Endocrine Abstracts

Neuroendocrine tumours of the GI tract originate from enterochromaffin cells. Somatostatin analogues are the mainstay drugs for therapy in these cancers as they ameliorate symptoms and lower hormone secretion, but only in 30–70% of patients. Such tumours are also associated with angiogenesis which has been used as a prognostic indicator; adenosine, the major regulator of angiogenesis, is released by enhanced degradation of ATP, during cellular stress, damage and hypoxia.

The aim of this study is thus to investigate adenosine signalling pathways in a human pancreatic neuroendocrine tumour cell line (BON1).

RT-PCR was used to identify expression of all four adenosine receptors and the enzymes involved in the catabolism (CD73) and metabolism (adenosine deaminase and adenosine kinase) of adenosine from ATP in BON1 cells. Adenosine and NECA (universal adenosine receptor agonist) stimulated cAMP levels (radioimmunoassay) 3- and 8-fold (P<0.01) respectively with ED₅₀ values of between 5×10⁻⁷ and 10⁻⁶ M. The A2a receptor agonist, CGS21680, also stimulated cAMP levels by 6-fold (P<0.01) with an ED₅₀ of 10⁻⁷ M. These findings demonstrate a functional predominance of the A2a and A2b receptors which was supported by quantitative (q) RT-PCR data. Immunostaining confirmed the presence of all four adenosine receptors. Adenosine and NECA also stimulated a 2-fold (P<0.05) secretion in CgA (radioimmunoassay), with ED₅₀ values of respectively 5×10⁻⁶ and 10⁻⁷ M. Prolonged exposure (1–3 days) to NECA (−5 M) stimulated vascular endothelial growth factor (VEGF) secretion by 25–35% (P<0.05) which was mimicked by the adenylate cyclase activator, forskolin.

In summary we have, to date, shown that BON-1 cells express all four adenosine receptors but predominantly the A2a and A2b subtypes. Activation of these receptors leads to stimulated secretion of CgA and VEGF. Targeting adenosine signal pathways may thus be useful in the therapeutic management of neuroendocrine tumours.