Translocator Protein Positron Emission Tomography Research Articles

Targeting TGFβ-activated kinase-1 activation in microglia reduces CAR T immune effector cell-associated neurotoxicity syndrome.

Cancer immunotherapy with chimeric antigen receptor (CAR) T cells can cause immune effector cell-associated neurotoxicity syndrome (ICANS). However, the molecular mechanisms leading to ICANS are not well understood. Here we examined the role of microglia using mouse models and cohorts of individuals with ICANS. CD19-directed CAR (CAR19) T cell transfer in B cell lymphoma-bearing mice caused microglia activation and neurocognitive deficits. The TGFβ-activated kinase-1 (TAK1)-NF-κB-p38 MAPK pathway was activated in microglia after CAR19 T cell transfer. Pharmacological TAK1 inhibition or genetic Tak1 deletion in microglia using Cx3cr1CreER:Tak1fl/fl mice resulted in reduced microglia activation and improved neurocognitive activity. TAK1 inhibition allowed for potent CAR19-induced antilymphoma effects. Individuals with ICANS exhibited microglia activation in vivo when studied by translocator protein positron emission tomography, and imaging mass cytometry revealed a shift from resting to activated microglia. In summary, we prove a role for microglia in ICANS pathophysiology, identify the TAK1-NF-κB-p38 MAPK axis as a pathogenic signaling pathway and provide a rationale to test TAK1 inhibition in a clinical trial for ICANS prevention after CAR19 T cell-based cancer immunotherapy.

Microglia measured by TSPO PET are associated with Alzheimer's disease pathology and mediate key steps in a disease progression model.

Evidence suggests microglial activation precedes regional tau and neurodegeneration in Alzheimer's disease (AD). We characterized microglia with translocator protein (TSPO) positron emission tomography (PET) within an AD progression model where global amyloid beta (Aβ) precedes local tau and neurodegeneration, resulting in cognitive impairment. Florbetaben, PBR28, and MK-6240 PET, T1 magnetic resonance imaging, and cognitive measures were performed in 19 cognitively unimpaired older adults and 22 patients with mild cognitive impairment or mild AD to examine associations among microglia activation, Aβ, tau, and cognition, adjusting for neurodegeneration. Mediation analyses evaluated the possible role of microglial activation along the AD progression model. Higher PBR28 uptake was associated with higher Aβ, higher tau, and lower MMSE score, independent of neurodegeneration. PBR28 mediated associations between tau in early and middle Braak stages, between tau and neurodegeneration, and between neurodegeneration and cognition. Microglia are associated with AD pathology and cognition and may mediate relationships between subsequent steps in AD progression.

The Traumatic Inoculation Process Affects TSPO Radioligand Uptake in Experimental Orthotopic Glioblastoma.

The translocator protein (TSPO) has been proven to have great potential as a target for the positron emission tomography (PET) imaging of glioblastoma. However, there is an ongoing debate about the potential various sources of the TSPO PET signal. This work investigates the impact of the inoculation-driven immune response on the PET signal in experimental orthotopic glioblastoma. Serial [18F]GE-180 and O-(2-[18F]fluoroethyl)-L-tyrosine ([18F]FET) PET scans were performed at day 7/8 and day 14/15 after the inoculation of GL261 mouse glioblastoma cells (n = 24) or saline (sham, n = 6) into the right striatum of immunocompetent C57BL/6 mice. An additional n = 25 sham mice underwent [18F]GE-180 PET and/or autoradiography (ARG) at days 7, 14, 21, 28, 35, 50 and 90 in order to monitor potential reactive processes that were solely related to the inoculation procedure. In vivo imaging results were directly compared to tissue-based analyses including ARG and immunohistochemistry. We found that the inoculation process represents an immunogenic event, which significantly contributes to TSPO radioligand uptake. [18F]GE-180 uptake in GL261-bearing mice surpassed [18F]FET uptake both in the extent and the intensity, e.g., mean target-to-background ratio (TBRmean) in PET at day 7/8: 1.22 for [18F]GE-180 vs. 1.04 for [18F]FET, p < 0.001. Sham mice showed increased [18F]GE-180 uptake at the inoculation channel, which, however, continuously decreased over time (e.g., TBRmean in PET: 1.20 at day 7 vs. 1.09 at day 35, p = 0.04). At the inoculation channel, the percentage of TSPO/IBA1 co-staining decreased, whereas TSPO/GFAP (glial fibrillary acidic protein) co-staining increased over time (p < 0.001). We identify the inoculation-driven immune response to be a relevant contributor to the PET signal and add a new aspect to consider for planning PET imaging studies in orthotopic glioblastoma models.

Sexually dimorphic murine brain uptake of the 18 kDa translocator protein PET radiotracer [18F]LW223.

The 18 kDa translocator protein is a well-known biomarker of neuroinflammation, but also plays a role in homeostasis. PET with 18 kDa translocator protein radiotracers [11C]PBR28 in humans and [18F]GE180 in mice has demonstrated sex-dependent uptake patterns in the healthy brain, suggesting sex-dependent 18 kDa translocator protein expression, although humans and mice had differing results. This study aimed to assess whether the 18 kDa translocator protein PET radiotracer [18F]LW223 exhibited sexually dimorphic uptake in healthy murine brain and peripheral organs. Male and female C57Bl6/J mice (13.6 ± 5.4 weeks, 26.8 ± 5.4 g, mean ± SD) underwent 2 h PET scanning post-administration of [18F]LW223 (6.7 ± 3.6 MBq). Volume of interest and parametric analyses were performed using standard uptake values (90-120 min). Statistical differences were assessed by unpaired t-test or two-way ANOVA with Šidak's test (alpha = 0.05). The uptake of [18F]LW223 was significantly higher across multiple regions of the male mouse brain, with the most pronounced difference detected in hypothalamus (P < 0.0001). Males also exhibited significantly higher [18F]LW223 uptake in the heart when compared to females (P = 0.0107). Data support previous findings on sexually dimorphic 18 kDa translocator protein radiotracer uptake patterns in mice and highlight the need to conduct sex-controlled comparisons in 18 kDa translocator protein PET imaging studies.

Microglial Imaging in Alzheimer's Disease and Its Relationship to Brain Amyloid: A Human 18F-GE180 PET Study.

Emerging evidence suggests a potential causal role of neuroinflammation in Alzheimer's disease (AD). Using positron emission tomography (PET) to image overexpressed 18 kDA translocator protein (TSPO) by activated microglia has gained increasing interest. The uptake of 18F-GE180 TSPO PET was observed to co-localize with inflammatory markers and have a two-stage association with amyloid PET in mice. Very few studies evaluated the diagnostic power of 18F-GE180 PET in AD population and its interpretation in human remains controversial about whether it is a marker of microglial activation or merely reflects disrupted blood-brain barrier integrity in humans. The goal of this study was to study human GE180 from the perspective of the previous animal observations. With data from twenty-four participants having 18F-GE180 and 18F-AV45 PET scans, we evaluated the group differences of 18F-GE180 uptake between participants with and without cognitive impairment. An association analysis of 18F-GE180 and 18F-AV45 was then conducted to test if the relationship in humans is consistent with the two-stage association in AD mouse model. Elevated 18F-GE180 was observed in participants with cognitive impairment compared to those with normal cognition. No regions showed reduced 18F-GE180 uptake. Consistent with mouse model, a two-stage association between 18F-GE180 and 18F-AV45 was observed. 18F-GE180 PET imaging showed promising utility in detecting pathological alterations in a symptomatic AD population. Consistent two-stage association between 18F-GE180 and amyloid PET in human and mouse suggested that 18F-GE180 uptake in human might be considerably influenced by microglial activation.

Positron emission tomography (PET) imaging of neuroinflammation in healthy and Alzheimer disease participants using TSPO tracers

AbstractBackgroundAlzheimer’s disease (AD) is the most common type of dementia. In addition to the widely recognized accumulation of amyloid and tau protein being the core pathology of AD, neuroinflammation is another cause of brain dysfunction and structural change. Expression of translocator protein (TSPO) on the outer mitochondrial membrane of activated microglia is strongly associated with neuroinflammation. With the development of TSPO positron emission tomography (PET) tracer, we were able to evaluate neuroinflammation non‐invasively in a clinical cohort of AD spectrum.MethodCognitively impaired patients (including AD and mild cognitive impairment (MCI)) and cognitively normal controls (CN) were recruited from single dementia clinic. [18F]FEPPA, the second‐generation PET ligand specifically binds TSPO was synthesized fully automated. Structural brain MRI and functional PET imaging were performed simultaneously with a PET/MR scanner (SIGNA, GE Company, USA). Kinetic analyses were performed using PMOD 4.2 modeling software. Total distribution volume (VT) in each ROI, including frontal, temporal, inferiolateral parietal, occipital, hippocampus and cerebellum, were derived from a two‐tissue compartment model (2‐TCM). In addition, APOE and rs6971 polymorphism genotyping were conducted in all subjects. Mann‐Whitney U Tet, Kruskal‐Wallis Test and linear correlation were performed.ResultA total of 39 participants (23 males and 16 females) participated, including 13 cognitively normal, 9 with MCI and 17 with Alzheimer’s disease. The rs6971 genotype had no significant effect on [18F]FEPPA binding to TSPO. The amount of TSPO expression was independent of age, gender, and APOE ε4 carrier status. The VT of each ROI did not differ significantly between cognitive groups. VT of frontal, temporal, inferiolateral parietal and occipital lobe were all negatively correlated with MMSE, Boston Naming Test and Trial Making A performance. However, such association was not observed between VT of hippocampus and cognitive tests.ConclusionAlthough there was no difference between TSPO expression in each ROI among cognitive groups, we still observed that higher TSPO expression in the cortex was associated with worse performance in certain cognitive tests. This implied that the increase in neuroinflammation was related to the decline of cognitive performance regardless of cognitive diagnosis.

Immune-Effector-Cell-Associated-Neurotoxicity-Syndrome (ICANS) Pathophysiology Is Mediated By Microglia TGF-β-Activated Kinase-1 Signaling

Chimeric antigen receptor (CAR)-T cell therapy has revolutionized the field of immune therapy in treating relapsed and refractory B cell malignancies. Despite remarkable progress, CD19 CAR-T cell therapy is associated with major side effects, most significantly are cytokine-release syndrome and neurotoxicity. Of note, 40-60% of patients receiving CD19 CAR-T cells suffer from severe neurotoxicity termed immune cell-associated-neurotoxicity-syndrome (ICANS), which remains a major obstacle limiting their therapeutic efficacy. Several pre-clinical reports using xenograft mouse models have been published to address ICANS, however, they do not fully recapitulate the clinical scenario. Identifying and targeting the molecular mediators of neurotoxicity could help ameliorate ICANS induced by CD19 CAR-T cells. In order to understand the molecular mechanisms leading to CD19 CAR-T cell-induced ICANS, we established syngeneic ICANS mouse models for B-cell malignancies including non-Hodgkin's Lymphoma (B-NHL) and Acute Lymphoblastic Leukemia (B-ALL). Micro-array and single-nuclei RNA sequencing analyses were performed to unveil key signaling pathways in microglia leading to ICANS pathophysiology. Cognitive impairment resulting from the transfer of CD19 CAR-T cells was assessed with behavior studies in murine models. Imaging mass cytometry was performed on autopsied ICANS and control patient cohorts to study the relevance of microglial activation in patients. We previously demonstrated that microglial upregulation of tumor necrosis factor-alpha (TNFα) results in graft versus host disease of the central nervous system (Mathew and Vinnakota et al. JCI 2020). Similarly, our ICANS mouse models exhibit morphological and functional signs of microglial activation with increased expression of TNFα and GM-CSF along with endothelial damage in lymphoma-bearing mice that received CD19 CAR-T cells when compared to non-transduced controls. Behavioral studies revealed that mice receiving CD19 CAR-T cells exhibit cognitive deficits and increased anxiety. The behavior deficits were however rescued by microglia depletion indicating an important role for microglia in mediating CD19 CAR-T cells induced ICANS. Mechanistically, we identified the activation of p-38 mitogen-activated protein kinase (MAPK) in microglia isolated from mice receiving CD19 CAR-T cells. Furthermore, pharmacological inhibition of TGF-β-activated kinase-1 (TAK1), an upstream target for p-38 MAPK significantly reduced microglial activation, lowered microglia production of TNF and GM-CSF, and improved cognitive function in these mice. In line with these results, microglia-specific knockdown of TAK1 using Cx3cr1 creER:Tak1 fl/fl mice revealed reduced microglial activation and improved cognitive function when compared to littermate controls. Moreover, TAK1 inhibition combined with CD19 CAR-T cell therapy synergistically improved anti-lymphoma/leukemia effects leading to better survival in B-cell malignancy-bearing mice. Translocator-protein-positron-emission-tomography (TSPO-PET) on ICANS patients revealed signs of microglial activation. In addition, Imaging-mass cytometry analysis on post-mortem ICANS patient cohort revealed upregulation of myeloid cell markers further confirming the in vivo findings. In summary, our results identify TAK1/p38 MAPK-pathway as a key mediator of CAR19 CAR-T cell-induced neurotoxicity. Targeting this axis diminished the neurotoxicity associated with this therapy. This study provides a rationale for testing TAK1-inhibition in a clinical trial for treating CD19 CAR-T cell-induced neurotoxicity.

18F]LW223 has low non-displaceable binding in murine brain, enabling high sensitivity TSPO PET imaging.

Neuroinflammation is associated with a number of brain diseases, making it a common feature of cerebral pathology. Among the best-known biomarkers for neuroinflammation in Positron Emission Tomography (PET) research is the 18 kDa translocator protein (TSPO). This study aims to investigate the binding kinetics of a novel TSPO PET radiotracer, [18F]LW223, in mice and specifically assess its volume of non-displaceable binding (VND) in brain as well as investigate the use of simplified analysis approaches for quantification of [18F]LW223 PET data. Adult male mice were injected with [18F]LW223 and varying concentrations of LW223 (0.003-0.55 mg/kg) to estimate VND of [18F]LW223. Dynamic PET imaging with arterial input function studies and radiometabolite studies were conducted. Simplified quantification methods, standard uptake values (SUV) and apparent volume of distribution (VTapp), were investigated. [18F]LW223 had low VND in the brain (<10% of total binding) and low radiometabolism (∼15-20%). The 2-tissue compartment model provided the best fit for [18F]LW223 PET data, although its correlation with SUV90-120min or VTapp allowed for [18F]LW223 brain PET data quantification in healthy animals while using simpler experimental and analytical approaches. [18F]LW223 has the required properties to become a successful TSPO PET radiotracer.

The mitochondrial protein TSPO in Alzheimer’s disease: relation to the severity of AD pathology and the neuroinflammatory environment

The 18kD translocator protein (TSPO) is used as a positron emission tomography (PET) target to quantify neuroinflammation in patients. In Alzheimer’s disease (AD), the cerebellum is the pseudo-reference region for comparison with the cerebral cortex due to the absence of AD pathology and lower levels of TSPO. However, using the cerebellum as a pseudo-reference region is debated, with other brain regions suggested as more suitable. This paper aimed to establish the neuroinflammatory differences between the temporal cortex and cerebellar cortex, including TSPO expression. Using 60 human post-mortem samples encompassing the spectrum of Braak stages (I–VI), immunostaining for pan-Aβ, hyperphosphorylated (p)Tau, TSPO and microglial proteins Iba1, HLA–DR and MSR-A was performed in the temporal cortex and cerebellum. In the cerebellum, Aβ but not pTau, increased over the course of the disease, in contrast to the temporal cortex, where both proteins were significantly increased. TSPO increased in the temporal cortex, more than twofold in the later stages of AD compared to the early stages, but not in the cerebellum. Conversely, Iba1 increased in the cerebellum, but not in the temporal cortex. TSPO was associated with pTau in the temporal cortex, suggesting that TSPO positive microglia may be reacting to pTau itself and/or neurodegeneration at later stages of AD. Furthermore, the neuroinflammatory microenvironment was examined, using MesoScale Discovery assays, and IL15 only was significantly increased in the temporal cortex. Together this data suggests that the cerebellum maintains a more homeostatic environment compared to the temporal cortex, with a consistent TSPO expression, supporting its use as a pseudo-reference region for quantification in TSPO PET scans.

Distinct molecular profiles of skull bone marrow in health and neurological disorders

The bone marrow in the skull is important for shaping immune responses in the brain and meninges, but its molecular makeup among bones and relevance in human diseases remain unclear. Here, we show that the mouse skull has the most distinct transcriptomic profile compared with other bones in states of health and injury, characterized by a late-stage neutrophil phenotype. In humans, proteome analysis reveals that the skull marrow is the most distinct, with differentially expressed neutrophil-related pathways and a unique synaptic protein signature. 3D imaging demonstrates the structural and cellular details of human skull-meninges connections (SMCs) compared with veins. Last, using translocator protein positron emission tomography (TSPO-PET) imaging, we show that the skull bone marrow reflects inflammatory brain responses with a disease-specific spatial distribution in patients with various neurological disorders. The unique molecular profile and anatomical and functional connections of the skull show its potential as a site for diagnosing, monitoring, and treating brain diseases.

Long-Term Pioglitazone Treatment Has No Significant Impact on Microglial Activation and Tau Pathology in P301S Mice.

Neuroinflammation is one disease hallmark on the road to neurodegeneration in primary tauopathies. Thus, immunomodulation might be a suitable treatment strategy to delay or even prevent the occurrence of symptoms and thus relieve the burden for patients and caregivers. In recent years, the peroxisome proliferator-activated receptor γ (PPARγ) has received increasing attention as it is immediately involved in the regulation of the immune system and can be targeted by the anti-diabetic drug pioglitazone. Previous studies have shown significant immunomodulation in amyloid-β (Aβ) mouse models by pioglitazone. In this study, we performed long-term treatment over six months in P301S mice as a tauopathy model with either pioglitazone or placebo. We performed serial 18 kDa translocator protein positron-emission-tomography (TSPO-PET) imaging and terminal immunohistochemistry to assess microglial activation during treatment. Tau pathology was quantified via immunohistochemistry at the end of the study. Long-term pioglitazone treatment had no significant effect on TSPO-PET, immunohistochemistry read-outs of microglial activation, or tau pathology levels in P301S mice. Thus, we conclude that pioglitazone modifies the time course of Aβ-dependent microglial activation, but does not significantly modulate microglial activation in response to tau pathology.

Longitudinal stability of progression-related microglial activity during teriflunomide treatment in patients with multiple sclerosis.

The aim was to study brain innate immune cell activation in teriflunomide-treated patients with relapsing-remitting multiple sclerosis. Imaging with 18-kDa translocator protein positron emission tomography (TSPO-PET) using the [11 C]PK11195 radioligand was employed to assess microglial activity in the white matter, thalamus and areas surrounding chronic white matter lesions in 12 patients with relapsing-remitting multiple sclerosis who had been treated with teriflunomide for at least 6 months before inclusion. Magnetic resonance imaging (MRI) was used to measure lesion load and brain volume, and quantitative susceptibility mapping (QSM) was used to detect iron rim lesions. These evaluations were repeated after 1 year of inclusion. Twelve age- and gender-matched healthy control subjects were imaged for comparison. Half of the patients had iron rim lesions. In TSPO-PET, the proportion of active voxels indicating innate immune cell activation was slightly greater amongst patients compared with healthy individuals (7.7% vs. 5.4%, p = 0.033). The mean distribution volume ratio of [11 C]PK11195 was not significantly different in the normal-appearing white matter or thalamus amongst patients versus controls. Amongst the treated patients, no significant alteration was observed in positron emission tomography distribution volume ratio, the proportion of active voxels, the number of iron-rim-positive lesions, lesion load or brain volume during follow-up. Compared to controls, treated patients exhibited modest signs of diffuse innate immune cell activity, which was unaltered during follow-up. Lesion-associated smoldering inflammation was negligible at both timepoints. To our knowledge, this is the first study applying both TSPO-PET and QSM-MRI to longitudinally evaluate smoldering inflammation.

Translocator protein PET imaging in temporal lobe epilepsy: A reliable test-retest study using asymmetry index.

Translocator protein (TSPO) targeting positron emission tomography (PET) imaging radioligands have potential utility in epilepsy to assess the efficacy of novel therapeutics for targeting neuroinflammation. However, previous studies in healthy volunteers have indicated limited test-retest reliability of TSPO ligands. Here, we examine test-retest measures using TSPO PET imaging in subjects with epilepsy and healthy controls, to explore whether this biomarker can be used as an endpoint in clinical trials for epilepsy. Five subjects with epilepsy and confirmed mesial temporal lobe sclerosis (mean age 36 years, 3 men) were scanned twice-on average 8 weeks apart-using a second generation TSPO targeting radioligand, [11C]PBR28. We evaluated the test-retest reliability of the volume of distribution and derived hemispheric asymmetry index of [11C]PBR28 binding in these subjects and compared the results with 8 (mean age 45, 6 men) previously studied healthy volunteers. The mean (± SD) of the volume of distribution (VT), of all subjects, in patients living with epilepsy for both test and retest scans on all regions of interest (ROI) is 4.49 ± 1.54 vs. 5.89 ± 1.23 in healthy volunteers. The bias between test and retest in an asymmetry index as a percentage was small (-1.5%), and reliability is demonstrated here with Bland-Altman Plots (test mean 1.062, retest mean 2.56). In subjects with epilepsy, VT of [11C]PBR28 is higher in the (ipsilateral) hippocampal region where sclerosis is present than in the contralateral region. When using TSPO PET in patients with epilepsy with hippocampal sclerosis (HS), an inter-hemispheric asymmetry index in the hippocampus is a measure with good test-retest reliability. We provide estimates of test-retest variability that may be useful for estimating power where group change in VT represents the clinical outcome.

A feasibility study for quantitative assessment of cerebrovascular malformations using flutriciclamide ([18F]GE-180) PET/MRI.

Neuroinflammation plays a key role in both the pathogenesis and the progression of cerebral cavernous malformations (CCM). Flutriciclamide ([18F]GE-180) is a translocator protein (TSPO) targeting positron emission tomography (PET) tracer, developed for imaging neuroinflammation. The objectives of this study were to describe characteristics of flutriciclamide uptake in different brain tissue regions in CCM patients compared to controls, and to evaluate flutriciclamide uptake and iron deposition within CCM lesions. Five patients with CCM and six controls underwent a 60 or 90 min continuous PET/MRI scan following 315 ± 68.9 MBq flutriciclamide administration. Standardized uptake value (SUV) and standardized uptake value ratio (SUVr) were obtained using the striatum as a pseudo-reference. Quantitative susceptibility maps (QSM) were used to define the location of the vascular malformation and calculate the amount of iron deposition in each lesion. Increased flutriciclamide uptake was observed in all CCM lesions. The temporal pole demonstrated the highest radiotracer uptake; the paracentral lobule, cuneus and hippocampus exhibited moderate uptake; while the striatum had the lowest uptake, with average SUVs of 0.66, 0.55, 0.63, 0.55, and 0.33 for patient with CCM and 0.57, 0.50, 0.48, 0.42, and 0.32 for controls, respectively. Regional SUVr showed similar trends. The average SUV and QSM values in CCM lesions were 0.58 ± 0.23 g/ml and 0.30 ± 0.10 ppm. SUVs and QSM were positively correlated in CCM lesions (r = 0.53, p = 0.03). The distribution of flutriciclamide ([18F]GE-180) in the human brain and CCM lesions demonstrated the potential of this TSPO PET tracer as a marker of neuroinflammation that may be relevant for characterizing CCM disease progression along with QSM.

Exploring the neuroprotective effects of montelukast on brain inflammation and metabolism in a rat model of quinolinic acid-induced striatal neurotoxicity

BackgroundOne intrastriatal administration of quinolinic acid (QA) in rats induces a lesion with features resembling those observed in Huntington’s disease. Our aim is to evaluate the effects of the cysteinyl leukotriene receptor antagonist montelukast (MLK), which exhibited neuroprotection in different preclinical models of neurodegeneration, on QA-induced neuroinflammation and regional metabolic functions.MethodsThe right and left striatum of Sprague Dawley and athymic nude rats were injected with QA and vehicle (VEH), respectively. Starting from the day before QA injection, animals were treated with 1 or 10 mg/kg of MLK or VEH for 14 days. At 14 and 30 days post-lesion, animals were monitored with magnetic resonance imaging (MRI) and positron emission tomography (PET) using [18F]-VC701, a translocator protein (TSPO)-specific radiotracer. Striatal neuroinflammatory response was measured post-mortem in rats treated with 1 mg/kg of MLK by immunofluorescence. Rats treated with 10 mg/kg of MLK also underwent a [18F]-FDG PET study at baseline and 4 months after lesion. [18F]-FDG PET data were then used to assess metabolic connectivity between brain regions by applying a covariance analysis method.ResultsMLK treatment was not able to reduce the QA-induced increase in striatal TSPO PET signal and MRI lesion volume, where we only detected a trend towards reduction in animals treated with 10 mg/kg of MLK. Post-mortem immunofluorescence analysis revealed that MLK attenuated the increase in striatal markers of astrogliosis and activated microglia in the lesioned hemisphere. We also found a significant increase in a marker of anti-inflammatory activity (MannR) and a trend towards reduction in a marker of pro-inflammatory activity (iNOS) in the lesioned striatum of MLK—compared to VEH-treated rats. [18F]-FDG uptake was significantly reduced in the striatum and ipsilesional cortical regions of VEH-treated rats at 4 months after lesion. MLK administration preserved glucose metabolism in these cortical regions, but not in the striatum. Finally, MLK was able to counteract changes in metabolic connectivity and measures of network topology induced by QA, in both lesioned and non-lesioned hemispheres.ConclusionsOverall, MLK treatment produced a significant neuroprotective effect by reducing neuroinflammation assessed by immunofluorescence and preserving regional brain metabolism and metabolic connectivity from QA-induced neurotoxicity in cortical and subcortical regions.

Quantitative assessment of translocator protein (TSPO) in the non-human primate brain and clinical translation of [18F]LW223 as a TSPO-targeted PET radioligand

ObjectivesTranslocator protein 18 kDa (TSPO) positron emission tomography (PET) can be harnessed for the non-invasive detection of macrophage-driven inflammation. [18F]LW223, a newly reported TSPO PET tracer which was insensitive to rs6971 polymorphism, showed favorable performance characteristics in a recent imaging study involving a rat myocardial infarction model. To enable quantitative neuroimaging with [18F]LW223, we conducted kinetic analysis in the non-human primate (NHP) brain. Further, we sought to assess the utility of [18F]LW223-based TSPO imaging in a first-in-human study. MethodsRadiosynthesis of [18F]LW223 was accomplished on an automated module, whereas molar activities, stability in formulation, lipophilicity and unbound free fraction (fu) of the probe were measured. Brain penetration and target specificity of [18F]LW223 in NHPs were corroborated by PET-MR imaging under baseline and pre-blocking conditions using the validated TSPO inhibitor, (R)-PK11195, at doses ranging from 5 to 10 mg/kg. Kinetic modeling was performed using one-tissue compartment model (1TCM), two-tissue compartment model (2TCM) and Logan graphical analyses, using dynamic PET data acquisition, arterial blood collection and metabolic stability testing. Clinical PET scans were performed in two healthy volunteers (HVs). Regional brain standard uptake value ratio (SUVr) was assessed for different time intervals. Results[18F]LW223 was synthesized in non-decay corrected radiochemical yields (n.d.c. RCYs) of 33.3 ± 6.5% with molar activities ranging from 1.8 ± 0.7 Ci/µmol (n = 11). [18F]LW223 was stable in formulation for up to 4 h and LogD7.4 of 2.31 ± 0.13 (n = 6) and fu of 5.80 ± 1.42% (n = 6) were determined. [18F]LW223 exhibited good brain penetration in NHPs, with a peak SUV value of ca. 1.79 in the whole brain. Pre-treatment with (R)-PK11195 substantially accelerated the washout and attenuated the area under the time-activity curve, indicating in vivo specificity of [18F]LW223 towards TSPO. Kinetic modeling demonstrated that 2TCM was the most suitable model for [18F]LW223-based neuroimaging. Global transfer rate constants (K1) and total volumes of distribution (VT) were found to be 0.10 ± 0.01 mL/cm3/min and 2.30 ± 0.17 mL/cm3, respectively. Dynamic PET data analyses across distinct time windows revealed that the VT values were relatively stable after 60 min post-injection. In a preliminary clinical study with two healthy volunteers, [18F]LW223 exhibited good brain uptake and considerable tracer retention across all analyzed brain regions. Of note, an excellent correlation between SUVr with VT was obtained when assessing the time interval from 20 to 40 min post tracer injection (SUVr(20–40 min), R2 = 0.94, p < 0.0001), suggesting this time window may be suitable to estimate specific binding to TSPO in human brain. ConclusionOur findings indicate that [18F]LW223 is suitable for quantitative TSPO-targeted PET imaging in higher species. Employing state-of-the-art kinetic modeling, we found that [18F]LW223 was effective in mapping TSPO throughout the NHP brain, with best model fits obtained from 2TCM and Logan graphical analyses. Overall, our results indicate that [18F]LW223 exhibits favorable tracer performance characteristics in higher species, and this novel imaging tool may hold promise to provide effective neuroinflammation imaging in patients with neurological disease.

High-Grade Glioma Radiation Therapy and Reirradiation Treatment Planning Using Translocator Protein Positron Emission Tomography With 18F-GE-180

Translocator protein (TSPO) positron emission tomography (PET) using 18F-GE-180 shows high tumor-to-brain contrast in high-grade glioma (HGG), even in areas without magnetic resonance imaging (MRI) contrast enhancement. Until now, the benefit of 18F-GE-180 PET in primary radiation therapy (RT) and reirradiation (reRT) treatment planning for patients with HGG has not been assessed. The possible benefit of 18F-GE-180 PET in RT and reRT planning was retrospectively evaluated through post hoc spatial correlations of PET-based biological tumor volumes (BTVs) with conventional MRI-based consensus gross tumor volumes (cGTVs). To find the ideal threshold for BTV definition in RT and reRT treatment planning, tumor-to-background activity thresholds of 1.6, 1.8, and 2.0 were applied. Spatial overlap of PET- and MRI-based tumor volumes was measured by the Sørensen-Dice coefficient (SDC) and the conformity index (CI). Additionally, the minimal margin to include the entire BTV into the expanded cGTV was determined. Thirty-five primary RT and 16 reRT cases were examined. BTV1.6, BTV1.8, and BTV2.0 were significantly larger than corresponding cGTV volumes in primary RT (median volumes: 67.4, 50.7, and 39.1, respectively, vs 22.6 cm3; P < .001, P < .001, and P=.017, respectively; Wilcoxon test) and reRT cases (median volumes: 80.5, 55.0, and 41.6, respectively, vs 22.7 cm3; P=.001, P=.005, and P=.144, respectively; Wilcoxon test). BTV1.6, BTV1.8, and BTV2.0 showed low but increasing conformity with cGTVs in the primary RT (SDC: 0.51, 0.55, and 0.58, respectively; CI: 0.35, 0.38, and 0.41, respectively) and reRT setting (SDC: 0.38, 0.40, and 0.40, respectively; CI: 0.24, 0.25, and 0.25, respectively). The minimal margin required to include the BTV within the cGTV was significantly smaller in the RT versus the reRT setting for thresholds 1.6 and 1.8 but not significantly different for threshold 2.0 (median margin: 16, 12, and 10, respectively, vs 21.5, 17.5, and 13 mm, respectively; P=.007, P=.031, and P=.093, respectively; Mann-Whitney U test). 18F-GE-180 PET provides valuable information in RT treatment planning for patients with HGG. 18F-GE-180-based BTVs with a threshold of 2.0 were most consistent in primary and reRT.

Choroid plexus imaging to track neuroinflammation - a translational model for mouse and human studies.

Choroid plexus imaging to track neuroinflammation - a translational model for mouse and human studies.

NIMG-26. UPTAKE OF [18F]GE-180 IN TSPO PET IS ASSOCIATED WITH SURVIVAL IN PATIENTS WITH RECURRENT GLIOMA

Abstract OBJECTIVE The 18 kDa translocator protein (TSPO) is expressed in both activated microglia and glioma cells. Elevated expression of TSPO has been reported to be associated with higher WHO grade. Here we analyze whether TSPO positron emission tomography (PET) signal using the tracer [18F]GE-180 is correlated with clinical outcome in a cohort of patients with recurrent glioma. METHODS Patients with suspected glioma recurrence received a [18F]GE-180 TSPO PET. All recurrent tumors were confirmed either by stereotactic biopsy or resection. Maximum standard uptake value SUVmax as well as tumor volume in MRI and, if available, in [18F]FET PET were evaluated together with patient characteristics (age, sex, Karnofsky-Performance score) and neuropathological features (WHO grade, IDH-mutation status). Uni- and multivariate Cox regression and Kaplan-Meier survival analyses were performed to identify prognostic factors for post-recurrence survival (PRS) and time to treatment failure (TTF). RESULTS 88 consecutive patients were evaluated. TSPO tracer uptake correlated with tumor grade at recurrence (p&amp;lt; 0.05), with no significant differences between IDH-wildtype and IDH-mutant tumors. Within the subgroup of IDH-mutant glioma (n= 46), patients with low SUVmax (median split, ≤ 1.60) had a significantly longer PRS (median 41.6 vs. 25.3 months, p= 0.031) and TTF (32.2 vs 8.7 months, p= 0.001). Also among IDH-wildtype tumors (n= 42), patients with low SUVmax (≤ 1.89) had a significantly longer PRS (median not reached vs 8.2 months, p= 0.002). SUVmax remained an independent prognostic factor for PRS in a multivariate analysis including WHO grade, IDH status and age. Tumor volume defined by [18F]FET PET or contrast-enhanced MRI correlated weakly with TSPO tracer uptake. Treatment regimen did not differ between the subgroups. CONCLUSION Our data suggest that uptake of [18F]GE-180 in TSPO PET can add prognostic information in patients with recurrent glioma even in molecular defined subgroups and might serve as an imaging biomarker.

TSPO PET signal using [18F]GE180 is associated with survival in recurrent gliomas

PurposeGlioma patients, especially recurrent glioma, suffer from a poor prognosis. While advances to classify glioma on a molecular level improved prognostication at initial diagnosis, markers to prognosticate survival in the recurrent situation are still needed. As 18 kDa translocator protein (TSPO) was previously reported to be associated with aggressive histopathological glioma features, we correlated the TSPO positron emission tomography (PET) signal using [18F]GE180 in a large cohort of recurrent glioma patients with their clinical outcome.MethodsIn patients with [18F]GE180 PET at glioma recurrence, [18F]GE180 PET parameters (e.g., SUVmax) as well as other imaging features (e.g., MRI volume, [18F]FET PET parameters when available) were evaluated together with patient characteristics (age, sex, Karnofsky-Performance score) and neuropathological features (e.g. WHO 2021 grade, IDH-mutation status). Uni- and multivariate Cox regression and Kaplan–Meier survival analyses were performed to identify prognostic factors for post-recurrence survival (PRS) and time to treatment failure (TTF).ResultsEighty-eight consecutive patients were evaluated. TSPO tracer uptake correlated with tumor grade at recurrence (p < 0.05), with no significant differences in IDH-wild-type versus IDH-mutant tumors. Within the subgroup of IDH-mutant glioma (n = 46), patients with low SUVmax (median split, ≤ 1.60) had a significantly longer PRS (median 41.6 vs. 25.3 months, p = 0.031) and TTF (32.2 vs 8.7 months, p = 0.001). Also among IDH-wild-type glioblastoma (n = 42), patients with low SUVmax (≤ 1.89) had a significantly longer PRS (median not reached vs 8.2 months, p = 0.002). SUVmax remained an independent prognostic factor for PRS in the multivariate analysis including CNS WHO 2021 grade, IDH status, and age. Tumor volume defined by [18F]FET PET or contrast-enhanced MRI correlated weakly with TSPO tracer uptake. Treatment regimen did not differ among the median split subgroups.ConclusionOur data suggest that TSPO PET using [18F]GE180 can help to prognosticate recurrent glioma patients even among homogeneous molecular subgroups and may therefore serve as valuable non-invasive biomarker for individualized patient management.Graphical abstract