⁹⁹Tc^m Labeling and in Vitro Biding of Dextran-somatostatin conjugate

Natural somatostatin and dextran-20 are used to synthesis somatostatin-dextran (SMS-Dx20). The in vitro somatostatin receptor competition binding study of somatostatin-dextran is carried out by using rat brain cortex membranes (express somatostatin receptor type 2) and 125I-Tyr3-Octreotide as a radioligand. The somatostatin-dextran conjugate is then labelled with 99Tcm using SnCl2 as reduce agent and tested for its in vitro binding properties. The somatostatin-dextran conjugate shows high somatostatin receptor binding affinity, i.e. in the same nM range as the reference ligand Octreotide (IC50 ~ 5.95 nmol/L). The labeling efficiency is more than 85%. The specific binding of 99Tcm labeled somatostatin-dextran conjugate Is 30%-40%. The somatostatin-dextran conjugate is worthy of further investigation for 99Tcm radiolabeling with diagnostic posibilities for somatostatin receptor positive tumors