Valproic acid suppresses the self-renewal and proliferation of head and neck cancer stem cells

The Differential Developmental Neurotoxicity of Valproic Acid on Anterior and Posterior Neural Induction of Human Pluripotent Stem Cells

Valproic acid (VPA), widely used as an antiepileptic drug, exhibits developmental neurotoxicity when exposure occurs during early or late pregnancy, resulting in various conditions ranging from neural tube defects to autism spectrum disorders. However, toxicity during the very early stages of neural development has not been addressed. Therefore, we investigated the effects of VPA in a model where human pluripotent stem cells differentiate into anterior or posterior neural tissues. Exposure to VPA during the induction of neural stem cells induced different developmental toxic effects in a dose-dependent manner. For instance, VPA induced cell death more profoundly during anteriorly guided neural progenitor induction, while inhibition of cell proliferation and enhanced differentiation were observed during posteriorly guided neural induction. Furthermore, acute exposure to VPA during the posterior induction step also retarded the subsequent neurulation-like tube morphogenesis process in neural organoid culture. These results suggest that VPA exposure during very early embryonic development might exhibit cytotoxicity and subsequently disrupt neural differentiation and morphogenesis processes.

Cancer Stem Cells in Oral Squamous Cell Carcinoma: A Narrative Review on Experimental Characteristics and Methodological Challenges

Cancer stem cells (CSCs) represent a subpopulation of cancer cells that are believed to initiate and drive cancer progression. In animal models, xenotransplanted CSCs have demonstrated the ability to produce tumors. Since their initial isolation in blood cancers, CSCs have been identified in various solid human cancers, including oral squamous cell carcinoma (OSCC). In addition to their tumorigenic properties, dysregulated stem-cell-related signaling pathways-Wnt family member (Wnt), neurogenic locus notch homolog protein (Notch), and hedgehog-have been shown to endow CSCs with characteristics like self-renewal, phenotypic plasticity, and chemoresistance, contributing to recurrence and treatment failure. Consequently, CSCs have become targets for new therapeutic agents, with some currently in different phases of clinical trials. Notably, small molecule inhibitors of the hedgehog signaling pathway, such as vismodegib and glasdegib, have been approved for the treatment of basal cell carcinoma and acute myeloid leukemia, respectively. Other strategies for eradicating CSCs include natural compounds, nano-drug delivery systems, targeting mitochondria and the CSC microenvironment, autophagy, hyperthermia, and immunotherapy. Despite the extensive documentation of CSCs in OSCC since its first demonstration in head and neck (HN) SCC in 2007, none of these novel pharmacological approaches have yet entered clinical trials for OSCC patients. This narrative review summarizes the in vivo and in vitro evidence of CSCs and CSC-related signaling pathways in OSCC, highlighting their role in promoting chemoresistance and immunotherapy resistance. Additionally, it addresses methodological challenges and discusses future research directions to improve experimental systems and advance CSC studies.

Methods for Overcoming Chemoresistance in Head and Neck Squamous Cell Carcinoma: Keeping the Focus on Cancer Stem Cells, a Systematic Review

According to the "cancer stem cell" (CSCs) theory, tumors are a diverse and expanding group of malignant cells that originate from a small number of CSCs. Despite treatment, these cells can still become active and proliferate, which can result in distant metastasis and local recurrences. A new paradigm in cancer treatment involves targeting both CSCs and the cancer cells in a tumor. This review aims to examine the literature on methods published to overcome chemoresistance due to the presence of CSCs in head and neck cancers. The review was registered with PROSPERO (ID# CRD42024512809). After Pub Med, Scopus, and WoS database searches, 31 relevant articles on oral squamous cell carcinoma (OSCC) were selected. Compounds that increased chemosensitivity by targeting CSCs in head and neck squamous cell carcinoma (HNSCC) were divided into (1) natural products, (2) adjuvant molecules to traditional chemotherapy, and (3) CSCs targeting patient-specific fresh biopsies for functional precision medicine.

A Regulator Role for the ATP-Binding Cassette Subfamily C Member 6 Transporter in HepG2 Cells: Effect on the Dynamics of Cell-Cell and Cell-Matrix Interactions

There is growing evidence that various ATP-binding cassette (ABC) transporters contribute to the growth and development of tumors, but relatively little is known about how the ABC transporter family behaves in hepatocellular carcinoma (HCC), one of the most common cancers worldwide. Cellular model studies have shown that ABCC6, which belongs to the ABC subfamily C (ABCC), plays a role in the cytoskeleton rearrangement and migration of HepG2 hepatocarcinoma cells, thus highlighting its role in cancer biology. Deep knowledge on the molecular mechanisms underlying the observed results could provide therapeutic insights into the tumors in which ABCC6 is modulated. In this study, differential expression levels of mRNA transcripts between ABCC6-silenced HepG2 and control groups were measured, and subsequently, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed. Real-Time PCR and Western blot analyses confirmed bioinformatics; functional studies support the molecular mechanisms underlying the observed effects. The results provide valuable information on the dysregulation of fundamental cellular processes, such as the focal adhesion pathway, which allowed us to obtain detailed information on the active role that the down-regulation of ABCC6 could play in the biology of liver tumors, as it is involved not only in cell migration but also in cell adhesion and invasion.

Targeting cancer stem cells as a strategy for reducing chemotherapy resistance in head and neck cancers

PURPOSE

Resistance to chemotherapy and radiotherapy is the primary cause of a poor prognosis in oncological patients. Researchers identified many possible mechanisms involved in gaining a therapy-resistant phenotype by cancer cells, including alterations in intracellular drug accumulation, detoxification, and enhanced DNA damage repair. All these features are characteristic of stem cells, making them the major culprit of chemoresistance. This paper reviews the most recent evidence regarding the association between the stemness phenotype and chemoresistance in head and neck cancers. It also investigates the impact of pharmacologically targeting cancer stem cell populations in this subset of malignancies.

METHODS

This narrative review was prepared based on the search of the PubMed database for relevant papers.

RESULTS

Head and neck cancer cells belonging to the stem cell population are distinguished by the high expression of certain surface proteins (e.g., CD10, CD44, CD133), pluripotency-related transcription factors (SOX2, OCT4, NANOG), and increased activity of aldehyde dehydrogenase (ALDH). Chemotherapy itself increases the percentage of stem-like cells. Importantly, the intratumor heterogeneity of stem cell subpopulations reflects cell plasticity which has great importance for chemoresistance induction.

CONCLUSIONS

Evidence points to the advantage of combining classical chemotherapeutics with stemness modulators thanks to the joint targeting of the bulk of proliferating tumor cells and chemoresistant cancer stem cells, which could cause recurrence.

The tumor ecosystem in head and neck squamous cell carcinoma and advances in ecotherapy

The development of head and neck squamous cell carcinoma (HNSCC) is a multi-step process, and its survival depends on a complex tumor ecosystem, which not only promotes tumor growth but also helps to protect tumor cells from immune surveillance. With the advances of existing technologies and emerging models for ecosystem research, the evidence for cell-cell interplay is increasing. Herein, we discuss the recent advances in understanding the interaction between tumor cells, the major components of the HNSCC tumor ecosystem, and summarize the mechanisms of how biological and abiotic factors affect the tumor ecosystem. In addition, we review the emerging ecological treatment strategy for HNSCC based on existing studies.

Valproate and lithium: Old drugs for new pharmacological approaches in brain tumors?

Beyond its use as an antiepileptic drug, over time valproate has been increasingly used for several other therapeutic applications. Among these, the antineoplastic effects of valproate have been assessed in several in vitro and in vivo preclinical studies, suggesting that this agent significantly inhibits cancer cell proliferation by modulating multiple signaling pathways. During the last years various clinical trials have tried to find out if valproate co-administration could enhance the antineoplastic activity of chemotherapy in glioblastoma patients and in patients suffering from brain metastases, demonstrating that the inclusion of valproate in the therapeutic schedule causes an improved median overall survival in some studies, but not in others. Thus, the effects of the use of concomitant valproate in brain cancer patients are still controversial. Similarly, lithium has been tested as an anticancer drug in several preclinical studies mainly using the unregistered formulation of lithium chloride salts. Although, there are no data showing that the anticancer effects of lithium chloride are superimposable to the registered lithium carbonate, this formulation has shown preclinical activity in glioblastoma and hepatocellular cancers. However, few but interesting clinical trials have been performed with lithium carbonate on a very small number of cancer patients. Based on published data, valproate could represent a potential complementary therapeutic approach to enhance the anticancer activity of brain cancer standard chemotherapy. Same advantageous characteristics are less convincing for lithium carbonate. Therefore, the planning of specific phase III studies is necessary to validate the repositioning of these drugs in present and future oncological research.

Benefits of the Neurogenic Potential of Melatonin for Treating Neurological and Neuropsychiatric Disorders

There are several neurological diseases under which processes related to adult brain neurogenesis, such cell proliferation, neural differentiation and neuronal maturation, are affected. Melatonin can exert a relevant benefit for treating neurological disorders, given its well-known antioxidant and anti-inflammatory properties as well as its pro-survival effects. In addition, melatonin is able to modulate cell proliferation and neural differentiation processes in neural stem/progenitor cells while improving neuronal maturation of neural precursor cells and newly created postmitotic neurons. Thus, melatonin shows relevant pro-neurogenic properties that may have benefits for neurological conditions associated with impairments in adult brain neurogenesis. For instance, the anti-aging properties of melatonin seem to be linked to its neurogenic properties. Modulation of neurogenesis by melatonin is beneficial under conditions of stress, anxiety and depression as well as for the ischemic brain or after a brain stroke. Pro-neurogenic actions of melatonin may also be beneficial for treating dementias, after a traumatic brain injury, and under conditions of epilepsy, schizophrenia and amyotrophic lateral sclerosis. Melatonin may represent a pro-neurogenic treatment effective for retarding the progression of neuropathology associated with Down syndrome. Finally, more studies are necessary to elucidate the benefits of melatonin treatments under brain disorders related to impairments in glucose and insulin homeostasis.

The paradigm of drug resistance in cancer: an epigenetic perspective

Innate and acquired resistance towards the conventional therapeutic regimen imposes a significant challenge for the successful management of cancer for decades. In patients with advanced carcinomas, acquisition of drug resistance often leads to tumor recurrence and poor prognosis after the first therapeutic cycle. In this context, cancer stem cells (CSCs) are considered as the prime drivers of therapy resistance in cancer due to their 'non-targetable' nature. Drug resistance in cancer is immensely influenced by different properties of CSCs such as epithelial-to-mesenchymal transition (EMT), a profound expression of drug efflux pump genes, detoxification genes, quiescence, and evasion of apoptosis, has been highlighted in this review article. The crucial epigenetic alterations that are intricately associated with regulating different mechanisms of drug resistance, have been discussed thoroughly. Additionally, special attention is drawn towards the epigenetic mechanisms behind the interaction between the cancer cells and their microenvironment which assists in tumor progression and therapy resistance. Finally, we have provided a cumulative overview of the alternative treatment strategies and epigenome-modifying therapies that show the potential of sensitizing the resistant cells towards the conventional treatment strategies. Thus, this review summarizes the epigenetic and molecular background behind therapy resistance, the prime hindrance of present day anti-cancer therapies, and provides an account of the novel complementary epi-drug-based therapeutic strategies to combat drug resistance.

Melatonin Ameliorates Valproic Acid-Induced Neurogenesis Impairment: The Role of Oxidative Stress in Adult Rats

Background

Valproic acid (anticonvulsant medication) has been found to inhibit histone deacetylase activity and suppress hippocampal neurogenesis, which causes memory impairment in both humans and rodents. The neurohormone melatonin, which regulates mammalian seasonal and circadian physiology, has recently been shown to have neuroprotective properties, counteracting memory impairment associated with VPA-caused hippocampal neurogenesis reduction. This study is aimed at investigating the molecular mechanisms of melatonin associated with VPA-induced hippocampal neurogenesis and memory impairment.

Methods

Male Spraque-Dawley rats received VPA (300 mg/kg) twice daily or melatonin (8 mg/kg/day) or some rats were given melatonin for 14 days during VPA administration.

Results

The VPA-treated rats showed a significant increase in malondialdehyde (MDA) levels in the hippocampus and p21-positive cells in the subgranular zone (SGZ) of the dentate gyrus (DG) but decreased superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPx) activities. Moreover, VPA significantly decreased levels of nestin, Notchl, nuclear factor erythroid 2-related factor 2 (Nrf2), doublecortin (DCX), sex determining region Y-box 2 (SOX2), and brain-derived neurotrophic factor (BDNF).

Conclusions

We found that melatonin was able to counteract these neurotoxic effects, acting as a neuroprotectant in VPA-induced memory hippocampal neurogenesis impairment by preventing intracellular oxidative stress and increasing antioxidant activity.

Tumor microenvironment - Unknown niche with powerful therapeutic potential

Head and neck squamous cell carcinomas (HNSCC) are in a group of cancers that are the most resistant to treatment. The survival rate of HNSCC patients has been still very low since last 20 years. The existence of relationship between oncogenic and surrounding cells is probably the reason for a poor response to treatment. Fibroblasts are an important element of tumor stroma which increases tumor cells ability to proliferate. Another highly resistance, tumorigenic and metastatic cell population in tumor microenvironment are cancer initiating cells (CICs). The population of cancer initiating cells can be found regardless of differentiation status of cancer and they seem to be crucial for HNSCC development. In this review, we describe the current state of knowledge about HNSCC biological and physiological tumor microenvironment.

alproic Acid Modulates the Multipotency in Periodontal Ligament Stem Cells via p53-Mediated Cell Cycle

Human periodontal ligament stem cells (PDLSCs), a type of mesenchymal stem cell, are a promising source for dental regeneration and are identified in human periodontal ligaments from extracted third molars. Valproic acid (VPA) is a histone deacetylase inhibitor that has been used as a wide-spectrum antiepileptic drug and a medication for mood disorders. VPA has shown several effects on increasing the pluripotency of embryonic stem cells and controlling osteogenic differentiation, besides the prevention of seizures. However, its effect on proliferation and osteogenesis depends on the cell type and concentration. The aim of this study was to investigate the effects of cyclic and constant VPA treatment on PDLSCs. Proliferation and apoptosis of PDLSCs were determined with cyclic and constant VPA treatment. In cemento/osteogenic differentiation, osteogenic markers decreased significantly after cyclic treatment with 0.5 mM VPA. In contrast, VPA enhanced osteogenic differentiation after constant treatment. With cyclic VPA treatment, p53 levels related to apoptotic pathway decreased to induce proliferation. These findings indicated that VPA has different roles in proliferation and differentiation of PDLSCs in vitro and in vivo via p53-related pathway.

How do tumor cells respond to HDAC inhibition?

It is now well recognized that mutations, deregulated expression, and aberrant recruitment of epigenetic readers, writers, and erasers are fundamentally important processes in the onset and maintenance of many human tumors. The molecular, biological, and biochemical characteristics of a particular class of epigenetic erasers, the histone deacetylases (HDACs), have been extensively studied and small-molecule HDAC inhibitors (HDACis) have now been clinically approved for the treatment of human hemopoietic malignancies. This review explores our current understanding of the biological and molecular effects on tumor cells following HDACi treatment. The predominant responses include induction of tumor cell death and inhibition of proliferation that in experimental models have been linked to therapeutic efficacy. However, tumor cell-intrinsic responses to HDACi, including modulating tumor immunogenicity have also been described and may have substantial roles in mediating the antitumor effects of HDACi. We posit that the field has failed to fully reconcile the biological consequences of exposure to HDACis with the molecular events that underpin these responses, however progress is being made. Understanding the pleiotrophic activities of HDACis on tumor cells will hopefully fast track the development of more potent and selective HDACi that may be used alone or in combination to improve patient outcomes.

Drug Delivery Using Nanoparticles for Cancer Stem-Like Cell Targeting

The theory of cancer stem-like cell (or cancer stem cell, CSC) has been established to explain how tumor heterogeneity arises and contributes to tumor progression in diverse cancer types. CSCs are believed to drive tumor growth and elicit resistance to conventional therapeutics. Therefore, CSCs are becoming novel target in both medical researches and clinical studies. Emerging evidences showed that nanoparticles effectively inhibit many types of CSCs by targeting various specific markers (aldehyde dehydrogenases, CD44, CD90, and CD133) and signaling pathways (Notch, Hedgehog, and TGF-β), which are critically involved in CSC function and maintenance. In this review, we briefly summarize the current status of CSC research and review a number of state-of-the-art nanomedicine approaches targeting CSC. In addition, we discuss emerging therapeutic strategies using epigenetic drugs to eliminate CSCs and inhibit cancer cell reprogramming.