title: Stability and in vivo behavior of Rh[16aneS4-diol]211 at complex: a potential precursor for astatine radiopharmaceuticals.
abstract: BACKGROUND
  The heavy halogen (211)At is of great interest for targeted radiotherapy because it decays by the emission of short-range, high-energy α-particles. However, many astatine compounds that have been synthesized are unstable in vivo, providing motivation for seeking other (211)At labeling strategies. One relatively unexplored approach is to utilize prosthetic groups based on astatinated rhodium (III) complex stabilized with a tetrathioether macrocyclic ligand - Rh[16aneS(4)-diol](211)At. The purpose of the current study was to evaluate the in vitro and in vivo stability of this complex in comparison to its iodine analog - Rh[16aneS(4)-diol](131)I.
  
  
  METHODS
  Rh[16aneS(4)-diol](211)At and Rh[16aneS(4)-diol](131)I complexes were synthesized and purified by HPLC. The stability of both complexes was evaluated in vitro by incubation in phosphate-buffered saline (PBS) and human serum at different temperatures. The in vivo behavior of the two radiohalogenated complexes was assessed by a paired-label biodistribution study in normal Balb/c mice.
  
  
  RESULTS
  Both complexes were synthesized in high yield and purity. Almost no degradation was observed for Rh[16aneS(4)-diol](131)I in PBS over a 72 h incubation. The astatinated analog exhibited good stability in PBS over 14 h. A slow decline in the percentage of intact complex was observed for both tracers in human serum. In the biodistribution study, retention of (211)At in most tissues was higher than that of (131)I at all time points, especially in spleen and lungs. Renal clearance of Rh[16aneS(4)-diol](211)At and Rh[16aneS(4)-diol](131)I predominated, with 84.1 ± 2.3% and 94.6 ± 0.9% of injected dose excreted via the urine at 4 h.
  
  
  CONCLUSIONS
  The Rh[16aneS(4)-diol](211)At complex might be useful for constructing prosthetic groups for the astatination of biomolecules and further studies are planned to evaluate this possibility.
authors: Centre of Radiochemistry and Nuclear Chemistry, Institute of Nuclear Chemistry and Technology, Dorodna 16, 03-195 Warsaw, Poland. Electronic address: m.pruszynski@ichtj.waw.pl.
authors: Marek
authors: M
authors: Pruszyński
authors: Centre of Radiochemistry and Nuclear Chemistry, Institute of Nuclear Chemistry and Technology, Dorodna 16, 03-195 Warsaw, Poland.
authors: Monika
authors: M
authors: Łyczko
authors: Centre of Radiochemistry and Nuclear Chemistry, Institute of Nuclear Chemistry and Technology, Dorodna 16, 03-195 Warsaw, Poland.
authors: Aleksander
authors: A
authors: Bilewicz
authors: Departments of Radiology and Radiation Oncology, Duke University Medical Center, Durham, NC, USA.
authors: Michael R
authors: MR
authors: Zalutsky
mesh_terms: D000818:Animals; D001246:Astatine / Q000737:chemistry*; D004355:Drug Stability; D004988:Ethers, Cyclic / Q000097:blood / Q000737:chemistry* / Q000493:pharmacokinetics; D006801:Humans; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009942:Organometallic Compounds / Q000097:blood / Q000737:chemistry* / Q000493:pharmacokinetics; D011854:Radiochemistry; D019275:Radiopharmaceuticals / Q000737:chemistry*; D014018:Tissue Distribution
chemical_list: D004988:Ethers, Cyclic; D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; C103148:rhodium tetrathiacyclohexadecanediol dichloride; D001246:Astatine
keywords: Astatine-211; Macrocyclic thioether; Prosthetic groups; Radioiodination; Rhodium complexes