ECE2007 Poster Presentations (1) (659 abstracts)
Department of Endocrinology, William Harvey Research Institute, Barts and the London, Queen Mary School of Medicine, University of London, EC1M 6BQ, UK, London, United Kingdom.
Background: Somatostatin analogues are very useful in the treatment of symptomatic neuroendocrine tumours, but effects on proliferation remain unclear. Overexpression of the proto-oncogene protein kinase Akt has been demonstrated in certain endocrine tumours, and activates downstream proteins including mTOR and p70S6K, which play a significant role in cell growth and proliferation. We have therefore explored the site of action of somatostatin in causing inhibition of proliferation in a neuroendocrine cell line.
Aims: To confirm the anti-proliferative effects of SS analogue treatment in a rat insulinoma cell line (INS-1), and to investigate whether the SS analogues act on the PI3K-Akt-p70S6K pathway.
Methods: RT-PCR was used to demonstrate SS receptors (SSTR) in the INS-1 cell lines. MTS and thymidine incorporation were used to determine the effects of the SS analogues octreotide (SSTR2 agonist) and pasireotide (SOM230, Novartis; activation of SSTR-1, 2, 3 and 5) on cell proliferation. Western blotting was used to characterise phosphorylated-Akt and p70S6K expression in the SS-treated cells.
Results: The INS-1 cells expressed SSTR 1, 2, 3 and 5. Treatment with octreotide and pasireotide caused significant dose-responsive inhibition of proliferation. No difference in phospho-Akt (either Ser473 or Ser308) expression was detected in the octreotide-treated INS-1 cell lysates. However, phospho-p70S6K (Thr389) expression was significantly reduced at 10 minutes-6 hours treatment with octreotide 10−9M (P=0.01), while no effect on phospho-p70S6K (Thr229) expression was observed at 30 and 60 minutes. It is known that Thr229 site of phosphorylation is affected by PDK1 upstream of Akt. Treatment with IGF-1 (10nM) increased both phospho-p70S6K (Thr389) and phospho-Akt expression.
Conclusions: Octreotide and pasireotide treatment inhibited proliferation of INS-1 cells and, at a concentration achieved in clinical human use, octreotide attenuated p70S6K (Thr389) phosphorylation, but not Akt phosphorylation. We conclude that SS analogues acts downstream of Akt to inhibit the mTOR-p70S6K pathway.