This study describes a method for the radiolabeling of
dextran with
rhenium-188 (188Re). In nuclear oncology 188Re is very useful for therapeutic applications. Its nuclear characteristics allow
radiotherapy and in situ monitoring of
tumor uptake as well as dosimetry calculations. Consequently new compounds with this radiolabel are of general interest.
Dextran was oxidized with
sodium periodate yielding reactive
aldehyde groups and subsequently reacted with
cysteine. The linkage was stabilized by reducing the
Schiff bases with
sodium cyanoborohydride. The conjugate was then radiolabeled with 188Re by using 188Re-gluconate as the transchelator, labeling the free
thiols. Synthesis and radiolabeling were done in the absence of
oxygen. The labeling efficiency was 60-70% and the radiochemical purity > 95%. The in vitro stability study, using "
cysteine challenge" demonstrated that 50% of the radiolabel was transcomplexed to the 100 mM
cysteine solution (after 1 h incubation at 37 degrees C). However, at physiologic conditions and presence of an
antioxidant good stability was achieved. The 188Re 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 backbone in a
tumor specific conjugate for systemic treatment.