Trithiols and their arsenic compounds for potential use in diagnostic and therapeutic radiopharmaceuticals

Abstract

IntroductionArsenic-72 (72As; 2.49MeV β+, 26h) and 77As (0.683MeV β−, 38.8h) have nuclear properties useful for positron emission tomography (PET) and radiotherapy applications, respectively. Their half-lives are sufficiently long for targeting tumors with antibodies, as well as peptides. Potential radiopharmaceuticals based on radioarsenic require development of suitable bifunctional chelates for stable conjugation of arsenic to vectors under in vivo conditions at high dilution. MethodsThe thiophilic nature of arsenic led to the synthesis and characterization of a simple trithiol ligand and its arsenic complex, and radiolabeling studies at the no carrier added (NCA) 77As level. Results1H- and 13C-NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and single crystal X-ray diffraction were used to characterize the trithiol ligand and its arsenic(III) complex. Radiotracer studies with no carrier added (NCA) 77As resulted in high radiolabeling yields (>96%) with high in vitro stability. ConclusionsThe high yield and stability of a single NCA 77As trithiol complex indicates that this framework is suitable for developing matched pair agents for non-invasive in vivo PET imaging and radiotherapy of tumors with 72,77As. This is the first reported chelate developed for NCA radioarsenic and studies are underway for developing a trithiol bifunctional chelate conjugated to a targeting vector, such as a peptide or monoclonal antibody.