SYNTHESIS, RADIOCHEMISTRY AND BIOLOGICAL EVALUATION OF A NEW SOMATOSTATIN ANALOG (SDZ-219-387) LABELED WITH TC-99M

A new derivative of octreotide SDZ 219-387 [PnAO-(D)Phe(1)-octreotide] was synthesized, which binds specifically and with high affinity to s omatostatin receptors in vitro (pK(1) = 9.79+/-0.16). This new somatos tatin analogue chelates technetium-99m under mild labelling conditions in good yields. The resulting [Tc-99m]SDZ 219-387 was stable up to 6 h after labelling and could be isolated in a pure radiochemical and ch emical form by high-performance liquid chromatographic purification. T he intravenous administration of purified [Tc-99m]SDZ 219-387 revealed that the radioligand was rapidly cleared from circulation, and tumour uptake of 0.38% ID/g was observed at 1.5 h post injection. [Tc-99m]SD Z 219-387 specifically interacted with somatostatin binding sites on t he tumour. However, the radioligand is highly lipophilic and excreted mainly through the hepatobiliary system. As a consequence, [Tc-99m]SDZ 219-387 exhibits increased background activity and therefore is not a ppropriate for the in vivo visualization of somatostatin receptor-posi tive tumours and/or their metastases in the abdomen.