177Lu-3BP-227 for Neurotensin Receptor 1-Targeted Therapy of Metastatic Pancreatic Adenocarcinoma: First Clinical Results.

Neurotensin receptor 1 (NTR1) is overexpressed in ductal pancreatic adenocarcinoma, which is still one of the deadliest cancers, with a very poor prognosis. Eligible patients were offered salvage radiopharmaceutical therapy with the novel NTR1 antagonist 177Lu-3BP-227. Methods: Six patients with confirmed ductal pancreatic adenocarcinoma who had exhausted all other treatment options received 177Lu-3BP-227 for evaluation of NTR1 expression in vivo. Three patients received treatment activities of 5.1-7.5 GBq. Results: Administration of 177Lu-3BP-227 was well tolerated by all patients. The kidneys were identified as the dose-limiting organ. The most severe adverse event was reversible grade 2 anemia. One patient achieved a partial response and experienced significant improvement of symptoms and quality of life. This patient survived 13 mo from diagnosis and 11 mo from the start of 177Lu-3BP-227 therapy. Conclusion: This initial report provides clinical evidence of the feasibility of treatment of ductal pancreatic adenocarcinoma using 177Lu-3BP-227.

First-in-Human PET/CT Imaging of Metastatic Neuroendocrine Neoplasms with Cyclotron-Produced 44Sc-DOTATOC: A Proof-of-Concept Study.

44Sc is a promising positron emission tomography (PET) radionuclide (T1/2 = 4.04 hours, Eß+average = 632 keV) and can be made available, using a cyclotron production route, in substantial quantities as a highly pure product. Herein, the authors report on a first-in-human PET/CT study using 44Sc-DOTATOC prepared with cyclotron-produced 44Sc. The production of 44Sc was carried out through the 44Ca(p,n)44Sc nuclear reaction at Paul Scherrer Institut, Switzerland. After separation, 44Sc was shipped to Zentralklinik Bad Berka, Germany, where radiolabeling was performed, yielding radiochemically pure 44Sc-DOTATOC. Two patients, currently followed up after peptide receptor radionuclide therapy of metastatic neuroendocrine neoplasms, participated in this proof-of-concept study. Blood sampling was performed before and after application of 44Sc-DOTATOC. PET/CT acquisitions, performed at different time points after injection of 44Sc-DOTATOC, allowed detection of even very small lesions on delayed scans. No clinical adverse effects were observed and the laboratory hematological, renal, and hepatic profiles remained unchanged. In this study, cyclotron-produced 44Sc was used in the clinic for the first time. It is attractive for theranostic application with 177Lu, 90Y, or 47Sc as therapeutic counterparts. 44Sc-based radiopharmaceuticals will be of particular value for PET facilities without radiopharmacy, to which they can be shipped from a centralized production site.

Theranostic Perspectives in Prostate Cancer with the Gastrin-Releasing Peptide Receptor Antagonist NeoBOMB1: Preclinical and First Clinical Results.

We recently introduced the potent gastrin-releasing peptide receptor (GRPR) antagonist 68Ga-SB3 (68Ga-DOTA-p-aminomethylaniline-diglycolic acid-DPhe-Gln-Trp-Ala-Val-Gly-His-Leu-NHEt), showing excellent tumor localizing efficacy in animal models and in patients. By replacement of the C-terminal Leu13-Met14-NH2 dipeptide of SB3 by Sta13-Leu14-NH2, the novel GRPR antagonist NeoBOMB1 was generated and labeled with different radiometals for theranostic use. We herein report on the biologic profile of resulting 67/68Ga-, 111In-, and 177Lu-NeoBOMB1 radioligands in GRPR-expressing cells and mouse models. The first evidence of prostate cancer lesion visualization in men using 68Ga-NeoBOMB1 and PET/CT is also presented. METHODS: NeoBOMB1 was radiolabeled with 67/68Ga, 111In, and 177Lu according to published protocols. The respective metalated species natGa-, natIn-, and natLu-NeoBOMB1 were also synthesized and used in competition binding experiments against [125I-Tyr4]BBN in GRPR-positive PC-3 cell membranes. Internalization of 67Ga-, 111In-, and 177Lu-NeoBOMB1 radioligands was studied in PC-3 cells at 37°C, and their metabolic stability in peripheral mouse blood was determined by high-performance liquid chromatography analysis of blood samples. Biodistribution was performed by injecting a 67Ga-, 111In-, or 177Lu-NeoBOMB1 bolus (74, 74, or 370 kBq, respectively, 100 µL, 10 pmol total peptide ± 40 nmol Tyr4-BBN: for in vivo GRPR blockade) in severe combined immunodeficiency mice bearing PC-3 xenografts. PET/CT images with 68Ga-NeoBOMB1 were acquired in prostate cancer patients. RESULTS: NeoBOMB1 and natGa-, natIn-, and natLu-NeoBOMB1 bound to GRPR with high affinity (half maximal inhibitory concentration, 1-2 nM). 67Ga-, 111In-, and 177Lu-NeoBOMB1 specifically and strongly bound on the cell membrane of PC-3 cells displaying low internalization, as expected for receptor antagonists. They showed excellent metabolic stability in peripheral mouse blood (>95% intact at 5 min after injection). After injection in mice, all 3 (67Ga-, 111In-, and 177Lu-NeoBOMB1) showed comparably high and GRPR-specific uptake in the PC-3 xenografts (e.g., 30.6 ± 3.9, 28.6 ± 6.0, and >35 percentage injected dose per gram at 4 h after injection, respectively), clearing from background predominantly via the kidneys. During a translational study in prostate cancer patients, 68Ga-NeoBOMB1 rapidly localized in pathologic lesions, achieving high-contrast imaging. CONCLUSION: The GRPR antagonist radioligands 67Ga-, 111In-, and 177Lu-NeoBOMB1, independent of the radiometal applied, have shown comparable behavior in prostate cancer models, in favor of future theranostic use in GRPR-positive cancer patients. Such translational prospects were further supported by the successful visualization of prostate cancer lesions in men using 68Ga-NeoBOMB1 and PET/CT.

Radiolabeling of DOTA-like conjugated peptides with generator-produced (68)Ga and using NaCl-based cationic elution method.

Gallium-68 ((68)Ga) is a generator-produced radionuclide with a short half-life (t½ = 68 min) that is particularly well suited for molecular imaging by positron emission tomography (PET). Methods have been developed to synthesize (68)Ga-labeled imaging agents possessing certain drawbacks, such as longer synthesis time because of a required final purification step, the use of organic solvents or concentrated hydrochloric acid (HCl). In our manuscript, we provide a detailed protocol for the use of an advantageous sodium chloride (NaCl)-based method for radiolabeling of chelator-modified peptides for molecular imaging. By working in a lead-shielded hot-cell system,(68)Ga(3+) of the generator eluate is trapped on a cation exchanger cartridge (100 mg, ∼8 mm long and 5 mm diameter) and then eluted with acidified 5 M NaCl solution directly into a sodium acetate-buffered solution containing a DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) or DOTA-like chelator-modified peptide. The main advantages of this procedure are the high efficiency and the absence of organic solvents. It can be applied to a variety of peptides, which are stable in 1 M NaCl solution at a pH value of 3-4 during reaction. After labeling, neutralization, sterile filtration and quality control (instant thin-layer chromatography (iTLC), HPLC and pH), the radiopharmaceutical can be directly administered to patients, without determination of organic solvents, which reduces the overall synthesis-to-release time. This procedure has been adapted easily to automated synthesis modules, which leads to a rapid preparation of (68)Ga radiopharmaceuticals (12-16 min).

177Lu-Labeled Prostate-Specific Membrane Antigen Radioligand Therapy of Metastatic Castration-Resistant Prostate Cancer: Safety and Efficacy.

UNLABELLED: The objective of this study was to analyze the safety and efficacy of the (177)Lu-labeled DOTAGA-based prostate-specific membrane antigen (PSMA) ligand (177)Lu-DOTAGA-(I-y)fk(Sub-KuE) ((177)Lu-PSMA) in patients with metastatic castration-resistant prostate cancer (mCRPC). METHODS: Fifty-six mCRPC patients underwent PSMA radioligand therapy (RLT) with (177)Lu-PSMA. (68)Ga-PSMA-(N,N'-bis-[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N'-diacetic acid) ((68)Ga-PSMA) PET/CT was used for patient selection and follow-up after PSMA RLT. Hematologic status, renal function, and serum prostate-specific antigen levels were documented before and after therapy. Dosimetry was performed in 30 patients. RESULTS: (177)Lu-PSMA demonstrated high absorbed tumor doses (median, 3.3 mGy/MBq) compared with the levels in normal organs. Parotid glands received higher doses (1.3 mGy/MBq) than kidneys (0.8 mGy/MBq). All patients tolerated the therapy without any acute adverse effects. Except for mild reversible xerostomia in 2 patients, no long-term side effects were observed. There was a small but statistically significant reduction in erythrocyte and leukocyte counts; only the reduction in erythrocyte counts decreased slightly below the reference range. No thrombocytopenia occurred. The severity of pain was significantly reduced in 2 of 6 patients (33.3%). A decrease in prostate-specific antigen levels was noted in 45 of 56 patients (80.4%). Of 25 patients monitored for at least 6 mo after 2 or more PSMA RLT cycles, a molecular response evaluation ((68)Ga-PSMA PET/CT) revealed partial remission in 14, stable disease in 2, and progressive disease in 9 patients. Contrast-enhanced CT revealed partial remission in 5, stable disease in 13, and progressive disease in 7 patients. The median progression-free survival was 13.7 mo, and the median overall survival was not reached during follow-up for 28 mo. CONCLUSION: PSMA RLT with (177)Lu-PSMA is feasible, safe, and effective in end-stage progressive mCRPC with appropriate selection and follow-up of patients by (68)Ga-PSMA PET/CT through application of the concept of theranostics.

68Ga- and 177Lu-Labeled PSMA I&T: Optimization of a PSMA-Targeted Theranostic Concept and First Proof-of-Concept Human Studies.

UNLABELLED: On the basis of the high and consistent expression of prostate-specific membrane antigen (PSMA) in metastatic prostate cancer (PC), the goal of this study was the development, preclinical evaluation, and first proof-of-concept investigation of a PSMA inhibitor for imaging and therapy (PSMA I&T) for (68)Ga-based PET and (177)Lu-based endoradiotherapeutic treatment in patients with metastatic and castration-resistant disease. METHODS: PSMA I&T was synthesized in a combined solid phase and solution chemistry strategy. The PSMA affinity of (nat)Ga-/(nat)Lu-PSMA I&T was determined in a competitive binding assay using LNCaP cells. Internalization kinetics of (68)Ga- and (177)Lu-PSMA I&T were investigated using the same cell line, and biodistribution studies were performed in LNCaP tumor-bearing CD-1 nu/nu mice. Initial human PET imaging studies using (68)Ga-PSMA I&T, as well as endoradiotherapeutic treatment of 2 patients with metastatic PC using (177)Lu-PSMA I&T, were performed. RESULTS: PSMA I&T and its cold gallium and lutetium analog revealed nanomolar affinity toward PSMA. The DOTAGA (1,4,7,10-tetraazacyclododecane-1-(glutamic acid)-4,7,10-triacetic acid) conjugate PSMA I&T allowed fast and high-yield labeling with (68)Ga(III) and (177)Lu(III). Uptake of (68)Ga-/(177)Lu-PSMA I&T in LNCaP tumor cells is highly efficient and PSMA-specific, as demonstrated by competition studies both in vitro and in vivo. Tumor targeting and tracer kinetics in vivo were fast, with the highest uptake in tumor xenografts and kidneys (both PSMA-specific). First-in-human (68)Ga-PSMA I&T PET imaging allowed high-contrast detection of bone lesions, lymph node, and liver metastases. Endoradiotherapy with (177)Lu-PSMA I&T in 2 patients was found to be effective and safe with no detectable side effects. CONCLUSION: (68)Ga-PSMA I&T shows potential for high-contrast PET imaging of metastatic PC, whereas its (177)Lu-labeled counterpart exhibits suitable targeting and retention characteristics for successful endoradiotherapeutic treatment. Prospective studies on larger cohorts of patients are warranted and planned.

Purification and labeling strategies for (68)Ga from (68)Ge/ (68)Ga generator eluate.

For successful labeling, (68)Ge/(68)Ga generator eluate has to be concentrated (from 10 mL or more to less than 1 mL) and to be purified of metallic impurities, especially Fe(III), and (68)Ge breakthrough. Anionic, cationic and fractional elution methods are well known. We describe two new methods: (1) a combined cationic-anionic purification and (2) an easy-to-use and reliable cationic purification with NaCl solution. Using the first method, (68)Ga from 10 mL generator eluate was collected on a SCX cartridge, then eluted with 1.0 mL 5.5 M HCl directly on an anion exchanger (30 mg AG1X8). After drying with a stream of helium, (68)Ga was eluted with 0.4 mL water into the reaction vial. We provide as an example labeling of BPAMD. Using the second method, (68)Ga from 10 mL generator eluate was collected on a SCX cartridge, then eluted with a hydrochloric solution of sodium chloride (0.5 mL 5 M NaCl, 12.5 µL 5.5 M HCl) into the reaction vial, containing 40 µg DOTATOC and 0.5 mL 1 M ammonium acetate buffer pH 4.5. After heating for 7 min at 90°C, the reaction was finished. Radiochemical purity was higher than 95% without further purification. No (68)Ge breakthrough was found in the final product.

Simplified NaCl based (68)Ga concentration and labeling procedure for rapid synthesis of (68)Ga radiopharmaceuticals in high radiochemical purity.

A simple sodium chloride (NaCl) based (68)Ga eluate concentration and labeling method that enables rapid, high-efficiency labeling of DOTA conjugated peptides in high radiochemical purity is described. The method utilizes relatively few reagents and comprises minimal procedural steps. It is particularly well-suited for routine automated synthesis of clinical radiopharmaceuticals. For the (68)Ga generator eluate concentration step, commercially available cation-exchange cartridges and (68)Ga generators were used. The (68)Ga generator eluate was collected by use of a strong cation exchange cartridge. 98% of the total activity of (68)Ga was then eluted from the cation exchange cartridge with 0.5 mL of 5 M NaCl solution containing a small amount of 5.5 M HCl. After buffering with ammonium acetate, the eluate was used directly for radiolabeling of DOTATOC and DOTATATE. The (68)Ga-labeled peptides were obtained in higher radiochemical purity compared to other commonly used procedures, with radiochemical yields greater than 80%. The presence of (68)Ge could not be detected in the final product. The new method obviates the need for organic solvents, which eliminates the required quality control of the final product by gas chromatography, thereby reducing postsynthesis analytical effort significantly. The (68)Ga-labeled products were used directly, with no subsequent purification steps, such as solid-phase extraction. The NaCl method was further evaluated using an automated fluid handling system and it routinely facilitates radiochemical yields in excess of 65% in less than 15 min, with radiochemical purity consistently greater than 99% for the preparation of (68)Ga-DOTATOC.

Synthesis of O-(2-[18F]fluoroethyl)-L-tyrosine based on a cartridge purification method.

INTRODUCTION: O-(2-[(18)F]fluoroethyl)-L-tyrosine (FET) is widely used as a positron emission tomography tracer for brain tumors. Usually, a high-performance liquid chromatography (HPLC) purification at the end of the two-step synthesis is applied. In this work, we report an automatic radiosynthesis of FET with a purification procedure based on standard cartridges. METHODS: O-(2-[(18)F]fluoroethyl)-L-tyrosine was prepared by [(18)F]fluoroethylation of L-tyrosine by a two-step synthesis using a modified [(11)C]methionine module (Nuclear Interface). In the first reaction step, we synthesized [(18)F]fluoroethyltosylate starting from [(18)F]fluoride. After a purification step, L-tyrosine was [(18)F]fluoroethylated with [(18)F]fluoroethyltosylate. The final reaction mixture was purified by means of solid phase extraction. The FET was trapped on an SCX cartridge, eluted with saline solution and trapped again on an HRX cartridge. For a second purification step, the FET was eluted from the HRX cartridge with ammonium acetate buffer and collected on two SCX cartridges followed by a washing step with water. The final product was eluted with saline solution and neutralised with 450 µl NaHCO(3) solution (8.4%). RESULTS: The synthesis was finished after 50 min and delivered the FET in a range of 3-16 GBq. The synthesis typically yielded 41% (21 experiments) of FET (d.c.) without an HPLC purification step. The radiochemical purity ranged between 97% and 100%. CONCLUSION: We present a radiosynthesis of FET where the usually used HPLC purification procedure has been substituted by a purification step based on standard cartridges. This method is useful for automatic modules without an expensive HPLC purification unit and for the routine production of FET.

Rhenium and 99m-technetium complexes of monosaccharide based tripodal triamines as potential radio imaging agents.

A synthetic pathway to new sugar containing tripodal triamines of the TAME type (1,1,1-tris(aminomethyl)ethane) is presented. The tripodal bromo substituted precursors Ac3Xyl-O-CH2C(CH2Br)3, Ac4Glc-O-CH2C(CH2Br)3 and Ac4Gal-O-CH2C(CH2Br)3 (2a-c) were obtained by glycosidation reaction of the fully acetylated glycopyranosides with pentaerythritol tribromide. Nucleophilic substitution to the corresponding azides with sodium azide and deprotection of the sugars, followed by hydrogenation reaction in the presence of PtO2 leads to the triamines Xyl-O-CH2C(CH2NH2)3, Glc-O-CH2C(CH2NH2)3 and Gal-O-CH2C(CH2NH2)3 (5a-c). The triamines form complexes of the type [Re(CO)3L]Cl (6a-c). The precursors as well as the final ligands and complexes were characterized by elemental analysis, IR and NMR spectroscopy as well as mass spectrometry. The synthesis of the analogous radiolabelled 99mTc complex with galactosyl appendage 7c (LGal-O-CH2C(CH2NH2)3) was achieved for 5c and its stability over a period of 24 h could be verified by HPLC analysis, confirming the significant stability of 7c against histidine exchange.

Synthesis and structure of novel sugar-substituted bipyridine complexes of rhenium and 99m-technetium.

Novel ligands have been obtained from the reaction of 4,4'-dibromomethyl-2,2'-bipyridine with 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosylthiol, 2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosylthiol or 2,3,4,6-tetra-O-acetyl-alpha-D-thioacetylmannopyranoside in which the sugar residues are thioglycosidically linked to the bipyridine in the 4,4'-position. Cleavage of the acetyl groups affords hydrophilic symmetric ligands with free hydroxyl groups. Reaction of the new glycoconjugated ligands (L) with [Re(CO)(5)Cl] yields fluorescent complexes of general formula [Re(L)(CO)(3)Cl], which were characterised by mass spectrometry, elemental analysis and (1)H and (13)C NMR, IR, UV/Vis and fluorescence spectroscopy. These complexes exhibit excellent solubility and stability in organic solvents or water, depending on the residues of the sugar. One complex, namely tricarbonyl-4,4'-bis[(2,3,4,6-tetra-O-acetyl-beta-D-glycopyranosyl)thiomethyl]-2,2'-bipyridinerheniumtricarbonylo chloride, has been characterised by X-ray crystallography. A non-symmetric structure of the complexes could be assigned. Radiolabelling of the unprotected ligands with [(99m)Tc(H(2)O)(3)(CO)(3)](+) affords the corresponding water-soluble technetium complexes (in quantitative yields), which were characterised by their HPLC radiation traces. The formed complexes are stable for several hours in the presence of histidine but show partial ligand-exchange after one day.