Arsenic-72, 77 as a matched pair radiopharmaceutical for imaging and radiotherapy
Radiopharmaceuticals deliver radionuclides to specific target sites via the bifunctional chelate approach, where the radionuclides are chelated with a ligand and linked to a targeting biomolecule. They can be categorized as imaging or therapeutic agents based on the physical properties of the radionuclides. Matched pair radionuclides have advantages because of identical chemistry of the imaging and therapy counterparts and true matched pair radionuclides are rare (e.g., 64,67Cu, 44,47Sc, 135,131I). Radioimmunoimaging and therapy commonly use antibodies (or antibody fragments) as targeting biomolecules, and may take a few days to accumulate in tumor cells. Thus they require radionuclides with longer half-lives. Arsenic-72 ([beta]+, 26 hour half-life) and 77As ([beta]- emitter, 38.8 hour half-life) have suitable physical properties as a true matched pair for radioimaging and therapy. This dissertation focuses on the development of 72,77As matched pair for potential PET imaging and radiotherapy. ... The production and separation of no carrier added (nca) 72,77As will be discussed in Chapter 2. No carrier added 77As separation was improved based on the reported method by decreasing the operation time and increasing capacity based on reported method. The parameters for a 72Se/72As generator were evaluated and nca 72Se was produced via the 70Ge([alpha], 2n)72Se nuclear reaction, separated and loaded onto a generator column. Further evaluations are underway. Radiochemistry of nca 72,77As will be discussed in Chapters 3 and 4 since two chelating approaches were evaluated. The aryl dithiol approach incorporates an aryl ring to nca radioarsenic and complexes it with dithiol ligands. After various modifications and optimizations, radiolabeling nca 72,77As affording dithioarylarsines were accomplished in high yields. The trithiol approach complexes nca 72,77As with a trithiol chelate. Its in vivo stability was evaluated by conjugating the trithiol chelate to a Bombesin receptor targeting peptide and investigating its biodistribution in normal mice. An improved trithiol chelate was proposed and synthesized based on the high in vivo stability but poor targeting efficacy of the initial trithiol complex.
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