title: Alternative method to determine Specific Activity of (177)Lu by HPLC.
abstract: Peptide Receptor Radionuclide Therapy (PRRT) with (177)Lu-DOTA-peptides requires (177)Lu with high specific activity (SA) and values >740 GBq (177)Lu per mg Lu to maximise the atom% of (177)Lu over total Lu. Vendors provide SA values which are based on activity and mass of the target, whereas due to "burn-up" of target, these SA values are not accurate. For a radiochemist the SA of (177)Lu is of interest prior to radiolabeling. An alternative method to determine SA was developed by HPLC, which includes a metal titration of a known amount of DOTA-peptide with a known amount of activity ((177)Lu), and a unknown amount of metal ((177+nat)Lu). Based on an HPLC separation of radiometal-DOTA-peptide and DOTA-peptide, and the concordant ratio of these components the metal content ((177+nat)Lu) can be calculated, and eventually the SA of (177)Lu can be accurately determined. These experimentally determined SA values exceeded the estimated values provided by vendors by 27 ± 16%, (range 6-73 %). The deviation of SA values for samples from the same Lu batch was <2% (n ≥ 10).
  
  
  CONCLUSIONS
  the SA of (177)Lu is apparently often higher as stated by vendors in comparison to the experimentally determined actual values. For this reason, the SA of (177)Lu-DOTA-TATE and other Lu-DOTA-peptides could be increased accordingly.
authors.affiliation: Department of Nuclear Medicine, Erasmus MC Rotterdam, 's Gravendijkwal 230, 3015CE Rotterdam, Netherlands. w.a.p.breeman@erasmusmc.nl.
authors.forename: Wouter A P
authors.initials: WA
authors.lastname: Breeman
authors.forename: Rory M S
authors.initials: RM
authors.lastname: de Zanger
authors.forename: Ho Sze
authors.initials: HS
authors.lastname: Chan
authors.forename: Erik
authors.initials: E
authors.lastname: de Blois
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry; D008187:Lutetium / Q000737:chemistry*; D015282:Octreotide / Q000031:analogs & derivatives / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D011854:Radiochemistry / Q000379:methods; D011868:Radioisotopes / Q000737:chemistry*; D018000:Receptors, Peptide / Q000737:chemistry
chemical_list: D006573:Heterocyclic Compounds, 1-Ring; D009942:Organometallic Compounds; D010455:Peptides; D011868:Radioisotopes; D018000:Receptors, Peptide; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid; D008187:Lutetium; C447941:lutetium Lu 177 dotatate; D015282:Octreotide