Background: Pheochromocytoma is a neuroendocrine (NE) tumor of the adrenal medulla for which surgical resection is the only therapy. However, 10-46% of tumors are metastatic or have malignant features, and are often inoperable. Our lab has demonstrated the importance of the Notch1 signaling pathway in NE neoplasia, indicating that this pathway could be a target for emergent treatments in pheochromocytoma. It has recently become clear that histone deacetylase (HDAC) inhibitors influence Notch1 signaling. We hypothesized that the HDAC inhibitor Sodium Butyrate (NaB) might activate Notch1 in pheochromocytoma resulting in altered tumor cell proliferation.
Methods: Pheochromocytoma (PC-12) cells were treated with increasing concentrations of NaB. MTT cellular proliferation assay was used to determine the effect of NaB on PC-12 cell growth. Expression of Notch1, NE markers, and cell cycle proteins was studied using Western analysis.
Results: Untreated PC-12 cells lack Notch1 activity. Treatment with NaB led to a dose-dependent induction of Notch1 signaling, reduction of NE markers ASCL1 and CgA, and a significant reduction in cellular proliferation. Levels of expression of cyclin D1, p21, cleaved PARP, and cleaved caspase 3 proteins indicated the presence of cell cycle arrest and apoptosis following NaB treatment.
Conclusion: NaB activated Notch1 signaling, inhibited cellular proliferation, reduced NE markers, and induced cell cycle arrest and apoptosis in pheochromocytoma cells. This data indicates that activation of Notch1 signaling is a promising potential therapy or palliative measure for pheochromocytoma that warrants further investigation.
Keywords: Butyrate; HDAC inhibitor; Notch1; PC-12; neuroendocrine; pheochromocytoma.