Antisecretory Effects of Chimeric Somatostatin/Dopamine Receptor Ligands on Gastroenteropancreatic Neuroendocrine Tumors.

OBJECTIVES: The recent finding that gastroenteropancreatic neuroendocrine tumors expressed the dopaminergic D2 receptor in addition to somatostatin (sst) receptors suggested that multiple targeting approaches might decrease hormone hypersecretion more effectively than sst agonists alone.

METHODS: To test this hypothesis, (i) we measured the expression of sst receptor type 2 (sst2 receptor) and D2 receptor in 11 gastroenteropancreatic neuroendocrine tumors and (ii) we compared the ability of lanreotide, cabergoline, their combination, and sst/D2 chimeric ligands to decrease chromogranin A (CgA), gastrin, or serotonin release in primary cultures derived from these tumors.

RESULTS: Moderate to high positivity was observed for sst2 receptor and D2 receptor, the latter being more expressed in pancreatic tumors. Lanreotide decreased CgA secretion in all cultures, but only 3 tumors responded to cabergoline. No additivity was observed in lanreotide. BIM 23A781 decreased CgA release to the same extent as lanreotide, whereas the other chimeric ligands were less efficient. However, BIM 23A781 was 50 times less potent than lanreotide. Similar patterns were found for gastrin or serotonin.

CONCLUSION: No improvement was brought by the sst/D2 combination or chimeric ligands. Factors that underlie these tissue-specific differences remain to be elucidated.