Preparation of indium-115-labeled diethylenetriaminetetraacetic acid monoacetamide peptides purified by 8-hydroxyquinoline

In this communication we describe a novel procedure for the preparation and purification of diethylenetriaminepentaacetic (DTPA)-acylated and In-115(3 +)- labeled oligopeptides using 8-hydroxyquinoline for the removal and quan tification of nonbound indium ions. First the N-alpha- or N-alpha,N-epsilon -DTPA oligopeptides containing C-terminal KDEL signal motif were produced b y solid-phase synthesis. For this the free carboxyl group of DTPA dianhydri de was activated in situ for a short period of time yielding a major produc t. Reversed-phase HPLC-purified DTPA oligopeptides were labeled with In-115 (3+) in aqueous buffer solution at pH 3.8. For the removal as well as for t he detection of uncoordinated In-115(3+) ions we have utilized the In-115(3 +) complex-forming ability of 8-hydroxyquinoline in chloroform. Following a n optimized extraction procedure the free indium ion content was measured b y spectrophotometry in the organic phase. Data obtained by this method and verified by total-reflection X-ray fluorescence spectroscopy and thin-layer chromatography demonstrated that free In-115(3+) could be efficiently remo ved and sensitively detected in the presence of DTPA oligopeptide chelator. No release of In-115(3+) from its DTPA complex was observed. This method c ould be useful for the preparation of indium complexes of peptides and perh aps proteins containing a DTPA moiety and nonradioactive isotope ligand. (C ) 2000 Academic Press.