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Background: Positron emission tomography (PET) is now an established diagnostic method for myocardial perfusion imaging (MPI) in coronary artery disease, which is the main cause of death globally. The available tracers show several limitations, therefore, the 18F-labelled tracer is in high demand nowadays. The preclinical studies on normal Wistar rats aimed to characterise two potential, novel radiotracers, [18F]SYN1 and [18F]SYN2, to evaluate which is a better candidate for PET MPI cardiotracer. Results: The dynamic microPET images showed rapid myocardial uptake for both tracers. However, the uptake was higher and also stable for [18F]SYN2, with an average standardized uptake value of 3.8. The biodistribution studies confirmed that [18F]SYN2 uptake in the cardiac muscle was high and stable (3.02%ID/g at 15 min and 2.79%ID/g at 6 h) compared to [18F]SYN1 (1.84%ID/g at 15 min and 0.32%ID/g at 6 h). The critical organs determined in dosimetry studies were the small intestine and the kidneys. The estimated effective dose for humans was 0.00714 mSv/MBq for [18F]SYN1 and 0.0109 mSv/MBq for [18F]SYN2. The tested dose level of 2 mg/kg was considered to be the No Observed Adverse Effect Level (NOAEL) for both candidates. The better results were achieved for [18F]SYN2, therefore, further preclinical studies were conducted only for this tracer. Radioligand binding assays showed significant responses in 3 from 68 assays: muscarinic acetylcholine M1 and M2 receptors and potassium channel hERG. The compound was mostly metabolised via an oxidative N-dealkylation, while the fluor substituent was not separated from the molecule. Conclusion: [18F]SYN2 showed a favourable pharmacodynamic and pharmacokinetic profile, which enabled a clear visualization of the heart in microPET. The compound was well-tolerated in studies in normal rats with moderate radiation exposure. The results encourage further exploration of [18F]SYN2 in clinical studies. [ABSTRACT FROM AUTHOR]

Background: Therapeutic radiopharmaceuticals [177Lu]Lu-DOTA-TATE and [90Y]Y-DOTA-TATE are used in peptide receptor radionuclide therapy (PRRT) of neuroendocrine tumors. One of the factors determining the efficacy of such therapy is administering the radiopharmaceutical dose to the patients in a way consistent with treatment planning. This paper evaluates the loss of [177Lu]Lu-DOTA-TATE and [90Y]Y-DOTA-TATE and their mixed doses during the administration to the patient either by direct infusion or by gravity method. Material and methods: The loss of [177Lu]Lu-DOTA-TATE and [90Y]Y-DOTA-TATE, was assessed in tests simulating the administration procedures and during infusion to the patients performed at four clinical centres. One clinical centre used a direct infusion, and three others used a gravity method to administer radiopharmaceuticals to the patient. Results: In the direct infusion the highest radioactivity loss was 3.88% ± 0.49% (n = 3) and 3.76% ± 0.83% (n = 3) for [177Lu] Lu-DOTA-TATE infusion with radioactivity of 3.71 GBq ± 0.08 GBq (n = 3) and 1.06 GBq ± 0.08 GBq (n = 3), respectively, and 4.04% ± 0.40% (n = 5) for infusion of [90Y]Y-DOTA-TATE dose of 1.98 GBq ± 0.05 GBq (n = 5). In the gravity method administration of [177Lu]Lu-DOTA-TATE generated losses of up to 1.31% ± 0.46% (n = 16) for a dose of 7.45 GBq ± 0.06 GBq (n = 16) and 2.93% ± 1.64% (n = 8) for a dose of 3.78 GBq ± 0.05 GBq (n = 8). However, the infusion of the lowest doses of 0.95 GBq ± 0.01 GBq (n = 4) [177Lu]Lu-DOTA-TATE and 1.96 GBq ± 0.03 GBq (n = 8) [90Y]Y-DOTA-TATE resulted in higher loss of radiopharmaceuticals up to 6.00% ± 0.97% (n = 4) and 4.00% ± 1.57% (n = 8), respectively. Conclusions: Both investigated methods of radiopharmaceutical administration are associated with the loss of the radioactivity of radiopharmaceutical. [ABSTRACT FROM AUTHOR]

Background: Targeted radionuclide therapy with [177Lu]Lu-PSMA I&T (zadavotide guraxetan) has proven high efficacy and safety in treating patients with advanced prostate cancer worldwide. Several methods to determine the radiochemical purity have been reported but also limitations in the HPLC analysis due to retention of the sample and tailing effects when using standard gradients containing trifluoroacetic acid (TFA). We here report on the validation of a method for quality control of [177Lu]Lu-PSMA I&T including determination of radiochemical purity, identity testing and limit test for PSMA I&T by HPLC using a Phosphate buffer /Acetonitrile gradient system, complemented with a TLC system with 0.1N Citrate buffer pH 5 as mobile phase including validation of the methods, batch and stability data as well as identification of the main radiochemical impurity by mass spectrometry. Results: The described HPLC method met the defined acceptance criteria in terms of accuracy, specificity, robustness, linearity, range and LOQ. HPLC analysis revealed symmetrical peaks and quantitative recovery from the column. Batch data showed a radiochemical purity > 95% as determined by HPLC, stability data a pronounced degradation due to radiolysis, which could be limited by addition of ascorbic acid, dilution and storage at low temperatures. The main radiochemical impurity was found to be the de-iodinated form of [177Lu]Lu-PSMA I&T. TLC analysis allowed to determine the amount of free Lu-177 even in the presence of DTPA in the final formulation. Conclusion: Overall the described combination of HPLC and TLC provides a reliable tool for quality control of [177Lu]Lu-PSMA I&T. [ABSTRACT FROM AUTHOR]

Broad availability and cost-effectiveness of 99Mo/99mTc generators worldwide support the use, and thus the development, of novel 99mTc-labelled radiopharmaceuticals. In recent years, preclinical and clinical developments for neuroendocrine neoplasms patient management focused on somatostatin receptor subtype 2 (SST2) antagonists, mainly due to their superiority in SST2-tumour targeting and improved diagnostic sensitivity over agonists. The goal of this work was to provide a reliable method for facile preparation of a 99mTc-labelled SST2 antagonist, [99mTc]Tc-TECANT-1, in a hospital radiopharmacy setting, suitable for a multi-centre clinical trial. To ensure successful and reproducible on-site preparation of the radiopharmaceutical for human use shortly before administration, a freeze-dried three-vial kit was developed. The final composition of the kit was established based on the radiolabelling results obtained during the optimisation process, in which variables such as precursor content, pH and buffer, as well as kit formulations, were tested. Finally, the prepared GMP-grade batches met all predefined specification parameters together with long-term kit stability and stability of the product [99mTc]Tc-TECANT-1. Furthermore, the selected precursor content complies with micro-dosing, based on an extended single-dose toxicity study, where histopathology NOEL was established at 0.5 mg/kg BW, being more than 1000 times higher than the planned human dose of 20 µg. In conclusion, [99mTc]Tc-TECANT-1 is suitable to be advanced into a first-in-human clinical trial. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Several gastrin-releasing peptide receptor (GRPR) antagonists with improved in vivo behavior have been recently developed and tested in the clinic. However, despite the generally mild side effects of peptide receptor radionuclide therapy (PRRT), toxicity has been observed due to high doses delivered to nontarget tissues, especially in the kidneys and pancreas. Previous experiences with radiolabeled peptides opened a unique opportunity to explore GRPR pretargeting using clickable bombesin antagonists. Toward this goal, we used clickable DOTA-like radiocomplexes which have been previously evaluated by our group. We functionalized a potent GRPR antagonist with a clickable TCO moiety using two different linkers. These precursors were then studied to select the compound with the highest GRPR binding affinity and the best pharmacokinetics to finally explore the advantages of the devised pretargeting approach. Our results provided an important proof of concept toward the development of bioorthogonal approaches to GRPR-expressing cancers, which are worth investigating further to improve the in vivo results. Moreover, the use of clickable GRPR antagonists and DOTA/DOTAGA derivatives allows for fine-tuning of their pharmacokinetics and metabolic stability, leading to a versatile synthesis of new libraries of (radio)conjugates useful for the development of theranostic tools toward GRPR-expressing tumors. [ABSTRACT FROM AUTHOR]

Despite significant advances in nuclear medicine for diagnosing and treating prostate cancer (PCa), research into new ligands with increasingly better biological properties is still ongoing. Prostate-specific membrane antigen (PSMA) ligands show great potential as radioisotope carriers for the diagnosis and therapy of patients with metastatic PCa. PSMA is expressed in most types of prostate cancer, and its expression is increased in poorly differentiated, metastatic, and hormone-refractory cancers; therefore, it may be a valuable target for the development of radiopharmaceuticals and radioligands, such as urea PSMA inhibitors, for the precise diagnosis, staging, and treatment of prostate cancer. Four developed PSMA-HYNIC inhibitors for technetium-99m labeling and subsequent diagnosis were subjected to preclinical in vitro and in vivo studies to evaluate and compare their diagnostic properties. Among the studied compounds, the PSMA-T4 (Glu-CO-Lys-L-Trp-4-Amc-HYNIC) inhibitor showed the best biological properties for the diagnosis of PCa metastases. [99mTc]Tc-PSMA-T4 also showed effectiveness in single-photon emission computed tomography (SPECT) studies in humans, and soon, its usefulness will be extensively evaluated in phase 2/3 clinical trials. [ABSTRACT FROM AUTHOR]

Design, synthesis, and evaluation of inhibitors for severe acute respiratory syndrome 3C-like protease based on phthalhydrazide ketones or heteroaromatic esters. Targeting zoonotic viruses: structure-based inhibition of the 3C-like protease from bat coronavirus HKU4 - the likely reservoir host to the human coronavirus that causes Middle East Respiratory Syndrome (MERS). Discovery of N-(benzo[1,2,3]triazol-1-yl)-N-(benzyl)acetamido) phenyl) carboxamides as severe acute respiratory syndrome coronavirus (SARS-CoV) 3CLpro inhibitors: identification of ML300 and noncovalent nanomolar inhibitors with an induced-fit binding. Ligand-induced dimerization of Middle East Respiratory Syndrome (MERS) coronavirus nsp5 protease (3CL pro). [Extracted from the article]

Gallium-68-labelled somatostatin analogues are a gold standard of neuroendocrine tumors (NETs) PET imaging being a tool for personalized treatment. SPECT radiopharmaceuticals represent the cornerstone of molecular imaging due to their wide availability [[2]] and the development of a radiopharmaceutical based on technetium-99 m-labeled SSTR antagonist would improve access to such clinically feasible diagnostic tool. Long-acting somatostatin analogue was withdrawn 4 weeks before imaging Although PET is considered more sensitive than SPECT [[4]], the presented new radiopharmaceutical holds promise to provide higher TBR values compared to the current gold standard SP 68 sp Ga-DOTA-TATE PET/CT. [Extracted from the article]

With the development of ever more radiopharmaceuticals suitable for theranostic applications, translation of novel compounds from the preclinical stage towards clinical application becomes a bottleneck for the advances in Nuclear Medicine. This review article summarizes the current regulatory framework for clinical trials with radiopharmaceuticals in the European Union, provides a general overview of the documentation required, and addresses quality, safety, and clinical aspects to be considered. By using a recent successful example of translating a theranostic peptide radioligand, namely 111In‐CP04, which targets receptors expressed in medullary thyroid carcinoma, the pathway from the preclinical development over establishing the required pharmaceutical documentation to designing and submitting a clinical trial is reviewed. Details regarding preclinical data, generation of the documentation, and final successful application are described. This article should provide an insight in an ever more complex process to bring innovations in the field of radiopharmaceuticals into patients. [ABSTRACT FROM AUTHOR]

BACKGROUND: 44Sc is becoming attractive as a PET radionuclide due to its decay characteristics. It can be produced from 44Ca present in natural calcium with 2.08% abundance. MATERIALS AND METHODS: The targets were mostly prepared from natural CaCO3 or metallic calcium in the form of pellets. After irradiation they were dissolved in 3 M hydrochloric acid and 44Sc was separated from excess of calcium by precipitation of scandium hydroxide using ammonia. Alternatively, targets were dissolved in 11 M hydrochloric acid and 44Sc was separated by extraction chromatography on UTEVA resin. As the next step, in both processes 44Sc was further purified on a cation exchange resin. Initially, the separation procedures were developed with 46Sc as a tracer. Gamma spectrometry with a high purity germanium detector was used to determine the separation efficiency. Finally, the CaCO3 pellet with 99.2% enrichment in 44Ca was activated with protons via 44Ca(p,n) 44Sc nuclear reaction. RESULTS: Altogether twenty two irradiations and separations were performed. The working procedures were developed and the quality of separated 44Sc solution was confirmed by radiolabeling of DOTATATE. The chemical purity of the product was sufficient for preclinical experiments. At the end of around 1 hour proton beam irradiation of CaCO3 pellet with 99.2% enrichment in 44Ca the obtained radioactivity of 44Sc was more than 4.8 GBq. CONCLUSION: 44Sc can be produced inexpensively with adequate yields and radionuclidic purity via 44Ca(p,n) 44Sc nuclear reaction in small cyclotrons. The recovery yield in both investigated separation methods was comparable and amounted above 90%. The obtained 44Sc was pure in terms of radionuclide and chemical purity, as shown by the results of peptide radiolabeling. [ABSTRACT FROM AUTHOR]

This work presents a comparative biological evaluation of 90Y- and 177Lu- labelled DOTA-SCN and DOTA-NHS conjugated to Rituximab in tumour-bearing mice. Two DOTA derivatives, p-SCN-Bn-DOTA and DOTA-NHS-ester were conjugated to Rituximab and then freeze-dried kit formulations were prepared, as previously described (1). Tissue distribution was investigated in tumour-bearing (Raji s.c.) male Rj: NMRI-Foxn1nu/Foxn1nu mice at different time points after administration of 177Lu-DOTA-Rituximab or 90Y-DOTA-Rituximab (6 MBq/10 μg per mouse). In addition, tumour images were acquired with a PhotonIMAGERTM after injection of 90Y-DOTA (SCN)-Rituximab. All radioimmunoconjugates were obtained with high radiolabelling yield (RCP > 98%) and specific activity of ca. 0.6 GBq/mg. The conjugates were stable in human serum and in 0.9% NaCl; however, progressive aggregation was observed with time, in particular for DOTA- (SCN) conjugates. Both 177Lu- and 90Y-DOTA -(SCN)-Rituximab revealed slow blood clearance. The maximum tumour uptake was found 72 h after injection of 177Lu-DOTA-(SCN)-Rituximab (9.3 ID/g). A high radioactivity uptake was observed in liver and spleen, confirming the hepatobiliary excretion route. The results obtained by the radioactive optical imaging harmonize with those from the biodistribution study. [ABSTRACT FROM AUTHOR]

BACKGROUND: Technetium Tc99m Exametazime (99mTc-HMPAO) is currently used as a radiopharmaceutical for determining regional cerebral blood flow and for the labelling of autologous leucocytes for infection and inflammation imaging. The HMPAO ligand exists in two diastereomeric forms: d,l and meso. Usually, the substance is obtained in low chemical yield in a time consuming procedure. Furthermore, the final product still contains some amounts of the meso-form. The aim of this study was to develop the efficient, reliable and fast method for isolation of the d,l-HMPAO, which would provide the ligand with high purity and free from the meso-diastereomer. MATERIAL AND METHODS: The mixture of the meso- and d,l-HMPAO was synthesized in two-steps by condensation of propanediamine with keto-oxime and the reduction of the obtained bisimine. The d- and l-enantiomers were separated individually directly from this mixture by repeated crystallizations from ethanol as their tartrate salts and pooled together in equal proportions. That substance was characterized for its identity and isomeric purity using IR, HPLC and GC methods. The meso-free d,l-HMPAO was used for the preparation of the radiopharmaceutical freeze-dried kit for technetium-99m radiolabelling. Quality assessment of obtained 99mTc-d,l-HMPAO complex was performed according to the current Ph.Eur. monograph 1925 and USP monograph — Technetium Tc99m Exametazime Injection. To verify its biological activity, the kit-prepared 99mTc-d,l-HMPAO has been used for the white blood cell (WBC) labelling. RESULTS: According to the proposed synthesis route the d,l-HMPAO was obtained with around 18–20% yield in the total time of 10 days. The ligand identity was confirmed and the HPLC analysis revealed more than 99% chemical purity. The undesired meso-form was not detected. Freeze dried kit formulation for 99mTc-labelling of d,l-HMPAO has been established and four batches of kits were manufactured. The radiochemical purity of 99mTc-d,l-HMPAO complex was high (> 95% of lipophilic technetium-99m exametazime). Brain uptake in rats reached 2.1 ± 0.3%. The in vitro labelling of WBC resulted in 68.3 ± 6.6% yield. CONCLUSION: A new synthesis method of d,l-HMPAO, drug substance for technetium-99m exametazime preparation has been developed. [ABSTRACT FROM AUTHOR]

Preliminary clinical evaluation of 99mTc-EDDA/HYNIC-Met14-Exendin-4 showed that the complex offers new diagnostic possibilities for insulinoma and MTC. Exendin-4 contains methionine at position 14 in the amino acid chain, which may be oxidized to methionine sulfoxide and, from the pharmaceutical point of view, the oxidized moiety becomes an undesired impurity in the final radioactive preparation. Therefore, the aim of this study was to investigate the influence of commonly used methods to eliminate the effect of methionine oxidation in peptides, i.e. the replacement of methionine by norleucine (Nle) and the addition of L-methionine, on the in vitro stability and the biodistribution.~Background~Background~99mTc-EDDA/HYNIC-Met14-Exendin-4, 99mTc-EDDA/HYNIC-Nle14-Exendin-4, 99mTc-EDDA/HYNIC-Met14-Ex-endin-4 with the addition of L-methionine and an oxidized form of Exendin-4, i.e. 99mTc-EDDA/HYNIC-Met14(ox)-Exendin-4 were compared in vivo with 68Ga-NODAGA-Nle14-Exendin-4 in normal Wistar rats. The stability and lipophilicity were determined in vitro.~Material and Methods~Methods~Biodistribution studies confirmed the specific uptake of all tested complexes in the GLP-1 positive organs: lungs, pancreas and stomach. The uptake of 99mTc-EDDA/HYNIC-Met14-Exendin-4 with the addition of L-methionine and for 68Ga-NODAGA-Nle14-Exendin-4 at 1h p.i. was around 2-fold higher than that of 99mTc-EDDA/HYNIC-Met14-Exendin-4 and 99mTc-EDDA/HYNIC-Nle14-Exendin-4.~Results~Results~Although the substitution of methionine by norleucine in the HYNIC-Exendin-4 did not result in improved bio-distribution, the use of L-methionine, as the excipient that inhibits the oxidation of methionine in the peptide chain resulted in higher lung/blood and stomach/blood uptake ratios. Our results confirmed that methionine at position 14 of amino acid chain of Exendin-4 plays an important role in the interaction with GLP-1 receptor positive tissue.~Conclusion~Conclusions [ABSTRACT FROM AUTHOR]

The use of [18F]labelled nortropane derivative 2 β-carbomethoxy-3 β-(4-chlorophenyl)-8-(2-fluoroethyl)-nortropane (FECNT) as a dopamine transporter ligand for PET imaging is dependent on efficient radiosynthesis method. Herein, the automated synthesis of [18F]FECNT from its chlorinated precursor in commercially available SynChrom [18F] R&D module has been developed. The synthesis unit was readily configured for the one-step synthesis from corresponding chlorinated precursor. The radiolabeling process involved a classical [18F]fluoride nucleophilic substitution performed at 110 °C for 12 min and finally HPLC and SPE purification. Crude [18F]FECNT was obtained with a radiolabeling yield of 59 ± 12% ( n = 5). The average uncorrected amount of [18F]FECNT in the final formulated dose was 2.0 ± 0.5 GBq (32 ± 7% overall decay-corrected yields) obtained with radiochemical purity over 99% and specific activity of 55 GBq/µmol. The total duration of the procedure was 80-90 min. An automated radiosynthesis of [18F]FECNT with high radiochemical purity may provide a simple and robust method of radiopharmaceutical preparation for routine clinical applications. [ABSTRACT FROM AUTHOR]

BACKGROUND: The minigastrin analogue — CP04: DOTA-(DGlu)6-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH2 has been developed for CCK2R targeting. This analogue can be radiolabelled with 111In or 68Ga for imaging, or with 90Y and 177Lu for therapy. However, affinity of the chelator-peptide conjugates to the cell membrane receptors may vary depending on the metal incorporated into the complex. So far, there are no such studies for the ligands of gastrin/cholecystokinin receptor CCK2R. It is supposed that the reason for the differentiation of receptor affinity to the respective receptors is in the changes of structure of chelating system and their influence on the bioactive conformations of the metal conjugated peptides. Herein, we report on the radiolabelling of CP04 with 90Y, 177Lu and 68Ga and synthesis of cold CP04 complexes with respective stable metals for further structural and physico-chemical and biological studies. MATERIALS AND METHODS: From 200 to 600 MBq of 90Y, 177Lu or 68Ga were used for radiolabelling of 20 μg of CP04 dissolved in ascorbic acid solution (50 mg/mL, pH 4.5). Non-radioactive complexes with Lu and Ga were synthesized in milligram amounts starting from 0.5 mg up to 5 mg of CP04 dissolved in ascorbic acid solution (50 mg/mL, pH 4.5) when using 2-molar excess of the metal ions. Complex formation needed 5 min in microwave oven or 12 min in thermo-block at 95°C. RP-HPLC isocratic method (Kinetex 150/4.6 mm; 25% AcN/0.1% TFA, 1 mL/min) with UV/Vis and radiometric detection was developed for investigation of the radiolabelled and “cold” complexes. For LC-MS investigations, HPLC method was modified replacing TFA by formic acid. RESULTS AND DISCUSSION: Yields of CP04 radiolabelling were greater than 90% for all three radionuclides. The HPLC method enabled identification of these radio-complexes based on comparison to their non-radioactive equivalents. In all cases, chromatograms revealed peaks that could be attributed to the metal-CP04 complexes and to impurities (including methionine oxidation). LC-MS analysis of Ga and Lu complexes revealed conformity of the observed molecular ions to the predicted formulas (m/z 2116 and 2220 Da for Ga and Lu, respectively). Different chromatographic behaviour observed for Ga-CP04 complex comparing to Lu- and Y- labelled peptide (relative retention to CP04: 1.08, 0.86 and 0.85, respectively) suggest different coordination of the metal ions. Therefore, further studies are planned using the non-radioactive complexes in order to assess their structural conformations. [ABSTRACT FROM AUTHOR]

The reliable method for determination of identity and radiochemical purity (RCP) is of great importance in radiopharmaceutical development. This is especially relevant when more than one form of radiometal/ligand complex can be formed during radiolabelling, such as complexes of 99mTc or 188Re with meso-2,3-dimercaptosuccinic acid (DMSA), where depending on the pH, metal can occur either at +3 or +5 oxidation state. The aim of our study was to evaluate possibilities for optimization of chromatographic systems leading to specific and reliable analytical method for determination of the identity and RCP of DMSA complexes with 99mTc or 188Re.~Background~Background~The commercial DMSA kits (POLATOM) were used for preparation of technetium-99m (III) and (V) complexes with DMSA. 99mTc(V)-DMSA complexes were prepared by addition of NaHCO3 to the kit vial prior to 99mTc-eluate to obtain pH ~8. 188Re(V)-DMSA was prepared either directly or using intermediate 188Re(III)-EDTA complex added to DMSA. RCP was evaluated by TLC using: ITLC-SG developed in methylethylketon, SG60 coated plates developed in: n-BuOH/H2O/CH3COOH and n-PrOH/H2O/CH3COOH systems, and in H2O. Comparative biodistribution studies were performed in normal Wistar rats.~Material and Methods~Methods~Using silica gel plates and n-PrOH, H2O and acetic acid in the developing solution, we observed that 99mTc/188Re(III)-DMSA and 99mTc/188Re(V)-DMSA complexes could be well separated from each other and from the impurities in the form of free pertechnetate/perrhenate. In vivo studies showed quite different biodistribution of 99mTc(III)- and 99mTc(V)-DMSA. The trivalent complex accumulated mainly in kidneys (>40%ID), while 99mTc(V)-DMSA revealed high excretion with urine and relatively high concentration in osseous tissue (ca. 2 %ID/g). Accumulation of this complex in kidneys was very low (ca. 2.5 %ID). Biodistribution pattern of 188Re(V)-DMSA prepared directly was almost identical to that of 99mTc(V)-DMSA. Biodistribution results of the 188Re preparation obtained using 188Re(III)-EDTA intermediate indicated that the preparation contained the mixture of penta- and trivalent 188Re complexes. The quite high accumulation of radioactivity in kidneys (23 %ID) gave evidence of the presence of 188Re(III)-DMSA in this preparation, what was also confirmed by the results of TLC analysis performed using silica gel plate and n-propanol/water/acetic acid as developing system.~Results~Results~Based on our study, we have made recommendation on the suitable methods for investigations of RCP of DMSA complexes, i.e.: SG60 plates developed in the mixture of n-propanol/water/acetic acid, which enable determination of the tri- and pentavalent DMSA complexes, as well as, the pertechnetate/perrhenate impurity, and developed in water for determination of the colloidal residue.~Conclusions~Conclusions [ABSTRACT FROM AUTHOR]

BACKGROUND: The reliable method for determination of identity and radiochemical purity (RCP) is of great importance in radiopharmaceutical development. This is especially relevant when more than one form of radiometal/ligand complex can be formed during radiolabelling, such as complexes of 99mTc or 188Re with meso-2,3-dimercaptosuccinic acid (DMSA), where depending on the pH, metal can occur either at +3 or +5 oxidation state. The aim of our study was to evaluate possibilities for optimization of chromatographic systems leading to specific and reliable analytical method for determination of the identity and RCP of DMSA complexes with 99mTc or 188Re. MATERIAL AND METHODS: The commercial DMSA kits (POLATOM) were used for preparation of technetium-99m (III) and (V) complexes with DMSA. 99mTc(V)-DMSA complexes were prepared by addition of NaHCO3 to the kit vial prior to 99mTc-eluate to obtain pH ~8. 188Re(V)-DMSA was prepared either directly or using intermediate 188Re(III)-EDTA complex added to DMSA. RCP was evaluated by TLC using: ITLC-SG developed in methylethylketon, SG60 coated plates developed in: n-BuOH/H2O/CH3COOH and n-PrOH/H2O/CH3COOH systems, and in H2O. Comparative biodistribution studies were performed in normal Wistar rats. RESULTS: Using silica gel plates and n-PrOH, H2O and acetic acid in the developing solution, we observed that 99mTc/188Re(III)-DMSA and 99mTc/188Re(V)-DMSA complexes could be well separated from each other and from the impurities in the form of free pertechnetate/perrhenate. In vivo studies showed quite different biodistribution of 99mTc(III)- and 99mTc(V)-DMSA. The trivalent complex accumulated mainly in kidneys (>40%ID), while 99mTc(V)-DMSA revealed high excretion with urine and relatively high concentration in osseous tissue (ca. 2 %ID/g). Accumulation of this complex in kidneys was very low (ca. 2.5 %ID). Biodistribution pattern of 188Re(V)-DMSA prepared directly was almost identical to that of 99mTc(V)-DMSA. Biodistribution results of the 188Re preparation obtained using 188Re(III)-EDTA intermediate indicated that the preparation contained the mixture of penta- and trivalent 188Re complexes. The quite high accumulation of radioactivity in kidneys (23 %ID) gave evidence of the presence of 188Re(III)-DMSA in this preparation, what was also confirmed by the results of TLC analysis performed using silica gel plate and n-propanol/water/acetic acid as developing system. CONCLUSIONS: Based on our study, we have made recommendation on the suitable methods for investigations of RCP of DMSA complexes, i.e.: SG60 plates developed in the mixture of n-propanol/water/acetic acid, which enable determination of the tri- and pentavalent DMSA complexes, as well as, the pertechnetate/perrhenate impurity, and developed in water for determination of the colloidal residue. [ABSTRACT FROM AUTHOR]

Myocardial perfusion studies are among the most often performed investigations in Nuclear Medicine. However, the development of radiopharmaceuticals for cardiology is an emerging discipline and several other radiotracers have been proven to be useful. Although the myocardial perfusion studies have a well-established role in the management of cardiac disorders, still a number of radiopharmaceuticals are under development for a variety of specific cardiac indications and their eventual clinical role remains to be seen. The paper provides a short overview of currently used radiopharmaceuticals and potential molecular imaging radiotracers applicable in cardiology. [ABSTRACT FROM AUTHOR]

Purpose: Identification of vulnerable plaques remains crucial for better cardiovascular risk assessment. At least 20% of inflammatory cells within unstable (vulnerable) plaques comprise T lymphocytes, which contain receptors for interleukin-2 (IL-2); those receptors can be identified by scintigraphy with radiolabelled IL-2.The aim of this study was to identify the 'inflamed' (vulnerable) plaques by scintigraphy using IL-2 labelled with Tc in the selected, high cardiovascular risk group of end-stage renal disease (ESRD) patients. Methods: A total of 28 patients (18 men, 10 women, aged 55.2 ± 9.6 years, 17 on peritoneal dialysis, 11 on haemodialysis) underwent common carotid artery (CCA) scintigraphy with the use of Tc-hydrazinonicotinamide (HYNIC)-IL-2. In all cases, ultrasound examination of the CCA was performed and levels of selected proinflammatory factors, atherogenic markers and calcium-phosphate balance parameters were measured. Finally, the target to non-target (T/nT) ratio of IL-2 uptake in atherosclerotic plaques with intima-media thickness (IMT), classic cardiovascular risk factors and concentrations of the measured factors were compared. Results: Increased Tc-HYNIC-IL-2 uptake in atherosclerotic plaques in 38/41 (91%) cases was detected. The median T/nT ratio of focal Tc-HYNIC-IL-2 uptake in atherosclerotic plaques was 2.35 (range 1.23-3.63). The mean IMT value on the side of plaques assessed by scintigraphy was 0.79 ± 0.18 mm (median 0.8, range 0.5-1.275). Correlations between T/nT ratio and homocysteine ( R = 0.22, p = 0.037), apolipoprotein B (apoB) ( R = 0.31, p = 0.008), apoB to apoA-I ratio ( R = 0.29, p = 0.012) and triglyceride concentration ( R = 0.26, p = 0.021) were detected. A lower T/nT ratio in patients with better parameters of nutritional status (haemoglobin, albumin, adiponectin) in comparison with patients with worse nutritional parameters (3.20 ± 0.5 vs 2.16 ± 0.68, p = 0.025) was revealed as well as a difference between values of T/nT ratio in groups of patients with values of apoB, soluble CD40 ligand and asymmetric dimethylarginine above and below median (3.18 ± 0.52 vs 2.16 ± 0.68, p = 0.031). No statistically significant association was found between T/nT ratio and mean value of either IMT or classic cardiovascular risk factors. Conclusion: Scintigraphy with the use of Tc-HYNIC-IL-2 can be a tool for inflamed atherosclerotic (vulnerable) plaque visualization within CCA in ESRD patients. Quantitative results of carotid artery scintigraphy with Tc-HYNIC-IL-2 correlate with serum concentration of selected cardiovascular risk markers. [ABSTRACT FROM AUTHOR]

Numerous different molecules of prostate-specific membrane antigen (PSMA) ligands are used to detect prostate cancer (PCa); most approaches utilize gallium PET and a few reports describe the role of SPECT/CT. [99mTc]Tc-PSMA-T4 is a new radiopharmaceutical designed for the diagnosis of patients with PCa. We conducted a single site, prospective, preliminary case series study that included 31 patients with PCa; all had undergone clinical, biochemical or imaging examination and exhibited clear or suspicious active disease or clinical/biochemical recurrence of PCa. Whole-body (WB) SPECT/CT after i.v. administration of [99mTc]Tc-PSMA-T4 was utilized; acquisition images were obtained at three time points. The clinical value of the images was assessed in regard to the evaluation of tumor extent in patients with confirmed PC that qualified for initial therapy and the evaluation of tumor recurrence; both provided encouraging results. The late acquisition of WB-SPECT resulted in better lesions delineation. The results of the analysis of the sensitivity/specificity were: 92%/100% in cases of primary cancer, 83%/100% in terms of pelvic lymph nodes disease, 100%/95% in other lymph nodes and soft tissue involvement, respectively, and bone mets were both 100%. An oncotropic SPECT [99mTc]Tc-PSMA-T4 can help in selecting a rational therapeutic strategy for a patient with an initial diagnosis of PCa by assessing the extent of cancer and also after complex radical or palliative therapy in case of biochemical recurrence for re-staging. [ABSTRACT FROM AUTHOR]

Metastatic castration-resistant prostate cancer (mCRPC) is a progressive and incurable disease with poor prognosis for patients. Despite introduction of novel therapies, the mortality rate remains high. An attractive alternative for extension of the life of mCRPC patients is PSMA-based targeted radioimmunotherapy. In this paper, we extended our in vitro study of 223Ra-labeled and PSMA-targeted NaA nanozeolites [223RaA-silane-PEG-D2B] by undertaking comprehensive preclinical in vitro and in vivo research. The toxicity of the new compound was evaluated in LNCaP C4-2, DU-145, RWPE-1 and HPrEC prostate cells and in BALB/c mice. The tissue distribution of 133Ba- and 223Ra-labeled conjugates was studied at different time points after injection in BALB/c and LNCaP C4-2 tumor-bearing BALB/c Nude mice. No obvious symptoms of antibody-free and antibody-functionalized nanocarriers cytotoxicity and immunotoxicity was found, while exposure to 223Ra-labeled conjugates resulted in bone marrow fibrosis, decreased the number of WBC and platelets and elevated serum concentrations of ALT and AST enzymes. Biodistribution studies revealed high accumulation of 223Ra-labeled conjugates in the liver, lungs, spleen and bone tissue. Nontargeted and PSMA-targeted radioconjugates exhibited a similar, marginal uptake in tumour lesions. In conclusion, despite the fact that NaA nanozeolites are safe carriers, the intravenous administration of NaA nanozeolite-based radioconjugates is dubious due to its high accumulation in the lungs, liver, spleen and bones. [ABSTRACT FROM AUTHOR]

A new PSMA ligand (PSMA-D4) containing the Glu-CO-Lys pharmacophore connected with a new linker system (L-Trp-4-Amc) and chelator DOTA was developed for radiolabeling with therapeutic radionuclides. Herein we describe the synthesis, radiolabeling, and preliminary biological evaluation of the novel PSMA-D4 ligand. Synthesized PSMA-D4 was characterized using TOF-ESI-MS, NMR, and HPLC methods. The novel compound was subject to molecular modeling with GCP-II to compare its binding mode to analogous reference compounds. The radiolabeling efficiency of PSMA-D4 with 177Lu, 90Y, 47Sc, and 225Ac was chromatographically tested. In vitro studies were carried out in PSMA-positive LNCaP tumor cells membranes. The ex vivo tissue distribution profile of the radioligands and Cerenkov luminescence imaging (CLI) was studied in LNCaP tumor-bearing mice. PSMA-D4 was synthesized in 24% yield and purity >97%. The radio complexes were obtained with high yields (>97%) and molar activity ranging from 0.11 to 17.2 GBq mcmol−1, depending on the radionuclide. In vitro assays confirmed high specific binding and affinity for all radiocomplexes. Biodistribution and imaging studies revealed high accumulation in LNCaP tumor xenografts and rapid clearance of radiocomplexes from blood and non-target tissues. These render PSMA-D4 a promising ligand for targeted therapy of prostate cancer (PCa) metastases. [ABSTRACT FROM AUTHOR]

Recently, radiolabelled antagonists targeting somatostatin receptors subtype 2 (SST2) in neuroendocrine neoplasms demonstrated certain superior properties over agonists. Within the ERA-PerMED project "TECANT" two 99mTc-Tetramine (N4)-derivatized SST2 antagonists (TECANT-1 and TECANT-2) were studied for the selection of the best candidate for clinical translation. Receptor-affinity, internalization and dissociation studies were performed in human embryonic kidney-293 (HEK293) cells transfected with the human SST2 (HEK-SST2). Log D, protein binding and stability in human serum were assessed. Biodistribution and SPECT/CT studies were carried out in nude mice bearing HEK-SST2 xenografts, together with dosimetric estimations from mouse-to-man. [99mTc]Tc-TECANT-1 showed higher hydrophilicity and lower protein binding than [99mTc]-TECANT-2, while stability was comparable. Both radiotracers revealed similar binding affinity, while [99mTc]Tc-TECANT-1 had higher cellular uptake (>50%, at 2 h/37 °C) and lower dissociation rate (<30%, at 2 h/37 °C). In vivo, [99mTc]Tc-TECANT-1 showed lower blood values, kidney and muscles uptake, whereas tumour uptake was comparable to [99mTc]Tc-TECANT-2. SPECT/CT imaging confirmed the biodistribution results, providing the best tumour-to-background image contrast for [99mTc]Tc-TECANT-1 at 4 h post-injection (p.i.). The estimated radiation dose amounted to approximately 6 µSv/MBq for both radiotracers. This preclinical study provided the basis of selection of [99mTc]Tc-TECANT-1 for clinical translation of the first 99mTc-based SST2 antagonist. [ABSTRACT FROM AUTHOR]

Endohedral structures with La0 or La3+ encapsulated in chiral (1,16)C 58 N 2 or achiral (1,4)C 58 N 2 diazafullerenes were studied at the B3LYP/G-31G*/SDD level. Two stable locations of La0 and La3+ are possible in each cage but only with La0@(1,16)C 58 N 2 can the two isomers coexist. We found that an AIM determined hapticity of the endohedral species selectively differentiates the systems. We predict that there will always exist IR and Raman bands which allow for them to be identified in the presence of the parent cage. For the La0@(1,16) C 58 N 2 molecules and the parent diazafullerene, the Raman spectra are likely to reveal a pre-resonance effect even at 785 nm and it seems possible to selectively excite only one isomer. The calculated electronic spectra suggested a chance to determine the less populated diazafullerene in the presence of the more populated one, be it chiral or achiral. For the chiral endohedral isomers, the calculated VCD spectra are quite dissimilar and the two endohedral isomers and the parent heterofullerene seem to be easily detected. Eventually, we defined the endohedral isomerism as follows: The endohedral isomerism is the phenomenon whereby an internal individuum captured in a cage can occupy more than one stable position without changing the cage connectivity. Unlabelled Image • Calculations indicate that only for La0@(1,16) C 58 N 2 system can the two endohedral isomers coexist. • The AIM estimated hapticity of the endohedral species selectively differentiates the isomers. • IR, Raman, UV–Vis, ECD, and VCD spectra were simulated for all molecules. • (1,16)C 58 N 2 and La0@(1,16)C 58 N 2 molecules are likely to reveal a resonance Raman effect at 532 nm. • The La0@(1,16)C58N2 endohedral isomers VCD spectra are substantially dissimilar. [ABSTRACT FROM AUTHOR]