Comparison of novel PSMA-targeting [177Lu]Lu-P17-087 with its albumin binding derivative [177Lu]Lu-P17-088 in metastatic castration-resistant prostate cancer patients: a first-in-human study.

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, [177Lu]Lu-P17-087, and its albumin binder modified derivative, [177Lu]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 [68Ga]Ga-PSMA-11 PET/CT scan. Five mCRPC patients received [177Lu]Lu-P17-087 and four other patients received [177Lu]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 [177Lu]Lu-P17-088 with longer blood circulation (due to its albumin binding) exhibited higher effective doses than [177Lu]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. [177Lu]Lu-P17-087 demonstrated excellent tumor uptake and faster kinetics; while [177Lu]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 [177Lu]Lu-P17-087 and [177Lu]Lu-P17-088, 3/5 and 3/4 patients showed reducing PSA values, respectively. CONCLUSION: [177Lu]Lu-P17-088 and [177Lu]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: 177Lu-P17-087/177Lu-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 .

Determining the optimal pharmacokinetic modelling and simplified quantification method of [18F]AlF-P16-093 for patients with primary prostate cancer (PPCa).

PURPOSE: This paper discusses the optimization of pharmacokinetic modelling and alternate simplified quantification method for [18F]AlF-P16-093, a novel tracer for in vivo imaging of prostate cancer. METHODS: Dynamic PET/CT scans were conducted on eight primary prostate cancer patients, followed by a whole-body scan at 60 min post-injection. Time-activity curves (TACs) were obtained by drawing volumes of interest for primary prostatic and metastatic lesions. Optimal kinetic modelling involved evaluating three compartmental models (1T2K, 2T3K, and 2T4K) accounting for fractional blood volume (Vb). The simplified quantification method was then determined based on the correlation between the static uptake measure and total distribution volume (Vt) obtained from the optimal pharmacokinetic analysis. RESULTS: In total, 17 intraprostatic lesions, 10 lymph nodes, and 36 osseous metastases were evaluated. Visually, the contrast of the tumor increased and showed the steepest incline within the first few minutes, whereas background activity decreased over time. Full pharmacokinetic analysis revealed that a reversible two-compartmental (2T4K) model is the preferred kinetic model for the given tracer. The kinetic parameters K1, k3, Vb, and Vt were all significantly higher in lesions when compared with normal tissue (P < 0.01). Several simplified protocols were tested for approximating comprehensive dynamic quantification in tumors, with image-based SURmean (the ratio of tumor SUVmean to blood SUVmean) within the 28-34 min window found to be sufficient for approximating the total distribution Vt values (R2 = 0.949, P < 0.01). Both Vt and SURmean correlated significantly with the total serum prostate-specific antigen (tPSA) levels (P < 0.01). CONCLUSIONS: This study introduced an optimized pharmacokinetic modelling approach and a simplified acquisition method for [18F]AlF-P16-093, a novel PSMA-targeted radioligand, highlighting the feasibility of utilizing one static PET imaging (between 30 and 60 min) for the diagnosis of prostate cancer. Note that the image-derived input function in this study may not reflect the true corrected plasma input function, therefore the interpretation of the associated kinetic parameter estimates should be done with caution.

First-in-human study of PSMA-targeting agent, [18F]AlF-P16-093: dosimetry and initial evaluation in prostate cancer patients.

PURPOSE: This is a first-in-human study to evaluate the radiation dosimetry of a new prostate-specific membrane antigen (PSMA)-targeted radiopharmaceutical, [18F]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 [18F]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: [18F]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 [68Ga]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 [18F]AlF-P16-093. Preliminary study in PCa patients has demonstrated its safety and acceptable radiation dosimetry. The initial diagnostic study indicated that [18F]AlF-P16-093 PET/CT is efficacious and potentially useful for a widespread application in the diagnosis of PCa patients.

Novel [68Ga/177Lu]Ga/Lu-AZ-093 as PSMA-Targeting Agent for Diagnosis and Radiotherapy.

Prostate-specific membrane antigen (PSMA) overexpressed in prostate cancer cells can serve as a target for imaging and radioligand therapy (RLT). Previously, [68Ga]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, [177Lu]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 [68Ga]GaCl3 or [177Lu]LuCl3 in a sodium acetate buffer solution (pH 4-5) at 50 °C in 5 to 15 min produced either [68Ga]Ga-1 or [177Lu]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 [68Ga]Ga-P16-093 and [177Lu]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 [68Ga]Ga-1 and [177Lu]Lu-1 displayed excellent uptake and retention in the tumor. Results indicate that [68Ga]Ga/[177Lu]Lu-1 (68Ga]Ga/[177Lu]Lu-AZ-093) is potentially useful as PSMA-targeting agent for both diagnosis and radiotherapy of prostate cancer.

Head-to-head comparison of [68Ga]Ga-P16-093 and 2-[18F]FDG PET/CT in patients with clear cell renal cell carcinoma: a pilot study.

PURPOSE: This pilot study was prospectively designed to evaluate and compare the diagnostic value of PET/CT using a PSMA-specific tracer [68Ga]Ga-P16-093 and a glucose metabolism probe 2-[18F]FDG in clear cell renal cell carcinoma (ccRCC) patients. METHODS: Forty-two pathologically confirmed ccRCC patients were included. Within 1 week, each patient underwent [68Ga]Ga-P16-093 and 2-[18F]FDG PET/CT. In addition to visual analysis of tumor number, the standardized uptake value (SUV) was measured for semiquantitative comparison and correlation analysis. RESULTS: For primary ccRCC patients, [68Ga]Ga-P16-093 PET/CT demonstrated a significantly higher detection rate (19/22 vs. 13/22, P = 0.031) and higher tumor uptake (15.7 ± 9.0 vs. 5.1 ± 3.4, P < 0.001) than 2-[18F]FDG PET/CT. In addition, the SUVmax of the primary tumor on [68Ga]Ga-P16-093 and 2-[18F]FDG PET/CT was significantly correlated with pT stage (for [68Ga]Ga-P16-093, r = 0.550, P = 0.008; for 2-[18F]FDG, r = 0.514, P = 0.014) and WHO/ISUP grade (for [68Ga]Ga-P16-093, r = 0.566, P = 0.006; for 2-[18F]FDG, r = 0.492, P = 0.020), respectively. For metastatic ccRCC patients, [68Ga]Ga-P16-093 PET/CT also demonstrated a better detection rate (21/22 vs. 14/22, P = 0.008) and higher tumor uptake (11.0 ± 6.4 vs. 4.4 ± 2.7, P < 0.001) than 2-[18F]FDG PET/CT. The SUVmax on [68Ga]Ga-P16-093 PET/CT had a significant association with PSMA expression in primary ccRCC (r = 0.776, P < 0.001) and metastatic ccRCC (r = 0.626, P = 0.029). CONCLUSIONS: [68Ga]Ga-P16-093 PET/CT demonstrates significantly better tumor detectability than 2-[18F]FDG PET/CT for ccRCC patients. TRIAL REGISTRATION: 68Ga-P16-093 and 18F-FDG PET/CT Imaging in the Same Group of Clear Cell Renal Cell Carcinoma Patients (NCT05432947, Registered 27 June 2021, retrospectively registered) URL OF REGISTRY: https://clinicaltrials.gov/ct2/show/NCT05432947 .

A prospective head-to-head comparison of [68Ga]Ga-P16-093 and [68Ga]Ga-PSMA-11 PET/CT in patients with primary prostate cancer.

PURPOSE: We aimed to compare the diagnostic performance and biodistribution of two similar PET agents, [68Ga]Ga-P16-093 and [68Ga]Ga-PSMA-11, in the same group of primary prostate cancer (PCa) patients. METHODS: Fifty patients with untreated, histologically confirmed PCa by needle biopsy were enrolled. Each patient underwent [68Ga]Ga-P16-093 and [68Ga]Ga-PSMA-11 PET/CT within a week. In addition to visual analysis, the standardized uptake value (SUV) was measured for semiquantitative comparison and correlation analysis. RESULTS: [68Ga]Ga-P16-093 PET/CT detected more positive tumors than [68Ga]Ga-PSMA-11 PET/CT (202 vs. 190, P = 0.002), both for intraprostatic lesions (48 vs. 41, P = 0.016) and metastatic lesions (154 vs. 149, P = 0.125), especially for intraprostatic lesions in low- and intermediate-risk PCa patients (21/23 vs. 15/23, P = 0.031). Furthermore, [68Ga]Ga-P16-093 PET/CT exhibited a significantly higher SUVmax for most matched tumors (13.7 ± 10.2 vs. 11.4 ± 8.3, P < 0.001). For normal organs, [68Ga]Ga-P16-093 PET/CT showed significantly lower activity in the kidney (SUVmean: 20.1 ± 6.1 vs. 29.3 ± 9.1, P < 0.001) and urinary bladder (SUVmean: 6.5 ± 7.1 vs. 20.9 ± 17.4, P < 0.001), but displayed a higher uptake in the parotid gland (SUVmean: 8.7 ± 2.6 vs. 7.6 ± 2.1, P < 0.001), liver (SUVmean: 7.0 ± 1.9 vs. 3.7 ± 1.3, P < 0.001), and spleen (SUVmean: 8.2 ± 3.0 vs. 5.2 ± 2.2, P < 0.001) than [68Ga]Ga-PSMA-11 PET/CT. CONCLUSION: [68Ga]Ga-P16-093 PET/CT demonstrated higher tumor uptake and better tumor detectability than [68Ga]Ga-PSMA-11 PET/CT, especially in low- and intermediate-risk PCa patients, which indicated that [68Ga]Ga-P16-093 may serve as an alternative agent for detection of PCa. TRIAL REGISTRATION: 68Ga-P16-093 and 68Ga-PSMA-11 PET/CT Imaging in the Same Group of Primary Prostate Cancer Patients (NCT05324332, Registered 12 April 2022, retrospectively registered). URL OF REGISTRY: https://clinicaltrials.gov/ct2/show/NCT05324332 .

[68Ga]Ga-HBED-CC-FAPI Derivatives with Improved Radiolabeling and Specific Tumor Uptake.

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 KGaL: 38.5), compared to that of Ga-DOTA (log KGaL: 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 [68Ga]Ga-DOTA-FAPI-02 and -04 were converted to the corresponding [68Ga]Ga-HBED-CC-FAPI-02 and -04 derivatives ([68Ga]Ga-4, [68Ga]Ga-5, [68Ga]Ga-6, and [68Ga]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 (IC50 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 [68Ga]Ga-HBED-CC-FAPI dimer, [68Ga]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.

Head-to-head comparison of [68 Ga]Ga-P16-093 and [68 Ga]Ga-PSMA-617 in dynamic PET/CT evaluation of the same group of recurrent prostate cancer patients.

PURPOSE: This study was prospectively designed to evaluate the early dynamic organ distribution and tumor detection capability of [68 Ga]Ga-P16-093, which was compared with [68 Ga]Ga-PSMA-617 in the same group of recurrent prostate cancer patients. METHODS: Twenty patients with recurrent prostate cancer were enrolled. In 2 consecutive days, each patient underwent a 60-min dynamic PET/CT scan after intravenous administration of 148-185 MBq (4-5 mCi) [68 Ga]Ga-P16-093 and [68 Ga]Ga-PSMA-617, respectively. Following a low-dose CT scan, serial dynamic PET scans were performed from head to proximal thigh at 9 time points (30 s/bed at 4, 7, 10, 13, and 16 min; 1 min/bed at 20, 30, and 45 min; and 2 min/bed at 60 min). Standardized uptake values were measured for semi-quantitative comparison. RESULTS: [68 Ga]Ga-P16-093 PET/CT revealed a significantly higher tumor uptake at 4 min (SUVmax 7.88 ± 5.26 vs. 6.01 ± 3.88, P < 0.001), less blood pool retention at 4 min (SUVmean 5.12 ± 1.16 vs. 6.14 ± 0.98, P < 0.001), and lower bladder accumulation at 60 min (SUVmean 31.33 ± 27.47 vs. 48.74 ± 34.01, P = 0.042) than [68 Ga]Ga-PSMA-617 scan. Significantly higher [68 Ga]Ga-P16-093 uptakes were also observed in the parotid gland, liver, spleen, and kidney. Besides, [68 Ga]Ga-P16-093 exhibited a better detectability of tumor than [68 Ga]Ga-PSMA-617 (366 vs. 321, P = 0.009). CONCLUSIONS: [68 Ga]Ga-P16-093 showed advantages over [68 Ga]Ga-PSMA-617 with higher tumor uptakes, tumor-to-blood pool ratio and detection capability, less blood pool, and bladder accumulation in recurrent prostate cancer patients. TRIAL REGISTRATION: [68 Ga]Ga-P16-093 and [68 Ga]Ga-PSMA-617 PET/CT Imaging in the Same Group of Prostate Cancer Patients (NCT04796467, Registered 12 March 2021, retrospectively registered) URL of registry: https://clinicaltrials.gov/ct2/show/NCT04796467.

In vivo and in vitro binding of [125 I]I-R-(+)-TISCH: A dopamine D1 receptor ligand for studying pancreatic ß-cell mass.

Diabetes mellitus (DM) and insulinoma are mainly affected by the status of pancreatic ß-cell mass (BCM). Development of imaging agents for BCM allows to study pancreatic ß cells and the relationship between ß cells and DM or insulinoma. In this study, we investigated the density of dopamine D1 receptor on the ß cells and measured BCM by statistical image processing. The pancreatic uptakes of [125 I]I-R-(+)-7-chloro-8-hydroxy-1-(3'-iodopheny1)-3-methyl-2,3,4,5-tetrahydro-1H-3-benzazepine ([125 I]I-R-(+)-TISCH), dopamine D1 receptor tracer, in normal and diabetic rats displayed significant differences at 30 min (1.11 ± 0.08% ID/g vs. 0.63 ± 0.09% ID/g, p < 0.0001). In the presence of SCH23390, the pancreatic uptake of [125 I]I-R-(+)-TISCH at 30 min in normal rats was lower (1.01 ± 0.04% ID/g, p < 0.05). Although the blocking was not complete, [125 I]I-R-(+)-TISCH showed specific binding signals to the pancreas. Furthermore, the uptakes of [125 I]I-R-(+)-TISCH in INS-1 cells were reduced in the presence of SCH23390 at different concentrations. [125 I]I-R-(+)-TISCH displayed a respectable uptake in insulinoma. Overall, [125 I]I-R-(+)-TISCH provided specific binding signals to pancreatic ß cells. Although the specific signal may not be sufficient for imaging in vivo, the dopamine D1 receptor can still be considered as a potential target for studying BCM. Further investigation will be required to optimize the ligand.

Radiolabeling Optimization and Preclinical Evaluation of the New PSMA Imaging Agent [18F]AlF-P16-093.

Prostate-specific membrane antigen (PSMA)-targeted radioligands have played an increasing role in the diagnosis of prostate cancer. [68Ga]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 18F via [18F]AlF2+ complex formation, and the biological properties of [18F]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 Al3+; 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 [18F]fluoride, 46 nmol of P16-093, 40 nmol of AlCl3·6 H2O, and 50% EtOH. [18F]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, [18F]AlF-P16-093 showed PSMA-specific high uptakes in PIP-PC3 cells. The binding affinity of [18F]AlF-P16-093 to PSMA was determined as Kd 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 [18F]AlF-P16-093 (2.83 ± 0.49% ID/g) in comparison to that of [68Ga]Ga-P16-093 (0.26 ± 0.07% ID/g). In summary, an efficient and simple radiosynthesis of [18F]AlF-P16-093 was achieved. [18F]AlF-P16-093 showed desirable in vivo pharmacokinetics and excellent PSMA-targeting properties for imaging PSMA expression in prostate cancer.

Dynamic PET/CT imaging of 18F-(2S, 4R)4-fluoroglutamine in healthy volunteers and oncological patients.

PURPOSE: The purpose of this study was to compare dynamic 18F-FGln PET/CT images of healthy subjects and cancer patients and explore the best imaging phase for different cancers. METHODS: Thirteen healthy volunteers and 31 cancer patients separately underwent 18F-FGln and 18F-FDG PET/CT scans within 1 week. The distributions of 18F-FGln and 18F-FDG in the whole body and the tumor avidity were analyzed and compared. The tumor maximum standardized uptake values (SUVmax) and tumor-to-nontumor SUV ratio (SUR) of 18F-FGln/PET at different scan phases were compared. RESULTS: Compared to the healthy subjects, the cancer patients had lower 18F-FGln activity (SUVmean) in most normal organs, especially in the lung, muscle, spleen, and heart (p < 0.05). Additionally, the FGln-avid tumors did not necessarily manifest as FDG-avid and vice versa. Overall, among the 31 primary malignant lesions confirmed by biopsy or postoperative pathological analysis, 29 showed increased radioactive uptake on all 18F-FGln PET/CT imaging phases. The peak of SUVmax in breast and thyroid cancers was within 10 min, while in lung cancers, the plateau of SUVmax was within 30 min to 60 min. The SURs of lung cancer (p = 0.046) and thyroid cancer (p = 0.794) increased from the early-phase to the late-phase acquisition; however, a significant decrease was observed in the breast lesions (p = 0.022). CONCLUSIONS: 18F-FGln images may further supplement the diagnostic ability of 18F-FDG in cancer patients and detect metabolic changes in different tumors. Furthermore, the imaging time for 18F-FGln PET/CT needs to be optimized for different cancer types to improve the contrast resolution of tumors.

Synthesis and Evaluation of 68Ga- and 177Lu-Labeled (R)- vs (S)-DOTAGA Prostate-Specific Membrane Antigen-Targeting Derivatives.

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, [68Ga]Ga-PSMA-093 ([68Ga]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 68Ga but is also amendable for complexing other radioactive metals for radionuclide therapy. The corresponding optically pure (R)- and (S)-[68Ga/177Lu]-DOTAGA derivatives, (R)-[68Ga/177Lu]-13 and (S)-[68Ga/177Lu]-13, were successfully prepared. Comparison of radiolabeling, binding affinity, cell uptake, and biodistribution between the two isomers was performed. Radiolabeling of (R)-[177Lu]Lu-13 and (S)-[177Lu]Lu-13 at 50 °C suggested that rates of complex formation were time-dependent and the formation of (S)-[177Lu]Lu-13 was distinctly faster. The rates of complex formation for the corresponding 68Ga agents were comparable between structural isomers. The natGa and natLu equivalents showed high binding PSMA affinity (IC50 = 24-111 nM), comparable to that of the parent agent, [natGa]Ga-PSMA-093 (IC50 = 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 [68Ga/177Lu]-(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 177Lu-DOTAGA-based radionuclide therapy agents in the future.

A New [68Ga]Ga-HBED-CC-Bisphosphonate as a Bone Imaging Agent.

Positron emission tomography (PET) imaging using 68Ga-labeled bisphosphonates to target bone metastasis could be a valuable tool in cancer diagnosis and monitoring therapeutic treatment. A 68Ga 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 [68Ga]Ga-1, via complexing with [68Ga]GaCl3 eluted from a commercially available 68Ge/68Ga generator (in a sodium acetate buffer at pH 4, reaching >95% labeling yield at room temperature in 5 min). The resulting [68Ga]Ga-1 showed excellent stability in vitro and in vivo. [68Ga]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 [68Ga]Ga-1 in normal mice and rats showed excellent bone uptake and retention comparable to that of Na[18F]F. The results suggested that [68Ga]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[18F]F, without the need of a near-by cyclotron. Also, an automated synthesis module was developed to produce clinical doses of [68Ga]Ga-1 in a consistent and reproducible manner. Currently, the investigation new drug application (IND) for [68Ga]Ga-HBED-CC-BP, [68Ga]Ga-1, has received FDA approval, and it is currently under clinical trial (IND #129870).

Synthesis and evaluation of novel radioiodinated PSMA targeting ligands for potential radiotherapy of prostate cancer.

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 125I by iododestannylation. All iodinated compounds displayed high binding affinities toward PSMA (IC50 = 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 [125I]8 and [125I]15 with higher lipophilicity exhibited higher nonspecific accumulations in the liver and intestinal tract, whereas [125I]19a/19b and [125I]23a/23b containing additional glutamic acid moieties showed higher accumulations in the kidney and implanted PC3-PIP (PSMA+) tumors. [125I]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 [125I]MIP-1095. [125/131I]23b may serve as an optimal PSMA ligand for radiotherapy treatment of prostate cancer over-expressing PSMA.

An improved preparation of [18 F]AV-45 by simplified solid-phase extraction purification.

Amyvid (florbetapir f18, [18 F]AV-45, [18 F]5) was the first FDA-approved positron emission tomography imaging agent targeting ß-amyloid (Aß) plaques for assisting the diagnosis of Alzheimer disease. This work aimed to improve the [18 F]AV-45 ([18 F]5) preparation by using solid-phase extraction (SPE) purification. [18 F]AV-45 ([18 F]5) was synthesized by direct nucleophilic radiofluorination of O-tosylated precursor (1 mg) at 120°C in anhydrous dimethyl sulfoxide (DMSO), followed by acid hydrolysis of the N-Boc protecting group. Purification was accomplished by loading the crude reaction mixture to a cartridge (Oasis HLB 3 cc) and eluting with different combinations of solvents. This method removed the chemical impurity while leaving [18 F]AV-45 ([18 F]5) on the cartridge. The final dose was eluted by ethanol. [18 F]AV-45 ([18 F]5) was produced within 51 minutes (radiochemical yield 42.7 ± 5.9%, decay corrected, n = 3), and the radiochemical purity was greater than 95%. Total chemical impurity per batch (24.1 ± 2.7 µg per batch) was below the limit described in the package insert of Amyvid, florbetapir f18 (chemical mass: less than 50 µg/dose). In summary, [18 F]AV-45 ([18 F]5) was produced efficiently and reproducibly using a cartridge-based SPE purification. This method brings the process closer for routine preparation, similar to the commercially used [18 F]FDG.

In Vivo Ester Hydrolysis as a New Approach in Development of Positron Emission Tomography Tracers for Imaging Hypoxia.

Hypoxia is an important biochemical and physiological condition associated with uncontrolled growth of tumor. Measurement of hypoxia in tumor tissue may be useful in characterization of tumor progression and monitoring drug treatment. [18F]FMISO is the most widely employed radiotracer for imaging of hypoxic tissue with positron emission tomography (PET). However, it showed relatively low uptake in hypoxic tissues, which led to low target-to-background contrast in PET images. To overcome these shortcomings, two novel 2-fluoroproprioic acid esters, nitroimidazole derivatives 2-fluoropropionic acid 2-(2-nitro-imidazol-1-yl)-ethyl ester (FNPFT, [19F]5) and 2-fluoropropionic acid 2-(2-methyl-5-nitro-imidazol-1-yl)-ethyl ester (FMNPFT, [19F]8), were prepared and tested. Radiolabeling of [18F]5 and [18F]8 was accomplished in 45 min (radiochemical purity >95%, the decay-corrected radiochemical yield of [18F]5 was 11 ± 2%, and that of [18F]8 was 13 ± 2%, n = 5). In vitro cell uptake studies using EMT-6 tumor cells showed that both radiotracers [18F]5 and [18F]8 displayed significantly higher uptake in hypoxic cells than those under normoxic condition, while 2-[18F]fluoropropionic acid (2-[18F]FPA) displayed no difference. Biodistribution studies in mice bearing EMT-6 tumor showed that [18F]5, [18F]8, and 2-[18F]FPA displayed similar tumor and major organ uptakes. Tumor uptake values for all three agents were higher than those of [18F]FMISO, respectively ( P < 0.05). This is likely due to a rapid in vivo hydrolysis of [18F]5 and [18F]8 to their metabolite, 2-[18F]FPA. Micro PET imaging studies in the same EMT-6 implanted mice tumor model also demonstrated that both [18F]5 and [18F]8 displayed similar tumor uptake comparable to that of 2-[18F]FPA. In conclusion, two new fluorine-18 labeled nitroimidazole derivatives, [18F]5 and [18F]8, showed good tumor uptakes in mice bearing EMT-6 tumor. However, in vivo biodistribution results suggested that they were more likely reflect the predominance of in vivo produced metabolite, 2-[18F]FPA, which may not be related to tumor hypoxic condition.

Synthesis and preliminary evaluation of a novel glutamine derivative: (2S,4S)4-[18F]FEBGln.

We report the preparation of a novel glutamine derivative, (2S,4S)-2,5-diamino-4-(4-(2-fluoroethoxy)benzyl)-5-oxopentanoic acid, (2S, 4S)4-[18F]FEBGln ([18F]4), through efficient organic and radiosyntheses. In vitro assays of [18F]4 using MCF-7 cells showed that it entered cells via multiple amino acid transporter systems including system L and ASC2 transporters but not through the system A transporter. [18F]4 showed promising properties for tumor imaging and may serve as a lead compound for further optimizing and targeting the system L transporter associated with enhanced glutamine metabolism in cancer cells.

Initial experience in synthesis of (2S,4R)-4-[18 F]fluoroglutamine for clinical application.

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.

In Vivo PET Assay of Tumor Glutamine Flux and Metabolism: In-Human Trial of 18F-(2S,4R)-4-Fluoroglutamine.

Purpose To assess the clinical safety, pharmacokinetics, and tumor imaging characteristics of fluorine 18-(2S,4R)-4-fluoroglutamine (FGln), a glutamine analog radiologic imaging agent. Materials and Methods This study was approved by the institutional review board and conducted under a U.S. Food and Drug Administration-approved Investigational New Drug application in accordance with the Helsinki Declaration and the Health Insurance Portability and Accountability Act. All patients provided written informed consent. Between January 2013 and October 2016, 25 adult patients with cancer received an intravenous bolus of FGln tracer (mean, 244 MBq ± 118, <100 µg) followed by positron emission tomography (PET) and blood radioassays. Patient data were summarized with descriptive statistics. FGln biodistribution and plasma amino acid levels in nonfasting patients (n = 13) were compared with those from patients who fasted at least 8 hours before injection (n = 12) by using nonparametric one-way analysis of variance with Bonferroni correction. Tumor FGln avidity versus fluorodeoxyglucose (FDG) avidity in patients with paired PET scans (n = 15) was evaluated with the Fisher exact test. P < .05 was considered indicative of a statistically significant difference. Results FGln PET depicted tumors of different cancer types (breast, pancreas, renal, neuroendocrine, lung, colon, lymphoma, bile duct, or glioma) in 17 of the 25 patients, predominantly clinically aggressive tumors with genetic mutations implicated in abnormal glutamine metabolism. Acute fasting had no significant effect on FGln biodistribution and plasma amino acid levels. FGln-avid tumors were uniformly FDG-avid but not vice versa (P = .07). Patients experienced no adverse effects. Conclusion Preliminary human FGln PET trial results provide clinical validation of abnormal glutamine metabolism as a potential tumor biomarker for targeted radiotracer imaging in several different cancer types. © RSNA, 2018 Online supplemental material is available for this article. Clinical trial registration no. NCT01697930.

PET Imaging of 18F-(2 S,4 R)4-Fluoroglutamine Accumulation in Breast Cancer: From Xenografts to Patients.

Sustaining the growth of tumor cells requires extra energy and metabolic building blocks. In addition to consuming glucose, glutamine may play the role as an alternative source of nutrient for growth and survival. We aim to characterize a glutamine analog, 18F-(2 S,4 R)4-fluoroglutamine (18F-(2 S,4 R)4-FGln), as an imaging agent for interrogating the role of glutamine from the in vitro study of tumor cells to clinical manifestation in breast cancer patients. Purity was measured by radio-high-performance liquid chromatography (radio-HPLC), and the stability after production was evaluated in phosphate buffer saline (PBS), saline, and mouse and human serum buffers. The presence of Myc expression in MCF-7 and U87 cells was conducted using qPCR. In vitro cell uptake of 18F-(2 S,4 R)4-FGln in MCF-7 and U87 cells was directly compared with 18F-fluorodeoxyglucose (18F-FDG). In vivo biodistribution and micro-PET imaging of 18F-(2 S,4 R)4-FGln in MCF-7 bearing BALB/c nude mice were performed. PET/CT imaging of 18F-(2 S,4 R)4-FGln was compared with 18F-FDG in the same group of breast cancer patients ( n = 10). We successfully synthesized 18F-(2 S,4 R)4-FGln with a high radiochemical purity (>98%), and the radiochemical purity was unchanged in PBS and saline buffers during a 2 h incubation. In vitro cell uptake studies of 18F-(2 S,4 R)4-FGln displayed a rapid and higher uptake in MCF-7 and U87 cells as compared with 18F-FDG. Biodistribution and micro-PET images showed excellent tumor accumulation of 18F-(2 S,4 R)4-FGln in the MCF-7-implanted mice tumor model. In a preliminary clinical study, 18F-(2 S,4 R)4-FGln/PET detected more lesions in breast cancer patients than 18F-FDG/PET (90% vs 80%). Additionally, in one patient with breast lobular carcinoma, there was a lesion mean standardized uptake value (SUVmean) and maximum standardized uptake value (SUVmax) for 18F-(2 S,4 R)4-FGln higher than those obtained by 18F-FDG, as determined by PET imaging. 18F-(2 S,4 R)4-FGln may be a useful glutamine-targeting metabolic probe for noninvasive imaging of breast cancer.