Figure - available from: EJNMMI Radiopharmacy and Chemistry
This content is subject to copyright. Terms and conditions apply.
Source publication
Background
⁶⁴ Cu is one of the few radioisotopes that can be used for both imaging and therapy, enabling theranostics with identical chemical composition. Development of stable chelators is essential to harness the potential of this isotope, challenged by the presence of endogenous copper chelators. Pyridyl type chelators show good coordination abi...
Citations
... The most prominent chelating ligands exploited in radiopharmaceutical design tend to be commercially available, given their ease of access and convenience for use. The ubiquitous commercial standard, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) (Figure 1), forms kinetically inert and thermodynamically stable complexes with a variety of trivalent and divalent radiometal ions, and is used prominently for complexation of radiometals such as 225 Ac 3+ , 44 Sc 3+ , 111 In 3+ , 177 Lu 3+ , 64 Cu 2+ , 203 Pb 2+ among others (Hanaoka et al., 2009;Paganelli et al., 2014;Price and Chris, 2014;Zhang et al., 2017;Kent et al., 2019;Ramogida et al., 2019;Stenberg et al., 2020;McNeil et al., 2021;Yang et al., 2021). ...
... The most prominent chelating ligands exploited in radiopharmaceutical design tend to be commercially available, given their ease of access and convenience for use. The ubiquitous commercial standard, 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) (Figure 1), forms kinetically inert and thermodynamically stable complexes with a variety of trivalent and divalent radiometal ions, and is used prominently for complexation of radiometals such as 225 Ac 3+ , 44 Sc 3+ , 111 In 3+ , 177 Lu 3+ , 64 Cu 2+ , 203 Pb 2+ among others (Hanaoka et al., 2009;Paganelli et al., 2014;Price and Chris, 2014;Zhang et al., 2017;Kent et al., 2019;Ramogida et al., 2019;Stenberg et al., 2020;McNeil et al., 2021;Yang et al., 2021). ...
... TCMC exchanges the "harder" carboxylic acids of DOTA for "softer" amide donor arms. TCMC is used almost exclusively for the complexation of lead radioisotopes (Chappell et al., 2000;McNeil et al., 2021)-an intermediate metal ion according to HSAB theory (Chappell et al., 2000). As a wellestablished chelate, the bifunctional isothiocyanate-based derivative of TCMC, S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraaza-1,4,7,10tetra(2-carbamoylmethyl)cyclododecane (p-SCN-Bn-TCMC), is also commercially available ( Figure 1). ...
A comprehensive investigation of the Hg²⁺ coordination chemistry and 197m/gHg radiolabeling capabilities of cyclen-based commercial chelators, namely, DOTA and DOTAM (aka TCMC), along with their bifunctional counterparts, p-SCN-Bn-DOTA and p-SCN-Bn-TCMC, was conducted to assess the suitability of these frameworks as bifunctional chelators for the 197m/gHg²⁺ theranostic pair. Radiolabeling studies revealed that TCMC and DOTA exhibited low radiochemical yields (0%–6%), even when subjected to harsh conditions (80°C) and high ligand concentrations (10–4 M). In contrast, p-SCN-Bn-TCMC and p-SCN-Bn-DOTA demonstrated significantly higher 197m/gHg radiochemical yields (100% ± 0.0% and 70.9% ± 1.1%, respectively) under the same conditions. The [197 m/gHg]Hg-p-SCN-Bn-TCMC complex was kinetically inert when challenged against human serum and glutathione. To understand the differences in labeling between the commercial chelators and their bifunctional counterparts, non-radioactive natHg²⁺ complexes were assessed using NMR spectroscopy and DFT calculations. The NMR spectra of Hg-TCMC and Hg-p-SCN-Bn-TCMC suggested binding of the Hg²⁺ ion through the cyclen backbone framework. DFT studies indicated that binding of the Hg²⁺ ion within the backbone forms a thermodynamically stable product. However, competition can form between isothiocyanate binding and binding through the macrocycle, which was experimentally observed. The isothiocyanate bound coordination product was dominant at the radiochemical scale as, in comparison, the macrocycle bound product was seen at the NMR scale, agreeing with the DFT result. Furthermore, a bioconjugate of TCMC (TCMC-PSMA) targeting prostate-specific membrane antigen was synthesized and radiolabeled, resulting in an apparent molar activity of 0.089 MBq/nmol. However, the complex demonstrated significant degradation over 24 h when exposed to human serum and glutathione. Subsequently, cell binding assays were conducted, revealing a Ki value ranging from 19.0 to 19.6 nM. This research provides crucial insight into the effectiveness of current commercial chelators in the context of 197m/gHg²⁺ radiolabeling. It underscores the necessity for the development of specific and customized chelators to these unique “soft” radiometals to advance 197m/gHg²⁺ radiopharmaceuticals.
... Demetallation can cause deleterious effects on the non-targeted tissues as well as alter the information in diagnosis [34,35]. So far, a wide range of BFCs has been introduced to the antibodies, including common acyclic chelators [30,36,37] and polyazamacrocyclic chelators [38][39][40][41][42]. In this study, we utilized the recently reported by our group PCB-TE2A-Tz BFC for better in vivo performance and bioorthogonal click reaction [43]. ...
Triple-negative breast cancer (TNBC) does not express estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. Because TNBC lacks the expression of commonly targeted receptors, it is challenging to develop a new imaging agent for this cancer subtype. Heterogeneous nuclear ribonucleoproteins (hnRNPs) are RNA–protein complexes that have been linked to tumor development and progression. Considering the high expression of hnRNPA2B1, an hnRNP subtype, in TNBC MDA-MB-231 cells, this study aimed to develop a novel hnRNPA2B1 antibody-based nuclear imaging agent. The hnRNPA2B1-specific antibody was radiolabeled with 64Cu and evaluated in vitro and in vivo. The trans cyclooctene (TCO) was functionalized on the antibody to obtain hnRNP-PEG4-TCO and reactive tetrazine (Tz) on the ultrastable bifunctional chelator PCB-TE2A-alkyne to yield PCB-TE2A-Tz for the inverse electron demand Diels–Alder reaction. The 64Cu-radiolabeled antibody was administered and imaged at 1–18 h time points for conventional imaging. Alternatively, the unlabeled antibody conjugate was administered, and 48 h later radiolabeled 64Cu-PCB-TE2A-Tz was administered to the same mice for the pretargeting strategy and imaged at the same time intervals for direct comparison. The tumor was successfully visualized in both strategies, and comparatively, pretargeting showed superior results. The 64Cu-PCB-TE2A-Tz was successfully clicked at the tumor site with hnRNP-PEG4-TCO and the non-clicked were concurrently eliminated. This led to increase the tumor uptake with extremely high tumor-to-background ratio manifested by positron emission tomography (PET) imaging and biodistribution studies.
... The multipurpose coordination chemistry of copper allows for its radiometallation with various chelators, such as DOTA (1,4,7,10-tetraazacyclododecane-tetraacetic acid), NOTA (1,4,7triazacyclononane-triacetic acid), TETA (1,4,8,11-tetraazacyclotetraadecane-1,4,8,11-tetraacetic acid), and CB-TE2A (4,11-bis(carboxymethyl)-1,4,8,11-tetraazabicyclo[6.6.2] hexadecane) (14)(15)(16)(17), which can be conjugated to various radiopharmaceuticals. 64 Cu(T 1/2 : 12.7 h) is an attractive radioisotope of significant interest for positron emission tomography (PET) with β + (E max : 653.03 keV and E mean : 278.21 keV) and EC (electron capture: 1675.03 and 1345.77 keV) (18,19). ...
64Cu and 67Cu are theragnostic pair radionuclides with promising application in the nuclear medicine. 64Cu is PET nuclide for the non-invasive diagnosis and 67Cu is beta emitter for therapy of various cancers. This study discusses optimization efforts in the production of these radioactive coppers carried out with 30 MeV cyclotron. Optimized conditions include target preparation, chemical separation, and quality control. The production routes of 64Cu and 67Cu were studied based on the nuclear reactions of 64Ni(p,n)64Cu and 70Zn(p,α)67Cu. The produced 64Cu and 67Cu have >99.9% of the radionuclidic purity. The yield at the end of bombardment (EOB) of 64Cu and 67Cu is 28.5 MBq/μAh and 67Cu is 0.58 MBq/μAh, respectively.
... Given Cu 2+ is a transition metal cation, preferring softer N-donors along with Odonor atoms, it can be effectively bound by aromatic nitrogen that is known to be less basic than aliphatic amines. Moreover, it has been recently shown that H 4 DOTA derivatives with a pyridine arm can significantly improve copper binding [9]. To the best of our knowledge, protonation and complexation constants of such hybrid ligands with the simultaneous presence of acetic and pyridyl pendant groups have not been described in the literature yet. ...
... There are examples of substitutions of all (two or three) acetates in azacrowns by pyridines [3,6,10,11] and it has been shown that pyridine, as a pendant arm, can significantly improve the chelation ability and kinetics of binding towards Cu 2+ and Bi 3+ , including direct comparison with well-known H 4 DOTA [9,12,13]. ...
... To the best of our knowledge, protonation and complexation constants of such hybrid ligands with the simultaneous presence of acetic and pyridyl pendant groups have not been described in the literature yet. There are examples of substitutions of all (two or three) acetates in azacrowns by pyridines [3,6,10,11] and it has been shown that pyridine, as a pendant arm, can significantly improve the chelation ability and kinetics of binding towards Cu 2+ and Bi 3+ , including direct comparison with well-known H4DOTA [9,12,13]. ...
A synthetic procedure for the synthesis of azacrown ethers with a combination of pendant arms has been developed and the synthesized ligand, characterized by various techniques, was studied. The prepared benzoazacrown ether with hybrid pendant arms and its complexes with copper and lead cations were studied in terms of biomedical applications. Similarly to a fully acetate analog, the new one binds both cations with close stability constants, despite the decrease in both constants. The calculated geometry of the complexes correlate with the data from X-ray absorption and NMR spectroscopy. Coordination of both cations differs due to the difference between the ionic radii. However, these chelation modes provide effective shielding of cations in both cases, that was shown by the stability of their complexes in the biologically relevant media towards transchelation and transmetallation.
... We present the production of the 203 Pb and 212 Pb theranostic pair using TRIUMF's TR13 (13 MeV) and 500 MeV cyclotron, subsequent radiochemical purification and isotope characterization. The separated radioisotopes were evaluated alongside each other for radiolabeling a series of TRIUMF developed, pyridine based-DOTA analogues (Yang et al. 2021) along with commercial standards DOTA and TCMC (Fig. 2), and the stability of each radiometal-complex was evaluated in vitro. ...
... Pb resin (Di-t-butylcyclohexano 18-crown-6, 100-150 μm particle size) was purchased from Eichrom Technologies (Lisle, IL were purchased from Macrocyclics (Plano, TX). DOTA-1Py (2,2′,2″-(10-(pyridin-2ylmethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl) triacetic acid), DOTA-2Py, (2,2′- (7,10-bis (pyridin-2-ylmethyl)-1,4,7,10-tetraazacyclododecane-1,4-diyl) diacetic acid) and DOTA-3Py (2-(4,7,10-tris (pyridin-2-ylmethyl)-1,4,7,10-tetraazacyclododecan-1-yl) acetic acid) were synthesized as previously described (Yang et al. 2021). Instant thin layer chromatography paper impregnated with silicic acid (iTLC-SA) was purchased from Agilent Technologies (Santa Clara, CA). ...
Background
Lead-212 ( ²¹² Pb, t 1/2 = 10.6 h) and lead-203 ( ²⁰³ Pb, t 1/2 = 51.9 h) are an element-equivalent, or a matched theranostic radioisotope pair that show great potential for application in targeted radionuclide therapy (TRT) and single-photon emission computed tomography (SPECT), respectively. At TRIUMF we have produced both ²⁰³ Pb and ²¹² Pb using TRIUMF’s TR13 (13 MeV) and 500 MeV cyclotrons, and subsequently purified and evaluated both radioisotopes using a series of pyridine-modified DOTA analogues in comparison to the commercially available chelates DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) and TCMC (1,4,7,10-tetraaza-1,4,7,10-tetra(2-carbamoylmethyl)cyclododecane).
Results
Proton irradiation (12.8 MeV) of natural and enriched thallium-203 ( ²⁰³ Tl) targets gave ²⁰³ Pb saturation yields of 134 ± 25 and 483 ± 3 MBq/μA, respectively. Thorium-228 ( ²²⁸ Th, t 1/2 = 1.9 y), a by-product of ²³² Th proton spallation on TRIUMF’s main 500 MeV beamline (beamline 1A, BL1A), was recovered to build a ²²⁸ Th/ ²¹² Pb generator with the ability to deliver up to 9–10 MBq of ²¹² Pb daily. Both lead isotopes were purified via solid phase extraction chromatography (Pb resin), and isolated in an acetate form ([ 203/212 Pb]Pb(OAc) 2 ) suitable for direct radiolabeling of chelators and bioconjugates. A series of cyclen-based chelators (herein referred to as DOTA-1Py, -2Py, and -3Py) along with established chelates DOTA and TCMC were evaluated for their ability to complex both ²⁰³ Pb and ²¹² Pb. All chelates incorporated ²¹² Pb/ ²⁰³ Pb efficiently, with higher radiolabeling yields observed for the ²¹² Pb-complexes.
Conclusion
The production of ²⁰³ Pb and ²¹² Pb was established using TRIUMF 13 MeV and 500 MeV cyclotrons, respectively. Both production methods provided radiometals suitable for subsequent radiolabeling reactions using known and novel chelates. Furthermore, the novel chelate DOTA-3Py may be a good candidate for biomolecule conjugation and further theranostic ²¹² Pb/ ²⁰³ Pb studies.
... We present the production of the 203 Pb and 212 Pb theranostic pair using TRIUMF's TR13 (13 MeV) and 500 MeV cyclotron, subsequent radiochemical purification and isotope characterization. The separated radioisotopes were evaluated alongside each other for radiolabeling a series of TRIUMF developed, pyridine based-DOTA analogues (Yang et al. 2021) along with commercial standards DOTA and TCMC (Fig. 2), and the stability of each radiometal-complex was evaluated in vitro. ...
... Pb resin (Di-t-butylcyclohexano 18-crown-6, 100-150 μm particle size) was purchased from Eichrom Technologies (Lisle, IL were purchased from Macrocyclics (Plano, TX). DOTA-1Py (2,2′,2″-(10-(pyridin-2ylmethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl) triacetic acid), DOTA-2Py, (2,2′- (7,10-bis (pyridin-2-ylmethyl)-1,4,7,10-tetraazacyclododecane-1,4-diyl) diacetic acid) and DOTA-3Py (2-(4,7,10-tris (pyridin-2-ylmethyl)-1,4,7,10-tetraazacyclododecan-1-yl) acetic acid) were synthesized as previously described (Yang et al. 2021). Instant thin layer chromatography paper impregnated with silicic acid (iTLC-SA) was purchased from Agilent Technologies (Santa Clara, CA). ...
Background: Lead-212 (²¹²Pb, t1/2 = 10.6 h) and lead-203 (²⁰³Pb, t1/2 = 51.9 h) are an element-equivalent, or a matched theranostic radioisotope pair that show great potential for application in targeted radionuclide therapy (TRT) and single-photon emission computed tomography (SPECT), respectively. At TRIUMF we have produced both ²⁰³Pb and ²¹²Pb using TRIUMF’s TR13 (13 MeV) and 500 MeV cyclotrons, and subsequently purified and evaluated both radioisotopes using a series of pyridine-modified DOTA analogues in comparison to the commercially available chelates DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) and TCMC (1,4,7,10-tetraaza-1,4,7,10-tetra(2-carbomoylmethyl)cyclododecane).
Results: Proton irradiation (12.8 MeV) of natural and enriched thalium-203 (²⁰³Tl) targets gave ²⁰³Pb saturation yields of 134 ± 25 and 483 ± 3 MBq/μA, respectively. Thorium-228 (²²⁸Th, t1/2 = 1.9 y), a by-product of ²³²Th proton spallation on TRIUMF’s main 500 MeV beamline (beamline 1A, BL1A), was recovered to build a ²²⁸Th/²¹²Pb generator with the ability to deliver up to 9-10 MBq of ²¹²Pb daily. Both lead isotopes were purified via solid phase extraction chromatography (Pb resin), and isolated in an acetate form ([203/212Pb]Pb(OAc)2) suitable for direct radiolabeling of chelators and bioconjugates. A series of cyclen-based chelators (herein referred to as DOTA-1Py, -2Py, and -3Py) along with established chelates DOTA and TCMC were evaluated for their ability to complex both ²⁰³Pb and ²¹²Pb. All chelates incorporated ²¹²Pb/²⁰³Pb efficiently, with higher radiolabeling yields observed for the ²¹²Pb-complexes.
Conclusion: The production of ²⁰³Pb and ²¹²Pb was established using TRIUMF 13 MeV and 500 MeV cyclotrons, respectively. Both production methods provided radiometals suitable for subsequent radiolabeling reactions using known and novel chelates. Furthermore, the novel chelate DOTA-3Py may be a good candidate for biomolecule conjugation and further theranostic ²¹²Pb/²⁰³Pb studies.
Neoplasias pose a significant threat to aging society, underscoring the urgent need to overcome the limitations of traditional chemotherapy through pioneering strategies. Targeted drug delivery is an evolving frontier in cancer therapy, aiming to enhance treatment efficacy while mitigating undesirable side effects. One promising avenue utilizes cell membrane receptors like the folate receptor to guide drug transporters precisely to malignant cells. Based on the cellular folate receptor as a cancer cell hallmark, targeted nanocarriers and small molecule–drug conjugates have been developed that comprise different (bio) chemistries and/or mechanical properties with individual advantages and challenges. Such modern folic acid-conjugated stimuli-responsive drug transporters provide systemic drug delivery and controlled release, enabling reduced dosages, circumvention of drug resistance, and diminished adverse effects. Since the drug transporters' structure-based de novo design is increasingly relevant for precision cancer remediation and diagnosis, this review seeks to collect and debate the recent approaches to deliver therapeutics or diagnostics based on folic acid conjugated Trojan Horses and to facilitate the understanding of the relevant chemistry and biochemical pathways. Focusing exemplarily on brain and breast cancer, recent advances spanning 2017 to 2023 in conjugated nanocarriers and small molecule drug conjugates were considered, evaluating the chemical and biological aspects in order to improve accessibility to the field and to bridge chemical and biomedical points of view ultimately guiding future research in FR-targeted cancer therapy and diagnosis.
A new, high-denticity, bifunctional ligand─H3TPAN-triazole-Bn-NH2─has been synthesized and studied in complexation with [225Ac]Ac3+ and [111In]In3+ for radiopharmaceutical applications. The bifunctional chelator is readily synthesized, using a high-yielding four-step prep, which is highly adaptable and allows for straightforward incorporation of different covalent linkers using CuI-catalyzed alkyne-azide cycloaddition (click) chemistry. Nuclear magnetic resonance (NMR) studies of H3TPAN-triazole-Bn-NH2 with La3+ and In3+ metal ions show the formation of a single, asymmetric complex with each ion in solution, corroborated by density functional theory (DFT) calculations. Radiolabeling studies with [225Ac]Ac3+ and [111In]In3+ showed highly effective complexation, achieving quantitative radiochemical conversions at low ligand concentrations (<10-6 M) under mild conditions (RT, 10 min), which is further accompanied by high stability in human serum. The bioconjugate─H3TPAN-triazole-Bn-Aoc-Pip-Nle-CycMSHhex─was prepared for targeting of MC1R-positive tumors, and the corresponding 111In-radiolabeled tracer was studied in vivo. SPECT/CT and biodistribution studies in C57BL/6J mice bearing B16-F10 tumors were performed, with the radiotracer showing good in vivo stability; tumor uptake was achieved. This work highlights a new promising and versatile bifunctional chelator, easily prepared and encouraging for 225Ac/111In theranostics.
Copper radioisotopes are generally employed for cancer imaging and therapy when firmly coordinated via a chelating agent coupled to a tumor-seeking vector. However, the biologically triggered Cu2+-Cu+ redox switching may constrain the in vivo integrity of the resulting complex, leading to demetallation processes. This unsought pathway is expected to be hindered by chelators bearing N, O, and S donors which appropriately complements the borderline-hard and soft nature of Cu2+ and Cu+. In this work, the labelling performances of a series of S-rich polyazamacrocyclic chelators with [64Cu]Cu2+ and the stability of the [64Cu]Cu-complexes thereof were evaluated. Among the chelators considered, the best results were obtained with 1,7-bis [2-(methylsulfanyl)ethyl]-4,10,diacetic acid-1,4,7,10-tetraazacyclododecane (DO2A2S). DO2A2S was labelled at high molar activities in mild reaction conditions, and its [64Cu]Cu2+ complex showed excellent integrity in human serum over 24 h. Biodistribution studies in BALB/c nude mice performed with [64Cu][Cu(DO2A2S)] revealed a behavior similar to other [64Cu]Cu-labelled cyclen derivatives characterized by high liver and kidney uptake, which could either be ascribed to transchelation phenomena or metabolic processing of the intact complex.
