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Purpose: 2-Fluorodeoxyglucose-PET (FDG-PET) is a powerful tool to study glucose metabolism in mammalian brains, but cellular sources of glucose uptake and metabolic connectivity during aging are not yet understood., Methods: Healthy wild-type mice of both sexes (2-21 months of age) received FDG-PET and cell sorting after in vivo tracer injection (scRadiotracing). FDG uptake per cell was quantified in isolated microglia, astrocytes and neurons. Cerebral FDG uptake and metabolic connectivity were determined by PET. A subset of mice received measurement of blood glucose levels to study associations with cellular FDG uptake during aging., Results: Cerebral FDG-PET signals in healthy mice increased linearly with age. Cellular FDG uptake of neurons increased between 2 and 12 months of age, followed by a strong decrease towards late ages. Contrarily, FDG uptake in microglia and astrocytes exhibited a U-shaped function with respect to age, comprising the predominant cellular source of higher cerebral FDG uptake in the later stages. Metabolic connectivity was closely associated with the ratio of glucose uptake in astroglial cells relative to neurons. Cellular FDG uptake was not associated with blood glucose levels and increasing FDG brain uptake as a function of age was still observed after adjusting for blood glucose levels., Conclusion: Trajectories of astroglial glucose uptake drive brain FDG-PET alterations and metabolic connectivity during aging., Competing Interests: Declaration of competing interest MB is a member of the Neuroimaging Committee of the EANM. MB received speaker honoraria from Roche, GE healthcare and Life Molecular Imaging, has advised Life Molecular Imaging and is currently in the advisory board of MIAC. All other authors do not report any conflict of interest., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Fibroblast activation protein (FAP) is specifically expressed on cancer-associated fibroblasts in over 90% of tumors and is considered a promising target for cancer theranostics. Here, we developed a novel tracer, DOTA-FAPT, and labeled it with gallium-68 and lutetium-177 as a theranostic pair. [ 68 Ga]Ga/[ 177 Lu]Lu-FAPT exhibited high stability and hydrophilicity, as well as strong affinity to the FAP target. Micro-PET/CT imaging revealed that [ 68 Ga]Ga-FAPT exhibited significantly increased uptake in tumors and extended retention in A549-FAP and U87MG tumor xenografts as compared to [ 68 Ga]Ga-FAPI-04, demonstrating favorable pharmacokinetic characteristics in vivo. Therapeutic studies showed that [ 177 Lu]Lu-FAPT had higher tumor accumulation compared to [ 177 Lu]Lu-FAPI-04, leading to stronger tumor growth inhibition. The first-in-human evaluation also revealed that [ 68 Ga]Ga-FAPT has good in vivo distribution and superior diagnostic efficacy on primary and lymph node metastases in a patient with lung cancer. Our encouraging results suggest that 68 Ga/ 177 Lu-labeled DOTA-FAPT is a theranostic pair with broad application prospect.

V-domain immunoglobulin suppressor of T cell activation (VISTA) plays a critical role in regulating innate and adaptive immune responses within the tumor immune microenvironment. Quantifying VISTA expression is necessary to determine whether patients respond to a related combination immunotherapy. This study developed two 68 Ga-labeled small-molecule probes ([ 68 Ga]Ga-DCA and [ 68 Ga]Ga-DNCA) for visualizing and differentiating VISTA expression. These probes exhibited excellent targeting capabilities for multiple tumor types (including B16-F10, 4T1, MC38, and CT26 tumors), consistent with the levels of VISTA expression determined by immunoblotting. Co-injection of inhibitor CA-170 led to decreased tumor uptake of both [ 68 Ga]Ga-DCA and [ 68 Ga]Ga-DNCA. [ 68 Ga]Ga-DCA was used to verify the feasibility of monitoring VISTA expression in lung metastasis models. In summary, this study describes the use of 68 Ga-labeled CA-170 analogues as small-molecule probes for imaging VISTA. This could provide a visual method and enable personalized immunotherapy in patients.

B7-H3 has emerged as a promising target and potential biomarker for diagnosing tumors, evaluating treatment efficacy, and determining patient prognosis. Hu4G4 is a recombinant humanized antibody that selectively targets the extracellular domain of human B7-H3. In this study, we describe the radiolabeling of hu4G4 with the positron emission tomography (PET) emitter radionuclide zirconium 89 ( 89 Zr) and evaluate its potency as an immuno-PET tracer for B7-H3-targeted imaging by comparing it in vitro and in vivo to [ 89 Zr]Zr-DFO-DS-5573a using various models. The radiolabeled compound, [ 89 Zr]Zr-desferrioxamine-hu4G4 ([ 89 Zr]Zr-DFO-hu4G4), demonstrated a high radiochemical purity (RCP) of greater than 99% and a specific activity of 74 MBq/mg following purification. Additionally, it maintained stability in human serum albumin (HSA) and acetate buffer, preserving over 90% of its RCP after 7 days. Three cell lines targeting human B7-H3(U87/CT26 -CD276 /GL261 -CD276 ) were used. Flow cytometry analysis indicated that the B7-H3-positive cells (U87/CT26 -CD276 /GL261 -CD276 ) had a higher B7-H3 protein level with no expression in the B7-H3-negative cells (CT26 -wt /GL261 -wt ) ( P < 0.001). Moreover, the cellular uptake was 45.71 ± 3.78% for [ 89 Zr]Zr-DFO-hu4G4 in CT26 -CD276 cells versus only 0.93 ± 0.47% in CT26 -wt cells and 30.26 ± 0.70% when [ 89 Zr]Zr-DFO-hu4G4 in CT26 -CD276 cells were blocked with 100× 8H9. The cellular uptake of [ 89 Zr]Zr-DFO-hu4G4 was akin to that observed with [ 89 Zr]Zr-DFO-DS-5573a with no significant differences (45.71 ± 3.78 % vs 47.07 ± 0.86 %) in CT26 -CD276 cells. Similarly, the CT26 -CD276 mouse model demonstrated markedly low organ uptake and elevated tumor uptake 48 h after [ 89 Zr]Zr-DFO-hu4G4 injection. PET/CT analysis showed that the tumor-to-muscle (T/M) ratios were substantially higher compared to other imaging groups: 27.65 ± 3.17 in CT26 -CD276 mice versus 11.68 ± 4.19 in CT26 -wt mice ( P < 0.001) and 16.40 ± 0.78 when 100× 8H9 was used to block [ 89 Zr]Zr-DFO-hu4G4 in CT26 -CD276 mice ( P < 0.01) at 48 h post-injection. Additionally, the tracer showed markedly high accumulation in the tumor region (22.57 ± 3.03% ID/g), comparable to the uptake of [ 89 Zr]Zr-DFO-DS-5573a (24.76 ± 5.36% ID/g). A dosimetry estimation study revealed that the effective dose for [ 89 Zr]Zr-DFO-hu4G4 was 2.96 × 10 -01 mSv/MBq, which falls within the acceptable range for further research in nuclear medicine. Collectively, these results indicated that [ 89 Zr]Zr-DFO-hu4G4 was successfully fabricated and applied in B7-H3-targeted tumor PET/CT imaging, which showed excellent imaging quality and tumor detection efficacy in tumor-bearing mice. It is a promising imaging agent for identifying tumors that overexpress B7-H3 for future clinical applications.

Heat shock protein 90 (Hsp90) is a promising target for cancer therapy and imaging. Accurate detection of Hsp90 levels in tumors via noninvasive PET imaging might be beneficial for management. To achieve this, the precursor compound Dimer-Sansalvamide A (Dimer-San A) was PEGylated and modified by conjugating it with the bifunctional chelator 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA). The 18 F-labeled PEGylated Dimer-SanA decapeptide ( 18 F-PEGylated San A) was completed within 30 min using a two-step process. In vitro stability and specificity were assessed, including competition studies with the Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG). MicroPET imaging was performed on PL45 tumor-bearing mice to evaluate probe accumulation and tumor-to-muscle ratios. Biodistribution studies determined the route of excretion. The probe resulted in a radiochemical yield of 23.11% with a purity exceeding 95%. In vitro , 18 F-PEGylated San A exhibited high stability and selectively accumulated in Hsp90-positive PL45 cells, with binding effectively blocked by the Hsp90 inhibitor 17AAG, confirming its specificity. MicroPET imaging of PL45 tumor-bearing mice showed significant probe accumulation in tumor tissues at 1 and 2 h postinjection (4.06 ± 0.30 and 3.72 ± 0.61%ID/g, respectively), with optimal tumor-to-muscle ratios observed at 2 h postinjection (6.09 ± 1.92). While 18 F-PEGylated San A demonstrates enhanced water solubility, as indicated by increased kidney uptake relative to liver accumulation. The study successfully incorporated PEG units to create the novel probe 18 F-PEGylated San A targeting to Hsp90 without affecting its targeting capability, aimed at improving the pharmacokinetics and PET imaging of Hsp90 expression noninvasively.

The specific expression of prostate-specific membrane antigen (PSMA) makes it an ideal target for the diagnosis and treatment of prostate cancer. Currently, many 99m Tc-labeled PSMA-targeted tracers have been developed. However, the high renal uptake of these 99m Tc-labeled tracers is a common problem that limits their clinical application. In this work, the ligand (EUKPG) using D Pro-Gly as the linker was synthesized and three 99m Tc-labeled complexes ([ 99m Tc]Tc-EUKPG-EDDA, [ 99m Tc]Tc-EUKPG-TPPTS, [ 99m Tc]Tc-EUKPG-TPPMS) with different coligands were prepared and evaluated. Among them, [ 99m Tc]Tc-EUKPG-EDDA showed the most favorable pharmacokinetic properties, with significantly reduced uptake in the kidney (14.04 ± 0.23% ID/g), rapid clearance and low uptake in nontarget organs, thus making it to exhibit high tumor-to-background ratios (tumor/blood: 7.47, tumor/muscle: 12.65). Affinity studies have shown that it has high specificity for PSMA both in vivo and in vitro . Therefore, [ 99m Tc]Tc-EUKPG-EDDA has great potential as a promising molecular tracer to target PSMA for tumor imaging.

The limited progress in treatment options and the alarming survival rates in advanced melanoma emphasize the significant research importance of early melanoma diagnosis. RFVT3, a crucial protein at the core of energy metabolism reprogramming in melanoma, might play a pivotal role in early detection. In this study, [ 68 Ga]Ga-NOTA-RF, based on riboflavin (RF), was rationally developed and validated, serving as an innovative tool for positron emission tomography (PET) imaging of RFVT3 expression in melanoma. The in vitro assays of RFVT3 specificity of [ 68 Ga]Ga-NOTA-RF were performed on B16F10 melanoma cells. Then, PET imaging of melanoma was investigated in B16F10 allograft mouse models with varying volumes. Biodistribution studies are used to clarify the behavior of [ 68 Ga]Ga-NOTA-RF in vivo . [ 68 Ga]Ga-NOTA-RF was obtained with high radiochemical purity (>95%). A significant uptake (37.79 ± 6.86%, n = 4) of [ 68 Ga]Ga-NOTA-RF was observed over time in B16F10 melanoma cells, which was significantly inhibited by RFVT3 inhibitors RF or methylene blue (MB), demonstrating the specific binding of [ 68 Ga]Ga-NOTA-RF. At 60 min postinjection, the tumor-to-muscle (T/M) ratio of [ 68 Ga]Ga-NOTA-RF was 4.03 ± 0.34, higher than that of the RF-blocked group (2.63 ± 0.19) and MB-blocked group (2.14 ± 0.20). The T/M ratios for three distinct tumor volumes-small (5 mm), medium (10 mm), and large (15 mm) were observed to be 5.25 ± 0.28, 4.03 ± 0.34, and 3.19 ± 0.55, respectively. The expression of RFVT3 was validated by immunohistochemical staining in various tumor models, with small B16F10 tumors exhibiting the highest expression. [ 68 Ga]Ga-NOTA-RF demonstrates promising properties for the early diagnosis of melanoma and the examination of minute metastatic lesions, indicating its potential to assist in guiding clinical treatment decisions.

Biodegradable radioactive microspheres labeled with positron emitters hold significant promise for diagnostic and therapeutic applications in cancers and other diseases, including arthritis. The alginate-based polymeric microspheres offer advantages such as biocompatibility, biodegradability, and improved stability, making them suitable for clinical applications. In this study, we developed novel positron emission tomography (PET) microspheres using alginate biopolymer radiolabeled with gallium-68 ( 68 Ga) through a straightforward conjugation reaction. Polyethylenimine (PEI)-decorated calcium alginate microspheres (PEI-CAMSs) were fabricated and further modified using azadibenzocyclooctyne- N -hydroxysuccinimide ester (ADIBO-NHS). Subsequently, azide-functionalized NOTA chelator (N 3 -NOTA) was labeled with [ 68 Ga]Ga to obtain [ 68 Ga]Ga-NOTA-N 3 , which was then reacted with the surface-modified PEI-CAMSs using strain-promoted alkyne-azide cycloaddition (SPAAC) reaction to develop [ 68 Ga]Ga-NOTA-PEI-CAMSs, a novel PET microsphere. The radiolabeling efficiency and radiochemical stability of [ 68 Ga]Ga-NOTA-PEI-CAMSs were determined using the radio-instant thin-layer chromatography-silica gel (radio-ITLC-SG) method. The in vivo PET images were also acquired to study the in vivo stability of the radiolabeled microspheres in normal mice. The radiolabeling efficiency of [ 68 Ga]Ga-NOTA-PEI-CAMSs was over 99%, and the microspheres exhibited high stability (92%) in human blood serum. PET images demonstrated the stability and biodistribution of the microspheres in mice for up to 2 h post injection. This study highlights the potential of biodegradable PET microspheres for preoperative imaging and targeted radionuclide therapy. Overall, the straightforward synthesis method and efficient radiolabeling technique provide a promising platform for the development of theranostic microspheres using other radionuclides such as 90 Y, 177 Lu, 188 Re, and 64 Cu.

The dopamine D3 receptor (D3R) is important in the pathophysiology of various neuropsychiatric disorders, such as depression, bipolar disorder, schizophrenia, drug addiction, and Parkinson's disease. Positron emission tomography (PET) with innovative radioligands provides an opportunity to assess D3R in vivo and to elucidate D3R-related disease mechanisms. Herein, we present the synthesis of eight 18 F-labeled phenylpiperazine-like D3R-selective radioligands possessing good radiochemical purity (>97%), in vitro stability (>95%), and befitting lipophilicity. Based on in vitro binding assays and static microPET studies, the phenylpiperazine-like radioligands [ 18 F]FBPC01 and [ 18 F]FBPC03 were chosen as lead radioligands targeting D3R. Molecular docking further elucidated their binding mechanism. Radiolabeling conditions were optimized and then applied to an automated radiolabeling process, affording products with high specific activity (>112 GBq/μmol). Dynamic rat PET study demonstrated the specific binding of [ 18 F]FBPC01 and [ 18 F]FBPC03 to D3R in the brain ventricles and the pituitary gland. Validated by dynamic PET data analysis, biodistribution study, and metabolism analysis, [ 18 F]FBPC03 exhibited the highest PET signal-to-noise ratio, good D3R-specific binding in the brain ventricles and pituitary gland of rats with few off-target binding, negligible defluorination, and stable brain metabolism, which indicated that [ 18 F]FBPC03 was a promising D3R radioligand.

Methods to shorten [ 18 F]FDG Patlak PET imaging procedures ranging from 65-90 to 20-30 min after injection, using a population-averaged input function (PIF) scaled to patient-specific image-derived input function (IDIF) values, were recently evaluated. The aim of the present study was to explore the feasibility of ultrashort 10-min [ 18 F]FDG Patlak imaging at 55-65 min after injection using a PIF combined with direct Patlak reconstructions to provide reliable quantitative accuracy of lung tumor uptake, compared with a full-duration 65-min acquisition using an IDIF. Methods: Patients underwent a 65-min dynamic PET acquisition on a long-axial-field-of-view (LAFOV) Biograph Vision Quadra PET/CT scanner. Subsequently, direct Patlak reconstructions and image-based (with reconstructed dynamic images) Patlak analyses were performed using both the IDIF (time to relative kinetic equilibrium between blood and tissue concentration (t*) = 30 min) and a scaled PIF at 30-60 min after injection. Next, direct Patlak reconstructions were performed on the system console using only the last 10 min of the acquisition, that is, from 55 to 65 min after injection, and a scaled PIF using maximum crystal ring difference settings of both 85 and 322. Tumor lesion and healthy-tissue uptake was quantified and compared between the differently obtained parametric images to assess quantitative accuracy. Results: Good agreement was obtained between direct- and image-based Patlak analyses using the IDIF (t* = 30 min) and scaled PIF at 30-60 min after injection, performed using the different approaches, with no more than 8.8% deviation in tumor influx rate value ( K i ) (mean difference ranging from -0.0022 to 0.0018 mL/[min × g]). When direct Patlak reconstruction was performed on the system console, excellent agreement was found between the use of a scaled PIF at 30-60 min after injection versus 55-65 min after injection, with 2.4% deviation in tumor K i (median difference, -0.0018 mL/[min × g]; range, -0.0047 to 0.0036 mL/[min × g]). For different maximum crystal ring difference settings using the scan time interval of 55-65 min after injection, only a 0.5% difference (median difference, 0.0000 mL/[min × g]; range, -0.0004 to 0.0013 mL/[min × g]) in tumor K i was found. Conclusion: Ultrashort whole-body [ 18 F]FDG Patlak imaging is feasible on an LAFOV Biograph Vision Quadra PET/CT system without loss of quantitative accuracy to assess lung tumor uptake compared with a full-duration 65-min acquisition. The ultrashort 10-min direct Patlak reconstruction with PIF allows for its implementation in clinical practice., (© 2024 by the Society of Nuclear Medicine and Molecular Imaging.)

Fibroblast activation protein (FAP) is abundantly expressed in the stroma of most human solid tumors. Clinical-stage radiolabeled FAP ligands are increasingly used as tools for the detection of various cancer lesions. To unleash the full therapeutic potential of FAP-targeting agents, ligands need to remain at the tumor site for several days after administration. We recently described the discovery of OncoFAP, a high-affinity small organic ligand of FAP with a rapid accumulation in tumors and low uptake in healthy tissues in cancer patients. Trimerization of OncoFAP provided a derivative (named TriOncoFAP, or OncoFAP-23) with improved FAP affinity. In this work, we evaluated the tissue biodistribution profile and the therapeutic performance of OncoFAP-23 in tumor-bearing mice. Methods: OncoFAP-23 was radiolabeled with the theranostic radionuclide 177 Lu. Preclinical experiments were conducted on mice bearing SK-RC-52.hFAP (BALB/c nude mice) or CT-26.hFAP (BALB/c mice) tumors. 177 Lu-OncoFAP and 177 Lu-FAP-2286 were included in the biodistribution study as controls. Toxicologic evaluation was performed on Wistar rats and CD1 mice by injecting high doses of OncoFAP-23 or its cold-labeled counterpart, respectively. Results: 177 Lu-OncoFAP-23 emerged for its best-in-class biodistribution profile, high and prolonged tumor uptake (i.e., ∼16 percentage injected dose/g at 96 h), and low accumulation in healthy organs, which correlates well with its potent single-agent anticancer activity at low levels of administered radioactivity. Combination treatment with the tumor-targeted interleukin 2 (L19-IL2, a clinical-stage immunocytokine) further expands the therapeutic window of 177 Lu-OncoFAP-23 by potentiating its in vivo antitumor activity. Proteomics studies revealed a potent tumor-directed immune response on treatment with the combination. OncoFAP-23 and nat Lu-OncoFAP-23 exhibited a favorable toxicologic profile, without showing any side effects or signs of toxicity. Conclusion: OncoFAP-23 presents enhanced tumor uptake and tumor retention and low accumulation in healthy organs, findings that correspond to a strongly improved in vivo antitumor efficacy. The data presented in this work support the clinical development of 177 Lu-OncoFAP-23 for the treatment of FAP-positive solid tumors., (© 2024 by the Society of Nuclear Medicine and Molecular Imaging.)

The peptide hormone ghrelin is produced in cardiomyocytes and acts through the myocardial growth hormone secretagogue receptor (GHSR) to promote cardiomyocyte survival. Administration of ghrelin may have therapeutic effects on post-myocardial infarction (MI) outcomes. Therefore, there is a need to develop molecular imaging probes that can track the dynamics of GHSR in health and disease to better predict the effectiveness of ghrelin-based therapeutics. We designed a high-affinity GHSR ligand labeled with 18 F for imaging by PET and characterized its in vivo properties in a canine model of MI. Methods: We rationally designed and radiolabeled with 18 F a quinazolinone derivative ([ 18 F]LCE470) with subnanomolar binding affinity to GHSR. We determined the sensitivity and in vivo and ex vivo specificity of [ 18 F]LCE470 in a canine model of surgically induced MI using PET/MRI, which allowed for anatomic localization of tracer uptake and simultaneous determination of global cardiac function. Uptake of [ 18 F]LCE470 was determined by time-activity curve and SUV analysis in 3 regions of the left ventricle-area of infarct, territory served by the left circumflex coronary artery, and remote myocardium-over a period of 1.5 y. Changes in cardiac perfusion were tracked by [ 13 N]NH 3 PET. Results: The receptor binding affinity of LCE470 was measured at 0.33 nM, the highest known receptor binding affinity for a radiolabeled GHSR ligand. In vivo blocking studies in healthy hounds and ex vivo blocking studies in myocardial tissue showed the specificity of [ 18 F]LCE470, and sensitivity was demonstrated by a positive correlation between tracer uptake and GHSR abundance. Post-MI changes in [ 18 F]LCE470 uptake occurred independently of perfusion tracer distributions and changes in global cardiac function. We found that the regional distribution of [ 18 F]LCE470 within the left ventricle diverged significantly within 1 d after MI and remained that way throughout the 1.5-y duration of the study. Conclusion: [ 18 F]LCE470 is a high-affinity PET tracer that can detect changes in the regional distribution of myocardial GHSR after MI. In vivo PET molecular imaging of the global dynamics of GHSR may lead to improved GHSR-based therapeutics in the treatment of post-MI remodeling., (© 2024 by the Society of Nuclear Medicine and Molecular Imaging.)

Single-domain antibodies (sdAbs) demonstrate favorable pharmacokinetic profiles for molecular imaging applications. However, their renal excretion and retention are obstacles for applications in targeted radionuclide therapy (TRT). Methods: Using a click-chemistry-based pretargeting approach, we aimed to reduce kidney retention of a fibroblast activation protein α (FAP)-targeted sdAb, 4AH29, for 177 Lu-TRT. Key pretargeting parameters (sdAb-injected mass and lag time) were optimized in healthy mice and U87MG (FAP + ) xenografts. A TRT study in a pancreatic ductal adenocarcinoma (PDAC) patient-derived xenograft (PDX) model was performed as a pilot study for sdAb-based pretargeting applications. Results: Modification of 4AH29 with trans -cyclooctene (TCO) moieties did not modify the sdAb pharmacokinetic profile. A 200-µg injected mass of 4AH29-TCO and an 8-h lag time for the injection of [ 177 Lu]Lu-DOTA-PEG 7 -tetrazine resulted in the highest kidney therapeutic index (2.0 ± 0.4), which was 5-fold higher than that of [ 177 Lu]Lu-DOTA-4AH29 (0.4 ± 0.1). FAP expression in the tumor microenvironment was validated in a PDAC PDX model with both immunohistochemistry and PET/CT imaging. Mice treated with the pretargeting high-activity approach (4AH29-TCO + [ 177 Lu]Lu-DOTA-PEG 7 -tetrazine; 3 × 88 MBq, 1 injection per week for 3 wk) demonstrated prolonged survival compared with the vehicle control and conventionally treated ([ 177 Lu]Lu-DOTA-4AH29; 3 × 37 MBq, 1 injection per week for 3 wk) mice. Mesangial expansion was reported in 7 of 10 mice in the conventional cohort, suggesting treatment-related kidney morphologic changes, but was not observed in the pretargeting cohort. Conclusion: This study validates pretargeting to mitigate sdAbs' kidney retention with no observation of morphologic changes on therapy regimen at early time points. Clinical translation of click-chemistry-based pre-TRT is warranted on the basis of its ability to alleviate toxicities related to biovectors' intrinsic pharmacokinetic profiles. The absence of representative animal models with extensive stroma and high FAP expression on cancer-associated fibroblasts led to a low mean tumor-absorbed dose even with high injected activity and consequently to modest survival benefit in this PDAC PDX., (© 2024 by the Society of Nuclear Medicine and Molecular Imaging.)

To prevent motion artifacts in small animal positron emission tomography (PET), animals are routinely scanned under anesthesia or physical restraint. Both may potentially alter metabolism and neurochemistry. This study investigates the feasibility of fully awake acquisition and subsequent absolute quantification of dynamic brain PET data via pharmacokinetic modelling in moving rats using the glutamate 5 receptor radioligand [ 11 C]ABP688 and point source based motion correction. Five male rats underwent three dynamic [ 11 C]ABP688 PET scans: two test-retest awake PET scans and one scan under anesthesia for comparison. Specific radioligand binding was determined via the simplified reference tissue model (reference: cerebellum) and outcome parameters BP ND and R 1 were evaluated in terms of stability and reproducibility. Test-retest measurements in awake animals gave reliable results with high correlations of BP ND (y = 1.08 × -0.2, r = 0.99, p < 0.01) and an acceptable variability (mean over all investigated regions 15.7 ± 2.4%). Regional [ 11 C]ABP688 BP ND s under awake and anesthetized conditions were comparable although in awake scans, absolute radioactive peak uptakes were lower and relative blood flow in terms of R 1 was higher. Awake small animal PET with absolute quantification of neuroreceptor availability is technically feasible and reproducible thereby providing a suitable alternative whenever effects of anesthesia are undesirable, e.g. in sleep research., Competing Interests: Declaration of conflicting interestsThe author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article:Alexander Drzezga: Research support: Siemens Healthineers, Life Molecular Imaging, GE Healthcare, AVID Radiopharmaceuticals, Sofie, Eisai, Novartis/AAA, Ariceum TherapeuticsSpeaker Honorary/Advisory Boards: Siemens Healthineers, Sanofi, GE Healthcare, Biogen, Novo Nordisk, Invicro, Novartis/AAA, Bayer VitalStock: Siemens Healthineers, Lantheus Holding, Structured therapeutics, ImmunoGenPatents: Patent for 18 F-JK-PSMA- 7 (Patent No.: EP3765097A1; Date of patent: Jan. 20, 2021).

Radiolabeled small-molecule DOTA-haptens can be combined with antitumor/anti-DOTA bispecific antibodies (BsAbs) for pretargeted radioimmunotherapy (PRIT). For optimized delivery of the theranostic γ- and β-emitting isotope 177 Lu with DOTA-based PRIT (DOTA-PRIT), bivalent Gemini (DOTA-Bn-thiourea-PEG4-thiourea-Bn-DOTA, aka (3,6,9,12-tetraoxatetradecane-1,14-diyl)bis(DOTA-benzyl thiourea)) was developed. Methods: Gemini was synthesized by linking 2 S -2-(4-isothiocyanatobenzyl)-DOTA molecules together via a 1,14-diamino-PEG4 linker. [ 177 Lu]Lu-Gemini was prepared with no-carrier-added 177 LuCl 3 to a molar-specific activity of 123 GBq/μmol and radiochemical purity of more than 99%. The specificity of BsAb- 177 Lu-Gemini was verified in vitro. Subsequently, we evaluated biodistribution and whole-body clearance for [ 177 Lu]Lu-Gemini and, for comparison, our gold-standard monovalent [ 177 Lu]Lu- S -2-(4-aminobenzyl)-DOTA ([ 177 Lu]Lu-DOTA-Bn) in naïve (tumor-free) athymic nude mice. For our proof-of-concept system, a 3-step pretargeting approach was performed with an established DOTA-PRIT regimen (anti-GPA33/anti-DOTA IgG-scFv BsAb, a clearing agent, and [ 177 Lu]Lu-Gemini) in mouse models. Results: Initial in vivo studies showed that [ 177 Lu]Lu-Gemini behaved similarly to [ 177 Lu]Lu-DOTA-Bn, with almost identical blood and whole-body clearance kinetics, as well as biodistribution and mouse kidney dosimetry. Pretargeting [ 177 Lu]Lu-Gemini to GPA33-expressing SW1222 human colorectal xenografts was highly effective, leading to absorbed doses of [ 177 Lu]Lu-Gemini for blood, tumor, liver, spleen, and kidneys of 3.99, 455, 6.93, 5.36, and 14.0 cGy/MBq, respectively. Tumor-to-normal tissue absorbed-dose ratios (i.e., therapeutic indices [TIs]) for the blood and kidneys were 114 and 33, respectively. In addition, we demonstrate that the use of bivalent [ 177 Lu]Lu-Gemini in DOTA-PRIT leads to improved TIs and augmented [ 177 Lu]Lu-Gemini tumor uptake and retention in comparison to monovalent [ 177 Lu]Lu-DOTA-Bn. Finally, we established efficacy in SW1222 tumor-bearing mice, demonstrating that a single injection of anti-GPA33 DOTA-PRIT with 44 MBq (1.2 mCi) of [ 177 Lu]Lu-Gemini (estimated tumor-absorbed dose, 200 Gy) induced complete responses in 5 of 5 animals and a histologic cure in 2 of 5 (40%) animals. Moreover, a significant increase in survival compared with nontreated controls was noted (maximum tolerated dose not reached). Conclusion: We have developed a bivalent DOTA-radiohapten, [ 177 Lu]Lu-Gemini, that showed improved radiopharmacology for DOTA-PRIT application. The use of bivalent [ 177 Lu]Lu-Gemini in DOTA-PRIT, as opposed to monovalent [ 177 Lu]Lu-DOTA-Bn, allows curative treatments with considerably less administered 177 Lu activity while still achieving high TIs for both the blood (>100) and the kidneys (>30)., (© 2024 by the Society of Nuclear Medicine and Molecular Imaging.)

Rationale and Objectives: Perianal fistulas on 18 F-fluorodeoxyglucose positron emission tomography-computed tomography (FDG-PET/CT) can be an incidental site of FDG uptake in patients undergoing PET for other indications. There are no longitudinal studies describing FDG uptake patterns in perianal fistulas. Therefore, we aimed to analyze changes in FDG uptake over time in patients with incidental perianal fistulas., Patients and Methods: Patients who underwent at least two FDG-PET/CTs between January 2011 and May 2023, with incidental perianal fistula, were retrospectively identified. We analyzed all sequential PET/CTs to determine the presence of a perianal fistula and recorded the fistula's maximum standardized uptake value (SUV max ). Statistical analysis compared fistula FDG-avidity in the initial versus final PET/CT examinations and assessed the correlation between initial fistula SUV max and percent change over time., Results: The study included 15 fistulas in 14 patients, with an average of 5 PET/CT examinations per patient. The average interval between the first and last PET/CT was 24 months (range: 6-64). The average initial fistula SUV max (11.28 ± 3.81) was significantly higher than the final fistula SUV max (7.22 ± 3.99) (p = 0.0067). The fistula SUV max declined by an average of 32.01 ± 35.33% with no significant correlation between initial fistula SUV max and percent change over time (r = -0.213, p = 0.443, 95% CI -0.66-0.35)., Conclusion: FDG uptake in perianal fistulas shows temporal fluctuations but follows a decreasing SUV max trend, possibly indicating a relationship with inflammatory activity. Further studies with larger cohorts paired with perianal fistula pelvic MR imaging are needed to validate these observations and their utility in guiding further management., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Dr. David H. Ballard reports a relationship with Takeda Pharmaceutical Company Limited that includes: funding grants. Dr. Parakkal Deepak reports a relationship with Janssen Pharmaceuticals Inc that includes: consulting or advisory and funding grants. Dr. Parakkal Deepak reports a relationship with Bristol Myers Squibb Co that includes: consulting or advisory and funding grants. Dr. Parakkal Deepak reports a relationship with Boehringer Ingelheim Pharmaceuticals Inc that includes: consulting or advisory and funding grants. Dr. Parakkal Deepak reports a relationship with AbbVie Inc that includes: consulting or advisory and funding grants. Dr. Parakkal Deepak reports a relationship with CorEvitas LLC that includes: consulting or advisory. Dr. Parakkal Deepak reports a relationship with Takeda Pharmaceuticals USA Inc that includes: consulting or advisory and funding grants. Dr. Parakkal Deepak reports a relationship with Sandoz Inc that includes: consulting or advisory. Dr. Parakkal Deepak reports a relationship with Landos Biopharma that includes: funding grants. Dr. Parakkal Deepak reports a relationship with Pfizer Inc that includes: consulting or advisory and funding grants. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Association of University Radiologists. Published by Elsevier Inc. All rights reserved.)

Competing Interests: The authors declare that they have no conflict of interest.

Radiolabelled autologous leukocytes have been used for the clinical diagnosis of inflammation and infection. To develop a stable and efficient radiopharmaceutical for labelling leukocytes, we prepared a novel radioiodinated cell-penetrating peptide, 125 I-TAT, using a bi-functional linker. 125 I-TAT was stable for two days under three different temperature conditions of -20 °C, 4 °C, and 40 °C, with its radiochemical purity remaining over 99%. Iodinated TAT was non-toxic to leukocytes with an IC 50 value of over 100 μM. The labelling efficiency of 125 I-TAT using 1ｘ10 7  cells ranged from 27% to 53% when the three leukocyte cell lines were pre-treated with DMSO. This is comparable to the labelling efficiency recommended by the guideline for conventional labelling agents using 2ｘ10 8  cells. Radioiodinated cell-penetrating peptide may be an improved radiopharmaceutical for white blood cell scans by further optimization., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Purpose: The reversibility of early liver fibrosis highlights the need for improved early detection and monitoring techniques. Fibroblast activation protein (FAP) is a promising theranostics target significantly upregulated during fibrosis. This preclinical and preliminary clinical study investigated a FAP-targeted probe, gallium-68-labeled FAP inhibitor 04 ([ 68 Ga]Ga-DOTA-FAPI-04), for its capability to visualize liver fibrosis., Methods: The preclinical study employed [ 68 Ga]Ga-DOTA-FAPI-04 micro-positron emission tomography (PET)/computed tomography (CT) on carbon tetrachloride-induced mice model (n = 34) and olive oil-treated control group (n = 26), followed by validation of the probe's biodistribution. Hepatic uptake was correlated with fibrosis and inflammation levels, quantified through histology and serum assays. FAP and α-smooth muscle actin expression were determined by immunohistochemistry, as well as immunofluorescence. The subsequent clinical trial enrolled 26 patients with suspected or confirmed liver fibrosis to undergo [ 68 Ga]Ga-DOTA-FAPI-04 PET/magnetic resonance imaging or PET/CT. Key endpoints included correlating [ 68 Ga]Ga-DOTA-FAPI-04 uptake with histological inflammation grades and fibrosis stages, and evaluating its diagnostic and differential efficacy compared to established serum markers and liver stiffness measurement (LSM)., Results: [ 68 Ga]Ga-DOTA-FAPI-04 mean uptake in mice livers was notably higher than in control mice, increasing from week 6 [0.70 ± 0.11 percentage injected dose per cubic centimeter (%ID/cc)], peaking at week 10 (0.97 ± 0.15%ID/cc) and slightly reducing at week 12 (0.89 ± 0.28%ID/cc). The hepatic biodistribution and FAP expression showed a consistent trend. In the patient cohort, hepatic [ 68 Ga]Ga-DOTA-FAPI-04 uptake presented moderate correlations with inflammation grades (r = 0.517 to 0.584, all P < 0.05) and fibrosis stages (r = 0.653 to 0.698, all P < 0.01). The average SUVmax to background ratio in the liver showed superior discriminative ability, especially between stage 0 and stage 1, outperforming LSM (area under curve 0.984 vs. 0.865)., Conclusion: [ 68 Ga]Ga-DOTA-FAPI-04 PET shows significant potential for non-invasive visualization and dynamic monitoring of liver fibrosis in both preclinical experiment and preliminary clinical trial, especially outperforming other common clinical indicators in the early stage., Trial Registration: NCT04605939. Registered October 25, 2020, https://clinicaltrials.gov/study/NCT04605939., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Purpose: 18 F-labelled somatostatin receptor (SSTR) analogs offer several advantages over 68 Ga in terms of yield, cost, spatial resolution and detection rate. This study presents an interim analysis of a prospective trial designed to assess the safety, biodistribution and dosimetry of [ 18 F]AlF-NOTA-LM3, and compare its diagnostic efficacy and clinical management outcomes with [ 68 Ga]Ga-DOTATATE or [ 68 Ga]Ga-NODAGA-LM3 in patients with well-differentiated NETs., Methods: Twenty-one patients with histologically confirmed well-differentiated neuroendocrine tumors (G1 and G2) were prospectively recruited. The first eight patients underwent serial PET scans at 5, 15, 30, 45, 60, and 120 min after [ 18 F]AlF-NOTA-LM3 injection to assess biodistribution and dosimetry. The remaining patients underwent whole-body PET/CT scans. [ 18 F]AlF-NOTA-LM3 and [68Ga]Ga-DOTATATE PET/CT were done within a week, with a minimum 24-hour interval between the two scans. Focal uptake above the surrounding background activity and could not be explained by physiologic uptake was considered lesions of NETs. Lesion number, tumor uptake, and tumor-to-background ratio (TBR) were compared. In patients with discrepant findings, the size of the smallest lesions (measured on coregistered CT) detected on [ 68 Ga]Ga-DOTATATE and [ 18 F]AlF-NOTA-LM3 was compared., Results: [ 18 F]AlF-NOTA-LM3 was safe and well-tolerated. Physiological uptake of [ 18 F]AlF-NOTA-LM3 was significantly lower than that of [ 68 Ga]Ga-DOTATATE in abdominal organs and bone marrow, but higher in blood pool and lung. The mean effective dose was 0.024 ± 0.014 mSv/MBq. [ 18 F]AlF-NOTA-LM3 detected significantly more liver lesions (457 vs. 291, P = 0.006) and lymph node lesions (30 vs. 22, P = 0.011) compared to [ 68 Ga]Ga-DOTATATE. The tumor uptake was comparable, but TBR was significantly higher with [ 18 F]AlF-NOTA-LM3 for lesions from all sites except for the duodenum. The size of the minimum liver lesions (0.54 ± 0.15 vs. 1.01 ± 0.49, P<0.001) and lymph node lesions (0.50 ± 0.19 vs. 1.26 ± 0.86, P = 0.024) detected on [ 18 F]ALF-NOTA-LM3 were significantly smaller than those detected on [ 68 Ga]Ga-DOTATATE., Conclusion: [ 18 F]AlF-NOTA-LM3 shows favorable biodistribution, higher spatial resolution and superior performance than [ 68 Ga]Ga-DOTATATE in detecting liver and lymph node metastases, with higher TBR. Notably, it is the first SSTR analog to show superiority in detecting lymph node lesions when compared to [ 68 Ga]Ga-DOTATATE., Trial Registration: ClinicalTrials.gov identifier NCT06056362., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Purpose: Prostate-Specific Membrane Antigen (PSMA)-targeted Positron Emission Tomography (PET) has revolutionised prostate cancer (PCa) diagnosis and treatment, offering superior diagnostic accuracy over traditional methods and enabling theragnostic applications. However, a significant diagnostic challenge has emerged with identifying unspecific bone uptakes (UBUs), which could lead to over-staging and inappropriate treatment decisions if misinterpreted. This systematic review explores the phenomenon of UBUs in PCa patients undergoing PSMA-PET imaging., Methods: Studies assessing the prevalence, topographical distribution, and potential clinical implications of UBUs were selected according to the Preferred Reporting Items for a Systematic Review and Meta-Analysis (PRISMA) method and evaluated with the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool., Results: The percentage of PCa patients with UBUs on PSMA-PET scans ranged from 0 to 71.7%, depending on the radiopharmaceutical used, with [ 18 F]PSMA-1007 showing the highest incidence. The ribs are the primary site of UBUs across all PSMA-targeted radiopharmaceuticals. The spine is the second most frequent UBU site for [ 68 Ga]Ga-PSMA-11, [ 18 F]DCFPyL, [ 18 F]rhPSMA-7, while the pelvic girdle represents the second most frequent site for [ 18 F]PSMA-1007. The average maximum Standardized Uptake Value (SUV max ) of UBUs varied from 3.4 to 7.7 and was generally lower than that of bone metastases., Conclusions: Our findings underscore the need for heightened awareness and precise interpretation of UBUs to avoid potential over-staging and subsequent inappropriate treatment decisions. Considering the radiopharmaceutical used, PET-derived semiquantitative parameters, the topographical distribution of UBUs, and accurately evaluating the pre-test probability based on clinical and laboratory parameters may aid nuclear medicine physicians in interpreting PSMA-PET findings., (© 2024. The Author(s).)

Colorectal cancer (CRC) is among the most lethal and prevalent malignancies in the world. Human epidermal growth factor receptor 2 (HER2) is a promising target for the diagnosis and treatment of CRC. In this study, we aimed to design, synthesize and label peptide-based positron emission tomography (PET) tracers targeting HER2-positive CRC, namely [ 68 Ga]Ga-ES-01 and [ 68 Ga]Ga-ES-02. The results show that [ 68 Ga]Ga-ES-01 and [ 68 Ga]Ga-ES-02 possessed hydrophilicity, rapid pharmacokinetic properties and excellent stabilities. [ 68 Ga]Ga-ES-02 demonstrated higher binding affinity (K d  = 24.29 ± 4.95 nM) toward the HER2 in CRC. In HER2-positive HT-29 CRC xenograft mouse model, PET study showed specific tumor uptake after injection of [ 68 Ga]Ga-ES-02 (SUV 15min max  = 0.87 ± 0.03; SUV 30min max  = 0.64 ± 0.02). In biodistribution study, the T/M ratios of 68 Ga-ES-02 at 30 min after injection reached a maximum of 4.07 ± 0.34. In summary, we successfully synthesized and evaluated two novel peptide-based PET tracers. Our data demonstrate that [ 68 Ga]Ga-ES-01/02 is capable of HER2-positive colorectal cancer, with [ 68 Ga]Ga-ES-02 showing superior imaging effect, enhanced targeting, and increased specificity., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Background: The aim of the present study was to develop a novel 64 Cu-labeled cyclic peptide ([ 64 Cu]Cu-FAP-NOX) that targets fibroblast activation protein (FAP) and may offer advantages in terms of image contrast, imaging time window, and low uptake in normal tissues., Methods: The novel cyclic peptide featuring with a N-oxalyl modified tail was constructed and conjugated to NOTA for 64 Cu labeling. Biochemical and cellular assays were performed with A549.hFAP cells. The performance of [ 64 Cu]Cu-FAP-NOX was compared to that of two established tracers ([ 64 Cu]Cu-FAPI-04 and [ 68 Ga]Ga-FAP-2286) and three different NOTA-conjugates in HEK-293T.hFAP xenograft mice using micro-PET imaging. Ex vivo biodistribution studies were performed to confirm the FAP specificity and to validate the PET data. Furthermore, a first-in-human study of this novel tracer was conducted on one patient with lung cancer., Results: Compared to [ 64 Cu]Cu-FAPI-04, [ 64 Cu]Cu-FAP-NOX demonstrated faster and higher rates of cellular uptake and internalization in A549.hFAP cells, but lower rates of cellular efflux. All six radiotracers were rapidly taken up by the tumor within the first 4 h post-injection. However, [ 64 Cu]Cu-FAP-NOX had more intense tumor accumulation and slower washout from the target. The ratios of the tumor to normal tissue (including kidneys and muscles) increased significantly over time, with [ 64 Cu]Cu-FAP-NOX reaching the highest ratio among all tracers. In the patient, [ 64 Cu]Cu-FAP-NOX PET showed a comparable result to FDG PET in the primary malignant lesion while exhibiting higher uptake in pleural metastases, consistent with elevated FAP expression as confirmed by immunohistochemistry., Conclusion: [ 64 Cu]Cu-FAP-NOX is a promising FAP-targeted tracer with a highly flexible imaging time window, as evidenced by preclinical evaluation encompassing biodistribution and micro-PET studies, along with a successful patient application. Furthermore, [ 64 Cu]Cu-FAP-NOX showed enhanced image contrast and favorable pharmacokinetic properties for FAP PET imaging, warranting translation into large cohort studies., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Triggering receptor expressed on myeloid cells 2 (TREM2) plays an essential role in microglia activation and is being investigated as a potential therapeutic target for modulation of microglia in several neurological diseases. In this study, we present the development and preclinical evaluation of 64 Cu-labeled antibody-based PET radiotracers as tools for non-invasive assessment of TREM2 expression. Furthermore, we tested the potential of an antibody transport vehicle (ATV) that binds human transferrin receptor to facilitate transcytosis of TREM2 antibody-based radiotracers to the CNS and improve target engagement. Methods: A TREM2 antibody with an engineered transport vehicle (ATV:4D9) and without (4D9) were covalently modified with p NCS-benzyl-NODAGA and labeled with copper-64. Potency, stability, and specificity were assessed in vitro followed by in vivo PET imaging at the early 2 h, intermediate 20 h, and late imaging time points 40 h post-injection using a human transferrin receptor (hTfR) expressing model for amyloidogenesis (5xFAD;TfR mu/hu ) or wild-type mice (WT;TfR mu/hu ), and hTfR negative controls. Organs of interest were isolated to determine biodistribution by ex vivo autoradiography. Cell sorting after in vivo tracer injection was used to demonstrate cellular specificity for microglia and to validate TREM2 PET results in an independent mouse model for amyloidogenesis (App SAA ;TfR mu/hu ). For translation to human imaging, a human TREM2 antibody (14D3) was radiolabeled and used for in vitro autoradiography on human brain sections. Results: The 64 Cu-labeled antibodies were obtained in high radiochemical purity (RCP), radiochemical yield (RCY), and specific activity. Antibody modification did not impact TREM2 binding. ATV:4D9 binding proved to be specific, and the tracer stability was maintained over 48 h. The uptake of [ 64 Cu]Cu-NODAGA-ATV:4D9 in the brains of hTfR expressing mice was up to 4.6-fold higher than [ 64 Cu]Cu-NODAGA-4D9 in mice without hTfR. TREM2 PET revealed elevated uptake in the cortex of 5xFAD mice compared to wild-type, which was validated by autoradiography. PET-to-biodistribution correlation revealed that elevated radiotracer uptake in brains of 5xFAD;TfR mu/hu mice was driven by microglia-rich cortical and hippocampal brain regions. Radiolabeled ATV:4D9 was selectively enriched in microglia and cellular uptake explained PET signal enhancement in App SAA ;TfR mu/hu mice. Human autoradiography showed elevated TREM2 tracer binding in the cortex of patients with Alzheimer's disease. Conclusion: [ 64 Cu]Cu-NODAGA-ATV:4D9 has potential for non-invasive assessment of TREM2 as a surrogate marker for microglia activation in vivo . ATV engineering for hTfR binding and transcytosis overcomes the blood-brain barrier restriction for antibody-based PET radiotracers. TREM2 PET might be a versatile tool for many applications beyond Alzheimer's disease, such as glioma and chronic inflammatory diseases., Competing Interests: Competing Interests: G.C.P., D.X., and K.M.M. are full-time employees and shareholders of Denali Therapeutics. The other authors have declared that no competing interest exists., (© The author(s).)

C-X-C motif chemokine receptor 4 (CXCR4) is an attractive target for the diagnosis and treatment of cancers. Here, we aimed to develop a new CXCR4-targeted PET tracer, and to investigate the translational potential for noninvasive imaging of CXCR4 expression in various cancer entities through preclinical and pilot clinical studies. Methods [ 18 F]AlF-NOTA-QHY-04 was synthesized and evaluated by cellular uptake, blocking and biolayer interferometry studies in vitro . The pharmacokinetics, biodistribution, and imaging specificity were researched in tumor-bearing mice. [ 18 F]AlF-NOTA-QHY-04 PET/CT imaging was performed on 55 patients with different types of cancers. Correlations between ex vivo CXCR4 expression and PET parameters, and CXCR4 expression characteristics in different tumors were analyzed by histopathological staining in patients. Results [ 18 F]AlF-NOTA-QHY-04 was prepared with high radiolabeling yield and radiochemical purity, exhibiting good stability, high binding affinity and specificity for CXCR4 . NCI-H69 (small cell lung cancer, SCLC) tumor-bearing mice showed the highest tumor uptake (4.98 ± 0.98%ID/mL, P < 0.0001) on PET imaging except for Daudi lymphoma xenograft model, which was consistent with the results of cellular and histological analyses. Patients with diffuse large B-cell lymphoma showed the highest tumor uptake (SUV max , 11.10 ± 4.79) followed by SCLC patients (SUV max , 7.51 ± 3.01), which were both significantly higher than other solid tumors ( P < 0.05). The radiotracer uptake of high-grade gliomas is significantly higher than that of low-grade gliomas (3.13 ± 0.58 vs. 1.18 ± 0.51, P = 0.005). Significant higher tumor-to-normal brain ratio of [ 18 F]AlF-NOTA-QHY-04 than [ 18 F]FDG was found in primary brain tumors (62.55 ± 43.24 vs 1.70 ± 0.25, P = 0.027). Positive correlations between ex vivo CXCR4 expression and [ 18 F]AlF-NOTA-QHY-04 uptake (all P < 0.01) were recorded. Multicolor immunofluorescence staining indicated the high tracer uptake in certain patients was mainly due to the high expression of CXCR4 in tumor cells, followed by macrophages. Conclusion The CXCR4-targeted radiotracer [ 18 F]AlF-NOTA-QHY-04 was successfully prepared with favorable yield, high specificity and binding affinity to CXCR4. Preclinical and pilot clinical studies demonstrated its feasibility and potential application in precise diagnosis for not only lymphoma but also SCLC and glioma. [ 18 F]AlF-NOTA-QHY-04 PET/CT can also provide a complementary mapping for brain tumors to [ 18 F]FDG PET/CT., Competing Interests: Competing Interests: The authors have declared that no competing interest exists., (© The author(s).)

The standard method for identifying active Brown Adipose Tissue (BAT) is [ 18 F]-Fluorodeoxyglucose ([ 18 F]-FDG) PET/CT imaging, which is costly and exposes patients to radiation, making it impractical for population studies. These issues can be addressed with computational methods that predict [ 18 F]-FDG uptake by BAT from CT; earlier population studies pave the way for developing such methods by showing some correlation between the Hounsfield Unit (HU) of BAT in CT and the corresponding [ 18 F]-FDG uptake in PET. In this study, we propose training convolutional neural networks (CNNs) to predict [ 18 F]-FDG uptake by BAT from unenhanced CT scans in the restricted regions that are likely to contain BAT. Using the Attention U-Net architecture, we perform experiments on datasets from four different cohorts, the largest study to date. We segment BAT regions using predicted [ 18 F]-FDG uptake values, achieving 23% to 40% better accuracy than conventional CT thresholding. Additionally, BAT volumes computed from the segmentations distinguish the subjects with and without active BAT with an AUC of 0.8, compared to 0.6 for CT thresholding. These findings suggest CNNs can facilitate large-scale imaging studies more efficiently and cost-effectively using only CT., (© 2024. The Author(s).)

Receptor-interacting serine/threonine protein kinase 1 (RIPK1) has emerged as an important regulator of pathologic cell death and inflammation and is implicated in the pathologies of various central nervous system diseases. In this study, we reported the development of three potent dihydropyrazole-cored RIPK1 positron emission tomography (PET) ligands [ 18 F] WL1 - 3 . Among these, [ 18 F] WL1 showed specific binding to RIPK1 in mouse brain sections in vitro through autoradiography and exhibited favorable brain kinetics in mice, characterized by a high initial uptake (brain 2 min = 4.89% ID/g) and rapid washout (brain 60 min = 0.21% ID/g). PET studies in rat brains revealed that [ 18 F] WL1 could readily penetrate the brain with specific binding confirmed by inhibition effects of unlabeled WL1 and GSK'547. Notably, [ 18 F] WL1 showed significant potential in imaging the alterations of RIPK1 in a rat brain of tumor necrosis factor α-induced systemic inflammatory response syndrome model. These findings may pave the way for the future design of potent RIPK1 PET ligands.

The Al 18 F-labeling approach offers a one-step access to radiofluorinated biomolecules by mimicking the labeling process for radiometals. Although these labeling conditions are considered to be mild compared to classic radiofluorinations, improvements of the chelating units have led to the discovery of (±)-H 3 RESCA , which allows Al 18 F-labeling already at ambient temperature. While the suitability of (±)-H 3 RESCA for functionalization and radiofluorination of proteins is well established, its use for small molecules or peptides is less explored. Herein, we advanced this acyclic pentadentate ligand by introducing an alkyne moiety for the late-stage functionalization of biomolecules via click chemistry. We show that in addition to Al 18 F-labeling, the cyclohexanediamine triazole (CHDT) moiety allows stable complexation of 68 Ga and 111 In. Three novel CHDT-functionalized PSMA inhibitors were synthesized and their Al 18 F-, 68 Ga-, and 111 In-labeled analogs were subjected to a detailed in vitro radiopharmacological characterization. Stability studies in vitro in human serum revealed among others a high kinetic inertness of all radiometal complexes. Furthermore, the Al 18 F-labeled PSMA ligands were characterized for their biodistribution in a LNCaP derived tumor xenograft mouse model by PET imaging. One radioligand, Al[ 18 F]F-CHDT-PSMA-1 , bearing a small azidoacetyl linker at the glutamate-urea-lysine motif, provided an in vivo performance comparable to that of [ 18 F]PSMA-1007 but with even higher tumor-to-blood and tumor-to-muscle ratios at 120 min p.i. Overall, our results highlight the suitability of the novel CHDT moiety for functionalization and radiolabeling of small molecules or peptides with Al 18 F, 68 Ga, and 111 In and the triazole ring seems to entail favorable pharmacokinetic properties for molecular imaging purposes.

18 F-Fluoromisonidazole ( 18 F-FMISO) is a highly promising positron emission tomography radiopharmaceutical for identifying hypoxic regions in solid tumors. This research employs spatiotemporal multi-scale mathematical modeling to explore how different levels of angiogenesis influence the transport of radiopharmaceuticals within tumors. In this study, two tumor geometries with heterogeneous and uniform distributions of capillary networks were employed to incorporate varying degrees of microvascular density. The synthetic image of the heterogeneous and vascularized tumor was generated by simulating the angiogenesis process. The proposed multi-scale spatiotemporal model accounts for intricate physiological and biochemical factors within the tumor microenvironment, such as the transvascular transport of the radiopharmaceutical agent, its movement into the interstitial space by diffusion and convection mechanisms, and ultimately its uptake by tumor cells. Results showed that both quantitative and semi-quantitative metrics of 18 F-FMISO uptake differ spatially and temporally at different stages during tumor growth. The presence of a high microvascular density in uniformly vascularized tumor increases cellular uptake, as it allows for more efficient release and rapid distribution of radiopharmaceutical molecules. This results in enhanced uptake compared to the heterogeneous vascularized tumor. In both heterogeneous and uniform distribution of microvessels in tumors, the diffusion transport mechanism has a more pronounced than convection. The findings of this study shed light on the transport phenomena behind 18 F-FMISO radiopharmaceutical distribution and its delivery in the tumor microenvironment, aiding oncologists in their routine decision-making processes., (Creative Commons Attribution license.)

B-cell maturation antigen (BCMA) has emerged as a promising tumor marker for the diagnosis and treatment of multiple myeloma. The noninvasive and rapid detection of BCMA expression in vivo provides significant value in screening and evaluating multiple myeloma patients receiving BCMA-targeted therapy. We identified the BCMA-targeting peptide BP1 from a one-bead-one-compound (OBOC) peptide library using a high-throughput microarray strategy. The BCMA-targeting specificity and affinity of BP1 were assessed by surface plasmon resonance imaging (SPRi), flow cytometry, and confocal imaging. BCMA-positive (H929) and BCMA-negative (K562) subcutaneous tumor models were established and labeled with 68 Ga for BP1, followed by PET imaging and biodistribution studies. PET imaging demonstrated that 68 Ga-labeled BP1 has significant specific uptake in multiple myeloma, enabling rapid identification of BCMA expression and precise delineation of the disease. Thus, BP1 represents an ideal candidate for multiple myeloma imaging.

18 F-2-fluoro-2-deoxy-d-glucose ([ 18 F]FDG) has been the most used positron emission tomography imaging agent for clinical applications. Single photon emission computed tomography (SPECT) imaging is cheaper and used more widely for diagnostic use, but there is no SPECT tumor imaging agent for clinical applications comparable to [ 18 F]FDG. Mannose is a C2 epimer of glucose and can also be transported into tumor cells via glucose transporters (GLUTs). To develop a novel SPECT tumor imaging agent with satisfactory tumor uptake and tumor/nontarget ratios, here a mannose derivative (CN7DM) was synthesized and radiolabeled with technetium-99m to prepare [ 99m Tc]Tc-CN7DM. The six-coordinated structure of [ 99m Tc]Tc-CN7DM was confirmed by the corresponding rhenium compound (Re-CN7DM). [ 99m Tc]Tc-CN7DM was transported into cancer cells via GLUTs and may be trapped in the cancer cells by electrostatic attraction. The probe exhibited high uptake in tumors and low uptake in nontarget tissues in mice bearing different tumors, indicating that [ 99m Tc]Tc-CN7DM exhibited promising potential for SPECT tumor imaging and warranted further clinical investigation.

Purpose: The purpose was to evaluate the pathological nature of focal thyroid uptake seen in 11C-Choline PET/CT performed for prostate cancer., Material and Methods: The study was IRB-approved. All 11C-Choline PET/CT exam reports for studies performed between January 01, 2018, and July 30, 2021, in male patients with prostate cancer in our institution were retrospectively reviewed. Exams with "focal thyroid uptake" on their final report were selected. Patients with surgery or ablation in the thyroid prior to the PET/CT, proven parathyroid adenomas or absent thyroid ultrasound were excluded. Repeated PET/CT exams of same patient were excluded. PET images were analyzed visually and semi-quantitatively by measuring the maximum standardized uptake value (SUVmax) of the focal thyroid uptake. Available thyroid ultrasound images, cytology and pathology reports were reviewed. Statistical analyses were performed., Results: Out of 10,047 sequential 11C-Choline PET/CT studies, 318 reports included "focal thyroid uptake." About 128 of these studies were repeat exams and were excluded. Additional 87 patients were excluded, because the uptake was determined to be adjacent, rather than confined to the thyroid gland. Out of the remaining 103 patients, 74 patients had focal thyroid uptake and concurrent thyroid sonographic evaluation. Out of the 74 focal uptakes evaluated with ultrasound, 21 were presumed benign thyroid nodules based on the ultrasound and 53 had further evaluation with biopsy. Sixty three nodules were benign (21 presumed benign on ultrasound and 42 cytology or surgical pathology-proven), 9 nodules were malignant and 2 remained indeterminate. There was no significant difference between the SUVs of the benign and malignant groups (P > .3)., Conclusion: In this retrospective study of patients with prostate cancer who underwent 11C-Choline PET/CT, we identified a group of patients who underwent thyroid ultrasound for incidental finding of focal 11C-Choline thyroid uptake. Incidence of malignancy in this group was 12%. Therefore, further investigation with ultrasound and possibly ultrasound-guided biopsy may be warranted when a choline avid thyroid nodule is found incidentally on choline PET., Competing Interests: The authors have no funding and conflicts of interest to declare., (Copyright © 2024 the Author(s). Published by Wolters Kluwer Health, Inc.)

In oncologic PET, the SUV and standardized uptake ratio (SUR) of a viable tumor generally increase during the postinjection period. In contrast, the net influx rate ( K i ), which is derived from dynamic PET data, should remain relatively constant. Uptake-time-corrected SUV (cSUV) and SUR (cSUR) have been proposed as uptake-time-independent, static alternatives to K i Our primary aim was to quantify the intrascan repeatability of K i , SUV, cSUV, SUR, and cSUR among malignant lesions on PET/CT. An exploratory aim was to assess the ability of cSUR to estimate K i Methods: This prospective, single-center study enrolled adults undergoing standard-of-care oncologic PET/CT. SUV and K i images were reconstructed from dynamic PET data obtained before (∼35-50 min after injection) and after (∼75-90 min after injection) standard-of-care imaging. Tumors were manually segmented. Quantitative metrics were extracted. cSUVs and cSURs were calculated for a 60-min postinjection reference uptake time. The magnitude of the intrascan test-retest percent change (test-retest |%Δ|) was calculated. Coefficients of determination ( R 2 ) and intraclass correlation coefficients (ICC) were also computed. Differences between metrics were assessed via the Wilcoxon signed-rank test (α, 0.05). Results: This study enrolled 78 subjects; 41 subjects (mean age, 63.8 y; 24 men) with 116 lesions were analyzed. For both tracers, SUV max and maximum SUR (SUR max ) had large early-to-late increases (i.e., poor intrascan repeatability). Among [ 18 F]FDG-avid lesions ( n = 93), there were no differences in intrascan repeatability (median test-retest |%Δ|; ICC) between the maximum K i ( K i ,max ) (13%; 0.97) and either the maximum cSUV (cSUV max ) (12%, P = 0.90; 0.96) or the maximum cSUR (cSUR max ) (13%, P = 0.67; 0.94). For DOTATATE-avid lesions ( n = 23), there were no differences in intrascan repeatability between the K i ,max (11%; 0.98) and either the cSUV max (13%, P = 0.41; 0.98) or the cSUR max (11%, P = 0.08; 0.94). The SUV max , cSUV max , SUR max , and cSUR max were all strongly correlated with the K i ,max for both [ 18 F]FDG ( R 2 , 0.81-0.92) and DOTATATE ( R 2 , 0.88-0.96), but the cSUR max provided the best agreement with the K i ,max across early-to-late time points for [ 18 F]FDG (ICC, 0.69-0.75) and DOTATATE (ICC, 0.90-0.91). Conclusion: K i ,max , cSUV max , and cSUR max had low uptake time dependence compared with SUV max and SUR max The K i ,max can be predicted from cSUR max ., (© 2024 by the Society of Nuclear Medicine and Molecular Imaging.)

Here we describe an anti-prostate-specific membrane antigen (PSMA) minibody (IAB2MA) conjugated to an octadentate, macrocyclic chelator based on four 1-hydroxypyridin-2-one coordinating units (Lumi804 [L804]) labeled with 89 Zr (PET imaging) and 177 Lu (radiopharmaceutical therapy), with the goal of developing safer and more efficacious treatment options for prostate cancer. Methods: L804 was compared with the current gold standard chelators, DOTA and deferoxamine (DFO), conjugated to IAB2MA for radiolabeling with 177 Lu and 89 Zr in cell binding, preclinical biodistribution, imaging, dosimetry, and efficacy studies in the PSMA-positive PC3-PIP tumor-bearing mouse model of prostate cancer. Results: Quantitative radiolabeling (>99% radiochemical yield) of L804-IAB2MA with 177 Lu or 89 Zr was achieved at ambient temperature in under 30 min, comparable to 89 Zr labeling of DFO-IAB2MA. In contrast, DOTA-IAB2MA was radiolabeled with 177 Lu for 30 min at 37°C in approximately 90% radiochemical yield, requiring further purification. Using europium(III) as a luminescent surrogate, high binding affinity of Eu-L804-IAB2MA to PSMA was demonstrated in PC3-PIP cells (dissociation constant, 4.6 ± 0.6 nM). All 4 radiolabeled constructs showed significantly higher levels of internalization after 30 min in the PC3-PIP cells than in PSMA-negative PC3-FLU cells. The accumulation of 177 Lu- and 89 Zr-L804-IAB2MA in PC3-PIP tumors and all organs examined (i.e., heart, liver, spleen, kidney, muscle, salivary glands, lacrimal glands, carcass, and bone) was significantly lower than that of 177 Lu-DOTA-IAB2MA and 89 Zr-DFO-IAB2MA at 96 and 72 h after injection, respectively. Generally, SPECT/CT and PET/CT imaging data showed no significant difference in the SUV mean of the tumors or muscle between the radiotracers. Dosimetry analysis via both organ-level and voxel-level dose calculation methods indicated significantly higher absorbed doses of 177 Lu-DOTA-IAB2MA in tumors, kidney, liver, muscle, and spleen than of 177 Lu-L804-IAB2MA. PC3-PIP tumor-bearing mice treated with single doses of 177 Lu-L804-IAB2MA (18.4 or 22.2 MBq) exhibited significantly prolonged survival and reduced tumor volume compared with unlabeled minibody control. No significant difference in survival was observed between groups of mice treated with 177 Lu-L804-IAB2MA or 177 Lu-DOTA-IAB2MA (18.4 or 22.2 MBq). Treatment with 177 Lu-L804-IAB2MA resulted in lower absorbed doses in tumors and less toxicity than that of 177 Lu-DOTA-IAB2MA. Conclusion: 89 Zr- and 177 Lu-L804-IAB2MA may be a promising theranostic pair for imaging and therapy of prostate cancer., (© 2024 by the Society of Nuclear Medicine and Molecular Imaging.)

The epidermal growth factor receptor (EGFR) protein is highly expressed in a range of malignancies. Although therapeutic interventions directed toward EGFR have yielded therapeutic responses in cancer patients, side effects are common because of normal-tissue expression of wild-type EGFR. We developed a novel tumor-specific anti-EGFR chimeric antibody ch806 labeled with 225 Ac and evaluated its in vitro properties and therapeutic efficacy in murine models of glioblastoma and colorectal cancer. Methods: 225 Ac-ch806 was prepared using different chelators, yielding [ 225 Ac]Ac-macropa-tzPEG 3 Sq-ch806 and [ 225 Ac]Ac-DOTA-dhPzPEG 4 -ch806. Radiochemical yield, purity, apparent specific activity, and serum stability of 225 Ac-ch806 were quantified. In vitro cell killing effect was examined. The biodistribution and therapeutic efficacy of 225 Ac-ch806 were investigated in mice with U87MG.de2-7 and DiFi tumors. Pharmacodynamic analysis of tumors after therapy was performed, including DNA double-strand break immunofluorescence of γH2AX, as well as immunohistochemistry for proliferation, cell cycle arrest, and apoptosis. Results: [ 225 Ac]Ac-macropa-tzPEG 3 Sq-ch806 surpassed [ 225 Ac]Ac-DOTA-dhPzPEG 4 -ch806 in radiochemical yield, purity, apparent specific activity, and serum stability. [ 225 Ac]Ac-macropa-tzPEG 3 Sq-ch806 was therefore used for both in vitro and in vivo studies. It displayed a significant, specific, and dose-dependent in vitro cell-killing effect in U87MG.de2-7 cells. 225 Ac-ch806 also displayed high tumor uptake and minimal uptake in normal tissues. 225 Ac-ch806 significantly inhibited tumor growth and prolonged survival in both U87MG.de2-7 and DiFi models. Enhanced γH2AX staining was observed in 225 Ac-ch806-treated tumors compared with controls. Reduced Ki-67 expression was evident in all 225 Ac-ch806-treated tumors. Increased expression of p21 and cleaved caspase 3 was shown in U87MG.de2-7 and DiFi tumors treated with 225 Ac-ch806. Conclusion: In glioblastoma and colorectal tumor models, 225 Ac-ch806 significantly inhibited tumor growth via induction of double-strand breaks, thereby constraining cancer cell proliferation while inducing cell cycle arrest and apoptosis. These findings underscore the potential clinical applicability of 225 Ac-ch806 as a potential therapy for EGFR-expressing solid tumors., (© 2024 by the Society of Nuclear Medicine and Molecular Imaging.)

The demand for PET tracers that target prostate-specific membrane antigen (PSMA) continues to increase. Meeting this demand with approved 68 Ga- and 18 F-labeled PSMA tracers is challenging outside of major urban centers. This is because the short physical half-life of these radionuclides makes it necessary to produce them near their sites of usage. To overcome this challenge, we propose cyclotron-produced 61 Cu for labeling PSMA PET tracers. 61 Cu can be produced on a large scale, and its 3.33-h half-life allows shipping over considerably longer distances than possible for 68 Ga and 18 F. Production of true theranostic twins using 61 Cu and the β - -emitter 67 Cu is also feasible. Methods: PSMA-I&T (DOTAGA-(l-y)fk(sub-KuE)) and its derivative in which the DOTAGA chelator was replaced by NODAGA (NODAGA-(l-y)fk(sub-KuE)), herein reported as DOTAGA-PSMA-I&T and NODAGA-PSMA-I&T, respectively, were labeled with 61 Cu and compared with [ 68 Ga]Ga-DOTAGA-PSMA-I&T, [ 68 Ga]Ga-NODAGA-PSMA-I&T, [ 68 Ga]Ga-PSMA-11, and [ 18 F]PSMA-1007. In vitro (lipophilicity, affinity, cellular uptake, and distribution) and in vivo (PET/CT, biodistribution, and stability) studies were performed in LNCaP cells and xenografts. Human dosimetry estimates were calculated for [ 61 Cu]Cu-NODAGA-PSMA-I&T. First-in-human imaging with [ 61 Cu]Cu-NODAGA-PSMA-I&T was performed in a patient with metastatic prostate cancer. Results: [ 61 Cu]Cu-DOTAGA-PSMA-I&T and [ 61 Cu]Cu-NODAGA-PSMA-I&T were synthesized with radiochemical purity of more than 97%, at an apparent molar activity of 24 MBq/nmol, without purification after labeling. In vitro, natural Cu ( nat Cu)-DOTAGA-PSMA-I&T and nat Cu-NODAGA-PSMA-I&T showed high affinity for PSMA (inhibitory concentration of 50%, 11.2 ± 2.3 and 9.3 ± 1.8 nM, respectively), although lower than the reference nat Ga-PSMA-11 (inhibitory concentration of 50%, 2.4 ± 0.4 nM). Their cellular uptake and distribution were comparable to those of [ 68 Ga]Ga-PSMA-11. In vivo, [ 61 Cu]Cu-NODAGA-PSMA-I&T showed significantly lower uptake in nontargeted tissues than [ 61 Cu]Cu-DOTAGA-PSMA-I&T and higher tumor uptake (14.0 ± 5.0 percentage injected activity per gram of tissue [%IA/g]) than [ 61 Cu]Cu-DOTAGA-PSMA-I&T (6.06 ± 0.25 %IA/g, P = 0.0059), [ 68 Ga]Ga-PSMA-11 (10.2 ± 1.5 %IA/g, P = 0.0972), and [ 18 F]PSMA-1007 (9.70 ± 2.57 %IA/g, P = 0.080) at 1 h after injection. Tumor uptake was also higher for [ 61 Cu]Cu-NODAGA-PSMA-I&T at 4 h after injection (10.7 ± 3.3 %IA/g) than for [ 61 Cu]Cu-DOTAGA-PSMA-I&T (4.88 ± 0.63 %IA/g, P = 0.0014) and [ 18 F]PSMA-1007 (6.28 ± 2.19 %IA/g, P = 0.0145). Tumor-to-nontumor ratios of [ 61 Cu]Cu-NODAGA-PSMA-I&T were superior to those of [ 61 Cu]Cu-DOTAGA-PSMA-I&T and comparable to those of [ 68 Ga]Ga-PSMA-11 and [ 18 F]PSMA-1007 at 1 h after injection and increased significantly between 1 and 4 h after injection in most cases. Human dosimetry estimates for [ 61 Cu]Cu-NODAGA-PSMA-I&T were similar to the ones reported for 18 F-PSMA ligands. First-in-human imaging demonstrated multifocal osseous and hepatic metastases. Conclusion: [ 61 Cu]Cu-NODAGA-PSMA-I&T is a promising PSMA radiotracer that compares favorably with [ 68 Ga]Ga-PSMA-11 and [ 18 F]PSMA-1007, while allowing delayed imaging., (© 2024 by the Society of Nuclear Medicine and Molecular Imaging.)

The high incidence and heavy disease burden of prostate cancer (PC) require accurate and comprehensive assessment for appropriate disease management. Prostate-specific membrane antigen (PSMA) positron emission tomography (PET) cannot detect PSMA-negative lesions, despite its key role in PC disease management. The overexpression of gastrin-releasing peptide receptor (GRPR) in PC lesions reportedly performs as a complementary target for the diagnosis and therapy of PC. Radiopharmaceuticals derived from the natural ligands of GRPR have been developed. These radiopharmaceuticals enable the visualization and quantification of GRPR within the body, which can be used for disease assessment and therapeutic guidance. Recently developed radiopharmaceuticals exhibit improved pharmacokinetic parameters without deterioration in affinity. Several heterodimers targeting GRPR have been constructed as alternatives because of their potential to detect tumor lesions with a low diagnostic efficiency of single target detection. Moreover, some GRPR-targeted radiopharmaceuticals have entered clinical trials for the initial staging or biochemical recurrence detection of PC to guide disease stratification and therapy, indicating considerable potential in PC disease management. Herein, we comprehensively summarize the progress of radiopharmaceuticals targeting GRPR. In particular, we discuss the impact of ligands, chelators, and linkers on the distribution of radiopharmaceuticals. Furthermore, we summarize a potential design scheme to facilitate the advancement of radiopharmaceuticals and, thus, prompt clinical translation.

The aim of this study was to evaluate the preclinical efficacy of [ 89 Zr]Zr-DFO-Ab253 as a novel positron emission tomography (PET) tracer for CD146-positive malignant melanoma imaging. Considering the high expression of CD146 in malignant melanoma, this study investigated the effect of different CD146 expression levels on the tumor uptake of [ 89 Zr]Zr-DFO-Ab253. CD146 selectivity was investigated by using the CD146-positive human melanoma cell A375 and the CD146-negative human alveolar epithelial cell A549. The cell uptake of [ 89 Zr]Zr-DFO-Ab253 tracers was investigated, and receptor-binding affinities were measured by radioactive enzyme-linked immunosorbent assay. Biodistribution studies and micro-PET imaging of the radiotracers were performed on mice bearing A375 and A549 xenografts under baseline and blocking conditions. An immunohistochemical test was performed using A375 and A549 tissue sections for CD146 expression level analysis. [ 89 Zr]Zr-DFO-Ab253 was obtained with a high radiochemical yield (87.86 ± 4.66%) and a satisfactory radiochemical purity (>98.0%). The specificity and affinity of [ 89 Zr]Zr-DFO-Ab253 were confirmed in melanoma A375 cells and in vivo PET imaging of A375 tumor models. [ 89 Zr]Zr-DFO-IgG and A549 lung tumors were prepared as control radiotracers and negative models to verify the specificity of [ 89 Zr]Zr-DFO-Ab253 on CD146. [ 89 Zr]Zr-DFO-Ab253 has a K d of 4.01 ± 0.50 nM. PET imaging and biodistribution showed a higher uptake of [ 89 Zr]Zr-DFO-Ab253 in A375 melanomas than that in A549 tumors (42.1 ± 4.04% vs 7.87 ± 1.30% ID/g at 120 h, P < 0.05). A low tumor uptake of [ 89 Zr]Zr-DFO-IgG was observed with uptakes of 1.91 ± 0.41 and 2.80 ± 0.14 ID%/g when blocked at 120 h. The radiation-absorbed dose was calculated to be 0.13 mSv/MBq. This study demonstrates the synthesis and preclinical evaluation of [ 89 Zr]Zr-DFO-Ab253 and indicates that the novel tracer has promising applications in malignant melanoma-specific PET imaging because of its high uptake and long-time retention in malignant melanoma. It also provides feasibility for the development of integrated molecular probes for diagnosis and treatment based on the CD146 target.

Occult nodal spread and metastatic disease require longstanding imaging and biochemical assessments for thyroid cancer, a disease that has a propensity for diffuse, small-volume disease. We have developed a 64 Cu-labeled platelet-derived growth factor receptor α (PDGFRA) antibody for immuno-PET of PDGFRA in metastatic papillary thyroid cancer (PTC). The present work describes the discovery of small cyclic PDGFRA-targeting peptides, their binding features, and radiolabeling with positron emitter gallium-68 ( 68 Ga) for in vitro and in vivo characterization in thyroid cancer models. Phage-display technology with two separate libraries and seven different cell lines was used through three rounds of biopanning as well as flow cytometry and comparative analysis with recombinant protein to select specific peptide sequences. Phenotypic binding analysis was completed by using phosphorylation and cell migration assays. In vitro protein binding was analyzed with thermophoresis and flow cytometry using the fluorescent-labeled PDGFRA peptide. Peptide candidates were modified with the NOTA chelator for radiolabeling with 68 Ga. In vitro cell uptake was studied in various thyroid cancer cell lines. In vivo studies of 68 Ga-labeled peptides included metabolic stability and PET imaging. From the original library (10 13 compounds), five different peptide groups were identified based on biopanning experiments with and without the α subunit of PDGFR, leading to ∼50 peptides. Subsequent phenotypic screening revealed two core peptide sequences ( CP16 and CP18 ) that demonstrated significant changes in the level of PDGFRA phosphorylation and cell migration. Alanine scan sublibraries were created from these two lead peptide sequences, and peptides were radiolabeled using 68 Ga-GaCl 3 at pH 4.5, resulting in RCP > 95% within 34-40 min, including SPE purification. Cyclic peptide CP18.5 showed the strongest effects on cell migration, flow cytometry, and binding by visual interference color assay. 68 Ga-labeled PDGFRA-targeting peptides showed elevated cell and tumor uptake in models of thyroid cancer, with 68 Ga-NOTA-CP18.5 being the lead candidate. However, metabolic stability in vivo was compromised for 68 Ga-NOTA-CP18.5 vs 68 Ga-NOTA-CP18 but without impacting tumor uptake or clearance profiles. First-generation radiolabeled cyclic peptides have been developed as novel radiotracers, particularly 68 Ga-NOTA-CP18.5 , for the molecular imaging of PDGFRA in thyroid cancer.

Nectin cell adhesion molecule 4 (Nectin-4) is overexpressed in various malignant tumors and has emerged as a promising target for tumor imaging. Bicyclic peptides, known for their conformational rigidity, metabolic stability, and membrane permeability, are ideal tracers for positron emission tomography (PET) imaging. In this study, we evaluated the feasibility of visualizing Nectin-4-positive tumors using radiolabeled bicyclic peptide derivatives and optimized the pharmacokinetics of radiotracers by introducing PEG chains of different lengths. Five PEGylated radiotracers radiolabeled with 68 Ga 3+ exhibited high radiochemical purity and stability. As the chain length increased, the Log  D values decreased from -2.32 ± 0.13 to -2.50 ± 0.16, indicating a gradual increase in the hydrophilicity of the radiotracers. In vitro cell-binding assay results showed that the PEGylated bicyclic peptide exhibits nanomolar affinity, and blocking experiments confirmed the specific binding of the tracers to the Nectin-4 receptor. In vivo PET imaging and biodistribution studies in SW780 and 5637 xenograft mice showed that [ 68 Ga]Ga-NOTA-PEG 12 -BP demonstrated optimal pharmacokinetics, characterized by rapid and good tumor uptake, faster background clearance, and improved tumor-to-tissue contrast. Finally, compared with 18 F-FDG, PET imaging, in vivo blocking assays of [ 68 Ga]Ga-NOTA-PEG 12 -BP and histological staining confirmed that specific tumor uptake was mediated by Nectin-4 receptors. The results indicated that [ 68 Ga]Ga-NOTA-PEG 12 -BP was a promising PET radiotracer for Nectin-4 targeting, with applications for clinical translation.

This study aimed to evaluate a novel albumin-binding strategy for addressing the challenge of insufficient tumor retention of fibroblast activation protein inhibitors (FAPIs). Maleimide, a molecule capable of covalent binding to free thiol groups, was modified to conjugate with FAPI-04 in order to enhance its binding to endogenous albumin, resulting in an extended blood circulation half-life and increased tumor uptake. DOTA-FAPI-maleimide was prepared and radiolabeled with Ga-68 and Lu-177, followed by cellular assays, pharmacokinetic analysis, PET/CT, and SPECT/CT imaging to assess the probe distribution in various tumor-bearing models. Radiolabeling of the modified probe was successfully achieved with a radiochemical yield of over 99% and remained stable for 144 h. Cellular assays showed that the ligand concentration required for 50% inhibition of the probe was 1.20 ± 0.31 nM, and the K d was 0.70 ± 0.07 nM with a B max of 7.94 ± 0.16 fmol/cell, indicative of higher specificity and affinity of DOTA-FAPI-maleimide compared to other FAPI-04 variants. In addition, DOTA-FAPI-maleimide exhibited a persistent blood clearance half-life of 7.11 ± 0.34 h. PET/CT images showed a tumor uptake of 2.20 ± 0.44%ID/g at 0.5 h p.i., with a tumor/muscle ratio of 5.64 in HT-1080-FAP tumor-bearing models. SPECT/CT images demonstrated long-lasting tumor retention. At 24 h p.i., the tumor uptake of [ 177 Lu]Lu-DOTA-FAPI-maleimide reached 5.04 ± 1.67%ID/g, with stable tumor retention of 3.40 ± 1.95%ID/g after 4 days p.i. In conclusion, we developed and evaluated the thiol group-attaching strategy, which significantly extended the circulation and tumor retention of the adapted FAPI tracer. We envision its potential application for clinical cancer theranostics.

The 2-nitroimidazole based 99m Tc-radiopharmaceuticals are widely explored for imaging tumor hypoxia. Radiopharmaceuticals for targeting hypoxia are often lipophilic and therefore, show significant uptake in liver and other vital organs. In this context, lipophilic radiopharmaceuticals with design features enabling faster clearance from liver may be more desirable. A dipicolylamine-NCS bifunctional chelator that could generate a thiourea-bridge up on conjugation to primary amine bearing molecule was used to synthesize a 2-nitroimidazole-dipicolyl amine ligand for radiolabeling with 99m Tc(CO) 3 core. Corresponding Re(CO) 3 -analogue was prepared to establish the structure of 2-nitroimidazole- 99m Tc(CO) 3 complex prepared in trace level. The 2-nitroimidazole- 99m Tc(CO) 3 complex showed a hypoxic to normoxic ratio of ~2.5 in CHO cells at 3 h. In vivo, the complex showed accumulation and retention in tumor with high tumor to blood and tumor to muscle ratio. The study demonstrated the utility of metabolizable thiourea-bridge in 2-nitroimidazole- 99m Tc(CO) 3 complex in inducing faster clearance of the radiotracer from liver. The dipicolylamine-NCS bifunctional chelator reported herein can also be used for radiolabeling other class of target specific molecules with 99m Tc(CO) 3 core., (© 2024 The Author(s). Drug Development Research published by Wiley Periodicals LLC.)

Purpose: The advancement of heterodimeric tracers, renowned for their high sensitivity, marks a significant trend in the development of radiotracers for cancer diagnosis. Our prior work on [ 68 Ga]Ga-HX01, a heterodimeric tracer targeting CD13 and integrin α v β 3 , led to its approval for phase I clinical trials by the China National Medical Production Administration (NMPA). However, its fast clearance and limited tumor retention pose challenges for broader clinical application in cancer treatment. This study aims to develop a new radiopharmaceutical with increased tumor uptake and prolonged retention, rendering it a potential therapeutic candidate., Methods: New albumin binder-conjugated compounds were synthesized based on the structure of HX01. In vitro and in vivo evaluation of these new compounds were performed after labelling with 68 Ga. Small-animal PET/CT imaging were conducted at different time points at 0.5-6 h post injection (p.i.) using BxPC-3 xenograft mice models. The one with the best imaging performance was further radiolabeled with 177 Lu for small-animal SPECT/CT and ex vivo biodistribution investigation., Results: We have synthesized novel albumin binder-conjugated compounds, building upon the structure of HX01. When radiolabeled with 68 Ga, all compounds demonstrated improved pharmacokinetics (PK). Small-animal PET/CT studies revealed that these new albumin binder-conjugated compounds, particularly [ 68 Ga]Ga-L6, exhibited significantly enhanced tumor accumulation and retention compared with [ 68 Ga]Ga-L0 without an albumin binder. [ 68 Ga]Ga-L6 outperformed [ 68 Ga]Ga-L7, a compound developed using a previously reported albumin binder. Furthermore, [ 177 Lu]Lu-L6 demonstrated rapid clearance from normal tissues, high tumor uptake, and prolonged retention in small-animal SPECT/CT and biodistribution studies, positioning it as an ideal candidate for radiotherapeutic applications., Conclusion: A new integrin α v β 3 and CD13 targeting compound was screened out. This compound bears a novel albumin binder and exhibits increased tumor uptake and prolonged tumor retention in BxPC-3 tumors and low background in normal organs, making it a perfect candidate for radiotherapy when radiolabeled with 177 Lu., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Purpose: Here, we evaluate a PET displacement model with a Single-step and Numerical solution in healthy individuals using the synaptic vesicle glycoprotein (SV2A) PET-tracer [ 11 C]UCB-J and the anti-seizure medication levetiracetam (LEV). We aimed to (1) validate the displacement model by comparing the brain LEV-SV2A occupancy from a single PET scan with the occupancy derived from two PET scans and the Lassen plot and (2) determine the plasma LEV concentration-SV2A occupancy curve in healthy individuals., Methods: Eleven healthy individuals (five females, mean age 35.5 [range: 25-47] years) underwent two 120-min [ 11 C]UCB-J PET scans where an LEV dose (5-30 mg/kg) was administered intravenously halfway through the first PET scan to partially displace radioligand binding to SV2A. Five individuals were scanned twice on the same day; the remaining six were scanned once on two separate days, receiving two identical LEV doses. Arterial blood samples were acquired to determine the arterial input function and plasma LEV concentrations. Using the displacement model, the SV2A-LEV target engagement was calculated and compared with the Lassen plot method. The resulting data were fitted with a single-site binding model., Results: SV2A occupancies and V ND estimates derived from the displacement model were not significantly different from the Lassen plot (p = 0.55 and 0.13, respectively). The coefficient of variation was 14.6% vs. 17.3% for the Numerical and the Single-step solution in Bland-Altman comparisons with the Lassen plot. The average half maximal inhibitory concentration (IC 50 ), as estimated from the area under the curve of the plasma LEV concentration, was 12.5 µg/mL (95% CI: 5-25) for the Single-Step solution, 11.8 µg/mL (95% CI: 4-25) for the Numerical solution, and 6.3 µg/mL (95% CI: 0.08-21) for the Lassen plot. Constraining Emax to 100% did not significantly improve model fits., Conclusion: Plasma LEV concentration vs. SV2A occupancy can be determined in humans using a single PET scan displacement model. The average concentration of the three computed IC 50 values ranges between 6.3 and 12.5 µg/mL. The next step is to use the displacement model to evaluate LEV occupancy and corresponding plasma concentrations in relation to treatment efficacy., Clinical Trial Registration: NCT05450822. Retrospectively registered 5 July 2022 https://clinicaltrials.gov/ct2/results? term=NCT05450822&Search=Search., (© 2024. The Author(s).)

Purpose: [ 18 F]PI-2620 positron emission tomography (PET) detects misfolded tau in progressive supranuclear palsy (PSP) and Alzheimer's disease (AD). We questioned the feasibility and value of absolute [ 18 F]PI-2620 PET quantification for assessing tau by regional distribution volumes (V T ). Here, arterial input functions (AIF) represent the gold standard, but cannot be applied in routine clinical practice, whereas image-derived input functions (IDIF) represent a non-invasive alternative. We aimed to validate IDIF against AIF and we evaluated the potential to discriminate patients with PSP and AD from healthy controls by non-invasive quantification of [ 18 F] PET., Methods: In the first part of the study, we validated AIF derived from radial artery whole blood against IDIF by investigating 20 subjects (ten controls and ten patients). IDIF were generated by manual extraction of the carotid artery using the average and the five highest (max5) voxel intensity values and by automated extraction of the carotid artery using the average and the maximum voxel intensity value. In the second part of the study, IDIF quantification using the IDIF with the closest match to the AIF was transferred to group comparison of a large independent cohort of 40 subjects (15 healthy controls, 15 PSP patients and 10 AD patients). We compared V T and V T ratios, both calculated by Logan plots, with distribution volume (DV) ratios using simplified reference tissue modelling and standardized uptake value (SUV) ratios., Results: AIF and IDIF showed highly correlated input curves for all applied IDIF extraction methods (0.78 < r < 0.83, all p < 0.0001; area under the curves (AUC): 0.73 < r ≤ 0.82, all p ≤ 0.0003). Regarding the V T values, correlations were mainly found between those generated by the AIF and by the IDIF methods using the maximum voxel intensity values. Lowest relative differences (RD) were observed by applying the manual method using the five highest voxel intensity values (max5) (AIF vs. IDIF manual, avg: RD = -82%; AIF vs. IDIF automated, avg: RD = -86%; AIF vs. IDIF manual, max5: RD = -6%; AIF vs. IDIF automated, max: RD = -26%). Regional V T values revealed considerable variance at group level, which was strongly reduced upon scaling by the inferior cerebellum. The resulting V T ratio values were adequate to detect group differences between patients with PSP or AD and healthy controls (HC) (PSP target region (globus pallidus): HC vs. PSP vs. AD: 1.18 vs. 1.32 vs. 1.16; AD target region (Braak region I): HC vs. PSP vs. AD: 1.00 vs. 1.00 vs. 1.22). V T ratios and DV ratios outperformed SUV ratios and V T in detecting differences between PSP and healthy controls, whereas all quantification approaches performed similarly in comparing AD and healthy controls., Conclusion: Blood-free IDIF is a promising approach for quantification of [ 18 F]PI-2620 PET, serving as correlating surrogate for invasive continuous arterial blood sampling. Regional [ 18 F]PI-2620 V T show large variance, in contrast to regional [ 18 F]PI-2620 V T ratios scaled with the inferior cerebellum, which are appropriate for discriminating PSP, AD and healthy controls. DV ratios obtained by simplified reference tissue modeling are similarly suitable for this purpose., (© 2024. The Author(s).)

Background: Quantitative technetium-99m-pyrophosphate cardiac single-photon emission computed tomography ( 99m Tc-PYP SPECT/CT) is an emerging method for estimating myocardial burden of transthyretin cardiac amyloidosis (ATTR-CA), but its efficacy in monitoring longitudinal changes remains uncertain. We aimed to investigate longitudinal changes in cardiac ATTR amyloid burden following transthyretin stabilization therapy using visual and quantitative 99m Tc-PYP SPECT/CT and to relate these with changes in cardiac biomarkers and function., Methods: This prospective longitudinal cohort study investigated changes in 99m Tc-PYP SPECT/CT in 23 participants with ATTR-CA on transthyretin stabilization therapy (median: 2.6 years). Quantitative analysis included left ventricular (LV) standardized uptake values (SUVs) (SUV max , SUV mean ), cardiac amyloid activity (CAA; SUV mean ∗LV activity volume), and percent injected dose (%ID) (mean activity concentration∗LV activity volume/injected activity), calculated using a threshold of >1.5 times left atrial blood pool activity concentration on SPECT/CT. Longitudinal changes of paired continuous and ordinal variables were analyzed using Wilcoxon signed-rank test., Results: Following therapy, visual grade decreased significantly (P = 0.003). Several quantitative 99m Tc-PYP metrics also decreased significantly: SUV max (median -0.75, P = 0.011), CAA (median: -406.6, P < 0.001), and %ID (median: -0.45, P < 0.001). Serum transthyretin levels improved (median: +6.5 mg/dL, P = 0.008). Echocardiographic parameters (global longitudinal strain, LV mass index, and LV wall thickness), N-terminal pro-B-type natriuretic peptide, and estimated glomerular filtration rate remained stable., Conclusions: Favorable changes in 99m Tc-PYP myocardial uptake were observed in participants on transthyretin stabilization therapy, whereas echocardiographic parameters and biomarkers remained stable. These results likely signify myocardial ATTR amyloid stabilization rather than amyloid burden regression. Further investigation is needed to understand the implications of these findings., (Copyright © 2024 American Society of Nuclear Cardiology. Published by Elsevier Inc. All rights reserved.)

Targeted radionuclide therapy (TRT) is an effective treatment for tumors. Self-condensation strategies can enhance the retention of radionuclides in tumors and enhance the anti-tumor effect. Considering legumain is overexpressed in multiple types of human cancers, a 131 I-labeled radiopharmaceutical ([ 131 I]MAAN) based on the self-condensation reaction between 2-cyanobenzothiazole (CBT) and cysteine (Cys) was developed by us recently for treating legumain-overexpressed tumors. However, liver enrichment limits its application. In this study, a new radiopharmaceutical [ 131 I]IM(HE) 3 AAN was designed and synthesized by introducing a hydrophilic peptide sequence His-Glu-His-Glu-His-Glu ((HE) 3 ) into [ 131 I]MAAN to optimize the pharmacokinetics. Upon activation by legumain under a reducing environment, hydrophilic [ 131 I]IM(HE) 3 AAN could react with its precursor to form heterologous dimer [ 131 I]H-Dimer that is highly hydrophobic. Cerenkov imaging revealed that [ 131 I]IM(HE) 3 AAN displayed superior tumor selectivity and longer tumor retention time as compared with [ 131 I]MAAN, with a significant reduction in the liver uptake. After an 18-day treatment with [ 131 I]IM(HE) 3 AAN, the tumor proliferation was obviously inhibited, while no obvious injury was observed in the normal organs. These findings suggest that [ 131 I]IM(HE) 3 AAN could serve as a promising drug candidate for treating legumain-overexpressed tumors., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2024. Published by Elsevier B.V.)