Radiolabeling of dextran with rhenium-188

This study describes a method for the radiolabeling of dextran with rhenium -188 (Re-188). In nuclear oncology Re-188 is very useful for therapeutic ap plications. Its nuclear characteristics allow radiotherapy and in situ moni toring of tumor uptake as well as dosimetry calculations. Consequently new compounds with this radiolabel are of general interest. Dextran was oxidize d with sodium periodate yielding reactive aldehyde groups and subsequently reacted with cysteine. The linkage was stabilized by reducing the Schiff ba ses with sodium cyanoborohydride. The conjugate was then radiolabeled with Re-188 by using Re-188-gluconate as the transchelator, labeling the free th iols. Synthesis and radiolabeling were done in the absence of oxygen. The l abeling efficiency was 60-70% and the radiochemical purity >95%. The in vit ro stability study, using "cysteine challenge" demonstrated that 50% of the radiolabel was transcomplexed to the 100 mM cysteine solution (after 1 h i ncubation at 37 degrees C). However, at physiologic conditions and presence of an antioxidant good stability was achieved. The Re-188 labeled dextran presented in this study provides a template with therapeutic and diagnostic potential in nuclear oncology, either alone for local treatment or as a ba ckbone in a tumor specific conjugate for systemic treatment. (C) 2000 Elsev ier Science Ltd. All rights reserved.