A role for cancer stem cells in therapy resistance: Cellular and molecular mechanisms

Autophagy in cancer: Recent advances and future directions

Autophagy is being explored as a potential therapeutic target for enhancing the cytotoxic effects of chemotherapeutic regimens in various malignancies. Autophagy plays a very important role in cancer pathogenesis. Here, we discuss the updates on the modulation of autophagy via dynamic interactions with different organelles and the exploitation of selective autophagy for exploring therapeutic strategies. We further discuss the role of autophagy inhibitors in cancer preclinical and clinical trials, novel autophagy inhibitors, and challenges likely to be faced by clinicians while inducting autophagy modulators in clinical practice.

Cellular, transcriptomic and isoform heterogeneity of breast cancer cell line revealed by full-length single-cell RNA sequencing

Tumor heterogeneity is generated through a combination of genetic and epigenetic mechanisms, the latter of which plays an important role in the generation of stem like cells responsible for tumor formation and metastasis. Although the development of single cell transcriptomic technologies holds promise to deconvolute this complexity, a number of these techniques have limitations including drop-out and uneven coverage, which challenge the further delineation of tumor heterogeneity. We adopted deep and full-length single-cell RNA sequencing on Fluidigm's Polaris platform to reveal the cellular, transcriptomic, and isoform heterogeneity of SUM149, a triple negative breast cancer (TNBC) cell line. We first validate the quality of the TNBC sequencing data with the sequencing data from erythroleukemia K562 cell line as control. We next scrutinized well-defined marker genes for cancer stem-like cell to identify different cell populations. We then profile the isoform expression data to investigate the heterogeneity of alternative splicing patterns. Though classified as triple-negative breast cancer, the SUM149 stem cells show heterogeneous expression of marker receptors (ER, PR, and HER2) across the cells. We identified three cell populations that express patterns of stemness: epithelial-mesenchymal transition (EMT) cancer stem cells (CSCs), mesenchymal-epithelial transition (MET) CSCs and Dual-EMT-MET CSCs. These cells also manifested a high level of heterogeneity in alternative splicing patterns. For example, CSCs have shown different expression patterns of the CD44v6 exon, as well as different levels of truncated EGFR transcripts, which may suggest different potentials for proliferation and invasion among cancer stem cells. Our study identified features of the landscape of previously underestimated cellular, transcriptomic, and isoform heterogeneity of cancer stem cells in triple-negative breast cancers.

Novel Therapeutic Strategies for Ovarian Cancer Stem Cells

Ovarian cancer (OC) is one of the most lethal gynecologic malignancies. Due to the lack of specific symptoms and screening methods, this disease is usually diagnosed only at an advanced and metastatic stage. The gold-standard treatment for OC patients consists of debulking surgery followed by taxane combined with platinum-based chemotherapy. Most patients show complete clinical remission after first-line therapy, but the majority of them ultimately relapse, developing radio- and chemoresistant tumors. It is now proposed that the cause of recurrence and reduced therapy efficacy is the presence of small populations of cancer stem cells (CSCs). These cells are usually resistant against conventional cancer therapies and for this reason, effective targeted therapies for the complete eradication of CSCs are urgently needed. In this review article, we highlight the mechanisms of CSC therapy resistance, epithelial-to-mesenchymal transition, stemness, and novel therapeutic strategies for ovarian CSCs.

Recent Progress of Stem Cell Therapy in Cancer Treatment: Molecular Mechanisms and Potential Applications

The insufficient and unspecific target of traditional therapeutic approaches in cancer treatment often leads to therapy resistance and cancer recurrence. Over the past decades, accumulating discoveries about stem cell biology have provided new potential approaches to cure cancer patients. Stem cells possess unique biological actions, including self-renewal, directional migration, differentiation, and modulatory effects on other cells, which can be utilized as regenerative medicine, therapeutic carriers, drug targeting, and generation of immune cells. In this review, we emphasize the mechanisms underlying the use of various types of stem cells in cancer treatment. In addition, we summarize recent progress in the clinical applications of stem cells, as well as common risks of this therapy. We finally give general directions for future studies, aiming to improve overall outcomes in the fight against cancer.

The Role of Cancer Stem Cells in Radiation Resistance

Cancer stem cells (CSC) are a distinct subpopulation within a tumor. They are able to self-renew and differentiate and possess a high capability to repair DNA damage, exhibit low levels of reactive oxygen species (ROS), and proliferate slowly. These features render CSC resistant to various therapies, including radiation therapy (RT). Eradication of all CSC is a requirement for an effective antineoplastic treatment and is therefore of utmost importance for the patient. This makes CSC the prime targets for any therapeutic approach. Albeit clinical data is still scarce, experimental data and first clinical trials give hope that CSC-targeted treatment has the potential to improve antineoplastic therapies, especially for tumors that are known to be treatment resistant, such as glioblastoma. In this review, we will discuss CSC in the context of RT, describe known mechanisms of resistance, examine the possibilities of CSC as biomarkers, and discuss possible new treatment approaches.

Cancer cell stemness, responses to experimental genotoxic treatments, cytomegalovirus protein expression and DNA replication stress in pediatric medulloblastomas

Despite recent progress in research on brain tumors, including identification of cancer stem-like cells (CSCs), little is known about the interplay of stemness with the commonly observed infection by the human cytomegalovirus (HCMV) and the widespread features of replication stress in these malignancies. To shed more light on these outstanding issues, here we combine immunohistochemical analysis of archival clinical specimens from a cohort of 25 human pediatric medulloblastomas, complemented by functional experiments and analytical approaches to examine three medulloblastoma cell lines. In the clinical samples, we find consistent, yet individually variable subsets of CSCs expressing the stem-cell markers CD133 and CD15, and a candidate marker VEGFR2, across the spectrum of endogenous DNA damage (γH2AX), expression of HCMV immediate early and late proteins, proliferation rate (Ki67) or molecular class of MB. Contrary to MB cell lines DAOY and D324, the D283 cells showed pronounced phenotypic features of stemness, associated with enhanced endogenous DNA damage, exceptionally high susceptibility to infection with HCMV, unorthodox signaling pathway response to ionizing radiation and hyperactive response to hydroxyurea-induced replication stress. Notably, single-molecule DNA fiber analysis revealed aberrantly slow replication fork progression, pronounced fork asymmetry and inability to timely recover from drug-induced fork stalling in stem-like D283 cells, all hallmarks of pronounced chronic replication stress and propensity to genomic instability. These findings provide insights into human medulloblastoma stemness phenotypes, with various susceptibilities to infection by HCMV and impact on replication fork (mal)function, with implications for better understanding pathogenesis and responses to treatment in pediatric brain malignancies.Abbreviations: CSC: cancer stem-like cells; FBS: fetal bovine serum; HCMV: human cytomegalovirus; MB: medulloblastoma; MBSC: medulloblastoma stem cells; MOI: multiplicity of infection; PBS: phosphate-buffered saline; RPA: replication protein A; RS: replication stress; SHH: sonic hedgehog; VEGFR2: vascular endothelia growth factor receptor 2.

Targeting cancer stem cell pathways for cancer therapy

Since cancer stem cells (CSCs) were first identified in leukemia in 1994, they have been considered promising therapeutic targets for cancer therapy. These cells have self-renewal capacity and differentiation potential and contribute to multiple tumor malignancies, such as recurrence, metastasis, heterogeneity, multidrug resistance, and radiation resistance. The biological activities of CSCs are regulated by several pluripotent transcription factors, such as OCT4, Sox2, Nanog, KLF4, and MYC. In addition, many intracellular signaling pathways, such as Wnt, NF-κB (nuclear factor-κB), Notch, Hedgehog, JAK-STAT (Janus kinase/signal transducers and activators of transcription), PI3K/AKT/mTOR (phosphoinositide 3-kinase/AKT/mammalian target of rapamycin), TGF (transforming growth factor)/SMAD, and PPAR (peroxisome proliferator-activated receptor), as well as extracellular factors, such as vascular niches, hypoxia, tumor-associated macrophages, cancer-associated fibroblasts, cancer-associated mesenchymal stem cells, extracellular matrix, and exosomes, have been shown to be very important regulators of CSCs. Molecules, vaccines, antibodies, and CAR-T (chimeric antigen receptor T cell) cells have been developed to specifically target CSCs, and some of these factors are already undergoing clinical trials. This review summarizes the characterization and identification of CSCs, depicts major factors and pathways that regulate CSC development, and discusses potential targeted therapy for CSCs.

miRNAs as radio-response biomarkers for breast cancer stem cells

In breast cancer (BC), the presence of cancer stem cells (CSCs) has been related to relapse, metastasis, and radioresistance. Radiotherapy (RT) is an extended BC treatment, but is not always effective. CSCs have several mechanisms of radioresistance in place, and some miRNAs are involved in the cellular response to ionizing radiation (IR). Here, we studied how IR affects the expression of miRNAs related to stemness in different molecular BC subtypes. Exposition of BC cells to radiation doses of 2, 4, or 6 Gy affected their phenotype, functional characteristics, pluripotency gene expression, and in vivo tumorigenic capacity. This held true for various molecular subtypes of BC cells (classified by ER, PR and HER‐2 status), and for BC cells either plated in monolayer, or being in suspension as mammospheres. However, the effect of IR on the expression of eight stemness‐ and radioresistance‐related miRNAs (miR‐210, miR‐10b, miR‐182, miR‐142, miR‐221, miR‐21, miR‐93, miR‐15b) varied, depending on cell line subpopulation and clinicopathological features of BC patients. Therefore, clinicopathological features and, potentially also, chemotherapy regimen should be both taken into consideration, for determining a potential miRNA signature by liquid biopsy in BC patients treated with RT. Personalized and precision RT dosage regimes could improve the prognosis, treatment, and survival of BC patients.

L1 Cell Adhesion Molecule Confers Radioresistance to Ovarian Cancer and Defines a New Cancer Stem Cell Population

Many solid tumors, including ovarian cancer, contain small populations of cancer stem cells (CSCs). These cells are usually resistant against conventional cancer therapies and play a role in disease recurrence. We demonstrated that the L1 cell adhesion molecule (L1CAM) is a new CSC target in ovarian cancer, triggering radioresistance. Using fluorescence-activated cell sorting, specific cell populations expressing L1CAM alone or in combination with the established CSC marker CD133 were isolated from three ovarian cancer cell lines. Double-positive L1CAM+/CD133+ cells displayed higher spherogenic and clonogenic properties in comparison to L1CAM-/CD133- cells. Furthermore, L1CAM+/CD133+ cells retained highest clonogenic capacity after irradiation and exhibited up-regulation of some CSC-specific genes, enhanced tumor-initiating capacity, self-renewal and higher tumor take rate in nude mice when compared with other cell populations. Superior radioresistance by L1CAM expression was confirmed by deletion of L1CAM using CRISPR-Cas9 technology. Moreover, we found expression signatures associated with epithelial-to-mesenchymal transition phenotype in L1CAM deleted cells. These results indicate that L1CAM in combination with CD133 defines a new cancer cell population of ovarian tumor-initiating cells with the implication of targeting L1CAM as a novel therapeutic approach for ovarian CSCs.

Breast Tumor Cells Highly Resistant to Drugs Are Controlled Only by the Immune Response Induced in an Immunocompetent Mouse Model

Background: The tumor cells responsible for metastasis are highly resistant to chemotherapy and have characteristics of stem cells, with a high capacity for self-regeneration and the use of detoxifying mechanisms that participate in drug resistance. In vivo models of highly resistant cells allow us to evaluate the real impact of the immune response in the control of cancer. Materials and Methods: A tumor population derived from the 4T1 breast cancer cell line that was stable in vitro and highly aggressive in vivo was obtained, characterized, and determined to exhibit cancer stem cell (CSC) phenotypes (CD44⁺, CD24⁺, ALDH⁺, Oct4⁺, Nanog⁺, Sox2⁺, and high self-renewal capacity). Orthotopic transplantation of these cells allowed us to evaluate their in vivo susceptibility to chemo and immune responses induced after vaccination. Results: The immune response induced after vaccination with tumor cells treated with doxorubicin decreased the formation of tumors and macrometastasis in this model, which allowed us to confirm the immune response relevance in the control of highly chemotherapy-resistant ALDH⁺ CSCs in an aggressive tumor model in immunocompetent animals. Conclusions: The antitumor immune response was the main element capable of controlling tumor progression as well as metastasis in a highly chemotherapy-resistant aggressive breast cancer model.

Actinomycin D and Telmisartan Combination Targets Lung Cancer Stem Cells Through the Wnt/Beta Catenin Pathway

The failure of lung cancer treatments has been attributed mostly to the development of drug resistance, however the underlying cellular and molecular mechanisms are poorly understood. Cancer initiating stem cells (CSCs), present in tumors in a small percentage, play critical roles in the development of drug resistance, metastasis, and cancer relapse. Hence, novel treatments targeting both bulk cancer cells and CSCs are under intense investigation. Herein, we report that lung cancer cells grown on a 3D fibrous scaffold form tumoroids that resemble in vivo tumors, expand CSCs, and provide a platform to identify anti-CSC drugs. The screening of an NCI library of FDA-approved drugs using tumoroid cultures led to identification of Actinomycin D (AD) as a top CSC inhibitor. Since CSCs are mostly resident in the tumor's inner core, AD was combined with an angiotensin receptor antagonist, Telmisartan (TS), which is known to increase drug permeability in tumors and was shown to have anti-CSC activity. Our results showed that AD + TS administered intra-tumorally was significantly more effective than either drug alone in both syngeneic and xenograft mouse models. The results of mechanistic studies revealed that CSC expansion in tumoroids was associated with activation of β catenin signaling and that AD + TS treatment reduced active β catenin levels in tumors. Together, these results establish the utility of the tumoroid culture system to expand CSCs ex vivo for targeted drug screening, to identify promising novel treatments with both anti-CSC and anti-cancer effects, and to individualize treatments for metastatic drug resistant lung cancer patients.

Novel Therapeutics Against Breast Cancer Stem Cells by Targeting Surface Markers and Signaling Pathways

Background:

Breast cancer remains to be one of the deadliest forms of cancers, owing to the drug resistance and tumor relapse caused by breast cancer stem cells (BCSCs) despite notable advancements in radio-chemotherapies.

Objective:

To find out novel therapeutics against breast cancer stem cells by aiming surface markers and signaling pathways.

Methods:

A systematic literature search was conducted through various electronic databases including, Pubmed, Scopus, Google scholar using the keywords "BCSCs, surface markers, signaling pathways and therapeutic options against breast cancer stem cell. Articles selected for the purpose of this review were reviewed and extensively analyzed.

Results:

Novel therapeutic strategies include targeting BCSCs surface markers and aberrantly activated signaling pathways or targeting their components, which play critical roles in self-renewal and defense, have been shown to be significantly effective against breast cancer. In this review, we represent a number of ways against BCSCs surface markers and hyper-activated signaling pathways to target this highly malicious entity of breast cancer more effectively in order to make a feasible and useful strategy for successful breast cancer treatment. In addition, we discuss some characteristics of BCSCs in disease progression and therapy resistance.

Conclusion:

BCSCs involved in cancer pathogenesis, therapy resistance and cancer recurrence. Thus, it is suggested that a multi-dimensional therapeutic approach by targeting surface markers and aberrantly activated signaling pathways of BCSCs alone or in combination with each other could really be worthwhile in the treatment of breast cancer.

Rewiring of Cancer Cell Metabolism by Mitochondrial VDAC1 Depletion Results in Time-Dependent Tumor Reprogramming: Glioblastoma as a Proof of Concept

Reprograming of the metabolism of cancer cells is an event recognized as a hallmark of the disease. The mitochondrial gatekeeper, voltage-dependent anion channel 1 (VDAC1), mediates transport of metabolites and ions in and out of mitochondria, and is involved in mitochondria-mediated apoptosis. Here, we compared the effects of reducing hVDAC1 expression in a glioblastoma xenograft using human-specific si-RNA (si-hVDAC1) for a short (19 days) and a long term (40 days). Tumors underwent reprograming, reflected in rewired metabolism, eradication of cancer stem cells (CSCs) and differentiation. Short- and long-term treatments of the tumors with si-hVDAC1 similarly reduced the expression of metabolism-related enzymes, and translocator protein (TSPO) and CSCs markers. In contrast, differentiation into cells expressing astrocyte or neuronal markers was noted only after a long period during which the tumor cells were hVDAC1-depleted. This suggests that tumor cell differentiation is a prolonged process that precedes metabolic reprograming and the “disappearance” of CSCs. Tumor proteomics analysis revealing global changes in the expression levels of proteins associated with signaling, synthesis and degradation of proteins, DNA structure and replication and epigenetic changes, all of which were highly altered after a long period of si-hVDAC1 tumor treatment. The depletion of hVDAC1 greatly reduced the levels of the multifunctional translocator protein TSPO, which is overexpressed in both the mitochondria and the nucleus of the tumor. The results thus show that VDAC1 depletion-mediated cancer cell metabolic reprograming involves a chain of events occurring in a sequential manner leading to a reversal of the unique properties of the tumor, indicative of the interplay between metabolism and oncogenic signaling networks.

Inhibition of aldehyde dehydrogenase-1 and p-glycoprotein-mediated multidrug resistance by curcumin and vitamin D3 increases sensitivity to paclitaxel in breast cancer

Treatment of breast cancer by paclitaxel (PAX) often encounters therapeutic failure most likely caused by innate/acquired resistance. Cancer stem cells (CSCs) and multidrug resistance complex (MDR-1 or P-glycoprotein) overexpression are main mechanisms implicated in chemoresistance. Increased aldehyde dehrogenase-1 (ALDH-1) was previously correlated with the stemness features of CSCs and hence is used as a marker for identification and CSCs targeting. The present study, therefore, aimed at investigating the effect of both curcumin (CUR) and vitamin D3 (D3) on MDR-1 and ALDH-1 expression and consequently the resistance to PAX both in vitro and in vivo. CUR was isolated from Turmeric rhizomes and identified using UPLC-ESI-MS/MS. For in vitro studies, the antiproliferative effect of PAX, CUR, 1,25(OH)2D3 (the active form of D3, also known as calcitriol) was determined, each alone and combined (PAX+CUR, PAX+1,25(OH)2D3, and PAX+CUR+1,25(OH)2D3) on MCF-7 breast cancer cells. Ehrlich ascites carcinoma solid tumor animal model was also used for in vivo studies. Combining CUR and/or 1,25(OH)2D3 to PAX showed synergistic cytotoxic interaction on MCF-7 cells. The apoptotic potential was also enhanced, as evidenced by a significant increase in caspase-7 and -9 as well as the pro-apoptotic Bax whereas a decrease in Bcl-2 levels was reported. Combining CUR and 1,25(OH)2D3 to PAX caused a downregulation in both MDR-1 and ALDH-1 gene expression in MCF-7 besides a decrease in their protein levels. In vivo, the triple therapy group (PAX+CUR+D3) showed the least tumor size. It also showed the lowest levels of MDR-1 and ALDH-1. PAX alone, however, showed increased levels of MDR-1 and ALDH-1 compared to control. Overall, the present study showed that PAX, as a monotherapy, demonstrated acquired resistance possibly by increasing MDR-1 expression and enriching CSCs population, as evidenced by increased ALDH-1. However, using CUR and D3 enhanced tumor response to PAX.

Long noncoding RNAs and exosomal lncRNAs: classification, and mechanisms in breast cancer metastasis and drug resistance

Breast cancer is the most common cancer, and the second cause of cancer-related deaths (after lung cancer) among women. Developing tumor metastasis and invasion is the most important cause of death in breast cancer patients. Several key factors participate in breast cancer metastasis including long noncoding RNAs (lncRNAs). lncRNAs are a category of cellular RNAs that are longer than 200 nucleotides in length. Accumulating evidence suggests that lncRNAs have the potential to be promising diagnostic, prognostic biomarkers and therapeutic targets in breast cancer. Understanding the role of lncRNAs and their mechanisms of functions might help to further discovery of breast cancer biological characteristics. In this review, we discuss physiological functions, epigenetic regulation, transcriptional regulation of lncRNAs, and their important role in tumor progression and metastasis. Some lncRNAs function as oncogenes and some function as tumor suppressors. Interestingly, recent reports depict that hypomethylation of promoters of lncRNAs play a pivotal role in cancer progression, suggesting the importance of epigenetic regulation. Furthermore, we discuss the role of lncRNAs in exosomes and their function in drug resistance, and therapeutic importance of exosomal lncRNAs in cancer biology. In summary, lncRNAs have a great potential to consider them as novel prognostic biomarkers as well as new therapeutic targets in breast cancer.

Identification of Two Protein-Signaling States Delineating Transcriptionally Heterogeneous Human Medulloblastoma

The brain cancer medulloblastoma consists of different transcriptional subgroups. To characterize medulloblastoma at the phosphoprotein-signaling level, we performed high-throughput peptide phosphorylation profiling on a large cohort of SHH (Sonic Hedgehog), group 3, and group 4 medulloblastomas. We identified two major protein-signaling profiles. One profile was associated with rapid death post-recurrence and resembled MYC-like signaling for which MYC lesions are sufficient but not necessary. The second profile showed enrichment for DNA damage, as well as apoptotic and neuronal signaling. Integrative analysis demonstrated that heterogeneous transcriptional input converges on these protein-signaling profiles: all SHH and a subset of group 3 patients exhibited the MYC-like protein-signaling profile; the majority of the other group 3 subset and group 4 patients displayed the DNA damage/apoptotic/neuronal signaling profile. Functional analysis of enriched pathways highlighted cell-cycle progression and protein synthesis as therapeutic targets for MYC-like medulloblastoma.

Immunomodulatory roles of nitric oxide in cancer: tumor microenvironment says "NO" to antitumor immune response

In recent years, an increasing number of studies have shown that there is an important connection between nitric oxide (NO) and the pathology of malignant diseases, but we are far from a complete comprehension of how this simple diatomic molecule contributes to tumorigenesis. The emerging identification of immune-mediated mechanisms regulated by NO may help to unravel the intricate and complex relationships between NO and cancer. Therefore, this review provides a summary of recent advances in our understanding of the immunomodulatory role of NO in cancer, and in particular the role of this pleiotropic signaling molecule as an immunosuppressive mediator in the tumor microenvironment. We will discuss the participation of NO in the different strategies used by tumors to escape from immune system-mediated recognition, including the acquisition of stem cell like capacities by tumor cells and the metabolic reprogramming of tumor infiltrating immune cells. Finally, we will also discuss different therapeutic strategies directed against NO for abating the immunosuppressive tumor microenvironment and to increase the efficacy of immunotherapy in cancer.

Lgr5 in cancer biology: functional identification of Lgr5 in cancer progression and potential opportunities for novel therapy

Cancer remains one of the leading lethal diseases worldwide. Identifying biomarkers of cancers might provide insights into the strategies for the development of novel targeted anti-cancer therapies. Leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5) has been recently discovered as a candidate marker of cancer stem cell populations. Aberrant increased expression of Lgr5 may represent one of the most common molecular alterations in some human cancers, leading to long-term potentiation of canonical Wnt/β-catenin signaling. On the other hand, however, Lgr5-mediated suppression in canonical Wnt/β-catenin signaling has also been reported in certain cancers, such as B cell malignancies. Until now, therapeutic approaches targeting Lgr5-associated signaling axis are not yet clinically available. Increasing evidence have indicated that endogenous Lgr5+ cell population is implicated in tumor initiation, progression, and metastasis. This review is to summarize our current knowledge about the importance of Lgr5 in cancer biology and the underlying molecular mechanisms of Lgr5-mediated tumor-promoting/suppressive activities, as well as potentially useful preventive strategies in treating tumor. Therefore, targeted therapeutic modulation of Lgr5+ cancer cell population by targeting Wnt/β-catenin signaling through targeted drug delivery system or targeted genome editing might be promising for potential novel anti-cancer treatments. Simultaneously, combination of therapeutics targeting both Lgr5+ and Lgr5- cancer cells may deserve further consideration considering the plasticity of cancer cells. Also, a more specific targeting of cancer cells using double biomarkers may be much safer and more effective for anti-cancer therapy.

Downregulation of FOXO3a by DNMT1 promotes breast cancer stem cell properties and tumorigenesis

Breast cancer stem cells (BCSCs) are tumor initiating cells that can self-renew and are highly tumorigenic and chemoresistant. Therefore, the identification of factors critical for BCSC function is vital for the development of therapies. Here, we report that DNMT1-mediated FOXO3a promoter hypermethylation leads to downregulation of FOXO3a expression in breast cancer. FOXO3a is functionally related to the inhibition of FOXM1/SOX2 signaling and to the consequent suppression of BCSCs properties and tumorigenicity. Moreover, we found that SOX2 directly transactivates DNMT1 expression and thereby alters the methylation landscape, which in turn feedback inhibits FOXO3a expression. Inhibition of DNMT activity suppressed tumor growth via regulation of FOXO3a/FOXM1/SOX2 signaling in breast cancer. Clinically, we observed a significant inverse correlation between FOXO3a and FOXM1/SOX2/DNMT1 expression levels, and loss of FOXO3a expression or increased expression of FOXM1, SOX2, and DNMT1 predicted poor prognosis in breast cancer. Collectively, our findings suggest an important role of the DNMT1/FOXO3a/FOXM1/SOX2 pathway in regulating BCSCs properties, suggesting potential therapeutic targets for breast cancer.

Enhanced anti-tumor efficacy and safety with metronomic intraperitoneal chemotherapy for metastatic ovarian cancer using biodegradable nanotextile implants

The objective of this study was to evaluate intraperitoneal (IP) metronomic chemotherapy using sustained release paclitaxel (PTX) delivery from electrospun biodegradable polymeric yarns woven into suturable nanotextiles. Following confirmation of in vitro PTX efficacy in ID8-VEGF epithelial ovarian cancer cells, in vivo studies were performed upon surgical peritoneal implantation of nanotextile implants in orthotopic, syngeneic ID8-VEGF tumor-bearing C57BL/6 mice. In comparison to the clinical PTX-solution, there was a significant enhancement of anti-tumor efficacy and safety with PTX-nanotextiles. After 35-days, the peritoneum of tumor-bearing mice with PTX-nanotextiles was completely devoid of tumor nodules and ascitic fluid. Additionally, VEGF levels measured in peritoneal lavage fluid were 300-fold lower compared to PTX-solution and 600-fold lower as compared to untreated tumor-bearing animals. PTX-solution treated group also developed severe metastatic lesions and progressive ascitic fluid buildup. More importantly, no signs of systemic/ organ toxicity were observed in PTX-nanotextile implanted mice, unlike the systemic toxic effects induced by PTX-solution. Collectively, our results show the therapeutic and safety advantages offered by combining clinically translatable metronomic low-dose chemotherapy and IP pharmacokinetics using biodegradable nanotextile implants in addressing the challenges of late-stage ovarian cancer.

Non-proteolytic ubiquitination of Hexokinase 2 by HectH9 controls tumor metabolism and cancer stem cell expansion

Enormous efforts have been made to target metabolic dependencies of cancer cells for developing new therapies. However, the therapeutic efficacy of glycolysis inhibitors is limited due to their inability to elicit cell death. Hexokinase 2 (HK2), via its mitochondrial localization, functions as a central nexus integrating glycolysis activation and apoptosis resilience. Here we identify that K63-linked ubiquitination by HectH9 regulates the mitochondrial localization and function of HK2. Through stable isotope tracer approach and functional metabolic analyses, we show that HectH9 deficiency impedes tumor glucose metabolism and growth by HK2 inhibition. The HectH9/HK2 pathway regulates cancer stem cell (CSC) expansion and CSC-associated chemoresistance. Histological analyses show that HectH9 expression is upregulated and correlated with disease progression in prostate cancer. This work uncovers that HectH9 is a novel regulator of HK2 and cancer metabolism. Targeting HectH9 represents an effective strategy to achieve long-term tumor remission by concomitantly disrupting glycolysis and inducing apoptosis.

Lumiflavin increases the sensitivity of ovarian cancer stem-like cells to cisplatin by interfering with riboflavin

Here, we used lumiflavin, an inhibitor of riboflavin, as a new potential therapeutic chemosensitizer to ovarian cancer stem‐like cells (CSCs). This study demonstrates that the enrichment of riboflavin in CSCs is an important cause of its resistance to chemotherapy. Lumiflavin can effectively reduce the riboflavin enrichment in CSCs and sensitize the effect of cisplatin Diamminedichloroplatinum (DDP) on CSCs. In this study, CSCs of human ovarian cancer cell lines HO8910 were separated using a magnetic bead (CD133+). We also show the overexpression of the mRNA and protein of riboflavin transporter 2 and the high content of riboflavin in CSCs compared to non‐CSCs (NON‐CSCs). Moreover, CSCs were less sensitive to DDP than NON‐CSCs, whereas, the synergistic effect of lumiflavin and DDP on CSCs was more sensitive than NON‐CSCs. Further research showed that lumiflavin had synergistic effects with DDP on CSCs in increasing mitochondrial function damage and apoptosis rates and decreasing clonic function. In addition, we found that the combination of DDP and lumiflavin therapy in vivo has a synergistic cytotoxic effect on an ovarian cancer nude mice model by enhancing the DNA‐damage response and increasing the apoptotic protein expression. Notably, the effect of lumiflavin is associated with reduced riboflavin concentration, and riboflavin could reverse the effect of DDP in vitro and in vivo. Accordingly, we conclude that lumiflavin interfered with the riboflavin metabolic pathways, resulting in a significant increase in tumour sensitivity to DDP therapy. Our study suggests that lumiflavin may be a novel treatment alternative for ovarian cancer and its recurrence.

Algae metabolites: from in vitro growth inhibitory effects to promising anticancer activity

Covering: 1957 to 2017 Algae constitute a heterogeneous group of eukaryotic photosynthetic organisms, mainly found in the marine environment. Algae produce numerous metabolites that help them cope with the harsh conditions of the marine environment. Because of their structural diversity and uniqueness, these molecules have recently gained a lot of interest for the identification of medicinally useful agents, including those with potential anticancer activities. In the current review, which is not a catalogue-based one, we first highlight the major biological events that lead to various types of cancer, including metastatic ones, to chemoresistance, thus to any types of current anticancer treatment relating to the use of chemotherapeutics. We then review algal metabolites for which scientific literature reports anticancer activity. Lastly, we focus on algal metabolites with promising anticancer activity based on their ability to target biological characteristics of cancer cells responsible for poor treatment outcomes. Thus, we highlight compounds that have, among others, one or more of the following characteristics: selectivity in reducing the proliferation of cancer cells over normal ones, potential for killing cancer cells through non-apoptotic signaling pathways, ability to circumvent MDR-related efflux pumps, and activity in vivo in relevant pre-clinical models.

MEK inhibitors activate Wnt signalling and induce stem cell plasticity in colorectal cancer

In colorectal cancer (CRC), aberrant Wnt signalling is essential for tumorigenesis and maintenance of cancer stem cells. However, how other oncogenic pathways converge on Wnt signalling to modulate stem cell homeostasis in CRC currently remains poorly understood. Using large-scale compound screens in CRC, we identify MEK1/2 inhibitors as potent activators of Wnt/β-catenin signalling. Targeting MEK increases Wnt activity in different CRC cell lines and murine intestine in vivo. Truncating mutations of APC generated by CRISPR/Cas9 strongly synergize with MEK inhibitors in enhancing Wnt responses in isogenic CRC models. Mechanistically, we demonstrate that MEK inhibition induces a rapid downregulation of AXIN1. Using patient-derived CRC organoids, we show that MEK inhibition leads to increased Wnt activity, elevated LGR5 levels and enrichment of gene signatures associated with stemness and cancer relapse. Our study demonstrates that clinically used MEK inhibitors inadvertently induce stem cell plasticity, revealing an unknown side effect of RAS pathway inhibition.

Multicellular gene network analysis identifies a macrophage-related gene signature predictive of therapeutic response and prognosis of gliomas

BACKGROUND

The tumor-associated microenvironment plays important roles in tumor progression and drug resistance. However, systematic investigations of macrophage-tumor cell interactions to identify novel macrophage-related gene signatures in gliomas for predicting patient prognoses and responses to targeted therapies are lacking.

METHODS

We developed a multicellular gene network approach to investigating the prognostic role of macrophage-tumor cell interactions in tumor progression and drug resistance in gliomas. Multicellular gene networks connecting macrophages and tumor cells were constructed from re-grouped drug-sensitive and drug-resistant samples of RNA-seq data in mice gliomas treated with BLZ945 (a CSF1R inhibitor). Subsequently, a differential network-based COX regression model was built to identify the risk signature using a cohort of 310 glioma samples from the Chinese Glioma Genome Atlas database. A large independent validation set of 690 glioma samples from The Cancer Genome Atlas database was used to test the prognostic significance and accuracy of the gene signature in predicting prognosis and targeted therapeutic response of glioma patients.

RESULTS

A macrophage-related gene signature was developed consisting of twelve genes (ANPEP, DPP4, PRRG1, GPNMB, TMEM26, PXDN, CDH6, SCN3A, SEMA6B, CCDC37, FANCA, NETO2), which was tested in the independent validation set to examine its prognostic significance and accuracy. The generation of 1000 random gene signatures by a bootstrapping scheme justified the non-random nature of the macrophage-related gene signature. Moreover, the discovered gene signature was verified to be predictive of the sensitivity or resistance of glioma patients to molecularly targeted therapeutics and outperformed other existing gene signatures. Additionally, the macrophage-related gene signature was an independent and the strongest prognostic factor when adjusted for clinicopathologic risk factors and other existing gene signatures.

CONCLUSION

The multicellular gene network approach developed herein indicates profound roles of the macrophage-mediated tumor microenvironment in the progression and drug resistance of gliomas. The identified macrophage-related gene signature has good prognostic value for predicting resistance to targeted therapeutics and survival of glioma patients, implying that combining current targeted therapies with new macrophage-targeted therapy may be beneficial for the long-term treatment outcomes of glioma patients.

MEK inhibitors activate Wnt signalling and induce stem cell plasticity in colorectal cancer

In colorectal cancer (CRC), aberrant Wnt signalling is essential for tumorigenesis and maintenance of cancer stem cells. However, how other oncogenic pathways converge on Wnt signalling to modulate stem cell homeostasis in CRC currently remains poorly understood. Using large-scale compound screens in CRC, we identify MEK1/2 inhibitors as potent activators of Wnt/β-catenin signalling. Targeting MEK increases Wnt activity in different CRC cell lines and murine intestine in vivo. Truncating mutations of APC generated by CRISPR/Cas9 strongly synergize with MEK inhibitors in enhancing Wnt responses in isogenic CRC models. Mechanistically, we demonstrate that MEK inhibition induces a rapid downregulation of AXIN1. Using patient-derived CRC organoids, we show that MEK inhibition leads to increased Wnt activity, elevated LGR5 levels and enrichment of gene signatures associated with stemness and cancer relapse. Our study demonstrates that clinically used MEK inhibitors inadvertently induce stem cell plasticity, revealing an unknown side effect of RAS pathway inhibition.

Wnt signaling is necessary for colorectal cancer tumorigenesis and stem cell maintenance. Here, the authors identify MEK1/2 inhibitors as potent activators of Wnt/β-catenin signalling and show that clinically approved MEK inhibitors inadvertently induce stem cell plasticity in colorectal cancer

BRCA Genes: The Role in Genome Stability, Cancer Stemness and Therapy Resistance

Carcinogenesis is a multistep process, and tumors frequently harbor multiple mutations regulating genome integrity, cell division and death. The integrity of cellular genome is closely controlled by the mechanisms of DNA damage signaling and DNA repair. The association of breast cancer susceptibility genes BRCA1 and BRCA2 with breast and ovarian cancer development was first demonstrated over 20 years ago. Since then the germline mutations within these genes were linked to genomic instability and increased risk of many other cancer types. Genomic instability is an engine of the oncogenic transformation of non-tumorigenic cells into tumor-initiating cells and further tumor evolution. In this review we discuss the biological functions of BRCA1 and BRCA2 genes and the role of BRCA mutations in tumor initiation, regulation of cancer stemness, therapy resistance and tumor progression.

Wnt Signaling: A Potential Therapeutic Target in Head and Neck Squamous Cell Carcinoma

Cellular maintenance and development are two fundamental mechanisms regulated by the canonical Wnt signaling pathway. Wnt/beta-catenin signaling pathway controls a myriad of cellular processes that are essential for normal cell functioning. Cell cycle progression, differentiation, fate determination, and migration are generally orchestrated by canonical Wnt signaling. Altered Wnt/beta-catenin signaling has been considered a promoting event for different types of cancers and the oncogenic potential of Wnt signaling have been discussed in many cancer types, including breast, colon, pancreatic as well as head and neck. Furthermore, Wnt signaling is critical for the maintenance and stemness of both the normal as well as cancer stem cells. This review sheds new light on Wnt signaling and explains how it can regulate normal physiological processes and curtail the development of cancer. It depicts the vital functions of Wnt signaling in the stem cell growth and differentiation by focusing on current druggable targets that have been ascribed by recent studies. Thus, Wnt signaling pathway retains a tremendous potential in eradicating head and neck squamous cell carcinoma.

Cancer stem cell immunology and immunotherapy: Harnessing the immune system against cancer's source

Despite recent advances in diagnosis and therapy having improved cancer outcome, many patients still do not respond to treatments, resulting in the progression or relapse of the disease, eventually impairing survival expectations. The limited efficacy of therapy is often attributable to its inability to affect cancer stem cells (CSCs), a small population of cells resistant to current radio- and chemo-therapies. CSCs are characterized by self-renewal and tumor-initiating capabilities, and function as a reservoir for the local and distant recurrence of the disease. Therefore, new therapeutic approaches able to effectively target and deplete CSCs are urgently needed. Immunotherapy is facing a renewed interest for its potential in cancer treatment, and the possibility of harnessing the immune system to target CSCs is being addressed by a new exciting research field. In this chapter, we discuss the cancer stem cell model and illustrate CSC biological and molecular properties, critically addressing theoretical and practical issues linked with their definition and study. We then review the existing literature regarding the immunological properties of CSCs and the complex interplay occurring between CSCs and immune cells. Finally, we present up-to-date studies on CSC immunotargeting and its potential future perspective. In conclusion, understanding the interplay between CSC biology and tumor immunology will provide a deeper understanding of the mechanisms that regulate CSC immunological properties. This will contribute to the design of new CSC-directed immunotherapeutic strategies with the potential of strongly improving cancer outcomes.

Cancer stem cells in radiation response: current views and future perspectives in radiation oncology

Purpose: Despite technological improvement and advances in biology-driven patient stratification, many patients still fail radiotherapy resulting in loco-regional and distant recurrence. Tumor heterogeneity remains a key challenge to effective cancer treatment, and reliable stratification of cancer patients for prediction of outcomes is highly important. Intratumoral heterogeneity is manifested at the different levels, including different tumorigenic properties of cancer cells. Since John Dick et al. isolated leukemia initiating cells in 1990, the populations of tumor initiating or cancer stem cells (CSCs) were identified and characterized also for a broad spectrum of solid tumor types. The properties of CSCs are of considerable clinical relevance: CSCs have self-renewal and tumor initiating potential, and the metastases are initiated by the CSC clones with the ability to disseminate from the primary tumor site. Conclusion: Evidence from both, experimental and clinical studies demonstrates that the probability of achieving local tumor control by radiation therapy depends on the complete eradication of CSC populations. The number, properties and molecular signature of CSCs are highly predictive for clinical outcome of radiotherapy, whereas targeted therapies against CSCs combined with conventional treatment are expected to provide an improved clinical response and prevent tumor relapse. In this review, we discuss the modern methods to study CSCs in radiation biology, the role of CSCs in personalized cancer therapy as well as future directions for CSC research in translational radiooncology.

Diversity of cancer stem cells in head and neck carcinomas: The role of HPV in cancer stem cell heterogeneity, plasticity and treatment response

Head and neck squamous cell carcinomas (HNSCC) resulting from oncogenic transformations following human papillomavirus (HPV) infection consistently demonstrate better treatment outcomes than HNSCC from other aetiologies. Squamous cell carcinoma of the oropharynx (OPSCC) shows the highest prevalence of HPV involvement at around 70-80%. While strongly prognostic, HPV status alone is not sufficient to predict therapy response or any potential dose de-escalation. Cancer stem cell (CSC) populations within these tumour types represent the most therapy-resistant cells and are the source of recurrence and metastases, setting a benchmark for tumour control. This review examines clinical and preclinical evidence of differences in response to treatment by the HPV statuses of HNSCC and the role played by CSCs in treatment resistance and their repopulation from non-CSCs. Evidence was collated from literature searches of PubMed, Scopus and Ovid for differential treatment response by HPV status and contribution by critical biomarkers including CSC fractions and chemo-radiosensitivity. While HPV and CSC are yet to fulfil promise as biomarkers of treatment response, understanding how HPV positive and negative aetiologies affect CSC response to treatment and tumour plasticity will facilitate their use for greater treatment individualisation.

Podoplanin in Inflammation and Cancer

Podoplanin is a small cell-surface mucin-like glycoprotein that plays a crucial role in the development of the alveoli, heart, and lymphatic vascular system. Emerging evidence indicates that it is also involved in the control of mammary stem-cell activity and biogenesis of platelets in the bone marrow, and exerts an important function in the immune response. Podoplanin expression is upregulated in different cell types, including fibroblasts, macrophages, T helper cells, and epithelial cells, during inflammation and cancer, where it plays important roles. Podoplanin is implicated in chronic inflammatory diseases, such as psoriasis, multiple sclerosis, and rheumatoid arthritis, promotes inflammation-driven and cancer-associated thrombosis, and stimulates cancer cell invasion and metastasis through a variety of strategies. To accomplish its biological functions, podoplanin must interact with other proteins located in the same cell or in neighbor cells. The binding of podoplanin to its ligands leads to modulation of signaling pathways that regulate proliferation, contractility, migration, epithelial⁻mesenchymal transition, and remodeling of the extracellular matrix. In this review, we describe the diverse roles of podoplanin in inflammation and cancer, depict the protein ligands of podoplanin identified so far, and discuss the mechanistic basis for the involvement of podoplanin in all these processes.

Silencing the OCT4-PG1 pseudogene reduces OCT-4 protein levels and changes characteristics of the multidrug resistance phenotype in chronic myeloid leukemia

Cancer stem cells show epigenetic plasticity and intrinsic resistance to anti-cancer therapy, rendering capable of initiating cancer relapse and progression. Transcription factor OCT-4 regulates various pathways in stem cells, but its expression can be regulated by pseudogenes. This work evaluated how OCT4-PG1 pseudogene can affect OCT-4 expression and mechanisms related to the multidrug resistance (MDR) phenotype in FEPS cells. Considering that OCT-4 protein is a transcription factor that regulates expression of ABC transporters, level of gene expression, activity of ABC proteins and cell sensitivity to chemotherapy were evaluated after OCT4-PG1 silencing. Besides we set up a STRING network. Results showed that after OCT4-PG1 silencing, cells expressed OCT-4 gene and protein to a lesser extent than mock cells. The gene and protein expression of ABCB1, as well as its activity were reduced. On the other hand, ALOX5 and ABCC1 genes was increased even as the activity of this transporter. Moreover, the silencing cells become sensitive to two chemotherapics tested. The network structure demonstrated that OCT4-PG1 protein interacts directly with OCT-4, SOX2, and NANOG and indirectly with ABC transporters. We conclude that OCT4-PG1 pseudogene plays a key role in the regulation OCT-4 transcription factor, which alters MDR phenotype in the FEPS cell line.

Cocktail Strategy Based on Spatio-Temporally Controlled Nano Device Improves Therapy of Breast Cancer

Metastatic breast cancer may be resistant to chemo-immunotherapy due to the existence of cancer stem cells (CSC). Also, the control of particle size and drug release of a drug carrier for multidrug combination is a key issue influencing the therapy effect. Here, a cocktail strategy is reported, in which chemotherapy against both bulk tumor cells and CSC and immune checkpoint blockade therapy are intergraded into one drug delivery system. The chemotherapeutic agent paclitaxel (PTX), the anti-CSC agent thioridazine (THZ), and the PD-1/PD-L1 inhibitor HY19991 (HY) are all incorporated into an enzyme/pH dual-sensitive nanoparticle with a micelle-liposome double-layer structure. The particle size shrinks when the nanoparticle transfers from circulation to tumor tissues, favoring both pharmacokinetics and cellular uptake, meanwhile achieving sequential drug release where needed. This nano device, named PM@THL, increases the intratumoral drug concentrations in mice and exhibits significant anticancer efficacy, with tumor inhibiting rate of 93.45% and lung metastasis suppression rate of 97.64%. It also reduces the proportion of CSC and enhances the T cells infiltration in tumor tissues, and thus prolongs the survival of mice. The cocktail therapy based on the spatio-temporally controlled nano device will be a promising strategy for treating breast cancer.

Identifying and targeting cancer stem cells in leiomyosarcoma: prognostic impact and role to overcome secondary resistance to PI3K/mTOR inhibition

Background

Leiomyosarcoma (LMS) is one of the most frequent soft tissue sarcoma subtypes and is characterized by a consistent deregulation of the PI3K/mTOR pathway. Cancer stem cells (CSCs) have been poorly studied in soft tissue sarcomas. In this study, we aimed to evaluate the association between CSCs, the outcome of LMS patients, and the resistance to PI3K/mTOR pathway inhibition.

Methods

We investigated the relationships between aldehyde dehydrogenase 1 (ALDH1) expression, a cancer stem cell marker, and the outcome of LMS patients in two independent cohorts. We assessed the impact of CSCs in resistance to PI3K/mTOR pathway inhibition using LMS cell lines, a xenograft mouse model, and human tumor samples.

Results

We found that enhanced ALDH1 activity is a hallmark of LMS stem cells and is an independent prognostic factor. We also identified that secondary resistance to PI3K/mTOR pathway inhibition was associated with the expansion of LMS CSCs. Interestingly, we found that EZH2 inhibition, a catalytic component of polycomb repressive complex which plays a critical role in stem cell maintenance, restored sensitivity to PI3K/mTOR pathway inhibition. Importantly, we confirmed the clinical relevance of our findings by analyzing tumor samples from patients who showed secondary resistance after treatment with a PI3Kα inhibitor.

Conclusions

Altogether, our findings suggest that CSCs have a strong impact on the outcome of patients with LMS and that combining PI3K/mTOR and EZH2 inhibitors may represent a promising strategy in this setting.

Electronic supplementary material

The online version of this article (10.1186/s13045-018-0694-1) contains supplementary material, which is available to authorized users.

Nanodiamonds: Minuscule gems that ferry antineoplastic drugs to resistant tumors

Remarkable efforts are currently devoted to the area of nanodiamonds (NDs) research due to their superior properties viz: biocompatibility, minute size, inert core, and tunable surface chemistry. The use of NDs for the delivery of anticancer drugs has been at the forefront of NDs applications owing to their ability to increase chemosensitivity, sustain drug release, and minimize drug side effects. Accelerated steps towards the move of NDs from bench side to bedside have been recently witnessed. In this review, the effects of NDs production and purification techniques on NDs' final properties are discussed. Special concern is given to studies focusing on NDs use for anticancer drug delivery, stability enhancement and mediated targeted delivery. The aim of this review is to put the results of studies oriented towards NDs-mediated anticancer drug delivery side by side such that the reader can assess the potential use of NDs in clinics and follow up the upcoming results of clinical testing of NDs on animals and humans.

Proteins Regulating Microvesicle Biogenesis and Multidrug Resistance in Cancer

Microvesicles (MV) are emerging as important mediators of intercellular communication. While MVs are important signaling vectors for many physiological processes, they are also implicated in cancer pathology and progression. Cellular activation is perhaps the most widely reported initiator of MV biogenesis, however, the precise mechanism remains undefined. Uncovering the proteins involved in regulating MV biogenesis is of interest given their role in the dissemination of deleterious cancer traits. MVs shed from drug-resistant cancer cells transfer multidrug resistance (MDR) proteins to drug-sensitive cells and confer the MDR phenotype in a matter of hours. MDR is attributed to the overexpression of ABC transporters, primarily P-glycoprotein and MRP1. Their expression and functionality is dependent on a number of proteins. In particular, FERM domain proteins have been implicated in supporting the functionality of efflux transporters in drug-resistant cells and in recipient cells during intercellular transfer by vesicles. Herein, the most recent research on the proteins involved in MV biogenesis and in the dissemination of MV-mediated MDR are discussed. Attention is drawn to unanswered questions in the literature that may prove to be of benefit in ongoing efforts to improve clinical response to chemotherapy and circumventing MDR.

Regulation of cancer stem cell properties by SIX1, a member of the PAX-SIX-EYA-DACH network

The PAX-SIX-EYA-DACH network (PSEDN) is a central developmental transcriptional regulatory network from Drosophila to humans. The PSEDN is comprised of four conserved protein families; including paired box (PAX), sine oculis (SIX), eyes absent (EYA), and dachshund (DACH). Aberrant expression of PSEDN members, particularly SIX1, has been observed in multiple human cancers, where SIX1 expression correlates with increased aggressiveness and poor prognosis. In conjunction with its transcriptional activator EYA, the SIX1 transcription factor increases cancer stem cell (CSC) numbers and induces epithelial-mesenchymal transition (EMT). SIX1 promotes multiple hallmarks and enabling characteristics of cancer via regulation of cell proliferation, senescence, apoptosis, genome stability, and energy metabolism. SIX1 also influences the tumor microenvironment, enhancing recruitment of tumor-associated macrophages and stimulating angiogenesis, to promote tumor development and progression. EYA proteins are multifunctional, possessing a transcriptional activation domain and tyrosine phosphatase activity, that each contributes to cancer stem cell properties. DACH proteins function as tumor suppressors in solid cancers, opposing the actions of SIX-EYA and reducing CSC prevalence. Multiple mechanisms can lead to increased SIX1 expression, including loss of SIX1-targeting tumor suppressor microRNAs (miRs), whose expression correlates inversely with SIX1 expression in cancer patient samples. In this review, we discuss the major mechanisms by which SIX1 confers CSC and EMT features and other important cancer cell characteristics. The roles of EYA and DACH in CSCs and cancer progression are briefly highlighted. Finally, we summarize the clinical significance of SIX1 in cancer to emphasize the potential therapeutic benefits of effective strategies to disrupt PSEDN protein interactions and functions.

MTA3-SOX2 Module Regulates Cancer Stemness and Contributes to Clinical Outcomes of Tongue Carcinoma

Cancer cell plasticity plays critical roles in both tumorigenesis and tumor progression. Metastasis-associated protein 3 (MTA3), a component of the nucleosome remodeling and histone deacetylase (NuRD) complex and multi-effect coregulator, can serve as a tumor suppressor in many cancer types. However, the role of MTA3 in tongue squamous cell cancer (TSCC) remains unclear although it is the most prevalent head and neck cancer and often with poor prognosis. By analyzing both published datasets and clinical specimens, we found that the level of MTA3 was lower in TSCC compared to normal tongue tissues. Data from gene set enrichment analysis (GSEA) also indicated that MTA3 was inversely correlated with cancer stemness. In addition, the levels of MTA3 in both samples from TSCC patients and TSCC cell lines were negatively correlated with SOX2, a key regulator of the plasticity of cancer stem cells (CSCs). We also found that SOX2 played an indispensable role in MTA3-mediated CSC repression. Using the mouse model mimicking human TSCC we demonstrated that the levels of MTA3 and SOX2 decreased and increased, respectively, during the process of tumorigenesis and progression. Finally, we showed that the patients in the MTA3^low/SOX2^high group had the worst prognosis suggesting that MTA3^low/SOX2^high can serve as an independent prognostic factor for TSCC patients. Altogether, our data suggest that MTA3 is capable of repressing TSCC CSC properties and tumor growth through downregulating SOX2 and MTA3^low/SOX2^high might be a potential prognostic factor for TSCC patients.

DNA Damage Response in Quiescent Hematopoietic Stem Cells and Leukemia Stem Cells

In humans, hematopoietic stem cells (HSCs) adopt unique responsive pathways counteracting with the DNA-damaging assaults to weigh the balance between the maintenance of normal stem cell poor for whole-life blood regeneration and the transformation to leukemia stem cells (LSCs) for leukemia initiation. LSCs also take actions of combating with the attack launched by externally therapeutic drugs that can kill most leukemic cells, to avoid extermination and promote disease relapse. Therefore, the collection of knowledge about all these underlined mechanisms would present a preponderance for later studies. In this chapter, the universal DNA damage response (DDR) mechanisms were firstly introduced, and then DDR of HSCs were presented focusing on the DNA double-strand breaks in the quiescent state of HSCs, which poses a big advantage in promoting its transformation into preleukemic HSCs. Lastly, the DDR of LSCs were summarized based on the major outcomes triggered by different pathways in specific leukemia, upon which some aspects for future investigations were envisioned under our currently limited scope of knowledge.

Oncogenic Metabolism Acts as a Prerequisite Step for Induction of Cancer Metastasis and Cancer Stem Cell Phenotype

Metastasis is a major obstacle to the efficient and successful treatment of cancer. Initiation of metastasis requires epithelial-mesenchymal transition (EMT) that is regulated by several transcription factors, including Snail and ZEB1/2. EMT is closely linked to the acquisition of cancer stem cell (CSC) properties and chemoresistance, which contribute to tumor malignancy. Tumor suppressor p53 inhibits EMT and metastasis by negatively regulating several EMT-inducing transcription factors and regulatory molecules; thus, its inhibition is crucial in EMT, invasion, metastasis, and stemness. Metabolic alterations are another hallmark of cancer. Most cancer cells are more dependent on glycolysis than on mitochondrial oxidative phosphorylation for their energy production, even in the presence of oxygen. Cancer cells enhance other oncogenic metabolic pathways, such as glutamine metabolism, pentose phosphate pathway, and the synthesis of fatty acids and cholesterol. Metabolic reprogramming in cancer is regulated by the activation of oncogenes or loss of tumor suppressors that contribute to tumor progression. Oncogenic metabolism has been recently linked closely with the induction of EMT or CSC phenotypes by the induction of several metabolic enzyme genes. In addition, several transcription factors and molecules involved in EMT or CSCs, including Snail, Dlx-2, HIF-1α, STAT3, TGF-β, Wnt, and Akt, regulate oncogenic metabolism. Moreover, p53 induces metabolic change by directly regulating several metabolic enzymes. The collective data indicate the importance of oncogenic metabolism in the regulation of EMT, cell invasion and metastasis, and adoption of the CSC phenotype, which all contribute to malignant transformation and tumor development. In this review, we highlight the oncogenic metabolism as a key regulator of EMT and CSC, which is related with tumor progression involving metastasis and chemoresistance. Targeting oncometabolism might be a promising strategy for the development of effective anticancer therapy.

Pancreatic cancer stem cells: Perspectives on potential therapeutic approaches of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma is one of the most aggressive solid tumours of the pancreas, characterised by a five-year survival rate less than 8%. Recent reports that pancreatic cancer stem cells (PCSCs) contribute to the tumorigenesis, progression, and chemoresistance of pancreatic cancer have prompted the investigation of new therapeutic approaches able to directly target PCSCs. In the present paper the non-cancer related drugs that have been proposed to target CSCs that could potentially combat pancreatic cancer are reviewed and evaluated. The role of some pathways and deregulated proteins in PCSCs as new therapeutic targets are also discussed with a focus on selected specific inhibitors. Finally, advances in the development of nanoparticles for targeting PCSCs and site-specific drug delivery are highlighted, and their limitations considered.

Mechanisms underlying acquired platinum resistance in high grade serous ovarian cancer - a mini review

BACKGROUND

Advanced epithelial ovarian cancer is one of the hardest human malignancies to treat. Standard treatment involves cytoreductive surgery and platinum-based chemotherapy, however, median progression-free survival for patients diagnosed with advanced stage disease (FIGO stages III and IV) is approximately 18 months. There has been little improvement in overall survival over the past decade and less than half of women with advanced stage disease will be living 5 years after diagnosis. A majority of patients initially have a favourable response to platinum-based chemotherapy, but most will eventually relapse and their disease will become platinum resistant.

SCOPE OF REVIEW

Here, we review our current understanding of mechanisms that promote recurrence and acquired resistance in epithelial ovarian cancer with particular focus on studies that describe differences observed between untreated primary tumors and recurrent tumors, post-first-line chemotherapy. Multiple molecular mechanisms contribute to recurrence in patients following initial treatment for advanced epithelial ovarian cancer including those involving the tumor microenvironment, tumor immune status, cancer stem cells, DNA repair/cell survival pathways and extracellular matrix.

MAJOR CONCLUSIONS

Due to the adaptive nature of recurrent tumors, the major contributing and specific resistance pattern may largely depend on the nature of the primary tumor itself.

GENERAL SIGNIFICANCE

Future work that aims to elucidate the complex pattern of acquired resistance will be useful for predicting chemotherapy response/recurrence following primary diagnosis and to develop novel treatment strategies to improve the survival of patients with advanced epithelial ovarian cancer, especially in tumors not harbouring homologous DNA recombination repair deficiencies.

Breast cancer stem cells and the challenges of eradication: a review of novel therapies

Breast cancer is a heterogeneous disease that accounts for 30% of all cancers diagnosed in women and over half a million deaths per year. Cancer stem cells (CSCs) make up a small subpopulation of cells within a tumor, are capable of self-renewal and, are responsible for tumor initiation, formation, and recurrence. Breast CSCs (BCSCs) have been the subject of concentrated research as potential targets for breast cancer therapies. Cell surface markers CD44+/CD24- have been established as minimum biomarkers for BCSCs and the upregulation of CD44 expression has been linked to tumor formation in numerous cancers. Additionally, the deregulation of Notch, Wnt/Frizzled/β-catenin, Hippo, and Hedgehog signaling pathways is believed to be responsible for the formation of CSCs and lead to tumor formation. Tumor heterogeneity is a key feature of therapy resistance and a major challenge. CSCs are predominantly senescent and inherently immune to chemotherapy drugs which rely on an overactive cell cycle. Current therapeutic strategies include targeting CSC signaling pathways that play critical roles in self-renewal and defense. Anti-CD44 antibodies have been shown to induce terminal differentiation in CSCs resulting in a significant decrease in tumor metastasis. Additionally, targeting the tumor microenvironment has been shown to increase the effectiveness of chemotherapy drugs. In this review, we attempt to provide an overview of breast cancer, the stem of its cause, and novel therapies currently being explored.

Codelivery of doxorubicin and elacridar to target both liver cancer cells and stem cells by polylactide-co-glycolide/d-alpha-tocopherol polyethylene glycol 1000 succinate nanoparticles

Purpose

Liver cancer is the third leading cause of cancer-related deaths worldwide. Liver cancer stem cells (LCSCs) are a subpopulation of cancer cells that are responsible for the initiation, progression, drug resistance, recurrence, and metastasis of liver cancer. Recent studies have suggested that the eradication of both LCSCs and liver cancer cells is necessary because the conversion of cancer stem cells (CSCs) to cancer cells occasionally occurs. As ATP-binding cassette (ABC) transporters are overexpressed in both CSCs and cancer cells, combined therapies using ABC transporter inhibitors and chemotherapy drugs could show superior therapeutic efficacy in liver cancer. In this study, we developed poly(lactide-co-glycolide)/d-alpha-tocopherol polyethylene glycol 1000 succinate nanoparticles to accomplish the simultaneous delivery of an optimized ratio of doxorubicin (DOX) and elacridar (ELC) to target both LCSCs and liver cancer cells.

Methods

Median-effect analysis was used for screening of DOX and ELC for synergy in liver cancer cells (HepG2 cells) and LCSCs (HepG2 tumor sphere [HepG2-TS]). Then, nanoparticles loaded with DOX and ELC at the optimized ratio (NDEs) were prepared by nanoprecipitation method. The cytotoxicity and colony and tumor sphere formation ability of nanoparticles were investigated in vitro, and the tissue distribution and antitumor activity of nanoparticles were evaluated in vivo.

Results

We demonstrated that a DOX/ELC molar ratio of 1:1 was synergistic in HepG2 cells and HepG2-TS. NDEs were shown to exhibit significantly increased cytotoxic effects against both HepG2 and HepG2-TS compared with DOX-loaded nanoparticles (NDs) or ELC-loaded nanoparticles (NEs) in vitro. In vivo studies demonstrated that the nanoparticles exhibited better tumor targeting, with NDE showing the strongest antitumor activity with lower systemic toxicity.

Conclusion

These results suggested that NDE represented a promising combination therapy against liver cancer by targeting both liver cancer cells and CSCs.

MiR-30-5p suppresses cell chemoresistance and stemness in colorectal cancer through USP22/Wnt/β-catenin signaling axis

Colorectal cancer (CRC) remains both common and fatal, and its successful treatment is greatly limited by the development of stem cell‐like characteristics (stemness) and chemoresistance. MiR‐30‐5p has been shown to function as a tumor suppressor by targeting the Wnt/β‐catenin signaling pathway, but its activity in CRC has never been assessed. We hypothesized that miR‐30‐5p exerts anti‐oncogenic effects in CRC by regulating the USP22/Wnt/β‐catenin signaling axis. In the present study, we demonstrate that tissues from CRC patients and human CRC cell lines show significantly decreased miR‐30‐5p family expression. After identifying the 3’UTR of USP22 as a potential binding site of miR‐30‐5p, we constructed a luciferase reporter containing the potential miR‐30‐5p binding site and measured the effects on USP22 expression. Western blot assays showed that miR‐30‐5p decreased USP22 protein expression in HEK293 and Caco2 CRC cells. To evaluate the effects of miR‐30‐5p on CRC cell stemness, we isolated CD133 + CRC cells (Caco2 and HCT15). We then determined that, while miR‐30‐5p is normally decreased in CD133 + CRC cells, miR‐30‐5p overexpression significantly reduces expression of stem cell markers CD133 and Sox2, sphere formation, and cell proliferation. Similarly, we found that miR‐30‐5p expression is normally reduced in 5‐fluorouracil (5‐FU) resistant CRC cells, whereas miR‐30‐5p overexpression in 5‐FU resistant cells reduces sphere formation and cell viability. Inhibition of miR‐30‐5p reversed the process. Finally, we determined that miR‐30‐5p attenuates the expression of Wnt/β‐catenin signaling target genes (Axin2 and MYC), Wnt luciferase activity, and β‐catenin protein levels in CRC stem cells.

Ovarian cancer stem cell: A potential therapeutic target for overcoming multidrug resistance

The cancer stem cell (CSC) model encompasses an advantageous paradigm that in recent decades provides a better elucidation for many important biological aspects of cancer initiation, progression, metastasis, and, more important, development of multidrug resistance (MDR). Such several other hematological malignancies and solid tumors and the identification and isolation of ovarian cancer stem cells (OV-CSCs) show that ovarian cancer also follows this hierarchical model. Gaining a better insight into CSC-mediated resistance holds promise for improving current ovarian cancer therapies and prolonging the survival of recurrent ovarian cancer patients in the future. Therefore, in this review, we will discuss some important mechanisms by which CSCs can escape chemotherapy, and then review the recent and growing body of evidence that supports the contribution of CSCs to MDR in ovarian cancer.