The median survival time has been reported to vary between 5 and 8 years in low-grade (WHO grade 2) astrocytoma, and between 10 and 15 years for grade 2 oligodendroglioma. Targeted alpha therapy (TAT), using the modified peptide vector [213Bi]Bi/[225Ac]Ac-DOTA-substance P, has been developed to treat glioblastoma (GBM), a prevalent malignant brain tumor. In order to assess the risk of late neurotoxicity, assuming that reduced tumor cell proliferation and invasion should directly translate into good responses in low-grade gliomas (LGGs), a limited number of patients with diffuse invasive astrocytoma (n = 8) and oligodendroglioma (n = 3) were offered TAT. In two oligodendroglioma patients, TAT was applied as a second-line treatment for tumor progression, 10 years after targeted beta therapy using [90Y]Y-DOTA-substance P. The radiopharmaceutical was locally injected directly into the tumor via a stereotactic insertion of a capsule–catheter system. The activity used for radiolabeling was 2–2.5 GBq of Bismuth-213 and 17 to 35 MBq of Actinium-225, mostly applied in a single fraction. The recurrence-free survival times were in the range of 2 to 16 years (median 11 years) in low-grade astrocytoma (n = 8), in which TAT was administered following a biopsy or tumor debulking. Regarding oligodendroglioma, the recurrence-free survival time was 24 years in the first case treated, and 4 and 5 years in the two second-line cases. In conclusion, TAT leads to long-term tumor control in the majority of patients with LGG, and recurrence has so far not manifested in patients with low-grade (grade 2) astrocytomas who received TAT as a first-line therapy. We conclude that targeted alpha therapy has the potential to become a new treatment paradigm in LGG.

Supplementary Data from Evaluation of a 1,4,7,10-Tetraazacyclododecane-1,4,7,10-Tetraacetic Acid–Conjugated Bombesin-Based Radioantagonist for the Labeling with Single-Photon Emission Computed Tomography, Positron Emission Tomography, and Therapeutic Radionuclides

AbstractRecurrent prostate cancer presents a challenge to conventional treatment, particularly so to address micrometastatic and small-volume disease. Use of α-radionuclide therapy is considered as a highly effective treatment in such applications due to the shorter range and exquisite cytotoxicity of α-particles as compared with β-particles. 213Bi is considered an α-emitter with high clinical potential, due to its short half-life (45.6 minutes) being well matched for use in peptide-receptor radionuclide α-therapy; however, there is limited knowledge available within this context of use. In this study, two novel 213Bi-labeled peptides, DOTA-PEG4-bombesin (DOTA-PESIN) and DO3A-CH2CO-8-aminooctanoyl-Q-W-A-V-G-H-L-M-NH2 (AMBA), were compared with 177Lu (β-emitter)-labeled DOTA-PESIN in a human androgen-independent prostate carcinoma xenograft model (PC-3 tumor). Animals were injected with 177Lu-DOTA-PESIN, 213Bi-DOTA-PESIN, or 213Bi-AMBA to determine the maximum tolerated dose (MTD), biodistribution, and dosimetry of each agent; controls were left untreated or were given nonradioactive 175Lu-DOTA-PESIN. The MTD of 213Bi-DOTA-PESIN and 213Bi-AMBA was 25 MBq (0.68 mCi) whereas 177Lu-DOTA-PESIN showed an MTD of 112 MBq (3 mCi). At these dose levels, 213Bi-DOTA-PESIN and 213Bi-AMBA were significantly more effective than 177Lu-DOTA-PESIN. At the same time, 177Lu-DOTA-PESIN showed minimal, 213Bi-DOTA-PESIN slight, and 213Bi-AMBA marked kidney damage 20 to 30 weeks posttreatment. These preclinical data indicate that α-therapy with 213Bi-DOTA-PESIN or 213Bi-AMBA is more efficacious than β-therapy. Furthermore, 213Bi-DOTA-PESIN has a better safety profile than 213Bi-AMBA, and represents a possible new approach for use in peptide-receptor radionuclide α-therapy treating recurrent prostate cancer. Cancer Res; 71(3); 1009–18. ©2011 AACR.

Supplementary Figures 1-4 from Alpha- versus Beta-Particle Radiopeptide Therapy in a Human Prostate Cancer Model (²¹³Bi-DOTA-PESIN and ²¹³Bi-AMBA versus¹⁷⁷Lu-DOTA-PESIN)

Supplementary Table 2 from Alpha- versus Beta-Particle Radiopeptide Therapy in a Human Prostate Cancer Model (²¹³Bi-DOTA-PESIN and ²¹³Bi-AMBA versus¹⁷⁷Lu-DOTA-PESIN)

The biologically triggered reduction of Cu2+ to Cu+ has been postulated as a possible in vivo decomplexation pathway in 64/67Cu-based radiopharmaceuticals. In an attempt to hinder this phenomenon, we have previously developed a family of S-containing polyazamacrocycles based on 12-, 13-, or 14-membered tetraaza rings able to stabilize both oxidation states. However, despite the high thermodynamic stability of the resulting Cu2+/+ complexes, a marked [64Cu]Cu2+ release was detected in human serum, likely as a result of the partially saturated coordination sphere around the copper center. In the present work, a new hexadentate macrocyclic ligand, 1,4,7-tris[2-(methylsulfanyl)ethyl)]-1,4,7-triazacyclononane (NO3S), was synthesized by hypothesizing that a smaller macrocyclic backbone could thwart the observed demetalation by fully encapsulating the copper ion. To unveil the role of the S donors in the metal binding, the corresponding alkyl analogue 1,4,7-tris-n-butyl-1,4,7-triazacyclononane (TACN-n-Bu) was considered as comparison. The acid-base properties of the free ligands and the kinetic, thermodynamic, and structural properties of their Cu2+ and Cu+ complexes were investigated in solution and solid (crystal) states through a combination of spectroscopic and electrochemical techniques. The formation of two stable mononuclear species was detected in aqueous solution for both ligands. The pCu2+ value for NO3S at physiological pH was 6 orders of magnitude higher than that computed for TACN-n-Bu, pointing out the significant stabilizing contribution arising from the Cu2+-S interactions. In both the solid state and solution, Cu2+ was fully embedded in the ligand cleft in a hexacoordinated N3S3 environment. Furthermore, NO3S exhibited a remarkable ability to form a stable complex with Cu+ through the involvement of all of the donors in the coordination sphere. Radiolabeling studies evidenced an excellent affinity of NO3S toward [64Cu]Cu2+, as quantitative incorporation was achieved at high apparent molar activity (∼10 MBq/nmol) and under mild conditions (ambient temperature, neutral pH, 10 min reaction time). Human serum stability assays revealed an increased stability of [64Cu][Cu(NO3S)]2+ when compared to the corresponding complexes formed by 12-, 13-, or 14-membered tetraaza rings.

Supplementary Figures 1-4 from Alpha- versus Beta-Particle Radiopeptide Therapy in a Human Prostate Cancer Model (213Bi-DOTA-PESIN and 213Bi-AMBA versus177Lu-DOTA-PESIN)

Silver-111 is an attractive unconventional candidate for targeted cancer therapy as well as for single photon emission computed tomography and can be complemented by silver-103 for positron emission tomography noninvasive diagnostic procedures. However, the shortage of chelating agents capable of forming stable complexes tethered to tumor-seeking vectors has hindered their in vivo application so far. In this study, a comparative investigation of a series of sulfur-containing structural homologues, namely, 1,4,7-tris[2-(methylsulfanyl)ethyl)]-1,4,7-triazacyclononane (NO3S), 1,5,9-tris[2-(methylsulfanyl)ethyl]-1,5,9-triazacyclododecane (TACD3S), 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclotridecane (TRI4S), and 1,4,8,11-tetrakis[2-(methylsulfanyl)ethyl]-1,4,8,11-tetraazacyclotetradecane (TE4S) was conducted to appraise the influence of different polyazamacrocyclic backbones on Ag+ complexation. The performances of these macrocycles were also compared with those of the previously reported Ag+/[111Ag]Ag+-chelator 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetraazacyclododecane (DO4S). Nuclear magnetic resonance data supported by density functional theory calculations and X-ray crystallographic results gave insights into the coordination environment of these complexes, suggesting that all of the donor atoms are generally involved in the metal coordination. However, the modifications of the macrocycle topology alter the dynamic binding of the pendant arms or the conformation of the ring around the metal center. Combined pH/pAg-potentiometric and spectroscopic experiments revealed that the 12-member N4 backbone of DO4S forms the most stable Ag+ complex while both the enlargement and the shrinkage of the macrocyclic frame dwindle the stability of the complexes. Radiolabeling experiments, conducted with reactor-produced [111Ag]Ag+, evidenced that the thermodynamic stability trend is reflected in the ligand's ability to incorporate the radioactive ion at high molar activity, even in the presence of a competing cation (Pd2+), as well as in the integrity of the corresponding complexes in human serum. As a consequence, DO4S proved to be the most favorable candidate for future in vivo applications.

INTRODUCTION:Medullary thyroid cancer (MTC) is a rare malignant tumour of the parafollicular C-cells with an unpredictable clinical course and currently suboptimal diagnostic and therapeutic options, in particular in advanced disease. Overexpression of cholecystokinin-2 receptors (CCK2R) represents a promising avenue to diagnostic imaging and targeted therapy, ideally through a theranostic approach. MATERIALS AND METHODS:A translational study (GRAN-T-MTC) conducted through a Phase I multicentre clinical trial of the indium-111 labelled CP04 ([111In]In-CP04), a CCK2R-seeking ligand was initiated with the goal of developing a theranostic compound. Patients with proven advanced/metastatic MTC or short calcitonin doubling time were enrolled. A two-step concept was developed through the use of low- and high-peptide mass (10 and 50 μg, respectively) for safety assessment, with the higher peptide mass considered appropriate for therapeutic application. Gelofusine was co-infused in a randomized fashion in the second step for the evaluation of potential reduction of the absorbed dose to the kidneys. Imaging for the purpose of biodistribution, dosimetry evaluation, and diagnostic assessment were performed as well as pre-, peri-, and postprocedural clinical and biochemical assessment. RESULTS:Sixteen patients were enrolled. No serious adverse events after application of the compound at both peptide amounts were witnessed; transient tachycardia and flushing were observed in two patients. No changes in biochemistry and clinical status were observed on follow-up. Preliminary dosimetry assessment revealed the highest dose to urinary bladder, followed by the kidneys and stomach wall. The effective dose for 200 MBq of [111In]In-CP04 was estimated at 7±3 mSv and 7±1 mSv for 10 μg and 50 μg CP04, respectively. Administration of Gelofusine reduced the dose to the kidneys by 53%, resulting in the organ absorbed dose of 0.044±0.019 mSv/MBq. Projected absorbed dose to the kidneys with the use of [177Lu]Lu-CP04 was estimated at 0.9±0.4 Gy/7.4 GBq. [111In]In-CP04 scintigraphy was positive in 13 patients (detection rate of 81%) with superior diagnostic performance over conventional imaging. CONCLUSION:In the present study, [111In]In-CP04 was shown to be a safe and effective radiopharmaceutical with promising theranostic characteristics for patients with advanced MTC.

The objective of this study was to assess the safety, dosimetry, and efficacy of the 177Lu-labeled somatostatin receptor (SSTR) antagonist DOTA-p-Cl-Phe-cyclo(d-Cys-Tyr-d-4-amino-Phe(carbamoyl)-Lys-Thr-Cys)d-Tyr-NH2 (177Lu-DOTA-LM3) in patients with metastatic neuroendocrine neoplasms (NENs). Methods: Fifty-one patients (aged 27-76 y; mean, 51.6 ± 13.9 y) with metastatic NENs underwent peptide receptor radionuclide therapy (PRRT) with 177Lu-DOTA-LM3 between August 2017 and December 2019. The median administered activity per cycle was 6.1 ± 0.88 GBq (range, 2.8-7.4 GBq). 68Ga-NODAGA-LM3 PET/CT was used for patient selection and follow-up after 177Lu-DOTA-LM3 PRRT. Morphologic and molecular responses were evaluated in accordance with RECIST 1.1 and the criteria of the European Organisation for Research and Treatment of Cancer (EORTC). Treatment-related adverse events were graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events, version 5.0. Dosimetry was performed on 11 patients and compared with the SSTR agonist 177Lu-DOTATOC in 247 patients undergoing PRRT on the same dosimetry protocol. Results: Higher uptake and a longer effective half-life were found for 177Lu-DOTA-LM3 than for the agonist 177Lu-DOTATOC in the whole body and in the kidneys, spleen, and metastases, resulting in higher mean absorbed organ and tumor doses. All patients tolerated therapy without any serious acute adverse effects. Mild nausea without vomiting was observed in 5 (9.8%) patients; no other symptoms were reported. The most severe delayed adverse event was Common Terminology Criteria (CTC)-3 thrombocytopenia in 3 (5.9%) patients. Neither CTC-4 thrombocytopenia nor CTC-3-4 anemia or leukopenia was observed after treatment. No significant decline in renal function was observed, nor was hepatotoxicity. According to RECIST 1.1, disease control could be reached in 40 patients (disease control rate, 85.1%) of the 47 patients monitored after 177Lu-DOTA-LM3 PRRT, with a partial response in 17 (36.2%) and stable disease in 23 (48.9%), whereas 7 patients (14.9%) had progressive disease, and by EORTC criteria, there was complete remission in 2 patients (4.3%), partial remission in 21 (44.7%), stable disease in 18 (38.3%), and progressive disease in 6 (12.8%). Conclusion: The antagonist PRRT with 177Lu-DOTA-LM3 could be administered without severe adverse effects and was well tolerated by most patients, with thrombocytopenia occurring in only a few. No other severe adverse effects were observed; in particular, there was no nephrotoxicity. The SSTR antagonist 177Lu-DOTA-LM3 appears to be promising for PRRT, provides a favorable biodistribution and higher tumor radiation doses than SSTR agonists, and was effective in treating advanced metastatic NENs, especially in patients with low or no SSTR agonist binding, even achieving complete remission in some patients.

414 Objectives: The objective of this study was to assess the safety and efficacy of the 177Lu-labeled somatostatin receptor (SSTR) antagonist DOTA-p-Cl-Phe-cyclo (D-Cys-Tyr-D-4-amino-Phe(carbamoyl)-Lys-Thr-Cys)D-Tyr-NH2 (177Lu-DOTA-LM3) in patients with advanced metastatic neuroendocrine neoplasms (NENs). Methods: Fifty-one patients (age 27-76 y, mean age 51.6 ± 13.9 y) with advanced metastatic NENs underwent peptide receptor radionuclide therapy (PRRT) with 177Lu-DOTA-LM3 between August 2017 and November 2019. The median administered activity per cycle was 6.1±0.88 GBq (range 2.8-7.4 GBq). 68Ga-1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid-LM3 (68Ga-NODAGA-LM3) PET/CT was used for patient selection and follow-up after 177Lu-DOTA-LM3 PRRT. Treatment response was evaluated according to RECIST 1.1 as well as by molecular imaging criteria (EORTC). Hematologic status, renal function and liver function were documented before and after therapy. Treatment-related adverse events (AEs) were graded according to the CTCAE v.5.0. Dosimetry was performed in 11 patients.Results: 177Lu-DOTA-LM3 demonstrated high absorbed tumor doses (e.g., liver lesions 15-81 Gy/GBq) as compared to dose levels in normal organs, like kidneys 2.3±0.9 Gy/GBq (0.5-3.6 Gy/GBq) and liver 0.39±0.05 Gy/GBq (0.35-0.44Gy/GBq). All patients tolerated the therapy without any serious acute adverse effects. Mild nausea without vomiting was observed in 5 patients (9.8%), no other symptoms were noticed or reported. The most severe delayed adverse event was CTC-3 thrombocytopenia in 3 (5.9%) patients. No CTC-4 thrombocytopenia and no CTC 3-4 anemia or leukopenia was observed after treatment. There was a statistically significant reduction in leukocyte counts (7.04±2.18 vs 5.81 ± 2.21 Gpt/l, p=0.0066) and platelet counts (232±104 vs 192±70 Gpt/l, p=0.0299), whereas no statistically significant reduction occurred in hemoglobin level (7.74±0.99 vs 7.46±1.00 mmol/l, p=0.1778). No significant decline in renal function was observed (88.17±37.2 vs 87.11±37.91, p=0.8899). No hepatotoxicity was observed. Of 47 patients monitored after 1-2 cycles of 177Lu-DOTA-LM3 PRRT, a molecular response evaluation based on EORTC criteria revealed complete remission in 2 (4.3%), partial remission in 21 (44.7%), stable disease in 18 (38.3%), and progressive disease in 6 (12.8%) patients, and by RECIST, partial remission in 17 (36.2%), stable disease in 23 (48.9%), and progressive disease in 7 (14.9%) patients. In 37 patients there was no or low SSTR2 agonist binging on baseline 68Ga-DOTATOC or DATATATE PET/CT, i.e. insufficient for agonist PRRT with DOTATOC or DOTATATE. Conclusion:The SSTR antagonist 177Lu-DOTA-LM3 appears very promising for PRRT, especially in patients with low or no SSTR agonist binging, achieving even complete remission in some patients. “Antagonist PRRT” could be performed without severe adverse effects, was well tolerated by the majority of patients with thrombocytopenia occurring only in few patients, and was very effective in advanced metastatic NENs. No other adverse effects were observed, especially no renal toxicity.

Targeting tumor-expressed receptors using selective molecules for diagnostic, therapeutic, or both diagnostic and therapeutic (theragnostic) purposes is a promising approach in oncologic applications. Such approaches have increased significantly over the past decade. Peptides such as gastrin-releasing peptide receptors targeting radiopharmaceuticals are small molecules with fast blood clearance and urinary excretion. They demonstrate good tissue diffusion, low immunogenicity, and highly selective binding to their target cell-surface receptors. They are also easily produced. Gastrin-releasing peptide receptors, part of the bombesin family, are overexpressed in many tumors, including breast and prostate cancer, and therefore represent an attractive target for future development.

Purpose Insulinomas are predominantly benign neuroendocrine tumors originating from beta cells within the islets of Langerhans of the endocrine pancreas. Because surgical resection represents the only curative therapy option, exact tumor localization and discrimination of insulinomas from focal or diffuse manifestations of congenital hyperinsulinism are crucial for optimal treatment strategies. We investigated the diagnostic value of glucagon-like peptide 1 receptor PET/CT using 68 Ga-DOTA-exendin 4 for detecting insulinomas and compared the diagnostic value of PET scans performed at 2 time points. Methods In 10 patients with clinically and biochemically suspected insulinoma, PET/CT was performed at 1 hour (PET1) and 2 hours (PET2) after injection of 68 Ga-DOTA-exendin 4. In this retrospective analysis, tracer uptake was visually assessed in both scans by 2 independent readers. SUVmax and tumor-to-background ratio (TBR) of focal lesions were assessed. Imaging results were compared with histopathologic findings, if patients underwent resection. Results Increased focal 68 Ga-DOTA-exendin 4 uptake was observed in 8 of 10 patients concordantly by both readers. Seven patients with focal uptake underwent surgery with tumor enucleation and histopathologic proof of insulinoma (7/8). Two of 10 patients without focal uptake were considered to suffer from diffuse form of congenital hyperinsulinism and consequently received medical treatment. A significant increase of tumoral SUVmax on PET2 (PET1: SUVmax 20.2 ± 8.2 g/mL; PET2: SUVmax 24.7 ± 7.9 g/mL; P = 0.0018) did not result in a significant improvement in TBR (PET1: TBR 4.9 ± 1.7; PET2: TBR 4.3 ± 1.2; P = 0.2892). Conclusions Focal uptake of 68 Ga-DOTA-exendin 4 reliably indicated insulinomas as histopathologically confirmed in all patients undergoing consecutive surgery. The diagnostic value of PET2 was not found to be superior to PET1, indicating that a single 1-hour 68 Ga-DOTA-exendin 4 PET/CT scan is a sufficient and convenient approach for patient care.

Precision oncology is being driven by rapid advances in novel diagnostics and therapeutic interventions, with treatments targeted to the needs of individual patients on the basis of genetic, biomarker, phenotypic, or psychosocial characteristics that distinguish a given patient from other patients with similar clinical presentations. Inherent in the theranostics paradigm is the assumption that diagnostic test results can precisely determine whether an individual is likely to benefit from a specific treatment. As part and integral in the current era of precision oncology, theranostics in the context of nuclear medicine aims to identify the appropriate molecular targets in neoplasms (diagnostic tool), so that the optimal ligands and radionuclides (therapeutic tool) with favorable labeling chemistry can be selected for personalized management of a specific disease, taking into consideration the specific patient, and subsequently monitor treatment response. Over the past two decades, the use of gallium-68 labeled peptides for somatostatin receptor (SSTR)-targeted PET/CT (or PET/MRI) imaging followed by lutetium-177 and yttrium-90 labeled SSTR-agonist for peptide receptor radionuclide therapy has demonstrated remarkable success in the management of neuroendocrine neoplasms, and paved the way to other indications of theranostics. Rapid advances are being made in the development of other peptide-based radiopharmaceuticals, small molecular-weight ligands and with newer radioisotopes with more favorable kinetics, potentially useful for theranostics strategies for the clinical application. The present review features the Bad Berka experience with first-in-human studies of new radiopharmaceuticals, for example, prostate-specific membrane antigen ligand, gastrin-releasing peptide receptor, neurotensin receptor 1 ligand, novel SSTR-targeting peptides and nonpeptide, and bone-seeking radiopharmaceuticals. Also new radioisotopes, for example, actinium (225Ac), copper (64Cu), scandium (44Sc), and terbium (152Tb/161Tb) will be discussed briefly demonstrating the development from basic science to precision oncology in the clinical setting.

Introduction: Prostate cancer (PCa) often shows an overexpression of the gastrin-releasing peptide receptor (GRPr). Therefore, GRPr is a possible theragnostic target. An interesting antagonist GRPr-ligand is RM2 or BAY86-7548. This study examines the accuracy of positron emission tomography (PET) with [Ga-68]Ga-RM2 for diagnostic imaging of primary PCa (pPCa) compared to histopathology in patients undergoing radical prostatectomy (RP). Methods: [Ga-68]Ga-RM2-PET examinations were performed in 15 patients before RP. All prostate specimens were histopathologically examined based on predefined spatial octants. Each prostate volume on PET was subdivided into octants, which were correlated to histopathology and evaluated according to presence of tumor by two experienced examiners. Additionally, PET data was evaluated by volume of interest (VOI) analyses in terms of maximum standardized uptake value (SUVmax) and normalized SUVmax relative to background activity (rSUVmax). Receiver operating characteristic (ROC) curves for SUVmax and rSUVmax were calculated. Results: At least one focus of increased [Ga-68]Ga-RM2 uptake corresponding to a tumor manifestation on histology was found in 14 of 15 patients (93%). Spatial concordance of visual PET readings with histopathology was very variable. Intraindividual agreement reached from <= 2 octants in three, 3-5 octants in six to >= 6 octants in six patients, resulting in a relatively low correlation of visual PET readings with histopathology (accuracy = 0.63; p = 0.0018). Lesion-based analysis found a sensitivity of 69% and a positive predictive value of 73%. Concordantly, the octant-based ROC curves for SUVmax and rSUVmax indicated a relatively low diagnostic performance (area under the curve of 0.59 and 0.61, respectively). Conclusions: [Ga-68]Ga-RM2-PET shows only a relatively low diagnostic accuracy for pPCa compared to histopathology on an octant basis, which may be explained to some extent by methodological weaknesses. Further studies need to explore, whether the observed high interindividual variability of agreement between [Ga-68]Ga-RM2-PET and histopathology can be explained by different tumor biologies or other coincident prostatic pathologies. (C) 2019 Elsevier Inc. All rights reserved.

Copper-64 is an attractive radionuclide for PET imaging and is frequently used in clinical applications. The aim of this study was to perform a side-by-side comparison of the in vitro and in vivo performance of 64Cu-NODAGA-JR11 (NODAGA = 1,4,7-triazacyclononane,1-glutaric acid,4,7-acetic acid, JR11 = p-Cl-Phe-cyclo(D-Cys-Aph(Hor)-D-Aph(cbm)-Lys-Thr-Cys)D-Tyr-NH2), a somatostatin receptor 2 antagonist, with the clinically used sst2 agonist 64Cu-DOTA-TATE ((TATE = D-Phe-cyclo(Cys-Tyr-D-Trp-Lys-Thr-Cys)Thr). In vitro studies demonstrated Kd values of 5.7±0.95 nM (Bmax = 4.1±0.18 nM) for the antagonist 64/natCu-NODAGA-JR11 and 20.1±4.4. nM (Bmax = 0.48±0.18 nM) for the agonist 64/natCu-DOTA-TATE. Cell uptake studies showed the expected differences between agonists and antagonists. Whereas 64Cu-DOTA-TATE (the agonist) showed very effective internalization in the cell culture assay (with 50% internalized at 4 hours post-peptide addition under the given experimental conditions), 64Cu-NODAGA-JR11 (the antagonist) showed little internalization but strong receptor-mediated uptake at the cell membrane. Biodistribution studies of 64Cu-NODAGA-JR11 showed rapid blood clearance and tumor uptake with increasing tumor-to-relevant organ ratios within the first 4 hours and in some cases, 24 hours, respectively. The tumor washout was slow or non-existent in the first 4 hours, whereas the kidney washout was very efficient, leading to high and increasing tumor-to-kidney ratios over time. Specificity of tumor uptake was proven by co-injection of high excess of non-radiolabeled peptide, which led to >80% tumor blocking. 64Cu-DOTA-TATE showed less favorable pharmacokinetics, with the exception of lower kidney uptake. Blood clearance was distinctly slower and persistent higher blood values were found at 24 hours. Uptake in the liver and lung was relatively high and also persistent. The tumor uptake was specific and similar to that of 64Cu-NODAGA-JR11 at 1 h, but release from the tumor was very fast, particularly between 4 and 24 hours. Tumor-to-normal organ ratios were distinctly lower after 1 hour. This is indicative of insufficient in vivo stability. PET studies of 64Cu-NODAGA-JR11 reflected the biodistribution data with nicely delineated tumor and low background. 64Cu-NODAGA-JR11 shows promising pharmacokinetic properties for further translation into the clinic.

42 Aim: The first clinical studies with somatostatin receptor (SSR) antagonist (DOTA-BASS, DOTA/NOTAGA-JR11) based PET/CT imaging have reported the feasibility and higher tumor detection rates in SSR-expressing tumors than the currently used SSR-agonists. This study aims to assess the diagnostic feasibility of 68Ga-based PET/CT imaging of the SSR-antagonist LM3 [p-Cl-Phe-cyclo(D-Cys-Tyr-D-4-amino-Phe(carbamoyl)-Lys-Thr-Cys)D-Tyr-NH2] conjugated to the chelator NODAGA (1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid) in humans with SSR-expressing solid tumors, and compare it qualitatively as well as quantitatively with the SSR-agonist 68Ga-DOTATOC PET/CT. Methods: From February to October 2017, 43 68Ga-NODAGA-LM3 PET/CT (LM3) studies were performed in 40 patients with SRR-expressing solid tumors (GEP-NEN, n=16; lung/mediastinal-NEN, n=8; paraganglioma/pheochromocytoma, n=7; thyroid cancer, n=3; renal cell carcinoma, n=1; meningioma, n=1; cervix MiNEN, n=1; CUP-NEN, n=1), as well as for establishing the initial diagnosis in the case of clinical suspicion of a neuroendocrine neoplasm (n=2). The acquired LM3 images were analyzed qualitatively (visually) and semi-quantitatively (SUVmax). Out of these, 3 patients (P1, pancreas-NEN; P2, paraganglioma; P3, pheochromocytoma) had a 68Ga-DOTATOC PET/CT (TOC) within 3 months, for comparative analyses. In these patients, 68Ga-NODAGA-LM3 (mean activity = 285 MBq, radiochemical purity >95%, specific activity 20-50 MBq/nmol) was administered followed by PET/CT imaging at 50 min p.i. Tumor-to-background ratios (TBR) were calculated using volume of interest (VOI) based SUVmax for 5 target lesions (TL) and SUVmean for reference tissue (RT), namely, liver, kidney, gluteus muscle, and spleen (P1 had previous splenectomy), for the corresponding LM3 and TOC studies. Results: With respect to the clinical indication, LM3 was positive in 36 and negative in 7 studies, respectively. Where positive, LM3 demonstrated excellent image quality with high specific uptake in SSR-expressing lesions. For patients P1, P2 and P3, LM3 enabled detection of additional lesions (P1, liver n=3, lymph node n=1, bone n=6; P2, n>140 skeletal; P3, liver n=3) compared to TOC. The comparative physiological uptake of LM3 to TOC (SUVmean LM3:TOC) in RT was for P1 (liver 3.5:4.2, kidney 11.7:4.6, gluteus 0.7:0.4), P2 (liver 3.7:5.4, kidney 9.9:6.3, spleen 13.9:26.5, gluteus 0.4:0.4), and P3 (liver 5.7:9.2, kidney 13.4:9.9, spleen 17.3:21.1, gluteus 0.5:0.5), respectively. Applying the same TL, LM3 associated TBR (SUVmax-TL:SUVmean-RT) was for P1 (TL-liver 5:0.3, TL-kidney 1.5:0.4, TL-gluteus 25:5), P2 (TL-liver 48:35.9, TL-kidney 18.1:30.8, TL-spleen 12.9:7.3, TL-gluteus 405:506.8), and P3 (TL-liver 52.7:31.7, TL-kidney 22.3:29.3, TL-spleen 17.3:13.7, TL-gluteus 599:582.2), respectively. Conclusion: PET/CT imaging with the SSR-antagonist 68Ga-NODAGA-LM3 demonstrated excellent image quality with high specific uptake in SSR-expressing lesions. Despite the limited number of patients for direct comparison with 68Ga-DOTATOC, 68Ga-NODAGA-LM3 detected more SSR-expressing lesions, which adheres to the recently reported results comparing radiolabeled SSR-antagonists with agonists. Compared to the agonists, it also provides a significant advantage of detecting more lesions in the liver due to the distinctively higher tumor-to-liver ratio. The results emphasize the potential of the SSR-antagonist 68Ga-NODAGA-LM3 for PET/CT imaging of SSR-expressing solid tumors in humans.

Somatostatin receptor targeting radiopeptides are successfully being used to image, stage, and monitor patients with neuroendocrine tumours. They are exclusively agonists that internalise upon binding to the relevant receptor. According to recent reports, antagonists may be preferable to agonists. To date, 99mTc-labelled somatostatin receptor antagonists have attracted little attention. Here, we report on a new somatostatin receptor subtype 2 (sst2) antagonist, SS-01 (p-Cl-Phe-cyclo(D-Cys-Tyr-D-Trp-Lys-Thr-Cys)D-Tyr-NH2), with the aim of developing 99mTc-labelled ligands for SPECT/CT imaging. SS-01 was prepared using Fmoc solid-phase synthesis and subsequently coupled to the chelators 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), 6-carboxy-1,4,8,11-tetraazaundecane (N4), and 6-hydrazinonicotinic acid (HYNIC) to form the corresponding peptide-chelator conjugates SS-03, SS-04, and SS-05, respectively. SS-04 and SS-05 were radiolabelled with 99mTc and SS-03 with 177Lu. Binding affinity and antagonistic properties were determined using autoradiography and immunofluorescence microscopy. Biodistribution and small animal SPECT/CT studies were performed on mice bearing HEK293-rsst2 xenografts.