Valproic acid activates Notch1 signaling and induces apoptosis in medullary thyroid cancer cells

Sodium butyrate activates Notch1 signaling, reduces tumor markers, and induces cell cycle arrest and apoptosis in pheochromocytoma

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.

Histone deacetylase inhibitors upregulate Notch-1 and inhibit growth in pheochromocytoma cells

BACKGROUND

The histone deacetylase (HDAC) inhibitors valproic acid (VPA) and suberoyl bis-hydroxamic acid (SBHA) have been demonstrated recently to be strong Notch-1 activators. Upregulation of the Notch-1 pathway has been shown to limit growth and suppress hormonal secretion in neuroendocrine (NE) neoplasms. We hypothesized that HDAC inhibition would be an effective strategy to activate the Notch-1 pathway and inhibit growth and hormonal secretion in pheochromocytoma cells.

METHODS

Pheochromocytoma PC-12 cells were treated with up to 8 mmol/L VPA or 40 micromol/L SBHA for 2 days. NE tumor markers achaete-scute complex-like 1 (ASCL1) and chromogranin A (CgA) were measured by Western analysis after treatment. Growth was assessed by a cellular proliferation assay; Western analysis was used to determine the mechanism of growth regulation.

RESULTS

HDAC inhibitor treatment caused a dose-dependent decrease in ASCL1 and CgA while increasing the amount of active Notch-1 protein; with a 6-day treatment, dose-dependent growth inhibition and cleavage of the apoptotic markers caspase-3 and poly-ADP ribose phosphate was observed.

CONCLUSION

VPA and SBHA upregulate Notch-1 effectively, suppress NE tumor markers, and decrease growth via apoptosis of pheochromocytoma cells in vitro. Activation of the Notch-1 signaling pathway with HDAC inhibitors may represent a new strategy for treating pheochromocytomas.

Combination therapy with histone deacetylase inhibitors and lithium chloride: a novel treatment for carcinoid tumors

In carcinoid cell lines, the histone deacetylase (HDAC) inhibitors valproic acid (VPA) and suberoyl bis-hydroxamic acid (SBHA) activate the Notch1 pathway, whereas lithium inhibits glycogen synthase kinase-3beta (GSK-3beta). These compounds limit growth and decrease hormonal secretion in vitro. We hypothesized that lower-dose combination therapy of HDAC inhibitors and lithium chloride could achieve similar growth inhibition to that of the drugs alone. Gastrointestinal and pulmonary carcinoid cells were treated with either VPA or SBHA and lithium chloride for up to 48 hours. Western blot analysis was used to measure the effects on the Notch1 and GSK-3beta pathways and the neuroendocrine tumor marker chromogranin A (CgA). Growth was measured by a cellular proliferation assay. With lower-dose combination therapy, a decrease in CgA was observed. The HDAC inhibitors increased the amount of active Notch1 protein, whereas treatment with lithium was associated with inhibition of GSK-3beta. Moreover, growth was inhibited with lower-dose combination therapy. Treatment of carcinoid cells with either VPA or SBHA and lithium chloride suppresses the neuroendocrine marker CgA while upregulating Notch1 and inhibiting GSK-3beta. This combination effectively reduces growth. Thus, lower-dose combination therapy may be a viable therapeutic approach for carcinoid tumors.

Terminal and progenitor lineage-survival oncogenes as cancer markers

Tumour classification has traditionally focused on differentiation and cellular morphology, and latterly on the application of genomic approaches. By combining chromatin immunoprecipitation with expression array, it has been possible to identify direct gene targets for transcription factors for nuclear hormone receptors. At the same time, there have been great strides in deriving stem and progenitor cells from tissues. It is therefore timely to propose that pairing the isolation of these cell subpopulations from tissues and tumours with these genomics approaches will reveal conserved gene targets for transcription factors. By focusing on transcription factors (lineage-survival oncogenes) with roles in both organogenesis and tumourigenesis at multiple organ sites, we suggest that this comparative genomics approach will enable developmental biology to be used more fully in relation to understanding tumour progression and will reveal new cancer markers. We focus here on neurogenesis and neuroendocrine differentiation in tumours.

Inhibition of growth in medullary thyroid cancer cells with histone deacetylase inhibitors and lithium chloride

BACKGROUND

While representing only 3% of thyroid malignancies, medullary thyroid cancer (MTC) accounts for 14% of thyroid cancer deaths. MTC has a high rate of recurrence and lacks effective treatments. The histone deacetylase (HDAC) inhibitors valproic acid (VPA) and suberoyl bis-hydroxamic acid (SBHA) activate the Notch1 signaling pathway, while lithium chloride inhibits the glycogen synthase kinase-3ss (GSK-3ss) pathway. These compounds have been shown to limit growth and suppress hormonal secretion; thus, targeting different signaling pathways may be an effective treatment.

METHODS

MTC cells were treated with varying combinations of up to 20 mM lithium chloride with either 3 mM VPA or 20 muM SBHA for 48 h. Western analysis was used to measure the effects on Notch1, GSK-3ss, and neuroendocrine (NE) markers. Growth was assessed by a methylthiazolyldiphenyl-tetrazolium (MTT) bromide cellular proliferation assay. Western analysis was used to determine the mechanism of growth regulation.

RESULTS

Combination therapy increased active Notch1, inhibited the GSK-3ss pathway, and decreased NE markers. Additive inhibition of growth was observed with combination therapy. Lower-dose combination therapy achieved greater decreases on NE markers and growth than treatment with any of the drugs alone. Moreover, an increase in the cleavage of the apoptotic markers caspase-3 and PARP was observed.

CONCLUSIONS

Combination therapy with lithium chloride and HDAC inhibitors suppresses NE markers and decreases growth via apoptosis of MTC cells in vitro. With the possibility of increased efficacy and decreased toxicity, combination therapy may represent a new strategy to treat MTC.

Valproic acid induces Notch1 signaling in small cell lung cancer cells

BACKGROUND

Small cell lung cancer (SCLC) is an aggressive malignancy. Current treatments yield dismal survival rates. We have previously demonstrated that histone deacetylase (HDAC) inhibitors can inhibit neuroendocrine tumor growth. Activation of the Notch1 signaling pathway also impairs SCLC cell viability. In this study, we investigated the ability of the HDAC inhibitor valproic acid (VPA) to activate Notch1 signaling and inhibit proliferation in SCLC cells.

MATERIALS AND METHODS

DMS53 human SCLC cells were treated with VPA (0-10 mM) for 2 d. Light microscopy was used to examine changes in cell morphology. Western analysis was performed using antibodies against various Notch1 pathway proteins to assess Notch1 activation. Additionally, immunoblotting was performed for two neuroendocrine tumor markers, chromogranin A and achaete-scute complex-like 1. Finally, a cell proliferation assay was used to measure the effects of VPA on SCLC growth over 8 d.

RESULTS

After treatment with VPA, DMS53 cells underwent dramatic changes in morphology. VPA induced expression of the full-length and active forms of Notch1 protein. Furthermore, VPA suppressed levels of neuroendocrine tumor markers chromogranin A and ASLC-1. Importantly, VPA treatment led to dose-dependent inhibition of SCLC cell proliferation.

CONCLUSIONS

The HDAC inhibitor VPA activates Notch1 signaling in SCLC cells. VPA induces changes in cell morphology and suppresses neuroendocrine tumor markers, indicating a change in phenotype. Additionally, VPA profoundly inhibits SCLC cell growth. These results suggest that VPA has potential as a novel therapeutic agent for SCLC.