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Purpose: Bisphosphonates are pivotal in managing bone tumors by inhibiting bone resorption. This study investigates the therapeutic potential of [ 177 Lu]Lu-P15-073, a novel bisphosphonate, for radioligand therapy (RLT) in bone metastases., Methods: Ten patients (age 35 to 75) with confirmed bone metastases underwent therapy with a single dose of [ 177 Lu]Lu-P15-073 (1,225 ± 84 MBq, or 33 ± 2 mCi). Prior to treatment, bone metastases were verified via [ 99m Tc]Tc-MDP bone scans. Serial planar whole-body scans monitored biodistribution over a 14-day period. Dosimetry was assessed for major organs and tumor lesions, while safety was evaluated through blood biomarkers and pain scores., Results: Serial planar whole-body scans demonstrated rapid and substantial accumulation of [ 177 Lu]Lu-P15-073 in bone metastases, with minimal uptake in blood and other organs. The absorbed dose in the critical organ, red marrow, was measured at (0.034 ± 0.010 mSv/MBq), with a notably low normalized effective dose (0.013 ± 0.005 mSv/MBq) compared to other 177 Lu-labeled bisphosphonates. Persistent high uptake in bone metastases was observed, resulting in elevated tumor doses (median 3.12 Gy/GBq). Patients exhibited favorable tolerance to [ 177 Lu]Lu-P15-073 therapy, with no new instances of side effects. Additionally, 87.5% (7/8) of patients experienced a significant reduction in pain scale (numerical rating scale, NRS, from 5.1 ± 2.3 to 3.0 ± 1.8). The tumor-background ratio (TBRmean) of [ 99m Tc]Tc-MDP correlated significantly with [ 177 Lu]Lu-P15-073 uptake (P < 0.01), indicating its potential for prediction of absorbed dose., Conclusions: This study demonstrates the safety, dosimetry, and efficacy of a single therapeutic dose of [ 177 Lu]Lu-P15-073 in bone metastases. The treatment was well-tolerated with no severe adverse events. These findings suggest that [ 177 Lu]Lu-P15-073 holds promise as a novel RLT agent for bone metastases., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Background: In the central nervous system, type 2 vesicular monoamine transporters (VMAT2) are responsible for the reuptake of monoamines from synaptic junction back to pre-synaptic terminal vesicles. These transporters are functionally crucial as they reflect the integrity of monoamine neurons. D6-[ 18 F]FP-(+)-DTBZ, a novel deuterated VMAT2 radioligand, has shown promise as a potential PET tracer for the diagnosis of Parkinson's disease (PD). This study evaluates the biodistribution and dosimetry of D6-[ 18 F]FP-(+)-DTBZ and includes a head-to-head comparison with its non-deuterated version, [ 18 F]FP-(+)-DTBZ (AV-133), in healthy individuals and PD patients., Results: The automated synthesis of D6-[ 18 F]FP-(+)-DTBZ using the SPE method was accomplished in 35 min, yielding a high radiochemical purity (> 99%) and high radiochemical yields (35 ± 5%). The biodistribution and dosimetry study indicated an effective dose of 37.1 ± 7.2 μSv/MBq, with the liver receiving the highest radiation dose (289.6 ± 42.1 μGy/MBq), followed by pancreas (185.2 ± 29.1 μGy/MBq). Brain imaging with D6-[ 18 F]FP-(+)-DTBZ exhibited a significantly increased uptake in VMAT2-rich regions, particularly the striatum. In a head-to-head comparison between [ 18 F]FP-(+)-DTBZ and D6-[ 18 F]FP-(+)-DTBZ, the latter exhibited approximately 15% higher SUVR in the caudate, putamen, and nucleus accumbens. Preliminary studies in PD patients showed a substantial reduction in VMAT2 uptake in the striatum, with the most pronounced decrease observed in the putamen (a 53% decline)., Conclusions: D6-[ 18 F]FP-(+)-DTBZ is a safe and improved VMAT2-specific imaging agent, which may be suitable for diagnosing PD by evaluating changes in VMAT2 binding of monoamine neurons in the brain. Trial registration Chinese Clinical Trial Registry, ChiCTR2200057218, Registered 16 August 2021, https://www.chictr.org.cn/bin/project/edit?pid=142725 ., (© 2024. The Author(s).)

Prostate-specific membrane antigen (PSMA) overexpressed in prostate cancer cells can serve as a target for imaging and radioligand therapy (RLT). Previously, [ 68 Ga]Ga-P16-093, containing a Ga(III) chelator, N , N '-bis[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine- N , N '-diacetic acid (HBED-CC), displayed excellent PSMA-targeting properties and showed a high tumor uptake and retention useful for diagnosis in prostate cancer patients. Recently, [ 177 Lu]Lu-PSMA-617 has been approved by the U.S. food and drug administration (FDA) for the treatment of prostate cancer patients. Derivatives of PSMA-093 using AAZTA (6-amino-6-methylperhydro-1,4-diazepinetetraacetic acid), as the chelator, were designed as alternative agents forming complexes with both diagnostic and therapeutic radiometals, such as gallium-68 (log K = 22.18) or lutetium-177 (log K = 21.85). The aim of this study is to evaluate AAZTA-Gly- O -(methylcarboxy)-Tyr-Phe-Lys-NH-CO-NH-Glu (designated as AZ-093, 1 ) leading to a gallium-68/lutetium-177 theranostic pair as potential PSMA targeting agents. Synthesis of the desired precursor, AZ-093, 1 , was effectively accomplished. Labeling with either [ 68 Ga]GaCl 3 or [ 177 Lu]LuCl 3 in a sodium acetate buffer solution (pH 4-5) at 50 °C in 5 to 15 min produced either [ 68 Ga]Ga- 1 or [ 177 Lu]Lu- 1 with high yields and excellent radiochemical purities. Results of in vitro binding studies, cell uptake, and retention (using PSMA-positive prostate carcinoma cells line, 22Rv1-FOLH1-oe) were comparable to that of [ 68 Ga]Ga-P16-093 and [ 177 Lu]Lu-PSMA-617, respectively. Specific cellular uptake was determined with or without the competitive blocking agent (2 μM of "cold" PSMA-11). Cellular binding and internalization showed a time-dependent increase over 2 h at 37 °C in the PSMA-positive cells. The cell uptakes were completely blocked by the "cold" PSMA-11 suggesting that they are competing for the same PSMA binding sites. In the mouse model with implanted PSMA-positive tumor cells, both [ 68 Ga]Ga- 1 and [ 177 Lu]Lu- 1 displayed excellent uptake and retention in the tumor. Results indicate that [ 68 Ga]Ga/[ 177 Lu]Lu- 1 ( 68 Ga]Ga/[ 177 Lu]Lu-AZ-093) is potentially useful as PSMA-targeting agent for both diagnosis and radiotherapy of prostate cancer.

Purpose: Prostate-specific membrane antigen (PSMA) is a promising target for diagnosis and radioligand therapy (RLT) of prostate cancer. Two novel PSMA-targeting radionuclide therapy agents, [ 177 Lu]Lu-P17-087, and its albumin binder modified derivative, [ 177 Lu]Lu-P17-088, were evaluated in metastatic castration-resistant prostate cancer (mCRPC) patients. The primary endpoint was dosimetry evaluation, the second endpoint was radiation toxicity assessment (CTCAE 5.0) and PSA response (PCWG3)., Methods: Patients with PSMA-positive tumors were enrolled after [ 68 Ga]Ga-PSMA-11 PET/CT scan. Five mCRPC patients received [ 177 Lu]Lu-P17-087 and four other patients received [ 177 Lu]Lu-P17-088 (1.2 GBq/patient). Multiple whole body planar scintigraphy was performed at 1.5, 4, 24, 48, 72, 120 and 168 h after injection and one SPECT/CT imaging was performed at 24 h post-injection for each patient. Dosimetry evaluation was compared in both patient groups., Results: Patients showed no major clinical side-effects under this low dose treatment. As expected [ 177 Lu]Lu-P17-088 with longer blood circulation (due to its albumin binding) exhibited higher effective doses than [ 177 Lu]Lu-P17-087 (0.151 ± 0.036 vs. 0.056 ± 0.019 mGy/MBq, P = 0.001). Similarly, red marrow received 0.119 ± 0.068 and 0.048 ± 0.020 mGy/MBq, while kidney doses were 0.119 ± 0.068 and 0.046 ± 0.022 mGy/MBq, respectively. [ 177 Lu]Lu-P17-087 demonstrated excellent tumor uptake and faster kinetics; while [ 177 Lu]Lu-P17-088 displayed a slower washout and higher average dose (7.75 ± 4.18 vs. 4.72 ± 2.29 mGy/MBq, P = 0.018). After administration of [ 177 Lu]Lu-P17-087 and [ 177 Lu]Lu-P17-088, 3/5 and 3/4 patients showed reducing PSA values, respectively., Conclusion: [ 177 Lu]Lu-P17-088 and [ 177 Lu]Lu-P17-087 displayed different pharmacokinetics but excellent PSMA-targeting dose delivery in mCRPC patients. These two agents are promising RLT agents for personalized treatment of mCRPC. Further studies with increased dose and frequency of RLT are warranted to evaluate the potential therapeutic efficacy., Trial Registration: 177 Lu-P17-087/ 177 Lu-P17-088 in Patients with Metastatic Castration-resistant Prostate Cancer (NCT05603559, Registered at 25 October, 2022). URL OF REGISTRY: https://classic., Clinicaltrials: gov/ct2/show/NCT05603559 ., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Purpose: This is a first-in-human study to evaluate the radiation dosimetry of a new prostate-specific membrane antigen (PSMA)-targeted radiopharmaceutical, [ 18 F]AlF-P16-093, and also initial investigation of its ability to detect PSMA-positive tumors using PET scans in a cohort of prostate cancer (PCa) patients., Methods: The [ 18 F]AlF-P16-093 was automatically synthesized with a GE TRACERlab. A total of 23 patients with histopathologically proven PCa were prospectively enrolled. Dosimetry and biodistribution study investigations were carried out on a subset of six (6) PCa patients, involving multiple time-point scanning. The mean absorbed doses were estimated with PMOD and OLINDA software., Results: [ 18 F]AlF-P16-093 was successfully synthesized, and radiochemical purity was > 95%, and average labeling yield was 36.5 ± 8.3% (decay correction, n = 12). The highest tracer uptake was observed in the kidneys, spleen, and liver, contributing to an effective dose of 16.8 ± 1.3 μSv/MBq, which was ~ 30% lower than that of [ 68 Ga]Ga-P16-093. All subjects tolerated the PET examination well, and no reportable side-effects were observed. The PSMA-positive tumors displayed rapid uptake, and they were all detectable within 10 min, and no additional lesions were observed in the following multi-time points scanning. Each patient had at least one detectable tumor lesion, and a total of 356 tumor lesions were observed, including intraprostatic, lymph node metastases, bone metastases, and other soft tissue metastases., Conclusions: We report herein a streamlined method for high yield synthesis of [ 18 F]AlF-P16-093. Preliminary study in PCa patients has demonstrated its safety and acceptable radiation dosimetry. The initial diagnostic study indicated that [ 18 F]AlF-P16-093 PET/CT is efficacious and potentially useful for a widespread application in the diagnosis of PCa patients., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Bone metastasis in cancer patients is a major disease advancement for various types of cancer. Previously, [ 68 Ga]Ga-HBED-CC-bisphosphonate ([ 68 Ga]Ga-P15-041) showed excellent bone uptake and efficient detection of bone metastasis in patients. To accommodate different α- or β - -emitting metals for radionuclide therapy, a novel DOTA-HBED-CC-bisphosphonate (P15-073, 1 ) was prepared and the corresponding [ 68 Ga]Ga- 1 and [ 177 Lu]Lu- 1 were successfully synthesized in high yields and purity. Gallium-68 conjugation to HBED-CC at room temperature and lutetium-177 conjugation to DOTA at 95 °C were verified in model compounds through secondary mass confirmation. These bisphosphonates, [ 68 Ga]Ga- 1 and [ 177 Lu]Lu- 1, displayed high binding affinity to hydroxyapatite in vitro . After an iv injection, it showed excellent uptake in the spine of normal mice, and micro-PET/CT imaging of nude mice model of bone metastasis showed high bone uptake in tumor tissue. The results indicated that [ 68 Ga]Ga/[ 177 Lu]Lu- 1 holds promise as a theranostic radioligand agent for managing cancer bone metastases.

Background: Recent advancements in positron emission tomograph (PET) using prostate specific membrane antigen (PSMA)-targeted radiopharmaceuticals have changed the standard of care for prostate cancer patients by providing more accurate information during staging of primary and recurrent disease. [ 68 Ga]Ga-P16-093 is a new PSMA-PET radiopharmaceutical that demonstrated superior imaging performance in recent head-to-head studies with [ 68 Ga]Ga-PSMA-11. To improve the availability of this new PSMA PET imaging agent, [ 18 F]AlF-P16-093 was developed. The 18 F-analog [ 18 F]AlF-P16-093 has been synthesized manually at low activity levels using [ 18 F]AlF 2+ and validated in pre-clinical models. This work reports the optimization of the production of > 15 GBq of [ 18 F]AlF-P16-093 using a custom automated synthesis platform., Results: The sensitivity of the radiochemical yield of [ 18 F]AlF-P16-093 to reaction parameters of time, temperature and reagent amounts was investigated using a custom automated system. The automated system is a low-cost, cassette-based system designed for 1-pot syntheses with flow-controlled solid phase extraction (SPE) workup and is based on the Raspberry Pi Zero 2 microcomputer/Python3 ecosystem. The optimized none-decay-corrected yield was 52 ± 4% (N = 3; 17.5 ± 2.2 GBq) with a molar activity of 109 ± 14 GBq/µmole and a radiochemical purity of 98.6 ± 0.6%. Run time was 30 min. A two-step sequence was used: SPE-purified [ 18 F]F - was reacted with 80 nmoles of freeze-dried AlCl 3 ·6H 2 O at 65 °C for 5 min followed by reaction with 160 nmoles of P16-093 ligand at 40 °C for 4 min in a 1:1 mixture of ethanol:0.5 M pH 4.5 NaOAc buffer. The mixture was purified by SPE (> 97% recovery). The final product formulation (5 mM pH 7 phosphate buffer with saline) exhibited a rate of decline in radiochemical purity of ~ 1.4%/h which was slowed to ~ 0.4%/h when stored at 4 °C., Conclusion: The optimized method using a custom automated system enabled the efficient (> 50% none-decay-corrected yield) production of [ 18 F]AlF-P16-093 with high radiochemical purity (> 95%). The method and automation system are simple and robust, facilitating further clinical studies with [ 18 F]AlF-P16-093., (© 2024. The Author(s).)

Prostate-specific membrane antigen (PSMA) is an excellent target for imaging and radionuclide therapy of prostate cancer. Recently, [ 177 Lu]Lu-PSMA-617 (Pluvicto) was approved by the FDA for radionuclide therapy. To develop hetero-bivalent agents targeting both PSMA and bone metastasis, [ 177 Lu]Lu-P17-079 ([ 177 Lu]Lu-1) and [ 177 Lu]Lu-P17-081 ([ 177 Lu]Lu-2) were prepared. In vivo biodistribution studies of [ 177 Lu]Lu-PSMA-617, [ 177 Lu]Lu-1, and [ 177 Lu]Lu-2 in mice bearing PC3-PIP (PSMA positive) tumor showed high uptake in PSMA-positive tumor (14.5, 14.7, and 11.3% ID/g at 1 h, respectively) and distinctively different bone uptakes (0.52, 6.52, and 5.82% ID/g at 1 h, respectively). PET imaging using [ 68 Ga]Ga-P17-079 ([ 68 Ga]Ga-1) in the same mouse model displayed excellent images confirming the expected dual-targeting to PSMA-positive tumor and bone. Results suggest that [ 177 Lu]Lu-P17-079 ([ 177 Lu]Lu-1) is a promising candidate for further development as a hetero-bivalent radionuclide therapy agent targeting both PSMA expression and bone metastases for the treatment of prostate cancer.

Fibroblast activation protein (FAP) is selectively expressed in tumors and highly important for maintaining the microenvironment in malignant tumors. Radioisotope-labeled FAP inhibitors (FAPIs) were proven to be useful for diagnosis and radionuclide therapy of cancer and are under active clinical investigations. Ga-HBED complex displays a higher in vivo stability constant (log  K GaL : 38.5), compared to that of Ga-DOTA (log  K GaL : 21.3). Such advantage in stability constant suggests that it may be useful for development of alternative FAPI imaging agents. In this study, previously reported [ 68 Ga]Ga-DOTA-FAPI-02 and -04 were converted to the corresponding [ 68 Ga]Ga-HBED-CC-FAPI-02 and -04 derivatives ([ 68 Ga]Ga- 4 , [ 68 Ga]Ga- 5 , [ 68 Ga]Ga- 6 , and [ 68 Ga]Ga- 7 ). It was found that substituting the DOTA chelating group with HBED-CC led to several unique and desirable tumor-targeting properties: (1) robust, fast, and high yield labeling─readily adaptable to a kit formulation; (2) high stabilities in vitro ; (3) excellent FAP binding affinities (IC 50 ranging between 4 and 7 nM) and improved cell uptake and retention (in HT1080 (FAP+) cells); and (4) excellent selective in vivo tumor uptake in nude mice bearing U87MG tumor. It appeared that Ga(III) chelation with HBED-CC improved the in vivo kinetics favoring higher tumor uptake and retention compared to the corresponding Ga-DOTA complex. Out of the four tested ligands the new [ 68 Ga]Ga-HBED-CC-FAPI dimer, [ 68 Ga]Ga- 6 , displayed the best tumor localization properties, and further studies are warranted to demonstrate that it is an alternative FAP imaging agent for cancer patients.

Prostate-specific membrane antigen (PSMA) is a promising target for the diagnosis and radionuclide therapy of prostate cancer. This study reports conversion of a previously reported 68 Ga-imaging agent, [ 68 Ga]Ga-P16-093, to a Lu-177 radionuclide therapeutic agent. Substitution of the HBED-CC metal chelating group with DOTA(GA) 2 led to P17-087 ( 4 ) and P17-088 ( 7 ). Both agents showed excellent PSMA binding affinity (IC 50 = 10-30 nM) comparable to that of recently FDA-approved [ 177 Lu]Lu-PSMA-617 (Pluvicto). Biodistribution studies in PSMA expressing tumor bearing mice showed that [ 177 Lu]Lu- 4 exhibited very high tumor uptake and a fast blood clearance similar to those of [ 177 Lu]Lu-PSMA-617. Conversely, [ 177 Lu]Lu- 7 , containing an albumin binder, extended its blood half-life and exhibited significantly higher uptake and longer tumor residence time than [ 177 Lu]Lu- 4 and [ 177 Lu]Lu-PSMA-617. The switch from chelator HBED-CC to DOTA(GA) 2 and the switch from the imaging isotope gallium-68 to the therapeutic isotope lutetium-177 have successfully transformed a PSMA-targeting agent from diagnosis to promising radionuclide therapeutic agents.

Purpose: Prostate-specific membrane antigen (PSMA) is an important biomarker for molecular imaging and a target for radionuclide therapy of prostate cancer. Recently, U.S. Food and Drug Administration (FDA) has approved [ 68 Ga]Ga-PSMA-11 as a PSMA-targeted positron emission tomography (PET) imaging agent for the diagnosis of prostate cancer. As an alternative PSMA imaging agent, [ 68 Ga]Ga-P16-093 ([ 68 Ga]Ga-PSMA-093) showed excellent blood clearance and rapid tumor uptake, desirable in vivo properties for avidly detecting primary tumor and metastatic lesions in patients. To improve the availability and test the robustness of radiolabeling reaction, eluents of 68 Ga/HCl from different sources of generators were evaluated., Procedures: Commercially available 68 Ge/ 68 Ga generators from Eckert & Ziegler, ITG and iThemba were eluted with varying molarities of hydrochloric acid (0.05-0.6 M, as recommended by each company) and reacted with P16-093 kits. Radiolabeling yields, in vitro stabilities, in vitro cell uptakes and drug release criteria of different preparations were investigated. PET/computed tomography (CT) imaging of prostate cancer patients with [ 68 Ga]Ga-P16-093 produced by using different sources of 68 Ga were performed., Results: Optimized P16-093 kit containing 15 μg of P16-093 (precursor) and 68 mg of sodium acetate trihydrate (buffer), a formulation previously tested in humans, was successfully labeled with eluents from Eckert & Ziegler, ITG and iThemba's generators. In vitro cell uptake studies showed that [ 68 Ga]Ga-P16-093, formulated with ITG and iThemba's generators, exhibited equivalent PSMA-specific uptakes. Clinical studies in prostate cancer patients exhibited exceedingly comparable maximum standardized uptake value (SUVmax) for each lesion regardless of source of the generator used in preparation., Conclusion: Using different vendors' generator and lyophilized P16-093 kits, [ 68 Ga]Ga-P16-093 could be conveniently and reliably prepared by a simple one-step reaction with excellent yields. Clinically useful doses of [ 68 Ga]Ga-P16-093 imaging tracer could be made available using different 68 Ge/ 68 Ga generators., Competing Interests: Declaration of competing interest Hank F. Kung is the president and founder of Five Eleven Pharma Inc. Karl Ploessl and Zhihao Zha are employees of Five Eleven Pharma Inc., which holds the patent rights for [(68)Ga]Ga-P16-093 and related technology. Other authors have no conflicts of interest or relevant financial activities to disclose., (Copyright © 2021. Published by Elsevier Inc.)

[ 18 F]AV-45 (florbetapir f18, Amyvid) is an FDA-approved PET imaging agent targeting Aβ plaques in the brain for diagnosis of Alzheimer's disease (AD). Its metabolites led to a high background in the brain and large bone uptake of [ 18 F]F - , produced from dealkylation of the PEG chain. To slow down the in vivo metabolism, we report the design, synthesis, and evaluation of a highly deuterated derivative, [ 18 F]D15FSP, and compared it with N -methyl-deuterated [ 18 F]D3FSP and nondeuterated [ 18 F]AV-45. D15FSP displayed excellent binding affinity ( K i = 7.52 nM) to Aβ aggregates. In vitro autoradiography of [ 18 F]D15FSP, [ 18 F]D3FSP, and [ 18 F]AV-45 showed excellent binding to Aβ plaques in human AD brain sections. Biodistribution studies displayed lower bone uptake at 120 min for [ 18 F]D15FSP compared to that for [ 18 F]D3FSP and [ 18 F]AV-45 (1.44 vs 4.23 and 4.03%ID/g, respectively). As the highly deuterated [ 18 F]D15FSP displayed excellent Aβ binding affinity, high initial brain penetration, and lower bone retention, it might be suitable for PET imaging in detecting Aβ plaques., Competing Interests: The authors declare no competing financial interest., (© 2021 American Chemical Society.)

Prostate-specific membrane antigen (PSMA)-targeted radioligands have played an increasing role in the diagnosis of prostate cancer. [ 68 Ga]Ga-P16-093 is a PSMA-targeting agent for positron emission tomography imaging, currently under a Phase 2 clinical trial. In the present study, P16-093 was labeled with 18 F via [ 18 F]AlF 2+ complex formation, and the biological properties of [ 18 F]AlF-P16-093 were evaluated. Optimization of radiolabeling efficiency was performed by testing a series of parameters, including the amount of free ligand; the amount of Al 3+ ; and the influence of solvent, pH, temperature, reaction time, and reaction volume. Optimal labeling results were achieved at pH 5 by reacting at 60 °C for 15 min in a vial containing 74-370 MBq of [ 18 F]fluoride, 46 nmol of P16-093, 40 nmol of AlCl 3 ·6 H 2 O, and 50% EtOH. [ 18 F]AlF-P16-093 was prepared with a non-decay-corrected radiochemical yield of 54.4 ± 4.4% ( n = 9) within 30 min (final radiochemical purity ≥95%). In vitro, [ 18 F]AlF-P16-093 showed PSMA-specific high uptakes in PIP-PC3 cells. The binding affinity of [ 18 F]AlF-P16-093 to PSMA was determined as K d of 12.4 ± 2.0 nM. The tumor uptake in mice with a xenografted PSMA-expressing PIP-PC3 tumor was high (18.8 ± 5.14% ID/g at 1 h postinjection) and retained without washout for 2 h. In addition, tumor uptake was almost completely blocked by coinjecting a PSMA inhibitor, 2-PMPA. The bone activity at 1 h post injection was higher with [ 18 F]AlF-P16-093 (2.83 ± 0.49% ID/g) in comparison to that of [ 68 Ga]Ga-P16-093 (0.26 ± 0.07% ID/g). In summary, an efficient and simple radiosynthesis of [ 18 F]AlF-P16-093 was achieved. [ 18 F]AlF-P16-093 showed desirable in vivo pharmacokinetics and excellent PSMA-targeting properties for imaging PSMA expression in prostate cancer.

One of the commonly performed studies in nuclear medicine are bone scans with [ 99m Tc]Tc-methylene diphosphonate (MDP) for detecting various bone lesions, including cancer metastasis. The recent emergence of commercially available 68 Ge/ 68 Ga radionuclide generators makes it possible to provide 68 Ga-labelled bisphosphonates as positron emission tomography (PET) tracers for bone imaging. Preliminary human studies suggested that [ 68 Ga]Ga-HBED-CC-BP ([ 68 Ga]Ga-P15-041) in conjunction with PET/computed tomography (CT) showed accumulation in known bone lesions, fast clearance from blood and soft tissue, and an ability to provide high contrast images. A simple and efficient lyophilized P15-041 kit formulation for the rapid production of [ 68 Ga]Ga-P15-041 with excellent radiochemical purity (RCP) under ambient temperature without the need for purification is described. It is demonstrated that clinical doses of [ 68 Ga]Ga-P15-041 can be prepared manually within minutes with an excellent purity (> 90%) and readily meet the dose release criteria. When [ 68 Ga]Ga-P15-041 was evaluated in a patient with cancer, the imaging agent clearly showed accumulations in multiple lesions. In conclusion, [ 68 Ga]Ga-P15-041, prepared by a lyophilized kit, might be an excellent bone imaging agent for widespread clinical application., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Introduction: Since the approval of three 18 F labeled β-amyloid-targeting PET imaging agents, Amyvid (florbetapir f18, AV-45), Neuraceq (florbetaben f18, AV-1) and Vizamyl (flutemetamol f18, F-PIB), they have increasingly been employed to assist differential diagnosis of Alzheimer's disease in patients with dementia. Also, they are frequently used in selecting patients participating drug trials aiming to reduce β-amyloid (Aβ) plaques in the brain. The first approved tracer in this class was [ 18 F]AV-45, which is metabolized rapidly in blood and some of its N-demethylated metabolites cross the blood brain barrier and resulted in lowering the image contrast. To improve metabolic stability of [ 18 F]AV-45, we hypothesized that substituting N-CH 3 with N-CD 3 at the metabolically labile position, creating [ 18 F]D3FSP, may reduce in vivo N-demethylation. We report the preclinical evaluation of [ 18 F]D3FSP as an Aβ imaging agent., Methods: Preclinical pharmacology of [ 18 F]D3FSP was evaluated using in vitro autoradiography and competitive binding assay. Biodistribution of [ 18 F]D3FSP was evaluated in wild-type CD-1 mice. In vivo metabolism in mice and in vitro microsomal metabolism were analyzed by HPLC. Single dose acute toxicity of D3FSP was also performed in rats., Results: [ 18 F]D3FSP showed high binding affinity to β-amyloid plaques (Ki = 3.44 ± 1.22 nM, a value similar as AV-45 (Ki = 4.02 ± 0.22 nM)), and displayed excellent β-amyloid binding in AD brain sections consistent with known Aβ regional distribution. After an iv injection it exhibited good initial brain uptake and fast washout in wild-type CD-1 mice. In vitro microsomal metabolism and in vivo metabolism in mice did not result in any significant differences between [ 18 F]D3FSP and [ 18 F]AV-45. No treatment-related mortality or any adverse effects were observed in single dose acute toxicity studies administered at hundred-folds of maximum human dose., Conclusion: A new small molecule, [ 18 F]D3FSP, was prepared and tested as an alternative to [ 18 F]AV-45 to reduce N-demethylation in vivo. This strategy did not lead to better in vivo stability. However, [ 18 F]D3FSP displayed very similar Aβ targeting property comparable to [ 18 F]AV-45. Preclinical studies suggest that [ 18 F]D3FSP is useful as a β-amyloid-targeting PET imaging agent., (Copyright © 2020. Published by Elsevier Inc.)

Prostate-specific membrane antigen (PSMA) is overexpressed in prostate cancer cells and therefore is an attractive target for prostate cancer diagnosis and radionuclide therapy. Recently, published results from clinical studies using a new PSMA-targeting PET imaging agent, [ 68 Ga]Ga-PSMA-093 ([ 68 Ga]Ga-HBED-CC- O -carboxymethyl-Tyr-CO-NH-Glu), support the development of this agent for the diagnosis of prostate cancer. In this study, the HBED-CC chelating group in PSMA-093 was replaced by stereoselective ( R )- or ( S )-DOTAGA. This chelating group serves not only for chelating 68 Ga but is also amendable for complexing other radioactive metals for radionuclide therapy. The corresponding optically pure ( R )- and ( S )-[ 68 Ga/ 177 Lu]-DOTAGA derivatives, ( R )-[ 68 Ga/ 177 Lu]- 13 and ( S )-[ 68 Ga/ 177 Lu]- 13 , were successfully prepared. Comparison of radiolabeling, binding affinity, cell uptake, and biodistribution between the two isomers was performed. Radiolabeling of ( R )-[ 177 Lu]Lu- 13 and ( S ) - [ 177 Lu]Lu- 13 at 50 °C suggested that rates of complex formation were time-dependent and the formation of ( S )-[ 177 Lu]Lu- 13 was distinctly faster. The rates of complex formation for the corresponding 68 Ga agents were comparable between structural isomers. The nat Ga and nat Lu equivalents showed high binding PSMA affinity (IC 50 = 24-111 nM), comparable to that of the parent agent, [ nat Ga]Ga-PSMA-093 (IC 50 = 34.0 nM). Results of cell uptake and biodistribution studies in PSMA-expressing PC3-PIP tumor-bearing mice appeared to show no difference between the labeled ( R )- and ( S )-isomers. This is the first time that a pair of [ 68 Ga/ 177 Lu]-( R )- and ( S )-DOTAGA isomers of PSMA agents were evaluated. Results of biological studies between the isomers showed no noticeable difference; however, the distinctions on the rate of Lu complex formation should be considered in the development of new 177 Lu-DOTAGA-based radionuclide therapy agents in the future.

Positron emission tomography (PET) imaging using 68 Ga-labeled bisphosphonates to target bone metastasis could be a valuable tool in cancer diagnosis and monitoring therapeutic treatment. A 68 Ga labeled ligand, N , N' -bis[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine- N , N' -diacetic acid (HBED-CC) containing one bisphosphonate group (HBED-CC-BP, 1 ) was prepared and evaluated. The new ligand, 1 , reacted rapidly to form [ 68 Ga]Ga- 1 , via complexing with [ 68 Ga]GaCl 3 eluted from a commercially available 68 Ge/ 68 Ga generator (in a sodium acetate buffer at pH 4, reaching >95% labeling yield at room temperature in 5 min). The resulting [ 68 Ga]Ga- 1 showed excellent stability in vitro and in vivo . [ 68 Ga]Ga- 1 displayed high binding affinity to hydroxyapatite and good uptake in the tibia and femur bone of normal mice. Biodistribution and MicroPET imaging studies of [ 68 Ga]Ga- 1 in normal mice and rats showed excellent bone uptake and retention comparable to that of Na[ 18 F]F. The results suggested that [ 68 Ga]Ga- 1 might be suitable as a bone imaging agent in humans and it could be useful as a convenient alternative to the current bone imaging PET agent, Na[ 18 F]F, without the need of a near-by cyclotron. Also, an automated synthesis module was developed to produce clinical doses of [ 68 Ga]Ga- 1 in a consistent and reproducible manner. Currently, the investigation new drug application (IND) for [ 68 Ga]Ga-HBED-CC-BP, [ 68 Ga]Ga- 1 , has received FDA approval, and it is currently under clinical trial (IND #129870).

Radioligand therapy (RLT) using prostate-specific membrane antigen (PSMA) targeting ligands is an attractive option for the treatment of Prostate cancer (PCa) and its metastases. We report herein a series of radioiodinated glutamate-urea-lysine-phenylalanine derivatives as new PSMA ligands in which l-tyrosine and l-glutamic acid moieties were added to increase hydrophilicity concomitant with improvement of in vivo targeting properties. Compounds 8, 15, 19a/19b and 23a/23b were synthesized and radiolabeled with 125 I by iododestannylation. All iodinated compounds displayed high binding affinities toward PSMA (IC 50  = 1-13 nM). In vitro cell uptake studies demonstrated that compounds containing an l-tyrosine linker moiety (8, 15 and 19a/19b) showed higher internalization than MIP-1095 and 23a/23b, both without the l-tyrosine linker moiety. Biodistribution studies in mice bearing PC3-PIP and PC3 xenografts showed that [ 125 I]8 and [ 125 I]15 with higher lipophilicity exhibited higher nonspecific accumulations in the liver and intestinal tract, whereas [ 125 I]19a/19b and [ 125 I]23a/23b containing additional glutamic acid moieties showed higher accumulations in the kidney and implanted PC3-PIP (PSMA+) tumors. [ 125 I]23b displayed a promising biodistribution profile with favorable tumor retention, fast clearance from the kidney, and 2-3-fold lower uptake in the liver and blood than that observed for [ 125 I]MIP-1095. [ 125/131 I]23b may serve as an optimal PSMA ligand for radiotherapy treatment of prostate cancer over-expressing PSMA., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

We report initial experience in synthesis of (2S,4R)-4-[ 18 F]fluoroglutamine, [ 18 F]FGln, which has been used as a tool for monitoring glutamine metabolism in cancer patients. [ 18 F]FGln was prepared by a fully automated PET-MF-2V-IT-I synthesizer under GMP-compliant conditions for routine clinical studies. The total radiosynthesis time was about 65 minutes, the decay-corrected radiochemical yield was 18.0 ± 4.2% (n = 59; failure n = 15), and the radiochemical purity was greater than 90%. In some situations, the yields were low (less than 5%), and the most likely cause of this problem is the initial fluorination step; the fluoride ion might not have been fully activated. In other occasions, low final radiochemical purity was often associated with the failure of the second step-removal of protection groups by anhydrous trifluoroacetic acid. A trace amount of water led to production of undesired 4-[ 18 F]fluoroglutamic acid. Knowledge learned from the successes and failures of synthesis may be helpful to identify critical steps and pitfalls for preparation of this clinically useful metabolic probe, [ 18 F]FGln, for imaging glutamine utilization in tumor of cancer patients., (© 2019 John Wiley & Sons, Ltd.)

Objectives: Recently, a deuterated tracer, D6-[ 18 F]FP-(+)-DTBZ, 9-O-hexadeutero-3-[ 18 F]fluoropropoxyl-(+)-dihydrotetrabenazine ([ 18 F]9), targeting vesicular monoamine transporter 2 (VMAT2) in the central nervous system, was reported as a useful imaging agent for the diagnosis of Parkinson's disease (PD). The production of [ 18 F]9 was optimized and simplified by using solid-phase extraction (SPE) purification., Methods: Three major nonradioactive impurities were synthesized and characterized. The preparation of [ 18 F]9 was optimized by using different labeling conditions, and an SPE purification method was evaluated. The influence of chemical impurities in the final dose of [ 18 F]9 was assessed by an in vitro binding assay, an assay of the in vivo biodistribution in mice, and ex vivo and in vitro autoradiography of brain sections., Results: Optimized fluorination conditions for [ 18 F]9 were found - heating at 130 °C for 10 min in DMSO, and a high radiochemical yield and three major chemical impurities were observed. An SPE method involving a Sep-Pak® tC18 Plus Light cartridge with a two-step elution process was successfully implemented. This process gave a good radiochemical yield (38.7 ± 10.5%, decay corrected; radiochemical purity >99%) and low chemical impurities. An in vivo biodistribution study and autoradiography of brain sections showed that there was no significant difference between HPLC-purified and SPE-purified [ 18 F]9., Conclusion: A VMAT2 targeting imaging agent, D6-[ 18 F]FP-(+)-DTBZ, [ 18 F]9, was prepared by optimized labeling conditions and an easy SPE purification. This method offers a short preparation time and operational simplicity. In conjunction with PET imaging, this new VMAT2 agent might be a useful clinical tool for diagnosing PD., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Introduction: Alzheimer's disease is a common neurodegenerative disease that is characterized by the presence of Aβ plaques in the brain. The FDA has approved the use of Amyvid (florbetapir f18, AV-45) as a PET imaging agent for detecting Aβ plaques in the living human brain. In an attempt to reduce N-demethylation in vivo by taking advantage of more stable C-D bonds, an analog of AV-45, [ 18 F]D3FSP ([ 18 F]7), was synthesized to improve image contrast for detecting and monitoring the Aβ plaques. A convenient and improved preparation of [ 18 F]D3FSP ([ 18 F]7) is needed for widespread clinical application. We report herein the optimization of the radiosynthesis and solid-phase extraction (SPE) procedure., Methods: Radiosyntheses of [ 18 F]D3FSP ([ 18 F]7) under different fluorination conditions were evaluated, and the intermediate, containing an N-Boc protecting group, was deprotected using different acids. One of the major objectives was to simplify the final purification step via SPE to avoid the commonly employed HPLC purification and maximize the radiochemical yields of [ 18 F]D3FSP ([ 18 F]7) while simultaneously removing several chemical impurities (pseudocarriers). Washing various solid-phase cartridges with different combinations of ethanol/water and acetonitrile/water was explored to optimize the purification step. To evaluate the potential interference in Aβ plaques imaging from the presence of pseudocarriers, each chemical was identified and quantified by LC/MS and HPLC. An in vitro binding assay was employed to evaluate the binding affinities of [ 18 F]D3FSP ([ 18 F]7) and the pseudocarriers to Aβ plaques using postmortem AD brain tissue., Results: Using the optimized radiosynthesis method and SPE purification, the final dose of [ 18 F]D3FSP ([ 18 F]7) was obtained in 50 min with a very low content of pseudocarriers (21.7 ± 5.5 μg). The radiochemical yield was 44.4 ± 5.7% (decay corrected), and the radiochemical purity was >95%. SPE-purified doses of [ 18 F]D3FSP ([ 18 F]7) displayed excellent binding affinity and specificity for Aβ plaques as measured in an in vitro binding assay using AD brain homogenates, and the OH-pseudocarrier, 8 (K i  = 19.5 ± 0.5 nM), and the Cl-pseudocarrier, 10 (K i  = 18.6 ± 3.9 nM), showed lower binding affinities for Aβ plaques than those of AV-45 (K i  = 8.6 ± 0.5 nM) and D3FSP, 7 (K i  = 9.8 ± 0.5 nM)., Conclusions: An optimized radiosynthesis and fast SPE purification method suitable for the preparation of clinical doses of [ 18 F]D3FSP ([ 18 F]7) was accomplished. The results of quality control tests and binding studies suggested that the SPE-purified doses of [ 18 F]D3FSP ([ 18 F]7) are appropriate for imaging Aβ plaques in the human brain., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Objectives: Serotonin transporters (SERT) play an important role in controlling serotonin concentration in the synaptic cleft and in managing postsynaptic signal transduction. Inhibitors of SERT binding are well known as selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine, sertraline, paroxetine, and escitalopram, that are commonly prescribed antidepressants. Positron emission tomography (PET) and single photon emission tomography (SPECT) imaging agents targeting SERT may be useful for studying its function and providing a tool for monitoring drug treatment., Methods: A series of novel 18 F-labeled diphenyl sulfide derivatives were prepared and tested for their binding affinity. Among them, 2-((2-((dimethylamino)-methyl)-4-(2-(2-fluoroethoxy)ethoxy)phenyl)thio)aniline, 1, which showed excellent binding toward serotonin transporter (SERT) in the brain (K i  = 0.09 nM), was selected for further evaluation. An active OTs intermediate, 7, was treated with [ 18 F]F - /K 222 to provide [ 18 F]1 in one step and in high radiochemical yields. This new SERT targeting agent was evaluated in rats by biodistribution studies and animal PET imaging studies., Results: The radiolabeling reaction led to the desired [ 18 F]1. After HPLC purification no-carrier-added [ 18 F]1 was obtained (radiochemical yield, 23-47% (n = 10,); radiochemical purity >99%; molar activity, 15-28 GBq/μmol). Biodistribution studies with [ 18 F]1 showed good brain uptake (1.04% dose/g at 2 min post-injection), high uptake into the hypothalamus (1.55% dose/g at 30 min), and a high target-to-non-target (hypothalamus to cerebellum) ratio of 6.1 at 120 min post-injection. A PET imaging study in normal rats showed excellent uptake in the midbrain and thalamus regions known to be rich in SERT binding sites at 60 min after iv injection. Chasing experiment with escitalopram (iv, 2 mg/kg) in a rat at 60 min after iv injection caused a noticeable reduction in the regional radioactivity and the target-to-non-target ratio, suggesting binding by [ 18 F]1 was highly specific and reversible for SERT binding sites in the brain., Conclusions: A novel diphenyl sulfide derivative, [ 18 F]1 for SERT imaging was successfully prepared and evaluated. Results suggest that this new chemical entity is targeting SERT binding sites in the brain, and it is a suitable candidate for future commercial development., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Introduction: Glutamine is an essential source of energy, metabolic substrates, and building block for supporting tumor proliferation. Previously, (2S,4R)-4-[ 18 F]fluoroglutamine (4F-Gln) was reported as a glutamine-related metabolic imaging agent. To improve the in vivo kinetics of this radiotracer, two new dipeptides, [ 18 F]Gly-(2S,4R)4-fluoroglutamine (Gly-4F-Gln) and [ 18 F]Ala-(2S,4R)4-fluoroglutamine (Ala-4F-Gln) were investigated., Methods: Radiolabeling was performed via 2-steps 18 F-fluorination. Cell uptake studies of Gly-4F-Gln and Ala-4F-Gln were investigated in 9 L cell lines. In vitro and in vivo metabolism studies were carried out in Fisher 344 rats. Biodistribution and microPET imaging studies were performed in 9 L tumor-bearing rats., Results: In vitro incubation of these [ 18 F]dipeptides in rat and human blood showed a rapid conversion to (2S,4R)-4-[ 18 F]fluoroglutamine (t 1/2  = 2.3 and 0.2 min for [ 18 F]Gly-4F-Gln and [ 18 F]Ala-4F-Gln, respectively for human blood). Biodistribution and PET imaging in Fisher 344 rats bearing 9 L tumor xenografts showed that these dipeptides rapidly localized in the tumors, comparable to that of (2S,4R)-4-[ 18 F]fluoroglutamine (4F-Gln)., Conclusions: The results support that these dipeptides, [ 18 F]Gly-4F-Gln and [ 18 F]Ala-4F-Gln, are prodrugs, which hydrolyze in the blood after an iv injection. They appear to be selectively taken up and trapped by tumor tissue in vivo. The dipeptide, [ 18 F]Ala-4F-Gln, may be suitable as a PET tracer for imaging glutaminolysis in tumors., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Introduction: Prostate specific membrane antigen (PSMA) is a well-established target for diagnostic and therapeutic applications for prostate cancer. It is know that [ 68 Ga]PSMA 11 ([ 68 Ga]Glu-NH-CO-NH-Lys(Ahx)-HBED-CC) is the most well studied PET imaging agent for detecting over expressed PSMA binding sites of tumors in humans. In an effort to provide new agents with improved characteristics for PET imaging, we report a novel [ 68 Ga]-Glu-NH-CO-NH-Lys(Ahx)-linker-HBED-CC conjugate with a novel O-(carboxymethyl)-L-tyrosine, as the linker group., Methods: Radiosynthesis was performed by a direct method. In vitro binding and cell internalization of [ 68 Ga]10 was investigated in PSMA positive LNCaP cell lines. Biodistribution and MicroPET imaging studies were performed in LNCaP tumor bearing mice., Results: In vitro binding to LNCaP cells showed that nat Ga labeled O-(carboxymethyl)-L-tyrosine conjugate, [ nat Ga]10, displayed excellent affinity and specificity (IC 50  = 16.5 nM) a value comparable to that of PSMA 11. In vitro cell binding and internalization showed excellent uptake and retention; [ 68 Ga]10 displayed significantly higher cellular internalization than [ 68 Ga]PSMA 11 (12.5 vs 7.4% ID/10 6 cells at 1 h). Biodistribution studies in LNCaP tumor-bearing mice exhibited a high specific uptake in PSMA expressing tumors and fast clearance in normal organs (19.7 tumor/blood; 20.7 tumor/muscle at 1 h after iv injection). MicroPET imaging studies in mice confirmed that [ 68 Ga]10 displayed excellent uptake and distinctive tumor localization, which was blocked by iv injection of a competing drug, 2-PMPA., Conclusions: The preliminary results strongly suggest that [ 68 Ga]10 may be promising candidates as a PET imaging radiotracer for detecting PSMA expression in prostate cancer., (Copyright © 2018. Published by Elsevier Inc.)

Introduction: Vesicular monoamine transporters 2 (VMAT2) in the brain serve as transporter for packaging monoamine in vesicles for normal CNS neurotransmission. Several VMAT2 imaging agents, [ 11 C]-(+)-DTBZ, dihydrotetrabenazine and [ 18 F]FP-(+)-DTBZ (9-O-fluoropropyl-(+)-dihydro tetrabenazine, a.k.a. [ 18 F]AV-133), are useful for studying the changes in brain function related to monoamine transmission by in vivo imaging. Deuterated analogs have been reported targeting VMAT2 binding sites., Methods: A novel deuterated [ 18 F]9-O-hexaduterofluoropropyl-(+)-dihydrotetrabenazine, [ 18 F]D6-FP-(+)-DTBZ, [ 18 F]1, was prepared as a VMAT2 imaging agent. This 18 F agent which targeted VMAT2 was evaluated by in vitro binding, in vivo biodistribution and microPET imaging studies in rodents., Results: The one step radiolabeling reaction led to the desired [ 18 F]D6-FP-(+)-DTBZ, [ 18 F]1, which showed excellent binding affinity to VMAT2 (Ki=0.32±0.07nM) comparable to that of FP-(+)-DTBZ (Ki=0.33±0.02nM) using [ 18 F]FP-(+)-DTBZ and rat striatum membrane homogenates. In vivo biodistribution in normal rats showed that 1, exhibited excellent brain uptake and comparable high ratio of striatum to cerebellum (target/background) ratio at 1h after injection (ratio of 6.05±0.43 vs 5.66±0.72 for [ 18 F]FP-(+)-DTBZ vs [ 18 F]1, respectively). MicroPET imaging studies in rats further confirm that the striatum with high VMAT2 concentration was clearly delineated in normal rat brain after iv injection of [ 18 F]1. We observed minor changes of metabolism in rat plasma between these two agents; however, the changes showed little effect on regional brain uptake and retention., Conclusions: The results reported here lend support for using [ 18 F]D6-FP-(+)-DTBZ, [ 18 F]1, as in vivo PET imaging agent for VMAT2 binding in the brain., (Copyright © 2017. Published by Elsevier Inc.)

Glucose and glutamine are the most abundant nutrients for producing energy and building blocks in normal and tumor cells. Increased glycolysis in tumors, the Warburg Effect, is the basis for 18 F-FDG PET imaging. Cancer cells can also be genetically reprogrammed to use glutamine. 5- 11 C-(2 S )-glutamine and 18 F-(2 S ,4 R )4-fluoroglutamine may be useful complementary tools to measure changes in tumor metabolism. In glioma patients, the tracer 18 F-(2 S ,4 R )4-fluoroglutamine showed tumor-to-background contrast different from that of 18 F-FDG and differences in uptake in glioma patients with clinical progression of disease versus stable disease (tumor-to-brain ratio > 3.7 in clinically active glioma tumors, minimal or no specific uptake in clinically stable tumors). These preliminary results suggest that 18 F-(2 S ,4 R )4-fluoroglutamine PET may be a new tool for probing in vivo metabolism of glutamine in cancer patients and for guiding glutamine-targeted therapeutics. Further studies of uptake mechanism, and comparison of kinetics for 18 F-(2 S ,4 R )4-fluoroglutamine versus the 11 C-labeled native glutamine, will be important and enlightening., (© 2017 by the Society of Nuclear Medicine and Molecular Imaging.)

Glutaminolysis is a metabolic pathway adapted by many aggressive cancers, including triple-negative breast cancers (TNBC), to utilize glutamine for survival and growth. In this study, we examined the utility of [ 18 F](2S,4R)4-fluoroglutamine ([ 18 F]4F-Gln) PET to measure tumor cellular glutamine pool size, whose change might reveal the pharmacodynamic (PD) effect of drugs targeting this cancer-specific metabolic pathway. High glutaminase (GLS) activity in TNBC tumors resulted in low cellular glutamine pool size assayed via high-resolution 1 H magnetic resonance spectroscopy (MRS). GLS inhibition significantly increased glutamine pool size in TNBC tumors. MCF-7 tumors, with inherently low GLS activity compared with TNBC, displayed a larger baseline glutamine pool size that did not change as much in response to GLS inhibition. The tumor-to-blood-activity ratios (T/B) obtained from [ 18 F]4F-Gln PET images matched the distinct glutamine pool sizes of both tumor models at baseline. After a short course of GLS inhibitor treatment, the T/B values increased significantly in TNBC, but did not change in MCF-7 tumors. Across both tumor types and after GLS inhibitor or vehicle treatment, we observed a strong positive correlation between T/B values and tumor glutamine pool size measured using MRS ( r 2 = 0.71). In conclusion, [ 18 F]4F-Gln PET tracked cellular glutamine pool size in breast cancers with differential GLS activity and detected increases in cellular glutamine pool size induced by GLS inhibitors. This study accomplished the first necessary step toward validating [ 18 F]4F-Gln PET as a PD marker for GLS-targeting drugs. Cancer Res; 77(6); 1476-84. ©2017 AACR ., (©2017 American Association for Cancer Research.)

Two 4-fluoro-L-glutamine diastereoisomers [(2 S ,4 R )-4-FGln, (2 S ,4 S )-4-FGln] were previously developed for positron emission tomography. Label uptake into two tumor cell types was greater with [ 18 F](2 S ,4 R )-4-FGln than with [ 18 F](2 S ,4 S )-4-FGln. In the present work we investigated the enzymology of two diastereoisomers of 4-FGln, two diastereoisomers of 4-fluoroglutamate (4-FGlu) (potential metabolites of the 4-FGln diastereoisomers) and another fluoro-derivative of L-glutamine [(2 S ,4 S )-4-(3-fluoropropyl)glutamine (FP-Gln)]. The two 4-FGlu diastereoisomers were found to be moderate-to-good substrates relative to L-glutamate of glutamate dehydrogenase, aspartate aminotransferase and alanine aminotransferase. Additionally, alanine aminotransferase was shown to catalyze an unusual γ-elimination reaction with both 4-FGlu diastereoisomers. Both 4-FGlu diastereoisomers were shown to be poor substrates, but strong inhibitors of glutamine synthetase. Both 4-FGln diastereoisomers were shown to be poor substrates compared to L-glutamine of glutamine transaminase L and α-aminoadipate aminotransferase. However, (2 S ,4 R )-4-FGln was found to be a poor substrate of glutamine transaminase K, whereas (2 S ,4 S )-4-FGln was shown to be an excellent substrate. By contrast, FP-Gln was found to be a poor substrate of all enzymes examined. Evidently, substitution of H in position 4 by F in L-glutamine/L-glutamate has moderate-to-profound effects on enzyme-catalyzed reactions. The present results: 1) show that 4-FGln and 4-FGlu diastereoisomers may be useful for studying active site topology of glutamate- and glutamine-utilizing enzymes; 2) provide a framework for understanding possible metabolic transformations in tumors of 18 F-labeled (2 S ,4 R )-4-FGln, (2 S ,4 S )-4-FGln, (2 S ,4 R )-4-FGlu or (2 S ,4 S )-4-FGlu; and 3) show that [ 18 F]FP-Gln is likely to be much less metabolically active in vivo than are the [ 18 F]4-FGln diastereoisomers., Competing Interests: The authors declare no conflict of interest

Aromatase (CYP19) is a rate-limiting enzyme that catalyzes the biosynthesis of estrogens. Imaging agents based on aromatase inhibitors (AIs) have been developed for a PET/SPECT study. A series of compounds was synthesized based on YM511, which has previously been used for breast cancer treatment. Two examples of these derivatives, 4-(((4-iodophenyl)methyl)-4H-1,2,4-triazol-4-yl-amino)-benzonitrile (5) and 4-((1H-imidazol-1-yl)(4-iodobenzyl)amino)benzonitrile (11), displayed potent binding affinities to human aromatase (IC 50 = 0.17 and 0.04 nM, respectively). Biodistribution and autoradiographic studies revealed that [ 125 I]5 and [ 125 I]11 were highly accumulated in the stomach (16.21 and 10.88% dose/g, respectively) and ovaries (8.56 and 3.32% dose/g, respectively) of female rats. Log P of [ 125 I]5 was 2.49, meaning good brain penetration. Autoradiograms of brain sections showed a high uptake in the bed nucleus of the stria terminalis and amygdala. These results suggest that [ 125 I]5 and [ 125 I]11 are potent probes for aromatase imaging in both the brain and peripheral organs.

Serotonin transporters (SERT) in the brain play an important role in normal brain function. Selective serotonin reuptake inhibitors such as fluoxetine, sertraline, paroxetine, escitalopram, etc., specifically target SERT binding in the brain. Development of SERT imaging agents may be useful for studying the function of SERT by in vivo imaging. A one-step preparation of [(18)F]FPBM, 2-(2'-(dimethylamino)methyl)-4'-(3-([(18)F]fluoropropoxy)phenylthio)benzenamine, for positron emission tomography (PET) imaging of SERT binding in the brain was achieved. An active OTs intermediate, 9, was reacted with [(18)F]F(-)/K222 to produce [(18)F]FPBM in one step and in high radiochemical yield. This labeling reaction was evaluated and optimized under different temperatures, bases, solvents, and varying amounts of precursor 9. The radiolabeling reaction led to the desired [(18)F]FPBM in one step and the crude product was purified by HPLC purification to give no-carrier-added [(18)F]FPBM (radiochemical yield, 24-33%, decay corrected; radiochemical purity >99%). PET imaging studies in normal monkeys (n=4) showed fast, pronounced uptakes in the midbrain and thalamus, regions known to be rich in SERT binding sites. A displacement experiment with escitalopram (5mg/kg iv injection at 30min after [(18)F]FPBM injection) showed a rapid and complete reversal of SERT binding, suggesting that binding by [(18)F]FPBM was highly specific and reversible. A one-step radiolabeling method coupled with HPLC purification for preparation of [(18)F]FPBM was developed. Imaging studies suggest that it is feasible to use this method to prepare [(18)F]FPBM for in vivo PET imaging of SERT binding in the brain., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Aβ plaques deposited on blood vessels are associated with cerebral amyloid angiopathy (CAA). In an effort to selectively map these Aβ plaques, we are reporting a new series of (68)Ga labeled styrylpyridine derivatives with high molecular weights. In vitro binding to Aβ plaques in post-mortem Alzheimer's disease (AD) brain tissue showed that these (68)Ga labeled bivalent styrylpyridines displayed good affinities and specificity (Ki < 30 nM). In vitro autoradiography using post-mortem AD brain sections showed specific binding of these (68)Ga complexes to Aβ plaques. Biodistribution studies in normal mice showed very low initial brain uptakes (<0.3% dose/g) indicating a low blood-brain barrier (BBB) penetration. The preliminary results suggest that (68)Ga labeled bivalent styrylpyridines may be promising candidates as PET imaging radiotracers for detecting CAA.

Glucose and glutamine are the two principal nutrients that cancer cells use to proliferate and survive. Many cancers show altered glucose metabolism, which constitutes the basis for in vivo positron emission tomography (PET) imaging with (18)F-fluorodeoxyglucose ((18)F-FDG). However, (18)F-FDG is ineffective in evaluating gliomas because of high background uptake in the brain. Glutamine metabolism is also altered in many cancers, and we demonstrate that PET imaging in vivo with the glutamine analog 4-(18)F-(2S,4R)-fluoroglutamine ((18)F-FGln) shows high uptake in gliomas but low background brain uptake, facilitating clear tumor delineation. Chemo/radiation therapy reduced (18)F-FGln tumor avidity, corresponding with decreased tumor burden. (18)F-FGln uptake was not observed in animals with a permeable blood-brain barrier or neuroinflammation. We translated these findings to human subjects, where (18)F-FGln showed high tumor/background ratios with minimal uptake in the surrounding brain in human glioma patients with progressive disease. These data suggest that (18)F-FGln is avidly taken up by gliomas, can be used to assess metabolic nutrient uptake in gliomas in vivo, and may serve as a valuable tool in the clinical management of gliomas., (Copyright © 2015, American Association for the Advancement of Science.)

Although the growth and proliferation of most tumors is fueled by glucose, some tumors are more likely to metabolize glutamine. In particular, tumor cells with the upregulated c-Myc gene are generally reprogrammed to utilize glutamine. We have developed new 3-fluoropropyl analogs of glutamine, namely [(18)F](2S,4R)- and [(18)F](2S,4S)-4-(3-fluoropropyl)glutamine, 3 and 4, to be used as probes for studying glutamine metabolism in these tumor cells. Optically pure isomers labeled with (18)F and (19)F (2S,4S) and (2S,4R)-4-(3-fluoropropyl)glutamine were synthesized via different routes and isolated in high radiochemical purity (≥95%). Cell uptake studies of both isomers showed that they were taken up efficiently by 9L tumor cells with a steady increase over a time frame of 120 min. At 120 min, their uptake was approximately two times higher than that of l-[(3)H]glutamine ([(3)H]Gln). These in vitro cell uptake studies suggested that the new probes are potential tumor imaging agents. Yet, the lower chemical yield of the precursor for 3, as well as the low radiochemical yield for 3, limits the availability of [(18)F](2S,4R)-4-(3-fluoropropyl)glutamine, 3. We, therefore, focused on [(18)F](2S,4S)-4-(3-fluoropropyl)glutamine, 4. The in vitro cell uptake studies suggested that the new probe, [(18)F](2S,4S)-4-(3-fluoropropyl)glutamine, 4, is most sensitive to the LAT transport system, followed by System N and ASC transporters. A dual-isotope experiment using l-[(3)H]glutamine and the new probe showed that the uptake of [(3)H]Gln into 9L cells was highly associated with macromolecules (>90%), whereas the [(18)F](2S,4S)-4-(3-fluoropropyl)glutamine, 4, was not (<10%). This suggests a different mechanism of retention. In vivo PET imaging studies demonstrated tumor-specific uptake in rats bearing 9L xenographs with an excellent tumor to muscle ratio (maximum of ∼8 at 40 min). [(18)F](2S,4S)-4-(3-fluoropropyl)glutamine, 4, may be useful for testing tumors that may metabolize glutamine related amino acids.

Single photon emission computed tomography (SPECT) or positron emission computed tomography (PET) imaging agents for neurodegenerative diseases have a significant impact on clinical diagnosis and patient care. The examples of Parkinson's Disease (PD) and Alzheimer's Disease (AD) imaging agents described in this paper provide a general view on how imaging agents, i.e. radioactive drugs, are selected, chemically prepared and applied in humans. Imaging the living human brain can provide unique information on the pathology and progression of neurodegenerative diseases, such as AD and PD. The imaging method will also facilitate preclinical and clinical trials of new drugs offering specific information related to drug binding sites in the brain. In the future, chemists will continue to play important roles in identifying specific targets, synthesizing target-specific probes for screening and ultimately testing them by in vitro and in vivo assays.

Herein, we describe an operationally straightforward radiosynthesis of a chiral transition metal fluoride catalyst, [(18)F](salen)CoF, and its use for late-stage enantioselective aliphatic radiofluorination. We demonstrate the utility of the method by preparing single enantiomer experimental and clinically validated PET tracers that contain base-sensitive functional groups, epimerizable stereocenters, and nitrogen-rich motifs. Unlike the conventional radiosyntheses of these targets with [(18)F]KF, labeling with (salen)CoF is possible in the last step and under exceptionally mild conditions. These results constitute a rare example of a nucleophilic radiofluorination using a transition metal fluoride and highlight the potential of such reagents to enhance traditional methods for labeling aliphatic hydrocarbons.

Introduction: O-(2-[(18)F]fluoroethyl)-L-tyrosine (FET, [(18)F]1) is a useful amino-acid-based imaging agent for brain tumors. This paper reports the synthesis and evaluation of three FET prodrugs, O-(2-[(18)F]fluoroethyl)-L-tyrosyl-L-glycine (FET-Gly, [(18)F]2), O-(2-[(18)F]fluoroethyl)-L-tyrosyl-L-alanine (FET-Ala, [(18)F]3) and N-acetyl O-(2-[(18)F]fluoroethyl)-L-tyrosine (AcFET, [(18)F]4), which could be readily hydrolyzed to FET in vivo for tumor imaging. We investigated their metabolism in the blood and imaging properties in comparison to FET ([(18)F]1)., Methods: Three new [(18)F]FET derivatives, 2-4, were prepared from their corresponding tosylate-precursors through nucleophilic fluorination and subsequent deprotection reactions. In vitro uptake studies were carried out in 9L glioma cancer cell lines. In vitro and in vivo hydrolysis studies were conducted to evaluate the hydrolysis of FET prodrugs in blood and in Fisher 344 rats. Biodistribution and PET imaging studies were then performed in rats bearing 9L tumors., Results: New FET prodrugs were prepared with 3-28% decay corrected radiochemical yields, good enantiomeric purity (>95%) and high radiochemical purity (>95%). FET-Gly ([(18)F]2), FET-Ala ([(18)F]3), and AcFET ([(18)F]4) exhibited negligible uptake in comparison to the high uptake of FET ([(18)F]1) in 9L cells. Metabolism studies of FET-Gly ([(18)F]2), FET-Ala ([(18)F]3), and AcFET ([(18)F]4) in rat and human blood showed that FET-Ala ([(18)F]3) was hydrolyzed to FET ([(18)F]1) faster than FET-Gly ([(18)F]2) or AcFET ([(18)F]4). Most of the FET-Ala (79%) was converted to FET ([(18)F]1) within 5min in blood in vivo. Biodistribution studies demonstrated that FET-Ala ([(18)F]3) displayed the highest tumor uptake. The tumor-to-background ratios of FET-Ala ([(18)F]3) and FET ([(18)F]1) were comparable and appeared to be better than those of FET-Gly ([(18)F]2) and AcFET ([(18)F]4). PET imaging studies showed that both FET ([(18)F]1) and FET-Ala ([(18)F]3) could visualize tumors effectively, and that they share similar imaging characteristics., Conclusions: FET-Ala ([(18)F]3) demonstrated promising properties as a prodrug of FET ([(18)F]1), which could be used in PET imaging of tumor amino acid metabolism., (© 2013.)

Introduction: Biological evaluation of ([(125)I]4), a new single-photon emission computed tomography (SPECT) radioligand for imaging the serotonin transporter (SERT) which displayed improved in vivo kinetics for mapping SERT binding sites in the brain., Methods: In vitro binding studies of [(125)I]4 were performed with membrane homogenates of LLC-PK1 cells stably transfected and overexpressing one of the monoamine transporter (SERT, DAT or NET) and rat cortical homogenates. Biodistribution and ex vivo autoradiography studies were carried out in rats. In vivo competition experiments were evaluated to determine the SERT selectivity of [(125)I]4 vs. ([(125)I]1)., Results: In vitro binding studies of 4 showed excellent binding affinity (Ki,SERT=0.90 ± 0.05 nM) and excellent selectivity over the other monoamine transporters (100 fold and >4000 fold for NET and DAT respectively). Scatchard analysis of saturation binding of [(125)I]4 to rat cortical homogenates gave a Kd value of 0.5 ± 0.09 nM and a Bmax value of 801.4 ± 58.08 fmol/mg protein. The biodistribution study showed rapid high brain uptake (3.09 ± 0.11% dose/organ at 2 min) and a good target to non-target ratio (hypothalamus to cerebellum) at 30 min (2.62) compared to [(125)I]1 (2.19). Ex vivo autoradiography showed that FlipIDAM localizes in accordance with SERT distribution patterns in the brain. In vivo and ex vivo competition experiments with specific and non-specific SERT compounds also showed that [(125)I]4 binds specifically to SERT rich regions., Conclusions: The biological evaluation of [(125)I]4 demonstrates that [(123)I]4 would be a good candidate for SPECT imaging of SERT., (Copyright © 2013. Published by Elsevier Inc.)

New ligands for in vivo brain imaging of serotonin transporter (SERT) with single photon emission tomography (SPECT) were prepared and evaluated. An efficient synthesis and radiolabeling of a biphenylthiol, FLIP-IDAM, 4, was accomplished. The affinity of FLIP-IDAM was evaluated by an in vitro inhibitory binding assay using [(125)I]-IDAM as radioligand in rat brain tissue homogenates (K(i) = 0.03 nM). New [(125)I]Flip-IDAM exhibited excellent binding affinity to SERT binding sites with a high hypothalamus to cerebellum ratio of 4 at 30 min post iv injection. The faster in vivo kinetics for brain uptake and a rapid washout from non-specific regions provide excellent signal to noise ratio. This new agent, when labeled with (123)I, may be a useful imaging agent for mapping SERT binding sites in the human brain., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Unlabelled: (18)F-labeled (2S,4R)-4-fluoro-l-glutamine (4F-GLN) has demonstrated high uptake in tumor cells that undergo high growth and proliferation. Similar tumor targeting properties have also been observed for (18)F-labeled (2S,4R)-4-fluoro-l-glutamate (4F-GLU), suggesting that both are useful imaging agents. A new labeling procedure facilitates the preparation of (18)F-(2S,4R)4F-GLN and (18)F-(2S,4R)4F-GLU with confirmed radiochemical and enantiomeric purity. Here, we report the preparation and comparative evaluation of (18)F-(2S,4R)4F-GLN and (18)F-(2S,4R)4F-GLU as tumor metabolic imaging agents., Methods: Uptake of enantiomerically pure (18)F-(2S,4R)4F-GLN and (18)F-(2S,4R)4F-GLU was determined in 3 tumor cell lines (9L, SF188, and PC-3) at selected time points. The in vitro cell uptake mechanism was evaluated by inhibition studies in 9L cells. In vivo biodistribution and PET studies were performed on male F344 rats bearing 9L tumor xenografts., Results: In vitro cell uptake studies showed that (18)F-(2S,4R)4F-GLN displayed higher uptake than (18)F-(2S,4R)4F-GLU. Amino acid transport system ASC (alanine-serine-cysteine-preferring; in particular, its subtype ASCT2 [SLC1A5 gene]) and system X(c)(-) (SLC7A11 gene) played an important role in transporting (18)F-(2S,4R)4F-GLN and (18)F-(2S,4R)4F-GLU, respectively, across the membrane. After being transported into cells, a large percentage of (18)F-(2S,4R)4F-GLN was incorporated into protein, whereas (18)F-(2S,4R)4F-GLU mainly remained as the free amino acid in its original form. In vivo studies of (18)F-(2S,4R)4F-GLN in the 9L tumor model showed a higher tumor uptake than (18)F-(2S,4R)4F-GLU, whereas (18)F-(2S,4R)4F-GLU had a slightly higher tumor-to-background ratio than (18)F-(2S,4R)4F-GLN. Imaging studies showed that both tracers had fast accumulation in 9L tumors. Compared with (18)F-(2S,4R)4F-GLU, (18)F-(2S,4R)4F-GLN exhibited prolonged tumor retention reflecting its incorporation into intracellular macromolecules., Conclusion: Differences in uptake and metabolism in tumor cells were found between (18)F-(2S,4R)4F-GLN and (18)F-(2S,4R)4F-GLU. Both agents are potentially useful as metabolic tracers for tumor imaging.

Objectives: Recently, 9-[(18)F]fluoropropyl-(+)-dihydrotetrabenazine ((18)F-AV-133) was reported as a new vesicular monoamine transporter (VMAT2) imaging agent for diagnosis of Parkinson's disease (PD). To shorten the preparation of (18)F-AV-133 and to make it more widely available, we evaluated a simple, rapid purification with a solid-phase extraction method (SPE) using an Oasis HLB cartridge instead of high pressure liquid chromatography (HPLC). The SPE method produced doses containing a pseudo-carrier, 9-hydroxypropyl-(+)-dihydrotetrabenazine (AV-149)., Methods: To test the possible side effects of this pseudo-carrier, comparative dynamic PET scans of the brains of normal monkeys (2 each) and uni-laterally 6-OH-dopamine-lesioned PD monkeys (2 each) were performed using (18)F-AV-133 doses prepared by either SPE (containing pseudo-carrier) or HPLC (containing no pseudo-carrier). Autoradiographs of post mortem monkey brain sections were evaluated to confirm the relative (18)F-AV-133 uptake in the PD monkey brains and the effects of the pseudo-carrier on VMAT2 binding., Results: The radiochemical purity of the (18)F-AV-133, whether prepared by SPE or by HPLC, was excellent (>99%). PET scans of normal and PD monkey brains showed an expected reduction of VMAT2 in the lesioned areas of the striatum. It was not affected by the presence of the pseudo-carrier, AV-149 (maximally 250 μg/dose). The reduced uptake in the striatum of the lesioned monkey brains was confirmed by autoradiography. Ex vivo inhibition studies of (18)F-AV-133 binding in rat brains, conducted with increasing amounts of AV-149, suggested that at the highest concentration (3.5mg/kg) the VMAT2 binding in the striatum was only moderately blocked (20% reduction)., Conclusions: The pseudo-carrier, AV-149, did not affect the (18)F-AV-133/PET imaging of VMAT2 binding sites in normal or uni-laterally lesioned monkey brains. The new streamlined SPE purification method will enable (18)F-AV-133 to be widely available for routine clinical application in determining changes in monoamine neurons for patient with movement disorders or other psychiatric illnesses., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Many cancer cells have a strong requirement for glutamine. As an aid for understanding this phenomenon the (18)F-labeled 2S,4R stereoisomer of 4-fluoroglutamine [(2S,4R)4-FGln] was previously developed for in vivo positron emission tomography (PET). In the present work, comparative enzymological studies of unlabeled (2S,4R)4-FGln and its deamidated product (2S,4R)4-FGlu were conducted as an adjunct to these PET studies. Our findings are as follows: Rat kidney preparations catalyze the deamidation of (2S,4R)4-FGln. (2,4R)4-FGln and (2S,4R)4-FGlu are substrates of various aminotransferases. (2S,4R)4-FGlu is a substrate of glutamate dehydrogenase, but not of sheep brain glutamine synthetase. The compound is, however, a strong inhibitor of this enzyme. Rat liver cytosolic fractions catalyze a γ-elimination reaction with (2S,4R)4-FGlu, generating α-ketoglutarate. Coupling of a deamidase reaction with this γ-elimination reaction provides an explanation for the previous detection of (18)F(-) in tumors exposed to [(18)F](2S,4R)4-FGln. One enzyme contributing to this reaction was identified as alanine aminotransferase, which catalyzes competing γ-elimination and aminotransferase reactions with (2S,4R)4-FGlu. This appears to be the first description of an aminotransferase catalyzing a γ-elimination reaction. The present results demonstrate that (2S,4R)4-FGln and (2S,4R)4-FGlu are useful analogues for comparative studies of various glutamine- and glutamate-utilizing enzymes in normal and cancerous mammalian tissues, and suggest that tumors may metabolize (2S,4R)4-FGln in a generally similar fashion to glutamine. In plants, yeast and bacteria a major route for ammonia assimilation involves the consecutive action of glutamate synthase plus glutamine synthetase (glutamate synthase cycle). It is suggested that (2S,4R)4-FGln and (2S,4R)4-FGlu will be useful probes in studies of ammonia assimilation by the glutamate synthase pathway in these organisms. Finally, glutamine transaminases are conserved in mammals, plants and bacteria, and probably serve to close the methionine salvage pathway, thus linking nitrogen metabolism to sulfur metabolism and one-carbon metabolism. It is suggested that (2S,4R)4-FGln may be useful in studies of the methionine salvage pathway in a variety of organisms., (Copyright © 2012 Elsevier Inc. All rights reserved.)