sympathetic innervation and perfusion in rabbit hearts.}, language = {en} } @article{ChenKudoLapaetal.2020, author = {Chen, Xinyu and Kudo, Takashi and Lapa, Constantin and Buck, Andreas and Higuchi, Takahiro}, title = {Recent advances in radiotracers targeting norepinephrine transporter: structural development and radiolabeling improvements}, series = {Journal of Neural Transmission}, volume = {127}, journal = {Journal of Neural Transmission}, doi = {10.1007/s00702-020-02180-4}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-241148}, pages = {851-873}, year = {2020}, abstract = {The norepinephrine transporter (NET) is a major target for the evaluation of the cardiac sympathetic nerve system in patients with heart failure and Parkinson's disease. It is also used in the therapeutic applications against certain types of neuroendocrine tumors, as exemplified by the clinically used \(^{123/131}\)I-MIBG as theranostic single-photon emission computed tomography (SPECT) agent. With the development of more advanced positron emission tomography (PET) technology, more radiotracers targeting NET have been reported, with superior temporal and spatial resolutions, along with the possibility of functional and kinetic analysis. More recently, fluorine-18-labelled NET tracers have drawn increasing attentions from researchers, due to their longer radiological half-life relative to carbon-11 (110 min vs. 20 min), reduced dependence on on-site cyclotrons, and flexibility in the design of novel tracer structures. In the heart, certain NET tracers provide integral diagnostic information on sympathetic innervation and the nerve status. In the central nervous system, such radiotracers can reveal NET distribution and density in pathological conditions. Most radiotracers targeting cardiac NET-function for the cardiac application consistent of derivatives of either norepinephrine or MIBG with its benzylguanidine core structure, e.g. \(^{11}\)C-HED and \(^{18}\)F-LMI1195. In contrast, all NET tracers used in central nervous system applications are derived from clinically used antidepressants. Lastly, possible applications of NET as selective tracers over organic cation transporters (OCTs) in the kidneys and other organs controlled by sympathetic nervous system will also be discussed.}, language = {en} } @article{MatsusakaWernerAriasLozaetal.2022, author = {Matsusaka, Yohji and Werner, Rudolf A. and Arias-Loza, Paula and Nose, Naoko and Sasaki, Takanori and Chen, Xinyu and Lapa, Constantin and Higuchi, Takahiro}, title = {Performance Evaluation of a Preclinical SPECT Scanner with a Collimator Designed for Medium-Sized Animals}, series = {Molecular Imaging}, volume = {2022}, journal = {Molecular Imaging}, doi = {10.1155/2022/9810097}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-300713}, year = {2022}, abstract = {Background. Equipped with two stationary detectors, a large bore collimator for medium-sized animals has been recently introduced for dedicated preclinical single-photon emission computed tomography (SPECT) imaging. We aimed to evaluate the basic performance of the system using phantoms and healthy rabbits. Methods. A general-purpose medium-sized animal (GP-MSA) collimator with 135 mm bore diameter and thirty-three holes of 2.5 mm diameter was installed on an ultrahigh-resolution scanner equipped with two large stationary detectors (U-SPECT5-E/CT). The sensitivity and uniformity were investigated using a point source and a cylinder phantom containing 99mTc-pertechnetate, respectively. Uniformity (in \%) was derived using volumes of interest (VOIs) on images of the cylinder phantom and calculated as , with lower values of \% indicating superior performance. The spatial resolution and contrast-to-noise ratios (CNRs) were evaluated with images of a hot-rod Derenzo phantom using different activity concentrations. Feasibility of in vivo SPECT imaging was finally confirmed by rabbit imaging with the most commonly used clinical myocardial perfusion SPECT agent [99mTc]Tc-sestamibi (dynamic acquisition with a scan time of 5 min). Results. In the performance evaluation, a sensitivity of 790 cps/MBq, a spatial resolution with the hot-rod phantom of 2.5 mm, and a uniformity of 39.2\% were achieved. The CNRs of the rod size 2.5 mm were 1.37, 1.24, 1.20, and 0.85 for activity concentration of 29.2, 1.0, 0.5, and 0.1 MBq/mL, respectively. Dynamic SPECT imaging in rabbits allowed to visualize most of the thorax and to generate time-activity curves of the left myocardial wall and ventricular cavity. Conclusion. Preclinical U-SPECT5-E/CT equipped with a large bore collimator demonstrated adequate sensitivity and resolution for in vivo rabbit imaging. Along with its unique features of SPECT molecular functional imaging is a superior collimator technology that is applicable to medium-sized animal models and thus may promote translational research for diagnostic purposes and development of novel therapeutics.}, language = {en} } @article{WernerChenHiranoetal.2018, author = {Werner, Rudolf A. and Chen, Xinyu and Hirano, Mitsuru and Rowe, Steven P. and Lapa, Constantin and Javadi, Mehrbod S. and Higuchi, Takahiro}, title = {SPECT vs. PET in Cardiac Innervation Imaging: Clash of the Titans}, series = {Clinical and Translational Imaging}, journal = {Clinical and Translational Imaging}, issn = {2281-5872}, doi = {10.1007/s40336-018-0289-4}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-163628}, year = {2018}, abstract = {Purpose: We aim to provide an overview of the conventional single photon emission computed tomography (SPECT) and emerging positron emission tomography (PET) catecholamine analogue tracers for assessing myocardial nerve integrity, in particular focusing on \(^{18}\)F-labeled tracers. Results: Increasingly, the cardiac sympathetic nervous system (SNS) is being studied by non-invasive molecular imaging approaches. Forming the backbone of myocardial SNS imaging, the norepinephrine (NE) transporter at the sympathetic nerve terminal plays a crucial role for visualizing denervated myocardium: in particular, the single-photon-emitting NE analogue \(^{123}\)I-meta-Iodobenzylguanidine (\(^{123}\)I-mIBG) has demonstrated favorable results in the identification of patients at a high risk for cardiac death. However, cardiac neuronal PET agents offer several advantages inlcuding improved spatio-temporal resolution and intrinsic quantifiability. Compared to their \(^{11}\)C-labeled counterparts with a short half-life (20.4 min), novel \(^{18}\)F-labeled PET imaging agents to assess myocardial nerve integrity have the potential to revolutionize the field of SNS molecular imaging: The longer half-life of \(^{18}\)F (109.8 min) allows for more flexibility in the study design and delivery from central cyclotron facilities to smaller hospitals may lead to further cost reduction. A great deal of progress has been made by the first in-human studies of such \(^{18}\)F-labeled SNS imaging agents. Moreover, dedicated animal platforms open avenues for further insights into the handling of radiolabeled catecholamine analogues at the sympathetic nerve terminal. Conclusions: \(^{18}\)F-labeled imaging agents demonstrate key properties for mapping cardiac sympathetic nerve integrity and might outperform current SPECT-based or \(^{11}\)C-labeled tracers in the long run.}, subject = {Positronen-Emissions-Tomografie}, language = {en} } @article{TutovChenWerneretal.2023, author = {Tutov, Anna and Chen, Xinyu and Werner, Rudolf A. and M{\"u}hlig, Saskia and Zimmermann, Thomas and Nose, Naoko and Koshino, Kazuhiro and Lapa, Constantin and Decker, Michael and Higuchi, Takahiro}, title = {Rationalizing the binding modes of PET radiotracers targeting the norepinephrine transporter}, series = {Pharmaceutics}, volume = {15}, journal = {Pharmaceutics}, number = {2}, issn = {1999-4923}, doi = {10.3390/pharmaceutics15020690}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-303949}, year = {2023}, abstract = {Purpose: A new PET radiotracer \(^{18}\)F-AF78 showing great potential for clinical application has been reported recently. It belongs to a new generation of phenethylguanidine-based norepinephrine transporter (NET)-targeting radiotracers. Although many efforts have been made to develop NET inhibitors as antidepressants, systemic investigations of the structure-activity relationships (SARs) of NET-targeting radiotracers have rarely been performed. Methods: Without changing the phenethylguanidine pharmacophore and 3-fluoropropyl moiety that is crucial for easy labeling, six new analogs of \(^{18}\)F-AF78 with different meta-substituents on the benzene-ring were synthesized and evaluated in a competitive cellular uptake assay and in in vivo animal experiments in rats. Computational modeling of these tracers was established to quantitatively rationalize the interaction between the radiotracers and NET. Results: Using non-radiolabeled reference compounds, a competitive cellular uptake assay showed a decrease in NET-transporting affinity from meta-fluorine to iodine (0.42 and 6.51 µM, respectively), with meta-OH being the least active (22.67 µM). Furthermore, in vivo animal studies with radioisotopes showed that heart-to-blood ratios agreed with the cellular experiments, with AF78(F) exhibiting the highest cardiac uptake. This result correlates positively with the electronegativity rather than the atomic radius of the meta-substituent. Computational modeling studies revealed a crucial influence of halogen substituents on the radiotracer-NET interaction, whereby a T-shaped π-π stacking interaction between the benzene-ring of the tracer and the amino acid residues surrounding the NET binding site made major contributions to the different affinities, in accordance with the pharmacological data. Conclusion: The SARs were characterized by in vitro and in vivo evaluation, and computational modeling quantitatively rationalized the interaction between radiotracers and the NET binding site. These findings pave the way for further evaluation in different species and underline the potential of AF78(F) for clinical application, e.g., cardiac innervation imaging or molecular imaging of neuroendocrine tumors.}, language = {en} }