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[Regulation of cell proliferation by somatostatin]
L Buscail1, F Vernejoul, P Faure
1INSERM U531 et Service de Gastro-entérologie et Nutrition, CHU Rangueil, 1, avenue Jean Poulhès, 31403 Toulouse Cedex 4, France.
Abstract:
Somatostatin and its stable analogues (octreotide, lanreotide and vapreotide) exert an antiproliferative effect on various normal and cancerous cells both in vitro and in vivo. This effect results from different mechanisms: an indirect effect by the inhibition of release of growth factors and trophic hormones (GH, IGF-1, insulin, gastrin, EGF), an inhibition of angiogenesis processes (endothelial cell proliferation, VEGF release, monocyte activity), an immunomodulatory effect (lymphocyte proliferation, interleukine or cytokine release, NK activity) and a direct effect on target cells. This direct antiproliferative effect is mediated through specific somatostatin receptors. Among them, sst(1), sst(2), sst(4) and sst(5) have been implicated in vitro in the G1-G0 cell cycle blockade, sst(3) and sst(2) mediating the apoptotic effect of somatostatin. In addition, sst(2) acts as an antioncogene in human pancreatic cancer cells. Coupling to membrane tyrosine phosphatases (SHP-1, SHP-2) is the main transduction pathway involved in the antiproliferative effect mediated by sst receptors. The dissociation observed clinically between a frequent antisecretory response and an inconstant antitumor effect after administration of somatostatin analogues may reflect an absence of expression or coupling of the receptor(s) involved in antiproliferative effect. Moreover, a desensitization or mutation of these receptors may also occur in tumors. All the potential mechanism involved should be elucidated in order to improve or better target the antitumor effect of somatostatin analogues clinically used.
Insights
Somatostatin analogues inhibit cancer cell growth via multiple pathways, including direct receptor interactions and indirect mechanisms like reduced growth factors. Understanding these pathways is key to improving antitumor effects.
Area of Science:
- Endocrinology and Molecular Biology
- Cancer Biology
- Pharmacology
Context:
- Somatostatin analogues like octreotide demonstrate antiproliferative effects on normal and cancerous cells.
- These effects are mediated through diverse mechanisms, including inhibition of growth factors, angiogenesis, and immune responses.
- Direct antiproliferative actions are linked to specific somatostatin receptors (sst).
Purpose:
- To elucidate the multifaceted mechanisms underlying the antiproliferative effects of somatostatin and its analogues.
- To investigate the role of specific somatostatin receptors (sst1-5) and their signaling pathways in mediating these effects.
- To explain the clinical discrepancy between antisecretory and antitumor responses to somatostatin analogues.
Summary:
- Somatostatin analogues exert antiproliferative effects through indirect mechanisms (inhibiting growth factors, angiogenesis, immune responses) and direct actions via somatostatin receptors.
- Specific receptors (sst1-5) are involved in cell cycle arrest (G1-G0) and apoptosis, with sst2 acting as an antioncogene.
- Signal transduction primarily involves coupling to tyrosine phosphatases (SHP-1, SHP-2).
Impact:
- Clinical efficacy of somatostatin analogues may be limited by absent or altered expression/coupling of antiproliferative receptors in tumors.
- Further research into receptor mechanisms is crucial for optimizing the antitumor efficacy of these agents.
- Understanding these pathways can lead to improved therapeutic strategies for cancers responsive to somatostatin analogues.