Toward imaging of alpha-synuclein with PET.

Development of radiopharmaceuticals for in vivo positron emission tomography imaging of alpha-synuclein aggregates has the potential to revolutionize Lewy body disease diagnosis and treatment. Reporting in this issue of Cell, Xiang et al. developed a high-affinity positron emission tomography tracer for alpha-synuclein.

Radiotheranostics in oncology: Making precision medicine possible.

A quintessential setting for precision medicine, theranostics refers to a rapidly evolving field of medicine in which disease is diagnosed followed by treatment of disease-positive patients using tools for the therapy identical or similar to those used for the diagnosis. Against the backdrop of only-treat-when-visualized, the goal is a high therapeutic index with efficacy markedly surpassing toxicity. Oncology leads the way in theranostics innovation, where the approach has become possible with the identification of unique proteins and other factors selectively expressed in cancer versus healthy tissue, advances in imaging technology able to report these tissue factors, and major understanding of targeting chemicals and nanodevices together with methods to attach labels or warheads for imaging and therapy. Radiotheranostics-using radiopharmaceuticals-is becoming routine in patients with prostate cancer and neuroendocrine tumors who express the proteins PSMA (prostate-specific membrane antigen) and SSTR2 (somatostatin receptor 2), respectively, on their cancer. The palpable excitement in the field stems from the finding that a proportion of patients with large metastatic burden show complete and partial responses, and this outcome is catalyzing the search for more radiotheranostics approaches. Not every patient will benefit from radiotheranostics; but, for those who cross the target-detected line, the likelihood of response is very high.

Covalent targeted radioligands potentiate radionuclide therapy.

Targeted radionuclide therapy, in which radiopharmaceuticals deliver potent radionuclides to tumours for localized irradiation, has addressed unmet clinical needs and improved outcomes for patients with cancer1-4. A therapeutic radiopharmaceutical must achieve both sustainable tumour targeting and fast clearance from healthy tissue, which remains a major challenge5,6. A targeted ligation strategy that selectively fixes the radiopharmaceutical to the target protein in the tumour would be an ideal solution. Here we installed a sulfur (VI) fluoride exchange (SuFEx) chemistry-based linker on radiopharmaceuticals to prevent excessively fast tumour clearance. When the engineered radiopharmaceutical binds to the tumour-specific protein, the system undergoes a binding-to-ligation transition and readily conjugates to the tyrosine residues through the 'click' SuFEx reaction. The application of this strategy to a fibroblast activation protein (FAP) inhibitor (FAPI) triggered more than 80% covalent binding to the protein and almost no dissociation for six days. In mice, SuFEx-engineered FAPI showed 257% greater tumour uptake than did the original FAPI, and increased tumour retention by 13-fold. The uptake in healthy tissues was rapidly cleared. In a pilot imaging study, this strategy identified more tumour lesions in patients with cancer than did other methods. SuFEx-engineered FAPI also successfully achieved targeted ß- and α-radionuclide therapy, causing nearly complete tumour regression in mice. Another SuFEx-engineered radioligand that targets prostate-specific membrane antigen (PSMA) also showed enhanced therapeutic efficacy. Considering the broad scope of proteins that can potentially be ligated to SuFEx warheads, it might be possible to adapt this strategy to other cancer targets.

[18F]Difluorocarbene for positron emission tomography.

The advent of total-body positron emission tomography (PET) has vastly broadened the range of research and clinical applications of this powerful molecular imaging technology1. Such possibilities have accelerated progress in fluorine-18 (18F) radiochemistry with numerous methods available to 18F-label (hetero)arenes and alkanes2. However, access to 18F-difluoromethylated molecules in high molar activity is mostly an unsolved problem, despite the indispensability of the difluoromethyl group for pharmaceutical drug discovery3. Here we report a general solution by introducing carbene chemistry to the field of nuclear imaging with a [18F]difluorocarbene reagent capable of a myriad of 18F-difluoromethylation processes. In contrast to the tens of known difluorocarbene reagents, this 18F-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 [18F]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.

Visualizing Immune Checkpoint Inhibitors Derived Inflammation in Atherosclerosis.

BACKGROUND: Immune checkpoint inhibitor (ICI) usage has resulted in immune-related adverse events in patients with cancer, such as accelerated atherosclerosis. Of immune cells involved in atherosclerosis, the role of CCR2+ (CC motif chemokine receptor 2-positive) proinflammatory macrophages is well documented. However, there is no noninvasive approach to determine the changes of these cells in vivo following ICI treatment and explore the underlying mechanisms of immune-related adverse events. Herein, we aim to use a CCR2 (CC motif chemokine receptor 2)-targeted radiotracer and positron emission tomography (PET) to assess the aggravated inflammatory response caused by ICI treatment in mouse atherosclerosis models and explore the mechanism of immune-related adverse events. METHODS: Apoe-/- mice and Ldlr-/- mice were treated with an ICI, anti-PD1 (programmed cell death protein 1) antibody, and compared with those injected with either isotype control IgG or saline. The radiotracer 64Cu-DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid)-ECL1i (extracellular loop 1 inverso) was used for PET imaging of CCR2+ macrophages. Atherosclerotic arteries were collected for molecular characterization. RESULTS: CCR2 PET revealed significantly higher radiotracer uptake in both Apoe-/- and Ldlr-/- mice treated with anti-PD1 compared with the control groups. The increased expression of CCR2+ cells in Apoe-/- and Ldlr-/- mice was confirmed by immunostaining and flow cytometry. Single-cell RNA sequencing revealed elevated expression of CCR2 in myeloid cells. Mechanistically, IFNγ (interferon gamma) was essential for aggravated inflammation and atherosclerotic plaque progression following anti-PD1 treatment. CONCLUSIONS: Accelerated atherosclerotic plaque inflammation triggered by anti-PD1 treatment can be noninvasively detected by 64Cu-DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid)-ECL1i (extracellular loop 1 inverso) PET. Aggravated plaque inflammation is time- and dose-dependent and predominately mediated by IFNγ signaling. This study warrants further investigation of CCR2 PET as a noninvasive approach to visualize atherosclerotic plaque inflammation and explore the underlying mechanism following ICI treatment.

A genetically targeted reporter for PET imaging of deep neuronal circuits in mammalian brains.

Positron emission tomography (PET) allows biomolecular tracking but PET monitoring of brain networks has been hampered by a lack of suitable reporters. Here, we take advantage of bacterial dihydrofolate reductase, ecDHFR, and its unique antagonist, TMP, to facilitate in vivo imaging in the brain. Peripheral administration of radiofluorinated and fluorescent TMP analogs enabled PET and intravital microscopy, respectively, of neuronal ecDHFR expression in mice. This technique can be used to the visualize neuronal circuit activity elicited by chemogenetic manipulation in the mouse hippocampus. Notably, ecDHFR-PET allows mapping of neuronal projections in non-human primate brains, demonstrating the applicability of ecDHFR-based tracking technologies for network monitoring. Finally, we demonstrate the utility of TMP analogs for PET studies of turnover and self-assembly of proteins tagged with ecDHFR mutants. These results establish opportunities for a broad spectrum of previously unattainable PET analyses of mammalian brain circuits at the molecular level.

[177Lu]Lu-DOTA-TATE plus long-acting octreotide versus high­dose long-acting octreotide for the treatment of newly diagnosed, advanced grade 2-3, well-differentiated, gastroenteropancreatic neuroendocrine tumours (NETTER-2): an open-label, randomised, phase 3 study.

BACKGROUND: There are currently no standard first-line treatment options for patients with higher grade 2-3, well-differentiated, advanced, gastroenteropancreatic neuroendocrine tumours. We aimed to investigate the efficacy and safety of first-line [177Lu]Lu-DOTA-TATE (177Lu-Dotatate) treatment. METHODS: NETTER-2 was an open-label, randomised, parallel-group, superiority, phase 3 trial. We enrolled patients (aged ≥15 years) with newly diagnosed higher grade 2 (Ki67 ≥10% and ≤20%) and grade 3 (Ki67 >20% and ≤55%), somatostatin receptor-positive (in all target lesions), advanced gastroenteropancreatic neuroendocrine tumours from 45 centres across nine countries in North America, Europe, and Asia. We used interactive response technologies to randomly assign (2:1) patients to receive four cycles (cycle interval was 8 weeks ± 1 week) of intravenous 177Lu-Dotatate plus intramuscular octreotide 30 mg long-acting repeatable (LAR) then octreotide 30 mg LAR every 4 weeks (177Lu-Dotatate group) or high-dose octreotide 60 mg LAR every 4 weeks (control group), stratified by neuroendocrine tumour grade (2 vs 3) and origin (pancreas vs other). Tumour assessments were done at baseline, week 16, and week 24, and then every 12 weeks until disease progression or death. The primary endpoint was progression-free survival by blinded, independent, central radiology assessment. We did the primary analysis at 101 progression-free survival events as the final progression-free survival analysis. NETTER-2 is registered with ClinicalTrials.gov, NCT03972488, and is active and not recruiting. FINDINGS: Between Jan 22, 2020, and Oct 13, 2022, we screened 261 patients, 35 (13%) of whom were excluded. We randomly assigned 226 (87%) patients (121 [54%] male and 105 [46%] female) to the 177Lu-Dotatate group (n=151 [67%]) and control group (n=75 [33%]). Median progression-free survival was 8·5 months (95% CI 7·7-13·8) in the control group and 22·8 months (19·4-not estimated) in the 177Lu-Dotatate group (stratified hazard ratio 0·276 [0·182-0·418]; p<0·0001). During the treatment period, adverse events (of any grade) occurred in 136 (93%) of 147 treated patients in the 177Lu-Dotatate group and 69 (95%) of 73 treated patients in the control group. There were no study drug-related deaths during the treatment period. INTERPRETATION: First-line 177Lu-Dotatate plus octreotide LAR significantly extended median progression-free survival (by 14 months) in patients with grade 2 or 3 advanced gastroenteropancreatic neuroendocrine tumours. 177Lu-Dotatate should be considered a new standard of care in first-line therapy in this population. FUNDING: Advanced Accelerator Applications, a Novartis Company.

3-year invasive disease-free survival with chemotherapy de-escalation using an 18F-FDG-PET-based, pathological complete response-adapted strategy in HER2-positive early breast cancer (PHERGain): a randomised, open-label, phase 2 trial.

BACKGROUND: PHERGain was designed to assess the feasibility, safety, and efficacy of a chemotherapy-free treatment based on a dual human epidermal growth factor receptor 2 (HER2) blockade with trastuzumab and pertuzumab in patients with HER2-positive early breast cancer (EBC). It used an 18fluorine-fluorodeoxyglucose-PET-based, pathological complete response (pCR)-adapted strategy. METHODS: PHERGain was a randomised, open-label, phase 2 trial that took place in 45 hospitals in seven European countries. It randomly allocated patients in a 1:4 ratio with centrally confirmed, HER2-positive, stage I-IIIA invasive, operable breast cancer with at least one PET-evaluable lesion to either group A, where patients received docetaxel (75 mg/m2, intravenous), carboplatin (area under the curve 6 mg/mL per min, intravenous), trastuzumab (600 mg fixed dose, subcutaneous), and pertuzumab (840 mg loading dose followed by 420 mg maintenance doses, intravenous; TCHP), or group B, where patients received trastuzumab and pertuzumab with or without endocrine therapy, every 3 weeks. Random allocation was stratified by hormone receptor status. Centrally reviewed PET was conducted at baseline and after two treatment cycles. Patients in group B were treated according to on-treatment PET results. Patients in group B who were PET-responders continued with trastuzumab and pertuzumab with or without endocrine therapy for six cycles, while PET-non-responders were switched to receive six cycles of TCHP. After surgery, patients in group B who were PET-responders who did not achieve a pCR received six cycles of TCHP, and all patients completed up to 18 cycles of trastuzumab and pertuzumab. The primary endpoints were pCR in patients who were group B PET-responders after two treatment cycles (the results for which have been reported previously) and 3-year invasive disease-free survival (iDFS) in patients in group B. The study is registered with ClinicalTrials.gov (NCT03161353) and is ongoing. FINDINGS: Between June 26, 2017, and April 24, 2019, a total of 356 patients were randomly allocated (71 patients in group A and 285 patients in group B), and 63 (89%) and 267 (94%) patients proceeded to surgery in groups A and B, respectively. At this second analysis (data cutoff: Nov 4, 2022), the median duration of follow-up was 43·3 months (range 0·0-63·0). In group B, the 3-year iDFS rate was 94·8% (95% CI 91·4-97·1; p=0·001), meeting the primary endpoint. No new safety signals were identified. Treatment-related adverse events and serious adverse events (SAEs) were numerically higher in patients allocated to group A than to group B (grade ≥3 62% vs 33%; SAEs 28% vs 14%). Group B PET-responders with pCR presented the lowest incidence of treatment-related grade 3 or higher adverse events (1%) without any SAEs. INTERPRETATION: Among HER2-positive EBC patients, a PET-based, pCR-adapted strategy was associated with an excellent 3-year iDFS. This strategy identified about a third of patients who had HER2-positive EBC who could safely omit chemotherapy. FUNDING: F Hoffmann-La Roche.

Exploring Aqueous Coordination Chemistry of Highly Lewis Acidic Metals with Emerging Isotopes for Nuclear Medicine.

Nuclear medicine harnesses radioisotopes for the diagnosis and treatment of disease. While the isotopes 99mTc and 111In have enabled the clinical diagnosis of millions of patients over the past 3 decades, more recent clinical translation of numerous 68Ga/177Lu-based radiopharmaceuticals for diagnostic imaging and therapy underscores the clinical utility of metal-based radiopharmaceuticals in mainstream cancer treatment. In addition to such established radionuclides, advancements in radioisotope production have enabled the production of radionuclides with a broad range of half-lives and emission properties of interest for nuclear medicine. Chemical means to form kinetically inert, in vivo-compatible species that can be modified with disease-targeting vectors is imperative. This presents a challenge for radiosiotopes of elements where the aqueous chemistry is still underdeveloped and poorly understood. Here, we discuss our efforts to date in exploring the aqueous, radioactive coordination chemistry of highly Lewis acidic metal ions and how our discoveries apply to the diagnosis and treatment of cancer in preclinical models of disease. The scope of this Account includes approaches to aqueous coordination of to-date understudied highly Lewis acidic metal ions with radioisotopes of emerging interest and the modulation of well-understood coordination environments of radio-coordination complexes to induce metal-catalyzed reactivity for separation and pro-drug applications.First, we discuss the development of seven-coordinate, small-cavity macrocyclic chelator platform mpatcn/picaga as an exemplary case study, which forms robust complexes with 44Sc/47Sc isotopes. Due to the high chemical hardness and pronounced Lewis acidity of the Sc3+ ion, the displacement of ternary ligand H2O by 18/natF- can be achieved to form an inert Sc-18/natF bond. Corresponding coordination complex natSc-18F is in vivo compatible and forms a theranostic tetrad with corresponding 44Sc/47Sc, 177Lu complexes all exhibiting homologous biodistribution profiles. Another exceptionally hard, highly Lewis acidic ion with underdeveloped aqueous chemistry and emerging interest in nuclear medicine is 45Ti4+. To develop de novo approaches to the mononuclear chelation of this ion under aqueous conditions, we employed a fragment-based bidentate ligand screening approach which identified two leads. The screen successfully predicted the formation of [45Ti][Ti(TREN-CAM)], a Ti-triscatechol complex that exhibits remarkable in vivo stability. Furthermore, the fragment-based screen also identified approaches that enabled solid-phase separation of Ti4+ and Sc3+ of interest in streamlining the isotope production of 45Ti and accessing new ways to separate 44Ti/44Sc for the development of a long-lived generator system. In addition to establishing the inert chelation of Ti4+ and Sc3+, we introduce controlled, metal-induced reactivity of corresponding coordination complexes on macroscopic and radiotracer scales. Metal-mediated autolytic amide bond cleavage (MMAAC) enables the temperature-dependent release of high-molar-activity, ready-to-inject radiopharmaceuticals; cleavage is selectively triggered by coordinated trivalent Lewis acid nat/68Ga3+ or Sc3+. Following the scope of reactivity and mechanistic studies, we validated MMAAC for the synthesis of high-molar-activity radiopharmaceuticals to image molecular targets with low expression and metal-mediated prodrug hydrolysis in vivo.This Account summarizes how developing the aqueous coordination chemistry and tuning the chemical reactivity of metal ions with high Lewis acidity at the macroscopic and tracer scales directly apply to the radiopharmaceutical synthesis with clinical potential.

Diagnostic Positron Emission Tomography Imaging with Zirconium-89 Desferrioxamine B Squaramide: From Bench to Bedside.

Molecular imaging with antibodies radiolabeled with positron-emitting radionuclides combines the affinity and selectivity of antibodies with the sensitivity of Positron Emission Tomography (PET). PET imaging allows the visualization and quantification of the biodistribution of the injected radiolabeled antibody, which can be used to characterize specific biological interactions in individual patients. This characterization can provide information about the engagement of the antibody with a molecular target such as receptors present in elevated levels in tumors as well as providing insight into the distribution and clearance of the antibody. Potential applications of clinical PET with radiolabeled antibodies include identifying patients for targeted therapies, characterization of heterogeneous disease, and monitoring treatment response.Antibodies often take several days to clear from the blood pool and localize in tumors, so PET imaging with radiolabeled antibodies requires the use of a radionuclide with a similar radioactive half-life. Zirconium-89 is a positron-emitting radionuclide that has a radioactive half-life of 78 h and relatively low positron emission energy that is well suited to radiolabeling antibodies. It is essential that the zirconium-89 radionuclide be attached to the antibody through chemistry that provides an agent that is stable in vivo with respect to the dissociation of the radionuclide without compromising the biological activity of the antibody.This Account focuses on our research using a simple derivative of the bacterial siderophore desferrioxamine (DFO) with a squaramide ester functional group, DFO-squaramide (DFOSq), to link the chelator to antibodies. In our work, we produce conjugates with an average ∼4 chelators per antibody, and this does not compromise the binding of the antibody to the target. The resulting antibody conjugates of DFOSq are stable and can be easily radiolabeled with zirconium-89 in high radiochemical yields and purity. Automated methods for the radiolabeling of DFOSq-antibody conjugates have been developed to support multicenter clinical trials. Evaluation of several DFOSq conjugates with antibodies and low molecular weight targeting agents in tumor mouse models gave PET images with high tumor uptake and low background. The promising preclinical results supported the translation of this chemistry to human clinical trials using two different radiolabeled antibodies. The potential clinical impact of these ongoing clinical trials is discussed.The use of DFOSq to radiolabel relatively low molecular weight targeting molecules, peptides, and peptide mimetics is also presented. Low molecular weight molecules typically clear the blood pool and accumulate in target tissue more rapidly than antibodies, so they are usually radiolabeled with positron-emitting radionuclides with shorter radioactive half-lives such as fluorine-18 (t1/2 ∼ 110 min) or gallium-68 (t1/2 ∼ 68 min). Radiolabeling peptides and peptide mimetics with zirconium-89, with its longer radioactive half-life (t1/2 = 78 h), could facilitate the centralized manufacture and distribution of radiolabeled tracers. In addition, the ability to image patients at later time points with zirconium-89 based agents (e.g. 4-24 h after injection) may also allow the delineation of small or low-uptake disease sites as the delayed imaging results in increased clearance of the tracer from nontarget tissue and lower background signal.

Spatial Atlas for Mapping Vascular Microcalcification Using 18F-NaF PET/CT: Application in Hyperphosphatemic Familial Tumoral Calcinosis.

BACKGROUND: Vascular calcification causes significant morbidity and occurs frequently in diseases of calcium/phosphate imbalance. Radiolabeled sodium fluoride positron emission tomography/computed tomography has emerged as a sensitive and specific method for detecting and quantifying active microcalcifications. We developed a novel technique to quantify and map total vasculature microcalcification to a common space, allowing simultaneous assessment of global disease burden and precise tracking of site-specific microcalcifications across time and individuals. METHODS: To develop this technique, 4 patients with hyperphosphatemic familial tumoral calcinosis, a monogenic disorder of FGF23 (fibroblast growth factor-23) deficiency with a high prevalence of vascular calcification, underwent radiolabeled sodium fluoride positron emission tomography/computed tomography imaging. One patient received serial imaging 1 year after treatment with an IL-1 (interleukin-1) antagonist. A radiolabeled sodium fluoride-based microcalcification score, as well as calcification volume, was computed at all perpendicular slices, which were then mapped onto a standardized vascular atlas. Segment-wise mCSmean and mCSmax were computed to compare microcalcification score levels at predefined vascular segments within subjects. RESULTS: Patients with hyperphosphatemic familial tumoral calcinosis had notable peaks in microcalcification score near the aortic bifurcation and distal femoral arteries, compared with a control subject who had uniform distribution of vascular radiolabeled sodium fluoride uptake. This technique also identified microcalcification in a 17-year-old patient, who had no computed tomography-defined calcification. This technique could not only detect a decrease in microcalcification score throughout the patient treated with an IL-1 antagonist but it also identified anatomic areas that had increased responsiveness while there was no change in computed tomography-defined macrocalcification after treatment. CONCLUSIONS: This technique affords the ability to visualize spatial patterns of the active microcalcification process in the peripheral vasculature. Further, this technique affords the ability to track microcalcifications at precise locations not only across time but also across subjects. This technique is readily adaptable to other diseases of vascular calcification and may represent a significant advance in the field of vascular biology.

Aortic Uptake of 18F-NaF and 18F-FDG and Calcification Predict the Development of Abdominal Aortic Aneurysms and Is Attenuated by Drug Therapy.

BACKGROUND: Abdominal aortic aneurysms expand over time and increase the risk of fatal ruptures. To predict expansion, the isolated assessment of 18F-fluorodeoxyglucose (FDG) and sodium fluoride (NaF) uptake or calcification volume in aneurysms has been investigated with variability in results. We systematically evaluated whether 18F-FDG and 18F-NaF uptake was predictive of abdominal aortic aneurysm expansion. METHODS: Seventy-four male Sprague-Dawley rat abdominal aortic aneurysm models were imaged using positron emission tomography-computed tomography with 18F-FDG and 18F-NaF at 1, 2, 4, 6, and 8 weeks after CaCl2 or saline stimulation. In the 1-week cohort (n=25), the correlation between 18F-FDG or 18F-NaF uptake and pathological markers was investigated. In the time course cohort (n=49), animals received either atorvastatin, losartan, aldactone, or risedronate to assess the effect of these drugs, and the relationship between aortic size and sequential 18F-FDG and 18F-NaF uptake or calcification volume was examined. RESULTS: In the 1-week cohort, the maximum standard unit value of 18F-FDG and 18F-NaF uptake correlated with CD68- (r=0.82; P=0.001) and von Kossa staining-positive areas (r=0.89; P<0.001), respectively. In the time course cohort, 18F-FDG and 18F-NaF uptake changed in a time-dependent manner and drugs attenuated this uptake. Specifically, 18F-FDG showed high uptake at weeks 1 and 2, whereas a high 18F-NaF uptake was noted throughout the study period. Atorvastatin and risedronate showed a decreased and increased aortic size, respectively. The final aortic area correlated well with 18F-FDG and 18F-NaF uptake and calcification volume, especially at 1 and 2 weeks (18F-NaF [1 week]: r=0.61, 18F-FDG [2 weeks]: r=0.51, calcification volume [1 week]: r=0.59; P<0.001). Multiple linear regression analysis showed that the combination of these factors predicted the final aortic size, with 18F-NaF uptake at 1 week being the strongest predictor. CONCLUSIONS: The uptake of 18F-NaF and 18F-FDG and the calcification volume at appropriate times correlated with the development of abdominal aortic aneurysms, with 18F-NaF uptake being the strongest predictor.

Radiosynthesis, Preclinical, and Clinical Positron Emission Tomography Studies of Carbon-11 Labeled Endogenous and Natural Exogenous Compounds.

The presence of positron emission tomography (PET) centers at most major hospitals worldwide, along with the improvement of PET scanner sensitivity and the introduction of total body PET systems, has increased the interest in the PET tracer development using the short-lived radionuclides carbon-11. In the last few decades, methodological improvements and fully automated modules have allowed the development of carbon-11 tracers for clinical use. Radiolabeling natural compounds with carbon-11 by substituting one of the backbone carbons with the radionuclide has provided important information on the biochemistry of the authentic compounds and increased the understanding of their in vivo behavior in healthy and diseased states. The number of endogenous and natural compounds essential for human life is staggering, ranging from simple alcohols to vitamins and peptides. This review collates all the carbon-11 radiolabeled endogenous and natural exogenous compounds synthesised to date, including essential information on their radiochemistry methodologies and preclinical and clinical studies in healthy subjects.

Theranostic Nuclear Medicine with Gallium-68, Lutetium-177, Copper-64/67, Actinium-225, and Lead-212/203 Radionuclides.

Molecular changes in malignant tissue can lead to an increase in the expression levels of various proteins or receptors that can be used to target the disease. In oncology, diagnostic imaging and radiotherapy of tumors is possible by attaching an appropriate radionuclide to molecules that selectively bind to these target proteins. The term "theranostics" describes the use of a diagnostic tool to predict the efficacy of a therapeutic option. Molecules radiolabeled with γ-emitting or ß+-emitting radionuclides can be used for diagnostic imaging using single photon emission computed tomography or positron emission tomography. Radionuclide therapy of disease sites is possible with either α-, ß-, or Auger-emitting radionuclides that induce irreversible damage to DNA. This Focus Review centers on the chemistry of theranostic approaches using metal radionuclides for imaging and therapy. The use of tracers that contain ß+-emitting gallium-68 and ß-emitting lutetium-177 will be discussed in the context of agents in clinical use for the diagnostic imaging and therapy of neuroendocrine tumors and prostate cancer. A particular emphasis is then placed on the chemistry involved in the development of theranostic approaches that use copper-64 for imaging and copper-67 for therapy with functionalized sarcophagine cage amine ligands. Targeted therapy with radionuclides that emit α particles has potential to be of particular use in late-stage disease where there are limited options, and the role of actinium-225 and lead-212 in this area is also discussed. Finally, we highlight the challenges that impede further adoption of radiotheranostic concepts while highlighting exciting opportunities and prospects.

Investigation of causal relationships between cortical structure and osteoporosis using two-sample Mendelian randomization.

The mutual interaction between bone characteristics and brain had been reported previously, yet whether the cortical structure has any relevance to osteoporosis is questionable. Therefore, we applied a two-sample bidirectional Mendelian randomization analysis to investigate this relationship. We utilized the bone mineral density measurements of femoral neck (n = 32,735) and lumbar spine (n = 28,498) and data on osteoporosis (7300 cases and 358,014 controls). The global surficial area and thickness and 34 specific functional regions of 51,665 patients were screened by magnetic resonance imaging. For the primary estimate, we utilized the inverse-variance weighted method. The Mendelian randomization-Egger intercept test, MR-PRESSO, Cochran's Q test, and "leave-one-out" sensitivity analysis were conducted to assess heterogeneity and pleiotropy. We observed suggestive associations between decreased thickness in the precentral region (OR = 0.034, P = 0.003) and increased chance of having osteoporosis. The results also revealed suggestive causality of decreased bone mineral density in femoral neck to declined total cortical surface area (ß = 1400.230 mm2, P = 0.003), as well as the vulnerability to osteoporosis and reduced thickness in the Parstriangularis region (ß = -0.006 mm, P = 0.002). Our study supports that the brain and skeleton exhibit bidirectional crosstalk, indicating the presence of a mutual brain-bone interaction.

Imaging of the brain-heart axis: prognostic value in a European setting.

BACKGROUND AND AIMS: Increasing data suggest that stress-related neural activity (SNA) is associated with subsequent major adverse cardiovascular events (MACE) and may represent a therapeutic target. Current evidence is exclusively based on populations from the U.S. and Asia where limited information about cardiovascular disease risk was available. This study sought to investigate whether SNA imaging has clinical value in a well-characterized cohort of cardiovascular patients in Europe. METHODS: In this single-centre study, a total of 963 patients (mean age 58.4 ± 16.1 years, 40.7% female) with known cardiovascular status, ranging from 'at-risk' to manifest disease, and without active cancer underwent 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography between 1 January 2005 and 31 August 2019. Stress-related neural activity was assessed with validated methods and relations between SNA and MACE (non-fatal stroke, non-fatal myocardial infarction, coronary revascularization, and cardiovascular death) or all-cause mortality by time-to-event analysis. RESULTS: Over a maximum follow-up of 17 years, 118 individuals (12.3%) experienced MACE, and 270 (28.0%) died. In univariate analyses, SNA significantly correlated with an increased risk of MACE (sub-distribution hazard ratio 1.52, 95% CI 1.05-2.19; P = .026) or death (hazard ratio 2.49, 95% CI 1.96-3.17; P < .001). In multivariable analyses, the association between SNA imaging and MACE was lost when details of the cardiovascular status were added to the models. Conversely, the relationship between SNA imaging and all-cause mortality persisted after multivariable adjustments. CONCLUSIONS: In a European patient cohort where cardiovascular status is known, SNA imaging is a robust and independent predictor of all-cause mortality, but its prognostic value for MACE is less evident. Further studies should define specific patient populations that might profit from SNA imaging.

Cortico-limbic interactions and carotid atherosclerotic burden during chronic stress exposure.

BACKGROUND AND AIMS: Chronic stress associates with cardiovascular disease, but mechanisms remain incompletely defined. Advanced imaging was used to identify stress-related neural imaging phenotypes associated with atherosclerosis. METHODS: Twenty-seven individuals with post-traumatic stress disorder (PTSD), 45 trauma-exposed controls without PTSD, and 22 healthy controls underwent 18F-fluorodeoxyglucose positron emission tomography/magnetic resonance imaging (18F-FDG PET/MRI). Atherosclerotic inflammation and burden were assessed using 18F-FDG PET (as maximal target-to-background ratio, TBR max) and MRI, respectively. Inflammation was assessed using high-sensitivity C-reactive protein (hsCRP) and leucopoietic imaging (18F-FDG PET uptake in spleen and bone marrow). Stress-associated neural network activity (SNA) was assessed on 18F-FDG PET as amygdala relative to ventromedial prefrontal cortex (vmPFC) activity. MRI diffusion tensor imaging assessed the axonal integrity (AI) of the uncinate fasciculus (major white matter tract connecting vmPFC and amygdala). RESULTS: Median age was 37 years old and 54% of participants were female. There were no significant differences in atherosclerotic inflammation between participants with PTSD and controls; adjusted mean difference in TBR max (95% confidence interval) of the aorta 0.020 (-0.098, 0.138), and of the carotids 0.014 (-0.091, 0.119). Participants with PTSD had higher hsCRP, spleen activity, and aorta atherosclerotic burden (normalized wall index). Participants with PTSD also had higher SNA and lower AI. Across the cohort, carotid atherosclerotic burden (standard deviation of wall thickness) associated positively with SNA and negatively with AI independent of Framingham risk score. CONCLUSIONS: In this study of limited size, participants with PTSD did not have higher atherosclerotic inflammation than controls. Notably, impaired cortico-limbic interactions (higher amygdala relative to vmPFC activity or disruption of their intercommunication) associated with carotid atherosclerotic burden. Larger studies are needed to refine these findings.

Production and regulatory issues for theranostics.

Theranostics has become a major area of innovation and progress in cancer care over the last decade. In view of the introduction of approved therapeutics in neuroendocrine tumours and prostate cancer in the last 10 years, the ability to provide access to these treatments has emerged as a key factor in ensuring global benefits from this cancer therapy approach. In this Series paper we explore the issues that affect access to and availability of theranostic radiopharmaceuticals, including supply and regulatory issues that might affect the availability of theranostic treatments for patients with cancer.

Trends in nuclear medicine and the radiopharmaceutical sciences in oncology: workforce challenges and training in the age of theranostics.

Although the promise of radionuclides for the diagnosis and treatment of disease was recognised soon after the discovery of radioactivity in the late 19th century, the systematic use of radionuclides in medicine only gradually increased over the subsequent hundred years. The past two decades, however, has seen a remarkable surge in the clinical application of diagnostic and therapeutic radiopharmaceuticals, particularly in oncology. This development is an exciting time for the use of theranostics in oncology, but the rapid growth of this area of nuclear medicine has created challenges as well. In particular, the infrastructure for the manufacturing and distribution of radiopharmaceuticals remains in development, and regulatory bodies are still optimising guidelines for this new class of drug. One issue of paramount importance for achieving equitable access to theranostics is building a sufficiently trained workforce in high-income, middle-income, and low-income countries. Here, we discuss the key challenges and opportunities that face the field as it seeks to build its workforce for the 21st century.

Recent advances and impending challenges for the radiopharmaceutical sciences in oncology.

This paper is the first of a Series on theranostics that summarises the current landscape of the radiopharmaceutical sciences as they pertain to oncology. In this Series paper, we describe exciting developments in radiochemistry and the production of radionuclides, the development and translation of theranostics, and the application of artificial intelligence to our field. These developments are catalysing growth in the use of radiopharmaceuticals to the benefit of patients worldwide. We also highlight some of the key issues to be addressed in the coming years to realise the full potential of radiopharmaceuticals to treat cancer.