Valproic acid induces apoptosis in prostate carcinoma cell lines by activation of multiple death pathways

Voltage-gated sodium channels, sodium transport and progression of solid tumours

Sodium (Na+) concentration in solid tumours of different origin is highly dysregulated, and this corresponds to the aberrant expression of Na+ transporters. In particular, the α subunits of voltage gated Na+ channels (VGSCs) raise intracellular Na+ concentration ([Na+]i) in malignant cells, which influences the progression of solid tumours, predominantly driving cancer cells towards a more aggressive and metastatic phenotype. Conversely, re-expression of VGSC β subunits in cancer cells can either enhance tumour progression or promote anti-tumourigenic properties. Metastasis is the leading cause of cancer-related mortality, highlighting an important area of research which urgently requires improved therapeutic interventions. Here, we review the extent to which VGSC subunits are dysregulated in solid tumours, and consider the implications of such dysregulation on solid tumour progression. We discuss current understanding of VGSC-dependent mechanisms underlying increased invasive and metastatic potential of solid tumours, and how the complex relationship between the tumour microenvironment (TME) and VGSC expression may further drive tumour progression, in part due to the interplay of infiltrating immune cells, cancer-associated fibroblasts (CAFs) and insufficient supply of oxygen (hypoxia). Finally, we explore past and present clinical trials that investigate utilising existing VGSC modulators as potential pharmacological options to support adjuvant chemotherapies to prevent cancer recurrence. Such research demonstrates an exciting opportunity to repurpose therapeutics in order to improve the disease-free survival of patients with aggressive solid tumours.

Repurposed Drugs in Gastric Cancer

Gastric cancer (GC) is one of the major causes of death worldwide, ranking as the fifth most incident cancer in 2020 and the fourth leading cause of cancer mortality. The majority of GC patients are in an advanced stage at the time of diagnosis, presenting a poor prognosis and outcome. Current GC treatment approaches involve endoscopic detection, gastrectomy and chemotherapy or chemoradiotherapy in an adjuvant or neoadjuvant setting. Drug development approaches demand extreme effort to identify molecular mechanisms of action of new drug candidates. Drug repurposing is based on the research of new therapeutic indications of drugs approved for other pathologies. In this review, we explore GC and the different drugs repurposed for this disease.

From HDAC to Voltage-Gated Ion Channels: What's Next? The Long Road of Antiepileptic Drugs Repositioning in Cancer

Simple Summary

Although in the last decades the clinical outcome of cancer patients considerably improved, the major drawbacks still associated with chemotherapy are the unwanted side effects and the development of drug resistance. Therefore, a continuous effort in trying to discover new tumor markers, possibly of diagnostic, prognostic and therapeutic value, is being made. This review is aimed at highlighting the anti-tumor activity that several antiepileptic drugs (AEDs) exert in breast, prostate and other types of cancers, mainly focusing on their ability to block the voltage-gated Na⁺ and Ca⁺⁺ channels, as well as to inhibit the activity of histone deacetylases (HDACs), all well-documented tumor markers and/or molecular targets. The existence of additional AEDs molecular targets is highly suspected. Therefore, the repurposing of already available drugs as adjuvants in cancer treatment would have several advantages, such as reductions in dose-related toxicity CVs will be sent in a separate mail to the indicated address of combined treatments, lower production costs, and faster approval for clinical use.

Abstract

Cancer is a major health burden worldwide. Although the plethora of molecular targets identified in the last decades and the deriving developed treatments, which significantly improved patients’ outcome, the occurrence of resistance to therapies remains the major cause of relapse and mortality. Thus, efforts in identifying new markers to be exploited as molecular targets in cancer therapy are needed. This review will first give a glance on the diagnostic and therapeutic significance of histone deacetylase (HDAC) and voltage gated ion channels (VGICs) in cancer. Nevertheless, HDAC and VGICs have also been reported as molecular targets through which antiepileptic drugs (AEDs) seem to exert their anticancer activity. This should be claimed as a great advantage. Indeed, due to the slowness of drug approval procedures, the attempt to turn to off-label use of already approved medicines would be highly preferable. Therefore, an updated and accurate overview of both preclinical and clinical data of commonly prescribed AEDs (mainly valproic acid, lamotrigine, carbamazepine, phenytoin and gabapentin) in breast, prostate, brain and other cancers will follow. Finally, a glance at the emerging attempt to administer AEDs by means of opportunely designed drug delivery systems (DDSs), so to limit toxicity and improve bioavailability, is also given.

Evaluation of the Effects of Valproic Acid Treatment on Cell Survival and Epithelial-Mesenchymal Transition-Related Features of Human Gastric Cancer Cells

PURPOSE

Metastasis is the most important feature of gastric cancer accounting for more than 90% of tumor-related mortality. As one of the main modulators of epithelial-mesenchymal transition (EMT), histone deacetylase inhibitors (HDACI) are considered rational candidates for cancer therapy. Valproic acid (VPA) is a HDACI with reported controversial effects on the EMT. The main aim of the current study was to evaluate the effects of VPA treatment on cell survival and EMT-related features of human gastric cancer cells (AGS).

METHODS

Methyl-thiazoltetrazolium (MTT) assay was utilized to assess the effect of VPA on the proliferation rate of cells. Apoptotic cell death was detected with Annexin V/PI staining. Migratory ability of cells following VPA treatment was assessed using a Boyden chamber test. The expression of EMT markers in AGS cells was analyzed using quantitative real-time RT-PCR.

RESULTS

Treatment with VPA significantly inhibited AGS cell proliferation compared with control. An increased rate of early and late apoptotic cells was observed following VPA exposure. It was demonstrated that VPA significantly diminished the cell migratory ability in AGS gastric cancer cells. Furthermore, treatment with VPA significantly decreased the expression of E-cadherin but increased the Vimentin expression.

CONCLUSIONS

Our results showed that VPA induces apoptosis and inhibits the cell proliferation and the migratory ability of AGS gastric cancer cells and may prove useful in the development of therapeutic agents for human gastric cancer. However, these preliminary findings call for further investigations to clarify the precise molecular mechanisms by which VPA modulates the EMT process in a cell type-specific manner.

Targeting Ion Channels for Cancer Treatment: Current Progress and Future Challenges

Ion channels are key regulators of cancer cell pathophysiology. They contribute to a variety of processes such as maintenance of cellular osmolarity and membrane potential, motility (via interactions with the cytoskeleton), invasion, signal transduction, transcriptional activity and cell cycle progression, leading to tumour progression and metastasis. Ion channels thus represent promising targets for cancer therapy. Ion channels are attractive targets because many of them are expressed at the plasma membrane and a broad range of existing inhibitors are already in clinical use for other indications. However, many of the ion channels identified in cancer cells are also active in healthy normal cells, so there is a risk that certain blockers may have off-target effects on normal physiological function. This review describes recent research advances into ion channel inhibitors as anticancer therapeutics. A growing body of evidence suggests that a range of existing and novel Na⁺, K⁺, Ca²⁺ and Cl^- channel inhibitors may be effective for suppressing cancer cell proliferation, migration and invasion, as well as enhancing apoptosis, leading to suppression of tumour growth and metastasis, either alone or in combination with standard-of-care therapies. The majority of evidence to date is based on preclinical in vitro and in vivo studies, although there are several examples of ion channel-targeting strategies now reaching early phase clinical trials. Given the strong links between ion channel function and regulation of tumour growth, metastasis and chemotherapy resistance, it is likely that further work in this area will facilitate the development of new therapeutic approaches which will reach the clinic in the future.

Induction of apoptosis and modulation of homologous recombination DNA repair pathway in prostate cancer cells by the combination of AZD2461 and valproic acid

Cancer therapies using defects in homologous recombination (HR) DNA repair pathway of tumor cells are not yet approved to be applicable in patients with malignancies other than BRCA1/2-mutated tumors. This study was designed to determine the efficacy of combination therapy of a histone deacetylase inhibitor, valproic acid (VPA) and a novel PARP inhibitor AZD2461 in both PC-3 (PTEN-mutated) and DU145 (PTEN-unmutated) prostate cancer cell lines. The Trypan blue dye exclusion assay and the tetrazolium-based colorimetric (MTT) assay were performed to measure the cytotoxicity while combination effects were assessed based on Chou-Talalay's principles. Flow-cytometric assay determined the type of cell death. The real-time PCR analysis was used to evaluate the alterations in mRNA levels of HR-related genes while their protein levels were measured using the ELISA method. γ-H2AX levels were determined as a marker of DNA damage. We observed a synergistic relationship between VPA and AZD2461 in all affected fractions of PC-3 cells (CI<0.9), but not in DU145 cells (CI>1.1). Annexin-V staining analysis revealed a significant induction of apoptosis when PC-3 cells were treated with VPA+AZD2461 (p<0.05). Both mRNA and protein levels of Rad51 and Mre11 were significantly decreased in PC-3 cells co-treated with VPA+AZD2461 while enhanced H2AX phosphorylation was found in PC-3 cells after 12 and 24 hours of co-treatment (p<0.05). Our findings established a preclinical rationale for selective targeting of HR repair pathways by a combination of VPA and AZD2461 as a mechanism for reducing the HR pathway sufficiency in PTEN-mutated prostate cancer cells.

Effect of DNA Methyltransferase in Comparison to and in Combination with Histone Deacetylase Inhibitors on Hepatocellular Carcinoma HepG2 Cell Line

Background:

DNA demethylating agents and histone deacetylase inhibitors can affect reactivation of gene expression and apoptosis induction by DNA acetylation and demethylation. The aim of the present study was to analyze the effects of DNA demethylating agent genistein (GE) and histone deacetylase inhibitor valproic acid VPA), alone and combined, on hepatocellular carcinoma Hep G2 cell line.

Methods:

The cells were treated with various doses of genistein and valproic acid (alone and combined) and the MTT assay and flow cytometry were used to determine cell viability and apoptosis.

Results:

Genistein and valproic acid inhibited the growth of HepG 2 cells significantly. Result of flow cytometry demonstrated that genistein and valproic acid (alone and combined) induce apoptosis significantly in a timedependent manner.

Conclusions:

Genistein and valproic acid can significantly inhibit proliferation and induce apoptosis in HepG2 cell line. The apoptotic effects of GE in combination with VPA were more significant that of each compound alone.

Valproic acid downregulates heme oxygenase-1 independently of Nrf2 by increasing ubiquitination and proteasomal degradation

AIMS

Heme oxygenase-1 (HO-1; HMOX1 in human, Hmox1 in mice) is an antioxidative enzyme affecting wide range of sub-cellular processes. It was shown to modulate tumor growth or vascular-related diseases, thus being putative molecular target for tailored therapies. Therefore it is of importance to elucidate novel compounds regulating HO-1 activity/expression and to delineate mechanisms of their action. In the present study we aimed to understand mode of action of valproic acid (VA), an antiepileptic drug, on HO-1 expression.

RESULTS

We demonstrated that HO-1 expression is decreased by VA at protein but not mRNA level in human alveolar rhabdomyosarcoma cell line CW9019. Nrf2 transcription factor, the activator of HO-1 expression through ARE sequence, was excluded as a mediator of HO-1 decrease, as VA downregulated Bach1, a Nrf2 repressor, concomitantly upregulating ARE activation. Also miRNA-dependent inhibition was excluded as a mechanism of HMOX1 regulation. However, co-immunoprecipitation assay showed a higher level of ubiquitinated HO-1 after VA treatment. Accordingly, MG132, an inhibitor of proteasomal degradation, reversed the effect of VA on HO-1 suggesting that decrease in HO-1 expression by VA is through protein stability. The inhibitory effect of VA on HO-1 was also observed in murine cells including embryonic fibroblasts isolated from Nrf2-deficient mice, what confirms Nrf2-independent effect of the compound. Importantly, VA decreased also HO-1 expression and activity in murine skeletal muscles in vivo.

CONCLUSION

Our data indicate that VA downregulates HO-1 by acting through ubiquitin-proteasomal pathway leading to decrease in protein level.

Sodium channel-inhibiting drugs and cancer survival: protocol for a cohort study using the CPRD primary care database

INTRODUCTION

Voltage-gated sodium channel (VGSC)-inhibiting drugs are commonly used to treat epilepsy and cardiac arrhythmia. VGSCs are also widely expressed in various cancers, including those of the breast, bowel and prostate. A number of VGSC-inhibiting drugs have been shown to inhibit cancer cell proliferation, invasion, tumour growth and metastasis in preclinical models, suggesting that VGSCs may be novel molecular targets for cancer treatment. Surprisingly, we previously found that prior exposure to VGSC-inhibiting drugs may be associated with reduced overall survival in patients with cancer, but we were unable to control for the cause of death or indication for prescription. The purpose of the present study is to interrogate a different database to further investigate the relationship between VGSC-inhibiting drugs and cancer-specific survival.

METHODS AND ANALYSIS

A cohort study using primary care data from the Clinical Practice Research Datalink database will include patients with diagnosis of breast, bowel and prostate cancer (13 000). The primary outcome will be cancer-specific survival from the date of cancer diagnosis. Cox proportional hazards regression will be used to compare survival of patients taking VGSC-inhibiting drugs (including antiepileptic drugs and class I antiarrhythmic agents) with patients with cancer not taking these drugs, adjusting for cancer type, age and sex. Drug exposure will be treated as a time-varying covariate to account for potential immortal time bias. Various sensitivity and secondary analyses will be performed.

ETHICS AND DISSEMINATION

The project has been reviewed and approved by the University of York Ethical Review Process. Results will be presented at an international conference and published in open access peer-reviewed journals according to the STROBE and RECORD guidelines.

Therapeutic Value of Voltage-Gated Sodium Channel Inhibitors in Breast, Colorectal, and Prostate Cancer: A Systematic Review

Although survival rates of breast, colon, and prostate cancers are improving, deaths from these tumors frequently occur due to metastasis. Voltage-gated Na(+) channels (VGSCs) are membrane proteins, which regulate membrane current and cellular migration during nervous system organogenesis. VGSCs are also expressed in fibroblasts, immune cells, glia, and metastatic cancer cells. VGSCs regulate migration and invasion of breast, bowel, and prostate cancer cells, suggesting that they may be novel anti-metastatic targets. We conducted a systematic review of clinical and preclinical studies testing the effects of VGSC-inhibiting drugs in cancer. Two-hundred and four publications were identified, of which two human, two mouse, and 20 in vitro publications were included. In the clinical studies, the effect of these drugs on survival and metastatic relapse is not clear. The 22 preclinical studies collectively suggest that several VGSC-inhibiting drugs inhibit cancer proliferation, migration, and invasion. None of the human and only six of the preclinical studies directly investigated the effect of the drugs on VGSC activity. Studies were difficult to compare due to lack of standardized methodology and outcome measures. We conclude that the benefits of VGSC inhibitors require further investigation. Standardization of future studies and outcome measures should enable meaningful study comparisons.

Dasatinib accelerates valproic acid-induced acute myeloid leukemia cell death by regulation of differentiation capacity

Dasatinib is a compound developed for chronic myeloid leukemia as a multi-targeted kinase inhibitor against wild-type BCR-ABL and SRC family kinases. Valproic acid (VPA) is an anti-epileptic drug that also acts as a class I histone deacetylase inhibitor. The aim of this research was to determine the anti-leukemic effects of dasatinib and VPA in combination and to identify their mechanism of action in acute myeloid leukemia (AML) cells. Dasatinib was found to exert potent synergistic inhibitory effects on VPA-treated AML cells in association with G₁ phase cell cycle arrest and apoptosis induction involving the cleavage of poly (ADP-ribose) polymerase and caspase-3, -7 and -9. Dasatinib/VPA-induced cell death thus occurred via caspase-dependent apoptosis. Moreover, MEK/ERK and p38 MAPK inhibitors efficiently inhibited dasatinib/VPA-induced apoptosis. The combined effect of dasatinib and VPA on the differentiation capacity of AML cells was more powerful than the effect of each drug alone, being sufficiently strong to promote AML cell death through G₁ cell cycle arrest and caspase-dependent apoptosis. MEK/ERK and p38 MAPK were found to control dasatinib/VPA-induced apoptosis as upstream regulators, and co-treatment with dasatinib and VPA to contribute to AML cell death through the regulation of differentiation capacity. Taken together, these results indicate that combined dasatinib and VPA treatment has a potential role in anti-leukemic therapy.

Canonical and new generation anticancer drugs also target energy metabolism

Significant efforts have been made for the development of new anticancer drugs (protein kinase or proteasome inhibitors, monoclonal humanized antibodies) with presumably low or negligible side effects and high specificity. However, an in-depth analysis of the side effects of several currently used canonical (platin-based drugs, taxanes, anthracyclines, etoposides, antimetabolites) and new generation anticancer drugs as the first line of clinical treatment reveals significant perturbation of glycolysis and oxidative phosphorylation. Canonical and new generation drug side effects include decreased (1) intracellular ATP levels, (2) glycolytic/mitochondrial enzyme/transporter activities and/or (3) mitochondrial electrical membrane potentials. Furthermore, the anti-proliferative effects of these drugs are markedly attenuated in tumor rho (0) cells, in which functional mitochondria are absent; in addition, several anticancer drugs directly interact with isolated mitochondria affecting their functions. Therefore, several anticancer drugs also target the energy metabolism, and hence, the documented inhibitory effect of anticancer drugs on cancer growth should also be linked to the blocking of ATP supply pathways. These often overlooked effects of canonical and new generation anticancer drugs emphasize the role of energy metabolism in maintaining cancer cells viable and its targeting as a complementary and successful strategy for cancer treatment.

PXD101 potentiates hormonal therapy and prevents the onset of castration-resistant phenotype modulating androgen receptor, HSP90, and CRM1 in preclinical models of prostate cancer

Aberrant activation or 'reactivation' of androgen receptor (AR) during androgen ablation therapy shows a potential cause for the development of castration-resistant prostate cancer. This study tested the hypothesis that PXD101, a potent pan histone deacetylase (HDAC) inhibitor, may prevent onset of castration-resistant phenotype and potentiate hormonal therapy. A panel of human prostate cancer cells with graded castration-resistant phenotype and in vivo models were used to verify this hypothesis. In this report, we demonstrated that hormonal manipulation favors the onset of castration-resistant phenotype increasing HDAC expression and activity as well as modulating expression and activity of AR, EGFR, HER2, and Akt. Consistent with these observations, the functional knockdown of HDACs by PXD101 prevented the onset of castration-resistant phenotype with a significant downregulation of AR, EGFR, HER2, and Akt expression/activity. The dysregulation of functional cooperation between HDAC6 with hsp90, on the one hand, and between GSK-3β with CRM1, on the other hand, may explain the biological effects of PXD101. In this regard, the HDAC6 silencing or the functional knockdown of hsp90 by 17AAG resulted in the selective downregulation of AR, EGFR, HER2, and Akt expression/activity, while the decreased phosphorylation of GSK-3β mediated by PXD101 increased the nuclear expression of CRM1, which in turn modified the AR and survivin recycling with increased caspase 3 activity. HDAC inhibitors retain the ability to prevent the onset of castration-resistant phenotype and, therefore, merit clinical investigation in this setting. However, additional data are needed to develop clinical treatment strategies for this disease stage.

Gene signature critical to cancer phenotype as a paradigm for anticancer drug discovery

Malignant cell transformation commonly results in the deregulation of thousands of cellular genes, an observation that suggests a complex biological process and an inherently challenging scenario for the development of effective cancer interventions. To better define the genes/pathways essential to regulating the malignant phenotype, we recently described a novel strategy based on the cooperative nature of carcinogenesis that focuses on genes synergistically deregulated in response to cooperating oncogenic mutations. These so-called 'cooperation response genes' (CRGs) are highly enriched for genes critical for the cancer phenotype, thereby suggesting their causal role in the malignant state. Here, we show that CRGs have an essential role in drug-mediated anticancer activity and that anticancer agents can be identified through their ability to antagonize the CRG expression profile. These findings provide proof-of-concept for the use of the CRG signature as a novel means of drug discovery with relevance to underlying anticancer drug mechanisms.

[Spontaneous regression of epithelial thymic tumours]

INTRODUCTION

Spontaneous regression of an epithelial thymic tumour has been reported but seems extremely rare. Its mechanism is unknown.

CASE REPORT

We report two cases of epithelial thymic tumour, either histologically proven or highly suspected on imaging, that regressed spontaneously (partially in one patient and totally in the other).

CONCLUSION

Spontaneous regression of an epithelial thymic tumour is very rare but this possibility could lead to clinical and radiological monitoring rather than surgery in selected patients.

Suberoylanilide hydroxamic acid partly reverses resistance to paclitaxel in human ovarian cancer cell lines

OBJECTIVES

The purpose of this study was to determine whether the addition of the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) to paclitaxel (PTX) can sensitize PTX-resistant human ovarian cancer cell lines (CABA-PTX and IGROV-PTX) in vitro.

METHODS

SAHA was studied in combination with paclitaxel in PTX-sensitive and PTX-resistant human ovarian cancer cell lines. Using cell proliferation analysis, immunofluorescence, and flow cytometric assays, we can determine whether the resistance was partly removed when the cells were treated with a combination of SAHA and PTX. Cells were also assayed for cytochrome c release. The levels of acetylated tubulin, β-tubulin, and HDAC6 were quantified by Western blots.

RESULTS

SAHA in combination with PTX led to a more pronounced inhibition of cell growth compared with PTX alone. In addition, the combined exposure to PTX and SAHA resulted in a marked arrest in the G2/M phase of the cell cycle and in a significant increase in the percentage of apoptotic cells. The expression of acetylated tubulin was dramatically increased by exposure to the combination of PTX and SAHA. These data paralleled the findings of an increased expression of HDAC6 in the presence of PTX in PTX-resistant cell lines.

CONCLUSIONS

The results of this study suggest the existence of a novel resistance mechanism based upon the upregulation of HDAC6 and that the histone deacetylase inhibitor SAHA holds promise to overcome PTX resistance in ovarian cancer cell lines.

Molecular and therapeutic potential and toxicity of valproic acid

Valproic acid (VPA), a branched short-chain fatty acid, is widely used as an antiepileptic drug and a mood stabilizer. Antiepileptic properties have been attributed to inhibition of Gamma Amino Butyrate (GABA) transaminobutyrate and of ion channels. VPA was recently classified among the Histone Deacetylase Inhibitors, acting directly at the level of gene transcription by inhibiting histone deacetylation and making transcription sites more accessible. VPA is a widely used drug, particularly for children suffering from epilepsy. Due to the increasing number of clinical trials involving VPA, and interesting results obtained, this molecule will be implicated in an increasing number of therapies. However side effects of VPA are substantially described in the literature whereas they are poorly discussed in articles focusing on its therapeutic use. This paper aims to give an overview of the different clinical-trials involving VPA and its side effects encountered during treatment as well as its molecular properties.

Differential effects of valproic acid on growth, proliferation and metastasis in HTB5 and HTB9 bladder cancer cell lines

High grade invasive bladder cancer is a leading cause of cancer deaths and treatment options are limited for this type of cancer. Recent studies have reported anticancer effects of valproic acid in many cancers and also in superficial bladder cancer. Acute valproic acid administration suppressed cell proliferation in a time- and dose-dependent manner in two muscle-invasive human bladder cancer cell lines (HTB5 and HTB9), with accompanying G1 phase cell cycle arrest. A significant decrease in colony formation ability and invasiveness was seen with valproic acid treatment though the effectiveness varied with cell type. Our results suggest a role for valproic acid in inhibiting growth and invasion of muscle-invasive bladder cancer.

Valproic acid (VPA), a histone deacetylase (HDAC) inhibitor, diminishes lymphoproliferation in the Fas -deficient MRL/lpr(-/-) murine model of autoimmune lymphoproliferative syndrome (ALPS)

OBJECTIVE

Autoimmune lymphoproliferative syndrome (ALPS) is a disorder of apoptosis, often presenting in childhood. Similarly, MRL/lpr(-/-) mice homozygous for Fas mutations develop an ALPS-like disease with autoimmunity, lymphadenopathy, splenomegaly, and expansion of double-negative T cells. Currently, there are no proven therapies with adequate safety margins for sustained abolition of the lymphoproliferation associated with ALPS. We sought to test the ability of valproic acid (VPA), a histone deacetylase inhibitor, to induce apoptosis and inhibit lymphoproliferation.

MATERIALS AND METHODS

Human peripheral blood mononuclear cells from patients with ALPS and normal controls were tested in vitro to determine the efficacy of VPA at inducing cell death. VPA was used in vivo to control lymphoproliferation in MRL/lpr(-/-) mice, a model for ALPS.

RESULTS

VPA induced cell death in vitro, and was partially inhibited by the pan caspase inhibitor, Z-VAD-FMK. MRL/lpr(-/-) mice treated with VPA for 8 weeks showed significant reductions in spleen and lymph node weights and cellularity compared to controls. A concomitant decrease in double-negative T cells was observed in the spleen, lymph nodes, and peripheral blood. Serum levels of VPA peaked 1 hour after injection, and a 2.5-fold increase in histone acetylation was observed in the spleen at 4 hours after injection.

CONCLUSION

Based on our data, VPA is effective at reducing lymphoproliferation in mice, and is currently being studied in a clinical trial as a lympholytic agent in patients with ALPS.

Sodium valproate, a histone deacetylase inhibitor, decreases the secretion of soluble Fas by human osteosarcoma cells and increases their sensitivity to Fas-mediated cell death

PURPOSE

Effects of valproic acid (VPA), a histone deacetylase inhibitor, on the susceptibility to cell death induced by agonistic anti-Fas antibody were examined using four human osteosarcoma cell lines.

METHOD

Cell growth, secretion of soluble Fas, expression of cell-surface Fas, and sensitivity to Fas-mediated cell death were examined using cell proliferation assay, flow cytometry, enzyme-linked immunosorbent assay, and agonistic anti-Fas antibody, respectively.

RESULTS

VPA suppressed the growth of all the four osteosarcoma cell lines and the secretion of soluble Fas from these cells. VPA showed no or slight suppressive effect on the expression of cell-surface Fas in the four osteosarcoma cell lines, but increased the sensitivity of three of four osteosarcoma cell lines to Fas-mediated cell death.

CONCLUSION

VPA enhances the susceptibility of human osteosarcoma cells to Fas-ligand-induced cell death by decreasing the secretion of soluble Fas and increasing the sensitivity to Fas-mediated cell death.

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.

Neuroendocrine transdifferentiation induced by VPA is mediated by PPARgamma activation and confers resistance to antiblastic therapy in prostate carcinoma

BACKGROUND

Prostate cancer (PCa) is the most commonly diagnosed cancer in men in the Western Countries. When prostatectomy fails to eradicate the primary tumor, PCa is generally refractory to all therapeutic approaches. Valproic acid (VPA) is a promising anticancer agent recently assigned to the class of histone deacetylase (HDAC) inhibitors. However molecular mechanisms underlying VPA action in PCa cells are largely unknown and further experimental validation to prove its potential application in clinic practice is needed.

RESULTS

In our study we show that VPA is a potent inducer of neuro-endocrine transdifferentiation (NET) in androgen receptor null PCa cells, both in vitro and in vivo. NET was an early event detectable through the expression of neuro-endocrine (NE) markers within 72 hr after VPA treatment and it was associated to a reduction in the overall cell proliferation. When we interrupted VPA treatment we observed the recovery in residual cells of the basal proliferation rate both in vitro and in a xenograft model. The NET process was related to Bcl-2 over-expression in non-NE PCa cells and to the activation of PPARgamma in NE cells. The use of specific PPARgamma antagonist was able to reduce significantly the expression of NE markers induced by VPA.

CONCLUSIONS

Our data indicate that the use of VPA as monotherapy in PCa has to be considered with extreme caution, since it may induce an unfavorable NET. In order to counteract the VPA-induced NET, the inhibition of PPARgamma may represent a suitable adjuvant treatment strategy and awaits further experimental validation.

New histone deacetylase inhibitors as potential therapeutic tools for advanced prostate carcinoma

The anti-epileptic drug valproic acid is also under trial as an anti-cancer agent due to its histone deacetylase (HDAC) inhibitory properties. However, the effects of valproic acid (VPA) are limited and concentrations required for exerting anti-neoplastic effects in vitro may not be reached in tumour patients. In this study, we tested in vitro and in vivo effects of two VPA-derivatives (ACS2, ACS33) on pre-clinical prostate cancer models. PC3 and DU-145 prostate tumour cell lines were treated with various concentrations of ACS2 or ACS33 to perform in vitro cell proliferation 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays and to evaluate tumour cell adhesion to endothelial cell monolayers. Analysis of acetylated histones H3 and H4 protein expression was performed by western blotting. In vivo tumour growth was conducted in subcutaneous xenograft mouse models. Tumour sections were assessed by immunohistochemistry for histone H3 acetylation and proliferation. ACS2 and ACS33 significantly up-regulated histone H3 and H4 acetylation in prostate cancer cell lines. In micromolar concentrations both compounds exerted growth arrest in PC3 and DU-145 cells and prevented tumour cell attachment to endothelium. In vivo, ACS33 inhibited the growth of PC3 in subcutaneous xenografts. Immunohistochemistry and western blotting confirmed increased histone H3 acetylation and reduced proliferation. ACS2 and ACS33 represent novel VPA derivatives with superior anti-tumoural activities, compared to the mother compound. This investigation lends support to the clinical testing of ACS2 or ACS33 for the treatment of prostate cancer.

Drug-induced apoptosis in yeast

In order to alter the impact of diseases on human society, drug development has been one of the most invested research fields. Nowadays, cancer and infectious diseases are leading targets for the design of effective drugs, in which the primary mechanism of action relies on the modulation of programmed cell death (PCD). Due to the high degree of conservation of basic cellular processes between yeast and higher eukaryotes, and to the existence of an ancestral PCD machinery in yeast, yeasts are an attractive tool for the study of affected pathways that give insights into the mode of action of both antitumour and antifungal drugs. Therefore, we covered some of the leading reports on drug-induced apoptosis in yeast, revealing that in common with mammalian cells, antitumour drugs induce apoptosis through reactive oxygen species (ROS) generation and altered mitochondrial functions. The evidence presented suggests that yeasts may be a powerful model for the screening/development of PCD-directed drugs, overcoming the problem of cellular specificity in the design of antitumour drugs, but also enabling the design of efficient antifungal drugs, targeted to fungal-specific apoptotic regulators that do not have major consequences for human cells.

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.

Prazosin displays anticancer activity against human prostate cancers: targeting DNA and cell cycle

Quinazoline-based alpha1-adrenoceptor antagonists, in particular doxazosin and terazosin, are suggested to display antineoplastic activity against prostate cancers. However, there are few studies elucidating the effect of prazosin. In this study, prazosin displayed antiproliferative activity superior to that of other alpha1-blockers, including doxazosin, terazosin, tamsulosin, and phentolamine. Prazosin induced G2 checkpoint arrest and subsequent apoptosis in prostate cancer PC-3, DU-145, and LNCaP cells. In p53-null PC-3 cells, prazosin induced an increase in DNA strand breaks and ATM/ATR checkpoint pathways, leading to the activation of downstream signaling cascades, including Cdc25c phosphorylation at Ser216, nuclear export of Cdc25c, and cyclin-dependent kinase (Cdk) 1 phosphorylation at Tyr15. The data, together with sustained elevated cyclin A levels (other than cyclin B1 levels), suggested that Cdk1 activity was inactivated by prazosin. Moreover, prazosin triggered mitochondria-mediated and caspase-executed apoptotic pathways in PC-3 cells. The oral administration of prazosin significantly reduced tumor mass in PC-3-derived cancer xenografts in nude mice. In summary, we suggest that prazosin is a potential antitumor agent that induces cell apoptosis through the induction of DNA damage stress, leading to Cdk1 inactivation and G2 checkpoint arrest. Subsequently, mitochondria-mediated caspase cascades are triggered to induce apoptosis in PC-3 cells.

Valproic acid induces neuroendocrine differentiation and UGT2B7 up-regulation in human prostate carcinoma cell line

Prostate cancer originates as an androgen-dependent hyperproliferation of the epithelial cells of the gland and it evolves in an androgen-independent, highly aggressive cancer for which no successful therapy is available to date. Neuroendocrine (NE) differentiation plays an important role in the progression of prostate cancer to an androgen-independent state with profound impact on prostate cancer (CaP) therapies. Actually, new approaches on treating advanced prostate cancer are focused on modulators of epigenetic transcriptional regulation. A new class of antitumoral agents is emerging: histone deacetylase (HDAC) inhibitors are interesting for their ability to arrest cell growth, to induce cell differentiation, and in some cases, to induce apoptosis of cancer cells. We studied the effect of valproic acid (VPA), an inhibitor of HDAC, in the human prostate androgen-dependent cancer cell line LNCaP. We observed that VPA promotes neuroendocrine-like differentiation associated with an increase in the expression of neuron-specific enolase, a decrease in prostate-specific antigen, and a down-regulation of androgen receptor protein, suggesting a modulation in the responsiveness to androgen therapy. Furthermore, selective gene expression profiling using a low-density microarray showed that VPA was able to modulate the expression of different androgen metabolism genes. We observed a down-regulation of androgen receptor coregulator (ARA24) and prostate-specific antigen, and an up-regulation of some of the UDP-glucuronosyltransferases (UGT2B11 and UGT2B7) implicated in catabolism of dihydrotestosterone (DHT) was detected. Even though UGT2B7 has only about one-tenth to one-hundredth the activity of UGT2B15 and 2B17 toward active androgens and we did not found any modulation in gene expression of these enzymes, it can be hypothesized that VPA might enhance DHT catabolism in this in vitro model and induces NE differentiation. Our data seem to raise concern about CaP treatment with VPA.