Mechanisms of Disease: cancer stem cells—targeting the evil twin

Deciphering genetic and nongenetic factors underlying tumour dormancy: insights from multiomics analysis of two syngeneic MRD models of melanoma and leukemia

BACKGROUND

Tumour dormancy, a resistance mechanism employed by cancer cells, is a significant challenge in cancer treatment, contributing to minimal residual disease (MRD) and potential relapse. Despite its clinical importance, the mechanisms underlying tumour dormancy and MRD remain unclear. In this study, we employed two syngeneic murine models of myeloid leukemia and melanoma to investigate the genetic, epigenetic, transcriptomic and protein signatures associated with tumour dormancy. We used a multiomics approach to elucidate the molecular mechanisms driving MRD and identify potential therapeutic targets.

RESULTS

We conducted an in-depth omics analysis encompassing whole-exome sequencing (WES), copy number variation (CNV) analysis, chromatin immunoprecipitation followed by sequencing (ChIP-seq), transcriptome and proteome investigations. WES analysis revealed a modest overlap of gene mutations between melanoma and leukemia dormancy models, with a significant number of mutated genes found exclusively in dormant cells. These exclusive genetic signatures suggest selective pressure during MRD, potentially conferring resistance to the microenvironment or therapies. CNV, histone marks and transcriptomic gene expression signatures combined with Gene Ontology (GO) enrichment analysis highlighted the potential functional roles of the mutated genes, providing insights into the pathways associated with MRD. In addition, we compared "murine MRD genes" profiles to the corresponding human disease through public datasets and highlighted common features according to disease progression. Proteomic analysis combined with multi-omics genetic investigations, revealed a dysregulated proteins signature in dormant cells with minimal genetic mechanism involvement. Pathway enrichment analysis revealed the metabolic, differentiation and cytoskeletal remodeling processes involved in MRD. Finally, we identified 11 common proteins differentially expressed in dormant cells from both pathologies.

CONCLUSIONS

Our study underscores the complexity of tumour dormancy, implicating both genetic and nongenetic factors. By comparing genomic, transcriptomic, proteomic, and epigenomic datasets, our study provides a comprehensive understanding of the molecular landscape of minimal residual disease. These results provide a robust foundation for forthcoming investigations and offer potential avenues for the advancement of targeted MRD therapies in leukemia and melanoma patients, emphasizing the importance of considering both genetic and nongenetic factors in treatment strategies.

Circulating tumor cells: from new biological insights to clinical practice

The primary reason for high mortality rates among cancer patients is metastasis, where tumor cells migrate through the bloodstream from the original site to other parts of the body. Recent advancements in technology have significantly enhanced our comprehension of the mechanisms behind the bloodborne spread of circulating tumor cells (CTCs). One critical process, DNA methylation, regulates gene expression and chromosome stability, thus maintaining dynamic equilibrium in the body. Global hypomethylation and locus-specific hypermethylation are examples of changes in DNA methylation patterns that are pivotal to carcinogenesis. This comprehensive review first provides an overview of the various processes that contribute to the formation of CTCs, including epithelial-mesenchymal transition (EMT), immune surveillance, and colonization. We then conduct an in-depth analysis of how modifications in DNA methylation within CTCs impact each of these critical stages during CTC dissemination. Furthermore, we explored potential clinical implications of changes in DNA methylation in CTCs for patients with cancer. By understanding these epigenetic modifications, we can gain insights into the metastatic process and identify new biomarkers for early detection, prognosis, and targeted therapies. This review aims to bridge the gap between basic research and clinical application, highlighting the significance of DNA methylation in the context of cancer metastasis and offering new avenues for improving patient outcomes.

Targeting of drug-tolerant persister cells as an approach to counter drug resistance in non-small cell lung cancer

The advent of targeted therapies revolutionized treatments of advanced oncogene-driven non-small cell lung cancer (NSCLC). Nonetheless, despite initial dramatic responses, development of drug resistance is inevitable. Although mechanisms underlying acquired resistance, such as on-target mutations, bypass pathways, or lineage transformation, have been described, overcoming drug resistance remains challenging. Recent evidence suggests that drug-tolerant persister (DTP) cells, which are tumor cells tolerant to initial drug exposure, give rise to cells that acquire drug resistance. Thus, the possibility of eradicating cancer by targeting DTP cells is under investigation, and various strategies are proposed. Here, we review overall features of DTP cells, current efforts to define DTP markers, and potential therapeutic strategies to target and eradicate DTP cells in oncogene-driven NSCLC. We also discuss future challenges in the field.

Interplay of p62-mTORC1 and EGFR signaling promotes cisplatin resistance in oral cancer

Cisplatin resistance poses a major challenge in the treatment of oral squamous cell carcinoma (OSCC). Deeper investigations into the mechanisms underlying this drug resistance is of great importance. Here, we used cellular assays and clinical immunohistochemistry to examine molecular pathways involved in both innate and acquired cisplatin resistance. We demonstrated that the p62-mTORC1 signaling complex plays a pivotal role, and is driven by the EGFR signaling network, specifically through the PI3K-Akt axis and the transcription factor C/EBP-β. Elevated p-mTOR expression was associated with cancer relapse and poor prognosis among oral cancer patients. Additionally, we illustrated that mTOR inhibitors enhance the cytotoxic effect of cisplatin, by employing cancer stem cell characteristics. Our work unveils fundamental mechanisms for cisplatin resistance, thereby presenting therapeutic implications for OSCC.

GPRC5C drives branched-chain amino acid metabolism in leukemogenesis

Leukemia stem cells (LSCs) share numerous features with healthy hematopoietic stem cells (HSCs). G-protein coupled receptor family C group 5 member C (GPRC5C) is a regulator of HSC dormancy. However, GPRC5C functionality in acute myeloid leukemia (AML) is yet to be determined. Within patient AML cohorts, high GPRC5C levels correlated with poorer survival. Ectopic Gprc5c expression increased AML aggression through the activation of NF-κB, which resulted in an altered metabolic state with increased levels of intracellular branched-chain amino acids (BCAAs). This onco-metabolic profile was reversed upon loss of Gprc5c, which also abrogated the leukemia-initiating potential. Targeting the BCAA transporter SLC7A5 with JPH203 inhibited oxidative phosphorylation and elicited strong antileukemia effects, specifically in mouse and patient AML samples while sparing healthy bone marrow cells. This antileukemia effect was strengthened in the presence of venetoclax and azacitidine. Our results indicate that the GPRC5C-NF-κB-SLC7A5-BCAAs axis is a therapeutic target that can compromise leukemia stem cell function in AML.

Molecular and functional profiling of chemotolerant cells unveils nucleoside metabolism-dependent vulnerabilities in medulloblastoma

Chemotherapy resistance is considered one of the main causes of tumor relapse, still challenging researchers for the identification of the molecular mechanisms sustaining its emergence. Here, we setup and characterized chemotherapy-resistant models of Medulloblastoma (MB), one of the most lethal pediatric brain tumors, to uncover targetable vulnerabilities associated to their resistant phenotype. Integration of proteomic, transcriptomic and kinomic data revealed a significant deregulation of several pathways in resistant MB cells, converging to cell metabolism, RNA/protein homeostasis, and immune response, eventually impacting on patient outcome. Moreover, resistant MB cell response to a large library of compounds through a high-throughput screening (HTS), highlighted nucleoside metabolism as a relevant vulnerability of chemotolerant cells, with peculiar antimetabolites demonstrating increased efficacy against them and even synergism with conventional chemotherapeutics. Our results suggest that drug-resistant cells significantly rewire multiple cellular processes, allowing their adaptation to a chemotoxic environment, nevertheless exposing alternative actionable susceptibilities for their specific targeting.

Vienna Cancer Stem Cell Club (VCSCC): 20 year jubilee and future perspectives

INTRODUCTION

The Vienna Cancer Stem Cell Club (VCSCC) was launched by a group of scientists in Vienna in 2002.

AREAS COVERED

Major aims of the VCSCC are to support research on cancer stem cells (CSC) in hematopoietic malignancies and to translate CSC-related markers and targets into clinical application. A primary focus of research in the VCSCC is the leukemic stem cell (LSC). Between 2013 and 2021, members of the VCSCC established a special research program on myeloproliferative neoplasms and since 2008, members of the VCSCC run the Ludwig Boltzmann Institute for Hematology and Oncology. In all these years, the VCSCC provided a robust intellectual platform for translational hematology and LSC research in Vienna. Furthermore, the VCSCC interacts with several national and international study groups and societies in the field. Representatives of the VCSCC also organized a number of international meetings and conferences on neoplastic stem cells, including LSC, in the past 15 years, and contributed to the definition and classification of CSC/LSC and related pre-malignant and malignant conditions.

EXPERT OPINION

The VCSCC will continue to advance the field and to develop LSC-detecting and LSC-eradicating concepts through which diagnosis, prognostication, and therapy of blood cancer patients should improve.

Role of Interleukins in Inflammation-Mediated Tumor Immune Microenvironment Modulation in Colorectal Cancer Pathogenesis

INTRODUCTION

Tumor cells invade and spread through a procedure termed as epithelial-to-mesenchymal cell transition (EMT). EMT is triggered by any alterations in the genes that encode the extracellular matrix (ECM) proteins, the enzymes that break down the ECM, and the activation of the genes that causes the epithelial cell to change into a mesenchymal type. The transcription factors NF-κB, Smads, STAT3, Snail, Zeb, and Twist are activated by inflammatory cytokines, for instance, Tumor Necrosis Factor, Tumor Growth Factors, Interleukin-1, Interleukin-8, and Interleukin-6, which promotes EMT.

MATERIALS

The current piece of work has been reviewed from the literature works published in last 10 years on the role interleukins in inflammation-mediated tumor immune microenvironment modulation in colorectal cancer pathogenesis utilizing the databases like Google Scholar, PubMed, Science Direct.

RESULTS

Recent studies have demonstrated that pathological situations, such as epithelial malignancies, exhibit EMT characteristics, such as the downregulation of epithelial markers and the overexpression of mesenchymal markers. Several growing evidence have also proved its existence in the human colon during the carcinogenesis of colorectal cancer. Most often, persistent inflammation is thought to be one factor contributing to the initiation of human cancers, such as colorectal cancer (CRC). Therefore, according to epidemiologic and clinical research, people with ulcerative colitis and Crohn's disease have a greater probability of developing CRC.

CONCLUSION

A substantial amount of data points to the involvement of the NF-κB system, SMAD/STAT3 signaling cascade, microRNAs, and the Ras-mitogen-activated protein kinase/Snail/Slug in the epithelial-to-mesenchymal transition-mediated development of colorectal malignancies. As a result, EMT is reported to play an active task in the pathogenesis of colorectal cancer, and therapeutic interventions targeting the inflammation-mediated EMT might serve as a novel strategy for treating CRC. The illustration depicts the relationship between interleukins and their receptors as a driver of CRC development and the potential therapeutic targets.

Modern approaches to treating cancer with oncolytic viruses

According to the World Health Organization, cancer is the second leading cause of death in the world. This serves as a powerful incentive to search for new effective cancer treatments. Development of new oncolytic viruses capable of selectively destroying cancer cells is one of the modern approaches to cancer treatment. The advantage of this method – the selective lysis of tumor cells with the help of viruses – leads to an increase in the antitumor immune response of the body, that in turn promotes the destruction of the primary tumor and its metastases. Significant progress in development of this method has been achieved in the last decade. In this review we analyze the literature data on families of oncolytic viruses that have demonstrated a positive therapeutic effect against malignant neoplasms in various localizations. We discuss the main mechanisms of the oncolytic action of viruses and assess their advantages over other methods of cancer therapy as well as the prospects for their use in clinical practice.

Mitochondrial Deep Dive into Hematopoietic Stem Cell Dormancy: Not Much Glycolysis but Plenty of Sluggish Lysosomes

The discovery of hematopoietic stem cells (HSCs) heterogeneity has had major implications for investigations of hematopoietic stem cell disorders, clonal hematopoiesis, and HSC aging. More recent studies of the heterogeneity of HSCs' organelles have begun to provide additional insights into HSCs' behavior with far-reaching ramifications for the mechanistic understanding of aging of HSCs and stem cell-derived diseases. Mitochondrial heterogeneity has been explored to expose HSC subsets with distinct properties and functions. Here we review some of the recent advances in these lines of studies that challenged the classic view of glycolysis in HSCs and led to the identification of lysosomes as dynamic pivotal switches in controlling HSC quiescence versus activation beyond their function in autophagy.

Radiochemotherapy-induced DNA repair promotes the biogenesis of gastric cancer stem cells

BACKGROUND

Clinically, metastasis and recurrence occurred after routine radiochemotherapy in dozens of cases of gastric cancer, mainly attributed to the role of cancer stem cells (CSCs). Actually, radiochemotherapy could induce DNA damages, leading to activation of DNA repair which might be associated with acquisition of stem cell phenotype. Hitherto, the contribution made by active DNA repair to stemness induction has not been extensively explored.

METHODS

Cisplatin/doxorubicin treatment and X-ray exposure were conducted in gastric cancer cell lines and gastric cancer cells derived from solid tumors to model clinical therapy. Quantitative real-time PCR, Western blot, and tumorsphere/tumor formation assay were further used to characterize CSCs and assess activation of DNA repair. RNA-seq was performed to identify which DNA repair genes were crucial for CSC traits induction, followed by the investigation of underlying mechanism and functional significance via in vitro and in vivo experiments.

RESULTS

Here, we report a mechanism through which gastric cancer cells in response to radiochemotherapy were reprogrammed into gastric cancer stem cell-like cells. In this mechanism, radiochemotherapy triggers DNA damage response accompanied by elevated levels of EID3, a typical DNA repair gene, which interacts with NAMPT to promote stemness via upregulating Wnt signaling pathway, manifested by enhanced tumorsphere/tumor formation in gastric cancer. In addition to involvement of EID3 in stemness acquisition, it also shows impacts on proliferation, cell cycle, apoptosis and therapy resistance to maintain the characteristics of CSC populations.

CONCLUSION

Our study indicates that gastric cancer cells can be endowed with stemness traits via EID3-NAMPT-Wnt/β-catenin axis in response to radiochemotherapy. Blocking this axis (i.e., targeting EID3) along with radiochemotherapy might represent a potential strategy to sensitize CSCs to radiochemotherapy and further reinforce the anti-tumor effects of conventional treatments.

MicroRNAs as the critical regulators of tyrosine kinase inhibitors resistance in lung tumor cells

Lung cancer is the second most common and the leading cause of cancer related deaths globally. Tyrosine Kinase Inhibitors (TKIs) are among the common therapeutic strategies in lung cancer patients, however the treatment process fails in a wide range of patients due to TKIs resistance. Given that the use of anti-cancer drugs can always have side effects on normal tissues, predicting the TKI responses can provide an efficient therapeutic strategy. Therefore, it is required to clarify the molecular mechanisms of TKIs resistance in lung cancer patients. MicroRNAs (miRNAs) are involved in regulation of various pathophysiological cellular processes. In the present review, we discussed the miRNAs that have been associated with TKIs responses in lung cancer. MiRNAs mainly exert their role on TKIs response through regulation of Tyrosine Kinase Receptors (TKRs) and down-stream signaling pathways. This review paves the way for introducing a panel of miRNAs for the prediction of TKIs responses in lung cancer patients.

The efficacy of PI3Kγ and EGFR inhibitors on the suppression of the characteristics of cancer stem cells

Cancer stem cells (CSCs) are capable of continuous proliferation, self-renewal and are proposed to play significant roles in oncogenesis, tumor growth, metastasis and cancer recurrence. We have established a model of CSCs that was originally developed from mouse induced pluripotent stem cells (miPSCs) by proposing miPSCs to the conditioned medium (CM) of cancer derived cells, which is a mimic of carcinoma microenvironment. Further research found that not only PI3K-Akt but also EGFR signaling pathway was activated during converting miPSCs into CSCs. In this study, we tried to observe both of PI3Kγ inhibitor Eganelisib and EGFR inhibitor Gefitinib antitumor effects on the models of CSCs derived from miPSCs (miPS-CSC) in vitro and in vivo. As the results, targeting these two pathways exhibited significant inhibition of cell proliferation, self-renewal, migration and invasion abilities in vitro. Both Eganelisib and Gefitinib showed antitumor effects in vivo while Eganelisib displayed more significant therapeutic efficacy and less side effects than Gefitinib on all miPS-CSC models. Thus, these data suggest that the inhibitiors of PI3K and EGFR, especially PI3Kγ, might be a promising therapeutic strategy against CSCs defeating cancer in the near future.

Purification of Colon Carcinoma Cells from Primary Colon Tumor Using a Filtration Method via Porous Polymeric Filters

Cancer stem cells (CSCs) or cancer-initiating cells (CICs) are key factors for tumor generation and metastasis. We investigated a filtration method to enhance CSCs (CICs) from colon carcinoma HT-29 cells and primary colon carcinoma cells derived from patient colon tumors using poly(lactide-co-glycolic acid)/silk screen (PLGA/SK) filters. The colon carcinoma cell solutions were permeated via porous filters to obtain a permeation solution. Then, the cell cultivation media were permeated via the filters to obtain the recovered solution, where the colon carcinoma cells that adhered to the filters were washed off into the recovered solution. Subsequently, the filters were incubated in the culture media to obtain the migrated cells via the filters. Colon carcinoma HT-29 cells with high tumorigenicity, which might be CSCs (CICs), were enhanced in the cells in the recovered solution and in the migrated cells based on the CSC (CIC) marker expression, colony-forming unit assay, and carcinoembryonic antigen (CEA) production. Although primary colon carcinoma cells isolated from colon tumor tissues contained fibroblast-like cells, the primary colon carcinoma cells were purified from fibroblast-like cells by filtration through PLGA/SK filters, indicating that the filtration method is effective in purifying primary colon carcinoma cells.

Evolutionary predictability of genetic versus nongenetic resistance to anticancer drugs in melanoma

Therapy resistance arises from heterogeneous drug-tolerant persister cells or minimal residual disease (MRD) through genetic and nongenetic mechanisms. A key question is whether specific molecular features of the MRD ecosystem determine which of these two distinct trajectories will eventually prevail. We show that, in melanoma exposed to mitogen-activated protein kinase therapeutics, emergence of a transient neural crest stem cell (NCSC) population in MRD concurs with the development of nongenetic resistance. This increase relies on a glial cell line-derived neurotrophic factor-dependent signaling cascade, which activates the AKT survival pathway in a focal adhesion kinase (FAK)-dependent manner. Ablation of the NCSC population through FAK inhibition delays relapse in patient-derived tumor xenografts. Strikingly, all tumors that ultimately escape this treatment exhibit resistance-conferring genetic alterations and increased sensitivity to extracellular signal-regulated kinase inhibition. These findings identify an approach that abrogates the nongenetic resistance trajectory in melanoma and demonstrate that the cellular composition of MRD deterministically imposes distinct drug resistance evolutionary paths.

Emerging Insights into Targeted Therapy-Tolerant Persister Cells in Cancer

Drug resistance is perhaps the greatest challenge in improving outcomes for cancer patients undergoing treatment with targeted therapies. It is becoming clear that "persisters," a subpopulation of drug-tolerant cells found in cancer populations, play a critical role in the development of drug resistance. Persisters are able to maintain viability under therapy but are typically slow cycling or dormant. These cells do not harbor classic drug resistance driver alterations, and their partial resistance phenotype is transient and reversible upon removal of the drug. In the clinic, the persister state most closely corresponds to minimal residual disease from which relapse can occur if treatment is discontinued or if acquired drug resistance develops in response to continuous therapy. Thus, eliminating persister cells will be crucial to improve outcomes for cancer patients. Using lung cancer targeted therapies as a primary paradigm, this review will give an overview of the characteristics of drug-tolerant persister cells, mechanisms associated with drug tolerance, and potential therapeutic opportunities to target this persister cell population in tumors.

Identification of leukemic and pre-leukemic stem cells by clonal tracking from single-cell transcriptomics

Cancer stem cells drive disease progression and relapse in many types of cancer. Despite this, a thorough characterization of these cells remains elusive and with it the ability to eradicate cancer at its source. In acute myeloid leukemia (AML), leukemic stem cells (LSCs) underlie mortality but are difficult to isolate due to their low abundance and high similarity to healthy hematopoietic stem cells (HSCs). Here, we demonstrate that LSCs, HSCs, and pre-leukemic stem cells can be identified and molecularly profiled by combining single-cell transcriptomics with lineage tracing using both nuclear and mitochondrial somatic variants. While mutational status discriminates between healthy and cancerous cells, gene expression distinguishes stem cells and progenitor cell populations. Our approach enables the identification of LSC-specific gene expression programs and the characterization of differentiation blocks induced by leukemic mutations. Taken together, we demonstrate the power of single-cell multi-omic approaches in characterizing cancer stem cells.

Isolating live cell clones from barcoded populations using CRISPRa-inducible reporters

We developed a functional lineage tracing tool termed CaTCH (CRISPRa tracing of clones in heterogeneous cell populations). CaTCH combines precise clonal tracing of millions of cells with the ability to retrospectively isolate founding clones alive before and during selection, allowing functional experiments. Using CaTCH, we captured rare clones representing as little as 0.001% of a population and investigated the emergence of resistance to targeted melanoma therapy in vivo.

Evolving insights: how DNA repair pathways impact cancer evolution

Viewing cancer as a large, evolving population of heterogeneous cells is a common perspective. Because genomic instability is one of the fundamental features of cancer, this intrinsic tendency of genomic variation leads to striking intratumor heterogeneity and functions during the process of cancer formation, development, metastasis, and relapse. With the increased mutation rate and abundant diversity of the gene pool, this heterogeneity leads to cancer evolution, which is the major obstacle in the clinical treatment of cancer. Cells rely on the integrity of DNA repair machineries to maintain genomic stability, but these machineries often do not function properly in cancer cells. The deficiency of DNA repair could contribute to the generation of cancer genomic instability, and ultimately promote cancer evolution. With the rapid advance of new technologies, such as single-cell sequencing in recent years, we have the opportunity to better understand the specific processes and mechanisms of cancer evolution, and its relationship with DNA repair. Here, we review recent findings on how DNA repair affects cancer evolution, and discuss how these mechanisms provide the basis for critical clinical challenges and therapeutic applications.

The Intimate Relationship Among EMT, MET and TME: A T(ransdifferentiation) E(nhancing) M(ix) to Be Exploited for Therapeutic Purposes

Simple Summary

Intratumoral heterogeneity is considered the major cause of drug resistance and hence treatment failure in cancer patients. Tumor cells are known for their phenotypic plasticity that is the ability of a cell to reprogram and change its identity to eventually adopt multiple phenotypes. Tumor cell plasticity involves the reactivation of developmental programs, the acquisition of cancer stem cell properties and an enhanced potential for retro- or transdifferentiation. A well-known transdifferentiation mechanism is the process of epithelial-mesenchymal transition (EMT). Current evidence suggests a complex interplay between EMT, genetic and epigenetic alterations, and various signals from the tumor microenvironment (TME) in shaping a tumor cell’s plasticity. The vulnerabilities exposed by cancer cells when residing in a plastic or stem-like state have the potential to be exploited therapeutically, i.e., by converting highly metastatic cells into less aggressive or even harmless postmitotic ones.

Abstract

Intratumoral heterogeneity is considered the major cause of drug unresponsiveness in cancer and accumulating evidence implicates non-mutational resistance mechanisms rather than genetic mutations in its development. These non-mutational processes are largely driven by phenotypic plasticity, which is defined as the ability of a cell to reprogram and change its identity (phenotype switching). Tumor cell plasticity is characterized by the reactivation of developmental programs that are closely correlated with the acquisition of cancer stem cell properties and an enhanced potential for retrodifferentiation or transdifferentiation. A well-studied mechanism of phenotypic plasticity is the epithelial-mesenchymal transition (EMT). Current evidence suggests a complex interplay between EMT, genetic and epigenetic alterations, and clues from the tumor microenvironment in cell reprogramming. A deeper understanding of the connections between stem cell, epithelial–mesenchymal, and tumor-associated reprogramming events is crucial to develop novel therapies that mitigate cell plasticity and minimize the evolution of tumor heterogeneity, and hence drug resistance. Alternatively, vulnerabilities exposed by tumor cells when residing in a plastic or stem-like state may be exploited therapeutically, i.e., by converting them into less aggressive or even postmitotic cells. Tumor cell plasticity thus presents a new paradigm for understanding a cancer’s resistance to therapy and deciphering its underlying mechanisms.

Mutational and functional genetics mapping of chemotherapy resistance mechanisms in relapsed acute lymphoblastic leukemia

Multi-agent combination chemotherapy can be curative in acute lymphoblastic leukemia (ALL). Still, patients with primary refractory disease or with relapsed leukemia have a very poor prognosis. Here we integrate an in-depth dissection of the mutational landscape across diagnostic and relapsed pediatric and adult ALL samples with genome-wide CRISPR screen analysis of gene-drug interactions across seven ALL chemotherapy drugs. By combining these analyses, we uncover diagnostic and relapse-specific mutational mechanisms as well as genetic drivers of chemoresistance. Functionally, our data identifies common and drug-specific pathways modulating chemotherapy response and underscores the effect of drug combinations in restricting the selection of resistance-driving genetic lesions. In addition, by identifying actionable targets for the reversal of chemotherapy resistance, these analyses open novel therapeutic opportunities for the treatment of relapse and refractory disease.

Emerging role of tumor cell plasticity in modifying therapeutic response

Resistance to cancer therapy is a major barrier to cancer management. Conventional views have proposed that acquisition of resistance may result from genetic mutations. However, accumulating evidence implicates a key role of non-mutational resistance mechanisms underlying drug tolerance, the latter of which is the focus that will be discussed here. Such non-mutational processes are largely driven by tumor cell plasticity, which renders tumor cells insusceptible to the drug-targeted pathway, thereby facilitating the tumor cell survival and growth. The concept of tumor cell plasticity highlights the significance of re-activation of developmental programs that are closely correlated with epithelial-mesenchymal transition, acquisition properties of cancer stem cells, and trans-differentiation potential during drug exposure. From observations in various cancers, this concept provides an opportunity for investigating the nature of anticancer drug resistance. Over the years, our understanding of the emerging role of phenotype switching in modifying therapeutic response has considerably increased. This expanded knowledge of tumor cell plasticity contributes to developing novel therapeutic strategies or combination therapy regimens using available anticancer drugs, which are likely to improve patient outcomes in clinical practice.

Loss of oral mucosal stem cell markers in oral submucous fibrosis and their reactivation in malignant transformation

The integrity of the basal stem cell layer is critical for epithelial homoeostasis. In this paper, we review the expression of oral mucosal stem cell markers (OM-SCMs) in oral submucous fibrosis (OSF), oral potentially malignant disorders (OPMDs) and oral squamous cell carcinoma (OSCC) to understand the role of basal cells in potentiating cancer stem cell behaviour in OSF. While the loss of basal cell clonogenicity triggers epithelial atrophy in OSF, the transition of the epithelium from atrophic to hyperplastic and eventually neoplastic involves the reactivation of basal stemness. The vacillating expression patterns of OM-SCMs confirm the role of keratins 5, 14, 19, CD44, β1-integrin, p63, sex-determining region Y box (SOX2), octamer-binding transcription factor 4 (Oct-4), c-MYC, B-cell-specific Moloney murine leukaemia virus integration site 1 (Bmi-1) and aldehyde dehydrogenase 1 (ALDH1) in OSF, OPMDs and OSCC. The downregulation of OM-SCMs in the atrophic epithelium of OSF and their upregulation during malignant transformation are illustrated with relevant literature in this review.

Biomaterial 3D collagen I gel culture model: A novel approach to investigate tumorigenesis and dormancy of bladder cancer cells induced by tumor microenvironment

The high potential for cancer relapse has emerged as a crucial challenge of human bladder cancer treatment. To date, those stem-like bladder cancer cells (BCSCs) have been considered as seeds that induce frequent tumor recurrence. However, the cell origin of cancer stem cells (CSCs) is still a controversial issue, due in part to the findings that CSCs not only origin from normal stem cells but also converted from differentiated tumor cells. Here, we describe a biomaterial 3D collagen I gel culture system, where non-tumorigenic cells can obtain tumorigenic potential and revert back into CSCs through the integrin α2β1/PI3K/AKT/NF-κB cascade, resulting in the tumorigenesis in bladder tissues. Furthermore, inhibiting this integrin α2β1/PI3K/AKT/NF-κB signal pathways can significantly impair the tumorigenic capacity of CSCs. Simultaneously, in vivo studies demonstrate that IFN-γ secreted by T cells can trigger those CSCs into dormancy through the IDO/Kyn/AHR/P27 cascade, which elicit chemotherapy resistance and cancer relapse. To address the challenges of suppressing bladder tumor growth and preventing tumor reoccurrence, we use IDO and integrin α2β1 signal pathway inhibitors combine with chemotherapeutic agents to awaken dormant bladder CSCs and inhibit their tumorigenic ability as well as effectively eliminate CSCs. The therapeutic approaches we propose provide new insights for eradicating tumors and reducing bladder cancer relapse after therapy.

3D culture technologies of cancer stem cells: promising ex vivo tumor models

Cancer stem cells have been shown to be important in tumorigenesis processes, such as tumor growth, metastasis, and recurrence. As such, many three-dimensional models have been developed to establish an ex vivo microenvironment that cancer stem cells experience under in vivo conditions. Cancer stem cells propagating in three-dimensional culture systems show physiologically related signaling pathway profiles, gene expression, cell-matrix and cell-cell interactions, and drug resistance that reflect at least some of the tumor properties seen in vivo. Herein, we discussed the presently available Cancer stem cell three-dimensional culture models that use biomaterials and engineering tools and the biological implications of these models compared to the conventional ones.

An FGFR/AKT/SOX2 Signaling Axis Controls Pancreatic Cancer Stemness

Cancer stemness is associated with high malignancy and low differentiation, as well as therapeutic resistance of tumors including pancreatic ductal adenocarcinoma (PDAC). Fibroblast growth factors (FGFs) exert pleiotropic effects on a variety of cellular processes and functions including embryonic stem cell pluripotency and cancer cell stemness via the activation of four tyrosine kinase FGF receptors (FGFRs). FGF ligands have been a major component of the cocktail of growth factors contained in the cancer stemness-inducing (CSI) and organoid culture medium. Although FGF/FGFR signaling has been hypothesized to maintain cancer stemness, its function in this process is still unclear. We report that inhibition of FGF/FGFR signaling impairs sphere-forming ability of PDAC in vitro, and knocking down FGFR1 and FGFR2 decreased their tumorigenesis abilities in vivo. Mechanistically, we demonstrated that SOX2 is down-regulated upon loss of FGFR signaling. The overexpression of SOX2 in SOX2-negative cells, which normally do not display stemness capabilities, is sufficient to induce spheroid formation. Additionally, we found that AKT phosphorylation was reduced upon FGFR signaling inhibition. The inhibition of AKT using specific pharmacological inhibitors in the context of CSI medium leads to the loss of spheroid formation associated with loss of SOX2 nuclear expression and increased degradation. We demonstrate that an FGFR/AKT/SOX2 axis controls cancer stemness in PDAC and therefore may represent an important therapeutic target in the fight against this very aggressive form of cancer.

The great escape: tumour cell plasticity in resistance to targeted therapy

The success of targeted therapies in cancer treatment has been impeded by various mechanisms of resistance. Besides the acquisition of resistance-conferring genetic mutations, reversible mechanisms that lead to drug tolerance have emerged. Plasticity in tumour cells drives their transformation towards a phenotypic state that no longer depends on the drug-targeted pathway. These drug-refractory cells constitute a pool of slow-cycling cells that can either regain drug sensitivity upon treatment discontinuation or acquire permanent resistance to therapy and drive relapse. In the past few years, cell plasticity has emerged as a mode of targeted therapy evasion in various cancers, ranging from prostate and lung adenocarcinoma to melanoma and basal cell carcinoma. Our understanding of the mechanisms that control this phenotypic switch has also expanded, revealing the crucial role of reprogramming factors and chromatin remodelling. Further deciphering the molecular basis of tumour cell plasticity has the potential to contribute to new therapeutic strategies which, combined with existing anticancer treatments, could lead to deeper and longer-lasting clinical responses.

Metastatic Phosphatase PRL-3 Induces Ovarian Cancer Stem Cell Sub-population through Phosphatase-Independent Deacetylation Modulations

Cancer stem cells (CSCs) are responsible for tumor initiation, chemoresistance, metastasis, and relapse, but the underlying molecular origin of CSCs remains elusive. Here we identified that metastatic phosphatase of regenerating liver 3 (PRL-3) transcriptionally upregulates SOX2 in the expansion of CSC sub-population from normal cancer cells. Mechanistically, SOX2 upregulation is attributed to the binding of the acetylated myocyte enhancer factor 2A (MEF2A) to SOX2 promoter in tumor cells. In parallel, PRL-3 competitively binds to Class IIa histone deacetylase 4 (HDAC4) to facilitate HDAC4 translocation, leading to the disassociation of HDAC4 from MEF2A and histones. The released MEF2A and histones thus remain acetylated and render the subsequent accessibility of the acetylated MEF2A to SOX2 promoter region. Clinical relevance among PRL-3, SOX2, and HDAC4 is validated in ovary cancer samples. Therefore, this PRL-3-HDAC4-MEF2A/histones-SOX2 signaling axis would be a potential therapeutic target in inhibiting ovarian cancer metastasis and relapse.

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PRL-3 promotes the expansion of CSC-like cells via transcriptional SOX2 upregulation

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Binding of MEF2A to SOX2 promoter bridges the PRL-3-induced SOX2 upregulation

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PRL-3 competitively binds HDAC4 to cause the disassociation of HDAC4 from MEF2A

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Acetylated histones render the accessibility of SOX2 promoter region to MEF2A

Models for Understanding Resistance to Chemotherapy in Liver Cancer

The lack of response to pharmacological treatment constitutes a substantial limitation in the handling of patients with primary liver cancers (PLCs). The existence of active mechanisms of chemoresistance (MOCs) in hepatocellular carcinoma, cholangiocarcinoma, and hepatoblastoma hampers the usefulness of chemotherapy. A better understanding of MOCs is needed to develop strategies able to overcome drug refractoriness in PLCs. With this aim, several experimental models are commonly used. These include in vitro cell-free assays using subcellular systems; studies with primary cell cultures; cancer cell lines or heterologous expression systems; multicellular models, such as spheroids and organoids; and a variety of in vivo models in rodents, such as subcutaneous and orthotopic tumor xenografts or chemically or genetically induced liver carcinogenesis. Novel methods to perform programmed genomic edition and more efficient techniques to isolate circulating microvesicles offer new opportunities for establishing useful experimental tools for understanding the resistance to chemotherapy in PLCs. In the present review, using three criteria for information organization: (1) level of research; (2) type of MOC; and (3) type of PLC, we have summarized the advantages and limitations of the armamentarium available in the field of pharmacological investigation of PLC chemoresistance.

A novel BMI-1 inhibitor QW24 for the treatment of stem-like colorectal cancer

Background

Cancer-initiating cell (CIC), a functionally homogeneous stem-like cell population, is resonsible for driving the tumor maintenance and metastasis, and is a source of chemotherapy and radiation-therapy resistance within tumors. Targeting CICs self-renewal has been proposed as a therapeutic goal and an effective approach to control tumor growth. BMI-1, a critical regulator of self-renewal in the maintenance of CICs, is identified as a potential target for colorectal cancer therapy.

Methods

Colorectal cancer stem-like cell lines HCT116 and HT29 were used for screening more than 500 synthetic compounds by sulforhodamine B (SRB) cell proliferation assay. The candidate compound was studied in vitro by SRB cell proliferation assay, western blotting, cell colony formation assay, quantitative real-time PCR, flow cytometry analysis, and transwell migration assay. Sphere formation assay and limiting dilution analysis (LDA) were performed for measuring the effect of compound on stemness properties. In vivo subcutaneous tumor growth xenograft model and liver metastasis model were performed to test the efficacy of the compound treatment. Student’s t test was applied for statistical analysis.

Results

We report the development and characterization of a small molecule inhibitor QW24 against BMI-1. QW24 potently down-regulates BMI-1 protein level through autophagy-lysosome degradation pathway without affecting the BMI-1 mRNA level. Moreover, QW24 significantly inhibits the self-renewal of colorectal CICs in stem-like colorectal cancer cell lines, resulting in the abrogation of their proliferation and metastasis. Notably, QW24 significantly suppresses the colorectal tumor growth without obvious toxicity in the subcutaneous xenograft model, as well as decreases the tumor metastasis and increases mice survival in the liver metastasis model. Moreover, QW24 exerts a better efficiency than the previously reported BMI-1 inhibitor PTC-209.

Conclusions

Our preclinical data show that QW24 exerts potent anti-tumor activity by down-regulating BMI-1 and abrogating colorectal CICs self-renewal without obvious toxicity in vivo, suggesting that QW24 could potentially be used as an effective therapeutic agent for clinical colorectal cancer treatment.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1392-8) contains supplementary material, which is available to authorized users.

Next-generation nanotheranostics targeting cancer stem cells

Cancer is depicted as the most aggressive malignancy and is one the major causes of death worldwide. It originates from immortal tumor-initiating cells called 'cancer stem cells' (CSCs). This devastating subpopulation exhibit potent self-renewal, proliferation and differentiation characteristics. Dynamic DNA repair mechanisms can sustain the immortality phenotype of cancer to evade all treatment strategies. To date, current conventional chemo- and radio-therapeutic strategies adopted against cancer fail in tackling CSCs. However, new advances in nanotechnology have paved the way for creating next-generation nanotheranostics as multifunctional smart 'all-in-one' nanoparticles. These particles integrate diagnostic, therapeutic and targeting agents into one single biocompatible and biodegradable carrier, opening up new avenues for breakthroughs in early detection, diagnosis and treatment of cancer through efficient targeting of CSCs.

Role of the Microenvironment in Regulating Normal and Cancer Stem Cell Activity: Implications for Breast Cancer Progression and Therapy Response

The epithelial cells in an adult woman’s breast tissue are continuously replaced throughout their reproductive life during pregnancy and estrus cycles. Such extensive epithelial cell turnover is governed by the primitive mammary stem cells (MaSCs) that proliferate and differentiate into bipotential and lineage-restricted progenitors that ultimately generate the mature breast epithelial cells. These cellular processes are orchestrated by tightly-regulated paracrine signals and crosstalk between breast epithelial cells and their tissue microenvironment. However, current evidence suggests that alterations to the communication between MaSCs, epithelial progenitors and their microenvironment plays an important role in breast carcinogenesis. In this article, we review the current knowledge regarding the role of the breast tissue microenvironment in regulating the special functions of normal and cancer stem cells. Understanding the crosstalk between MaSCs and their microenvironment will provide new insights into how an altered breast tissue microenvironment could contribute to breast cancer development, progression and therapy response and the implications of this for the development of novel therapeutic strategies to target cancer stem cells.

[Study on colorectal cancer using air-liquid interface organoid culture method]

Colorectal cancer is a disease with high unmet medical needs. An increase in the number of cancer patients who are resistant to anti-cancer drugs is one of factors that increase the number of fatalities. Since there was no suitable experimental model to recapitulate the tumor environment in which various cells in the tissues exist, it was extremely difficult to develop a medicine that overcomes the anti-cancer drug resistance in each colorectal cancer patient. In this review, we describe the current status and problems of drug therapy for colorectal cancer patients, and introduce our study to develop the new targeting drugs using human colon tissue-derived air liquid interface organoid culture method.

Commonly integrated epigenetic modifications of differentially expressed genes lead to adaptive resistance in cancer

Aim:

To investigate the integrated epigenetic regulation of acquired drug resistance in cancer.

Materials & methods:

Our gene expression data of five induced drug-tolerant cell models, one resistant cell line and one publicly available drug-resistant dataset were integrated to identify common differentially expressed genes and pathways. ChIP-seq and DNA methylation by HM450K beadchip were used to study the epigenetic profile of differential expressed genes.

Results & conclusion:

Integrated transcriptomic analysis identified a common ‘viral mimicry’ related gene signature in induced drug-tolerant cells and the resistant state. Analysis of the epigenetic regulation revealed a common set of down-regulated genes, which are marked and regulated by a concomitant loss of H3K4me3, gain of H3K9me3 and increment of regional DNA methylation levels associated with tumor suppressor genes and apoptotic signaling.

Heterogeneity in Circulating Tumor Cells: The Relevance of the Stem-Cell Subset

The release of circulating tumor cells (CTCs) into vasculature is an early event in the metastatic process. The analysis of CTCs in patients has recently received widespread attention because of its clinical implications, particularly for precision medicine. Accumulated evidence documents a large heterogeneity in CTCs across patients. Currently, the most accepted view is that tumor cells with an intermediate phenotype between epithelial and mesenchymal have the highest plasticity. Indeed, the existence of a meta-stable or partial epithelial–mesenchymal transition (EMT) cell state, with both epithelial and mesenchymal features, can be easily reconciled with the concept of a highly plastic stem-like state. A close connection between EMT and cancer stem cells (CSC) traits, with enhanced metastatic competence and drug resistance, has also been described. Accordingly, a subset of CTCs consisting of CSC, present a stemness profile, are able to survive chemotherapy, and generate metastases after xenotransplantation in immunodeficient mice. In the present review, we discuss the current evidence connecting CTCs, EMT, and stemness. An improved understanding of the CTC/EMT/CSC connections may uncover novel therapeutic targets, irrespective of the tumor type, since most cancers seem to harbor a pool of CSCs, and disclose important mechanisms underlying tumorigenicity.

Cancer stem cell self-renewal as a therapeutic target in human oral cancer

Tumor recurrence following treatment remains a major clinical challenge in oral cavity cancer. Cancer stem cells (CSCs) have been isolated from human oral cancers and been considered as the driving force of tumor recurrence and metastasis. However, it still remains unclear whether targeting CSCs in oral cancer is a clinically relevant strategy to combat cancer recurrence and metastasis. Here, using clinical cancer specimens and patient-derived xenografts, we show that the self-renewal regulator BMI1 is highly expressed in CSCs of oral cavity squamous cell carcinoma. Inhibition of BMI1 decreases oral CSCs' self-renewal and tumor-initiating potential. Treatment of pre-established human oral cancer xenografts with a BMI1 inhibitor resulted in abrogation of tumor progression and reduced the frequency of CSCs in the xenografts. Remarkably, the BMI1 inhibitor has therapeutic effects in cisplatin-resistant tumors and can reduce metastases initiated by circulating CSCs. Mechanistically, BMI1-inhibition leads to oral CSC necroptotic cell death, which underlies the self-renewal impairment after inhibiting BMI1. Our data provide a pre-clinical proof-of-concept that targeting BMI1-related CSC self-renewal is a clinically relevant anti-cancer therapy in human oral cavity squamous cell carcinoma.

Caveolin-1: a multifaceted driver of breast cancer progression and its application in clinical treatment

Human breast cancer is one of the most frequent cancer diseases and causes of death among female population worldwide. It appears at a high incidence and has a high malignancy, mortality, recurrence rate and poor prognosis. Caveolin-1 (Cav1) is the main component of caveolae and participates in various biological events. More and more experimental studies have shown that Cav1 plays a critical role in the progression of breast cancer including cell proliferation, apoptosis, autophagy, invasion, migration and breast cancer metastasis. Besides, Cav1 has been found to be involved in chemotherapeutics and radiotherapy resistance, which are still the principal problems encountered in clinical breast cancer treatment. In addition, stromal Cav1 may be a potential indicator for breast cancer patients' prognosis. In the current review, we cover the state-of-the-art study, development and progress on Cav1 and breast cancer, altogether describing the role of Cav1 in breast cancer progression and application in clinical treatment, in the hope of providing a basis for further research and promoting CAV1 gene as a potential target to diagnose and treat aggressive breast cancers.

Evaluation of cancer stemness in breast cancer and glioblastoma spheroids in vitro

In this study, the effect of spheroid formation, as a model of three-dimensional (3D) culture systems, on the cancer stemness of human breast cancer (MCF-7) and human glioma (U87-MG) cell lines was analyzed. We compared the expression of pluripotency genes, the presence of various cancer stem cell populations, migration and proliferation capacities of cells cultured as monolayers or spheroids. MCF-7 cells formed uniform spheroids in vitro, upregulated the expression of stem cell markers both at gene and protein levels and increased their migration capacities when cultured in 3D systems. When a CSC targeting metabolic drug, metformin was used, multiple drug resistance genes (ABC transporters) were downregulated and the anti-cancer activity of 5-fluorouracil was enhanced. In summary, this study proved that the use of 3D culture systems such as spheroids can be used in CSC-related research. Therefore, studies involving 3D culture systems will help scientists to discover new CSC markers, show more realistic drug responses, and better evaluate tumor proliferation and morphology changes.

Ludwig Boltzmann Cluster Oncology (LBC ONC): first 10 years and future perspectives

In 2008 the Ludwig Boltzmann Cluster Oncology (LBC ONC) was established on the basis of two previous Ludwig Boltzmann Institutes working in the field of hematology and cancer research. The general aim of the LBC ONC is to improve treatment of hematopoietic neoplasms by eradicating cancer-initiating and disease-propagating cells, also known as leukemic stem cells (LSC) in the context of leukemia. In a first phase, the LBC ONC characterized the phenotype and molecular aberration profiles of LSC in various malignancies. The LSC phenotypes were established in acute and chronic myeloid leukemia, in acute lymphoblastic leukemia and in chronic lymphocytic leukemia. In addition, the concept of preleukemic (premalignant) neoplastic stem cells (pre-L-NSC) was coined by the LBC ONC and was tested in myelodysplastic syndromes and myeloproliferative neoplasms. Phenotypic characterization of LSC provided a solid basis for their purification and for the characterization of specific target expression profiles. In a second phase, molecular markers and targets were validated. This second phase is ongoing and should result in the development of new diagnostics parameters and novel, more effective, LSC-eradicating, treatment strategies; however, many issues still remain to be solved, such as sub-clonal evolution, LSC niche interactions, immunologic control of LSC, and LSC resistance. In the forthcoming years, the LBC ONC will concentrate on developing LSC-eradicating strategies, with special focus on LSC resistance, precision medicine and translation of LSC-eradicating concepts into clinical application.

Toward Minimal Residual Disease-Directed Therapy in Melanoma

Many patients with advanced cancers achieve dramatic responses to a panoply of therapeutics yet retain minimal residual disease (MRD), which ultimately results in relapse. To gain insights into the biology of MRD, we applied single-cell RNA sequencing to malignant cells isolated from BRAF mutant patient-derived xenograft melanoma cohorts exposed to concurrent RAF/MEK-inhibition. We identified distinct drug-tolerant transcriptional states, varying combinations of which co-occurred within MRDs from PDXs and biopsies of patients on treatment. One of these exhibited a neural crest stem cell (NCSC) transcriptional program largely driven by the nuclear receptor RXRG. An RXR antagonist mitigated accumulation of NCSCs in MRD and delayed the development of resistance. These data identify NCSCs as key drivers of resistance and illustrate the therapeutic potential of MRD-directed therapy. They also highlight how gene regulatory network architecture reprogramming may be therapeutically exploited to limit cellular heterogeneity, a key driver of disease progression and therapy resistance.

Effects of baicalein on pancreatic cancer stem cells via modulation of sonic Hedgehog pathway

Recent studies have suggested that sonic Hedgehog (Shh) signaling pathway is aberrantly activated in cancer stem cells (CSCs). A seven-herb Chinese medicinal formula composed of Amorphophallus rivieri Durieu, Oldenlandia diffusa (Wild) Roxb, Scutellaria barbata D. Don, Gynostemma pentaphyllum (Thunb.) Mak and Amomum cardamomum L, i.e. Qingyihuaji (QYHJ) formula, has been shown to inhibit proliferation of pancreatic CSCs by inhibiting Shh signaling pathway and thereby prolong the overall survival of pancreatic cancer patients. Mass spectrometry analysis revealed that baicalein is one of the major compounds of QYHJ formula. The objective of this study was to investigate the role of Shh pathway in pancreatic cancer and to examine the molecular mechanisms of baicalein involved in pancreatic cancer treatment. We examined the effects of baicalein on pancreatic CSCs both in vivo and in vitro. The results indicated that baicalein attenuated the pluripotency of pancreatic CSCs. Then, we investigated the underlying mechanism and found that nuclear transcription factors, such as Sox-2 and Oct-4 as well as members in Shh signaling pathway, e.g. SHH, SMO, and Gli-2, were downregulated after baicalein treatment. Furthermore, silencing Gli-2 expression by small interfering RNA decreased Sox-2 expression and blocked the inhibitory effects of baicalein, suggesting that the effects of baicalein may be mediated through inhibition of Shh pathway. Our results suggested that baicalein, an active compound in QYHJ formula, could suppress the self-renewal of pancreatic CSCs through inhibition of Shh signaling pathway.

Development of an Experimental Model for Analyzing Drug Resistance in Colorectal Cancer

Colorectal cancer (CRC) is one of the most common cancers, for which combination treatment of chemotherapy is employed. However, most patients develop drug resistance during the course of treatment. To clarify the mechanisms of drug resistance, various research models have been developed. Recently, we established a human CRC patients-derived three-dimensional (3D) culture system using an air-liquid interface organoid method. It contained numerous cancer stem cells and showed resistance to 5-fluorouracil and Irinotecan. In this review, we introduce conventional and our established models for studying drug resistance in CRC.

Oncolytic Virotherapy versus Cancer Stem Cells: A Review of Approaches and Mechanisms

A growing body of evidence suggests that a subset of cells within tumors are resistant to conventional treatment modalities and may be responsible for disease recurrence. These cells are called cancer stem cells (CSC), which share properties with normal stem cells including self-renewal, pluripotency, drug resistance, and the ability to maintain quiescence. While most conventional therapies can efficiently destroy rapidly dividing cancer cells comprising the bulk of a tumor, they often fail to kill the less abundant and quiescent CSCs. Furthermore, killing of only differentiated cells in the tumor may actually allow for enrichment of CSCs and thereby portend a bad prognosis. Therefore, targeting of CSCs is important to achieve long-term success in cancer therapy. Oncolytic viruses represent a completely different class of therapeutics that can kill cancer cells in a variety of ways, which differ from those of conventional therapies. Hence, CSCs that are inherently resistant to conventional therapies may be susceptible to oncolytic virus-mediated killing. Recent studies have shown that oncolytic viruses can efficiently kill CSCs in many types of cancer. Here, we discuss the mechanism through which CSCs can escape conventional therapies and how they may still be susceptible to different classes of oncolytic viruses. Furthermore, we provide a summary of recent studies that have tested oncolytic viruses on CSCs of different origins and discuss possible future directions for this fascinating subset of oncolytic virus research.

Non-coding RNAs as emerging regulators of epithelial to mesenchymal transition in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) remains a major health problem that patients suffer from around the world. The epithelial to mesenchymal transition (EMT) has attractive roles in increasing malignant potential and reducing sensitivity to conventional therapeutics in NSCLC cells. Meanwhile, it is now evident that non-coding RNAs (ncRNAs), primarily microRNAs and long non-coding RNAs contribute to tumorigenesis partially via regulating EMT. This article briefly summarizes current researches about EMT-related ncRNAs in NSCLC and discusses their crucial roles in the complex regulatory network. Also, the authors will show the evidence that ncRNAs not only contribute to cancer cells migration and invasion, but also take charge of the resistance of chemotherapy, radiotherapy and EGFR-TIKs. Then, we will further discuss the potential of inhibition of EMT via manipulating relevant ncRNAs to change our current treatment of NSCLC patients.

Immune checkpoint blockade combined with IL-6 and TGF-β inhibition improves the therapeutic outcome of mRNA-based immunotherapy

Improved understanding of cancer immunology has provided insight into the phenomenon of frequent tumor recurrence after initially successful immunotherapy. A delicate balance exists between the capacity of the immune system to control tumor growth and various resistance mechanisms that arise to avoid or even counteract the host's immune system. These resistance mechanisms include but are not limited to (i) adaptive expression of inhibitory checkpoint molecules in response to the proinflammatory environment and (ii) amplification of cancer stem cells, a small fraction of tumor cells possessing the capacity for self-renewal and mediating treatment resistance and formation of metastases after long periods of clinical remission. Several individual therapeutic agents have so far been developed to revert T-cell exhaustion or disrupt the cross-talk between cancer stem cells and the tumor-promoting microenvironment. Here, we demonstrate that a three-arm combination therapy-consisting of an mRNA-based vaccine to induce antigen-specific T-cell responses, monoclonal antibodies blocking inhibitory checkpoint molecules (PD-1, TIM-3, LAG-3), and antibodies targeting IL-6 and TGF-β-improves the therapeutic outcome in subcutaneous TC-1 tumors and significantly prolongs survival of treated mice. Our findings point to a need for a rational development of multidimensional anticancer therapies, aiming at the induction of tumor-specific immunity and simultaneously targeting multiple resistance mechanisms.

Acquired Resistance to Drugs Targeting Tyrosine Kinases

Resistance to chemotherapeutic drugs exemplifies the greatest hindrance to effective treatment of cancer patients. The molecular mechanisms responsible have been investigated for over 50 years and have revealed the lack of a single cause, but instead, multiple mechanisms including induced expression of membrane transporters that pump drugs out of cells (multidrug resistance (MDR) phenotype), changes in the glutathione system, and altered metabolism. Treatment of cancer patients/cancer cells with chemotherapeutic agents and/or molecularly targeted drugs is accompanied by acquisition of resistance to the treatment administered. Chemotherapeutic agent resistance was initially assumed to be due to induction of mutations leading to a resistant phenotype. While this has occurred for molecularly targeted drugs, it is clear that drugs selectively targeting tyrosine kinases (TKs) cause the acquisition of mutational changes and resistance to inhibition. The first TK to be targeted, Bcr-Abl, led to the generation of several drugs including imatinib, dasatinib, and sunitinib that provided a rich understanding of this phenomenon. It became clear that mutations alone were not the only cause of resistance. Additional mechanisms were involved, including alternative splicing, alternative/compensatory signaling pathways, and epigenetic changes. This review will focus on resistance to tyrosine kinase inhibitors (TKIs), receptor TK (RTK)-directed antibodies, and antibodies that inactivate specific RTK ligands. New approaches and concepts aimed at avoiding the generation of drug resistance will be examined. Many RTKs, including the IGF-1R, are dependence receptors that induce ligand-independent apoptosis. How this signaling paradigm has implications on therapeutic strategies will also be considered.

MiR-128 reverses the gefitinib resistance of the lung cancer stem cells by inhibiting the c-met/PI3K/AKT pathway

Gefitinib is a first line anti-tumor drug used for the treatment of patients with non-small cell lung cancer (NSCLC) harboring EGFR mutations. However, the drug resistance to gefitinib limits its clinical application. Here, we observed the CSCs of PC9 are obviously resistant to gefitinib compared with the non-CSCs. Furthermore, we found the gefitinib failed to suppress the PI3K/AKT pathway in the PC9-CSCs. Mechanically, we showed significant down-regulation of miR-128 in the PC9-CSCs compared with the non-CSCs. Overexpression of miR-128 significantly increased the sensitivity of PC9-CSCs to gefitinib-induced apoptosis. In addition, the gene of c-met was proved to be directly inhibited by miR-128. Enforced expression of c-met could "rescue" the miR-128 promoted apoptosis and cleavage of caspases in PC9-CSCs treated with gefitinib. Thus, these results indicate that the miR-128/c-met pathway enhances the gefitinib sensitivity of the lung cancer stem cells by suppressing the PI3K/AKT pathway.