Synthesis of somatostatin by breast cancer cells and their inhibition by exogenous somatostatin and sandostatin.

Three human breast cancer cell lines ZR-75-1, MDA-MB-436 and MCF-7 were found to contain respectively, 3.06, 2.69 and 1.86 fmol of somatostatin-like immunoreactivity (SLI) per 10(6) cells. Since SLI is undetectable in the passaging media it must, therefore, be synthesised by the cells. In the presence of fetal calf serum the cells were growth inhibited by addition of somatostatin or its long-lasting analogue, Sandostatin, but only after 3 days of continuous exposure. A 1-day exposure to either peptide had little or no effect on subsequent cell growth in peptide-free medium. Inhibition of cell proliferation is not due to cytotoxic effects of the dose used (500 ng ml-1, each) since both peptides caused short-term stimulation of growth in the absence of serum.