A new β-amyloid (Aβ) targeting radiotracer, [18F]D3FSP ([18F]P16-129), for diagnosis of Alzheimer’s disease (AD) is reported. This radiotracer is a deuterated N-methyl derivative of Amyvid (AV-45, florbetapir f18) which was FDA-approved in 2013. Deuteration may alter a tracer’s PK such that imaging performance is improved. A head-to-head comparison between these two imaging agents was conducted in AD patients. A separate biodistribution study was conducted on six healthy subjects, and radiation dosimetry estimation was obtained. Eight patients, clinically diagnosed with Alzheimer’s disease, had an average age of 61.1 ± 10.0 years, and an average MMSE score of 21 ± 4. Each patient underwent paired 90-minute dynamic PET/CT scans separately within a few weeks (323 ± 31 MBq of [18F]D3FSP or [18F]AV45; florbetapir f18). SUVR (50–70 min) and Distribution Volume Ratio (DVR) of 43 brain regions were evaluated. The average SUVR across cortical gray matter was 1.65 ± 0.21 for [18F]AV45 and 1.65 ± 0.23 for [18F]D3FSP, while global DVRs were 1.36 ± 0.14 and 1.37 ± 0.13 for [18F]AV45 and [18F]D3FSP respectively. Strong correlations (R2 = 0.8–0.9) were observed between tracers for both SUVR and DVR, with slopes of 0.9 (SUVR) and 1 (DVR). No image artifacts or confounds influenced the visual interpretation of [18F]D3FSP compared to [18F]AV45. Results showed no difference between [18F]D3FSP and [18F]AV45 and no benefit of deuteration at the N-methyl site. Even so, [18F]D3FSP may be a useful alternative for PET/CT imaging of Aβ deposits in the brain as its binding characteristics were very similar to its non-deuterated analog, the FDA-approved drug [18F]AV45. Clinicaltrials.org, NCT03902548. Registered 01/07/2018.

Objectives: Virally suppressed people with HIV (VS-PWH) show heterogeneity in patterns of cognitive dysfunction. To better understand the relationship between the neuroimmune response and cognition, we used PET to image the translocator protein 18 kDa (TSPO). The study examined HIV-serostatus differences in TSPO as well as associations between regional TSPO and select cognitive processes defined using the Research Domain Criteria (RDoC) framework. Design: Cross-sectional investigation in VS-PWH (n = 25) versus HIV-uninfected individuals (n = 18) of cognitive control and declarative memory, as well as [C-11]DPA-713 PET measures of TSPO within cognitive control and declarative memory regions of interest (ROI). Methods: Group differences in [C-11]DPA-713 binding (V-T) in cognitive control or declarative memory regions were examined using linear mixed models. Tests of associations between factor-derived cognitive system measures and PET measures were performed, controlling for TSPO genotype. Results: There were no group differences in any of the four factor-derived cognitive system measures. VS-PWH had higher log [C-11]DPA-713 V-T across cognitive control regions [unstandardized beta coefficient reflecting mean difference [B] = 0.23, SE = 0.11, 95% confidence interval (CI) 0.01-0.45, P = 0.04] and declarative memory regions (B = 0.24, SE = 0.11, 95% CI 0.02-0.45, P = 0.03). Higher log [C-11]DPA-713 V-T in cognitive control regions related to poorer cognitive control in each group, and to worse self-reported cognitive performance in VS-PWH. Log [C-11]DPA-713 V-T in each declarative memory region did not associate with measured declarative memory. Conclusion: A localized neuroimmune response marked by high TSPO in brain regions that subserve cognitive control may contribute to poorer cognitive control in VS-PWH.

[68Ga]Ga-DK223 PET reveals differential activity of PD-L1 antibodies over time in BFTC909 xenografts.

A, Synthesis of DK223. B, RP-HPLC chromatogram of DK223.

BACKGROUND:Positron-emission tomography (PET) imaging of the complement system could advance understanding of the innate immune system in central nervous system (CNS) diseases and development of new drugs. The goal of this study was to develop a PET radiotracer targeting the C3a receptor (C3aR) of the complement system. METHODS:C3aR radiotracer [18F]1 was synthesized in one step. Imaging properties of the radiotracer in the brain were tested in ex vivo experiments in mice. RESULTS:[18F]1 was radiolabeled with radiochemical yield of 4 %, radiochemical purity >95 % and molar activity ~155 GBq/μmol. In control mice [18F]1 demonstrated high brain uptake (9 %ID/g tissue) which gradually increased over the 90 min of the study period and represented mainly non-specific binding. The C3aR specificity (18 %) of [18F]1 binding in the brain of control mice was determined in a blocking experiment. The brain uptake of [18F]1 was significantly increased (~2 - fold) in a murine model of neuroinflammation [lipopolysaccharide (LPS) - treated mice]. The blocking experiments in LPS-treated mice showed a dose-dependent reduction in whole-brain uptake of [18F]1 demonstrating that the blocked binding is partially specific (43 %) and dependent upon C3aR. This study demonstrated the feasibility of development a PET radiotracer for specific imaging of C3aR in neuroinflammation. However, [18F]1 is suboptimal for further studies, because of its insufficient specific binding in neuroinflammation model, high non-specific binding and slow irreversible kinetics in the mouse brain. Future research should focus on developing of optimized C3aR PET tracers with improved specific binding, reduced non-specific binding, reversible pharmacokinetics and, also, better radiochemistry.

A, Comparison of DOTA and DOTAGA analogs of DK221.

BACKGROUNDMicroglia-mediated brain immune changes play a role in the pathogenesis of Parkinson's disease (PD), but imaging microglia in living people with PD has relied on positron emission tomography (PET) ligands that lack specificity in labeling immune cells in the nervous system. We aimed to develop imaging of colony stimulating factor 1 receptor (CSF1R) as a microglial-sensitive marker of innate immunity.METHODSIHC using a CSF1R antibody evaluated colocalization with Iba-1 in PD (n = 4) and control (n = 4) human brain samples. Autoradiography using a CSF1R tritiated ligand in human brain samples from individuals with PD (n = 5) and in a control group (n = 4) was performed to obtain Bmax. PET imaging using a CSF1R radioligand was performed in 10 controls and 12 people with PD, and VT was compared between groups and correlated with disease severity.RESULTSIHC of CSF1R in human brain samples shows colocalization with Iba-1 and is significantly increased in brain samples from individuals with PD compared with individuals in a control group. Autoradiography revealed significantly increased CSF1R ligand binding in the inferior parietal cortex of patients with PD. [11C]CPPC PET showed higher binding in people with moderate PD compared with people in a control group and ligand binding correlated with more severe motor disability and poorer verbal fluency.CONCLUSIONThis study underscores the significance of CSF1R imaging as a promising biomarker for brain immune function in Parkinson's disease, which may be associated with cognitive and motor disease severity.FUNDINGPET imaging: the Michael J. Fox Foundation and the RMS Family Foundation. Radiotracer development: NIH (R01AG066464 and P41 EB024495). Postmortem brain tissues: NIH P30 AG066507 and BIOCARD study NIH U19 AG033655.

Positron emission tomography (PET) reporter systems are a valuable means of estimating the level of expression of a transgene in vivo. For example, the safety and efficacy of gene therapy approaches for the treatment of neurological and neuropsychiatric disorders could be enhanced via the monitoring of exogenous gene expression levels in the brain. The present study evaluated the ability of a newly developed PET reporter system [18F]fluoroestradiol ([18F]FES) and the estrogen receptor-based PET reporter ChRERα, to monitor expression levels of a small hairpin RNA (shRNA) designed to suppress choline acetyltransferase (ChAT) expression in rhesus monkey brain. The ChRERα gene and shRNA were expressed from the same transcript via lentivirus injected into monkey striatum. In two monkeys that received injections of viral vector, [18F]FES binding increased by 70% and 86% at the target sites compared with pre-injection, demonstrating that ChRERα expression could be visualized in vivo with PET imaging. Post-mortem immunohistochemistry confirmed that ChAT expression was significantly suppressed in regions in which [18F]FES uptake was increased. The consistency between PET imaging and immunohistochemical results suggests that [18F]FES and ChRERα can serve as a PET reporter system in rhesus monkey brain for in vivo evaluation of the expression of potential therapeutic agents, such as shRNAs.

Aluminum fluoride (AlF) complexes have been used over the past decade to incorporate [18F]fluoride into large biomolecules in a highly selective fashion by using relatively facile conditions. However, despite their widespread usage, there are a large number of variations in the reaction conditions, without a definitive discussion provided on the mechanism to understand how these changes would alter the end result. Herein, we report a detailed mechanistic investigation of the reaction, using a mixture of theoretical studies, fluorine-19 and fluorine-18 chemistry, and the consequences it has on the efficient clinical translation of AlF-containing imaging agents.

Abstract Background Reactive microglia and recruited peripheral macrophages contribute to the pathogenesis of Alzheimer’s dementia (AD). Monocytes, macrophages and microglia all express the marker colony-stimulating factor 1 receptor (CSF1R). 4-Cyano-N-(4-(4-methylpiperazin-1-yl)-2-(4-methylpiperidin-1-yl)phenyl)-1H-pyrrole-2-carboxamide (1) is a high-affinity antagonist for CSF1R. We report the radiosynthesis of both [3H]1 and [11C]1. The PET imaging properties of [11C]1 in mice and baboon were investigated. [3H]1 was studied in Bmax measurement in post-mortem autoradiography in the frontal cortex, inferior parietal cortex and hippocampus from donors diagnosed with AD and age-matched controls. In vitro binding affinity of 1 was measured commercially. Nor-methyl-1 precursor was radiolabeled with [11C]iodomethane or [3H]iodomethane to produce [11C]1 and [3H]1, respectively. Ex vivo brain biodistribution of [11C]1 was compared in normal mice versus lipopolysaccharide-administered (LPS) murine model of neuroinflammation. Dynamic PET imaging was performed in a healthy male Papio anubis baboon. Post-mortem autoradiography with [3H]1 was performed in frozen sections using a standard saturation binding technique. Results Compound 1 exhibits a high in vitro CSF1R binding affinity (0.59 nM). [11C]1 was synthesized with high yield. [3H]1 was synthesized similarly (commercially). Biodistribution of [11C]1 in healthy mice demonstrated moderate brain uptake. In LPS-treated mice the brain uptake of [11C]1 was ~ 50% specific for CSF1R. PET/CT [11C]1 study in baboon revealed low brain uptake (0.36 SUV) of [11C]1. Autoradiography with [3H]1 gave significantly elevated Bmax values in AD frontal cortex versus control (47.78 ± 26.80 fmol/mg vs. 12.80 ± 5.30 fmol/mg, respectively, P = 0.023) and elevated, but not significantly different binding in AD hippocampus grey matter and inferior parietal cortex (IPC) white matter. Conclusions Compound 1 exhibits a high in vitro CSF1R binding affinity. [11C]1 specifically labels CSF1R in the mouse neuroinflammation, but lacks the ability to efficiently cross the blood–brain barrier in baboon PET. [3H]1 specifically labels CSF1R in post-mortem human brain. The binding of [3H]1 is significantly higher in the post-mortem frontal cortex of AD versus control subjects.

Importance Studies using human postmortem tissue and imaging with positron emission tomography (PET) support a low hippocampal availability of the α7 nicotinic acetylcholine receptor (α7-nAChR) in psychotic conditions, particularly in schizophrenia or schizoaffective disorder (nonaffective psychosis). If validated further, the finding may have implications for clinical diagnosis and treatment. Objective To test for lower availability of the α7-nAChR in the hippocampus of individuals with recent-onset psychosis compared with healthy control individuals and its association with lower cognitive performance or higher psychotic symptom burden within recent-onset psychosis. Design, Setting, and Participants In this cross-sectional study, healthy individuals without history of psychosis and patients within 10 years of a first onset of psychotic disorder were recruited from the greater Baltimore, Maryland, and Washington, DC, area. Fluorine 18–labeled ASEM ([ 18 F] ASEM) PET data were acquired from participants enrolled between March 1, 2014, and July 31, 2023, from an academic research institution. Data acquired between March 1, 2014, and January 31, 2018 (n = 26), were published as a pilot study and were combined with new data acquired between January 1, 2019, and July 31, 2023 (n = 33). Main Outcome and Measures Regional [ 18 F]ASEM total distribution volume (V T ) that measures α7-nAChR availability, global cognition composite score, and total scores on the Scale for the Assessment of Positive Symptoms and the Scale for the Assessment of Negative Symptoms. Results A total of 59 participants (30 women [51%]; mean [SD] age, 25.5 [5.2] years), including 35 with recent-onset psychosis and 24 healthy controls, completed the study. In age-adjusted analyses, lower hippocampal [ 18 F]ASEM V T was found in individuals with recent-onset psychosis (mean [SE], 17.87 [0.60]) compared with healthy controls (mean [SE], 19.82 [0.73]) ( P = .04). In addition, [ 18 F]ASEM V T was lower in individuals with nonaffective psychosis (mean [SE], 16.30 [0.83]) compared with healthy controls ( P = .006) or those with affective psychosis (mean [SE], 19.34 [0.80]) ( P = .03). Across recent-onset psychosis and after controlling for age, lower hippocampal [ 18 F]ASEM V T was associated with more positive ( r = −0.44; P = .009) but not negative symptoms, and higher hippocampal V T was associated with better global cognition composite score ( r = 0.38; P = .03). Conclusions and Relevance In this cross-sectional study of individuals with recent-onset psychosis compared with healthy controls, a lower hippocampal α7-nAChR availability was found in recent-onset psychosis, and its availability was lower in those with nonaffective vs affective psychosis. Further study of the association between low availability of the α7-nAChR and recent-onset psychosis is warranted toward informing diagnostic or therapeutic strategies related to these findings.

Key Points Question Is high 18 kDa translocator protein (TSPO) that marks brain injury and repair detected in the brains of a large group of young, former American National Football League (NFL) players? Findings In this large cross-sectional study of 54 athletes, [11C]DPA-713 positron emission tomography imaging revealed high brain TSPO in former NFL players compared with elite, noncollision sport athletes, consistent with high TSPO after cessation of NFL play. The NFL players also had lower performance in learning and memory. Meaning These findings suggest that because brain injury with cognitive impairment was found in these relatively young, former NFL players, further tracking of TSPO levels in relation to neuropsychological performance over time is needed to understand whether these signs persist, progress, and/or warrant neuroimmune-modulating interventions.

AbstractPurpose: Immune checkpoint therapy (ICT) is currently ineffective in a majority of patients. Tumor drug exposure measurements can provide vital insights into mechanisms involved in the resistance of solid tumors to those therapeutics; however, tools to quantify in situ drug exposure are few. We have investigated the potential of programmed death-ligand 1 (PD-L1) pharmacodynamics, quantified using PET, to inform on the tumor exposure of anti–PD-L1 (aPD-L1) therapeutics. Experimental Design: To noninvasively quantify PD-L1 levels, we first developed a novel peptide-based gallium-68–labeled binder, [68Ga]Ga-DK223, and evaluated its in vivo distribution, pharmacokinetics, and PD-L1 specificity in preclinical models of triple-negative breast cancer and urothelial carcinoma with variable PD-L1 expression. We then quantified baseline and accessible PD-L1 levels in tumors as a noninvasive pharmacodynamic measure to assess tumor exposure to two aPD-L1 antibodies (avelumab and durvalumab). Results: DK223 exhibited a KD of 1.01±0.83 nmol/L for PD-L1 and inhibited the PD-1:PD-L1 interaction in a dose-dependent manner. [68Ga]Ga-DK223 provides high-contrast PET images within 60 minutes of administration and detects PD-L1 in an expression-dependent manner in xenograft models. PD-L1 pharmacodynamics measured using [68Ga]Ga-DK223-PET revealed that avelumab and durvalumab had similar exposure early during therapy, but only durvalumab exhibited sustained exposure at the tumor. Conclusions: [68Ga]Ga-DK223 detected variable PD-L1 levels and exhibited salient features required for clinical translation. [68Ga]Ga-DK223-PET could be useful for quantifying total PD-L1 levels at baseline and accessible PD-L1 levels during therapy to understand drug exposure at the tumor, thus supporting its use for guiding and optimizing ICT.

The pretargeting approach separates the biological half-life of an antibody from the physical half-life of the radioisotope label, providing a strategy for reducing the radiation burden. A widely explored pretargeting approach makes use of the bioorthogonal click reaction between tetrazines (Tzs) and trans-cyclooctenes (TCOs), combining the targeting specificity of monoclonal antibodies (mAbs) with the rapid clearance and precise reaction of Tzs and TCOs. Such a strategy can allow for the targeting and imaging (e.g., by positron emission tomography (PET)) of molecular markers, which cannot be addressed by solely relying on small molecules. Tz derivatives that undergo inverse electron-demand Diels-Alder (IEDDA) reactions with an antibody bearing TCO moieties have been investigated. This study describes the synthesis and characterization of 11 cold Tz imaging agent candidates. These molecules have the potential to be radiolabeled with 18F or 3H, and with the former label, they could be of use as imaging tracers for positron emission tomography studies. Selection was made using a multiparameter optimization score for the central nervous system (CNS) PET tracers. Novel tetrazines were tested for their pH-dependent chemical stability. Those which turned out to be stable in a pH range of 6.5-8 were further characterized in in vitro assays with regard to their passive permeability, microsomal stability, and P-glycoprotein transport. Furthermore, selected Tzs were examined for their systemic clearance and CNS penetration in a single-dose pharmacokinetic study in rats. Two tetrazines were successfully labeled with 18F, one of which showed brain penetration in a biodistribution study in mice. Another Tz was successfully tritium-labeled and used to demonstrate a bioorthogonal click reaction on a TCO-modified antibody. As a result, we identified one Tz as a potential fluorine-18-labeled CNS-PET agent and a second as a 3H-radioligand for an IEDDA-based reaction with a modified brain-penetrating antibody.

Background: Neuropathological and neuroimaging studies have demonstrated degeneration of the serotonin system in Alzheimer’s disease (AD). Neuroimaging studies have extended these observations to the preclinical stages of AD, mild cognitive impairment (MCI). Serotonin degeneration has been observed also in transgenic amyloid mouse models, prior to widespread cortical distribution of amyloid-β (Aβ). Objective: The present study evaluated the regional distribution of the serotonin transporter (5-HTT) and of Aβ in individuals with MCI and healthy older controls, as well as the contribution of 5-HTT and Aβ to cognitive deficits. Methods: Forty-nine MCI participants and 45 healthy older controls underwent positron emission tomography (PET) imaging of 5-HTT and Aβ, structural magnetic resonance imaging and neuropsychological assessments. Results: Lower cortical, striatal, and limbic 5-HTT and higher cortical Aβ was observed in MCIs relative to healthy controls. Lower 5-HTT, mainly in limbic regions, was correlated with greater deficits in auditory-verbal and visual-spatial memory and semantic, not phonemic fluency. Higher cortical A β was associated with greater deficits in auditory-verbal and visual-spatial memory and in semantic, not phonemic fluency. When modeling the association between cognition, gray matter volumes and Aβ, inclusion of 5-HTT in limbic and in select cortical regions significantly improved model fit for auditory-verbal and visual-spatial memory and semantic, but not phonemic fluency. Conclusions: These results support the role of serotonin degeneration in the memory and semantic fluency deficits observed in MCI.

Objective: Neuroimmune activation is a putative driver of cognitive impairment in people with HIV (PWH), even in the age of modern antiretroviral therapy. Nevertheless, imaging of the microglial marker, the 18 kDa translocator protein (TSPO), with positron emission tomography (PET) in treated PWH has yielded inconclusive findings. One potential reason for the varied TSPO results is a lack of cell-type specificity of the TSPO target. Design: [11C]CPPC, 5-cyano-N-(4-(4-[11C]methylpiperazin-1-yl)-2-(piperidin-1-yl)phenyl) furan-2-carboxaminde, is a radiotracer for use with PET to image the colony stimulating factor 1 receptor (CSF1R). The CSF1R is expressed on microglia and central nervous system macrophages, with little expression on other cell types. We used [11C]CPPC PET in virally-suppressed- (VS)-PWH and HIV-uninfected individuals to estimate the effect sizes of higher CSF1R in the brains of VS-PWH. Methods: Sixteen VS-PWH and 15 HIV-uninfected individuals completed [11C]CPPC PET. [11C]CPPC binding (VT) in nine regions was estimated using a one-tissue compartmental model with a metabolite-corrected arterial input function, and compared between groups. Results: Regional [11C]CPPC VT did not significantly differ between groups after age- and sex- adjustment [unstandardized beta coefficient (B) = 1.84, standard error (SE) = 1.18, P = 0.13]. The effect size was moderate [Cohen's d = 0.56, 95% confidence interval (CI) −0.16, 1.28), with strongest trend of higher VT in VS-PWH in striatum and parietal cortex (each P = 0.04; Cohen's d = 0.71 and 0.72, respectively). Conclusions: A group difference in [11C]CPPC VT was not observed between VS-PWH and HIV-uninfected individuals in this pilot, although the observed effect sizes suggest the study was underpowered to detect regional group differences in binding.

A radiochemical synthesis of [ 18 F]DK222, a peptide binder of programmed death ligand 1 protein, suitable for human PET studies is described, and results from validation productions are presented. The high specific activity radiotracer product is prepared as a sterile, apyrogenic solution that conforms to current Good Manufacturing Practice (cGMP) requirements. In addition, the production is extended to use a commercial synthesizer platform (General Electric FASTlab 2).

The beta‐site amyloid precursor protein cleaving enzyme (BACE1) is responsible for initiating the generation of beta‐amyloid, the major constituent of amyloid plaques in Alzheimer's disease (AD). The purpose of this study was to develop a specific BACE1 radioligand for visualization of the distribution pattern and quantification of the BACE1 protein in the rodent and monkey brain both in vitro by autoradiography and in vivo by positron emission tomography (PET). The BACE1 inhibitor RO6807936 originating from an in‐house chemical drug optimization program was selected based on its PET tracer‐like physicochemical properties and a favorable pharmacokinetic profile. Saturation binding analysis of [ 3 H]RO6807936 revealed specific and high‐affinity binding ( K D = 2.9 nM) and a low B max value (4.3 nM) of the BACE1 protein in native rat brain membranes. [ 3 H]RO6807936 binding showed a ubiquitous distribution on rat brain slices in vitro with higher levels in the CA3 pyramidal cell layer and the granule cell layer of the hippocampus. In a next step, RO6807936 was successfully radiolabeled with carbon‐11 and showed acceptable uptake in the baboon brain as well as a widespread and rather homogeneous distribution consistent with rodent data. In vivo blockade studies with a specific BACE1 inhibitor reduced uptake of the tracer to homogenous levels across brain regions and demonstrated specificity of the signal. Our data warrant further profiling of this PET tracer candidate in humans to investigate BACE1 expression in normal individuals and those with AD and as an imaging biomarker for target occupancy studies in clinical drug trials.

The aims of this study were to investigate the utility of [18F]F-Florastamin, a novel prostate-specific membrane antigen (PSMA)-targeted PET radiotracer with facile radiochemistry, relative to the conventional imaging for the detection of sties of disease and evaluate the effect of multi-timepoint imaging with [18F]F-Florastamin PET on lesion detectability. Eight prostate cancer patients with known or suspected recurrence who underwent [18F]F-Florastamin PET/CT at 1-h and 2-h imaging time-points were included in this prospective pilot study. [18F]F-Florastamin PET images were interpreted visually and quantitatively at both time points and compared with CIM. [18F]F-Florastamin PET was superior to CT in the detection of active osseous metastases and small-sized metastatic lymph nodes that do not fall under the anatomic imaging size criteria for metastasis. Multi-timepoint imaging showed a significant reduction in the blood pool, bone marrow and muscular uptake, and increase in liver uptake over time. There is a significant improvement in tumor-to-background ratio (TBR) at the 2-h imaging time-point (P = 0.04). The mean percentage change in TBR at 2-h was 21