Identification and Validation of Notch Pathway Activating Compounds Through a Novel High-Throughput Screening Method

BACKGROUND: Carcinoids are neuroendocrine (NE) tumors with limited treatment options. Notch activation has been shown to suppress growth and hormone production in carcinoid cells. METHODS: The purpose of this study was to provide a process for identifying Notch activating compounds via high-throughput screening (HTS) and to validate the effects of the strongest hit from the 7264 compounds analyzed: resveratrol (RESV). RESULTS: Treatment of carcinoid cells with RESV resulted in up-regulation of the Notch signaling pathway as measured by suppression of its downstream target achaete-scute complex-like 1. Luciferase reporter assays incorporating the centromere-binding factor 1 binding site also confirmed the functional activity of RESV-induced Notch. Because activation of the Notch pathway has been shown to suppress carcinoid proliferation, RESV treatment of carcinoid cells led to a dose-dependent inhibition of cellular growth. Immunoblotting revealed phosphorylation of cdc2 (Tyr15) and up-regulation of p21Cip1/Waf, markers of cell cycle arrest, with RESV treatment. Flow cytometry confirmed the mechanism of RESV-induced growth inhibition is S phase cell cycle arrest. Furthermore, because Notch has been shown to inhibit bioactive hormone production from NE tumors, RESV also suppressed expression of the NE peptides/hormones chromogranin A and serotonin. RNA interference assays demonstrated that the hormone suppressing capacity of RESV was due to up-regulation of the Notch2 isoform. CONCLUSIONS: HTS can be used to identify novel Notch activating compounds, which may have the potential to suppress carcinoid tumor growth and the associated endocrinopathies. Cancer 2011; 117: 1386-98. (C) 2010 American Cancer Society.