Antitumorigenic effect of plumbagin by induction of SH2-containing protein tyrosine phosphatase 1 in human gastric cancer cells

Consideration of SHP-1 as a Molecular Target for Tumor Therapy

Abnormal activation of receptor tyrosine kinases (RTKs) contributes to tumorigenesis, while protein tyrosine phosphatases (PTPs) contribute to tumor control. One of the most representative PTPs is Src homology region 2 (SH2) domain-containing phosphatase 1 (SHP-1), which is associated with either an increased or decreased survival rate depending on the cancer type. Hypermethylation in the promoter region of PTPN6, the gene for the SHP-1 protein, is a representative epigenetic regulation mechanism that suppresses the expression of SHP-1 in tumor cells. SHP-1 comprises two SH2 domains (N-SH2 and C-SH2) and a catalytic PTP domain. Intramolecular interactions between the N-SH2 and PTP domains inhibit SHP-1 activity. Opening of the PTP domain by a conformational change in SHP-1 increases enzymatic activity and contributes to a tumor control phenotype by inhibiting the activation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT3) pathway. Although various compounds that increase SHP-1 activation or expression have been proposed as tumor therapeutics, except sorafenib and its derivatives, few candidates have demonstrated clinical significance. In some cancers, SHP-1 expression and activation contribute to a tumorigenic phenotype by inducing a tumor-friendly microenvironment. Therefore, developing anticancer drugs targeting SHP-1 must consider the effect of SHP-1 on both cell biological mechanisms of SHP-1 in tumor cells and the tumor microenvironment according to the target cancer type. Furthermore, the use of combination therapies should be considered.

The signaling pathways and targets of natural products from traditional Chinese medicine treating gastric cancer provide new candidate therapeutic strategies

Gastric cancer (GC) is one of the severe malignancies with high incidence and mortality, especially in Eastern Asian countries. Significant advancements have been made in diagnosing and treating GC over the past few decades, resulting in tremendous improvements in patient survival. In recent years, traditional Chinese medicine (TCM) has garnered considerable attention as an alternative therapeutic approach for GC due to its multicomponent and multitarget characteristics. Consequently, natural products found in TCM have attracted researchers' attention, as growing evidence suggests that these natural products can impede GC progression by regulating various biological processes. Nevertheless, their molecular mechanisms are not systematically uncovered. Here, we review the major signaling pathways involved in GC development. Additionally, clinical GC samples were analyzed. Moreover, the anti-GC effects of natural products, their underlying mechanisms and potential targets were summarized. These summaries are intended to facilitate further relevant research, and accelerate the clinical applications of natural products in GC treatment.

Exploitation of the antifungal and antibiofilm activities of plumbagin against Cryptococcus neoformans

Cryptococcus neoformans is an important opportunistic fungal pathogen that causes various infections. Here, the antifungal and antibiofilm activities of plumbagin against C. neoformans and the underlying mechanisms were evaluated. The minimum inhibitory concentration (MIC) of plumbagin against C. neoformans H99 was 8 μg ml^-1. Plumbagin disrupted the cell membrane integrity and reduced the metabolic activities of C. neoformans H99. C. neoformans H99 biofilm cells were damaged by plumbagin at a concentration of 64 μg ml^-1, whereas 48-h mature biofilms were dispersed at a plumbagin concentration of 128 μg ml^-1. Whole-transcriptome analysis of plumbagin-treated C. neoformans H99 in the biofilm and planktonic states identified differentially expressed genes enriched in several important cellular processes (cell membrane, ribosome biogenesis, fatty acid synthesis, melanin and capsule production). Notably, plumbagin damaged biofilm cells by downregulating FAS1 and FAS2 expression. Thus, plumbagin can be exploited as an antifungal agent to combat C. neoformans-related infections.

Naphthoquinone-induced arylation inhibits Sirtuin 7 activity

Natural or synthetic naphthoquinones have been identified as interfering with biological systems and in particular exhibiting anticancer properties. As redox cyclers, they may first generate in cells reactive oxygen species and second, as electrophiles, they may react with nucleophiles, mainly thiols, and form covalent adducts. To further decipher the molecular mechanism of action of naphthoquinones in human cells, we have mainly analysed their effects in HeLa cells. First, we have demonstrated that menadione and plumbagin inhibit the nucleolar NAD+-dependent deacetylase Sirtuin 7 in vitro. As assessed by their inhibitions of rDNA transcription, pre-rRNA processing and formation of etoposide-induced 53BP1 foci, menadione and plumbagin inhibit also Sirtuin 7 catalytic activity in vivo. Second, we have established that in experimental conditions in which the sulfhydryl arylation by menadione or plumbagin is prevented by the thiol reducing agent N-acetyl-L-cysteine, the inhibition of Sirtuin 7 catalytic activity is also prevented. Finally, we discuss here how inhibition of Sirtuin 7 might be critical in determining menadione or plumbagin as anti-tumor agents that can be used in combination in anti-tumoral strategies.

A comprehensive review on the role of protein tyrosine phosphatases in gastric cancer development and progression

The main post-translational reversible modulation of proteins is phosphorylation and dephosphorylation, catalyzed by protein kinases (PKs) and protein phosphatases (PPs) which is crucial for homeostasis. Imbalance in this crosstalk can be related to diseases, including cancer. Plenty of evidence indicates that protein tyrosine phosphatases (PTPs) can act as tumor suppressors and tumor promoters. In gastric cancer (GC), there is a lack of understanding of the molecular aspects behind the tumoral onset and progression. Here we describe several members of the PTP family related to gastric carcinogenesis. We discuss the associated molecular mechanisms which support the down or up modulation of different PTPs. We emphasize the Helicobacter pylori (H. pylori) virulence which is in part associated with the activation of PTP receptors. We also explore the involvement of intracellular redox state in response to H. pylori infection. In addition, some PTP members are under influence by genetic mutations, epigenetics mechanisms, and miRNA modulation. The understanding of multiple aspects of PTPs in GC may provide new targets and perspectives on drug development.

Inhibition or Reversal of the Epithelial-Mesenchymal Transition in Gastric Cancer: Pharmacological Approaches

Epithelial-mesenchymal transition (EMT) constitutes one of the hallmarks of carcinogenesis consisting in the re-differentiation of the epithelial cells into mesenchymal ones changing the cellular phenotype into a malignant one. EMT has been shown to play a role in the malignant transformation and while occurring in the tumor microenvironment, it significantly affects the aggressiveness of gastric cancer, among others. Importantly, after EMT occurs, gastric cancer patients are more susceptible to the induction of resistance to various therapeutic agents, worsening the clinical outcome of patients. Therefore, there is an urgent need to search for the newest pharmacological agents targeting EMT to prevent further progression of gastric carcinogenesis and potential metastases. Therapies targeted at EMT might be combined with other currently available treatment modalities, which seems to be an effective strategy to treat gastric cancer patients. In this review, we have summarized recent advances in gastric cancer treatment in terms of targeting EMT specifically, such as the administration of polyphenols, resveratrol, tangeretin, luteolin, genistein, proton pump inhibitors, terpenes, other plant extracts, or inorganic compounds.

Anticancer Effects and Mechanisms of Action of Plumbagin: Review of Research Advances

Plumbagin (PLB), a natural naphthoquinone constituent isolated from the roots of the medicinal plant Plumbago zeylanica L., exhibited anticancer activity against a variety of cancer cell lines including breast cancer, hepatoma, leukemia, melanoma, prostate cancer, brain tumor, tongue squamous cell carcinoma, esophageal cancer, oral squamous cell carcinoma, lung cancer, kidney adenocarcinoma, cholangiocarcinoma, gastric cancer, lymphocyte carcinoma, osteosarcoma, and canine cancer. PLB played anticancer activity via many molecular mechanisms, such as targeting apoptosis, autophagy pathway, cell cycle arrest, antiangiogenesis pathway, anti-invasion, and antimetastasis pathway. Among these signaling pathways, the key regulatory genes regulated by PLB were NF-kβ, STAT3, and AKT. PLB also acted as a potent inducer of reactive oxygen species (ROS), suppressor of cellular glutathione, and novel proteasome inhibitor, causing DNA double-strand break by oxidative DNA base damage. This review comprehensively summarizes the anticancer activity and mechanism of PLB.

Dietary molecules and experimental evidence of epigenetic influence in cancer chemoprevention: An insight

The world-wide rate of incidence of cancer disease has been only modestly contested by the past and current preventive and interventional strategies. Hence, the global effort towards novel ideas to contain the disease still continues. Constituents of human diets have in recent years emerged as key regulators of carcinogenesis, with studies reporting their inhibitory potential against all the three stages vis-a-vis initiation, promotion and progression. Unlike drugs which usually act on single targets, these dietary factors have an advantage of multi-targeted effects and pleiotropic action mechanisms, which are effective against cancer that manifest as a micro-evolutionary and multi-factorial disease. Since most of the cellular targets have been identified and their consumption considered relatively safe, these diet-derived agents often appear as molecules of interest in repurposing strategies. Currently, many of these molecules are being investigated for their ability to influence the aberrant alterations in cell's epigenome for epigenetic therapy against cancer. Targeting the epigenetic regulators is a new paradigm in cancer chemoprevention which acts to reverse the warped-up epigenetic alterations in a cancer cell, thereby directing it towards a normal phenotype. In this review, we discuss the significance of dietary factors and natural products as chemopreventive agents. Further, we corroborate the experimental evidence from existing literature, reflecting the ability of a series of such molecules to act as epigenetic modifiers in cancer cells, by interfering with molecular events that map the epigenetic imprints such as DNA methylation, histone acetylation and non-coding RNA mediated gene regulation.

Shp1 in Solid Cancers and Their Therapy

Shp1 is a cytosolic tyrosine phosphatase that regulates a broad range of cellular functions and targets, modulating the flow of information from the cell membrane to the nucleus. While initially studied in the hematopoietic system, research conducted over the past years has expanded our understanding of the biological role of Shp1 to other tissues, proposing it as a novel tumor suppressor gene functionally involved in different hallmarks of cancer. The main mechanism by which Shp1 curbs cancer development and progression is the ability to attenuate and/or terminate signaling pathways controlling cell proliferation, survival, migration, and invasion. Thus, alterations in Shp1 function or expression can contribute to several human diseases, particularly cancer. In cancer cells, Shp1 activity can indeed be affected by mutations or epigenetic silencing that cause failure of Shp1-mediated homeostatic maintenance. This review will discuss the current knowledge of the cellular functions controlled by Shp1 in non-hematopoietic tissues and solid tumors, the mechanisms that regulate Shp1 expression, the role of its mutation/expression status in cancer and its value as potential target for cancer treatment. In addition, we report information gathered from the public available data from The Cancer Genome Atlas (TCGA) database on Shp1 genomic alterations and correlation with survival in solid cancers patients.

The diverse mechanisms and anticancer potential of naphthoquinones

Cancer is one of the leading causes of death around the world and although the different clinical approaches have helped to increase survival rates, incidence is still high and so its mortality. Chemotherapy is the only approach which is systemic, reaching cancer cells in all body tissues and the search for new potent and selective drugs is still an attractive field within cancer research. Naphthoquinones, natural and synthetic, have garnered much attention in the scientific community due to their pharmacological properties, among them anticancer action, and potential therapeutic significance. Many mechanisms of action have been reported which also depend on structural differences among them. Here, we describe some of the most relevant mechanisms of action reported so far for naphthoquinones and highlight novel targets which are being described in the literature. Furthermore, we gather some of the most impressive efforts done by researchers to harness the anticancer properties of these compounds through specifically designed structural modifications.

Emerging role of plumbagin: Cytotoxic potential and pharmaceutical relevance towards cancer therapy

Plumbagin is a naphthoquinone derived yellow crystalline phytochemical. Plumbagin has a wide range of biological effects including cytotoxicity against cancer cells both in vitro and in vivo. Due to the pleiotropic nature of plumbagin, it shows the anticancer effect by targeting several molecular mechanisms including apoptosis and autophagic pathways, cell cycle arrest, anti-angiogenic pathways, anti-invasion and anti-metastasis pathways. Among many signaling pathways the key regulatory genes regulated by plumbagin are NF-kβ, STAT3, and AKT, etc. Plumbagin is also a potent inducer of ROS, suppressor of cellular glutathione, and causes DNA strand break by oxidative DNA base damages. In vivo studies suggested that plumbagin significantly reduces the tumor weight and volume in dose-dependent manner without any side effects in tested model organisms. Another exciting aspect of plumbagin is the ability to re-sensitize the chemo and radioresistant cancer cells when used in combination or alone. Nano encapsulation of plumbagin overcomes the poor water solubility and bioavailability obstacles, enhancing the pharmaceutical relevance with better therapeutic efficacy. Moreover, plumbagin can be introduced as a future phytotherapeutic anticancer drug after fully satisfied preclinical and clinical trials.

TMEM119 promotes gastric cancer cell migration and invasion through STAT3 signaling pathway

Objective

TMEM119 is a member of transmembrane proteins family, which is abnormally expressed in human cancers and associated with tumorigenesis. In this study, we focused on the expression of TMEM119 and its role in cell invasion and migration in gastric cancer.

Methods

Real-time polymerase chain reaction, Western blotting, and immunohistochemistry were performed to examine the expression of TMEM119 in gastric cancer tissues and cell lines. After transfection with TMEM119 siRNA or recombined TMEM119-expressing vector, the invasion and migration ability of MKN45 and SGC-7901 cells was measured by transwell assay. The expression of TMEM119, p-STAT3, STAT3, VEGF, MMP2, and MMP9 proteins in SGC-7901 and MKN45 cells treated with TMEM119 siRNA, TMEM119-expressing vector, or AG490 was measured by Western blotting.

Results

We found that higher TMEM119 expression was found in gastric cancer tissues and cell lines and was associated with lower survival rate. TMEM119 knockdown inhibited SGC-7901 cell invasion and migration, along with the expression of p-STAT3, VEGF, MMP2, and MMP9. TMEM119 overexpression promoted MKN45 cell invasion and migration, along with the expression of p-STAT3, VEGF, MMP2, and MMP9. Additionally, AG490 treatment significantly corrected TMEM119-induced MKN45 cell migration and invasion and expression of p-STAT3, VEGF, MMP9, and MMP2 proteins.

Conclusion

The results indicated that TMEM119 promotes gastric cancer cell migration and invasion through activation of STAT3 signaling pathway, and TMEM119 may therefore act as a novel therapeutic target for gastric cancer.

Plumbagin, a natural naphthoquinone, inhibits the growth of esophageal squamous cell carcinoma cells through inactivation of STAT3

Although plumbagin, a natural naphthoquinone, has exhibited antiproliferative activity in numerous types of cancer, its anticancer potential in esophageal squamous cell carcinoma (ESCC) remains unclear. In the present study, the effect of plumbagin on the growth of ESCC cells was investigated in vitro and in vivo. ESCC cells were treated with plumbagin and tested for cell cycle distribution and apoptosis. The involvement of STAT3 signaling in the effect of plumbagin was examined. The results demonstrated that plumbagin treatment suppressed ESCC cell viability and proliferation, yet normal esophageal epithelial cell viability was not affected. Plumbagin treatment increased the proportion of cells in the G0/G1 phase of the cell cycle and decreased the proportion of cells in the S phase. Furthermore, plumbagin‑treated ESCC cells displayed a significantly greater % of apoptotic cells. Western blot analysis confirmed that plumbagin upregulated tumor protein p53 and cyclin‑dependent kinase inhibitor 1A (also known as p21), while it downregulated cyclin D1, cyclin‑dependent kinase 4, and induced myeloid leukemia cell differentiation protein Mcl‑1. Mechanistically, plumbagin inhibited STAT3 activation, and overexpression of constitutively active STAT3 reversed the plumbagin‑mediated growth suppression in ESCC cells. In vivo studies demonstrated that plumbagin delayed the growth of ESCC xenograft tumors and reduced STAT3 phosphorylation. Overall, plumbagin was demonstrated to target STAT3 signaling and to inhibit the growth of ESCC cells both in vitro and in vivo, suggesting that it may represent a potential anticancer agent for ESCC.

Arsenic trioxide attenuates STAT-3 activity and epithelial-mesenchymal transition through induction of SHP-1 in gastric cancer cells

BACKGROUND

We investigated the effect of arsenic trioxide (ATO) for inhibition of signal transducer and activator of transcription 3 (STAT3) and epithelial-mesenchymal transition (EMT) in gastric cancer cells, and the role of SH2 domain-containing phosphatase-1 (SHP-1) during this process.

METHODS

We used AGS cells, which showed minimal SHP-1 expression and constitutive STAT3 expression. After treatment of ATO, cellular migration and invasion were assessed by using wound closure assay, Matrigel invasion assay and 3-D culture invasion assay. To validate the role of SHP-1, pervanadate, a pharmacologic phosphatase inhibitor, and SHP-1 siRNA were used. Xenograft tumors were produced, and ATO or pervanadate were administered via intraperitoneal (IP) route.

RESULTS

Treatment of ATO 5 and 10 μM significantly decreased cellular migration and invasion in a dose-dependent manner. Western blot showed that ATO upregulated SHP-1 expression and downregulated STAT3 expression, and immunofluorescence showed upregulation with E-cadherin (epithelial marker) and downregulation of Snail1 (mesenchymal marker) expression by ATO treatment. Anti-migration and invasion effect and modulation of SHP-1/STAT3 axis by ATO were attenuated by pervanadate or SHP-1 siRNA. IP injection of ATO significantly decreased the xenograft tumor volume and upregulated SHP-1 expression, which were attenuated by co-IP injection of pervanadate.

CONCLUSION

Our data suggest that ATO inhibits STAT3 activity and EMT process by upregulation of SHP-1 in gastric cancer cells.

Plumbagin Suppresses the Invasion of HER2-Overexpressing Breast Cancer Cells through Inhibition of IKKα-Mediated NF-κB Activation

HER2-overexpressing breast cancers account for about 30% of breast cancer occurrences and have been correlated with increased tumor aggressiveness and invasiveness. The nuclear factor-κB (NF-κB) is overexpressed in a subset of HER2-positive breast cancers and its upregulation has been associated with the metastatic potential of HER2-overexpressing tumors. The present study aimed at determining the potential of plumbagin, a naturally occurring naphthoquinone, to inhibit the invasion of HER2-overexpressing breast cancer cells and determine the involvement of NF-κB inhibition in plumbagin-mediated cell invasion suppression. In the present research we showed that plumbagin inhibited the transcriptional activity of NF-κB in HER2-positive breast cancer cells. The suppression of NF-κB activation corresponded with the inhibition of NF-κB p65 phosphorylation and downregulation of NF-κB-regulated matrix metalloproteinase 9 (MMP-9) expression. Plumbagin suppressed the invasion of HER2-overexpressing breast cancer cells and the inhibition of cell invasion was associated with the ability of plumbagin to inhibit NF-κB transcriptional activity. The silencing of NF-κB p65 increased the sensitivity of HER2-overexpressing breast cancer cells to plumbagin-induced cell invasion inhibition. NF-κB inhibition was associated with IκB kinase α (IKKα) activity suppression and inhibition of IκBα phosphorylation and degradation. The knockdown of IKKα resulted in increased sensitivity of HER2-positive cells to plumbagin-induced suppression of NF-κB transcriptional activity and expression of MMP-9. In conclusion, plumbagin inhibits the invasion of HER2-overexpressing breast cancer cells through the inhibition of IKKα-mediated NF-κB activation and downregulation of NF-κB-regulated MMP-9 expression.

The roles of HOXB7 in promoting migration, invasion, and anti-apoptosis in gastric cancer

BACKGROUND AND AIM

The aim of this study was to compare HOXB7 expression level between gastric cancer and non-cancerous gastric tissues. Additionally, the functional effects of HOXB7, including its pro-migration or invasion and anti-apoptosis roles, were evaluated in gastric cancer cells.

METHODS

Both gene and protein expression levels of HOXB7 were examined in gastric cancer cell lines, and HOXB7 expression was compared between primary or metastatic gastric cancer tissues and chronic gastritis or intestinal metaplasia tissues. Functional studies included a wound healing assay, a Matrigel invasion assay, and an Annexin-V assay were performed, and Akt/PTEN activity was measured by western blotting.

RESULTS

Both gene and protein expression levels of HOXB7 could be clearly detected in various gastric cancer cell lines except MKN-28 cell. HOXB7 expression was significantly higher in primary or metastatic gastric cancer tissues than in chronic gastritis or intestinal metaplasia tissues. HOXB7 knockdown led to inhibition of cell invasion and migration, had an apoptotic effect, downregulated phosphor-Akt, and upregulated PTEN in AGS and SNU-638 cells. Reinforced expression of HOXB7 caused the opposite effects in MKN-28 and MKN-45 cells.

CONCLUSION

Our study suggests that HOXB7 has an oncogenic role in gastric cancer, which might be related to the modulation of Akt/PTEN activity to induce cell migration/invasion and anti-apoptotic effects.

Evaluation of the inhibition potential of plumbagin against cytochrome P450 using LC-MS/MS and cocktail approach

Plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone), a natural naphthoquinone compound isolated from roots of Plumbago zeylanica L., has drawn a lot of attention for its plenty of pharmacological properties including antidiabetes and anti-cancer. The aim of this study was to investigate the effects of plumbagin on CYP1A2, CYP2B1/6, CYP2C9/11, CYP2D1/6, CYP2E1 and CYP3A2/4 activities in human and rat liver and evaluate the potential herb-drug interactions using the cocktail approach. All CYP substrates and their metabolites were analyzed using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). Plumbagin presented non-time-dependent inhibition of CYP activities in both human and rat liver. In humans, plumbagin was not only a mixed inhibitor of CYP2B6, CYP2C9, CYP2D6, CYP2E1 and CYP3A4, but also a non-competitive inhibitor of CYP1A2, with Ki values no more than 2.16 μM. In rats, the mixed inhibition of CYP1A2 and CYP2D1, and competitive inhibition for CYP2B1, CYP2C11 and CYP2E1 with Ki values less than 9.93 μM were observed. In general, the relatively low Ki values of plumbagin in humans would have a high potential to cause the toxicity and drug interactions involving CYP enzymes.

Recent updates of precision therapy for gastric cancer: Towards optimal tailored management

Signaling pathways of gastric carcinogenesis and gastric cancer progression are being avidly studied to seek optimal treatment of gastric cancer. Among them, hepatocyte growth factor (HGF)/c-MET, phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) and janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) pathways have been widely investigated. Their aberrant expression or mutation has been significantly associated with advanced stage or poor prognosis of gastric cancer. Recently, aberrations of immune checkpoints including programmed cell death-1/programmed cell death ligand-1 (PD-1/PD-L1) have been suggested as an important step in the formation of a microenvironment favorable for gastric cancer. Accomplishments in basic research have led to the development of novel agents targeting these signaling pathways. However, phase III studies of selective anti-HGF/c-MET antibodies and mTOR inhibitor failed to show significant benefits in terms of overall survival and progression-free survival. Few agents directly targeting STAT3 have been developed. However, this target is still critical issue in terms of chemoresistance, and SH2-containing protein tyrosine phosphatase 1 might be a significant link to effectively inhibit STAT3 activity. Inhibition of PD-1/PD-L1 showed durable efficacy in phase I studies, and phase III evaluation is warranted. Therapeutic strategy to concurrently inhibit multiple tyrosine kinases is a reasonable option, however, lapatinib needs to be further evaluated to identify good responders. Regorafenib has shown promising effectiveness in prolonging progression-free survival in a phase II study. In this topic highlight, we review the biologic roles and outcomes of clinical studies targeting these signaling pathways.