Antiangiogenic therapy with somatostatin receptor-mediated in situ radiation.

Tumor growth and the development of metastases require an angiogenic response. Angiogenic vessels uniquely express somatostatin subtype 2 (sst 2) receptors that can transport somatostatin or its analogs into the cell. We hypothesized that radiolabeled somatostatin analogs could inhibit the angiogenic response by selectively destroying proliferating endothelial cells. We evaluated the antiangiogenic effects of 111In-pentetreotide, an sst 2-preferring somatostatin analog in a human vessel model. Disks of human placental vein were embedded in fibrin gels in culture and observed for angiogenic sprouting for 14 days. Vein disks were treated with 111In-pentetreotide (1.5, 15, and 150 microCi/mL) on the day of implantation. Control groups included disks treated with nutrient medium alone, with 111In-chloride, and with unlabeled pentetreotide. The percentage of wells that initiated an angiogenic response and the overall length and density of neovessel sprouts were assessed on Day 14. 111In-pentetreotide treatment did not completely block initiation of the angiogenic response but significantly decreased the growth of neovessels after initiation. Both the receptor-specific Auger electron-induced and nonspecific gamma radiation-mediated effects contributed to the angiotoxicity.