Longitudinal preclinical evaluation of the novel radioligand [11C]CHDI-626 for PET imaging of mutant huntingtin aggregates in Huntington's disease.

PURPOSE: As several therapies aimed at lowering mutant huntingtin (mHTT) brain levels in Huntington's disease (HD) are currently being investigated, noninvasive positron emission tomography (PET) imaging of mHTT could be utilized to directly evaluate therapeutic efficacy and monitor disease progression. Here we characterized and longitudinally assessed the novel radioligand [11C]CHDI-626 for mHTT PET imaging in the zQ175DN mouse model of HD. METHODS: After evaluating radiometabolites and radioligand kinetics, we conducted longitudinal dynamic PET imaging at 3, 6, 9, and 13 months of age (M) in wild-type (WT, n = 17) and heterozygous (HET, n = 23) zQ175DN mice. Statistical analysis was performed to evaluate temporal and genotypic differences. Cross-sectional cohorts at each longitudinal time point were included for post-mortem [3H]CHDI-626 autoradiography. RESULTS: Despite fast metabolism and kinetics, the radioligand was suitable for PET imaging of mHTT. Longitudinal quantification could discriminate between genotypes already at premanifest stage (3 M), showing an age-associated increase in signal in HET mice in parallel with mHTT aggregate load progression, as supported by the post-mortem [3H]CHDI-626 autoradiography. CONCLUSION: With clinical evaluation underway, [11C]CHDI-626 PET imaging appears to be a suitable preclinical candidate marker to monitor natural HD progression and for the evaluation of mHTT-lowering therapies.

Molecular Imaging of mGluR5 Availability with [11C]ABP68 in Glutaminase Heterozygous Mice.

Many PET tracers enable determination of fluctuations in neurotransmitter release, yet glutamate specifically can not be visualized in a noninvasive manner. Several studies point to the possibility of visualizing fluctuations in glutamate release by changes in affinity of the mGluR5 radioligand [11C]ABP688. These studies use pharmacological challenges to alter glutamate levels, and so probe release, but have not measured chronic alterations in receptor occupancy due to altered neurotransmission relevant to chronic neuropsychiatric disorders or their treatment. In this regard, the GLS1 heterozygous mouse has known reductions in activity of the glutamate-synthetic enzyme glutaminase, brain glutamate levels and release. We imaged this model to elucidate glutamatergic systems. Dynamic [11C]ABP688 microPET scans were performed for mGluR5. Western blot was used as an ex vivo validation. No significant differences were found in BPND between WT and GLS1 Hets. SPM showed voxel-wise increased in BPND in GLS1 Hets compared to WT consistent with lower synaptic glutamate. This was not due to alterations in mGluR5 levels, as western blot results showed lower mGluR5 levels in GLS1 Hets. We conclude that because of the chronic glutaminase deficiency and subsequent decrease in glutamate, the mGluR5 protein levels are lowered. Due to these decreased endogenous glutamate levels, however, there is increased [11C]ABP688 binding to the allosteric site in selected regions. We speculate that lower endogenous glutamate leads to less conformational change to the receptors, and thus higher availability of the binding site. The lower mGluR5 levels, however, lessen [11C]ABP688 binding in GLS1 Hets, in part masking the increase in binding due to diminished endogenous glutamate levels as confirmed with voxel-wise analysis.

State-associated changes in longitudinal [18F]-PBR111 TSPO PET imaging of psychosis patients: Evidence for the accelerated ageing hypothesis?

OBJECTIVE: To determine whether state-associated changes in microglial activity, measured with translocator-protein positron emission tomography (TSPO PET), can be identified in psychosis patients through longitudinal evaluation of their regional tracer uptake over the clinical course from acute psychosis to post-treatment follow-up, and comparison to healthy controls. We also evaluated the relation between tracer uptake, clinical symptoms and peripheral immunological markers. METHOD: Second-generation radioligand [18F]-PBR111 TSPO PET-CT was used for longitudinal dynamic imaging in 14 male psychosis patients and 17 male age-matched healthy control subjects. Patients were first scanned during an acute psychotic episode followed by a second scan after treatment. Prior genotyping of subjects for the rs6917 polymorphism distinguished high- and mixed-affinity binders. The main outcome was regional volume of distribution (VT), representing TSPO binding. Plasma concentrations of CRP, cytokines and kynurenines were measured at each timepoint. RESULTS: We found a significant three-way interaction between time of scan, age and cohort (cortical grey matter F6.50, p.020). Age-dependent differences in VT existed between cohorts during the psychotic state, but not at follow-up. Patients' relative change in VT over time correlated with age (cortical grey matter Pearson's r.574). PANSS positive subscale scores correlated with regional VT during psychosis (cortical grey matter r.767). Plasma CRP and quinolinic acid were independently associated with lower VT. CONCLUSIONS: We identified a differential age-dependent pattern of TSPO binding from psychosis to follow-up in our cohort of male psychosis patients. We recommend future TSPO PET studies in psychosis patients to differentiate between clinical states and consider potential age-related effects.

Caspase-3 probes for PET imaging of apoptotic tumor response to anticancer therapy.

Apoptosis is a highly regulated process involved in the normal organism development and homeostasis. In the context of anticancer therapy, apoptosis is also studied intensively in an attempt to induce cell death in cancer cells. Caspase activation is a known key event in the apoptotic process. In particular, active caspase-3 and -7 are the common effectors in several apoptotic pathways, therefore effector caspase activation may be a promising biomarker for response evaluation to anticancer therapy. Quantitative imaging of apoptosis in vivo could provide early assessment of therapeutic effectiveness and could also be used in drug development to evaluate the efficacy as well as potential toxicity of novel treatments. Positron Emission Tomography (PET) is a highly sensitive molecular imaging modality that allows non-invasive in vivo imaging of biological processes such as apoptosis by using radiolabeled probes. Here we describe the development and evaluation of fluorine-18-labeled caspase-3 activity-based probes (ABPs) for PET imaging of apoptosis. ABPs were selected by screening of a small library of fluorine-19-labeled DEVD peptides containing different electrophilic warhead groups. An acyloxymethyl ketone was identified with low nanomolar affinity for caspase-3 and was radiolabeled with fluorine-18. The resulting radiotracer, [18F]MICA-302, showed good labeling of active caspase-3 in vitro and favorable pharmacokinetic properties. A µPET imaging experiment in colorectal tumor xenografts demonstrated an increased tumor accumulation of [18F]MICA-302 in drug-treated versus control animals. Therefore, our data suggest this radiotracer may be useful for clinical PET imaging of response to anticancer therapy.

18F-FDG PET, the early phases and the delivery rate of 18F-AV45 PET as proxies of cerebral blood flow in Alzheimer's disease: Validation against 15O-H2O PET.

INTRODUCTION: Dual-biomarker positron emission tomography (PET), providing complementary information on cerebral blood flow and amyloid-ß deposition, is of clinical interest for Alzheimer's disease (AD). The purpose of this study was to validate the perfusion components of early-phase 18F-florbetapir (eAV45), the 18F-AV45 delivery rate (R1), and 18F-FDG against 15O-H2O PET and assess how they change with disease severity. METHODS: This study included ten controls, 19 amnestic mild cognitive impairment, and 10 AD dementia subjects. Within-subject regional correlations between modalities, between-group regional and voxel-wise analyses of covariance per modality, and receiver operating characteristic analyses for discrimination between groups were performed. RESULTS: FDG standardized uptake value ratio, eAV45 (0-2 min) standardized uptake value ratio, and AV45-R1 were significantly associated with H2O PET (regional Pearson r = 0.54-0.82, 0.70-0.94, and 0.65-0.92, respectively; P < .001). All modalities confirmed reduced cerebral blood flow in the posterior cingulate of patients with amnestic mild cognitive impairment and AD dementia, which was associated with lower cognition (r = 0.36-0.65, P < .025) and could discriminate between patient and control groups (area under the curve > 0.80). However, eAV45 was less sensitive to reflect the disease severity than AV45-R1 or FDG. DISCUSSION: R1 is preferable over eAV45 for accurate representation of brain perfusion in dual-biomarker PET for AD.

Acute Ketamine Infusion in Rat Does Not Affect In Vivo [11C]ABP688 Binding to Metabotropic Glutamate Receptor Subtype 5.

Detecting changes in metabotropic glutamate receptor 5 (mGluR5) availability through molecular imaging with the positron emission tomography (PET) tracer [11C]ABP688 is valuable for studying dysfunctional glutamate transmission associated with neuropsychiatric disorders. Using an infusion protocol in rats, we visualized the acute effect of subanesthetic doses of ketamine on mGluR5 in rat brain. Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist known to increase glutamate release. Imaging was performed with a high-affinity PET ligand [11C]ABP688, a negative allosteric modulator of mGluR5. Binding did not change significantly from baseline to ketamine in any region, thereby confirming previous literature with other NMDA receptor antagonists in rodents. Hence, in rats, we could not reproduce the findings in a human setup showing significant decreases in the [11C]ABP688 binding after a ketamine bolus followed by ketamine infusion. Species differences may have contributed to the different findings in the present study of rats. In conclusion, we could not confirm in rats that endogenous glutamate increases by ketamine infusion are reflected in [11C]ABP688 binding decreases as was previously shown for humans.

Mass spectrometric characterization of intact desferal-conjugated monoclonal antibodies for immuno-PET imaging.

RATIONALE: Immuno-PET imaging may prove to be a diagnostic and progression/intervention biomarker for Alzheimer's disease (AD) with improved sensitivity and specificity. Immuno-PET imaging is based on the coupling of an antibody with a chelator that captures a radioisotope thus serving as an in-vivo PET ligand. A robust and quality controlled process for linking the chelator to the-antibody is fundamental for the success of this approach. METHODS: The structural integrities of two monoclonal antibodies (trastuzumab and JRF/AßN/25) and the quantity of desferal-based chelator attached following modification of the antibodies were assessed by online desalting and intact mass analysis. Enzymatic steps for the deglycosylation and removal of C-terminal lysine was performed sequentially and in a single tube to improve intact mass data. RESULTS: Intact mass analysis demonstrated that inclusion of enzymatic processing was critical to correctly derive the quantity of chelator linked to the monoclonal antibodies. For trastuzumab, enzymatic cleaving of the glycans was sufficient, whilst additional removal of the C-terminal lysine was necessary for JRF/AßN/25 to ensure reproducible assessment of the relatively low amount of attached chelator. CONCLUSIONS: An efficient intact mass analysis-based process was developed to reproducibly determine the integrity of monoclonal antibodies and the quantity of attached chelator. This technique could serve as an essential quality control approach for the development and production of immuno-PET tracers.

Phosphatidylethanolamine targeting for cell death imaging in early treatment response evaluation and disease diagnosis.

Phosphatidylethanolamine (PE) is one of the most abundant phospholipids in mammalian plasma membranes. In healthy cells, PE resides predominantly in the inner leaflet of the cell membrane. In dead or dying cells on the other hand, PE is externalized to the outer leaflet of the plasma membrane. The exposure of PE on the cell surface has therefore become an attractive target for the molecular imaging of cell death using single-photon emission computed tomography (SPECT) and positron emission tomography (PET). This has motivated the development of PE-specific probes to measure cell death in vitro and non-invasively in vivo. In this review, we highlight the biological roles of PE on cell membranes, and PE exposure as a biomarker of cell death in disease processes, along with the use of PE-binding molecular probes to target PE for the characterization of cell death on a cellular and tissue level. We specifically emphasize the preclinical applications of radiolabeled duramycin for the non-invasive imaging of cell death in animal models of disease and in tumors after therapy. In addition, we discuss the clinical relevance, limitations and future perspectives of this imaging approach of cell death.

Non-invasive PET imaging of brain inflammation at disease onset predicts spontaneous recurrent seizures and reflects comorbidities.

Brain inflammation is an important factor in the conversion of a healthy brain into an epileptic one, a phenomenon known as epileptogenesis, offering a new entry point for prognostic tools. The development of anti-epileptogenic therapies to treat before or at disease onset is hampered by our inability to predict the severity of the disease outcome. In a rat model of temporal lobe epilepsy we aimed to assess whether in vivo non-invasive imaging of brain inflammation at disease onset was predictive of spontaneous recurrent seizures (SRS) frequency and severity of depression-like and sensorimotor-related comorbidities. To this end, translocator protein, a biomarker of inflammation, was imaged by means of positron emission tomography (PET) 2 and 4weeks post-status epilepticus using [18F]-PBR111. Translocator protein was highly upregulated 2weeks post-status epilepticus in limbic structures (up to 2.1-fold increase compared to controls in temporal lobe, P<0.001), whereas 4weeks post-status epilepticus, upregulation decreased (up to 1.6-fold increase compared to controls in temporal lobe, P<0.01) and was only apparent in a subset of these regions. Animals were monitored with video-electroencephalography during all stages of disease (acute, latent - first seizures appearing around 2weeks post-status epilepticus - and chronic phases), for a total of 12weeks, in order to determine SRS frequency for each subject (range 0.00-0.83SRS/day). We found that regional PET uptake at 2 and 4weeks post-status epilepticus correlated with the severity of depression-like and sensorimotor-related comorbidities during chronic epilepsy (P<0.05 for each test). Regional PET imaging did not correlate with SRS frequency, however, by applying a multivariate data-driven modeling approach based on translocator protein PET imaging at 2weeks post-status epilepticus, we accurately predicted the frequency of SRS (R=0.92; R2=0.86; P<0.0001) at the onset of epilepsy. This study not only demonstrates non-invasive imaging of translocator protein as a prognostic biomarker to ascertain SRS frequency, but also shows its capability to reflect the severity of depression-like and sensorimotor-related comorbidities. Our results are an encouraging step towards the development of anti-epileptogenic treatments by providing early quantitative assessment of SRS frequency and severity of comorbidities with high clinical relevance.

The Label Matters: µPET Imaging of the Biodistribution of Low Molar Mass 89Zr and 18F-Labeled Poly(2-ethyl-2-oxazoline).

Poly(2-alkyl-2-oxazoline)s (PAOx) have received increasing interest for biomedical applications. Therefore, it is of fundamental importance to gain an in-depth understanding of the biodistribution profile of PAOx. We report the biodistribution of poly(2-ethyl-2-oxazoline) (PEtOx) with a molar mass of 5 kDa radiolabeled with PET isotopes 89Zr and 18F. 18F-labeled PEtOx is prepared by the strain-promoted azide-alkyne cycloaddition (SPAAC) of [18F]fluoroethylazide to bicyclo[6.1.0]non-4-yne (BCN)-functionalized PEtOx as many common labeling strategies were found to be unsuccessful for PEtOx. 89Zr-labeled PEtOx is prepared using desferrioxamine end-groups as a chelator. Five kDa PEtOx shows a significantly faster blood clearance compared to PEtOx of higher molar mass while uptake in the liver is lower, indicating a minor contribution of the liver in excretion of the 5 kDa PEtOx. While [18F]-PEtOx displays a rapid and efficient clearance from the kidneys, 5 kDa [89Zr]-Df-PEtOx is not efficiently cleared over the time course of the study, which is most likely caused by trapping of 89Zr-labeled metabolites in the renal tubules and not the polymer itself, demonstrating the importance of selecting the appropriate label for biodistribution studies.

Evaluation of [18 F]BR420 and [18 F]BR351 as radiotracers for MMP-9 imaging in colorectal cancer.

MMP-9 is a zinc-dependent endopeptidase that is involved in the proteolytic degradation of the extracellular matrix and plays an important role in cancer migration, invasion, and metastasis. The aim of this study was to evaluate the potential of MMP-tracers [18 F]BR420 and [18 F]BR351 for MMP-9 imaging in a colorectal cancer xenograft model. [18 F]BR420 and [18 F]BR351 were synthesized using an automated synthesis module. For [18 F]BR420, a novel and improved radiosynthesis was developed. Plasma stability and MMP-9-targeting capacity of both radiotracers was compared in the Colo205 colorectal cancer model. MMP-9 and MMP-2 expression levels in the tumors were evaluated by immunohistochemistry and in situ zymography. µPET imaging as well as ex vivo biodistribution revealed a higher tumor uptake for [18 F]BR420 (3.15% ± 0.03% ID/g vs 0.94% ± 0.18% ID/g for [18 F]BR351 at 2 hours pi) but slower blood clearance compared with [18 F]BR351. [18 F]BR351 was quickly metabolized in plasma with 20.28% ± 5.41% of intact tracer remaining at 15 minutes postinjection (PI). By contrast, [18 F]BR420 displayed a higher metabolic stability with >86% intact tracer remaining at 2 hours PI. Immunohistochemistry revealed the presence of MMP-9 and MMP-2 in the tumor tissue, which was confirmed by in situ zymography. However, an autoradiography analysis of tracer distribution in the tumors did not correlate with MMP-9 expression. [18 F]BR420 displayed a higher tumor uptake and higher stability compared with [18 F]BR351 but a low tumor-to-blood ratio and discrepancy between tracer distribution and MMP-9 immunohistochemistry. Therefore, both tracers will not be usefulness for MMP-9 imaging in colorectal cancer.

Development of a novel antibody-tetrazine conjugate for bioorthogonal pretargeting.

Recently, bioorthogonal chemistry based on the Inverse Electron-Demand Diels-Alder (IEDDA) cycloaddition between 1,2,4,5-tetrazines and trans-cyclooctene (TCO) analogues added an interesting dimension to molecular imaging. Until now, antibodies (Abs) were tagged with TCO and after pretargeting they were reacted with tetrazines substituted with reporters. However, TCO tags have the tendency to degrade under physiological conditions, and due to their hydrophobic nature are buried within the protein. This results in loss of reactivity and a low Ab functional loading. To circumvent these problems, we report for the first time an approach in which tetrazines are used as tags for antibody (Ab) modification, and TCO as the imaging agent. We developed a new Ab-tetrazine conjugate, which displays a high functional loading, good stability and reactivity. We utilized this immunoconjugate for live-cell imaging together with novel TCO probes, resulting in selective and rapid labeling of SKOV-3 cells. Our approach may be useful for in vivo pretargeted imaging.

Towards a reproducible protocol for repetitive and semi-quantitative rat brain imaging with (18) F-FDG: exemplified in a memantine pharmacological challenge.

The standard uptake value (SUV), commonly used to quantify (18)F-FluoroDeoxyGlucose (FDG) uptake in small animal brain PET imaging, is affected by many factors. In this study the influence of fasting times, inter-scan duration and repetitive scanning on the variability of different SUV measures is investigated. Additionally it is demonstrated that these variables could adversely influence the outcome of a pharmacological challenge when not accounted for. Naive Sprague-Dawley rats (n=20) were randomly divided into five different fasting groups (no fasting up to 24h of fasting). SUV brain uptake values were reproducible in naive animals when a fasting period of at least 12h is used and for shorter fasting periods SUV values need to be corrected for the glucose level. Additionally, a separate animal group (n=6) was sufficiently fasted for 16h and in a longitudinal setting being scanned six times in three weeks. Especially with short inter-scan durations, increasing glucose levels were found over time which was attributed to increased stress due to repeated food deprivation, altered food intake or scan manipulations. As a result, even with controlled and sufficient fasting, blood glucose levels should be taken into account for data quantification. Strikingly, even the brain activation effects of an NMDA-antagonist challenge with memantine could not be detected in experiments with a short inter-scan duration if glucose levels were not taken into account. Correcting for glucose levels decreases the inter- and intra-animal variability for rat brain imaging. SUV corrected for glucose levels yields the lowest inter-animal variation. However, if the body weight changes significantly, as in a long experiment, quantification based on the glucose corrected percentage injected dose (and not SUV) is recommendable as this yields the lowest intra-animal variation.

Rat brain normalization templates for robust regional analysis of [11C]ABP688 positron emission tomography/computed tomography.

A methodology to generate rat brain templates for spatial normalization of positron emission tomographic (PET)/computed tomographic (CT) images is described and applied to generate three different templates for imaging of [11C]ABP688, a PET ligand binding to the metabotropic glutamate 5 receptor. The templates are based on functional (PET), structural (CT), and combined PET and CT information, respectively. The templates are created from a test-retest study under normal conditions and are used to assess the different templates by using them in the analysis pipeline of a test-retest and a blocking experiment. The resulting average nondisplaceable binding potentials (BPND) show significant (analysis of variance, p < .05) and substantial (up to 23%) differences between the different approaches in several brain regions. The highest BPND values in receptor-rich regions are obtained using the PET-based approach. This approach also had the smallest variability in all tested regions (standard error of measurement of 9% versus 14% [PET/CT] and 20% [CT]). All approaches showed similar relative changes in BPND values with increased blocking. Taken together, these results suggest that the use of the tracer-specific PET-based template outperforms the other approaches with the performance of the combined PET/CT template between those of the PET and the tracer-independent CT template.

The [18F]FDG µPET readout of a brain activation model to evaluate the metabotropic glutamate receptor 2 positive allosteric modulator JNJ-42153605.

Using [(18)F]fluorodeoxyglucose µ-positron emission tomography ([(18)F]FDG µPET), we compared subanesthetic doses of memantine and ketamine on their potential to induce increases in brain activation. We also studied the reversal effect of the well-known metabotropic glutamate receptor (mGluR)-2/3 agonist LY404039 [(-)-(1R,4S,5S,6S)-4-amino-2-sulfonylbicyclo[3.1.0]hexane-4,6-dicarboxylic acid] and the novel mGluR2 positive allosteric modulator (PAM) JNJ-42153605 [3-cylcopropylmethyl-7-(4-phenylpiperidin-1-yl)-8-trifluoromethyl [1,2,4] triazolo[4,3-a]pyridine]. First, rats (n = 12) were subjected to LY404039 (10 mg/kg s.c.) or vehicle, 30 minutes prior to saline, ketamine (30 mg/kg i.p.), or memantine (20 mg/kg i.p.). Second, rats (n = 12) were subjected to 2.5 mg/kg or 10 mg/kg mGluR2 PAM JNJ-42153605 or vehicle (s.c.), 30 minutes prior to memantine (20 mg/kg i.p.) or saline. Fifteen minutes later, [(18)F]FDG was injected (37 MBq i.v.) followed by a µPET/computed tomography scan. The increase due to memantine is significant for all relevant brain areas, whereas for ketamine this is not the case. Standard uptake values (SUVs) of the LY404039 pretreated and memantine-challenged group display a full reversal. Pretreatment with JNJ-42153605 also dose-dependently decreases SUV with a full reversal as well (for 10 mg/kg). Moreover, specificity of JNJ-42153605 is reached at this dose. In conclusion, this µPET experiment clearly indicates that subanesthetic doses of memantine induce significant increases of [(18)F]FDG SUVs in discrete brain areas and that the novel mGluR2 PAM has the capacity to dose-dependently and specifically reverse memantine-induced brain activation.

First-in-human study of a novel cell death tracer [99mTc]Tc-Duramycin: safety, biodistribution and radiation dosimetry in healthy volunteers.

BACKGROUND: Imaging of cell death can provide an early indication of treatment response in cancer. [99mTc]Tc-Duramycin is a small-peptide SPECT tracer that recognizes both apoptotic and necrotic cells by binding to phosphatidylethanolamine present in the cell membrane. Preclinically, this tracer has shown to have favorable pharmacokinetics and selective tumor accumulation early after the onset of anticancer therapy. In this first-in-human study, we report the safety, biodistribution and internal radiation dosimetry of [99mTc]Tc-Duramycin in healthy human volunteers. RESULTS: Six healthy volunteers (3 males, 3 females) were injected intravenously with [99mTc]Tc-Duramycin (dose: 6 MBq/kg; 473 ± 36 MBq). [99mTc]Tc-Duramycin was well tolerated in all subjects, with no serious adverse events reported. Following injection, a 30-min dynamic planar imaging of the abdomen was performed, and whole-body (WB) planar scans were acquired at 1, 2, 3, 6 and 23 h post-injection (PI), with SPECT acquisitions after each WB scan and one low-dose CT after the first SPECT. In vivo 99mTc activities were determined from semi-quantitative analysis of the images, and time-activity curves were generated. Residence times were calculated from the dynamic and WB planar scans. The mean effective dose was 7.61 ± 0.75 µSv/MBq, with the kidneys receiving the highest absorbed dose (planar analysis: 43.82 ± 4.07 µGy/MBq, SPECT analysis: 19.72 ± 3.42 µGy/MBq), followed by liver and spleen. The median effective dose was 3.61 mSv (range, 2.85-4.14). The tracer cleared slowly from the blood (effective half-life of 2.0 ± 0.4 h) due to high plasma protein binding with < 5% free tracer 3 h PI. Excretion was almost exclusively renal. CONCLUSION: [99mTc]Tc-Duramycin demonstrated acceptable dosimetry (< 5 mSv) and a favorable safety profile. Due to slow blood clearance, optimal target-to-background ratios are expected 5 h PI. These data support the further assessment of [99mTc]Tc-Duramycin for clinical treatment response evaluation. TRIAL REGISTRATION: NCT05177640, Registered April 30, 2021, https://clinicaltrials.gov/study/NCT05177640 .

Detection of myocardial ischemia-reperfusion injury using a fluorescent near-infrared zinc(II)-dipicolylamine probe and 99mTc glucarate.

A fluorescent zinc 2,2'-dipicolylamine coordination complex PSVue®794 (probe 1) is known to selectively bind to phosphatidylserine exposed on the surface of apoptotic and necrotic cells. In this study, we investigated the cell death targeting properties of probe 1 in myocardial ischemia-reperfusion injury. A rat heart model of ischemia-reperfusion was used. Probe 1, control dye, or 99mTc glucarate was intravenously injected in rats subjected to 30-minute and 5-minute myocardial ischemia followed by 2-hour reperfusion. At 90 minutes or 20 hours postinjection, myocardial uptake was evaluated ex vivo by fluorescence imaging and autoradiography. Hematoxylin-eosin and cleaved caspase-3 staining was performed on myocardial sections to demonstrate the presence of ischemia-reperfusion injury and apoptosis. Selective accumulation of probe 1 could be detected in the area at risk up to 20 hours postinjection. Similar topography and extent of uptake of probe 1 and 99mTc glucarate were observed at 90 minutes postinjection. Histologic analysis demonstrated the presence of necrosis, but only a few apoptotic cells could be detected. Probe 1 selectively accumulates in myocardial ischemia-reperfusion injury and is a promising cell death imaging tool.

Synaptic Vesicle Glycoprotein 2A Is Affected in the Central Nervous System of Mice with Huntington Disease and in the Brain of a Human with Huntington Disease Postmortem.

Synaptic dysfunction is a primary mechanism underlying Huntington disease (HD) progression. This study investigated changes in synaptic vesicle glycoprotein 2A (SV2A) density by means of 11C-UCB-J small-animal PET imaging in the central nervous system of mice with HD. Methods: Dynamic 11C-UCB-J small-animal PET imaging was performed at clinically relevant disease stages (at 3, 7, 10, and 16 mo) in the heterozygous knock-in Q175DN mouse model of HD and wild-type littermates (16-18 mice per genotype and time point). Cerebral 11C-UCB-J analyses were performed to assess genotypic differences during presymptomatic (3 mo) and symptomatic (7-16 mo) disease stages. 11C-UCB-J binding in the spinal cord was quantified at 16 mo. 3H-UCB-J autoradiography and SV2A immunofluorescence were performed postmortem in mouse and human brain tissues. Results:11C-UCB-J binding was lower in symptomatic heterozygous mice than in wild-type littermates in parallel with disease progression (7 and 10 mo: P < 0.01; 16 mo: P < 0.0001). Specific 11C-UCB-J binding was detectable in the spinal cord, with symptomatic heterozygous mice displaying a significant reduction (P < 0.0001). 3H-UCB-J autoradiography and SV2A immunofluorescence corroborated the in vivo measurements demonstrating lower SV2A in heterozygous mice (P < 0.05). Finally, preliminary analysis of SV2A in the human brain postmortem suggested lower SV2A in HD gene carriers than in controls without dementia. Conclusion:11C-UCB-J PET detected SV2A deficits during symptomatic disease in heterozygous mice in both the brain and the spinal cord and therefore may be suitable as a novel marker of synaptic integrity widely distributed in the central nervous system. On clinical application, 11C-UCB-J PET imaging may have promise for SV2A measurement in patients with HD during disease progression and after disease-modifying therapeutic strategies.

Synthesis and preliminary evaluation of radiolabeled bis(zinc(II)-dipicolylamine) coordination complexes as cell death imaging agents.

The aim of this study was the development of (99m)Tc labeled bis(zinc(II)-dipicolylamine) (Zn²âº-DPA) coordination complexes, and the in vivo evaluation of their usefulness as radiotracers for the detection of cell death. DPA ligand 1 was labeled with (99m)Tc via the (99m)Tc-tricarbonyl core ([(99m)Tc(CO)3-1]³âº) or via HYNIC ((99m)Tc-HYNIC-1) in good radiochemical yields. Highest in vitro stabilities were demonstrated for [(99m)Tc(CO)3-1]³âº. A mouse model of hepatic apoptosis (anti-Fas mAb) was used to demonstrate binding to apoptotic cells. (99m)Tc-HYNIC-1 showed the best targeting of apoptotic hepatic tissue with a 2.2 times higher liver uptake in anti-Fas treated mice as compared to healthy animals. A rat model of ischemia-reperfusion injury was used to further explore the ability of the (99m)Tc-labeled Zn²âº-DPA coordination complexes to target cell death. Selective accumulation could be detected for both tracers in the area at risk, correlating with histological proof of cell death. Area at risk to normal tissue uptake ratios were 3.82 for [(99m)Tc(CO)3-1]³âº and 5.45 for (99m)Tc-HYNIC-1.

Kinetic Modelling and Test-Retest Reproducibility for the Dopamine D1R Radioligand [11C]SCH23390 in Healthy and Diseased Mice.

PURPOSE: Our aim in this study was to compare different non-invasive pharmacokinetic models and assess test-retest reproducibility of the radioligand [11C]SCH23390 for the quantification of dopamine D1-like receptor (D1R) in both wild-type (WT) mice and heterozygous (HET) Q175DN mice as Huntington's disease (HD) model. PROCEDURES: Adult WT (n = 9) and HET (n = 14) mice underwent a 90-min [11C]SCH23390 positron emission tomography (PET) scan followed by computed tomography (CT) to evaluate the pharmacokinetic modelling in healthy and diseased conditions. Additionally, 5 WT mice and 7 HET animals received a second [11C]SCH23390 PET scan for test-retest reproducibility. Parallel assessment of the simplified reference tissue model (SRTM), the multilinear reference tissue model (MRTM) and the Logan reference tissue model (Logan Ref) using the striatum as a receptor-rich region and the cerebellum as a receptor-free (reference) region was performed to define the most suitable method for regional- and voxel-based quantification of the binding potential (BPND). Finally, standardised uptake value ratio (SUVR-1) was assessed as a potential simplified measurement. RESULTS: For all models, we measured a significant decline in dopamine D1R density (e.g. SRTM = - 38.5 ± 5.0 %, p < 0.0001) in HET mice compared to WT littermates. Shortening the 90-min scan duration resulted in large underestimation of striatal BPND in both WT mice (SRTM 60 min: - 17.7 ± 2.8 %, p = 0.0078) and diseased HET (SRTM 60 min: - 13.1 ± 4.1 %, p = 0.0001). Striatal BPND measurements were very reproducible with an average test-retest variability below 5 % when using both MRTM and SRTM. Parametric BPND maps generated with SRTM were highly reliable, showing nearly perfect agreement to the regional analysis (r2 = 0.99, p < 0.0001). Finally, SRTM provided the most accurate estimate for relative tracer delivery R1 with both regional- and voxel-based analyses. SUVR-1 at different time intervals were not sufficiently reliable when compared to BPND (r2 < 0.66). CONCLUSIONS: Ninety-minute acquisition and the use of SRTM for pharmacokinetic modelling is recommended. [11C]SCH23390 PET imaging demonstrates optimal characteristics for the study of dopamine D1R density in models of psychiatric and neurological disorders as exemplified in the Q175DN mouse model of HD.