68Ga/177Lu-Labeled Bivalent Agents for Targeting Hypoxia and PSMA-Binding in Prostate Cancer.

Prostate-specific membrane antigen (PSMA) is an excellent target for cancer detection and therapy. Hypoxia is prevalent in solid tumors, and various nitroimidazole (NI) radioligands can be trapped inside hypoxic cells for diagnosis and therapy. To enhance tumor uptake and retention, we designed bivalent agents (compounds 1-8) incorporating a hypoxia-sensitive NI-moiety and a PSMA-targeting group. Ligands 1-8 were successfully prepared and labeled with 68Ga or 177Lu. Among them, [68Ga]Ga-8 ([68Ga]Ga-AAZTA-NI-PSMA-093) demonstrated significantly higher cellular accumulation under hypoxic conditions than under normoxic conditions, suggesting hypoxia-selective trapping by the introduction of NI group. PET/CT imaging at 60 min postinjection of [68Ga]Ga-8 revealed high tumor uptake (SUVmax: 10.68%ID/mL) in the tumor-bearing mice model. SPECT/CT imaging of [177Lu]Lu-8 at 24 and 48 h postinjection demonstrated excellent accumulation and retention. Preliminary studies indicate that [68Ga]Ga/[177Lu]Lu-8 may be promising bivalent agents targeting hypoxia and PSMA binding for diagnosis and radiotherapy.

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.

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 .

Theranostic Agent Targeting Bone Metastasis: A Novel [68Ga]Ga/[177Lu]Lu-DOTA-HBED-bisphosphonate.

Bone metastasis in cancer patients is a major disease advancement for various types of cancer. Previously, [68Ga]Ga-HBED-CC-bisphosphonate ([68Ga]Ga-P15-041) showed excellent bone uptake and efficient detection of bone metastasis in patients. To accommodate different α- or ß--emitting metals for radionuclide therapy, a novel DOTA-HBED-CC-bisphosphonate (P15-073, 1) was prepared and the corresponding [68Ga]Ga-1 and [177Lu]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, [68Ga]Ga-1 and [177Lu]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 [68Ga]Ga/[177Lu]Lu-1 holds promise as a theranostic radioligand agent for managing cancer bone metastases.

Serotonin transporter imaging agent as a probe for ß-cells of pancreas.

OBJECTIVE: Diabetes mellitus (DM) is one of the major diseases in the world. Nuclear medicine imaging may be able to detect functional status of pancreatic ß cells in vivo, which might elucidate the pathological mechanisms of diabetes and develop individualized treatment plans. In this study, we evaluated the ability of [125I]ADAM, a serotonin transporter (SERT) imaging agent, as a probe for detecting pancreatic ß-cell mass (BCM). METHODS: In vitro cell studies were evaluated in INS-1 cells (rat islet ß cell line). Biodistribution studies were performed in male normal Sprague-Dawley rats and alloxan-induced type 1 diabetes mellitus (T1DM) rats. Distribution and expression of SERT protein in pancreas of rats were also measured by immunofluorescence staining and Western blot. RESULTS: In vitro cell studies showed that the concentration of [125I]ADAM associated with the INS-1 cells was increased gradually with incubation time, and the SERT specific inhibitor, escitalopram, exhibited the inhibitory effect on this interaction. Biodistribution studies also showed that the uptake of [125I]ADAM in the pancreas of normal rats was decreased in the presence of escitalopram. However, in the T1DM rat model with a significant ß cells reduction, the uptake of pancreas was increased when compared with the control. Through immunofluorescence staining and Western blot, it was found that both the endocrine and exocrine cells of the normal pancreas expressed SERT protein, and the level of SERT protein in the exocrine cells was higher than islets. In the diabetic state, the expression of SERT in the exocrine cells was further increased. CONCLUSIONS: The SERT imaging agent, [125I]ADAM, at the present form will not be suitable for imaging ß cells, specifically because there were extraordinarily high non-specific signals contributing from the exocrine cells of pancreas. In addition, we noticed that the level of SERT expression was abnormally elevated in the diabetic state, which might provide an unexpected target for studying the pathological mechanisms of diabetes.

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.

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.

Lu-177-Labeled Hetero-Bivalent Agents Targeting PSMA and Bone Metastases for Radionuclide Therapy.

Prostate-specific membrane antigen (PSMA) is an excellent target for imaging and radionuclide therapy of prostate cancer. Recently, [177Lu]Lu-PSMA-617 (Pluvicto) was approved by the FDA for radionuclide therapy. To develop hetero-bivalent agents targeting both PSMA and bone metastasis, [177Lu]Lu-P17-079 ([177Lu]Lu-1) and [177Lu]Lu-P17-081 ([177Lu]Lu-2) were prepared. In vivo biodistribution studies of [177Lu]Lu-PSMA-617, [177Lu]Lu-1, and [177Lu]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 [68Ga]Ga-P17-079 ([68Ga]Ga-1) in the same mouse model displayed excellent images confirming the expected dual-targeting to PSMA-positive tumor and bone. Results suggest that [177Lu]Lu-P17-079 ([177Lu]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.

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-P16-093 and 68 Ga-PSMA-617 PET/CT in Patients With Primary Prostate Cancer : A Pilot Study.

PURPOSE: We aimed to compare the diagnostic performance of 68 Ga-P16-093 and 68 Ga-PSMA-617 PET/CT in primary prostate cancer (PCa) patients. PATIENTS AND METHODS: Thirty untreated primary PCa patients were enrolled. Each patient underwent 68 Ga-P16-093 and 68 Ga-PSMA-617 PET/CT within a week. In addition to visual analysis, SUV was measured for semiquantitative comparison and correlation analysis. RESULTS: 68 Ga-P16-093 PET/CT detected more positive tumors than 68 Ga-PSMA-617 PET/CT (67 vs 56, P = 0.002), especially for intraprostatic lesions (29 vs 24, P = 0.025) and lymph node metastases (23 vs 17, P = 0.034). Further, 68 Ga-P16-093 PET/CT exhibited significantly higher SUV max of matched tumors (18.3 ± 14.4 vs 13.9 ± 11.8, P < 0.001). Besides, the SUV max of high-risk patients (based on D'Amico classification) on 68 Ga-P16-093 PET/CT was significantly higher than that of low- and intermediate-risk PCa patients (20.9 ± 9.9 vs 8.9 ± 9.1 vs 10.1 ± 5.2, P = 0.007). The SUV max of tumor measured by 68 Ga-P16-093 PET/CT had a moderate association with biopsy Gleason score ( r = 0.462, P = 0.005) and prostate-specific antigen value ( r = 0.491, P = 0.002), and significantly correlated with PSMA expression ( r = 0.732, P < 0.001). CONCLUSIONS: 68 Ga-P16-093 PET/CT exhibited higher tumor uptake and potentially better tumor detection capability than 68 Ga-PSMA-617 PET/CT, which suggested that 68 Ga-P16-093 may be more suitable in the diagnosis and staging of primary PCa patients.

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 .

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.

New PSMA-Targeting Ligands: Transformation from Diagnosis (Ga-68) to Radionuclide Therapy (Lu-177).

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 68Ga-imaging agent, [68Ga]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 (IC50 = 10-30 nM) comparable to that of recently FDA-approved [177Lu]Lu-PSMA-617 (Pluvicto). Biodistribution studies in PSMA expressing tumor bearing mice showed that [177Lu]Lu-4 exhibited very high tumor uptake and a fast blood clearance similar to those of [177Lu]Lu-PSMA-617. Conversely, [177Lu]Lu-7, containing an albumin binder, extended its blood half-life and exhibited significantly higher uptake and longer tumor residence time than [177Lu]Lu-4 and [177Lu]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.

Preliminary Evaluation of 68Ga-P16-093, a PET Radiotracer Targeting Prostate-Specific Membrane Antigen in Prostate Cancer.

PURPOSE: Prostate-specific membrane antigen (PSMA) is a promising molecular target for imaging of prostate adenocarcinoma. 68Ga-P16-093, a small molecule PSMA ligand, previously showed equivalent diagnostic performance compared to 68Ga-PSMA-11 PET/CT in a pilot study of prostate cancer patients with biochemical recurrence (BCR). We performed a pilot study for further characterization of 68Ga-P16-093 including comparison to conventional imaging. PROCEDURES: Patients were enrolled into two cohorts. The biodistribution cohort included 8 treated prostate cancer patients without recurrence, who underwent 6 whole body PET/CT scans with urine sampling for dosimetry using OLINDA/EXM. The dynamic cohort included 15 patients with BCR and 2 patients with primary prostate cancer. Two patients with renal cell carcinoma were also enrolled for exploratory use. A dynamic PET/CT was followed by 2 whole body scans for imaging protocol optimization based on bootstrapped replicates. 68Ga-P16-093 PET/CT was compared for diagnostic performance against available 18F-fluciclovine PET/CT, 99mTc-MDP scintigraphy, diagnostic CT, and MRI. RESULTS: 68Ga-P16-093 deposited similar effective dose (0.024 mSv/MBq) and lower urinary bladder dose (0.064 mSv/MBq) compared to 68Ga-PSMA-11. The kidneys were the critical organ (0.290 mSv/MBq). While higher injected activities were preferable, lower injected activities at 74-111 MBq (2-3 mCi) yielded 80% retention in signal-to-noise ratio. The optimal injection-to-scan interval was 60 min, with acceptable delay up to 90 min. 68Ga-P16-093 PET/CT showed superior diagnostic performance over conventional imaging with overall patient-level lesion detection rate of 71%, leading to a change in management in 42% of the patients. CONCLUSIONS: Based on its favorable imaging characteristics and diagnostic performance in prostate cancer, 68Ga-P16-093 PET/CT merits further investigation in larger clinical studies.

Kit-based preparation of [68Ga]Ga-P16-093 (PSMA-093) using different commercial 68Ge/68Ga generators.

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 [68Ga]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, [68Ga]Ga-P16-093 ([68Ga]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 68Ga/HCl from different sources of generators were evaluated. PROCEDURES: Commercially available 68Ge/68Ga 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 [68Ga]Ga-P16-093 produced by using different sources of 68Ga 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 [68Ga]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, [68Ga]Ga-P16-093 could be conveniently and reliably prepared by a simple one-step reaction with excellent yields. Clinically useful doses of [68Ga]Ga-P16-093 imaging tracer could be made available using different 68Ge/68Ga generators.

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.

68Ga-P15-041, A Novel Bone Imaging Agent for Diagnosis of Bone Metastases.

OBJECTIVES: 68Ga-P15-041 (68Ga-HBED-CC-BP) is a novel bone-seeking PET radiotracer, which can be readily prepared by using a simple kit formulation and an in-house 68Ga/68Ge generator. The aim of this study is to assess the potential human application of 68Ga-P15-041 for clinical PET/CT imaging and to compare its efficacy to detect bone metastases of different cancers with 99mTc-MDP whole-body bone scintigraphy (WBBS). METHODS: Initial kinetic study using Patlak analysis and parametric maps were performed in five histopathologically proven cancer patients (three males, two females) using 68Ga-P15-041 PET/CT scan only. Another group of 51 histopathologically proven cancer patients (22 males, 29 females) underwent both 99mTc-MDP WBBS and 68Ga-P15-041 PET/CT scans within a week, sequentially. Using either pathology examination or follow-up CT or MRI scans as the gold standard, the diagnostic efficacy and receiver operating characteristic curve (ROC) of the two methods in identifying bone metastases were compared (p <0.05, statistically significant). RESULTS: Fifty-one patients were imaged, and 174 bone metastatic sites were identified. 68Ga-P15-041 PET/CT and 99mTc-MDP WBBS detected 162 and 81 metastases, respectively. Sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 68Ga-P15-041 PET/CT and 99mTc-MDP WBBS were 93.1% vs 81.8%, 89.8% vs 90.7%, 77.5% vs 69.2%, 97.2% vs 93.4% and 90.7% vs 88.4%, respectively. Our results showed that the mean of SUVmax was significantly higher in metastases than that in benign lesions, 15.1 ± 6.9 vs. 5.6 ± 1.3 (P <0.001). Using SUVmax = 7.6 as the cut-off value by PET/CT, it was possible to predict the occurrence of metastases (AUC = 0.976; P <0.001; 95% CI: 0.946-0.999). However, it was impossible to distinguish osteoblastic bone metastases from osteolytic bone lesions. Parametric maps based on Patlak analysis provided excellent images and highly valuable quantitative information. CONCLUSIONS: 68Ga-P15-041 PET/CT, offering a rapid bone scan and high contrast images in minutes, is superior to the current method of choice in detecting bone metastases. It is reasonable to suggest that 68Ga-P15-041 PET/CT could become a valuable routine nuclear medicine procedure in providing excellent images for detecting bone metastases in cancer patients. 68Ga-P15-041 could become a valuable addition expanding the collection of 68Ga-based routine nuclear medicine procedures where 18F fluoride is not currently available.

Evaluating [68Ga]Ga-p14-032 as a Novel PET Tracer for Diagnosis Cerebral Amyloid Angiopathy.

Objective: We aimed to investigate the distribution of [68Ga]Ga-p14-032, a novel PET ligand that binds to vascular amyloid, in patients diagnosed clinically with probable cerebral amyloid angiopathy (CAA) compared with patients with Alzheimer's disease (AD) and normal controls (NC). Methods: This longitudinal cohort study was composed of 10 subjects (three probable CAA patients, two AD patients, five NC subjects), recruited from a clinic in China. CAA patients had a history of lobar intracerebral hemorrhage (ICH) and met modified Boston criteria for probable CAA. All participants were aged at least 55 years and underwent [68Ga] Ga-p14-032 PET/CT or/and PET/MRI, and the Montreal Cognitive Assessment on initial assessment. Demographics were measured at baseline (diabetes, hypertension, hypercholesterolemia, ischemic stroke, and ICH). Two PET imaging experts reviewed the PET images with cortical standardized uptake value ratio (SUVr) displayed on a color scale and visually classified the images as positive or negative. The mean of SUVr was calculated using the pons as reference. Results: In CAA patients, PET scans were positive in regions with higher numbers of CMBs. No significant signal was seen in AD subjects or controls. The relative [68Ga]Ga-p14-032 retention in the cortex was stronger in patients with CAA than AD and NC (median SUVr 2.68 ± 1.53 vs. 1.77 ± 0.08 and 0.83 ± 0.24). Conclusions: Our results provide early evidence that the [68Ga] Ga-p14-032 PET probe binds preferentially to vascular amyloid and may be a useful tracer for diagnosing CAA.

68Ga-labelled-exendin-4: New GLP1R targeting agents for imaging pancreatic ß-cell and insulinoma.

OBJECTIVE: Glucagon-like peptide-1 receptor (GLP1R) specifically expressed on the surface of pancreatic ß-cells and insulinoma, is a potential biomarker for imaging ß-cell mass (BCM). In this study, two new 68Ga-labelled GLP1R targeting agents were prepared and their biological properties for imaging BCM and insulinoma were evaluated. METHODS: [68Ga]Ga-HBED-CC-MAL-Cys39-exendin-4 ([68Ga]Ga-4) and its dimer ([68Ga]Ga-5) were synthesized from corresponding precursors. Cell uptake studies were evaluated in INS-1 cells. Biodistribution and microPET studies were performed in male normal Sprague-Dawley rats, diabetic rats and insulinoma xenograft NOD/SCID mice. RESULTS: [68Ga]Ga-4 and [68Ga]Ga-5 were efficiently radiolabelled by a simple one-step reaction without purification leading to high radiochemical yields and radiochemical purities (both >95%, decay corrected, n = 6, molar activity 15 GBq/µmol). They both showed excellent stability (~95%) in phosphate-buffered saline, pH 7.4, and in rat serum (~90%) for 2 h. Biodistribution studies and small animal PET/CT imaging showed that [68Ga]Ga-4 displayed specific uptake in rat pancreas and mouse insulinoma, and a reduced uptake in the pancreas of diabetic rat was observed (~62% reduction). Notably, it exhibited a rapid time-to-peak pancreatic uptake (0.96 ± 0.19%ID/g in 15 min) and fast clearance from the kidney (42% clearance in 30 min). Results suggested a favorable in vivo kinetics for human imaging studies. CONCLUSIONS: [68Ga]Ga-4 targeting GLP1R of pancreatic ß-cells may be a potentially useful PET agent and a suitable candidate for further structural modification studies. This agent has demonstrated several advantages, rapid time-to-peak pancreatic uptake and faster clearance from the kidney, factors may enhance diagnosis of diabetes and insulinoma.