Understanding and targeting cancer stem cells: therapeutic implications and challenges

Continuous exposure of pancreatic cancer cells to dietary bioactive agents does not induce drug resistance unlike chemotherapy

The repeated treatment of cancer cells with chemo- or radiotherapy induces therapy resistance, but it was previously unknown whether the same effect occurs upon continuous exposure of cancer cells to diet-derived chemopreventive agents. We elucidated this interesting question in pancreatic ductal adenocarcinoma, which is a highly aggressive cancer entity with a marked resistance toward gemcitabine and other cytotoxic drugs. The isothiocyanate sulforaphane, present in cruciferous vegetables, and the polyphenol quercetin, present in many fruits and vegetables induced apoptosis and reduced viability in gemcitabine-sensitive BxPC-3 cells but not in non-malignant ductal pancreas cells and mesenchymal stromal cells. In turn, BxPC-3 cells were treated with increasing concentrations of gemcitabine, sulforaphane or quercetin for more than 1 year and the surviving subclones Bx-GEM, Bx-SF and Bx-Q were selected, respectively. While Bx-GEM cells acquired a total resistance, Bx-SF or Bx-Q cells largely kept their sensitivity as proved by MTT assay, annexin staining and FACS analysis. The evaluation of the self-renewal-, differentiation- and migration-potential by colony formation, differentiation or migration assays demonstrated that cancer stem cell features were enriched in gemcitabine-resistant cells, but decreased in sulforaphane- and quercetin-long time-treated cells. These results were confirmed by orthotopic xenotransplantation of cancer cells to the mouse pancreas, where Bx-GEM formed large, Bx-Q small and Bx-SF cells almost undetectable tumors. An mRNA expression profiling array and subsequent gene set enrichment analysis and qRT-PCR confirmed that tumor progression markers were enriched in Bx-GEM, but reduced in Bx-SF and Bx-Q cells. This study demonstrates that the continuous exposure of pancreatic cancer cells to sulforaphane or quercetin does not induce resistance in surviving cells but reduces tumorigenicity by inhibition of tumor progression markers. These results highlight that cancer cells may not adapt to the preventive and therapeutic effects of a regular fruit- and vegetable-based diet.

Calmidazolium chloride inhibits growth of murine embryonal carcinoma cells, a model of cancer stem-like cells

Calmidazolium chloride (CMZ) is widely used as a calmodulin (CaM) antagonist, but is also known to induce apoptosis in certain cancer cell lines. However, in spite of the importance of cancer stem cells (CSCs) in cancer therapy, the effects of CMZ on CSCs are not yet well understood. We investigated the effects of CMZ on the F9 embryonal carcinoma cell (ECC) line as a surrogate model of CSCs. To avoid bias due to culture conditions, F9 ECCs and E14 embryonic stem cells (ESCs) were grown in the same culture medium. Results obtained using a cell-counting kit showed that CMZ significantly inhibited growth in F9 ECCs compared with growth in E14 ESCs. CMZ also induced apoptosis of F9 ECCs, but not of E14 ESCs, which was associated with caspase-3 activation and an increased fraction of the sub-G1 cell population. In addition, our data revealed that the expression of stemness-related genes including c-Myc was selectively down regulated in CMZ-treated F9 ECCs. Our results suggest that CMZ can inhibit the growth of ECCs by inducing apoptosis and down regulating stemness-related genes, without causing any harm to normal stem cells. These findings indicate a potential application of CMZ in the development of anti-CSC therapeutics.

Stem cell technology in breast cancer: current status and potential applications

Breast cancer, the leading cause of cancer among females, is supported by the presence of a rare subset of undifferentiated cells within the tumor, identified as breast cancer stem cells (BCSCs). BCSCs underlie the mechanisms of tumor initiation and sustenance and are implicated in the dissemination of the primary tumor to metastatic sites, as they have been found circulating in the blood of breast cancer patients. The discovery of BCSCs has generated a great amount of interest among the scientific community toward their isolation, molecular characterization, and therapeutic targeting. In this review, after summarizing the literature on molecular characterization of BCSCs and methodologies used for their isolation, we will focus on recent data supporting their molecular and functional heterogeneity. Additionally, following a synopsis of the latest approaches for BCSC targeting, we will specifically emphasize on the therapeutic use of naïve or engineered normal stem cells in the treatment of breast cancer and present contradictory findings challenging their safety.

Unaccounted uncertainty from qPCR efficiency estimates entails uncontrolled false positive rates

Background

Accurate adjustment for the amplification efficiency (AE) is an important part of real-time quantitative polymerase chain reaction (qPCR) experiments. The most commonly used correction strategy is to estimate the AE by dilution experiments and use this as a plug-in when efficiency correcting the ΔΔC_q. Currently, it is recommended to determine the AE with high precision as this plug-in approach does not account for the AE uncertainty, implicitly assuming an infinitely precise AE estimate. Determining the AE with such precision, however, requires tedious laboratory work and vast amounts of biological material. Violation of the assumption leads to overly optimistic standard errors of the ΔΔC_q, confidence intervals, and p-values which ultimately increase the type I error rate beyond the expected significance level. As qPCR is often used for validation it should be a high priority to account for the uncertainty of the AE estimate and thereby properly bounding the type I error rate and achieve the desired significance level.

Results

We suggest and benchmark different methods to obtain the standard error of the efficiency adjusted ΔΔC_q using the statistical delta method, Monte Carlo integration, or bootstrapping. Our suggested methods are founded in a linear mixed effects model (LMM) framework, but the problem and ideas apply in all qPCR experiments. The methods and impact of the AE uncertainty are illustrated in three qPCR applications and a simulation study. In addition, we validate findings suggesting that MGST1 is differentially expressed between high and low abundance culture initiating cells in multiple myeloma and that microRNA-127 is differentially expressed between testicular and nodal lymphomas.

Conclusions

We conclude, that the commonly used efficiency corrected quantities disregard the uncertainty of the AE, which can drastically impact the standard error and lead to increased false positive rates. Our suggestions show that it is possible to easily perform statistical inference of ΔΔC_q, whilst properly accounting for the AE uncertainty and better controlling the false positive rate.

CSCdb: a cancer stem cells portal for markers, related genes and functional information

Cancer stem cells (CSCs), which have the ability to self-renew and differentiate into various tumor cell types, are a special class of tumor cells. Characterizing the genes involved in CSCs regulation is fundamental to understand the mechanisms underlying the biological process and develop treatment methods for tumor therapy. Recently, much effort has been expended in the study of CSCs and a large amount of data has been generated. However, to the best of our knowledge, database dedicated to CSCs is not available until now. We have thus developed a CSCs database (CSCdb), which includes marker genes, CSCs-related genes/microRNAs and functional annotations. The information in the CSCdb was manual collected from about 13 000 articles. The CSCdb provides detailed information of 1769 genes that have been reported to participate in the functional regulation of CSCs and 74 marker genes that can be used for identification or isolation of CSCs. The CSCdb also provides 9475 annotations about 13 CSCs-related functions, such as oncogenesis, radio resistance, tumorigenesis, differentiation, etc. Annotations of the identified genes, which include protein function description, post-transcription modification information, related literature, Gene Ontology (GO), protein-protein interaction (PPI) information and regulatory relationships, are integrated into the CSCdb to help users get information more easily. CSCdb provides a comprehensive resource for CSCs research work, which would assist in finding new CSCs-related genes and would be a useful tool for biologists.

Database URL:http://bioinformatics.ustc.edu.cn/cscdb

Construction and expression of an anti-VEGFR2 Nanobody-Fc fusionbody in NS0 host cell

Angiogenesis is the formation of new blood vessels which is involved in migration, growth and differentiation of endothelial cells. This process regularly occurs during growth and development in children however, in adults is usually part of a disease process such as cancer. The vascular endothelial growth factor (VEGF) is a vital player in the vascular development and angiogenesis in physiological and pathological processes. Camelid's immune system has unique antibodies which are composed of only a heavy chain homodimer and the variable domain (VHH, Nanobody). Nanobodies are small, around 15 kDa and stable. In this study, we engineered and constructed a new Nanobody-Fc fusion protein (fusionbody) composed of an anti-VEGFR2 Nanobody and an Fc fragment of human IgG1 antibody. The recombinant vector was transfected into NS0 host cells. Stable producer clones were developed and the recombinant fusionbody was expressed and purified. Functional assay showed the anti-VEGFR2 fusionbody could bind to VEGFR2 on cell surface via VHH part and could mediate killing the targeted cells through direct cell death and complement-dependent cytotoxicity (CDC).

Molecular Control of Atypical Protein Kinase C: Tipping the Balance between Self-Renewal and Differentiation

Complex organisms are faced with the challenge of generating and maintaining diverse cell types, ranging from simple epithelia to neurons and motile immune cells [1-3]. To meet this challenge, a complex set of regulatory pathways controls nearly every aspect of cell growth and function, including genetic and epigenetic programming, cytoskeleton dynamics, and protein trafficking. The far reach of cell fate specification pathways makes it particularly catastrophic when they malfunction, both during development and for tissue homeostasis in adult organisms. Furthermore, the therapeutic promise of stem cells derives from their ability to deftly navigate the multitude of pathways that control cell fate [4]. How the molecular components making up these pathways function to specify cell fate is beginning to become clear. Work from diverse systems suggests that the atypical Protein Kinase C (aPKC) is a key regulator of cell fate decisions in metazoans [5-7]. Here, we examine some of the diverse physiological outcomes of aPKC's function in differentiation, along with the molecular pathways that control aPKC and those that are responsive to changes in its catalytic activity.

The safety of treatment options for elderly people with acute myeloid leukemia

INTRODUCTION

Life expectancy in elderly patients with acute myeloid leukemia (AML) is a function of age, disability, and co-morbidity, combined with leukemia characteristics. There is currently no consensus regarding the optimal therapeutic strategy for older adults with AML. Although selected older adults with AML can benefit from intensive therapies, recent evidence supports the use of lower-intensity therapies in most patients and emphasizes the importance of tolerability and quality of life.

AREAS COVERED

Results of the current clinical trials and safety data are reviewed.

EXPERT OPINION

Treatment recommendations for elderly patients with AML need to be individualized. In order to avoid toxicities, hematologists should collaborate more with geriatricians to identify clues of vulnerability in elderly patients through the study of functional physical, physiological, cognitive, social, and psychological parameters.

Combination of carbon ion beam and gemcitabine causes irreparable DNA damage and death of radioresistant pancreatic cancer stem-like cells in vitro and in vivo

We try to elucidate whether a carbon ion beam alone or in combination with gemcitabine has advantages over X-ray in targeting putative pancreatic cancer stem-like cells (CSCs) in vitro and in vivo. Colony, spheroid formation and tumorigenicity assays confirmed that CD44+/ESA+ cells sorted from PANC1 and PK45 cells have more CSC properties than CD44−/ESA− cells. The number of colonies and spheroids formed from CSCs after carbon ion beam irradiation was significantly reduced compared to after X-ray irradiation, and they were extremely highly suppressed when carbon ion beam combined with gemcitabine. The relative biological effectiveness (RBE) values for the carbon ion beam relative to X-ray at the D10 levels for CSCs were 2.23-2.66. Expressions of multiple cell death-related genes were remarkably highly induced, and large numbers of γH2AX foci in CSCs were formed after carbon ion beam combined with gemcitabine. The highly expressed CSC markers were significantly inhibited after 30 Gy of carbon ion beam and almost lost after 25 Gy carbon ion beam combined with 50 mg/kg gemcitabine. In conclusion, a carbon ion beam combined with gemcitabine has superior potential to kill pancreatic CSCs via irreparable clustered DSB compared to a carbon ion alone or X-rays combined with gemcitabine.

Effect of Melatonin in Epithelial Mesenchymal Transition Markers and Invasive Properties of Breast Cancer Stem Cells of Canine and Human Cell Lines

Cancer stem cells (CSCs) have been associated with metastasis and therapeutic resistance and can be generated via epithelial mesenchymal transition (EMT). Some studies suggest that the hormone melatonin acts in CSCs and may participate in the inhibition of the EMT. The objectives of this study were to evaluate the formation of mammospheres from the canine and human breast cancer cell lines, CMT-U229 and MCF-7, and the effects of melatonin treatment on the modulation of stem cell and EMT molecular markers: OCT4, E-cadherin, N-cadherin and vimentin, as well as on cell viability and invasiveness of the cells from mammospheres. The CMT-U229 and MCF-7 cell lines were subjected to three-dimensional culture in special medium for stem cells. The phenotype of mammospheres was first evaluated by flow cytometry (CD44⁺/CD24^low/- marking). Cell viability was measured by MTT colorimetric assay and the expression of the proteins OCT4, E-cadherin, N-cadherin and vimentin was evaluated by immunofluorescence and quantified by optical densitometry. The analysis of cell migration and invasion was performed in Boyden Chamber. Flow cytometry proved the stem cell phenotype with CD44⁺/CD24^low/- positive marking for both cell lines. Cell viability of CMT-U229 and MCF-7 cells was reduced after treatment with 1mM melatonin for 24 h (P<0.05). Immunofluorescence staining showed increased E-cadherin expression (P<0.05) and decreased expression of OCT4, N-cadherin and vimentin (P<0.05) in both cell lines after treatment with 1 mM melatonin for 24 hours. Moreover, treatment with melatonin was able to reduce cell migration and invasion in both cell lines when compared to control group (P<0.05). Our results demonstrate that melatonin shows an inhibitory role in the viability and invasiveness of breast cancer mammospheres as well as in modulating the expression of proteins related to EMT in breast CSCs, suggesting its potential anti-metastatic role in canine and human breast cancer cell lines.

Tumor-Initiating Cells: Emerging Biophysical Methods of Isolation

The discovery and subsequent isolation of tumor-initiating cells (TICs), a small population of highly tumorigenic and drug-resistant cancer cells also called cancer stem cells (CSCs), have revolutionized our understanding of cancer. TICs are isolated using various methodologies, including selection of surface marker expression, ALDH activity, suspension culture, and chemotherapy/drug resistance. These methods have several drawbacks, including their variability, lack of robustness and scalability, and low specificity. Alternative methods of purification take advantage of biophysical properties of TICs including their adhesion and stiffness. This review will provide a brief overview of TIC biology as well as review the most important methods of TIC isolation with a focus on biophysical methods of TIC purification.

[Cancer stem cell markers and their prognostic value]

Based on an analysis of a large number of sources of literature, the paper gives general information on the markers for cancer stem cells (CSCs), which allow the detection of this rare cell subpopulation, on the possibilities of estimating their immunohistochemical or immunofluorescent expression in tumors, and on the prognostic and predictive values of these molecules. For their detection, investigators generally use definite molecules, the so-called markers of CSCs, among which there are CD44, CD133, CD24, aldehyde dehydrogenase, and others. The expression of these molecules in the tumor tissue obtained from patients affects survival rates and permits the prediction of a response to therapy. A better insight into the immunophenotype of CSCs, the role of CSC markers in retaining the special properties of this call population, and the clinical significance of the expression of CSC markers will be able to elaborate new approaches to therapy for malignancies.

Cancer Stem Cell and Gastrointestinal Cancer: Current Status, Targeted Therapy and Future Implications

The cancer stem cells (CSCs) are biologically distinct subset of rare cancer cells with inherent ability of self-renewal, de-differentiation, and capacity to initiate and maintain malignant tumor growth. Studies have further reported that CSCs prime cancer recurrence and therapy resistance. Therefore, targeting CSCs to inhibit cancer progression has become an attractive anti-cancer therapeutical strategy. Recent technical advances have provided a greater appreciation of the multistep nature of the oncogenesis and also clarified that CSC concept is not universally applicable. Irrespective, the role of the CSCs in gastrointestinal (GI) cancers, responsible for the most cancer-associated death, has been widely accepted and appreciated. However, despite the tremendous progress made in the last decade in developing markers to identify CSCs, and assays to assess tumorigenic function of CSCs, it remains an area of active investigation. In current article, we review findings related to the role and identification of CSCs in GI-cancers and discuss the crucial pathways involved in regulating CSCs populations’ development and drug resistance, and use of the tumoroid culture to test novel CSCs-targeted cancer therapies.

Nuclear AURKA acquires kinase-independent transactivating function to enhance breast cancer stem cell phenotype

Centrosome-localized mitotic Aurora kinase A (AURKA) facilitates G2/M events. Here we show that AURKA translocates to the nucleus and causes distinct oncogenic properties in malignant cells by enhancing breast cancer stem cell (BCSC) phenotype. Unexpectedly, this function is independent of its kinase activity. Instead, AURKA preferentially interacts with heterogeneous nuclear ribonucleoprotein K (hnRNP K) in the nucleus and acts as a transcription factor in a complex that induces a shift in MYC promoter usage and activates the MYC promoter. Blocking AURKA nuclear localization inhibits this newly discovered transactivating function of AURKA, sensitizing resistant BCSC to kinase inhibition. These findings identify a previously unknown oncogenic property of the spatially deregulated AURKA in tumorigenesis and provide a potential therapeutic opportunity to overcome kinase inhibitor resistance.

Lung cancer stem cells: The root of resistance

In the absence of specific treatable mutations, platinum-based chemotherapy remains the gold standard of treatment for lung cancer patients. However, 5-year survival rates remain poor due to the development of resistance and eventual relapse. Resistance to conventional cytotoxic therapies presents a significant clinical challenge in the treatment of this disease. The cancer stem cell (CSC) hypothesis suggests that tumors are arranged in a hierarchical structure, with the presence of a small subset of stem-like cells that are responsible for tumor initiation and growth. This CSC population has a number of key properties such as the ability to asymmetrically divide, differentiate and self-renew, in addition to having increased intrinsic resistance to therapy. While cytotoxic chemotherapy kills the bulk of tumor cells, CSCs are spared and have the ability to recapitulate the heterogenic tumor mass. The identification of lung CSCs and their role in tumor biology and treatment resistance may lead to innovative targeted therapies that may ultimately improve clinical outcomes in lung cancer patients. This review will focus on lung CSC markers, their role in resistance and their relevance as targets for future therapies.

CD19 chimeric antigen receptor (CD19 CAR)-redirected adoptive T-cell immunotherapy for the treatment of relapsed or refractory B-cell Non-Hodgkin's Lymphomas

Recovery rates for B-cell Non-Hodgkin's Lymphoma (NHL) are up to 70% with current standard-of-care treatments including rituximab (chimeric anti-CD20 monoclonal antibody) in combination with chemotherapy (R-CHOP). However, patients who do not respond to first-line treatment or develop resistance have a very poor prognosis. This signifies the need for the development of an optimal treatment approach for relapsed/refractory B-NHL. Novel CD19- chimeric antigen receptor (CAR) T-cell redirected immunotherapy is an attractive option for this subset of patients. Anti-CD19 CAR T-cell therapy has already had remarkable efficacy in various leukemias as well as encouraging outcomes in phase I clinical trials of relapsed/refractory NHL. In going forward with additional clinical trials, complementary treatments that may circumvent potential resistance mechanisms should be used alongside anti-CD19 T-cells in order to prevent relapse with resistant strains of disease. Some such supplementary tactics include conditioning with lymphodepletion agents, sensitizing with kinase inhibitors and Bcl-2 inhibitors, enhancing function with multispecific CAR T-cells and CD40 ligand-expressing CAR T-cells, and safeguarding with lymphoma stem cell-targeted treatments. A therapy regimen involving anti-CD19 CAR T-cells and one or more auxiliary treatments could dramatically improve prognoses for patients with relapsed/refractory B-cell NHL. This approach has the potential to revolutionize B-NHL salvage therapy in much the same way rituximab did for first-line treatments.

What Do We Learn from Spheroid Culture Systems? Insights from Tumorspheres Derived from Primary Colon Cancer Tissue

Due to their self-renewal and tumorigenic properties, tumor-initiating cells (TICs) have been hypothesized to be important targets for colorectal cancer (CRC). However the study of TICs is hampered by the fact that the identification and culturing of TICs is still a subject of extensive debate. Floating three-dimensional spheroid cultures (SC) that grow in serum-free medium supplemented with growth factors are supposed to be enriched in TICs. We generated SC from fresh clinical tumor specimens and compared them to SC isolated from CRC cell-lines as well as to adherent differentiated counterparts. Patient-derived SC display self-renewal capacity and can induce serial transplantable tumors in immuno-deficient mice, which phenotypically resemble the tumor of origin. In addition, the original tumor tissue and established SC retain several similar CRC-relevant mutations. Primary SC express key stemness proteins such as SOX2, OCT4, NANOG and LGR5 and importantly show increased chemoresistance ability compared to their adherent differentiated counterparts and to cell line-derived SC. Strikingly, cells derived from spheroid or adherent differentiating culture conditions displayed similar self-renewal capacity and equally formed tumors in immune-deficient mice, suggesting that self-renewal and tumor-initiation capacity of TICs is not restricted to phenotypically immature spheroid cells, which we describe to be highly plastic and able to reacquire stem-cell traits even after long differentiation processes. Finally, we identified two genes among a sphere gene expression signature that predict disease relapse in CRC patients. Here we propose that SC derived from fresh patient tumor tissue present interesting phenotypic features that may have clinical relevance for chemoresistance and disease relapse and therefore represent a valuable tool to test for new CRC-therapies that overcome drug resistance.

Transmembrane protein CD9 is glioblastoma biomarker, relevant for maintenance of glioblastoma stem cells

The cancer stem cell model suggests that glioblastomas contain a subpopulation of stem-like tumor cells that reproduce themselves to sustain tumor growth. Targeting these cells thus represents a novel treatment strategy and therefore more specific markers that characterize glioblastoma stem cells need to be identified. In the present study, we performed transcriptomic analysis of glioblastoma tissues compared to normal brain tissues revealing sensible up-regulation of CD9 gene. CD9 encodes the transmembrane protein tetraspanin which is involved in tumor cell invasion, apoptosis and resistance to chemotherapy. Using the public REMBRANDT database for brain tumors, we confirmed the prognostic value of CD9, whereby a more than two fold up-regulation correlates with shorter patient survival. We validated CD9 gene and protein expression showing selective up-regulation in glioblastoma stem cells isolated from primary biopsies and in primary organotypic glioblastoma spheroids as well as in U87-MG and U373 glioblastoma cell lines. In contrast, no or low CD9 gene expression was observed in normal human astrocytes, normal brain tissue and neural stem cells. CD9 silencing in three CD133+ glioblastoma cell lines (NCH644, NCH421k and NCH660h) led to decreased cell proliferation, survival, invasion, and self-renewal ability, and altered expression of the stem-cell markers CD133, nestin and SOX2. Moreover, CD9-silenced glioblastoma stem cells showed altered activation patterns of the Akt, MapK and Stat3 signaling transducers. Orthotopic xenotransplantation of CD9-silenced glioblastoma stem cells into nude rats promoted prolonged survival. Therefore, CD9 should be further evaluated as a target for glioblastoma treatment.

Design, synthesis and evaluation of cytotoxic properties of bisamino glucosylated antitumor ether lipids against cancer cells and cancer stem cells

Glycosylated antitumor ether lipids (GAELs) are a class of amphiphilic antitumor agents that kill cancer cells by a non-apoptotic pathway.

Mutual regulation and targeting of multidrug resistance and cancer stem phenotype

Targeting stemness mechanisms leads to the suppression of ABC transporter activity and elimination of CSCs.

The breast cancer stem cell potency of copper(ii) complexes bearing nonsteroidal anti-inflammatory drugs and their encapsulation using polymeric nanoparticles

This is the first report to demonstrate that polymeric nanoparticles can be used to effectively deliver CSC-potent metal complexes into CSCs.

Cancer Stem Cells and Their Interaction with the Tumor Microenvironment in Neuroblastoma

Neuroblastoma, a solid tumor arising from neural crest cells, accounts for over 15% of all pediatric cancer deaths. The interaction of neuroblastoma cancer-initiating cells with their microenvironment likely plays an integral role in the maintenance of resistant disease and tumor relapse. In this review, we discuss the interaction between neuroblastoma cancer-initiating cells and the elements of the tumor microenvironment and how these interactions may provide novel therapeutic targets for this difficult to treat disease.

Evodiamine selectively targets cancer stem-like cells through the p53-p21-Rb pathway

In spite of the recent improvements, the resistance to chemotherapy/radiotherapy followed by relapse is the main hurdle for the successful treatment of breast cancer, a leading cause of death in women. A small population of breast cancer cells that have stem-like characteristics (cancer stem-like cells; CSLC) may contribute to this resistance and relapse. Here, we report on a component of a traditional Chinese medicine, evodiamine, which selectively targets CSLC of breast cancer cell lines MCF7 and MDAMB 231 at a concentration that does show a little or no cytotoxic effect on bulk cancer cells. While evodiamine caused the accumulation of bulk cancer cells at the G2/M phase, it did not hold CSLC in a specific cell cycle phase but instead, selectively killed CSLC. This was not due to the culture of CSLC in suspension or without FBS. A proteomic analysis and western blotting revealed that evodiamine changed the expression of cell cycle regulating molecules more efficiently in CSLC cells than in bulk cancer cells. Surprisingly, evodiamine selectively activated p53 and p21 and decreased inactive Rb, the master molecules in G1/S checkpoint. These data collectively suggest a novel mechanism involving CSLC-specific targeting by evodiamine and its possible use to the therapy of breast cancer.

T cell therapies-are T memory stem cells the answer?

T memory stem cells (TSCM) are the earliest developmental stage of memory T cells, displaying stem cell-like properties and exhibiting a gene profile between naive and central memory (CM) T cells. Their long-lifespan, robust proliferative potential and self-renewal capacity has generated much research and clinical interest particularly for therapeutic use. Here, we discuss recent findings published in Science Translational Medicine by Biasco and colleagues [2015 Feb 4;7(273):273ra13], which provided evidence for the persistence of TSCM in humans for up to 12 years after infusion of genetically modified lymphocytes, and we examine the implications for the development of novel immunotherapies using TSCM.

Specific targeting and noninvasive imaging of breast cancer stem cells using single-walled carbon nanotubes as novel multimodality nanoprobes

BACKGROUND

The limitation of current breast cancer treatments was elucidated by the presence of cancer stem cells (CSCs) that play essential role in cancer initiation, progression, resistance, recurrence and metastasis. Materials & methods: Biocompatible multimodality single-walled carbon nanotube (SWCNT) nanoprobes were developed. The biodistribution and preferential homing of CD44 antibody-conjugated SWCNTs toward the tumor site were monitored using MRI, single-photon emission computed tomography and near-infrared fluorescence imaging noninvasive imaging modalities.

RESULTS

Quantification of SWCNTs by sensitively measuring iron content in sorted CSC populations using inductively coupled plasma-mass spectrometry confirmed the enhanced selective targeting of anti-CD44 SWCNT and immunohistochemistry analyses revealed enhanced colocalization with areas rich in CD44 receptors.

DISCUSSION & CONCLUSION

This preclinical study provided encouraging results for efficient targeting of breast CSCs and perspectives for further clinical studies to confirm the efficacy and safety of the designed nanocarriers.

Downregulation of COMMD1 by miR-205 promotes a positive feedback loop for amplifying inflammatory- and stemness-associated properties of cancer cells

Sustained activation of nuclear factor-κB (NF-κB) in cancer cells has been shown to promote inflammation, expansion of cancer stem cell (CSC) population, and tumor development. In contrast, recent studies reveal that CSCs exhibit increased inflammation due to constitutive NF-κB activation; however, the underlying molecular mechanism remains unclear. In the present study, the analysis of microarray data revealed upregulation of NF-κB-regulated pro-inflammatory genes and downregulation of copper metabolism MURR1 domain-containing 1 (COMMD1) during the enrichment for stemness in SAS head and neck squamous-cell carcinoma (HNSCC) cells. The 3′-UTR of COMMD1 mRNA contains microRNA (miR)-205 target site. Parallel studies with HNSCC and NSCLC cells indicated that miR-205 is upregulated upon NF-κB activation and suppresses COMMD1 expression in stemness-enriched cancer cells. COMMD1 negatively regulates the inflammatory responses induced by TLR agonists, IL-1β, and TNF-α by targeting RelA for degradation. The shRNA-mediated downregulation of COMMD1 in cancer cells enhanced inflammatory response, generating favorable conditions for macrophage recruitment. In addition, genes associated with stemness were also upregulated in these cells, which exhibited increased potential for anchorage-independent growth. Furthermore, COMMD1 downregulation promoted in vivo tumorigenesis and tumor growth, and tumors derived from COMMD1-knockdown cells displayed elevated level of NF-κB activation, increased expression of inflammatory- and stemness-associated genes, and contain expanded population of tumor-associated leukocytes and stemness-enriched cancer cells. These results suggest that COMMD1 downregulation by miR-205 promotes tumor development by modulating a positive feedback loop that amplifies inflammatory- and stemness-associated properties of cancer cells.

Cancer stem cell markers: premises and prospects

Over the last decade, compelling evidence has shown that cancer stem cells (CSCs) exist in a variety of malignancies. The conventional method for anticancer therapy involves targeting only the proliferating mitotic cells, sparing the slow-cycling cells that eventually evade chemotherapy and become a source of post therapy relapses. With the increasing awareness of CSCs supported by sophisticated experimental evidence, therapeutic strategies today are aimed at selectively identifying and targeting CSCs using biomarkers. The ability to identify CSCs allows targeted elimination of these cancer-initiating cells. Herein, we discuss CSC markers in the context of different types of cancers, their significance in selectively identifying CSCs and the therapeutic implications of using these biomarkers to prevent invasion and metastasis of cancer.

Polyphenols as Modulator of Oxidative Stress in Cancer Disease: New Therapeutic Strategies

Cancer onset and progression have been linked to oxidative stress by increasing DNA mutations or inducing DNA damage, genome instability, and cell proliferation and therefore antioxidant agents could interfere with carcinogenesis. It is well known that conventional radio-/chemotherapies influence tumour outcome through ROS modulation. Since these antitumour treatments have important side effects, the challenge is to develop new anticancer therapeutic strategies more effective and less toxic for patients. To this purpose, many natural polyphenols have emerged as very promising anticancer bioactive compounds. Beside their well-known antioxidant activities, several polyphenols target epigenetic processes involved in cancer development through the modulation of oxidative stress. An alternative strategy to the cytotoxic treatment is an approach leading to cytostasis through the induction of therapy-induced senescence. Many anticancer polyphenols cause cellular growth arrest through the induction of a ROS-dependent premature senescence and are considered promising antitumour therapeutic tools. Furthermore, one of the most innovative and interesting topics is the evaluation of efficacy of prooxidant therapies on cancer stem cells (CSCs). Several ROS inducers-polyphenols can impact CSCs metabolisms and self-renewal related pathways. Natural polyphenol roles, mainly in chemoprevention and cancer therapies, are described and discussed in the light of the current literature data.

Transcriptional repression of cancer stem cell marker CD133 by tumor suppressor p53

Novel therapeutic strategies are needed to overcome cancer recurrence, metastasis, and resistance to chemo- and radiotherapy. Cancer stem cells (CSCs) are major contributors to the malignant transformation of cells due to their capacity for self-renewal. Although various CSC markers have been identified in several types of tumors, they are primarily used as cancer-prediction markers and for the isolation of CSC populations. CD133, one of the best-characterized CSC markers in distinct solid tumor types, was shown to be correlated with CSC tumor-initiating capacity; however, the regulation of CD133 expression and its function in cancer are poorly understood. Here, we show that CD133 expression is negatively regulated by direct binding of the p53 tumor suppressor protein to a noncanonical p53-binding sequence in the CD133 promoter. Binding of p53 recruits Histone Deacetylase 1 (HDAC1) to the CD133 promoter and subsequently suppresses CD133 expression by reducing histone H3 acetylation. Furthermore, CD133 depletion suppresses tumor cell proliferation, colony formation, and the expression of core stemness transcription factors including NANOG, octamer-binding transcription factor 4 (OCT4), SOX2, and c-MYC. Critically, the anti-proliferative effects of p53 are antagonized by rescue of CD133 expression in a p53 overexpressing cell line, indicating that the tumor suppressive activity of p53 might be mediated by CD133 suppression. Taken together, our results suggest that p53-mediated transcriptional regulation of CD133 is a key underlying mechanism for controlling the growth and tumor-initiating capacity of CSCs and provide a novel perspective on targeting CSCs for cancer therapy.

Curcumin improves the efficacy of cisplatin by targeting cancer stem-like cells through p21 and cyclin D1-mediated tumour cell inhibition in non-small cell lung cancer cell lines

Natural compounds such as curcumin have the ability to enhance the therapeutic effectiveness of common chemotherapy agents through cancer stem-like cell (CSC) sensitisation. In the present study, we showed that curcumin enhanced the sensitivity of the double-positive (CD166⁺/EpCAM⁺) CSC subpopulation in non-small cell lung cancer (NSCLC) cell lines (A549 and H2170) to cisplatin-induced apoptosis and inhibition of metastasis. Our results revealed that initial exposure of NSCLC cell lines to curcumin (10–40 µM) markedly reduced the percentage of viability to an average of ~51 and ~54% compared to treatment with low dose cisplatin (3 µM) with only 94 and 86% in both the A549 and H2170 cells. Moreover, sensitisation of NSCLC cell lines to curcumin through combined treatment enhanced the single effect induced by low dose cisplatin on the apoptosis of the double-positive CSC subpopulation by 18 and 20% in the A549 and H2170 cells, respectively. Furthermore, we found that curcumin enhanced the inhibitory effects of cisplatin on the highly migratory CD166⁺/EpCAM⁺ subpopulation, marked by a reduction in cell migration to 9 and 21% in the A549 and H2170 cells, respectively, indicating that curcumin may increase the sensitivity of CSCs to cisplatin-induced migratory inhibition. We also observed that the mRNA expression of cyclin D1 was downregulated, while a substantial increased in p21 expression was noted, followed by Apaf1 and caspase-9 activation in the double-positive (CD166⁺/EpCAM⁺) CSC subpopulation of A549 cells, suggested that the combined treatments induced cell cycle arrest, therefore triggering CSC growth inhibition via the intrinsic apoptotic pathway. In conclusion, we provided novel evidence of the previously unknown therapeutic effects of curcumin, either alone or in combination with cisplatin on the inhibition of the CD166⁺/EpCAM⁺ subpopulation of NSCLC cell lines. This finding demonstrated the potential therapeutic approach of using curcumin that may enhance the effects of cisplatin by targeting the CSC subpopulation in NSCLC.

Therapies targeting cancer stem cells: Current trends and future challenges

Traditional therapies against cancer, chemo- and radiotherapy, have multiple limitations that lead to treatment failure and cancer recurrence. These limitations are related to systemic and local toxicity, while treatment failure and cancer relapse are due to drug resistance and self-renewal, properties of a small population of tumor cells called cancer stem cells (CSCs). These cells are involved in cancer initiation, maintenance, metastasis and recurrence. Therefore, in order to develop efficient treatments that can induce a long-lasting clinical response preventing tumor relapse it is important to develop drugs that can specifically target and eliminate CSCs. Recent identification of surface markers and understanding of molecular feature associated with CSC phenotype helped with the design of effective treatments. In this review we discuss targeting surface biomarkers, signaling pathways that regulate CSCs self-renewal and differentiation, drug-efflux pumps involved in apoptosis resistance, microenvironmental signals that sustain CSCs growth, manipulation of miRNA expression, and induction of CSCs apoptosis and differentiation, with specific aim to hamper CSCs regeneration and cancer relapse. Some of these agents are under evaluation in preclinical and clinical studies, most of them for using in combination with traditional therapies. The combined therapy using conventional anticancer drugs with CSCs-targeting agents, may offer a promising strategy for management and eradication of different types of cancers.

The Emerging Role of Extracellular Vesicle-Mediated Drug Resistance in Cancers: Implications in Advanced Prostate Cancer

Emerging evidence has shown that the extracellular vesicles (EVs) regulate various biological processes and can control cell proliferation and survival, as well as being involved in normal cell development and diseases such as cancers. In cancer treatment, development of acquired drug resistance phenotype is a serious issue. Recently it has been shown that the presence of multidrug resistance proteins such as Pgp-1 and enrichment of the lipid ceramide in EVs could have a role in mediating drug resistance. EVs could also mediate multidrug resistance through uptake of drugs in vesicles and thus limit the bioavailability of drugs to treat cancer cells. In this review, we discussed the emerging evidence of the role EVs play in mediating drug resistance in cancers and in particular the role of EVs mediating drug resistance in advanced prostate cancer. The role of EV-associated multidrug resistance proteins, miRNA, mRNA, and lipid as well as the potential interaction(s) among these factors was probed. Lastly, we provide an overview of the current available treatments for advanced prostate cancer, considering where EVs may mediate the development of resistance against these drugs.

Therapies targeting cancer stem cells: Current trends and future challenges

Traditional therapies against cancer, chemo- and radiotherapy, have multiple limitations that lead to treatment failure and cancer recurrence. These limitations are related to systemic and local toxicity, while treatment failure and cancer relapse are due to drug resistance and self-renewal, properties of a small population of tumor cells called cancer stem cells (CSCs). These cells are involved in cancer initiation, maintenance, metastasis and recurrence. Therefore, in order to develop efficient treatments that can induce a long-lasting clinical response preventing tumor relapse it is important to develop drugs that can specifically target and eliminate CSCs. Recent identification of surface markers and understanding of molecular feature associated with CSC phenotype helped with the design of effective treatments. In this review we discuss targeting surface biomarkers, signaling pathways that regulate CSCs self-renewal and differentiation, drug-efflux pumps involved in apoptosis resistance, microenvironmental signals that sustain CSCs growth, manipulation of miRNA expression, and induction of CSCs apoptosis and differentiation, with specific aim to hamper CSCs regeneration and cancer relapse. Some of these agents are under evaluation in preclinical and clinical studies, most of them for using in combination with traditional therapies. The combined therapy using conventional anticancer drugs with CSCs-targeting agents, may offer a promising strategy for management and eradication of different types of cancers.

Novel delivery approaches for cancer therapeutics

Currently, a majority of cancer treatment strategies are based on the removal of tumor mass mainly by surgery. Chemical and physical treatments such as chemo- and radiotherapies have also made a major contribution in inhibiting rapid growth of malignant cells. Furthermore, these approaches are often combined to enhance therapeutic indices. It is widely known that surgery, chemo- and radiotherapy also inhibit normal cells growth. In addition, these treatment modalities are associated with severe side effects and high toxicity which in turn lead to low quality of life. This review encompasses novel strategies for more effective chemotherapeutic delivery aiming to generate better prognosis. Currently, cancer treatment is a highly dynamic field and significant advances are being made in the development of novel cancer treatment strategies. In contrast to conventional cancer therapeutics, novel approaches such as ligand or receptor based targeting, triggered release, intracellular drug targeting, gene delivery, cancer stem cell therapy, magnetic drug targeting and ultrasound-mediated drug delivery, have added new modalities for cancer treatment. These approaches have led to selective detection of malignant cells leading to their eradication with minimal side effects. Lowering multi-drug resistance and involving influx transportation in targeted drug delivery to cancer cells can also contribute significantly in the therapeutic interventions in cancer.

Galectin-3 modulates the EGFR signalling-mediated regulation of Sox2 expression via c-Myc in lung cancer

Galectin-3 is a ubiquitous lectin exerting multiple cellular functions such as RNA splicing, protein trafficking and apoptosis. Its expression is positively correlated with the poor prognosis in lung cancer patients. Galectin-3 can promote cancer progression through its effects on cell proliferation, cell survival or cancer metastasis. However, the role of galectin-3 in the regulation of cancer stem-like cells (CSCs) is still unclear. Here, we investigated the hypothesis that galectin-3 might regulate lung CSCs via the EGF receptor (EGFR) signaling pathway. In our study, galectin-3 facilitated EGFR activation and enhanced the sphere formation activity of lung cancer cells. Furthermore, galectin-3 promoted Sox2 expression in an EGFR activation-dependent manner; importantly, forced expression of Sox2 blunted the effect of galectin-3 knockdown on lung cancer sphere formation ability. These results suggest that galectin-3 promotes EGFR activation leading to the upregulation of Sox2 expression and lung CSCs properties. Moreover, we showed that the carbohydrate-binding activity of galectin-3 was important for the regulation of EGFR activation, Sox2 expression and sphere formation. We have recently reported that c-Myc is a transcriptional activator of Sox2. We further found that galectin-3 enhanced c-Myc protein stability leading to increased c-Myc binding to the Sox2 gene promoter. We also examined the effect of the stemness factors, Oct4, Nanog and Sox2 on the expression of galectin-3. We found that Oct4 enhanced galectin-3 expression. Our results together suggest that galectin-3 enhances lung cancer stemness through the EGFR/c-Myc/Sox2 axis; Oct4, in turn, promotes galectin-3 expression, forming a positive regulatory loop in lung CSCs.

Therapeutic effect of anti CEACAM6 monoclonal antibody against lung adenocarcinoma by enhancing anoikis sensitivity

Carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6) plays a crucial role in tumorigenesis of lung cancer. However, the therapeutic potential for anti CEACAM6 monoclonal antibody (mAb) has only been limitedly explored. Here, we evaluate the therapeutic potential of naked anti CEACAM6 mAb against lung adenocarcinoma. Clone 8F5, recognizing B domain of CEACAM6, is established by immunizing A549 cells and screening for clones double positive for A549 and CEACAM6-Fc recombinant protein. We found that 85.7% of 70 resected lung adenocarcinoma tissue sections were positive for CEACAM6, whereas all squamous cell carcinoma examined were negative. A549 cells with high levels of CEACAM6 demonstrated more aggressive growth nature and showed increased paclitaxel chemosensitivity upon 8F5 binding. Treatment with 8F5 to A549 decreased cellular CEACAM6 expression and reversed anoikis resistance. 8F5 also decreased cellular status of Akt phosphorylation and increased apoptosis via caspase activation. In a mouse model of lung adenocarcinoma with xenotransplanted A549 cells, 8F5 treatment alone demonstrated 40% tumor growth inhibition. When combined with paclitaxel treatment, 8F5 markedly enhanced tumor growth inhibition, up to 80%. In summary, we demonstrate that anti CEACAM6 mAb is an effective therapeutic treatment for lung adenocarcinoma whose effect is further enhanced by combined treatment with paclitaxel.

Nanomedicine-mediated cancer stem cell therapy

Circumstantial evidence suggests that most tumours are heterogeneous and contain a small population of cancer stem cells (CSCs) that exhibit distinctive self-renewal, proliferation and differentiation capabilities, which are believed to play a crucial role in tumour progression, drug resistance, recurrence and metastasis in multiple malignancies. Given that the existence of CSCs is a primary obstacle to cancer therapy, a tremendous amount of effort has been put into the development of anti-CSC strategies, and several potential approaches to kill therapeutically-resistant CSCs have been explored, including inhibiting ATP-binding cassette transporters, blocking essential signalling pathways involved in self-renewal and survival of CSCs, targeting CSCs surface markers and destroying the tumour microenvironment. Meanwhile, an increasing number of therapeutic agents (e.g. small molecule drugs, nucleic acids and antibodies) to selectively target CSCs have been screened or proposed in recent years. Drug delivery technology-based approaches hold great potential for tackling the limitations impeding clinical applications of CSC-specific agents, such as poor water solubility, short circulation time and inconsistent stability. Properly designed nanocarrier-based therapeutic agents (or nanomedicines) offer new possibilities of penetrating CSC niches and significantly increasing therapeutic drug accumulation in CSCs, which are difficult for free drug counterparts. In addition, intelligent nanomedicine holds great promise to overcome pump-mediated multidrug resistance which is driven by ATP and to decrease detrimental effects on normal somatic stem cells. In this review, we summarise the distinctive biological processes related to CSCs to highlight strategies against inherently drug-resistant CSCs. We then focus on some representative examples that give a glimpse into state-of-the-art nanomedicine approaches developed for CSCs elimination. A perspective on innovative therapeutic strategies and the potential direction of nanomedicine-based CSC therapy in the near future is also presented.

Targeting CD133(+) laryngeal carcinoma cells with chemotherapeutic drugs and siRNA against ABCG2 mediated by thermo/pH-sensitive mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSNs) represent a new form of drug nanocarrier with thermo/pH-coupling sensitivity and site-specificity. CD133(+) Hep-2 laryngeal cancer cells are responsible for multidrug resistance due to elevated expression of ABCG2. Since positively charged nanoparticles could easily uptake nucleic acids, we examined the possibility of using this new drug delivery system to simultaneously deliver different chemotherapeutic drugs and siRNA targeting ABCG2. Our results demonstrated that both antitumor drugs and siRNA against ABCG2 were successfully delivered into CD133(+) cancer cells by loaded MSNs. Down-regulation of ABCG2 significantly enhanced the efficacy of chemotherapeutic drug-induced apoptosis in laryngeal carcinoma cells. Furthermore, the chemotherapeutic drug and siRNA loaded nanoparticles inhibited tumor growth in vivo in a laryngeal cancer mouse model.

Alternative Treatments For Melanoma: Targeting BCL-2 Family Members to De-Bulk and Kill Cancer Stem Cells

For the first time new treatments in melanoma have produced significant responses in advanced diseases, but 30-90% of melanoma patients do not respond or eventually relapse after the initial response to the current treatments. The resistance of these melanomas is likely due to tumor heterogeneity, which may be explained by models such as the stochastic, hierarchical, and phenotype-switching models. This review will discuss the recent advancements in targeting BCL-2 family members for cancer treatments, and how this approach can be applied as an alternative option to combat melanoma, and overcome melanoma relapse or resistance in current treatment regimens.

A critical role of Oct4A in mediating metastasis and disease-free survival in a mouse model of ovarian cancer

BACKGROUND

High grade epithelial ovarian cancer (EOC) is commonly characterised by widespread peritoneal dissemination and ascites. Metastatic EOC tumour cells can attach directly to neighbouring organs or alternatively, maintain long term tumourigenicity and chemoresistance by forming cellular aggregates (spheroids). Cancer stem-like cells are proposed to facilitate this mechanism. This study aimed to investigate the role of Oct4A, an embryonic stem cell factor and known master regulator of pluripotency in EOC progression, metastasis and chemoresistance.

METHODS

To investigate the expression of Oct4A in primary EOC tumours, IHC and qRT-PCR analyses were used. The expression of Oct4A in chemonaive and recurrent EOC patient ascites-derived tumour cells samples was investigated by qRT-PCR. The functional role of Oct4A in EOC was evaluated by generating stable knockdown Oct4A clones in the established EOC cell line HEY using shRNA-mediated silencing technology. Cellular proliferation, spheroid forming ability, migration and chemosensitivty following loss of Oct4A in HEY cells was measured by in vitro functional assays. These observations were further validated in an in vivo mouse model using intraperitoneal (IP) injection of established Oct4A KD clones into Balb/c nu/nu mice.

RESULTS

We demonstrate that, compared to normal ovaries Oct4A expression significantly increases with tumour dedifferentiation. Oct4A expression was also significantly high in the ascites-derived tumour cells of recurrent EOC patients compared to chemonaive patients. Silencing of Oct4A in HEY cells resulted in decreased cellular proliferation, migration, spheroid formation and increased chemosensitivity to cisplatin in vitro. IP injection of Oct4A knockdown cells in vivo produced significantly reduced tumour burden, tumour size and invasiveness in mice, which overall resulted in significantly increased mouse survival rates compared to mice injected with control cells.

CONCLUSIONS

This data highlights a crucial role for Oct4A in the progression and metastasis of EOC. Targeting Oct4A may prove to be an effective strategy in the treatment and management of epithelial ovarian tumours.

Hedgehog Signaling in the Maintenance of Cancer Stem Cells

Cancer stem cells (CSCs) represent a rare population of cells with the capacity to self-renew and give rise to heterogeneous cell lineages within a tumour. Whilst the mechanisms underlying the regulation of CSCs are poorly defined, key developmental signaling pathways required for normal stem and progenitor functions have been strongly implicated. Hedgehog (Hh) signaling is an evolutionarily-conserved pathway essential for self-renewal and cell fate determination. Aberrant Hh signaling is associated with the development and progression of various types of cancer and is implicated in multiple aspects of tumourigenesis, including the maintenance of CSCs. Here, we discuss the mounting evidence suggestive of Hh-driven CSCs in the context of haematological malignancies and solid tumours and the novel strategies that hold the potential to block many aspects of the transformation attributed to the CSC phenotype, including chemotherapeutic resistance, relapse and metastasis.

Long non-coding RNA HOTAIR: A novel oncogene (Review)

Long non-coding RNAs (lncRNAs) have been found to be pervasively transcribed in the genome and are critical regulators of the epigenome. Increasing evidence suggests that lncRNAs are aberrantly expressed in several types of human cancer and that they are important in the initiation, development and metastasis of human cancer. Previous studies have revealed that HOX transcript antisense intergenic RNA (HOTAIR) was frequently upregulated in various types of cancer, including breast cancer, esophageal cancer, lung cancer and gastric cancer. In addition, patients with high expression levels of HOTAIR have a significantly poorer prognosis, compared with those with low levels of expression. HOTAIR is involved in the control of cell apoptosis, growth, metastasis, angiogenesis, DNA repair and tumor cells metabolism. The present review provides an overview of the current knowledge concerning the role of HOTAIR in tumor development and progression.

A literature mining-based approach for identification of cellular pathways associated with chemoresistance in cancer

Chemoresistance is a major obstacle to the successful treatment of many human cancer types. Increasing evidence has revealed that chemoresistance involves many genes and multiple complex biological mechanisms including cancer stem cells, drug efflux mechanism, autophagy and epithelial-mesenchymal transition. Many studies have been conducted to investigate the possible molecular mechanisms of chemoresistance. However, understanding of the biological mechanisms in chemoresistance still remains limited. We surveyed the literature on chemoresistance-related genes and pathways of multiple cancer types. We then used a curated pathway database to investigate significant chemoresistance-related biological pathways. In addition, to investigate the importance of chemoresistance-related markers in protein-protein interaction networks identified using the curated database, we used a gene-ranking algorithm designed based on a graph-based scoring function in our previous study. Our comprehensive survey and analysis provide a systems biology-based overview of the underlying mechanisms of chemoresistance.