Nepalolide A inhibits the expression of inducible nitric oxide synthase by modulating the degradation of IkappaB-alpha and IkappaB-beta in C6 glioma cells and rat primary astrocytes

Natural Products as Anticancer Agents: Current Status and Future Perspectives

Natural products have been an invaluable and useful source of anticancer agents over the years. Several compounds have been synthesized from natural products by modifying their structures or by using naturally occurring compounds as building blocks in the synthesis of these compounds for various purposes in different fields, such as biology, medicine, and engineering. Multiple modern and costly treatments have been applied to combat cancer and limit its lethality, but the results are not significantly refreshing. Natural products, which are a significant source of new therapeutic drugs, are currently being investigated as potential cytotoxic agents and have shown a positive trend in preclinical research and have prompted numerous innovative strategies in order to combat cancer and expedite the clinical research. Natural products are becoming increasingly important for drug discovery due to their high molecular diversity and novel biofunctionality. Furthermore, natural products can provide superior efficacy and safety due to their unique molecular properties. The objective of the current review is to provide an overview of the emergence of natural products for the treatment and prevention of cancer, such as chemosensitizers, immunotherapeutics, combinatorial therapies with other anticancer drugs, novel formulations of natural products, and the molecular mechanisms underlying their anticancer properties.

Natural Small Molecules Targeting NF-κB Signaling in Glioblastoma

Nuclear factor-κB (NF-κB) is a transcription factor that regulates various genes that mediate various cellular activities, including propagation, differentiation, motility, and survival. Abnormal activation of NF-κB is a common incidence in several cancers. Glioblastoma multiforme (GBM) is the most aggressive brain cancer described by high cellular heterogeneity and almost unavoidable relapse following surgery and resistance to traditional therapy. In GBM, NF-κB is abnormally activated by various stimuli. Its function has been associated with different processes, including regulation of cancer cells with stem-like phenotypes, invasion of cancer cells, and radiotherapy resistance identification of mesenchymal cells. Even though multimodal therapeutic approaches such as surgery, radiation therapy, and chemotherapeutic drugs are used for treating GBM, however; the estimated mortality rate for GBM patients is around 1 year. Therefore, it is necessary to find out new therapeutic approaches for treating GBM. Many studies are focusing on therapeutics having less adverse effects owing to the failure of conventional chemotherapy and targeted agents. Several studies of compounds suggested the involvement of NF-κB signaling pathways in the growth and development of a tumor and GBM cell apoptosis. In this review, we highlight the involvement of NF-κB signaling in the molecular understanding of GBM and natural compounds targeting NF-κB signaling.

Phytochemicals targeting NF-κB signaling: Potential anti-cancer interventions

Nuclear factor κB (NF-κB) is a ubiquitous regulator of the signalome and is indispensable for various biological cell functions. NF-κB consists of five transcription factors that execute both cytoplasmic and nuclear signaling processes in cells. NF-κB is the only signaling molecule that governs both pro- and anti-apoptotic, and pro- and anti-inflammatory responses. This is due to the canonical and non-canonical components of the NF-κB signaling pathway. Together, these pathways orchestrate cancer-related inflammation, hyperplasia, neoplasia, and metastasis. Non-canonical NF-κB pathways are particularly involved in the chemoresistance of cancer cells. In view of its pivotal role in cancer progression, NF-κB represents a potentially significant therapeutic target for modifying tumor cell behavior. Several phytochemicals are known to modulate NF-κB pathways through the stabilization of its inhibitor, IκB, by inhibiting phosphorylation and ubiquitination thereof. Several natural pharmacophores are known to inhibit the nuclear translocation of NF-κB and associated pro-inflammatory responses and cell survival pathways. In view of this and the high degree of specificity exhibited by various phytochemicals for the NF-κB component, we herein present an in-depth overview of these phytochemicals and discuss their mode of interaction with the NF-κB signaling pathways for controlling the fate of tumor cells for cancer-directed interventions.

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NF-κB plays a pivotal role in the maintenance of homeostasis and various inflammation-mediated pathologies.

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NF-κB is involved in cancer development and progression by modulating growth signaling and apoptosis pathways.

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Phytochemicals modulating NF-κB activity should be exploited to design anticancer drugs with minimal side effects.

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Use of these phytochemicals in adjunctive chemotherapy may enhance the chemosensitivity of existing chemotherapeutic drugs.

Protective Role of Natural Products in Glioblastoma Multiforme: A Focus on Nitric Oxide Pathway

In spite of therapeutic modalities such as surgical resection, chemotherapy, and radiotherapy, Glioblastoma Multiforme (GBM) remains an incurable fatal disease. This necessitates further therapeutic options that could enhance the efficacy of existing modalities. Nitric Oxide (NO), a short-lived small molecule, has been revealed to play a crucial role in the pathophysiology of GBM. Several studies have demonstrated that NO is involved in apoptosis, metastasis, cellular proliferation, angiogenesis, invasion, and many other processes implicated in GBM pathobiology. Herein, we elaborate on the role of NO as a therapeutic target in GBM and discuss some natural products affecting the NO signaling pathway.

NOS Expression and NO Function in Glioma and Implications for Patient Therapies

SIGNIFICANCE

Gliomas are central nervous system tumors that primarily occur in the brain and arise from glial cells. Gliomas include the most common malignant brain tumor in adults known as grade IV astrocytoma, or glioblastoma (GBM). GBM is a deadly disease for which the most significant advances in treatment offer an improvement in survival of only ∼2 months.

CRITICAL ISSUES

To develop novel treatments and improve patient outcomes, we and others have sought to determine the role of molecular signals in gliomas. Recent Advances: One signaling molecule that mediates important biologies in glioma is the free radical nitric oxide (NO). In glioma cells and the tumor microenvironment, NO is produced by three isoforms of nitric oxide synthase (NOS), NOS1, NOS2, and NOS3. NO and NOS affect glioma growth, invasion, angiogenesis, immunosuppression, differentiation state, and therapeutic resistance.

FUTURE DIRECTIONS

These multifaceted effects of NO and NOS on gliomas both in vitro and in vivo suggest the potential of modulating the pathway for antiglioma patient therapies. Antioxid. Redox Signal. 26, 986-999.

Withania somnifera Suppresses Tumor Growth of Intracranial Allograft of Glioma Cells

Gliomas are the most frequent type of primary brain tumor in adults. Their highly proliferative nature, complex cellular composition, and ability to escape therapies have confronted investigators for years, hindering the advancement toward an effective treatment. Agents that are safe and can be administered as dietary supplements have always remained priority to be most feasible for cancer therapy. Withania somnifera (ashwagandha) is an essential ingredient of Ayurvedic preparations and is known to eliminate cancer cells derived from a variety of peripheral tissues. Although our previous studies have addressed the in vitro anti-proliferative and differentiation-inducing properties of ashwagandha on neuronal cell lines, in vivo studies validating the same are lacking. While exploring the mechanism of its action in vitro, we observed that the ashwagandha water extract (ASH-WEX) induced the G2/M phase blockade and caused the activation of multiple pro-apoptotic pathways, leading to suppression of cyclin D1, bcl-xl, and p-Akt, and reduced the expression of polysialylated form of neural cell adhesion molecule (PSA-NCAM) as well as the activity of matrix metalloproteinases. ASH-WEX reduced the intracranial tumor volumes in vivo and suppressed the tumor-promoting proteins p-nuclear factor kappa B (NF-κB), p-Akt, vascular endothelial growth factor (VEGF), heat shock protein 70 (HSP70), PSA-NCAM, and cyclin D1 in the rat model of orthotopic glioma allograft. Reduction in glial fibrillary acidic protein (GFAP) and upregulation of mortalin and neural cell adhesion molecule (NCAM) expression specifically in tumor-bearing tissue further indicated the anti-glioma efficacy of ASH-WEX in vivo. Combining this enhanced understanding of the molecular mechanisms of ASH-WEX in glioma with in vivo model system offers new opportunities to develop therapeutic strategy for safe, specific, and effective formulations for treating brain tumors.

Falcarindiol impairs the expression of inducible nitric oxide synthase by abrogating the activation of IKK and JAK in rat primary astrocytes

The effects of falcarindiol on the expression of inducible nitric oxide synthase (iNOS) induced by lipopolysaccharide/interferon-gamma (LPS/IFN-gamma) in rat primary astrocytes were investigated. The molecular mechanisms underlying falcarindiol that confers its effect on iNOS expression were also elucidated. Falcarindiol abrogated the LPS/IFN-gamma-mediated induction of iNOS by about 80%. Falcarindiol attenuated the induction of iNOS in a concentration-dependent manner. The inhibitory effect of falcarindiol on iNOS induction was attributable to decrease in the protein content and the mRNA level of iNOS. Treatment with 50 microM of falcarindiol for 30 min decreased LPS/IFN-gamma-induced nuclear factor-kappaB (NF-kappaB) activation by 32%. Treatment with 50 microM of falcarindiol for 60 min diminished the LPS/IFN-gamma-mediated activation of IkappaB kinase-alpha (IKK-alpha) and IKK-beta by 28.2 and 29.7%, respectively. Falcarindiol modulated the nuclear translocation of signal transducer and activator of transcription 1 (Stat1) in a time-dependent manner. Falcarindiol (50 microM) decreased the tyrosine phosphorylation of janus kinase 1 (JAK1) by 84.8% at 5 min. Falcarindiol also abrogated the tyrosine phoshorylation of JAK2 by 82.3% at 10 min.The present study demonstrates that falcarindiol attenuated the activation of IKK and JAK contributing to the blockade of activation of NF-kappaB and Stat1, thereby leading to the suppression of iNOS expression.

A novel member of the leucine-rich repeat superfamily induced in rat astrocytes by beta-amyloid

beta-Amyloid (Abeta) deposition and senile plaque-associated astrocytes are common neuropathological features of Alzheimer's disease (AD). Although the molecular mechanisms by which Abeta contributes to the progression of neuropathologic changes have not been established entirely, there is little doubt that the association of Abeta with astrocytes, the predominant cell type in brain, has significant influence on exacerbation of the disease. In an effort to identify key molecules involved in AD, we investigated Abeta-responsive genes using rat astrocytes. In this study, we identified a novel Abeta-induced rat gene, designated as Lib, encoding a type I transmembrane protein with an extracellular domain that contains fifteen leucine-rich repeats (LRRs). Human counterpart of rat Lib is located on chromosome 3q29 and human Lib mRNA found in particularly placenta. Lib mRNA levels in rat C6 astrocytoma cells can be increased by pro-inflammatory cytokines and the rat Lib-transfected cells express Lib protein on the cell surfaces. Lib appears to be a member of the LRR superfamily which is involved in cell-cell and/or -extracellular matrix interactions including adhesion or target recognition in neuroinflammatory states.

Neuronal injury-induced expression and release of apolipoprotein E in mixed neuron/glia co-cultures: nuclear factor kappaB inhibitors reduce basal and lesion-induced secretion of apolipoprotein E

In order to better delineate the intracellular signaling pathways underlying glial apolipoprotein E (apoE) expression and release, we have characterized an in vitro model of induction of glial apoE production induced by neuronal death. Exposure of mixed fetal cortical neuron/glia co-cultures to the neurotoxin N-methyl-D-aspartate results in increased apoE expression and release in a time- and concentration-dependent manner. Increased expression of apoE messenger RNA precedes the increase in intracellular apoE, followed by accumulation of the holoprotein in the culture medium. Neuronal injury induced by N-methyl-D-aspartate is accompanied by a reactive astrogliosis as measured by an increase in glial fibrillary acidic protein messenger RNA and protein at 48 and 72h post-lesion, respectively. A similar microgliosis was observed using the microglial marker ED-1. Neuronal injury-induced glial apoE secretion is attenuated by the nuclear factor kappaB inhibitors, aspirin, Bay 11-7082 and MG-132, suggesting that this transcription factor is involved in both constitutive and induced glial apoE expression. The present data show that up-regulation of apoE is an early event in the glial activation triggered by neurodegeneration in vitro and that activation of nuclear factor kappaB directly or indirectly mediates the increase in apoE expression.