Bifunctional (64)Cu-labelled macrobicyclic cage amine isothiocyanates for immuno-positron emission tomography

• Published in: Dalton transactions : an international journal of inorganic chemistry 2015-03, Vol.44 (11), p.4901-4909
• Main Authors: Paterson, Brett M, Buncic, Gojko, McInnes, Lachlan E, Roselt, Peter, Cullinane, Carleen, Binns, David S, Jeffery, Charmaine M, Price, Roger I, Hicks, Rodney J, Donnelly, Paul S
• Format: Article
• Language: English
• Subjects: Amines - chemistry; Animals; Cell Line, Tumor; Chelating Agents - chemistry; Copper Radioisotopes; Drug Stability; Humans; Immunoconjugates - chemistry; Immunoconjugates - pharmacokinetics; Isothiocyanates - chemistry; Isotope Labeling; Macrocyclic Compounds - chemistry; Magnesium - chemistry; Mammary Neoplasms, Experimental - diagnostic imaging; Mammary Neoplasms, Experimental - metabolism; Mice; Positron-Emission Tomography - methods; Receptor, ErbB-2 - metabolism; Trastuzumab - chemistry
• ISSN: 1477-9234
• DOI: 10.1039/c4dt02983f

New macrobicyclic cage amine or "sarcophagine" (sar) bifunctional chelators have been synthesised that form copper complexes of exceptional in vivo stability and incorporate isothiocyanate (-NCS) functional groups for conjugation to an antibody. The chelators were synthesised from the methyl-capped complex [Mg(II)(CH3)(NH2)sar](2+). Coordination of Mg(II) within the cavity of the cage amine ligand protects the secondary amine atoms from reacting with the -NCS functional groups. Two different [Mg(II)(NCS-sar)](2+) derivatives were conjugated to the HER2/neu-targeting antibody trastuzumab and the progress of the reaction monitored by electrospray mass spectrometry. The Mg(II) ion was removed from the immunoconjugates under mild conditions (0.1 M citrate buffer, pH 6). Labelling of the (CH3)(p-NCS-Ph)sar-trastuzumab conjugate with (64)Cu(II), a radioisotope suitable for positron emission tomography (PET), was fast (∼5 min) and easily performed at room temperature with high radiochemical purity (>95%). Biodistribution and PET imaging studies in vivo showed that (64)Cu-labelled (CH3)(p-NCS-Ph)sar-trastuzumab maintained high stability under physiological conditions with high and selective uptake in a HER2-positive cancer cell line. The stability of the copper complex and the 12.7 h half-life of the radioisotope allows clear visualisation of tumours out to 48 h.