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Rigby A, Firth G, Rivas C, Pham T, Kim J, Phanopoulos A, Wharton L, Ingham A, Li L, Ma MT, Orvig C, Blower PJ, Terry SY, Abbate V. Toward Bifunctional Chelators for Thallium-201 for Use in Nuclear Medicine. Bioconjug Chem 2022; 33:1422-1436. [PMID: 35801668 PMCID: PMC9305974 DOI: 10.1021/acs.bioconjchem.2c00284] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Auger electron therapy exploits the cytotoxicity of low-energy electrons emitted during radioactive decay that travel very short distances (typically <1 μm). 201Tl, with a half-life of 73 h, emits ∼37 Auger and other secondary electrons per decay and can be tracked in vivo as its gamma emissions enable SPECT imaging. Despite the useful nuclear properties of 201Tl, satisfactory bifunctional chelators to incorporate it into bioconjugates for molecular targeting have not been developed. H4pypa, H5decapa, H4neunpa-NH2, and H4noneunpa are multidentate N- and O-donor chelators that have previously been shown to have high affinity for 111In, 177Lu, and 89Zr. Herein, we report the synthesis and serum stability of [nat/201Tl]Tl3+ complexes with H4pypa, H5decapa, H4neunpa-NH2, and H4noneunpa. All ligands quickly and efficiently formed complexes with [201Tl]Tl3+ that gave simple single-peak radiochromatograms and showed greatly improved serum stability compared to DOTA and DTPA. [natTl]Tl-pypa was further characterized using nuclear magnetic resonance spectroscopy (NMR), mass spectroscopy (MS), and X-ray crystallography, showing evidence of the proton-dependent presence of a nine-coordinate complex and an eight-coordinate complex with a pendant carboxylic acid group. A prostate-specific membrane antigen (PSMA)-targeting bioconjugate of H4pypa was synthesized and radiolabeled. The uptake of [201Tl]Tl-pypa-PSMA in DU145 PSMA-positive and PSMA-negative prostate cancer cells was evaluated in vitro and showed evidence of bioreductive release of 201Tl and cellular uptake characteristic of unchelated [201Tl]TlCl. SPECT/CT imaging was used to probe the in vivo biodistribution and stability of [201Tl]Tl-pypa-PSMA. In healthy animals, [201Tl]Tl-pypa-PSMA did not show the myocardial uptake that is characteristic of unchelated 201Tl. In mice bearing DU145 PSMA-positive and PSMA-negative prostate cancer xenografts, the uptake of [201Tl]Tl-pypa-PSMA in DU145 PSMA-positive tumors was higher than that in DU145 PSMA-negative tumors but insufficient for useful tumor targeting. We conclude that H4pypa and related ligands represent an advance compared to conventional radiometal chelators such as DOTA and DTPA for Tl3+ chelation but do not resist dissociation for long periods in the biological environment due to vulnerability to reduction of Tl3+ and subsequent release of Tl+. However, this is the first report describing the incorporation of [201Tl]Tl3+ into a chelator-peptide bioconjugate and represents a significant advance in the field of 201Tl-based radiopharmaceuticals. The design of the next generation of chelators must include features to mitigate this susceptibility to bioreduction, which does not arise for other trivalent heavy radiometals.
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Affiliation(s)
- Alex Rigby
- School
of Biomedical Engineering and Imaging Sciences, King’s College London, 4th Floor Lambeth Wing, St Thomas’ Hospital, London SE1 7EH, United Kingdom
| | - George Firth
- School
of Biomedical Engineering and Imaging Sciences, King’s College London, 4th Floor Lambeth Wing, St Thomas’ Hospital, London SE1 7EH, United Kingdom
| | - Charlotte Rivas
- School
of Biomedical Engineering and Imaging Sciences, King’s College London, 4th Floor Lambeth Wing, St Thomas’ Hospital, London SE1 7EH, United Kingdom
| | - Truc Pham
- School
of Biomedical Engineering and Imaging Sciences, King’s College London, 4th Floor Lambeth Wing, St Thomas’ Hospital, London SE1 7EH, United Kingdom
| | - Jana Kim
- School
of Biomedical Engineering and Imaging Sciences, King’s College London, 4th Floor Lambeth Wing, St Thomas’ Hospital, London SE1 7EH, United Kingdom
| | - Andreas Phanopoulos
- Department
of Chemistry, Molecular Sciences Research Hub, Imperial College London, London W12 0BZ, United Kingdom
| | - Luke Wharton
- Medicinal
Inorganic Chemistry Group, Department of Chemistry, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
- Life
Sciences Division, TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada
| | - Aidan Ingham
- Medicinal
Inorganic Chemistry Group, Department of Chemistry, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
- Life
Sciences Division, TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada
| | - Lily Li
- Medicinal
Inorganic Chemistry Group, Department of Chemistry, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
- Life
Sciences Division, TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada
| | - Michelle T Ma
- School
of Biomedical Engineering and Imaging Sciences, King’s College London, 4th Floor Lambeth Wing, St Thomas’ Hospital, London SE1 7EH, United Kingdom
| | - Chris Orvig
- Medicinal
Inorganic Chemistry Group, Department of Chemistry, University of British Columbia, Vancouver, BC V6T 1Z1, Canada
| | - Philip J. Blower
- School
of Biomedical Engineering and Imaging Sciences, King’s College London, 4th Floor Lambeth Wing, St Thomas’ Hospital, London SE1 7EH, United Kingdom
| | - Samantha Y.A. Terry
- School
of Biomedical Engineering and Imaging Sciences, King’s College London, 4th Floor Lambeth Wing, St Thomas’ Hospital, London SE1 7EH, United Kingdom
| | - Vincenzo Abbate
- School
of Cancer & Pharmaceutical Sciences, King’s College London, Franklin-Wilkins Building, Stamford Street, London SE1 9NH, United Kingdom
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Rigby A, Blower JE, Blower PJ, Terry SY, Abbate V. Targeted Auger electron-emitter therapy: Radiochemical approaches for thallium-201 radiopharmaceuticals. Nucl Med Biol 2021; 98-99:1-7. [PMID: 33906122 PMCID: PMC7610824 DOI: 10.1016/j.nucmedbio.2021.03.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Revised: 03/25/2021] [Accepted: 03/30/2021] [Indexed: 01/13/2023]
Abstract
INTRODUCTION Thallium-201 is a radionuclide that has previously been used clinically for myocardial perfusion scintigraphy. Although in this role it has now been largely replaced by technetium-99 m radiopharmaceuticals, thallium-201 remains attractive in the context of molecular radionuclide therapy for cancer micrometastases or single circulating tumour cells. This is due to its Auger electron (AE) emissions, which are amongst the highest in total energy and number per decay for AE-emitters. Currently, chemical platforms to achieve this potential through developing thallium-201-labelled targeted radiopharmaceuticals are not available. Here, we describe convenient methods to oxidise [201Tl]Tl(I) to chelatable [201Tl]Tl(III) and identify challenges in stable chelation of thallium to support future synthesis of effective [201Tl]-labelled radiopharmaceuticals. METHODS A plasmid pBR322 assay was carried out to determine the DNA damaging properties of [201Tl]Tl(III). A range of oxidising agents (ozone, oxygen, hydrogen peroxide, chloramine-T, iodogen, iodobeads, trichloroisocyanuric acid) and conditions (acidity, temperature) were assessed using thin layer chromatography. Chelators EDTA, DTPA and DOTA were investigated for their [201Tl]Tl(III) radiolabelling efficacy and complex stability. RESULTS Isolated plasmid studies demonstrated that [201Tl]Tl(III) can induce single and double-stranded DNA breaks. Iodo-beads, iodogen and trichloroisocyanuric acid enabled more than 95% conversion from [201Tl]Tl(I) to [201Tl]Tl(III) under conditions compatible with future biomolecule radiolabelling (mild pH, room temperature and post-oxidation removal of oxidising agent). Although chelation of [201Tl]Tl(III) was possible with EDTA, DTPA and DOTA, only radiolabeled DOTA showed good stability in serum. CONCLUSIONS Decay of [201Tl]Tl(III) in proximity to DNA causes DNA damage. Iodobeads provide a simple, mild method to convert thallium-201 from a 1+ to 3+ oxidation state and [201Tl]Tl(III) can be chelated by DOTA with moderate stability. Of the well-established chelators evaluated, DOTA is most promising for future molecular radionuclide therapy using thallium-201; nevertheless, a new generation of chelating agents offering resistance to reduction and dissociation of [201Tl]Tl(III) complexes is required.
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Affiliation(s)
- Alex Rigby
- King’s College London, School of Biomedical Engineering and Imaging Sciences, 4th Floor Lambeth Wing, St Thomas’ Hospital, London SE1 7EH, United Kingdom
| | - Julia E. Blower
- King’s College London, School of Biomedical Engineering and Imaging Sciences, 4th Floor Lambeth Wing, St Thomas’ Hospital, London SE1 7EH, United Kingdom
| | - Philip J. Blower
- King’s College London, School of Biomedical Engineering and Imaging Sciences, 4th Floor Lambeth Wing, St Thomas’ Hospital, London SE1 7EH, United Kingdom
| | - Samantha Y.A. Terry
- King’s College London, School of Biomedical Engineering and Imaging Sciences, 4th Floor Lambeth Wing, St Thomas’ Hospital, London SE1 7EH, United Kingdom,Corresponding authors. (S.Y.A. Terry), (V. Abbate)
| | - Vincenzo Abbate
- King’s College London, School of Population Health and Environmental Sciences, Analytical, Environmental and Forensic Sciences, Franklin-Wilkins Building, Stamford Street, London SE1 9NH, United Kingdom,Corresponding authors. (S.Y.A. Terry), (V. Abbate)
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Jalilian AR, Shanehsazzadeh S, Akhlaghi M, Garoosi J, Rajabifar S, Tavakoli MB. Preparation and evaluation of [67Ga]-DTPA-β-1–24-corticotrophin in normal rats. RADIOCHIM ACTA 2009. [DOI: 10.1524/ract.2008.1512] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
β-1–24-corticotrophin was successively labeled with [67Ga]-gallium chloride after residulation with freshly prepared cyclic DTPA-dianhydride. The best results of the conjugation were obtained by the addition of 1 ml of a β-1–24-corticotrophin pharmaceutical solution (1 mg/mL, pH=6.5) to a glass tube pre-coated with DTPA-dianhydride (0.01 mg) at 25 °C with continuous mild stirring for 30 min. Radio-thin layer chromatography showed an overall radiochemical purity of >90% at optimized conditions after labeling. HPLC showed a radiochemical purity more than 95% (specific activity =300–500 MBq/mg, labeling efficiency 77%). The stability of the radioconjugate was tested in presence of human serum at 37 °C. Preliminary in vivo studies in normal rats were performed to determine the biodistribution of the radioimmunoconjugate up to 30 min. Lungs showed to have the major tracer uptake which is consistent with the natural distribution of ACTH receptors in human body. Pretreatment of animals with cold peptide following labeled compound administration reduced lung uptake at least 10 and 3 times after 15 and 30 min, respectively, as well as significant decrease in adrenal uptake after 15 min. These data support the specific receptor binding of the radiolabeled compound. This tracer can be used in detection of ACTH receptor in lung and adrenal malignancies.
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