Technetium-99m labelling of glycosylated somatostatin-14

This study presents a technetium-99m labelling method based on organometall ic chemistry. It describes the simple mixing of a Tc-99m(I)-carbonyl compou nd [Tc-99m(OH2)(3)(CO)(3)](+) with a histidine-tagged somatostatin-dextran (SMS-Dx-His) conjugate. Somatostatin and histidine was coupled to periodate activated dextran. The linkage was stabilised by reductive amination. The conjugate was then radiolabelled with Tc-99m by using the Tc-99m(CO)(3) cor e. The labelling efficiency was 65-80% and the radiochemical purity > 95%, In the in vitro cysteine challenge, the result showed that 25% of the radio label was released after Ih incubation at 37 degreesC (cysteine-conjugate a t 1000:1molar ratio). The radiolabelled SMS-Dx-His showed similar HPLC prof ile as the unlabelled conjugate. This labelling method, employing non reduc ing conditions. is useful for the labelling of peptides containing disulphi de bonds. It should be possible to be used also for labelling with rhenium- 188 for therapeutic applications. (C) 2001 Elsevier Science Ltd, All rights reserved.