OctreoScan 111 for imaging of a somatostatin receptor-positive islet cell tumor in rat

We report here the in vitro characterization of SDZ 215-811 and the in vivo imaging of a islet cell tumor gown in rats using [111In]SDZ 215-811. In vitro autoradiographies revelaed a high density of SRIF receptors on the pancreatic tumor tissue. As early as 5 min after intravenous injection of [111In]SDZ 215-811 into tumour-bearing rats, the tumors were clearly localized by gamma-camera scintigraphy. Even 24 h post injection, the islet cell tumor was still detectable. The radioligand was mainly cleared from the circulation via the Kidneys, with a rapid α-phase (t1/2=5.6 min) and a slow elimination phase (t1/2=7.3 h). Biodistribution studies revealed a relatively high accumulation of radioactivity in the kidneys, but low uptake into the liver and the intestine. High uptake of [111In]SDZ 215-811 was observed for the tumor tissue (0.92±0.07% ID/g; 1 h post injection). Interestingly, a tumor load of 0.14±0.01% ID/g was still measured after 24 h. The tumor/blood ratio was 4.93 after 24 h, indicating specific accumulation of radioactivity in the islet cell tumour. [111In]SDZ 215-811 appears to be sensitive and specific ligand for SRIF receptorpositive tumors and offers an easy procedure for scintigraphic imaging of such tumors in man. (orig.)