title: Optimization of the small-scale synthesis of DOTA-Tyr3 -octreotide.
abstract: The clinical potential of 111In and 90Y labelled 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid conjugated Tyr3-octreotide (DOTA-TOC) have been reported in a number of publications, and Phase II clinical trials of 90Y-DOTA-TOC are currently in progress. However, to date, only a summary of the large-scale preparation of these radiopharmaceuticals has been published. This publication aims to describe our experience of the small-scale synthesis of DOTA-TOC in the hope that this will assist others in the preparation of this and other similar radioconjugates. DOTA in the form of the tri-t-butyl ester was coupled to the Lys5 (BOC) protected Tyr3-octreotide in N,N-dimethylformamide or N-methyl-2-pyrolidinone, in a three-step reaction involving conjugation, using O-(7-azabenzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HATU) and diisopropylethyamine (DIPEA) as coupling reagents, deprotection with trifluoroacetic acid and HPLC purification of the conjugates. The product was obtained in final yields of 60+/-5%. The purified product was characterized by mass spectroscopy, showing a molecular weight of 1421.55+/-0.08. In somatostatin receptor binding assays, the unlabelled DOTA-TOC showed an effective displacement of 99mTc labelled HYNIC-TOC (where HYNIC is hydrazinonicotinamide) (IC50=0.31+/-0.07 nm), confirming the retention of receptor-binding affinity. The conjugate could be efficiently labelled with 111In by addition of 111InCl3 and ammonium acetate buffer pH5 and heating (95 degrees C, 20 min).
authors.affiliation: ICRF Nuclear Medicine Research Laboratory, St Bartholomew's Hospital, London, UK.
authors.forename: M
authors.initials: M
authors.lastname: Edreira
authors.forename: L
authors.initials: L
authors.lastname: Melendez-Alafort
authors.forename: S J
authors.initials: SJ
authors.lastname: Mather
mesh_terms: D000818:Animals; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry; D007205:Indium Radioisotopes / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D008970:Molecular Weight; D015282:Octreotide / Q000031:analogs & derivatives* / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism*; D051381:Rats; D017481:Receptors, Somatostatin / Q000378:metabolism*
chemical_list: D006573:Heterocyclic Compounds, 1-Ring; D007205:Indium Radioisotopes; D017481:Receptors, Somatostatin; C071349:1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid; D015282:Octreotide; C106246:Edotreotide