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Can current preclinical strategies for radiopharmaceutical development meet the needs of targeted alpha therapy? Eur J Nucl Med Mol Imaging 2024:10.1007/s00259-024-06719-5. [PMID: 38676735 DOI: 10.1007/s00259-024-06719-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2024] [Accepted: 04/15/2024] [Indexed: 04/29/2024]
Abstract
Preclinical studies are essential for effectively evaluating TAT radiopharmaceuticals. Given the current suboptimal supply chain of these radionuclides, animal studies must be refined to produce the most translatable TAT agents with the greatest clinical potential. Vector design is pivotal, emphasizing harmonious physical and biological characteristics among the vector, target, and radionuclide. The scarcity of alpha-emitting radionuclides remains a significant consideration. Actinium-225 and lead-212 appear as the most readily available radionuclides at this stage. Available animal models for researchers encompass xenografts, allografts, and PDX (patient-derived xenograft) models. Emerging strategies for imaging alpha-emitters are also briefly explored. Ultimately, preclinical research must address two critical aspects: (1) offering valuable insights into balancing safety and efficacy, and (2) providing guidance on the optimal dosing of the TAT agent.
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The LUTIA trial: a small step for PRRT, a giant leap for intra-arterial radionuclide therapy trial methodology. Eur J Nucl Med Mol Imaging 2024; 51:1133-1135. [PMID: 38158435 DOI: 10.1007/s00259-023-06581-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2024]
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Equilibrium Thermodynamics of Macropa Complexes with Selected Metal Isotopes of Radiopharmaceutical Interest. Inorg Chem 2023; 62:20699-20709. [PMID: 37702665 PMCID: PMC10731647 DOI: 10.1021/acs.inorgchem.3c01983] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Indexed: 09/14/2023]
Abstract
To pursue the design of in vivo stable chelating systems for radiometals, a concise and straightforward method toolbox was developed combining NMR, isothermal titration calorimetry (ITC), and europium time-resolved laser-induced fluorescence spectroscopy (Eu-TRLFS). For this purpose, the macropa chelator was chosen, and Lu3+, La3+, Pb2+, Ra2+, and Ba2+ were chosen as radiopharmaceutically relevant metal ions. They differ in charge (2+ and 3+) and coordination properties (main group vs lanthanides). 1H NMR was used to determine four pKa values (±0.15; carboxylate functions, 2.40 and 3.13; amino functions, 6.80 and 7.73). Eu-TRLFS was used to validate the exclusive existence of the 1:1 Mn+/ligand complex in the chosen pH range at tracer level concentrations. ITC measurements were accomplished to determine the resulting stability constants of the desired complexes, with log K values ranging from 18.5 for the Pb-mcp complex to 7.3 for the Lu-mcp complex. Density-functional-theory-calculated structures nicely mirror the complexes' order of stabilities by bonding features. Radiolabeling with macropa using ligand concentrations from 10-3 to 10-6 M was accomplished by pointing out the complex formation and stability (212Pb > 133La > 131Ba ≈ 224Ra > 177Lu) by means of normal-phase thin-layer chromatography analyses.
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Construction of the Bioconjugate Py-Macrodipa-PSMA and Its In Vivo Investigations with Large 132/135La 3+ and Small 47Sc 3+ Radiometal Ions. Eur J Inorg Chem 2023; 26:e202300457. [PMID: 38495596 PMCID: PMC10939043 DOI: 10.1002/ejic.202300457] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2023] [Indexed: 03/19/2024]
Abstract
To harness radiometals in clinical settings, a chelator forming a stable complex with the metal of interest and targets the desired pathological site is needed. Toward this goal, we previously reported a unique set of chelators that can stably bind to both large and small metal ions, via a conformational switch. Within this chelator class, py-macrodipa is particularly promising based on its ability to stably bind several medicinally valuable radiometals including large 132/135La3+, 213Bi3+, and small 44Sc3+. Here, we report a 10-step organic synthesis of its bifunctional analogue py-macrodipa-NCS, which contains an amine-reactive -NCS group that is amenable for bioconjugation reactions to targeting vectors. The hydrolytic stability of py-macordipa-NCS was assessed, revealing a half-life of 6.0 d in pH 9.0 aqueous buffer. This bifunctional chelator was then conjugated to a prostate-specific membrane antigen (PSMA)-binding moiety, yielding the bioconjugate py-macrodipa-PSMA, which was subsequently radiolabeled with large 132/135La3+ and small 47Sc3+, revealing efficient and quantitative complex formation. The resulting radiocomplexes were injected into mice bearing both PSMA-expressing and PSMA-non-expressing tumor xenografts to determine their biodistribution patterns, revealing delivery of both 132/135La3+ and 47Sc3+ to PSMA+ tumor sites. However, partial radiometal dissociation was observed, suggesting that py-macrodipa-PSMA needs further structural optimization.
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Gamma radiation effects on AG MP-50 cation exchange resin and sulfonated activated carbon for bismuth-213 separation. RSC Adv 2023; 13:30990-31001. [PMID: 37881760 PMCID: PMC10594081 DOI: 10.1039/d3ra06130b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2023] [Accepted: 10/16/2023] [Indexed: 10/27/2023] Open
Abstract
Medical 225Ac/213Bi radionuclide generators are designed to provide a local supply of the short-lived 213Bi for cancer treatment. However, radiation-induced damage to the sorbents commonly used in such radionuclide generators remains a major concern. In this study, the effects of gamma radiation on AG MP-50 cation exchange resin and sulfonated activated carbon (SAC) were studied by analyzing the changes in the morphological characteristics, functional groups, and the La3+/Bi3+ sorption performance, with La3+ being a suitable non-radioactive substitute for Ac3+. The surface sulfonic acid groups of AG MP-50 resin suffered from severe radiation-induced degradation, while the particle morphology was changed markedly after being exposed to absorbed doses of approximately 11 MGy. As a result, the sorption performance of irradiated AG MP-50 for La3+ and Bi3+ was significantly decreased with increasing absorbed doses. In contrast, no apparent changes in acquired morphological characteristics were observed for pristine and irradiated SAC based on SEM and XRD characterization. The surface oxygen content (e.g., O-C[double bond, length as m-dash]O) of irradiated SAC increased for an absorbed dose of 11 MGy due to free radical-induced oxidation. The sorption performance of pristine and irradiated SAC materials for La3+ and Bi3+ remained generally the same at pH values of 1 and 2. Furthermore, the applicability of AG MP-50 and SAC in the 225Ac/213Bi generators was illustrated in terms of their radiolytic stability. This study provides further evidence for the practical implementation of both AG MP-50 and SAC in 225Ac/213Bi radionuclide generators.
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Bi-HPDO3A as a novel contrast agent for X-ray computed tomography. Sci Rep 2023; 13:16747. [PMID: 37798332 PMCID: PMC10556142 DOI: 10.1038/s41598-023-43031-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2023] [Accepted: 09/18/2023] [Indexed: 10/07/2023] Open
Abstract
A new bismuth-based CT agent was synthesized through a facile synthesis strategy. The in vitro stability, toxicity and CT performance were evaluated. The in vivo imaging performance was investigated using three different doses (0.5, 1.2 and 5 mmol/kg) and the result obtained at 1.2 mmol/kg was compared with the clinically approved CT agent iopamidol at the same dosage.
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Evaluation of the therapeutic efficacy of 213Bi-labelled DOTA-conjugated alpha-melanocyte stimulating hormone peptide analogues in melanocortin-1 receptor positive preclinical melanoma model. Int J Pharm 2023; 644:123344. [PMID: 37634663 DOI: 10.1016/j.ijpharm.2023.123344] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2023] [Revised: 07/20/2023] [Accepted: 08/21/2023] [Indexed: 08/29/2023]
Abstract
Melanocortin-1 receptor (MC1-R) targeting alpha-melanocyte stimulating hormone-analogue (α-MSH) biomolecules labelled with α-emitting radiometal seem to be valuable in the targeted radionuclide therapy of MC1-R positive melanoma malignum (MM). Herein is reported the anti-tumor in vivo therapeutic evaluation of MC1-R-affine [213Bi]Bi-DOTA-NAPamide and HOLDamide treatment in MC1-R positive B16-F10 melanoma tumor-bearing C57BL/6J mice. On the 6th, 8th and 10th days post tumor cell inoculation; the treated groups of mice were intravenously injected with approximately 5 MBq of both amide derivatives. Beyond body weight and tumor volume assessment, [68Ga]Ga-DOTA-HOLDamide and NAPamide-based PET/MRI scans, and ex vivo biodistribution studies were executed 30,- and 90 min postinjection. In the PET/MRI imaging studies the B16-F10 tumors were clearly visualized with both 68Ga-labelled tracers, however, significantly lower tumor-to-muscle (T/M) ratios were observed by using [68Ga]Ga-DOTA-HOLDamide. After alpha-radiotherapy treatment the tumor size of the control group was larger relative to both treated cohorts, while the smallest tumor volumes were observed in the NAPamide-treated subclass on the 10th day. Relatively higher [213Bi]Bi-DOTA-NAPamide accumulation in the B16-F10 tumors (%ID/g: 2.71 ± 0.15) with discrete background activity led to excellent T/M ratios, particularly 90 min postinjection. Overall, the therapeutic application of receptor selective [213Bi]Bi-DOTA-NAPamide seems to be feasible in MC1-R positive MM management.
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In Vivo evaluation of newly synthesized 213Bi-conjugated alpha-melanocyte stimulating hormone (α-MSH) peptide analogues in melanocortin-1 receptor (MC1-R) positive experimental melanoma model. J Pharm Biomed Anal 2023; 229:115374. [PMID: 37001274 DOI: 10.1016/j.jpba.2023.115374] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2023] [Revised: 03/27/2023] [Accepted: 03/27/2023] [Indexed: 03/30/2023]
Abstract
Given the rising pervasiveness of melanocortin-1 receptor (MC1-R) positive melanoma malignum (MM) and pertinent metastases, radiolabelled receptor-affine alpha-melanocyte stimulating hormone-analogue (α-MSH analogue) imaging probes would be of crucial importance in timely tumor diagnostic assessment. Herein we aimed at investigating the biodistribution and the MM targeting potential of newly synthesized 213Bi-conjugated MC1-R specific peptide-based radioligands with the establishment of MC1-R overexpressing MM preclinical model. DOTA-conjugated NAP, -HOLD, -FOLD, -and MARSamide were labelled with 213Bi. Ex vivo biodistribution studies were conducted post-administration of 3.81 ± 0.32 MBq [213Bi]Bi-DOTA conjugated deriva-tives into twenty B16-F10 tumor-bearing C57BL/6 J and healthy mice. Organ Level Internal Dose Assessment (OLINDA) and IDAC-Dose were used to calculate translational data-based absorbed radiation dose in human organs. Moderate or low %ID/g uptake of [213Bi]Bi-DOTA conjugated NAP, -HOLD, -and MARSamide and significantly increased [213Bi]Bi-DOTA-FOLDamide accumulation was observed in the thoracic and abdominal organs (p ≤ 0.01). High [213Bi]Bi-DOTA-NAP (%ID/g:3.76 ± 0.96), -and FOLDamide (%ID/g:3.28 ± 0.95) tumor tracer activity confirmed their MC1-R-affinity. The bladder wall received the highest radiation absorbed dose followed by the kidneys (bladder wall: 1.95·10-2 and 8.97·10-2 mSv/MBq; kidneys: 7.47·10-3 vs. 5.88·10-2 mSv/MBq measured by IDAC and OLINDA; respectively) indicating the suitability of the NAPamide derivative for clinical use. These novel [213Bi]Bi-DOTA-linked peptide probes displaying meaningful MC1-R affinity could be promising molecular probes in MM imaging.
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Insights into recent preclinical studies on labelled cyclodextrin-based imaging probes: towards a novel oncological era. Int J Pharm 2023; 640:122978. [PMID: 37121492 DOI: 10.1016/j.ijpharm.2023.122978] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Revised: 03/23/2023] [Accepted: 04/18/2023] [Indexed: 05/02/2023]
Abstract
As malignancies remain one of the major health concerns worldwide, increasing focus has been centered around the application of cyclodextrins (CDs) in cancer imaging and therapy due to their outstanding inclusion forming capability. Albeit the physicochemical properties of CDs were intensively elucidated, the spread of their clinical application is limited by the relative paucity of knowledge about their pharmacokinetic profile, especially biodistribution. Studies applying fluorescently- CDs, or CD-based MRI contrast agents revealed much about pharmacokinetics and diagnostic applications; however, derivatives labelled with positron emitters seem superior molecular probes in the investigation of the route of CDs in biological niche. In vivo imaging based on preclinical tumor-bearing model systems are well-suited to evaluate the whole-body distribution of the two most frequently assessed CDs: randomly methylated β-cyclodextrin (RAMEB), and hydroxypropyl-β-cyclodextrin (HPBCD). Exploiting the firm signaling interaction between cancer-related cyclooxygenase-2, prostaglandin E2 (PGE2) and RAS oncoprotein, radioconjugated, PGE2-affine CDs project the establishment of novel imaging probes and therapeutic agents. Currently, we provide an overview of the preclinical studies on CD pharmacokinetics highlighting the significance of the integration of translational discoveries into human patient care.
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Rigid H 4OCTAPA derivatives as model chelators for the development of Bi(III)-based radiopharmaceuticals. Chem Commun (Camb) 2023; 59:3443-3446. [PMID: 36857648 DOI: 10.1039/d2cc06876a] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/25/2023]
Abstract
Octadentate ligands containing ethyl (H4OCTAPA), cyclohexyl (H4CHXOCTAPA) or cyclopentyl (H4CpOCTAPA) spacers were assessed as chelators for Bi(III)-based radiopharmaceuticals. The H4CHXOCTAPA chelator displays excellent properties, including 205/206Bi-nuclide radiolabelling under mild conditions, excellent stability in serum and in the presence of competing cations or H5DTPA. The poor performance of H4CpOCTAPA appears to be related to the stereochemical activity of the Bi(III) lone pair.
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Novel candidate theranostic radiopharmaceutical based on strontium hexaferrite nanoparticles conjugated with azacrown ligand. Dalton Trans 2023; 52:1731-1741. [PMID: 36655497 DOI: 10.1039/d2dt03548k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
In this article, we report to the best of our knowledge the first modification of NPs with ligands for combined radiopharmaceuticals. Nanoparticles with suitable magnetic properties can be used both for diagnostics as a contrast for MRI and for therapy, including the insufficiently studied magneto-mechanical therapy. Strontium hexaferrite is one of the few hard-magnetic materials for which stable biocompatible colloidal solutions can be obtained. Strontium hexaferrite nanoparticles coated with silicon dioxide (SHF@SiO2) were modified with an amino silane coupling agent (3-aminopropyl)triethoxysilane and azacrown ether derivatives with six heteroatoms in rings were covalently linked to the amine group through the carboxyl group. The hard magnetic nanoparticles were then radiolabeled with 207Bi with a labelling yield of up to 99.8%. In vitro experiments showed that the complex SHF@SiO2-APTES-L2-207Bi is stable enough to be a potential theranostic radiopharmaceutical.
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Commercial and business aspects of alpha radioligand therapeutics. Front Med (Lausanne) 2023; 9:1070497. [PMID: 36816719 PMCID: PMC9932801 DOI: 10.3389/fmed.2022.1070497] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Accepted: 12/29/2022] [Indexed: 02/05/2023] Open
Abstract
Radioligand therapy (RLT) is gaining traction as a safe and effective targeted approach for the treatment of many cancer types, reflected by a substantial and growing commercial market (valued at $7.78 billion in 2021, with a projected value of $13.07 billion by 2030). Beta-emitting RLTs have a long history of clinical success dating back to the approval of Zevalin and Bexxar in the early 2000s, later followed by Lutathera and Pluvicto. Alpha radioligand therapeutics (ARTs) offer the potential for even greater success. Driven by ground-breaking clinical results in early trials, improved isotope availability, and better understanding of isotope and disease characteristics, the global market for alpha emitters was estimated at $672.3 million for the year 2020, with projected growth to $5.2 billion by 2027. New company formations, promising clinical trial data, and progression for many radioligand therapy products, as well as an inflow of investor capital, are contributing to this expanding field. Future growth will be fueled by further efficacy and safety data from ART clinical trials and real-world results, but challenges remain. Radionuclide supply, manufacturing, and distribution are key obstacles for growth of the field. New models of delivery are needed, along with cross-disciplinary training of specialized practitioners, to ensure patient access and avoid challenges faced by early RLT candidates such as Zevalin and Bexxar. Understanding of the history of radiation medicine is critical to inform what may be important to the success of ART-most past projections were inaccurate and it is important to analyze the reasons for this. Practical considerations in how radiation medicine is delivered and administered are important to understand in order to inform future approaches.
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Alpha-peptide receptor radionuclide therapy using actinium-225 labeled somatostatin receptor agonists and antagonists. Front Med (Lausanne) 2022; 9:1034315. [PMID: 36569154 PMCID: PMC9767967 DOI: 10.3389/fmed.2022.1034315] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2022] [Accepted: 11/21/2022] [Indexed: 12/12/2022] Open
Abstract
Peptide receptor radionuclide therapy (PRRT) has over the last two decades emerged as a very promising approach to treat neuroendocrine tumors (NETs) with rapidly expanding clinical applications. By chelating a radiometal to a somatostatin receptor (SSTR) ligand, radiation can be delivered to cancer cells with high precision. Unlike conventional external beam radiotherapy, PRRT utilizes primarily β or α radiation derived from nuclear decay, which causes damage to cancer cells in the immediate proximity by irreversible direct or indirect ionization of the cells' DNA, which induces apoptosis. In addition, to avoid damage to surrounding normal cells, PRRT privileges the use of radionuclides that have little penetrating and more energetic (and thus more ionizing) radiations. To date, the most frequently radioisotopes are β- emitters, particularly Yttrium-90 (90Y) and Lutetium-177 (177Lu), labeled SSTR agonists. Current development of SSTR-targeting is triggering the shift from using SSTR agonists to antagonists for PRRT. Furthermore, targeted α-particle therapy (TAT), has attracted special attention for the treatment of tumors and offers an improved therapeutic option for patients resistant to conventional treatments or even beta-irradiation treatment. Due to its short range and high linear energy transfer (LET), α-particles significantly damage the targeted cancer cells while causing minimal cytotoxicity toward surrounding normal tissue. Actinium-225 (225Ac) has been developed into potent targeting drug constructs including somatostatin-receptor-based radiopharmaceuticals and is in early clinical use against multiple neuroendocrine tumor types. In this article, we give a review of preclinical and clinical applications of 225Ac-PRRT in NETs, discuss the strengths and challenges of 225Ac complexes being used in PRRT; and envision the prospect of 225Ac-PRRT as a future alternative in the treatment of NETs.
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Radioimmunoconjugates in the age of modern immuno-oncology. Life Sci 2022; 310:121126. [DOI: 10.1016/j.lfs.2022.121126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Revised: 10/14/2022] [Accepted: 10/22/2022] [Indexed: 11/09/2022]
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Bismuth chelation for targeted alpha therapy: Current state of the art. Nucl Med Biol 2022; 114-115:168-188. [PMID: 35753940 DOI: 10.1016/j.nucmedbio.2022.06.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 05/22/2022] [Accepted: 06/14/2022] [Indexed: 12/27/2022]
Abstract
Current interest in the α-emitting bismuth radionuclides, bismuth-212 (212Bi) and bismuth-213 (213Bi), stems from their great potential for targeted alpha therapy (TAT), an expanding and promising approach for the treatment of micrometastatic disease and the eradication of single malignant cells. To selectively deliver their emission to the cancer cells, these radiometals must be firmly coordinated by a bifunctional chelator (BFC) attached to a tumour-seeking vector. This review provides a comprehensive overview of the current state-of-the-art chelating agents for bismuth radioisotopes. Several aspects are reported, from their 'cold' chelation chemistry (thermodynamic, kinetic, and structural properties) and radiolabelling investigations to the preclinical and clinical studies performed with a variety of bioconjugates. The aim of this review is to provide both a guide for the rational design of novel optimal platforms for the chelation of these attractive α-emitters and emphasize the prospects of the most encouraging chelating agents proposed so far.
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Boosting Bismuth(III) Complexation for Targeted α-Therapy (TAT) Applications with the Mesocyclic Chelating Agent AAZTA. Angew Chem Int Ed Engl 2022; 61:e202207120. [PMID: 36073561 PMCID: PMC9828418 DOI: 10.1002/anie.202207120] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2022] [Indexed: 01/12/2023]
Abstract
Targeted α therapy (TAT) is a promising tool in the therapy of cancer. The radionuclide 213 BiIII shows favourable physical properties for this application, but the fast and stable chelation of this metal ion remains challenging. Herein, we demonstrate that the mesocyclic chelator AAZTA quickly coordinates BiIII at room temperature, leading to a robust complex. A comprehensive study of the structural, thermodynamic and kinetic properties of [Bi(AAZTA)]- is reported, along with bifunctional [Bi(AAZTA-C4-COO- )]2- and the targeted agent [Bi(AAZTA-C4-TATE)]- , which incorporates the SSR agonist Tyr3 -octreotate. An unexpected increase in the stability and kinetic inertness of the metal chelate was observed for the bifunctional derivative and was maintained for the peptide conjugate. A cyclotron-produced 205/206 Bi mixture was used as a model of 213 Bi in labelling, stability, and biodistribution experiments, allowing the efficiency of [213 Bi(AAZTA-C4-TATE)]- to be estimated. High accumulation in AR42J tumours and reduced kidney uptake were observed with respect to the macrocyclic chelate [213 Bi(DOTA-TATE)]- .
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Gamma counting protocols for the accurate quantification of 225Ac and 213Bi without the need for a secular equilibrium between parent and gamma-emitting daughter. EJNMMI Radiopharm Chem 2022; 7:28. [PMID: 36274098 PMCID: PMC9588853 DOI: 10.1186/s41181-022-00174-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Accepted: 08/22/2022] [Indexed: 11/22/2022] Open
Abstract
BACKGROUND Quantification of actinium-225 through gamma counter measurements, when there is no secular equilibrium between actinium-225 and its gamma emitting daughters bismuth-213 and/or francium-221, can provide valuable information regarding the possible relocation of recoiled daughters such that related radiotoxicity effects can be evaluated. This study proposes a multiple time-point protocol using the bismuth-213 photopeak with measurements before secular equilibrium between actinium-225 and bismuth-213, and a single time-point protocol using both the francium-221 and bismuth-213 photopeak while assuming secular equilibrium between actinium-225 and francium-221 but not between bismuth-213 and actinium-225. RESULTS Good agreement (i.e. 3% accuracy) was obtained when relying on a multiple time-points measurement of bismuth-213 to quantify both actinium-225 and excess of bismuth-213. Following scatter correction, actinium-225 can be accurately quantified using the francium-221 in a single time-point measurement within 3% of accuracy. The analysis performed on the stability data of [225Ac]Ac-DEPA and [225Ac]Ac-DOTA complexes, before secular equilibrium between bismuth-213 and actinium-225 was formed, revealed considerable amounts of unbound bismuth-213 (i.e. more than 90%) after 24 h of the radiolabeling most likely due to the recoiled daughter effect. CONCLUSION Both protocols were able to accurately estimate 225Ac-activities provided the francium-221 energy window was corrected for the down scatter of the higher-energy gamma-emissions by bismuth-213. This could prove beneficial to study the recoiled daughter effect and redistribution of free bismuth-213 by monitoring the accumulation or clearance of bismuth-213 in different tissues during biodistribution studies or in patient samples during clinical studies. On the other hand, the single gamma counter measurement protocol, although required a 30 min waiting time, is more time and cost efficient and therefore more appropriate for standardized quality control procedures of 225Ac-labeled radiopharmaceuticals.
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Abstract
The application of radiopharmaceutical therapy for the treatment of certain diseases is well established, and the field is expanding. New therapeutic radiopharmaceuticals have been developed in recent years, and more are in the research pipeline. Concurrently, there is growing interest in the use of internal dosimetry as a means of personalizing, and potentially optimizing, such therapy for patients. Internal dosimetry is multifaceted, and the current state of the art is discussed in this continuing education article. Topics include the context of dosimetry, internal dosimetry methods, the advantages and disadvantages of incorporating dosimetry calculations in radiopharmaceutical therapy, a description of the workflow for implementing patient-specific dosimetry, and future prospects in the field.
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Boosting Bismuth(III) Complexation for Targeted α‐Therapy (TAT) Applications with the Mesocyclic Chelating Agent AAZTA. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202207120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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In vivo investigation of Gallium-68 and Bismuth-205/206 labeled beta cyclodextrin for targeted alpha therapy of prostaglandin E2 receptor-expressing tumors in mice. Int J Pharm 2022; 625:122132. [PMID: 36028082 DOI: 10.1016/j.ijpharm.2022.122132] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2022] [Revised: 07/26/2022] [Accepted: 08/18/2022] [Indexed: 11/23/2022]
Abstract
Prostaglandin E2 (PGE2) molecule and its receptors play an important role in the development of malignancies and metastases therefore PGE2 may play a crucial role in the diagnosis and a new therapeutic target in the field of radionuclide therapy of PGE2-positive tumors. PGE2 form complexes with RAMEB (randomly-methylated-beta-cyclodextrin) with high affinity therefore the aim of this present study was to synthesize a PGE2-specific DOTAGA-RAMEB, which can be labeled with diagnostic and therapeutic isotopes also and binds to PGE2-positive tumors. DOTAGA-RAMEB was labeled with 68Ga and 205/206Bi radionuclides and their radiochemical purity (RCP%), partition coefficient (logP values), and in vitro and in vivo stability were determined. For the assessment of the biological properties and the PGE2 specificity of [68Ga]Ga-DOTAGA-RAMEB and [205/206Bi]Bi-DOTAGA-RAMEB in vivo PET imaging and ex vivo biodistribution studies were performed using healthy control and PGE2-positive BxPC-3 tumor-bearing CB17 SCID mice. The RCP% of the newly synthesized [68Ga]Ga-DOTAGA-RAMEB and [205/206Bi]Bi-DOTAGA-RAMEB was higher than 98 %. In vivo studies showed that the tumor-to-background ratio of [68Ga]Ga-DOTAGA-RAMEB was 2.5 ± 0.2 as a result BxPC-3 tumors were clearly identified on PET images. Beside this the ex vivo biodistribution studies showed that the accumulation rate of [68Ga]Ga-DOTAGA-RAMEB and [205/206Bi]Bi-DOTAGA-RAMEB was similar in the PGE2-positive BxPC-3 tumors.
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3p-C-NETA: A versatile and effective chelator for development of Al 18F-labeled and therapeutic radiopharmaceuticals. Am J Cancer Res 2022; 12:5971-5985. [PMID: 35966589 PMCID: PMC9373814 DOI: 10.7150/thno.75336] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Accepted: 07/29/2022] [Indexed: 11/05/2022] Open
Abstract
Background: Radiolabeled somatostatin analogues (e.g. [68Ga]Ga-DOTATATE and [177Lu]Lu-DOTATATE) have been used to diagnose, monitor, and treat neuroendocrine tumour (NET) patients with great success. [18F]AlF-NOTA-octreotide, a promising 18F-labeled somatostatin analogue and potential alternative for 68Ga-DOTA-peptides, is under clinical evaluation. However, ideally, the same precursor (combination of chelator-linker-vector) can be used for production of both diagnostic and therapeutic radiopharmaceuticals with very similar (e.g. Al18F-method in combination with therapeutic radiometals 213Bi/177Lu) or identical (e.g. complementary Tb-radionuclides) pharmacokinetic properties, allowing for accurate personalised dosimetry estimation and radionuclide therapy of NET patients. In this study we evaluated 3p-C-NETA, as potential theranostic Al18F-chelator and present first results of radiosynthesis and preclinical evaluation of [18F]AlF-3p-C-NETA-TATE. Methods: 3p-C-NETA was synthesized and radiolabeled with diagnostic (68Ga, Al18F) or therapeutic (177Lu, 161Tb, 213Bi, 225Ac and 67Cu) radionuclides at different temperatures (25-95 °C). The in vitro stability of the corresponding radiocomplexes was determined in phosphate-buffered saline (PBS) and human serum. 3p-C-NETA-TATE was synthesized using standard solid/liquid-phase peptide synthesis. [18F]AlF-3p-C-NETA-TATE was synthesized in an automated AllinOne® synthesis module and the in vitro stability of [18F]AlF-3p-C-NETA-TATE was evaluated in formulation buffer, PBS and human serum. [18F]AlF-3p-C-NETA-TATE pharmacokinetics were evaluated using µPET/MRI in healthy rats, with [18F]AlF-NOTA-Octreotide as benchmark. Results: 3p-C-NETA quantitatively sequestered 177Lu, 213Bi and 67Cu at 25 °C while heating was required to bind Al18F, 68Ga, 161Tb and 225Ac efficiently. The [18F]AlF-, [177Lu]Lu- and [161Tb]Tb-3p-C-NETA-complex showed excellent in vitro stability in both PBS and human serum over the study period. In contrast, [67Cu]Cu- and [225Ac]Ac-, [68Ga]Ga-3p-C-NETA were stable in PBS, but not in human serum. [18F]AlF-3p-C-NETA-TATE was obtained in good radiochemical yield and radiochemical purity. [18F]AlF-3p-C-NETA-TATE displayed good in vitro stability for 4 h in all tested conditions. Finally, [18F]AlF-3p-C-NETA-TATE showed excellent pharmacokinetic properties comparable with the results obtained for [18F]AlF-NOTA-Octreotide. Conclusions: 3p-C-NETA is a versatile chelator that can be used for both diagnostic applications (Al18F) and targeted radionuclide therapy (213Bi, 177Lu, 161Tb). It has the potential to be the new theranostic chelator of choice for clinical applications in nuclear medicine.
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Radiopharmaceutical Treatments for Cancer Therapy, Radionuclides Characteristics, Applications, and Challenges. Molecules 2022; 27:molecules27165231. [PMID: 36014472 PMCID: PMC9415873 DOI: 10.3390/molecules27165231] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2022] [Revised: 08/09/2022] [Accepted: 08/10/2022] [Indexed: 11/16/2022] Open
Abstract
Advances in the field of molecular biology have had an impact on biomedical applications, which provide greater hope for both imaging and therapeutics. Work has been intensified on the development of radionuclides and their application in radiopharmaceuticals (RPS) which will certainly influence and expand therapeutic approaches in the future treatment of patients. Alpha or beta particles and Auger electrons are used for therapy purposes, and each has advantages and disadvantages. The radionuclides labeled drug delivery system will deliver the particles to the specific targeting cell. Different radioligands can be chosen to uniquely target molecular receptors or intracellular components, making them suitable for personal patient-tailored therapy in modern cancer therapy management. Advances in nanotechnology have enabled nanoparticle drug delivery systems that can allow for specific multivalent attachment of targeted molecules of antibodies, peptides, or ligands to the surface of nanoparticles for therapy and imaging purposes. This review presents fundamental radionuclide properties with particular reference to tumor biology and receptor characteristic of radiopharmaceutical targeted therapy development.
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Abstract
A new decadentate chelator, H2ampa, was designed to be a potential radiopharmaceutical chelator component. The chelator involves both amide and picolinate functional groups on a large non-macrocyclic, ether-bridged backbone. With its large scaffold, H2ampa was paired with [nat/203Pb]Pb2+, [nat/213Bi]Bi3+, and natLa3+/[225Ac]Ac3+ ions. Nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry were used to study the non-radioactive metal complexes. A single crystal of [Bi(ampa)](NO3) was obtained; its asymmetric, 10-coordinate complex structure was revealed by X-ray diffraction. Optimal conformations of the metal complexes were assessed by density functional theory studies to provide further structural information. Solution studies providing thermodynamic insights into metal complex formation revealed H2ampa coordinated Bi3+, Pb2+, and La3+ ions to obtain pM values of 26, 14.8, and 15.1, respectively. Preliminary concentration-dependent radiolabeling experiments were carried out between H2ampa and three different radiometals to evaluate their compatibility for radiopharmaceutical applications. The chelator radiolabeled [203Pb]Pb2+, [213Bi]Bi3+, and [225Ac]Ac3+ in short reaction times (7-30 min), at dilute concentrations, and under mild conditions. Thus, H2ampa was proven to be a versatile chelator able to well coordinate a small range of radiometals frequently considered to be alpha therapeutic candidates.
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Production of 230Pa as a Source for Medical Radionuclides 230U and 226Th Including Isolation by Liquid–liquid Extraction. SOLVENT EXTRACTION AND ION EXCHANGE 2022. [DOI: 10.1080/07366299.2022.2088059] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Applications of radiocomplexes with thiosemicarbazones and bis(thiosemicarbazones) in diagnostic and therapeutic nuclear medicine. Coord Chem Rev 2022. [DOI: 10.1016/j.ccr.2022.214418] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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Abstract
Theranostics is a term coined by combining the words “therapeutics” and “diagnostics,” referring to single chemical entities developed to deliver therapy and diagnosis simultaneously. Neuroendocrine tumors are rare cancers that occur in various organs of the body, and they express neuroendocrine factors such as chromogranin A and somatostatin receptor. Somatostatin analogs bind to somatostatin receptor, and when combined with diagnostic radionuclides, such as gamma‐emitters, are utilized for diagnosis of neuroendocrine tumor. Somatostatin receptor scintigraphy when combined with therapeutic radionuclides, such as beta‐emitters, are effective in treating neuroendocrine tumor as peptide receptor radionuclide therapy. Somatostatin receptor scintigraphy and peptide receptor radionuclide therapy are some of the most frequently used and successful theranostics for neuroendocrine tumor. In Japan, radiopharmaceuticals are regulated under a complex law system, creating a significant drug lag, which is a major public concern. It took nearly 10 years to obtain the approval for somatostatin receptor scintigraphy and peptide receptor radionuclide therapy use by the Japanese government. In 2021, 111Lu‐DOTATATE (Lutathera), a drug for peptide receptor radionuclide therapy, was covered by insurance in Japan. In this review, we summarize the history of the development of neuroendocrine tumor theranostics and theranostics in general, as therapeutic treatment for cancer in the future. Furthermore, we briefly address the Japanese point of view regarding the development of new radiopharmaceuticals.
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Solid-phase extraction of 225Ac using ion-imprinted resin and 243Am as a radioactive tracer for internal dosimetry and incorporation measurements. Anal Chim Acta 2022; 1194:339421. [DOI: 10.1016/j.aca.2021.339421] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Revised: 12/27/2021] [Accepted: 12/29/2021] [Indexed: 11/15/2022]
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Alpha particle microdosimetry calculations using a shallow neural network. Phys Med Biol 2022; 67. [DOI: 10.1088/1361-6560/ac499c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Accepted: 01/10/2022] [Indexed: 11/12/2022]
Abstract
Abstract
A shallow neural network was trained to accurately calculate the microdosimetric parameters, 〈z
1〉 and 〈z
1
2〉 (the first and second moments of the single-event specific energy spectra, respectively) for use in alpha-particle microdosimetry calculations. The regression network of four inputs and two outputs was created in MATLAB and trained on a data set consisting of both previously published microdosimetric data and recent Monte Carlo simulations. The input data consisted of the alpha-particle energies (3.97–8.78 MeV), cell nuclei radii (2–10 μm), cell radii (2.5–20 μm), and eight different source-target configurations. These configurations included both single cells in suspension and cells in geometric clusters. The mean square error (MSE) was used to measure the performance of the network. The sizes of the hidden layers were chosen to minimize MSE without overfitting. The final neural network consisted of two hidden layers with 13 and 20 nodes, respectively, each with tangential sigmoid transfer functions, and was trained on 1932 data points. The overall training/validation resulted in a MSE = 3.71 × 10−7. A separate testing data set included input values that were not seen by the trained network. The final test on 892 separate data points resulted in a MSE = 2.80 × 10−7. The 95th percentile testing data errors were within ±1.4% for 〈z
1〉 outputs and ±2.8% for 〈z
1
2〉 outputs, respectively. Cell survival was also predicted using actual versus neural network generated microdosimetric moments and showed overall agreement within ±3.5%. In summary, this trained neural network can accurately produce microdosimetric parameters used for the study of alpha-particle emitters. The network can be exported and shared for tests on independent data sets and new calculations.
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Chelating the Alpha Therapy Radionuclides 225Ac 3+ and 213Bi 3+ with 18-Membered Macrocyclic Ligands Macrodipa and Py-Macrodipa. Inorg Chem 2021; 61:801-806. [PMID: 34965102 DOI: 10.1021/acs.inorgchem.1c03670] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The radionuclides 225Ac3+ and 213Bi3+ possess favorable physical properties for targeted alpha therapy (TAT), a therapeutic approach that leverages α radiation to treat cancers. A chelator that effectively binds and retains these radionuclides is required for this application. The development of ligands for this purpose, however, is challenging because the large ionic radii and charge-diffuse nature of these metal ions give rise to weaker metal-ligand interactions. In this study, we evaluated two 18-membered macrocyclic chelators, macrodipa and py-macrodipa, for their ability to complex 225Ac3+ and 213Bi3+. Their coordination chemistry with Ac3+ was probed computationally and with Bi3+ experimentally via NMR spectroscopy and X-ray crystallography. Furthermore, radiolabeling studies were conducted, revealing the efficient incorporation of both 225Ac3+ and 213Bi3+ by py-macrodipa that matches or surpasses the well-known chelators macropa and DOTA. Incubation in human serum at 37 °C showed that ∼90% of the 225Ac3+-py-macrodipa complex dissociates after 1 d. The Bi3+-py-macrodipa complex possesses remarkable kinetic inertness reflected by an EDTA transchelation challenge study, surpassing that of Bi3+-macropa. This work establishes py-macrodipa as a valuable candidate for 213Bi3+ TAT, providing further motivation for its implementation within new radiopharmaceutical agents.
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Peptide Receptor Radionuclide Therapy Targeting the Somatostatin Receptor: Basic Principles, Clinical Applications and Optimization Strategies. Cancers (Basel) 2021; 14:cancers14010129. [PMID: 35008293 PMCID: PMC8749814 DOI: 10.3390/cancers14010129] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Revised: 12/13/2021] [Accepted: 12/22/2021] [Indexed: 12/12/2022] Open
Abstract
Simple Summary Peptide receptor radionuclide therapy (PRRT) is a systemic treatment consisting of the administration of a tumor-targeting radiopharmaceutical into the circulation of a patient. The radiopharmaceutical will bind to a specific peptide receptor leading to tumor-specific binding and retention. This will subsequently cause lethal DNA damage to the tumor cell. The only target that is currently used in widespread clinical practice is the somatostatin receptor, which is overexpressed on a range of tumor cells, including neuroendocrine tumors and neural-crest derived tumors. Academia played an important role in the development of PRRT, which has led to heterogeneous literature over the last two decades, as no standard radiopharmaceutical or regimen has been available for a long time. This review focuses on the basic principles and clinical applications of PRRT, and discusses several PRRT-optimization strategies. Abstract Peptide receptor radionuclide therapy (PRRT) consists of the administration of a tumor-targeting radiopharmaceutical into the circulation of a patient. The radiopharmaceutical will bind to a specific peptide receptor leading to tumor-specific binding and retention. The only target that is currently used in clinical practice is the somatostatin receptor (SSTR), which is overexpressed on a range of tumor cells, including neuroendocrine tumors and neural-crest derived tumors. Academia played an important role in the development of PRRT, which has led to heterogeneous literature over the last two decades, as no standard radiopharmaceutical or regimen has been available for a long time. This review provides a summary of the treatment efficacy (e.g., response rates and symptom-relief), impact on patient outcome and toxicity profile of PRRT performed with different generations of SSTR-targeting radiopharmaceuticals, including the landmark randomized-controlled trial NETTER-1. In addition, multiple optimization strategies for PRRT are discussed, i.e., the dose–effect concept, dosimetry, combination therapies (i.e., tandem/duo PRRT, chemoPRRT, targeted molecular therapy, somatostatin analogues and radiosensitizers), new radiopharmaceuticals (i.e., SSTR-antagonists, Evans-blue containing vector molecules and alpha-emitters), administration route (intra-arterial versus intravenous) and response prediction via molecular testing or imaging. The evolution and continuous refinement of PRRT resulted in many lessons for the future development of radionuclide therapy aimed at other targets and tumor types.
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PSMA-Targeting Radiopharmaceuticals for Prostate Cancer Therapy: Recent Developments and Future Perspectives. Cancers (Basel) 2021; 13:cancers13163967. [PMID: 34439121 PMCID: PMC8393521 DOI: 10.3390/cancers13163967] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2021] [Revised: 07/22/2021] [Accepted: 07/28/2021] [Indexed: 12/12/2022] Open
Abstract
Simple Summary One of the most frequently diagnosed cancer in men is adenocarcinoma of the prostate. Once the disease is metastatic, only very limited treatment options are available, resulting in a very short median survival time of 13 months; however, this reality is gradually changing due to the discovery of prostate-specific membrane antigen (PSMA), a protein that is present in cancerous prostate tissue. Researchers have developed pharmaceuticals specific for PSMA, ranging from antibodies (mAb) to low-molecular weight molecules coupled to beta minus and alpha-emitting radionuclides for their use in targeted radionuclide therapy (TRT). TRT offers the possibility of selectively removing cancer tissue via the emission of radiation or radioactive particles within the tumour. In this article, the major milestones in PSMA ligand research and the therapeutic developments are summarised, together with a future perspective on the enhancement of current therapeutic approaches. Abstract Prostate cancer (PC) is the second most common cancer among men, with 1.3 million yearly cases worldwide. Among those cancer-afflicted men, 30% will develop metastases and some will progress into metastatic castration-resistant prostate cancer (mCRPC), which is associated with a poor prognosis and median survival time that ranges from nine to 13 months. Nevertheless, the discovery of prostate specific membrane antigen (PSMA), a marker overexpressed in the majority of prostatic cancerous tissue, revolutionised PC care. Ever since, PSMA-targeted radionuclide therapy has gained remarkable international visibility in translational oncology. Furthermore, on first clinical application, it has shown significant influence on therapeutic management and patient care in metastatic and hormone-refractory prostate cancer, a disease that previously had remained immedicable. In this article, we provide a general overview of the main milestones in the development of ligands for PSMA-targeted radionuclide therapy, ranging from the firstly developed monoclonal antibodies to the current state-of-the-art low molecular weight entities conjugated with various radionuclides, as well as potential future efforts related to PSMA-targeted radionuclide therapy.
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A Radionuclide Generator of High-Purity Bi-213 for Instant Labeling. Pharmaceutics 2021; 13:pharmaceutics13060914. [PMID: 34205580 PMCID: PMC8234463 DOI: 10.3390/pharmaceutics13060914] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2021] [Revised: 06/12/2021] [Accepted: 06/17/2021] [Indexed: 11/17/2022] Open
Abstract
A new two-column 225Ac/213Bi generator was developed specifically for using 225Ac containing an impurity of long lived 227Ac. The parent 225Ac was retained on the first Actinide Resin column, while 213Bi was accumulated on the second column filled with AG MP-50 resin via continuous elution and decay of intermediate 221Fr. The 213Bi accumulation was realized in circulation mode which allowed a compact generator design. It was demonstrated that 213Bi could be quickly and effectively extracted from AG MP-50 in form of complexes with various chelating agents including DTPA and DOTA. The performance of the generator presented and a conventional single-column generator on the base of AG MP-50 was tested and both generators were loaded with 225Ac containing 227Ac impurity. The 213Bi generation efficiencies were comparable and greater than 70%, whereas the developed generator provided a deeper degree of purification of 213Bi from Ac isotopes and decay products of 227Ac.
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