Radioarsenic from a Portable 72Se/72As Generator: A Current Perspective

Abstract

Positron emission tomography (PET) of slower biological processes calls for the use of longer lived positron emitting radioisotopes. Beyond radionuclide production considerations, practicality and rapidity of subsequent labeling chemistry further limits the selection of radioisotopes with potentially favorable nuclear properties. One additional limitation is the availability of PET radiotracers at the point-of-care with appropriate on-site production methodologies or robust radionuclide generator systems. The positron emitter (72)As (half-life 26 h) is generated via decay of (72)Se (half-life 8.5 d); this pair comprises and excellent generator system for clinical availability of a longer lived PET isotope. Many (72)Se/As generator systems have been introduced utilizing the rich interplay of Se(IV)/Se(VI) and As(III) /As(V) chemical behavior. This paper describes available generator concepts, and briefly outlines some current arsenic labeling methodologies for the introduction of radioarsenic into biomolecules.

Labelling with positron emitters of pnicogens and chalcogens

“…An alternative availability is the indirect way as a daughter radionuclide of the relatively long‐lived 72 Se using a generator system . Selenium‐72 can be produced via various charged particle reactions on Ge, Br, or As targets, the most common routes being the 70 Ge(α,2n) 72 Se or 75 As(p,4n) 72 Se reaction, which are feasible only at multiparticle and intermediate‐energy cyclotrons …”

Mapping biological behaviors by application of longer-lived positron emitting radionuclides

“…The optimal method for production and purification of 72 As via a rapid and practical generator system remains under investigation [51,52]. Presently, 72 As can be generated either from a 72 Se/ 72 As generator system or cyclotron produced from a germanium target [53]. Because of the limited 72 As supply, research progress towards developing and evaluating 72 As continues to be slow and thereby impedes its further development towards translation to clinical settings.…”

Chromatographic separation of selenium and arsenic: A potential 72Se/72As generator

“…Selenium-72, the parent of 72 As, can be produced from charged particle reactions on Ge, Br, or As targets [14]. The most common production routes involve α or 3 He irradiation of 70 Ge, 72 Ge, or nat Ge, generally as the oxide (e.g., 70 Ge(α,2n) 72 Se or 70 Ge( 3 He,n) 72 Se), or a proton induced nuclear reaction on stable arsenic ( 75 As(p,5n) 72 Se) [15–18].…”

“…Selenium-72/Arsenic-72 ( 72 Se/ 72 As) radionuclide generators have been proposed in the literature [14], however complex separation/isolation methods are required. Separation of the daughter from the parent can occur via repeated distillation of “grown-in” 72 AsCl 3 from carrier added 72 Se stock solutions [16,21]; electroplating of 72 Se as Cu 2 Se on Cu backings [23], solvent extraction [22] or solid phase extraction of 72 Se [17,24].…”