Synthesis, radiochemistry and biological evaluation of a new somatostatin analogue (SDZ 219?387) labelled with technetium-99m

Abstract

A new derivative of octreotide SDZ 219-387 [PnAO-(D)Phe¹-octreotide] was synthesized, which binds specifically and with high affinity to somatostatin receptors in vitro (pK= 9.79±0.16). This new somatostatin analogue chelates technetium-99m under mild labelling conditions in good yields. The resulting [^99mTc]SDZ 219–387 was stable up to 6 h after labelling and could be isolated in a pure radiochemical and chemical form by high-performance liquid chromatographic purification. The intravenous administration of purified [^99mTc]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. [^99mTc]SDZ 219–387 specifically interacted with somatostatin binding sites on the tumour. However, the radioligand is highly lipophilic and excreted mainly through the hepatobiliary system. As a consequence, [^99mTc]SDZ 219–387 exhibits increased background activity and therefore is not appropriate for the in vivo visualization of somatostatin receptor-positive tumours and/or their metastases in the abdomen.