Enhanced MDR1 expression and chemoresistance of cancer stem cells derived from glioblastoma

Involvement of Mitochondria in the Selective Response to Microsecond Pulsed Electric Fields on Healthy and Cancer Stem Cells in the Brain

In the last few years, pulsed electric fields have emerged as promising clinical tools for tumor treatments. This study highlights the distinct impact of a specific pulsed electric field protocol, PEF-5 (0.3 MV/m, 40 μs, 5 pulses), on astrocytes (NHA) and medulloblastoma (D283) and glioblastoma (U87 NS) cancer stem-like cells (CSCs). We pursued this goal by performing ultrastructural analyses corroborated by molecular/omics approaches to understand the vulnerability or resistance mechanisms triggered by PEF-5 exposure in the different cell types. Electron microscopic analyses showed that, independently of exposed cells, the main targets of PEF-5 were the cell membrane and the cytoskeleton, causing membrane filopodium-like protrusion disappearance on the cell surface, here observed for the first time, accompanied by rapid cell swelling. PEF-5 induced different modifications in cell mitochondria. A complete mitochondrial dysfunction was demonstrated in D283, while a mild or negligible perturbation was observed in mitochondria of U87 NS cells and NHAs, respectively, not sufficient to impair their cell functions. Altogether, these results suggest the possibility of using PEF-based technology as a novel strategy to target selectively mitochondria of brain CSCs, preserving healthy cells.

How Much is Enough? Impact of Efflux Transporters on Drug delivery Leading to Efficacy in the Treatment of Brain Tumors

The lack of effective chemotherapeutic agents for the treatment of brain tumors is a serious unmet medical need. This can be attributed, in part, to inadequate delivery through the blood-brain barrier (BBB) and the tumor-cell barrier, both of which have active efflux transporters that can restrict the transport of many potentially effective agents for both primary and metastatic brain tumors. This review briefly summarizes the components and function of the normal BBB with respect to drug penetration into the brain and the alterations in the BBB due to brain tumor that could influence drug delivery. Depending on what is rate-limiting a compound's distribution, the limited permeability across the BBB and the subsequent delivery into the tumor cell can be greatly influenced by efflux transporters and these are discussed in some detail. Given these complexities, it is necessary to quantify the extent of brain distribution of the active (unbound) drug to compare across compounds and to inform potential for use against brain tumors. In this regard, the metric, Kp,uu, a brain-to-plasma unbound partition coefficient, is examined and its current use is discussed. However, the extent of active drug delivery is not the only determinant of effective therapy. In addition to Kp,uu, drug potency is an important parameter that should be considered alongside drug delivery in drug discovery and development processes. In other words, to answer the question - How much is enough? - one must consider how much can be delivered with how much needs to be delivered.

Frizzled-3 suppression overcomes multidrug chemoresistance by Wnt/β-catenin signaling pathway inhibition in hepatocellular carcinoma cells

Multidrug resistance (MDR) is a major obstacle to the efficacy of hepatocellular carcinoma (HCC) chemotherapy. Previous studies have identified that low FZD3 predicted decreased survival after intraperitoneal versus intravenous-only chemotherapy in ovarian cancer. This study aimed to identify a potential target in HCC chemotherapy. The FZD3 expression variant in HCC cell lines was detected by RT-qPCR and western blotting. The FZD3 expression in the early recurrent HCC group (RE group) and the non-early recurrent HCC group (non-RE group) was measured by RT-qPCR. Then, the 50% inhibitory concentrations (IC50) in HCC cell lines were studied by MTT assay. TOP/FOP FLASH luciferase assay was performed to measure TCF-binding activities. We found that FZD3 was upregulated in three HCC cell lines, and the FZD3 expression was significantly higher in the RE group than in the non-RE group (P = 0.0344). A positive correlation between FZD3 and MDR1 was observed in HCC tissues (R2 = 0.6368, P = 0.0001). Then, we found that FZD3 knockdown significantly altered Huh-7 cell chemotherapeutic sensitivity to cisplatin [50.43 µM in the FZD3 siRNA (siFZD3) group vs 98.59 µM in the siRNA negative control (siNC) group; P = 0.007] or doxorubicin (7.43 µM in the siFZD3 group vs 14.93 µM in the siNC group; P = 0.017). TOP/FOP FLASH luciferase assay showed FZD3 could inhibit Wnt/β-catenin signaling in HCC cells. Moreover, FZD3 expression knockdown in SNU-449 and Huh-7 cells markedly reduced β-catenin and phosho-β-catenin (S37) protein expression, and Cyclin D1, c-myc and MDR1 were significantly decreased. This is the first study to describe the significantly increased FZD3 expression in patients with early recurrent HCC. FZD3 knockdown led to increased sensitivity to chemotherapy by Wnt/β-catenin signaling inhibition in HCC cell lines. Our study suggests FZD3 as a potential target for reversing chemoresistance in HCC.

Cancer-selective metabolic vulnerabilities in MYC-amplified medulloblastoma

MYC-driven medulloblastoma (MB) is an aggressive pediatric brain tumor characterized by therapy resistance and disease recurrence. Here, we integrated data from unbiased genetic screening and metabolomic profiling to identify multiple cancer-selective metabolic vulnerabilities in MYC-driven MB tumor cells, which are amenable to therapeutic targeting. Among these targets, dihydroorotate dehydrogenase (DHODH), an enzyme that catalyzes de novo pyrimidine biosynthesis, emerged as a favorable candidate for therapeutic targeting. Mechanistically, DHODH inhibition acts on target, leading to uridine metabolite scarcity and hyperlipidemia, accompanied by reduced protein O-GlcNAcylation and c-Myc degradation. Pyrimidine starvation evokes a metabolic stress response that leads to cell-cycle arrest and apoptosis. We further show that an orally available small-molecule DHODH inhibitor demonstrates potent mono-therapeutic efficacy against patient-derived MB xenografts in vivo. The reprogramming of pyrimidine metabolism in MYC-driven medulloblastoma represents an unappreciated therapeutic strategy and a potential new class of treatments with stronger cancer selectivity and fewer neurotoxic sequelae.

ABCB1 Is Frequently Methylated in Higher-Grade Gliomas and May Serve as a Diagnostic Biomarker of More Aggressive Tumors

ABCB1 belongs to a superfamily of membrane transporters that use ATP hydrolysis to efflux various endogenous compounds and drugs outside the cell. Cancer cells upregulate ABCB1 expression as an adaptive response to evade chemotherapy-mediated cell death. On the other hand, several reports highlight the role of the epigenetic regulation of ABCB1 expression. In fact, the promoter methylation of ABCB1 was found to be methylated in several tumor types, including gliomas, but its role as a biomarker is not fully established yet. Thus, the aim of this study was to analyze the methylation of the ABCB1 promoter in tumor tissues from 50 glioma patients to verify its incidence and to semi-quantitively detect ABCB1 methylation levels in order to establish its utility as a potential biomarker. The results of this study show a high interindividual variability in the ABCB1 methylation level of the samples derived from gliomas of different grades. Additionally, a positive correlation between ABCB1 methylation, the WHO tumor grade, and an IDH1 wild-type status has been observed. Thus, ABCB1 methylation can be regarded as a potential diagnostic or prognostic biomarker for glioma patients, indicating more aggressive tumors.

Cancer Stem Cells: From an Insight into the Basics to Recent Advances and Therapeutic Targeting

Cancer is characterized by an abnormal growth of the cells in an uncontrolled manner. These cells have the potential to invade and can eventually turn into malignancy, leading to highly fatal forms of tumor. Small subpopulations of cancer cells that are long-lived with the potential of excessive self-renewal and tumor formation are called cancer stem cells (CSCs) or cancer-initiating cells or tumor stem cells. CSCs can be found in tissues, such as breast, brain, lung, liver, ovary, and testis; however, their origin is still a matter of debate. These cells can differentiate and possess self-renewal capacity maintained by numerous intracellular signal transduction pathways, such as the Wnt/β-catenin signaling, Notch signaling, transforming growth factor-β signaling, and Hedgehog signaling. They can also contribute to numerous malignancies and are an important reason for tumor recurrence and metastasis because they are resistant to the known therapeutic strategies that mainly target the bulk of the tumor cells. This review contains collected and compiled information after analyzing published works of the last three decades. The goal was to gather information of recent breakthroughs related to CSCs, strategies to target CSCs' niche (e.g., nanotechnology with tumor biology), and their signaling pathways for cancer therapy. Moreover, the role of metformin, an antidiabetic drug, acting as a chemotherapeutic agent on CSCs by inhibiting cellular transformation and its selective killing is also addressed.

Temporal profiling of therapy resistance in human medulloblastoma identifies novel targetable drivers of recurrence

Medulloblastoma (MB) remains a leading cause of cancer-related mortality among children. The paucity of MB samples collected at relapse has hindered the functional understanding of molecular mechanisms driving therapy failure. New models capable of accurately recapitulating tumor progression in response to conventional therapeutic interventions are urgently needed. In this study, we developed a therapy-adapted PDX MB model that has a distinct advantage of generating human MB recurrence. The comparative gene expression analysis of MB cells collected throughout therapy led to identification of genes specifically up-regulated after therapy, including one previously undescribed in the setting of brain tumors, bactericidal/permeability-increasing fold-containing family B member 4 (BPIFB4). Subsequent functional validation resulted in a markedly diminished in vitro proliferation, self-renewal, and longevity of MB cells, translating into extended survival and reduced tumor burden in vivo. Targeting endothelial nitric oxide synthase, a downstream substrate of BPIFB4, impeded growth of several patient-derived MB lines at low nanomolar concentrations.

The Prognostic Value of CD133 in Predicting the Relapse and Recurrence Pattern of High-Grade Gliomas on MRI: A Meta-Analysis

Background

Cancer stem cells have been implicated in tumor relapse, tumor invasion, and cancer therapy resistance in high-grade gliomas; thus, characterizing cancer stem cell-related markers can help determine the prognosis of affected patients. Preclinical studies have reported that CD133 is implicated in tumor recurrence and cancer therapy resistance in high-grade gliomas; however, clinical studies have reported inconclusive results regarding its prognostic value in patients with high-grade gliomas.

Methods

We systematically searched the PubMed, Scopus, Web of Science, and Embase databases to obtain peer-reviewed studies published before March 10, 2021. Then, we conducted the current systematic review and meta-analysis based on the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statements. By applying the random-effect model, the effect size of studies investigating the progression-free survival (PFS), time to local recurrence (TTL), and time to distant recurrence (TTD) were calculated using RevMan version 5.4. The heterogeneity between the included studies was studied by the I² index and Cochran’s Q test. Egger test was performed on funnel plots to investigate the potential asymmetry and publication bias among the included studies using CMA version 2.

Results

With the 10% cut-off, CD133 protein overexpression is associated with the inferior PFS of patients with high-grade gliomas. Increased CD133 protein expression is associated with sooner distant tumor recurrence on MRI in glioblastoma patients and patients with high-grade gliomas and improved TTL on MRI in glioblastoma patients.

Conclusion

Based on the current evidence from 1086 patients with high-grade gliomas, CD133 overexpression is a valuable marker to predict tumor relapse and tumor recurrence patterns in patients with high-grade gliomas.

The interaction between PDCD4 and YB1 is critical for cervical cancer stemness and cisplatin resistance

Cancer multidrug resistance (MDR) is existence in stem cell-like cancer cells characterized by stemness including high-proliferation and self-renewal. Programmed cell death 4 (PDCD4), as a proapoptotic gene, whether it engaged in cancer stemness and cisplatin resistance is still unknown. Here we showed that PDCD4 expressions in Hela/DDP (cisplatin resistance) cells were lower than in parental Hela cells. Moreover, the levels of drug resistance genes and typical stemness markers were markedly elevated in Hela/DDP cells. In vivo, xenograft tumor assay confirmed that knockdown of PDCD4 accelerated the grafted tumor growth. In vitro, colony formation and MTT assay demonstrated that PDCD4 overexpression inhibited cells proliferation in conditions with or without cisplatin. By contrast, PDCD4 deficiency provoked cell proliferation and cisplatin resistance. On mechanism, PDCD4 decreased the protein levels of pAKT and pYB1, accompanied by reduced MDR1 expression. Correspondingly, luciferase reporter assay showed PDCD4 regulated MDR1 promoter activity entirely relied on YB1. Furthermore, Ch-IP, GST-pulldown, and Co-IP assays provided novel evidence that PDCD4 could directly bind with YB1 by the nucleolar localization signal (NOLS) segment, causing the reduced YB1 binding into the MDR1 promoter region through blocking YB1 nucleus translocation, triggering the decreased MDR1 transcription. Taken together, PDCD4-pAKT-pYB1 forms the integrated molecular network to regulate MDR1 transcription during the process of stemness-associated cisplatin resistance.

A novel synthetic microtubule inhibitor exerts antiproliferative effects in multidrug resistant cancer cells and cancer stem cells

The success of cancer chemotherapy is limited by multidrug resistance (MDR), which is mainly caused by P-glycoprotein (P-gp) overexpression. In the present study, we describe a novel microtubule inhibitor, 5-(N-methylmaleimid-3-yl)-chromone (SPC-160002), that can be used to overcome MDR. A synthetic chromone derivative, SPC-160002, showed a broad spectrum of anti-proliferative effects on various human cancer cells without affecting P-gp expression and its drug efflux function. Treatment with SPC-160002 arrested the cell cycle at the M phase, as evidenced using fluorescence-activated cell sorting analysis, and increased the levels of mitotic marker proteins, including cyclin B, pS10-H3, and chromosomal passenger complex. This mitotic arrest by SPC-160002 was mediated by promoting and stabilizing microtubule polymerization, similar to the mechanism observed in case of taxane-based drugs. Furthermore, SPC-160002 suppressed the growth and sphere-forming activity of cancer stem cells. Our data herein strongly suggest that SPC-160002, a novel microtubule inhibitor, can be used to overcome MDR and can serve as an attractive candidate for anticancer drugs.

Role of glioblastoma stem cells in cancer therapeutic resistance: a perspective on antineoplastic agents from natural sources and chemical derivatives

Glioblastoma (GBM) is the highest-grade form of glioma, as well as one of the most aggressive types of cancer, exhibiting rapid cellular growth and highly invasive behavior. Despite significant advances in diagnosis and therapy in recent decades, the outcomes for high-grade gliomas (WHO grades III-IV) remain unfavorable, with a median overall survival time of 15–18 months. The concept of cancer stem cells (CSCs) has emerged and provided new insight into GBM resistance and management. CSCs can self-renew and initiate tumor growth and are also responsible for tumor cell heterogeneity and the induction of systemic immunosuppression. The idea that GBM resistance could be dependent on innate differences in the sensitivity of clonogenic glial stem cells (GSCs) to chemotherapeutic drugs/radiation prompted the scientific community to rethink the understanding of GBM growth and therapies directed at eliminating these cells or modulating their stemness. This review aims to describe major intrinsic and extrinsic mechanisms that mediate chemoradioresistant GSCs and therapies based on antineoplastic agents from natural sources, derivatives, and synthetics used alone or in synergistic combination with conventional treatment. We will also address ongoing clinical trials focused on these promising targets. Although the development of effective therapy for GBM remains a major challenge in molecular oncology, GSC knowledge can offer new directions for a promising future.

Role of ATP-Binding Cassette Transporter Proteins in CNS Tumors: Resistance- Based Perspectives and Clinical Updates

Despite gigantic advances in medical research and development, chemotherapeutic resistance remains a major challenge in complete remission of CNS tumors. The failure of complete eradication of CNS tumors has been correlated with the existence of several factors including overexpression of transporter proteins. To date, 49 ABC-transporter proteins (ABC-TPs) have been reported in humans, and the evidence of their strong association with chemotherapeutics' influx, dissemination, and efflux in CNS tumors, is growing. Research studies on CNS tumors are implicating ABC-TPs as diagnostic, prognostic and therapeutic biomarkers that may be utilised in preclinical and clinical studies. With the current advancements in cell biology, molecular analysis of genomic and transcriptomic interplay, and protein homology-based drug-transporters interaction, our research approaches are streamlining the roles of ABC-TPs in cancer and multidrug resistance. Potential inhibitors of ABC-TP for better clinical outcomes in CNS tumors have emerged. Elacridar has shown to enhance the chemo-sensitivity of Dasatanib and Imatinib in various glioma models. Tariquidar has improved the effectiveness of Temozolomide's in CNS tumors. Although these inhibitors have been effective in preclinical settings, their clinical outcomes have not been as significant in clinical trials. Thus, to have a better understanding of the molecular evaluations of ABC-TPs, as well as drug-interactions, further research is being pursued in research labs. Our lab aims to better comprehend the biological mechanisms involved in drug resistance and to explore novel strategies to increase the clinical effectiveness of anticancer chemotherapeutics, which will ultimately improve clinical outcomes.

Targeting Glioma Stem Cells

Only a small fraction of the tumor cell population, glioma-initiating cells (GICs) help glioblastoma propagate, invade, evade immune recognition, repair DNA in response to radiation more efficiently, remodel the microenvironment for optimal growth, and actively pump out chemotherapies. Recent data hint that efforts toward GIC characterization and quantification can help predict patient outcomes, and yet the different subpopulations of GICs remain incompletely understood. A better understanding of GIC subtypes and functions proves critical for engineering targeted therapies. Challenges for doing so are discussed, and dopamine receptor antagonists are introduced as new means to enhance the efficacy of the current standard-of-care against GICs.

SOX2 in cancer stemness: tumor malignancy and therapeutic potentials

Cancer stem cells (CSCs), a minor subpopulation of tumor bulks with self-renewal and seeding capacity to generate new tumors, posit a significant challenge to develop effective and long-lasting anti-cancer therapies. The emergence of drug resistance appears upon failure of chemo-/radiation therapy to eradicate the CSCs, thereby leading to CSC-mediated clinical relapse. Accumulating evidence suggests that transcription factor SOX2, a master regulator of embryonic and induced pluripotent stem cells, drives cancer stemness, fuels tumor initiation, and contributes to tumor aggressiveness through major drug resistance mechanisms like epithelial-to-mesenchymal transition, ATP-binding cassette drug transporters, anti-apoptotic and/or pro-survival signaling, lineage plasticity, and evasion of immune surveillance. Gaining a better insight and comprehensive interrogation into the mechanistic basis of SOX2-mediated generation of CSCs and treatment failure might therefore lead to new therapeutic targets involving CSC-specific anti-cancer strategies.

Drug Resistance in Glioblastoma: The Two Faces of Oxidative Stress

Glioblastomas (GBM) are the most common primary brain tumor with a median survival of 15 months. A population of cells with stem cell properties (glioblastoma stem cells, GSCs) drives the initiation and progression of GBM and is localized in specialized microenvironments which support their behavior. GBM are characterized as extremely resistant to therapy, resulting in tumor recurrence. Reactive oxygen species (ROS) control the cellular stability by influencing different signaling pathways. Normally, redox systems prevent cell oxidative damage; however, in gliomagenesis, the cellular redox mechanisms are highly impaired. Herein we review the dual nature of the redox status in drug resistance. ROS generation in tumor cells affects the cell cycle and is involved in tumor progression and drug resistance in GBM. However, excess ROS production has been found to induce cell death programs such as apoptosis and autophagy. Since GBM cells have a high metabolic rate and produce high levels of ROS, metabolic adaptation in these cells plays an essential role in resistance to oxidative stress-induced cell death. Finally, the microenvironment with the stromal components participates in the enhancement of the oxidative stress to promote tumor progression and drug resistance.

The Great Escape: The Power of Cancer Stem Cells to Evade Programmed Cell Death

Cancer is one of the primary causes of death worldwide. Tumour malignancy is related to tumor heterogeneity, which has been suggested to be due to a small subpopulation of tumor cells named cancer stem cells (CSCs). CSCs exert a key role in metastasis development, tumor recurrence, and also epithelial-mesenchymal transition, apoptotic resistance, self-renewal, tumorigenesis, differentiation, and drug resistance. Several current therapies fail to eradicate tumors due to the ability of CSCs to escape different programmed cell deaths. Thus, developing CSC-selective and programmed death-inducing therapeutic approaches appears to be of primary importance. In this review, we discuss the main programmed cell death occurring in cancer and the promising CSC-targeting agents developed in recent years. Even if the reported studies are encouraging, further investigations are necessary to establish a combination of agents able to eradicate CSCs or inhibit their growth and proliferation.

Expression of P-gp in Glioblastoma: What we can Learn from Brain Development

P-Glycoprotein (P-gp) is a 170-kDa transmembrane glycoprotein that works as an efflux pump and confers multidrug resistance (MDR) in normal tissues and tumors, including nervous tissues and brain tumors. In the developing telencephalon, the endothelial expression of P-gp, and the subcellular localization of the transporter at the luminal endothelial cell (EC) plasma membrane are early hallmarks of blood-brain barrier (BBB) differentiation and suggest a functional BBB activity that may complement the placental barrier function and the expression of P-gp at the blood-placental interface. In early fetal ages, P-gp has also been immunolocalized on radial glia cells (RGCs), located in the proliferative ventricular zone (VZ) of the dorsal telencephalon and now considered to be neural progenitor cells (NPCs). RG-like NPCs have been found in many regions of the developing brain and have been suggested to give rise to neural stem cells (NSCs) of adult subventricular (SVZ) neurogenic niches. The P-gp immunosignal, associated with RG-like NPCs during cortical histogenesis, progressively decreases in parallel with the last waves of neuroblast migrations, while 'outer' RGCs and the deriving astrocytes do not stain for the efflux transporter. These data suggest that in human glioblastoma (GBM), P-gp expressed by ECs may be a negligible component of tumor MDR. Instead, tumor perivascular astrocytes may dedifferentiate and resume a progenitor-like P-gp activity, becoming MDR cells and contribute, together with perivascular P-gpexpressing glioma stem-like cells (GSCs), to the MDR profile of GBM vessels. In conclusion, the analysis of Pgp immunolocalization during brain development may contribute to identify the multiple cellular sources in the GBM vessels that may be involved in P-gp-mediated chemoresistance and can be responsible for GBM therapy failure and tumor recurrence.

Cancer stem cell plasticity in glioblastoma multiforme: a perspective on future directions in oncolytic virotherapy

The cancer stem cell (CSC) hypothesis suggests that a rare population of stem-like cells underpin tumorigenesis. Oncolytic viruses (OVs) demonstrate novel mechanisms of targeting the elusive CSCs with greater selectivity - promising therapeutic potential against solid tumors such as glioblastoma (GBM) that are resistant to conventional treatment. In general, OVs have failed to translate the efficacy from bench to bedside. The success of OVs rely on the hypothesis that eliminating CSCs is key to preventing recurrence. However, newly emerging evidence of CSC plasticity challenge this hypothesis by proposing that the CSC pool can be regenerated from non-CSCs post-treatment. We review this evidence surrounding the CSC hypothesis to propose an original perspective on why several advanced OVs may be failing to reflect their true potential in clinical trials. We argue that preventing non-CSC to CSC dedifferentiation may be critical to achieving long-term treatment efficacy in future OV clinical trials.

Advances in histone deacetylase inhibitors in targeting glioblastoma stem cells

Glioblastoma multiforme (GBM) is a lethal grade IV glioma (WHO classification) and widely prevalent primary brain tumor in adults. GBM tumors harbor cellular heterogeneity with the presence of a small subpopulation of tumor cells, described as GBM cancer stem cells (CSCs) that pose resistance to standard anticancer regimens and eventually mediate aggressive relapse or intractable progressive GBM. Existing conventional anticancer therapies for GBM do not target GBM stem cells and are mostly palliative; therefore, exploration of new strategies to target stem cells of GBM has to be prioritized for the development of effective GBM therapy. Recent developments in the understanding of GBM pathophysiology demonstrated dysregulation of epigenetic mechanisms along with the genetic changes in GBM CSCs. Altered expression/activity of key epigenetic regulators, especially histone deacetylases (HDACs) in GBM stem cells has been associated with poor prognosis; inhibiting the activity of HDACs using histone deacetylase inhibitors (HDACi) has been promising as mono-therapeutic in targeting GBM and in sensitizing GBM stem cells to an existing anticancer regimen. Here, we review the development of pan/selective HDACi as potential anticancer agents in targeting the stem cells of glioblastoma as a mono or combination therapy.

Oncogenic Ras downregulates mdr1b expression through generation of reactive oxygen species

In the present study, we investigated the effect of oncogenic H-Ras on rat mdr1b expression in NIH3T3 cells. The constitutive expression of H-RasV12 was found to downregulate the mdr1b promoter activity and mdr1b mRNA expression. The doxorubicin-induced mdr1b promoter activity of the H-RasV12 expressing NIH3T3 cells was markedly lower than that of control NIH3T3 cells. Additionally, there is a positive correlation between the level of H-RasV12 expression and a sensitivity to doxorubicin toxicity. To examine the detailed mechanism of H-RasV12-mediated down-regulation of mdr1b expression, antioxidant N-acetylcysteine (NAC) and NADPH oxidase inhibitor diphenylene iodonium (DPI) were used. Pretreating cells with either NAC or DPI significantly enhanced the oncogenic H-Ras-mediated down-regulation of mdr1b expression and markedly prevented doxorubicin-induced cell death. Moreover, NAC and DPI treatment led to a decrease in ERK activity, and the ERK inhibitors PD98059 or U0126 enhanced the mdr1b-Luc activity of H-RasV12-NIH3T3 and reduced doxorubicin-induced apoptosis. These data suggest that RasV12 expression could downregulate mdr1b expression through intracellular reactive oxygen species (ROS) production, and ERK activation induced by ROS, is at least in part, contributed to the downregulation of mdr1b expression.

Validation of Thiosemicarbazone Compounds as P-Glycoprotein Inhibitors in Human Primary Brain-Blood Barrier and Glioblastoma Stem Cells

P-glycoprotein (Pgp) is highly expressed on blood-brain barrier (BBB) and glioblastoma (GB) cells, particularly on cancer stem cells (SC). Pgp recognizes a broad spectrum of substrates, limiting the therapeutic efficacy of several chemotherapeutic drugs in eradicating GB SC. Finding effective and safe inhibitors of Pgp that improve drug delivery across the BBB and target GB SC is open to investigation. We previously identified a series of thiosemicarbazone compounds that inhibit Pgp with an EC₅₀ in the nanomolar range, and herein, we investigate the efficacy of three of them in bypassing Pgp-mediated drug efflux in primary human BBB and GB cells. At 10 nM, the compounds were not cytotoxic for the brain microvascular endothelial hCMEC/D3 cell line, but they markedly enhanced the permeability of the Pgp-substrate doxorubicin through the BBB. Thiosemicarbazone derivatives increased doxorubicin uptake in GB, with greater effects in the Pgp-rich SC clones than in the differentiated clones derived from the same tumor. All compounds increased intratumor doxorubicin accumulation and consequent toxicity in GB growing under competent BBB, producing significant killing of GB SC. The compounds crossed the BBB monolayer. The most stable derivative, 10a, had a half-life in serum of 4.2 h. The coadministration of doxorubicin plus 10a significantly reduced the growth of orthotopic GB-SC xenografts, without eliciting toxic side effects. Our work suggests that the thiosemicarbazone compounds are able to transform doxorubicin, a prototype BBB-impermeable drug, into a BBB-permeable drug. Bypassing Pgp-mediated drug efflux in both BBB and GB SC, thiosemicarbazones might increase the success of chemotherapy in targeting GB SC, which represent the most aggressive and difficult components to eradicate.

Characterization of Ablation Thresholds for 3D-Cultured Patient-Derived Glioma Stem Cells in Response to High-Frequency Irreversible Electroporation

High-frequency irreversible electroporation (H-FIRE) is a technique that uses pulsed electric fields that have been shown to ablate malignant cells. In order to evaluate the clinical potential of H-FIRE to treat glioblastoma (GBM), a primary brain tumor, we have studied the effects of high-frequency waveforms on therapy-resistant glioma stem-like cell (GSC) populations. We demonstrate that patient-derived GSCs are more susceptible to H-FIRE damage than primary normal astrocytes. This selectivity presents an opportunity for a degree of malignant cell targeting as bulk tumor cells and tumor stem cells are seen to exhibit similar lethal electric field thresholds, significantly lower than that of healthy astrocytes. However, neural stem cell (NSC) populations also exhibit a similar sensitivity to these pulses. This observation may suggest that different considerations be taken when applying these therapies in younger versus older patients, where the importance of preserving NSC populations may impose different restrictions on use. We also demonstrate variability in threshold among the three patient-derived GSC lines studied, suggesting the need for personalized cell-specific characterization in the development of potential clinical procedures. Future work may provide further useful insights regarding this patient-dependent variability observed that could inform targeted and personalized treatment.

MDR1 in immunity: friend or foe?

MDR1 is an ATP-dependent transmembrane transporter primarily studied for its role in the detoxification of tissues and for its implication in resistance of tumor cells to chemotherapy treatment. Several studies also report on its expression on immune cells where it plays a protective role from xenobiotics and toxins. This review provides an overview of what is known on MDR1 expression in immune cells in human, and its implications in different pathologies and their treatment options.

Update on the effects of the sodium pump α1 subunit on human glioblastoma: from the laboratory to the clinic

INTRODUCTION

Glioblastoma is a debilitating disease that is associated with poor prognosis and a very limited response to therapies; thus, molecularly targeted therapeutics and personalized therapy are urgently needed. The Na⁺/K⁺-ATPase sodium pump is a transmembrane protein complex that has recently been recognized as an important transducer and integrator of various signals. The sodium pump α1 subunit, which is highly expressed in most glioblastomas compared with that in normal brain tissues, is an emerging cancer target that merits further investigation.

AREAS COVERED

The purpose of this narrative review is to explore the important roles of the sodium pump α1 subunit in glioblastoma and analyze its potential therapeutic applications.

EXPERT OPINION

Expression of the sodium pump α1 subunit in glioblastoma tissues is generally higher than that in normal tissues. Sodium pump α1 subunit-mediated pivotal antiglioblastoma signaling pathways have been reviewed, and their impact on the sensitivity of glioblastoma cells to anticancer drugs has recently been clarified. In addition, various pharmacologically optimized sodium pump inhibitors have recently reached early clinical trials, and explorations of sodium pump α1 subunit inhibitors may hold promise for the development of stratification strategies in which patients are treated based on their isoform expression status.

Celecoxib enhances the therapeutic efficacy of epirubicin for Novikoff hepatoma in rats

Epirubicin is a chemotherapy agent for hepatocellular carcinoma (HCC). However, the outcome of HCC patients receiving epirubicin remains unsatisfactory. Moreover, our previous study indicated that celecoxib suppresses HCC progression and liver cancer stemness. This study evaluated the potential of celecoxib to serve as a complementary therapy during epirubicin treatment. Cell proliferation, apoptosis, invasiveness, and anchorage-independent growth were analyzed in hepatoma cells. Therapeutic efficacy was validated in rat orthotopic Novikoff hepatoma. After animal sacrifice, the antitumor mechanism of celecoxib and epirubicin combined therapy was investigated by histological analysis. Celecoxib enhanced the cytotoxic activity of epirubicin in HCC cells by promoting apoptosis. Besides, celecoxib potentiated the antineoplastic function of epirubicin in inhibiting the invasiveness and anchorage-independent growth of HCC cells. Ultrasound monitoring showed that combined therapy was more potent than either therapy alone in perturbing HCC progression. Consistently, the size and weight of dissected HCC tissues from rats receiving combined therapy were smallest among all groups. HCC treated with combined therapy exhibited the highest prevalence of apoptotic cells, which was accompanied by reduced proliferating and angiogenic activities in tumor tissues. Moreover, the expression levels of cancer stemness markers (CD44 and CD133) and drug transporter MDR-1 were significantly diminished in rats receiving combined therapy. Besides, celecoxib treatment increased the infiltration of cytotoxic T lymphocytes (CTLs) and reduced the number of regulatory T cells (Tregs), tumor-associated macrophages (TAMs), and the expression of immune checkpoint PD-L1 in HCC tissues during epirubicin therapy. Celecoxib augmented the therapeutic efficacy while modulated cancer stemness and antitumor immunity. Thus, celecoxib may serve as complementary therapy to improve the outcome of patients with advanced HCC during epirubicin treatment.

Natural products: a hope for glioblastoma patients

Glioblastoma (GBM) is one of the most aggressive malignant tumors with an overall dismal survival averaging one year despite multimodality therapeutic interventions including surgery, radiotherapy and concomitant and adjuvant chemotherapy. Few drugs are FDA approved for GBM, and the addition of temozolomide (TMZ) to standard therapy increases the median survival by only 2.5 months. Targeted therapy appeared promising in in vitro monolayer cultures, but disappointed in preclinical and clinical trials, partly due to the poor penetration of drugs through the blood brain barrier (BBB). Cancer stem cells (CSCs) have intrinsic resistance to initial chemoradiation therapy (CRT) and acquire further resistance via deregulation of many signaling pathways. Due to the failure of classical chemotherapies and targeted drugs, research efforts focusing on the use of less toxic agents have increased. Interestingly, multiple natural compounds have shown antitumor and apoptotic effects in TMZ resistant and p53 mutant GBM cell lines and also displayed synergistic effects with TMZ. In this review, we have summarized the current literature on natural products or product analogs used to modulate the BBB permeability, induce cell death, eradicate CSCs and sensitize GBM to CRT.

Obstacles to Brain Tumor Therapy: Key ABC Transporters

The delivery of cancer chemotherapy to treat brain tumors remains a challenge, in part, because of the inherent biological barrier, the blood-brain barrier. While its presence and role as a protector of the normal brain parenchyma has been acknowledged for decades, it is only recently that the important transporter components, expressed in the tightly knit capillary endothelial cells, have been deciphered. These transporters are ATP-binding cassette (ABC) transporters and, so far, the major clinically important ones that functionally contribute to the blood-brain barrier are ABCG2 and ABCB1. A further limitation to cancer therapy of brain tumors or brain metastases is the blood-tumor barrier, where tumors erect a barrier of transporters that further impede drug entry. The expression and regulation of these two transporters at these barriers, as well as tumor derived alteration in expression and/or mutation, are likely obstacles to effective therapy.

Resistance to Cell Death and Its Modulation in Cancer Stem Cells

Accumulating evidence has demonstrated that human cancers arise from various tissues of origin that initiate from cancer stem cells (CSCs) or cancer-initiating cells. The extrinsic and intrinsic apoptotic pathways are dysregulated in CSCs, and these cells play crucial roles in tumor initiation, progression, cell death resistance, chemo- and radiotherapy resistance, and tumor recurrence. Understanding CSC-specific signaling proteins and pathways is necessary to identify specific therapeutic targets that may lead to the development of more efficient therapies selectively targeting CSCs. Several signaling pathways-including the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR), maternal embryonic leucine zipper kinase (MELK), NOTCH1, and Wnt/Β-catenin&and expression of the CSC markers CD133, CD24, CD44, Oct4, Sox2, Nanog, and ALDH1A1 maintain CSC properties. Studying such pathways may help to understand CSC biology and lead to the development of potential therapeutic interventions to render CSCs more sensitive to cell death triggered by chemotherapy and radiation therapy. Moreover, recent demonstrations of dedifferentiation of differentiated cancer cells into CSC-like cells have created significant complexity in the CSCs hypothesis. Therefore, any successful therapeutic agent or combination of drugs for cancer therapy must eliminate not only CSCs but differentiated cancer cells and the entire bulk of tumor cells. This review article expands on the CSC hypothesis and paradigm with respect to major signaling pathways and effectors that regulate CSC apoptosis resistance. Moreover, selective CSC apoptotic modulators and their therapeutic potential for making tumors more responsive to therapy are discussed. The use of novel therapies, including small-molecule inhibitors of specific proteins in signaling pathways that regulate stemness, proliferation and migration of CSCs, immunotherapy, and noncoding microRNAs may provide better means of treating CSCs.

Overexpression of TIMP-1 and Sensitivity to Topoisomerase Inhibitors in Glioblastoma Cell Lines

The multifunctional protein - tissue inhibitor of metalloproteinases-1 (TIMP-1) - has been associated with a poor prognosis in several types of cancers including glioblastomas. In addition, TIMP-1 has been associated with decreased response to chemotherapy, and especially the efficacy of the family of topoisomerase (TOP) inhibitors has been related to TIMP-1. As a second line treatment of glioblastomas, the vascular endothelial growth factor (VEGF) antibody bevacizumab is administered in combination with the TOP1 inhibitor irinotecan and glioblastoma cell levels of TIMP-1 could therefore potentially influence the efficacy of such treatment. In the present study, we aimed to investigate whether a high TIMP-1 expression in glioblastoma cell lines would affect the sensitivity to TOP inhibitors, and whether TIMP-1 overexpressing cells would have alterered growth and invasion. We established TIMP-1 overexpressing subclones from two human glioblastoma cell lines. TIMP-1 overexpressing U87MG cells were significantly more resistant than low TIMP-1 expressing clones and parental cells when exposed to SN-38 (TOP1 inhibitor) or epirubicin (TOP2 inhibitor). No significant differences were observed for the TIMP-1 transfected A172 cells. Implantation of both U87MG and A172 spheroids into organotypic brain slice cultures revealed a reduced growth of TIMP-1 overexpressing U87MG spheroids, however, no significant differences in invasion were observed. The present study suggests that TIMP-1 overexpression reduces the effect of TOP inhibitors in glioblastoma. TIMP-1 also appeared to reduce spheroid growth, but did not influence invasion. Whether TIMP-1 plays a role in irinotecan resistance and has a predictive potential in glioblastoma patients remains to be elucidated.

Secreted heat shock protein 90 promotes prostate cancer stem cell heterogeneity

Heat-shock protein 90 (Hsp90), a highly conserved molecular chaperone, is frequently upregulated in tumors, and remains an attractive anti-cancer target. Hsp90 is also found extracellularly, particularly in tumor models. Although extracellular Hsp90 (eHsp90) action is not well defined, eHsp90 targeting attenuates tumor invasion and metastasis, supporting its unique role in tumor progression. We herein investigated the potential role of eHsp90 as a modulator of cancer stem-like cells (CSCs) in prostate cancer (PCa). We report a novel function for eHsp90 as a facilitator of PCa stemness, determined by its ability to upregulate stem-like markers, promote self-renewal, and enhance prostasphere growth. Moreover, eHsp90 increased the side population typically correlated with the drug-resistant phenotype. Intriguingly, tumor cells with elevated surface eHsp90 exhibited a marked increase in stem-like markers coincident with increased expression of the epithelial to mesenchymal (EMT) effector Snail, indicating that surface eHsp90 may enrich for a unique CSC population. Our analysis of distinct effectors modulating the eHsp90-dependent CSC phenotyperevealed that eHsp90 is a likely facilitator of stem cell heterogeneity. Taken together, our findings provide unique functional insights into eHsp90 as a modulator of PCa plasticity, and provide a framework towards understanding its role as a driver of tumor progression.

n-Butylidenephthalide Regulated Tumor Stem Cell Genes EZH2/AXL and Reduced Its Migration and Invasion in Glioblastoma

Glioblastoma (GBM) is one of the most common and aggressive types of brain tumor. Due to its highly recurrent rate and poor prognosis, the overall survival time with this type of tumor is only 20–21 months. Recent knowledge suggests that its recurrence is in part due to the presence of cancer stem cells (CSCs), which display radioresistant, chemoresistant, self-renewal and tumorigenic potential. Enhancers of Zeste 2 (EZH2) and AXL receptor tyrosine kinase (AXL) are both highly expressed in GBM. Additionally, they are an essential regulator involved in CSCs maintenance, migration, invasion, epithelial-to-mesenchymal transition (EMT), stemness, metastasis and patient survival. In this study, we used a small molecule, n-butylidenephthalide (BP), to assess the anti-GBM stem-like cells potential, and then tried to find out the associated genes involved with regulation in migration and invasion. We demonstrated that BP reduced the expression of AXL and stemness related genes in a dose-dependent manner. The migratory and invasive capabilities of GBM stem-like cells could be reduced by AXL/EZH2. Finally, in the overexpression of AXL, EZH2 and Sox2 by transfection in GBM stem-like cells, we found that AXL/EZH2/TGF-β1, but not Sox2, might be a key regulator in tumor invasion, migration and EMT. These results might help in the development of a new anticancer compound and can be a target for treating GBM.

Requirement of ABC transporter inhibition and Hoechst 33342 dye deprivation for the assessment of side population-defined C6 glioma stem cell metabolism using fluorescent probes

Background

Elucidating the precise properties of cancer stem cells (CSCs) is indispensable for the development of effective therapies against tumors, because CSCs are key drivers of tumor development, metastasis and relapse. We previously reported that the Hoechst 33342 dye-low staining side population (SP) method can enrich for CSCs in the C6 glioma cell line, and that the positively stained main population (MP) cells are non-CSCs. Presence of cancer stem-like SP cells is reported in various types of cancer. Although altered cellular energy metabolism is a hallmark of cancer, very little has been studied on the applicability of fluorescent probes for the understanding of CSC energy metabolism.

Methods

The metabolic status of C6 SP and MP cells are evaluated by CellROX, MitoTracker Green (MTG) and JC-1 for cellular oxidative stress, mitochondrial amount, and mitochondrial membrane potential, respectively.

Results

SP cells were found to exhibit significantly lower fluorescent intensities of CellROX and MTG than MP cells. However, inhibition of ATP binding cassette (ABC) transporters by verapamil enhanced the intensities of these probes in SP cells to the levels similar to those in MP cells, indicating that SP cells expel the probes outside of the cells through ABC transporters. Next, SP cells were stained with JC-1 dye which exhibits membrane potential dependent accumulation in mitochondrial matrix, followed by formation of aggregates. The mitochondrial membrane potential indicated by the aggregates of JC-1 was 5.0-fold lower in SP cells than MP cells. Inhibition of ABC transporters enhanced the fluorescent intensities of the JC-1 aggregates in both SP and MP cells, the former of which was still 2.2-fold lower than the latter. This higher JC-1 signal in MP cells was further found to be due to the Hoechst 33342 dye existing in MP cells. When SP and MP cells were recultured to deprive the intracellular Hoechst 33342 dye and then stained with JC-1 in the presence of verapamil, the intensities of JC-1 aggregates in such SP and MP cells became comparable.

Conclusion

Inhibiting ABC transporters and depriving Hoechst 33342 dye are required for the accurate assessment of side population-defined C6 glioma stem cell metabolism using fluorescent probes.

Involvement of NRF2 Signaling in Doxorubicin Resistance of Cancer Stem Cell-Enriched Colonospheres

Cancer stem cells (CSCs) are a subset of tumor cells, which are characterized by resistance against chemotherapy and environmental stress, and are known to cause tumor relapse after therapy. A number of molecular mechanisms underlie the chemoresistance of CSCs, including high expression levels of drug efflux transporters. We investigated the role of the antioxidant transcription factor NF-E2-related factor 2 (NRF2) in chemoresistance development, using a CSC-enriched colonosphere system. HCT116 colonospheres were more resistant to doxorubicin-induced cell death and expressed higher levels of drug efflux transporters such as P-glycoprotein (Pgp) and breast cancer resistance protein (BCRP) compared to HCT116 monolayers. Notably, levels of NRF2 and expression of its target genes were substantially elevated in colonospheres, and these increases were linked to doxorubicin resistance. When NRF2 expression was silenced in colonospheres, Pgp and BCRP expression was downregulated, and doxorubicin resistance was diminished. Collectively, these results indicate that NRF2 activation contributes to chemoresistance acquisition in CSC-enriched colonospheres through the upregulation of drug efflux transporters.

Aminopeptidase N (APN/CD13) as a target molecule for scirrhous gastric cancer

BACKGROUND

Scirrhous gastric cancer is associated with peritoneal dissemination and advanced lymph node metastasis from an early stage, and the prognosis is still poor. In this study, we aimed to analyze candidate molecules for targeted therapy of scirrhous gastric cancer. We searched for molecules/metabolic activity that might be predominantly expressed in a subpopulation of scirrhous gastric cancer cells and might function as cancer stem cell markers.

RESULTS

For this purpose, we investigated the expression of various cell surface markers and of aldehyde dehydrogenase (ALDH) activity. These analyses showed that the scirrhous gastric cancer cell lines HSC-58 and HSC-44PE heterogeneously expressed CD13, while CD44, CDCP1, EpCAM and ABCG2 were expressed uniformly. Moreover, 10% of the total HSC-58 cell population expressed ALDH enzyme activity. A subpopulation of cells strongly positive for ALDH also expressed high levels of CD13, both of which are known as cancer stem cell markers. HSC-58 cells expressing high levels of CD13 showed lower sensitivity to a cancer drug cisplatin than cells with low levels of CD13. In contrast, CD13(-high) subpopulation of HSC-58 was more sensitive to an aminopeptidase N inhibitor bestatin. In terms of antibody-drug therapy, anti-CD13-immunotoxin was highly cytotoxic towards HSC-58 cells and was more cytotoxic than anti-EpCAM-immunotoxin.

CONCLUSION

These data suggest that CD13 is a suitable cell surface candidate for targeted antibody-drug therapy of scirrhous gastric cancer.

Recent insights in nanotechnology-based drugs and formulations designed for effective anti-cancer therapy

The rapid development of nanotechnology provides alternative approaches to overcome several limitations of conventional anti-cancer therapy. Drug targeting using functionalized nanoparticles to advance their transport to the dedicated site, became a new standard in novel anti-cancer methods. In effect, the employment of nanoparticles during design of antineoplastic drugs helps to improve pharmacokinetic properties, with subsequent development of high specific, non-toxic and biocompatible anti-cancer agents. However, the physicochemical and biological diversity of nanomaterials and a broad spectrum of unique features influencing their biological action requires continuous research to assess their activity. Among numerous nanosystems designed to eradicate cancer cells, only a limited number of them entered the clinical trials. It is anticipated that progress in development of nanotechnology-based anti-cancer materials will provide modern, individualized anti-cancer therapies assuring decrease in morbidity and mortality from cancer diseases. In this review we discussed the implication of nanomaterials in design of new drugs for effective antineoplastic therapy and describe a variety of mechanisms and challenges for selective tumor targeting. We emphasized the recent advantages in the field of nanotechnology-based strategies to fight cancer and discussed their part in effective anti-cancer therapy and successful drug delivery.

Novel chemical library screen identifies naturally occurring plant products that specifically disrupt glioblastoma-endothelial cell interactions

Tumor growth is not solely a consequence of autonomous tumor cell properties. Rather, tumor cells act upon and are acted upon by their microenvironment. It is tumor tissue biology that ultimately determines tumor growth. Thus, we developed a compound library screen for agents that could block essential tumor-promoting effects of the glioblastoma (GBM) perivascular stem cell niche (PVN). We modeled the PVN with three-dimensional primary cultures of human brain microvascular endothelial cells in Matrigel. We previously demonstrated stimulated growth of GBM cells in this PVN model and used this to assay PVN function. We screened the Microsource Spectrum Collection library for drugs that specifically blocked PVN function, without any direct effect on GBM cells themselves. Three candidate PVN-disrupting agents, Iridin, Tigogenin and Triacetylresveratrol (TAR), were identified and evaluated in secondary in vitro screens against a panel of primary GBM isolates as well as in two different in vivo intracranial models. Iridin and TAR significantly inhibited intracranial tumor growth and prolonged survival in these mouse models. Together these data identify Iridin and TAR as drugs with novel GBM tissue disrupting effects and validate the importance of preclinical screens designed to address tumor tissue function rather than the mechanisms of autonomous tumor cell growth.

ABCG2 and ABCB1 Limit the Efficacy of Dasatinib in a PDGF-B-Driven Brainstem Glioma Model

Dasatinib is a multikinase inhibitor in clinical trials for glioma, and thus far has failed to demonstrate significant efficacy. We investigated whether the ABC efflux transporters ABCG2 and ABCB1 expressed in the blood-brain barrier (BBB), are limiting the efficacy of dasatinib in the treatment of glioma using genetic and pharmacologic approaches. We utilized a genetic brainstem glioma mouse model driven by platelet-derived growth factor-B and p53 loss using abcg2/abcb1 wild-type (ABC WT) or abcg2/abcb1 knockout mice (ABC KO). First, we observed that brainstem glioma tumor latency is significantly prolonged in ABC KO versus ABC WT mice (median survival of 47 vs. 34 days). Dasatinib treatment nearly doubles the survival of brainstem glioma-bearing ABC KO mice (44 vs. 80 days). Elacridar, an ABCG2 and ABCB1 inhibitor, significantly increases the efficacy of dasatinib in brainstem glioma-bearing ABC WT mice (42 vs. 59 days). Pharmacokinetic analysis demonstrates that dasatinib delivery into the normal brain, but not into the tumor core, is significantly increased in ABC KO mice compared with ABC WT mice. Surprisingly, elacridar did not significantly increase dasatinib delivery into the normal brain or the tumor core of ABC WT mice. Next, we demonstrate that the tight junctions of the BBB of this model are compromised as assessed by tissue permeability to Texas Red dextran. Finally, elacridar increases the cytotoxicity of dasatinib independent of ABCG2 and ABCB1 expression in vitro In conclusion, elacridar improves the efficacy of dasatinib in a brainstem glioma model without significantly increasing its delivery to the tumor core. Mol Cancer Ther; 15(5); 819-29. ©2016 AACR.

Common stemness regulators of embryonic and cancer stem cells

Pluripotency of embryonic stem cells (ESCs) and induced pluripotent stem cells is regulated by a well characterized gene transcription circuitry. The circuitry is assembled by ESC specific transcription factors, signal transducing molecules and epigenetic regulators. Growing understanding of stem-like cells, albeit of more complex phenotypes, present in tumors (cancer stem cells), provides a common conceptual and research framework for basic and applied stem cell biology. In this review, we highlight current results on biomarkers, gene signatures, signaling pathways and epigenetic regulators that are common in embryonic and cancer stem cells. We discuss their role in determining the cell phenotype and finally, their potential use to design next generation biological and pharmaceutical approaches for regenerative medicine and cancer therapies.

Gamma tocotrienol targets tyrosine phosphatase SHP2 in mammospheres resulting in cell death through RAS/ERK pathway

Background

There is increasing evidence supporting the concept of cancer stem cells (CSCs), which are responsible for the initiation, growth and metastasis of tumors. CSCs are thus considered the target for future cancer therapies. To achieve this goal, identifying potential therapeutic targets for CSCs is essential.

Methods

We used a natural product of vitamin E, gamma tocotrienol (gamma-T3), to treat mammospheres and spheres from colon and cervical cancers. Western blotting and real-time RT-PCR were employed to identify the gene and protein targets of gamma-T3 in mammospheres.

Results

We found that mammosphere growth was inhibited in a dose dependent manner, with total inhibition at high doses. Gamma-T3 also inhibited sphere growth in two other human epithelial cancers, colon and cervix. Our results suggested that both Src homology 2 domain-containing phosphatase 1 (SHP1) and 2 (SHP2) were affected by gamma-T3 which was accompanied by a decrease in K- and H-Ras gene expression and phosphorylated ERK protein levels in a dose dependent way. In contrast, expression of self-renewal genes TGF-beta and LIF, as well as ESR signal pathways were not affected by the treatment. These results suggest that gamma-T3 specifically targets SHP2 and the RAS/ERK signaling pathway.

Conclusions

SHP1 and SHP2 are potential therapeutic targets for breast CSCs and gamma-T3 is a promising natural drug for future breast cancer therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1614-1) contains supplementary material, which is available to authorized users.

Cytokine-induced killer cells induce apoptosis and inhibit the Akt/nuclear factor-κB signaling pathway in cisplatin-resistant human glioma U87MG cells

Despite advances in the development of treatment methods, glioma remains among the cancer types with a high rate of mortality. Therefore, significant efforts are made to develop novel strategies for the treatment of glioma. Ineffective, long-term cancer chemotherapy can lead to multidrug resistance (MDR), which is one of the most common reasons for the failure of chemotherapy. The present study investigated the effects of cytokine‑induced killer cells (CIK) on reversing MDR in cisplatin-resistant U87MG cells (U87MG/DDP). Mononuclear cells were isolated from the peripheral blood of healthy individuals and cultured in vitro in the presence of a combination of cytokines to generate CIK for the treatment of U87MG/DDP. An MTS assay, flow cytometric analysis of apoptosis, ELISA, western blotting and reverse transcription quantitative polymerase chain reaction were used to investigate the MDR-reversing effects of CIK as well as the underlying mechanisms. The results showed that cisplatin sensitivity and the apoptotic rate following cisplatin treatment were increased, P‑glycoprotein expression was decreased and the intracellular rhodamine‑123 content was increased in U87MG/DDP co‑cultured with CIK. In addition, the present study also identified increased mRNA and protein expression levels of MDR gene 1 (MDR1), MDR‑associated protein 1 (MRP1), B-cell lymphoma 2, Survivin and glutathione S-transferase‑π, while the phosphorylation of AKT and the transcriptional activity of nuclear factor‑κB in CIK co‑cultured U87MG/DDP was decreased. These results indicated that pre‑treatment with CIK reversed the MDR of U87MG/DDP, and that CIK‑induced apoptosis of U87MG/DDP was associated with the inhibition of Akt/NF‑κB. These findings suggested that treatment with CIK may be an effective method to enhance the sensitivity of patients with glioma to chemotherapy.

Positive-charged solid lipid nanoparticles as paclitaxel drug delivery system in glioblastoma treatment

Paclitaxel loaded solid lipid nanoparticles (SLN) of behenic acid were prepared with the coacervation technique. Generally, spherical shaped SLN with mean diameters in the range 300–600 nm were obtained. The introduction of charged molecules, such as stearylamine and glycol chitosan into the formulation allowed to obtain positive SLN with Zeta potential in the 8-20 mV range and encapsulation efficiency in the 25–90% range.Blood–brain barrier (BBB) permeability, tested in vitro through hCMEC/D3 cells monolayer, showed a significantly increase in the permeation of Coumarin-6, used as model drug, when vehicled in SLN. Positive-charged SLN do not seem to enhance permeation although stearylamine-positive SLN resulted the best permeable formulation after 24 h.Cytotoxicity studies on NO3 glioblastoma cell line demonstrated the maintenance of cytotoxic activity of all paclitaxel-loaded SLN that was always unmodified or greater compared with free drug. No difference in cytotoxicity was noted between neutral and charged SLN.Co-culture experiments with hCMEC/D3 and different glioblastoma cells evidenced that, when delivered in SLN, paclitaxel increased its cytotoxicity towards glioblastoma cells.

Targeting glioblastoma cancer stem cells: the next great hope?

Glioblastoma multiforme (GBM) is the most common primary brain tumor and is notorious for its poor prognosis. The highly invasive nature of GBM and its inherent resistance to therapy lead to very high rates of recurrence. Recently, a small cohort of tumor cells, called cancer stem cells (CSCs), has been recognized as a subset of tumor cells with self-renewal ability and multilineage capacity. These properties, along with the remarkable tumorigenicity of CSCs, are thought to account for the high rates of tumor recurrence after treatment. Recent research has been geared toward understanding the unique biological characteristics of CSCs to enable development of targeted therapy. Strategies include inhibition of CSC-specific pathways and receptors; agents that increase sensitivity of CSCs to chemotherapy and radiotherapy; CSC differentiation agents; and CSC-specific immunotherapy, virotherapy, and gene therapy. These approaches could inform the development of newer therapeutics for GBM.

Chemoresistance of CD133(+) colon cancer may be related with increased survivin expression

CD133, putative cancer stem cell marker, deemed to aid chemoresistance. However, this claim has been challenged recently and we previously reported that patients with CD133(+) colon cancer have benefit from 5-fluorouracil (5-FU) chemotherapy incontrast to no benefit in patients with CD133(-) cancer. To elucidate the role of CD133 expression in chemoresistance, we silenced the CD133 expression in a colon cancer cell line and determined its effect on the biological characteristics downstream. We comparatively analyzed the sequential changes of MDR1, ABCG2, AKT1 and survivin expression and the result of proliferation assay (WST-1 assay) with 5-FU treatment in CD133(+) and siRNA-induced CD133(-) cells, derived from Caco-2 colon cancer cell line. 5-FU treatment induced significantly increase of the mRNA expression of MDR1, ABCG2 and AKT1genes, but not protein level. CD133 had little to no effect on the mRNA and protein expression of these genes. However, survivin expression at mRNA and protein level were significantly increased in CD133(+) cells compared with siRNA-induced CD133-cells and Mock (not sorted CD133(+) cells) at 96 h after siRNA transfection. The cytotoxicity assay demonstrated notable increase of chemoresistance to 5-FU treatment (10 μM) in CD133(+) cells at 96 h after siRNA transfection. From this study, we conclude that CD133(+) cells may have chemoresistance to 5-FU through the mechanism which is related with survivin expression, instead of MDR1, ABCG2 and AKT1 expression. Therefore a survivin inhibitor can be a new target for effective treatment of CD133(+) colon cancer.

CD133 and DNA-PK regulate MDR1 via the PI3K- or Akt-NF-κB pathway in multidrug-resistant glioblastoma cells in vitro

Chemotherapy is an adjuvant treatment for glioblastomas, however, chemotherapy remains palliative because of the development of multidrug resistance (MDR). Following prolonged chemotherapy, MDR protein 1 (MDR1) and CD133 increase in recurrent glioblastomas. CD133 positive (CD133+) glioma cancer stem-like cells (GCSCs) markedly promote drug resistance and exhibit increased DNA damage repair capability; thus they have a key role in determining tumor chemosensitivity. Although CD133, DNA-dependent protein kinase (DNA-PK), and MDR1 are elevated in CD133+ GCSCs, the relationship among these molecules has not been elucidated. In this study, MDR glioblastoma cell lines were created in response to prolonged doxorubicin chemotherapy. CD133, DNA-PK and MDR1 were markedly elevated in these cells. CD133 and DNA-PK may increase MDR1 via the phosphatidylinositol-3-kinase (PI3K)-Akt signal pathway. PI3K downstream targets Akt and nuclear factor (NF)-κB, which interacts with the MDR1 promoter, were also elevated in these cells. Downregulation of CD133 and DNA-PK by small interfering RNA, or inhibition of PI3K or Akt, decreased Akt, NF-κB and MDR1 expression. The results indicate that CD133 and DNA-PK regulate MDR1 through the PI3K- or Akt-NF-κB signal pathway. Consequently, a novel chemotherapeutic regimen targeting CD133 and DNA-PK in combination with traditional protocols may increase chemotherapeutic efficacy and improve prognosis for individuals who present with glioblastoma.

Cancer stem cells in basic science and in translational oncology: can we translate into clinical application?

Since their description and identification in leukemias and solid tumors, cancer stem cells (CSC) have been the subject of intensive research in translational oncology. Indeed, recent advances have led to the identification of CSC markers, CSC targets, and the preclinical and clinical evaluation of the CSC-eradicating (curative) potential of various drugs. However, although diverse CSC markers and targets have been identified, several questions remain, such as the origin and evolution of CSC, mechanisms underlying resistance of CSC against various targeted drugs, and the biochemical basis and function of stroma cell-CSC interactions in the so-called ‘stem cell niche.’ Additional aspects that have to be taken into account when considering CSC elimination as primary treatment-goal are the genomic plasticity and extensive subclone formation of CSC. Notably, various cell fractions with different combinations of molecular aberrations and varying proliferative potential may display CSC function in a given neoplasm, and the related molecular complexity of the genome in CSC subsets is considered to contribute essentially to disease evolution and acquired drug resistance. In the current article, we discuss new developments in the field of CSC research and whether these new concepts can be exploited in clinical practice in the future.

Autoregulation and heterogeneity in expression of human Cripto-1

Cripto-1 (CR-1) is involved in various processes in embryonic development and cancer. Multiple pathways regulate CR-1 expression. Our present work demonstrates a possible positive feedback circuit where CR-1 induces its own expression. Using U-87 MG cells treated with exogenous CR-1, we show that such induction involves ALK4/SMAD2/3 pathway. Stochasticity in gene expression gives rise to heterogeneity in expression in genetically identical cells. Positive feedback increases such heterogeneity and often gives rise to two subpopulations of cells, having higher and lower expression of a gene. Using flow cytometry, we show that U-87 MG cells have a minuscule subpopulation with detectable expression of CR-1. Induction of CR-1 expression, by exogenous CR-1, increases the size of this CR-1 positive subpopulation. However, even at very high dose, most of the cells remain CR-1 negative. We show that population behavior of CR-1 induction has a signature similar to bimodal expression expected in a transcriptional circuit with positive feedback. We further show that treatment of U-87 MG cells with CR-1 leads to higher expression of drug efflux protein MDR-1 in the CR-1 positive subpopulation, indicating correlated induction of these two proteins. Positive feedback driven heterogeneity in expression of CR-1 may play crucial role in phenotypic diversification of cancer cells.