Valproic acid activates notch-1 signaling and regulates the neuroendocrine phenotype in carcinoid cancer cells

Notch signaling in pediatric malignancies

Notch signaling plays crucial roles in many developmental pathways, with Notch mutations linked to several developmental disorders. Because many pediatric malignancies arise from dysregulated development, roles for Notch signaling in these cancers are to be expected. Evidence to support this is now emerging as the Notch pathway is being explored in more pediatric cancers. Not surprisingly, Notch appears to play diverse roles in different malignancies, effecting differentiation, metastasis, cancer "stem cells," and angiogenesis. As examples, although activating mutations of Notch1 are found in the majority of T-cell acute lymphoblastic leukemia (ALL) cases, Notch/HES1 signaling appears to play a tumor suppressor role in precursor B-cell ALL; although Notch/HES1 signaling appears to contribute to osteosarcoma metastasis, Notch signaling also promotes medulloblastoma "stem cell" survival and contributes to angiogenesis in neuroblastoma. Further understanding of the roles of Notch signaling in specific pediatric cancers will provide a rationale for Notch-based therapeutic strategies.

Role of menin in neuroendocrine tumorigenesis

The menin protein encoded by the MEN1 tumor suppressor gene is ubiquitously expressed and highly conserved evolutionarily. The combination of findings from current in vitro and in vivo studies has not yielded a comprehensive understanding of the mechanisms of menin's tumor suppressor activity or the specific role for menin in endocrine tumorigenesis, although its diverse interactions suggest possible pivotal roles in transcriptional regulation, DNA processing and repair and cytoskeletal integrity. This manuscript summarizes recent research findings including studies of global gene expression in MEN1-associated neuroendocrine tumors and pivotal changes in intracellular signaling pathways associated with neuroendocrine tumorigenesis. Finally, the clinical applications provided by the understanding of the effects of MEN1 gene mutations on neuroendocrine tumor development in patients with this familial cancer syndrome are discussed.

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.

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.

The histone deacetylase inhibitor valproic acid alters growth properties of renal cell carcinoma in vitro and in vivo

Histone deacetylase (HDAC) inhibitors represent a promising class of antineoplastic agents which affect tumour growth, differentiation and invasion. The effects of the HDAC inhibitor valproic acid (VPA) were tested in vitro and in vivo on pre-clinical renal cell carcinoma (RCC) models. Caki-1, KTC-26 or A498 cells were treated with various concentrations of VPA during in vitro cell proliferation 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays and to evaluate cell cycle manipulation. In vivo tumour growth was conducted in subcutaneous xenograft mouse models. The anti-tumoural potential of VPA combined with low-dosed interferon-alpha (IFN-alpha) was also investigated. VPA significantly and dose-dependently up-regulated histones H3 and H4 acetylation and caused growth arrest in RCC cells. VPA altered cell cycle regulating proteins, in particular CDK2, cyclin B, cyclin D3, p21 and Rb. In vivo, VPA significantly inhibited the growth of Caki-1 in subcutaneous xenografts, accompanied by a strong accumulation of p21 and bax in tissue specimens of VPA-treated animals. VPA-IFN-alpha combination markedly enhanced the effects of VPA monotherapy on RCC proliferation in vitro, but did not further enhance the anti-tumoural potential of VPA in vivo. VPA was found to have profound effects on RCC cell growth, lending support to the initiation of clinical testing of VPA for treating advanced RCC.

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

OBJECTIVE

To examine the effects of valproic acid (VPA) on Notch1 expression and cancer cell proliferation in medullary thyroid cancer (MTC) cells.

BACKGROUND

Other than surgery, there are no effective treatments for MTC, a neuroendocrine malignancy that frequently metastasizes. We have previously shown that over-expression of Notch1 in MTC cells inhibits cell growth and hormone production. VPA, a drug long used for the treatment of epilepsy, has recently been identified as a potential Notch1 activator. We hypothesized that VPA might activate Notch1 signaling in MTC cells, with antiproliferative effects.

METHODS

Human MTC cells were treated with VPA (0-5 mM) and Western blotting was performed to measure levels of Notch1 pathway proteins and neuroendocrine tumor markers. After confirming that VPA is a Notch1 activator in MTC cells, we performed cell proliferation assay. Finally, to determine the mechanism of growth inhibition, we measured protein levels of various markers of apoptosis.

RESULTS

Notch1 was absent in MTC cells at baseline. VPA treatment resulted in an increase in both full-length and active Notch1 protein. Notch1 activation with VPA suppressed 2 neuroendocrine tumor markers, ASCL1 and chromogranin A. Importantly, VPA inhibited the growth of MTC cells in a dose-dependent manner. Immunoblot analysis demonstrated caspase activation and poly(ADP-ribose) polymerase cleavage, indicating the induction of apoptosis.

CONCLUSIONS

VPA activates Notch1 signaling in MTC cells and inhibits their growth by inducing apoptosis. As the safety of VPA in human beings is well established, a clinical trial using this drug to treat patients with advanced MTC could be initiated in the near future.

Cancer stem cells and the ontogeny of lung cancer

Lung cancer is the leading cause of cancer death in the world today and is poised to claim approximately 1 billion lives during the 21st century. A major challenge in treating this and other cancers is the intrinsic resistance to conventional therapies demonstrated by the stem/progenitor cell that is responsible for the sustained growth, survival, and invasion of the tumor. Identifying these stem cells in lung cancer and defining the biologic processes necessary for their existence is paramount in developing new clinical approaches with the goal of preventing disease recurrence. This review summarizes our understanding of the cellular and molecular mechanisms operating within the putative cancer-initiating cell at the core of lung neoplasia.

Suberoyl bishydroxamic acid activates notch1 signaling and suppresses tumor progression in an animal model of medullary thyroid carcinoma

BACKGROUND

Medullary thyroid carcinoma (MTC) is a neuroendocrine malignancy that frequently metastasizes and has few treatments. This study was aimed at assessing the antitumor effects of suberoyl bishydroxamic acid (SBHA) in an in vivo model of MTC.

METHODS

Nude mice were injected with human MTC cells, and the groups were treated with SBHA (200 mg/kg) or vehicle (dimethyl sulfoxide) in saline injection every other day for 12 days. Tumors were measured every 4 days and collected at 12 days for Western blot analysis.

RESULTS

Treatment with SBHA resulted in an average 55% inhibition of tumor growth in the treatment group (P < .05). Analysis of SBHA-treated MTC tumors revealed a marked increase in the active form of Notch1 (NICD) with a concomitant decrease in achaete-scute complex-like 1 (ASCL1), a downstream target of Notch1 signaling, as well as the neuroendocrine tumor marker chromogranin A. Importantly, SBHA treatment resulted in an increase in protein levels of p21(CIP1/WAF1), p27(KIP1), cleaved caspase-9, cleaved caspase-3, and cleaved poly ADP-ribose polymerase and concomitant with a decrease in cyclin D1 and cyclin B1, indicating that the growth inhibition was due to both cell cycle arrest and apoptosis. Moreover, SBHA downregulated cell survival proteins Bcl-2 and Bcl-X(L), but upregulated apoptotic proteins Bax, Bad, and Bmf.

CONCLUSION

These results demonstrate that SBHA inhibits MTC growth in vivo. SBHA is a promising candidate for further preclinical and clinical studies in MTC.

Suberoyl bis-hydroxamic acid activates Notch-1 signaling and induces apoptosis in medullary thyroid carcinoma cells

Medullary thyroid carcinoma (MTC) is a neuroendocrine (NE) malignancy that frequently metastasizes and has limited treatments. We recently reported that ectopic expression of Notch-1 in human MTC cells suppresses growth. The objective of this study was to evaluate the ability of suberoyl bis-hydroxamic acid (SBHA) to modulate Notch-1 signaling in MTC cells. At baseline, no active Notch-1 protein was present in MTC cells. Treatment with SBHA resulted in a dose-dependent induction of the Notch-1 intracellular domain, the active form of the protein. Furthermore, with Notch-1 activation there was a concomitant decrease in achaete-scute complex-like 1 (ASCL-1), a downstream target of Notch-1 signaling, as well as the NE tumor marker chromogranin A (CgA). Transfection of Notch-1 small-interfering RNA into MTC cells blocked the effects of SBHA on Notch-1 activation, ASCL-1, and CgA. Importantly, SBHA treatment resulted in a dose-dependent decrease in cell viability. Treated cells had an increase in protein levels of cleaved caspase-3 and poly ADP-ribose polymerase, and changes in the expression of apoptotic mediators including Bcl-X(L) and Bad, indicating that the growth inhibition was a result of apoptosis. These results demonstrate that SBHA activates Notch-1 signaling, which is associated with the antiproliferative and apoptotic effects in MTC cells. Therefore, Notch-1 activation with SBHA is an attractive new strategy for the treatment of patients with 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.

Valproic acid as epigenetic cancer drug: preclinical, clinical and transcriptional effects on solid tumors

Among many anticancer drugs collectively named "targeted or molecular therapies" epigenetic drugs are clearly promising. Differently from other agents targeting a single gene product, epigenetic drugs have chromatin as their target through inhibition of histone deacetylases (HDACs) and DNA methyltransferases (DNMTs) therefore, yet unspecific, they may act upon most or all tumor types, as deregulation of the methylation and deacetylation machinery are a common hallmark of neoplasia. In the last years, valproic acid (VPA) as emerged as a promising drug for cancer treatment. VPA has shown potent antitumor effects in a variety of in vitro and in vivo systems, and encouraging results in early clinical trials either alone or in combination with demethylating and/or cytotoxic agents. In addition, whole genome expression by microarray analysis from the primary tumors of patients treated with VPA show significant up-regulation of hundred of genes belonging to multiple pathways including ribosomal proteins, oxidative phosphorylation, MAPK signaling; focal adhesion, cell cycle, antigen processing and presentation, proteasome, apoptosis, PI3K, Wnt signaling, calcium signaling, TGF-beta signaling, and ubiquitin-mediated proteolysis among others. Despite in general, industry is not particularly interested in funding the clinical development of VPA, -at least in comparison to novel HDAC inhibitors-, existing preclinical and preliminary clinical data strongly suggest that VPA could be a drug that eventually will be used in combination therapies, either with classical cytotoxics, other molecular-targeted drugs or radiation in a number of solid tumors.