Somatostatin Analogue

Somatostatin analogues solve the problem that native somatostatin is cleared in minutes. The first-generation agents, octreotide and lanreotide, are short cyclic peptides built around the receptor-binding core and stabilised with D-amino acids, giving half-lives of hours rather than minutes and binding mainly SSTR2 with some SSTR5 activity. Pasireotide, developed later, binds four of the five receptor subtypes, which broadens its effect and also changes its adverse effect profile.

Octreotide was approved by the FDA in 1988; depot formulations followed, allowing roughly monthly rather than daily administration, and an oral octreotide using a permeation enhancer was approved in the United States in 2020. The indications are acromegaly, symptom control in carcinoid syndrome and other functioning neuroendocrine tumours, and for pasireotide, Cushing's disease. Radiolabelled analogues extend the same receptor targeting to imaging and to peptide receptor radionuclide therapy.

In acromegaly they are the principal medical option when surgery does not achieve remission, with the treatment goal expressed as normalised age-adjusted IGF-1 rather than symptom relief. Response correlates with tumour SSTR2 expression, so some patients need another mechanism, such as the growth hormone receptor antagonist pegvisomant. Acting on the receptor rather than on the tumour's autonomy, they control biochemistry without curing it.

The adverse effects follow directly from somatostatin's lack of selectivity. Gallstones and biliary sludge are common with long-term use, diarrhoea and steatorrhoea are frequent early on, and glucose metabolism is disturbed because insulin secretion is inhibited alongside growth hormone. Pasireotide's broader binding makes hyperglycaemia substantially more likely, the clearest illustration that broader is not better.