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Purpose Fibroblast activation protein (FAP), which has high expression in cancer-associated fibroblasts of epithelial cancers, can be used as a theranostic target. Our previous study used 64 Cu and 225 Ac-labelled FAP inhibitors (FAPI-04) for a FAP-expressing pancreatic cancer xenograft imaging and therapy. However, the optimal therapeutic radionuclide for FAPI needs to be investigated further. In this study, we evaluated the therapeutic effects of beta-emitter ( 177 Lu)-labelled FAPI-46 and alpha-emitter ( 225 Ac)-labelled FAPI-46 in pancreatic cancer models. Methods PET scans (1 h post injection) were acquired in PANC-1 xenograft mice ( n  = 9) after the administration of [ 18 F]FAPI-74 (12.4 ± 1.7 MBq) for the companion imaging. The biodistribution of [ 177 Lu]FAPI-46 and [ 225 Ac]FAPI-46 were evaluated in the xenograft model (total n  = 12). For the determination of treatment effects, [ 177 Lu]FAPI-46 and [ 225 Ac]FAPI-46 were injected into PANC-1 xenograft mice at different doses: 3 MBq ( n  = 6), 10 MBq ( n  = 6), 30 MBq ( n  = 6), control ( n  = 4) for [ 177 Lu]FAPI-46, and 3 kBq ( n  = 3), 10 kBq ( n  = 2), 30 kBq ( n  = 6), control ( n  = 7) for [ 225 Ac]FAPI-46. Tumour sizes and body weights were followed. Results [ 18 F]FAPI-74 showed rapid clearance by the kidneys and high accumulation in the tumour and intestine 1 h after administration. [ 177 Lu]FAPI-46 and [ 225 Ac]FAPI-46 also showed rapid clearance by the kidneys and relatively high accumulation in the tumour at 3 h. Both [ 177 Lu]FAPI-46 and [ 225 Ac]FAPI-46 showed tumour-suppressive effects, with a mild decrease in body weight. The treatment effects of [ 177 Lu]FAPI-46 were relatively slow but lasted longer than those of [ 225 Ac]FAPI-46. Conclusion This study suggested the possible application of FAPI radioligand therapy in FAP-expressing pancreatic cancer. Further evaluation is necessary to find the best radionuclide with shorter half-life, as well as the combination with therapies targeting tumour cells directly.

Compelling experimental evidence suggests that microglial activation is involved in the spread of tau tangles over the neocortex in Alzheimer’s disease (AD). We tested the hypothesis that the spatial propagation of microglial activation and tau accumulation colocalize in a Braak-like pattern in the living human brain. We studied 130 individuals across the aging and AD clinical spectrum with positron emission tomography brain imaging for microglial activation ([ 11 C]PBR28), amyloid-β (Aβ) ([ 18 F]AZD4694) and tau ([ 18 F]MK-6240) pathologies. We further assessed microglial triggering receptor expressed on myeloid cells 2 ( TREM2 ) cerebrospinal fluid (CSF) concentrations and brain gene expression patterns. We found that [ 11 C]PBR28 correlated with CSF soluble TREM2 and showed regional distribution resembling TREM2 gene expression. Network analysis revealed that microglial activation and tau correlated hierarchically with each other following Braak-like stages. Regression analysis revealed that the longitudinal tau propagation pathways depended on the baseline microglia network rather than the tau network circuits. The co-occurrence of Aβ, tau and microglia abnormalities was the strongest predictor of cognitive impairment in our study population. Our findings support a model where an interaction between Aβ and activated microglia sets the pace for tau spread across Braak stages. Microglial activation and tau accumulation propagate together in patients with Alzheimer’s disease, suggesting an interaction that determines disease progression.

PurposeFAPI ligands (fibroblast activation protein inhibitor), a novel class of radiotracers for PET/CT imaging, demonstrated in previous studies rapid and high tumor uptake. The purpose of this study is the head-to-head intra-individual comparison of 68Ga-FAPI versus standard-of-care 18F-FDG in PET/CT in organ biodistribution and tumor uptake in patients with various cancers.Material and MethodsThis international retrospective multicenter analysis included PET/CT data from 71 patients from 6 centers who underwent both 68Ga-FAPI and 18F-FDG PET/CT within a median time interval of 10 days (range 1–89 days). Volumes of interest (VOIs) were manually drawn in normal organs and tumor lesions to quantify tracer uptake by SUVmax and SUVmean. Furthermore, tumor-to-background ratios (TBR) were generated (SUVmax tumor/ SUVmax organ).ResultsA total of 71 patients were studied of, which 28 were female and 43 male (median age 60). In 41 of 71 patients, the primary tumor was present. Forty-three of 71 patients exhibited 162 metastatic lesions. 68Ga-FAPI uptake in primary tumors and metastases was comparable to 18F-FDG in most cases. The SUVmax was significantly lower for 68Ga-FAPI than 18F-FDG in background tissues such as the brain, oral mucosa, myocardium, blood pool, liver, pancreas, and colon. Thus, 68Ga-FAPI TBRs were significantly higher than 18F-FDG TBRs in some sites, including liver and bone metastases.ConclusionQuantitative tumor uptake is comparable between 68Ga-FAPI and 18F-FDG, but lower background uptake in most normal organs results in equal or higher TBRs for 68Ga-FAPI. Thus, 68Ga-FAPI PET/CT may yield improved diagnostic information in various cancers and especially in tumor locations with high physiological 18F-FDG uptake.

The advent of total-body positron emission tomography (PET) has vastly broadened the range of research and clinical applications of this powerful molecular imaging technology 1 . Such possibilities have accelerated progress in fluorine-18 ( 18 F) radiochemistry with numerous methods available to 18 F-label (hetero)arenes and alkanes 2 . However, access to 18 F-difluoromethylated molecules in high molar activity is mostly an unsolved problem, despite the indispensability of the difluoromethyl group for pharmaceutical drug discovery 3 . Here we report a general solution by introducing carbene chemistry to the field of nuclear imaging with a [ 18 F]difluorocarbene reagent capable of a myriad of 18 F-difluoromethylation processes. In contrast to the tens of known difluorocarbene reagents, this 18 F-reagent is carefully designed for facile accessibility, high molar activity and versatility. The issue of molar activity is solved using an assay examining the likelihood of isotopic dilution on variation of the electronics of the difluorocarbene precursor. Versatility is demonstrated with multiple [ 18 F]difluorocarbene-based reactions including O–H, S–H and N–H insertions, and cross-couplings that harness the reactivity of ubiquitous functional groups such as (thio)phenols, N -heteroarenes and aryl boronic acids that are easy to install. The impact is illustrated with the labelling of highly complex and functionalized biologically relevant molecules and radiotracers. Carbene chemistry is used to introduce difluoromethyl groups labelled with fluorine-18 into compounds for positron emission tomography imaging, using a reagent designed for high molar activity and versatility.

Purpose Early detection of hepatocellular carcinoma (HCC) remains a clinical challenge. Glypican 3 (GPC3) is a proteoglycan highly specific for HCC and is a potential diagnostic and therapeutic target for HCC. This work aims to develop GPC3-targeted immuno-positron emission tomography (immunoPET) imaging strategies and to assess the diagnostic values in preclinical HCC models. Methods Flow cytometry was used to screen GPC3-positive HCC cell lines. The expression of GPC3 in HCCs was detected by immunohistochemistry on tissue microarray. A novel GPC3-specific single domain antibody (sdAb) was produced and labeled with gallium-68 ( 68 Ga, T 1/2  = 1.1 h) and fluorine-18 ( 18 F, T 1/2  = 1.8 h) to develop radiotracers with different half-lives. The diagnostic efficacies of the developed probes (i.e., [ 68 Ga]Ga-NOTA-G2, [ 18 F]F-G2, and [ 68 Ga]Ga-NOTA-ABDG2) were interrogated in preclinical HCC models bearing varying GPC3 levels. Results GPC3 was strongly expressed on HCC cell lines and patients with poorly differentiated HCC. [ 68 Ga]Ga-NOTA-G2 immunoPET imaging specifically delineated the subcutaneous HCC lesions, outperforming the traditional 18 F-fluorodeoxyglucose PET and the nonspecific [ 68 Ga]Ga-NOTA-NbGFP immunoPET. ImmunoPET imaging with [ 18 F]F-G2 also efficiently diagnosed the tumors with clarity. Moreover, the fusion of G2 to an albumin-binding domain (ABD) significantly increased the tumor uptake and decreased kidney accumulation of the radiotracer when compared to [ 68 Ga]Ga-NOTA-G2. Conclusions In the work, we successfully developed sdAb-derived GPC3-targeted immunoPET imaging strategies and characterized the superior diagnostic accuracies in preclinical HCC models. Furthermore, we synthesized a fusion protein ABDG2 with improved targeting and pharmacokinetic properties, serving as a promising candidate for developing radioimmunotherapy agents.

Positron emission tomography (PET) plays key roles in drug discovery and development, as well as medical imaging. However, there is a dearth of efficient and simple radiolabeling methods for aromatic C–H bonds, which limits advancements in PET radiotracer development. Here, we disclose a mild method for the fluorine-18 (18F)–fluorination of aromatic C–H bonds by an [18F]F⁻ salt via organic photoredox catalysis under blue light illumination. This strategy was applied to the synthesis of a wide range of 18F-labeled arenes and heteroaromatics, including pharmaceutical compounds. These products can serve as diagnostic agents or provide key information about the in vivo fate of the labeled substrates, as showcased in preliminary tracer studies in mice.

PurposeWe evaluated the potential usefulness of [68Ga]Ga-DOTA-FAPI-04 positron emission tomography/computed tomography (PET/CT) for the diagnosis of primary and metastatic lesions in various types of cancer, compared with [18F] FDG PET/CT.MethodsA total of 75 patients with various types of cancer underwent contemporaneous [68Ga]Ga-DOTA-FAPI-04 and [18F] FDG PET/CT either for an initial assessment or for recurrence detection. Tumour uptake was quantified by the maximum standard uptake value (SUVmax). The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of [18F] FDG and [68Ga]Ga-DOTA-FAPI-04 PET/CT were calculated and compared to evaluate the diagnostic efficacy.ResultsThe study cohort consisted of 75 patients (47 males and 28 females; median age, 61.5 years; age range, 32–85 years). Fifty-four patients with 12 different tumour entities underwent paired [68Ga]Ga-DOTA-FAPI-04 and [18F] FDG PET/CT for initial assessment, while the other 21 patients underwent paired scans for recurrence detection. [68Ga]Ga-DOTA-FAPI-04 PET/CT was able to clearly identify 12 types of malignant tumours with favourable tumour-to-background contrast, which resulted in a higher detection rate of primary tumours than did [18F] FDG PET/CT (98.2% vs. 82.1%, P = 0.021). Meanwhile, [68Ga]Ga-DOTA-FAPI-04 PET/CT showed a better sensitivity than [18F] FDG PET/CT in the detection of lymph nodes (86.4% vs. 45.5%, P = 0.004) and bone and visceral metastases (83.8% vs. 59.5%, P = 0.004).Conclusion[68Ga]Ga-DOTA-FAPI-04 PET/CT showed a superior diagnostic efficacy than [18F] FDG PET/CT for the diagnosis of primary and metastatic lesions in patients with various types of cancer, especially in identifying liver metastases, peritoneal carcinomatosis, and brain tumours.

White fat stores excess energy, whereas brown and beige fat are thermogenic and dissipate energy as heat. Thermogenic adipose tissues markedly improve glucose and lipid homeostasis in mouse models, although the extent to which brown adipose tissue (BAT) influences metabolic and cardiovascular disease in humans is unclear 1 , 2 . Here we retrospectively categorized 134,529 18 F-fluorodeoxyglucose positron emission tomography–computed tomography scans from 52,487 patients, by presence or absence of BAT, and used propensity score matching to assemble a study cohort. Scans in the study population were initially conducted for indications related to cancer diagnosis, treatment or surveillance, without previous stimulation. We report that individuals with BAT had lower prevalences of cardiometabolic diseases, and the presence of BAT was independently correlated with lower odds of type 2 diabetes, dyslipidemia, coronary artery disease, cerebrovascular disease, congestive heart failure and hypertension. These findings were supported by improved blood glucose, triglyceride and high-density lipoprotein values. The beneficial effects of BAT were more pronounced in individuals with overweight or obesity, indicating that BAT might play a role in mitigating the deleterious effects of obesity. Taken together, our findings highlight a potential role for BAT in promoting cardiometabolic health. Retrospective analysis of 18 F-FDG PET/CT scans from over 50,000 patients reveals correlations between presence of brown adipose tissue and lower odds of having cardiometabolic conditions, such as type 2 diabetes, cardiovascular disease and hypertension.

Cerebrospinal fluid (CSF) p-tau181 (tau phosphorylated at threonine 181) is an established biomarker of Alzheimer’s disease (AD), reflecting abnormal tau metabolism in the brain. Here we investigate the performance of CSF p-tau217 as a biomarker of AD in comparison to p-tau181. In the Swedish BioFINDER cohort ( n  = 194), p-tau217 shows stronger correlations with the tau positron emission tomography (PET) tracer [ 18 F]flortaucipir, and more accurately identifies individuals with abnormally increased [ 18 F]flortaucipir retention. Furthermore, longitudinal increases in p-tau217 are higher compared to p-tau181 and better correlate with [ 18 F]flortaucipir uptake. P-tau217 correlates better than p-tau181 with CSF and PET measures of neocortical amyloid-β burden and more accurately distinguishes AD dementia from non-AD neurodegenerative disorders. Higher correlations between p-tau217 and [ 18 F]flortaucipir are corroborated in an independent EXPEDITION3 trial cohort ( n  = 32). The main results are validated using a different p-tau217 immunoassay. These findings suggest that p-tau217 might be more useful than p-tau181 in the diagnostic work up of AD. Cerebrospinal fluid (CSF) p-tau181 (tau phosphorylated at threonine 181) is an established biomarker of Alzheimer’s disease (AD) reflecting abnormal tau metabolism in the AD brain. Here the authors demonstrate that CSF p-tau217 shows better performance as an AD biomarker than p-tau181.

PurposeIn this study, a novel aluminium-[18F]fluoride (Al18F)-labelled 1,4,7‑triazacyclononane-N,N′,N″-triacetic acid (NOTA)-conjugated fibroblast activation protein inhibitor (FAPI) probe, named Al18F-NOTA-FAPI, was developed for fibroblast activation protein (FAP)-targeted tumour imaging; it could deliver hundreds of millicuries of radioactivity using automated synthesis. The tumour detection efficacy of Al18F-NOTA-FAPI was further validated in both preclinical and clinical translational studies.MethodsThe radiolabelling procedure of Al18F-NOTA-FAPI was optimized. Cell uptake and competitive binding assays were completed with the U87MG and A549 cell lines to evaluate the affinity and specificity of the Al18F-NOTA-FAPI probe. The biodistribution, pharmacokinetics, radiation dosimetry and tumour imaging efficacy of the Al18F-NOTA-FAPI probe were researched in healthy Kunming (KM) and/or U87MG model mice. After the approval of the ethical committee, the Al18F-NOTA-FAPI probe was translated into the clinic for PET/CT imaging of the first 10 cancer patients.ResultsThe radiolabelling yield of Al18F-NOTA-FAPI was 33.8 ± 3.2% using manual synthesis (n = 10), with a radiochemical purity over 99% and the specific activity of 9.3–55.5 MBq/nmol. The whole body effective dose of Al18F-NOTA-FAPI was estimated to be 1.24E − 02 mSv/MBq, which was lower than several other FAPI probes (68Ga-FAPI-04, 68Ga-FAPI-46 and 68Ga-FAPI-74). In U87MG tumour-bearing mice, Al18F-NOTA-FAPI showed good tumour detection efficacy based on the results of micro PET/CT imaging and biodistribution studies. In an organ biodistribution study of patients, Al18F-NOTA-FAPI showed a lower SUVmean than 2-[18F]-fluoro-2-deoxy-D-glucose (2-[18F]FDG) in most organs, especially in the liver (1.1 ± 0.2 vs. 2.0 ± 0.9), brain (0.1 ± 0.0 vs. 5.9 ± 1.3), and bone marrow (0.9 ± 0.1 vs. 1.7 ± 0.4). Meanwhile, Al18F-NOTA-FAPI did not show extensive bone uptake, and was able to detect more lesions than 2-[18F]FDG in the PET/CT imaging of several patients.ConclusionThe Al18F-NOTA-FAPI probe was successfully fabricated and applied in fibroblast activation protein-targeted tumour PET/CT imaging, which showed excellent imaging quality and tumour detection efficacy in U87MG tumour-bearing mice as well as in cancer patients.Trial registrationChinese Clinical Trial Registry ChiCTR2000038080. Registered 09 September 2020. http://www.chictr.org.cn/showproj.aspx?proj=61192