Cancer stem cells: problems for therapy?

Advances in ovarian tumor stem cells and therapy

Ovarian cancer is considered the most lethal among all gynecological malignancies due to its early metastatic dissemination, extensive spread, and malignant ascites. The current standard of care for advanced ovarian cancer involves a combination of cytoreductive surgery and chemotherapy utilizing platinum-based and taxane-based agents. Although initial treatment yields clinical remission in 70-80% of patients, the majority eventually develop treatment resistance and tumor recurrence. A growing body of evidence indicates the existence of cancer stem cells within diverse solid tumors, including ovarian cancer, which function as a subpopulation to propel tumor growth and disease advancement by means of drug resistance, recurrence, and metastasis. The presence of ovarian cancer stem cells is widely considered to be a significant contributor to the unfavorable clinical outcomes observed in patients with ovarian cancer, as they play a crucial role in mediating chemotherapy resistance, recurrence, and metastasis. Ovarian cancer stem cells possess the capacity to reassemble within the entirety of the tumor following conventional treatment, thereby instigating the recurrence of ovarian cancer and inducing resistance to treatment. Consequently, the creation of therapeutic approaches aimed at eliminating ovarian cancer stem cells holds great potential for the management of ovarian cancer. These cells are regarded as one of the most auspicious targets and mechanisms for the treatment of ovarian cancer. There is a pressing need for a comprehensive comprehension of the fundamental mechanisms of ovarian cancer's recurrence, metastasis, and drug resistance, alongside the development of effective strategies to overcome chemoresistance, metastasis, and recurrence. The implementation of cancer stem cell therapies may potentially augment the tumor cells' sensitivity to existing chemotherapy protocols, thereby mitigating the risks of tumor metastasis and recurrence, and ultimately improving the survival rates of ovarian cancer patients.

Comprehensive characterization of stemness-related lncRNAs in triple-negative breast cancer identified a novel prognostic signature related to treatment outcomes, immune landscape analysis and therapeutic guidance: a silico analysis with in vivo experiments

BACKGROUND

Cancer stem cells (CSCs) and long non-coding RNAs (lncRNAs) are known to play a crucial role in the growth, migration, recurrence, and drug resistance of tumor cells, particularly in triple-negative breast cancer (TNBC). This study aims to investigate stemness-related lncRNAs (SRlncRNAs) as potential prognostic indicators for TNBC patients.

METHODS

Utilizing RNA sequencing data and corresponding clinical information from the TCGA database, and employing Weighted Gene Co-expression Network Analysis (WGCNA) on TNBC mRNAsi sourced from an online database, stemness-related genes (SRGs) and SRlncRNAs were identified. A prognostic model was developed using univariate Cox and LASSO-Cox analysis based on SRlncRNAs. The performance of the model was evaluated using Kaplan-Meier analysis, ROC curves, and ROC-AUC. Additionally, the study delved into the underlying signaling pathways and immune status associated with the divergent prognoses of TNBC patients.

RESULTS

The research identified a signature of six SRlncRNAs (AC245100.6, LINC02511, AC092431.1, FRGCA, EMSLR, and MIR193BHG) for TNBC. Risk scores derived from this signature were found to correlate with the abundance of plasma cells. Furthermore, the nominated chemotherapy drugs for TNBC exhibited considerable variability between different risk score groups. RT-qPCR validation confirmed abnormal expression patterns of these SRlncRNAs in TNBC stem cells, affirming the potential of the SRlncRNAs signature as a prognostic biomarker.

CONCLUSION

The identified signature not only demonstrates predictive power in terms of patient outcomes but also provides insights into the underlying biology, signaling pathways, and immune status associated with TNBC prognosis. The findings suggest the possibility of guiding personalized treatments, including immune checkpoint gene therapy and chemotherapy strategies, based on the risk scores derived from the SRlncRNA signature. Overall, this research contributes valuable knowledge towards advancing precision medicine in the context of TNBC.

MicroRNA-561-3p indirectly regulates the PD-L1 expression by targeting ZEB1, HIF1A, and MYC genes in breast cancer

Globally, breast cancer is the second most common cause of cancer-related deaths among women. In breast cancer, microRNAs (miRNAs) are essential for both the initiation and development of tumors. It has been suggested that the tumor suppressor microRNA-561-3p (miR-561-3p) is crucial in arresting the growth of cancer cells. Further research is necessary to fully understand the role and molecular mechanism of miR-561 in human BC. The aim of this study was to investigate the inhibitory effect of miR-561-3p on ZEB1, HIF1A, and MYC expression as oncogenes that have the most impact on PD-L1 overexpression and cellular processes such as proliferation, apoptosis, and cell cycle in breast cancer (BC) cell lines. The expression of ZEB1, HIF1A, and MYC genes and miR-561-3p were measured in BC clinical samples and cell lines via qRT-PCR. The luciferase assay, MTT, Annexin-PI staining, and cell cycle experiments were used to assess the effect of miR-561-3p on candidate gene expression, proliferation, apoptosis, and cell cycle progression. Flow cytometry was used to investigate the effects of miR-561 on PD-L1 suppression in the BC cell line. The luciferase assay showed that miRNA-561-3p targets the 3'-UTRs of ZEB1, HIF1A and MYC genes significantly. In BC tissues, the qRT-PCR results demonstrated that miR-561-3p expression was downregulated and the expression of ZEB1, HIF1A and MYC genes was up-regulated. It was shown that overexpression of miR-561-3p decreased PD-L1 expression and BC cell proliferation, and induced apoptosis and cell cycle arrest through downregulation of candidate oncogenes. Furthermore, inhibition of candidate genes by miR-561-3p reduced PD-L1 at both mRNA and protein levels. Our research investigated the impact of miR-561-3p on the expression of ZEB1, HIF1A and MYC in breast cancer cells for the first time. Our findings may help clarify the role of miR-561-3p in PD-L1 regulation and point to this miR as a potential biomarker and novel therapeutic target for cancer immunotherapy.

Regulation of cancer stem cells by CXCL1, a chemokine whose secretion is controlled by MCM2

BACKGROUND

A high expression pattern of minichromosome maintenance 2 (MCM2) has been observed in various cancers. MCM2 is a protein involved in the cell cycle and plays a role in cancer growth and differentiation by binding to six members of the MCM subfamily. The MCM protein family includes MCM2 through MCM7.

METHODS

MCM2 has shown high expression in both lung cancer stem cells (LCSCs) and glioma stem cells (GSCs). We investigated the characteristics of CSCs and the regulation of the epithelial-to-mesenchymal transition (EMT) phenomenon in LCSCs and GSCs by MCM2. Additionally, we explored secreted factors regulated by MCM2.

RESULTS

There was a significant difference in survival rates between lung cancer patients and brain cancer patients based on MCM2 expression. MCM2 was found to regulate both markers and regulatory proteins in LCSCs. Moreover, MCM2 is thought to be involved in cancer metastasis by regulating cell migration and invasion, not limited to lung cancer but also identified in glioma. Among chemokines, chemokine (C-X-C motif) ligand 1 (CXCL1) was found to be regulated by MCM2.

CONCLUSIONS

MCM2 not only participates in the cell cycle but also affects cancer cell growth by regulating the external microenvironment to create a favorable environment for cells. MCM2 is highly expressed in malignant carcinomas, including CSCs, and contributes to the malignancy of various cancers. Therefore, MCM2 may represent a crucial target for cancer therapeutics.

Emerging Role of Autophagy in Governing Cellular Dormancy, Metabolic Functions, and Therapeutic Responses of Cancer Stem Cells

Tumors are composed of heterogeneous populations of dysregulated cells that grow in specialized niches that support their growth and maintain their properties. Tumor heterogeneity and metastasis are among the major hindrances that exist while treating cancer patients, leading to poor clinical outcomes. Although the factors that determine tumor complexity remain largely unknown, several genotypic and phenotypic changes, including DNA mutations and metabolic reprograming provide cancer cells with a survival advantage over host cells and resistance to therapeutics. Furthermore, the presence of a specific population of cells within the tumor mass, commonly known as cancer stem cells (CSCs), is thought to initiate tumor formation, maintenance, resistance, and recurrence. Therefore, these CSCs have been investigated in detail recently as potential targets to treat cancer and prevent recurrence. Understanding the molecular mechanisms involved in CSC proliferation, self-renewal, and dormancy may provide important clues for developing effective therapeutic strategies. Autophagy, a catabolic process, has long been recognized to regulate various physiological and pathological processes. In addition to regulating cancer cells, recent studies have identified a critical role for autophagy in regulating CSC functions. Autophagy is activated under various adverse conditions and promotes cellular maintenance, survival, and even cell death. Thus, it is intriguing to address whether autophagy promotes or inhibits CSC functions and whether autophagy modulation can be used to regulate CSC functions, either alone or in combination. This review describes the roles of autophagy in the regulation of metabolic functions, proliferation and quiescence of CSCs, and its role during therapeutic stress. The review further highlights the autophagy-associated pathways that could be used to regulate CSCs. Overall, the present review will help to rationalize various translational approaches that involve autophagy-mediated modulation of CSCs in controlling cancer progression, metastasis, and recurrence.

Overcoming BCR::ABL1 dependent and independent survival mechanisms in chronic myeloid leukaemia using a multi-kinase targeting approach

BACKGROUND

Despite improved patient outcome using tyrosine kinase inhibitors (TKIs), chronic myeloid leukaemia (CML) patients require life-long treatment due to leukaemic stem cell (LSC) persistence. LSCs reside in the bone marrow (BM) niche, which they modify to their advantage. The BM provides oncogene-independent signals to aid LSC cell survival and quiescence. The bone-morphogenetic pathway (BMP) is one pathway identified to be highly deregulated in CML, with high levels of BMP ligands detected in the BM, accompanied by CML stem and progenitor cells overexpressing BMP type 1 receptors- activin-like kinases (ALKs), especially in TKI resistant patients. Saracatinib (SC), a SRC/ABL1 dual inhibitor, inhibits the growth of CML cells resistant to the TKI imatinib (IM). Recent studies indicate that SC is also a potent ALK inhibitor and BMP antagonist. Here we investigate the efficacy of SC in overcoming CML BCR::ABL1 dependent and independent signals mediated by the BM niche both in 2D and 3D culture.

METHODS

CML cells (K562 cell line and CML CD34+ primary cells) were treated with single or combination treatments of: IM, SC and the BMP receptors inhibitor dorsomorphin (DOR), with or without BMP4 stimulation in 2D (suspension) and 3D co-culture on HS5 stroma cell line and mesenchymal stem cells in AggreWell and microfluidic devices. Flow cytometry was performed to investigate apoptosis, cell cycle progression and proliferation, alongside colony assays following treatment. Proteins changes were validated by immunoblotting and transcriptional changes by Fluidigm multiplex qPCR.

RESULTS

By targeting the BMP pathway, using specific inhibitors against ALKs in combination with SRC and ABL TKIs, we show an increase in apoptosis, altered cell cycle regulation, fewer cell divisions, and reduced numbers of CD34+ cells. Impairment of long-term proliferation and differentiation potential after combinatorial treatment also occurred.

CONCLUSION

BMP signalling pathway is important for CML cell survival. Targeting SRC, ABL and ALK kinases is more effective than ABL inhibition alone, the combination efficacy importantly being demonstrated in both 2D and 3D cell cultures highlighting the need for combinatorial therapies in contrast to standard of care single agents. Our study provides justification to target multiple kinases in CML to combat LSC persistence.

Tumor microenvironment-induced tumor cell plasticity: relationship with hypoxic stress and impact on tumor resistance

The role of tumor interaction with stromal components during carcinogenesis is crucial for the design of efficient cancer treatment approaches. It is widely admitted that tumor hypoxic stress is associated with tumor aggressiveness and thus impacts susceptibility and resistance to different types of treatments. Notable biological processes that hypoxia functions in include its regulation of tumor heterogeneity and plasticity. While hypoxia has been reported as a major player in tumor survival and dissemination regulation, the significance of hypoxia inducible factors in cancer stem cell development remains poorly understood. Several reports indicate that the emergence of cancer stem cells in addition to their phenotype and function within a hypoxic tumor microenvironment impacts cancer progression. In this respect, evidence showed that cancer stem cells are key elements of intratumoral heterogeneity and more importantly are responsible for tumor relapse and escape to treatments. This paper briefly reviews our current knowledge of the interaction between tumor hypoxic stress and its role in stemness acquisition and maintenance. Our review extensively covers the influence of hypoxia on the formation and maintenance of cancer stem cells and discusses the potential of targeting hypoxia-induced alterations in the expression and function of the so far known stem cell markers in cancer therapy approaches. We believe that a better and integrated understanding of the effect of hypoxia on stemness during carcinogenesis might lead to new strategies for exploiting hypoxia-associated pathways and their targeting in the clinical setting in order to overcome resistance mechanisms. More importantly, at the present time, efforts are oriented towards the design of innovative therapeutical approaches that specifically target cancer stem cells.

Stemness-related lncRNAs signature as a biologic prognostic model for head and neck squamous cell carcinoma

Cancer stem cells (CSCs) and long non-coding RNAs (lncRNAs) are particularly important for tumor cell growth and migration, and recurrence and drug resistance, including head and neck squamous cell carcinoma (HNSCC). The purpose of this study was to explore stemness-related lncRNAs (SRlncRNAs) that could be used for prognosis of patients with HNSCC. HNSCC RNA sequencing data and matched clinical data were obtained from TCGA database, and stem cell characteristic genes related to HNSCC mRNAsi were obtained from the online database by WGCNA analysis, respectively. Further, SRlncRNAs were obtained. Then, the prognostic model was constructed to forecast patient survival through univariate Cox regression and LASSO-Cox method based on SRlncRNAs. Kaplan-Meier, ROC and AUC were used to evaluate the predictive ability of the model. Moreover, we probed the underlying biological functions, signalling pathways and immune status hidden within differences in prognosis of patients. We explored whether the model could guide personalized treatments included immunotherapy and chemotherapy for HNSCC patients. At last, RT-qPCR was performed to analyze the expressions levels of SRlncRNAs in HNSCC cell lines. A SRlncRNAs signature was identified based on 5 SRlncRNAs (AC004943.2, AL022328.1, MIR9-3HG, AC015878.1 and FOXD2-AS1) in HNSCC. Also, risk scores were correlated with the abundance of tumor-infiltrating immune cells, whereas HNSCC-nominated chemotherapy drugs were considerably different from one another. The final finding was that these SRlncRNAs were abnormally expressed in HNSCCCS according to the results of RT-qPCR. These 5 SRlncRNAs signature, as a potential prognostic biomarker, can be utilized for personalized medicine in HNSCC patients.

Hypoxia Controls the Glycome Signature and Galectin-8-Ligand Axis to Promote Protumorigenic Properties of Metastatic Melanoma

The prognosis for patients with metastatic melanoma (MM) involving distant organs is grim, and treatment resistance is potentiated by tumor-initiating cells (TICs) that thrive under hypoxia. MM cells, including TICs, express a unique glycome featuring i-linear poly-N-acetyllactosamines through the loss of I-branching enzyme, β1,6 N-acetylglucosaminyltransferase 2. Whether hypoxia instructs MM TIC development by modulating the glycome signature remains unknown. In this study, we explored hypoxia-dependent alterations in MM glycome‒associated genes and found that β1,6 N-acetylglucosaminyltransferase 2 was downregulated and a galectin (Gal)-8-ligand axis, involving both extracellular and cell-intrinsic Gal-8, was induced. Low β1,6 N-acetylglucosaminyltransferase 2 levels correlated with poor patient outcomes, and patient serum samples were elevated for Gal-8. Depressed β1,6 N-acetylglucosaminyltransferase 2 in MM cells upregulated TIC marker, NGFR/CD271, whereas loss of MM cell‒intrinsic Gal-8 markedly lowered NGFR and reduced TIC activity in vivo. Extracellular Gal-8 bound preferentially to i-linear poly-N-acetyllactosamines on N-glycans of the TIC marker and prometastatic molecule CD44, among other receptors, and activated prosurvival factor protein kinase B. This study reveals the importance of hypoxia governing the MM glycome by enforcing i-linear poly-N-acetyllactosamine and Gal-8 expression. This mechanistic investigation also uncovers glycome-dependent regulation of pro-MM factor, NGFR, implicating i-linear poly-N-acetyllactosamine and Gal-8 as biomarkers and therapeutic targets of MM.

The Concept of Cancer Stem Cells: Elaborating on ALDH1B1 as an Emerging Marker of Cancer Progression

Cancer is a multifactorial, complex disease exhibiting extraordinary phenotypic plasticity and diversity. One of the greatest challenges in cancer treatment is intratumoral heterogeneity, which obstructs the efficient eradication of the tumor. Tumor heterogeneity is often associated with the presence of cancer stem cells (CSCs), a cancer cell sub-population possessing a panel of stem-like properties, such as a self-renewal ability and multipotency potential. CSCs are associated with enhanced chemoresistance due to the enhanced efflux of chemotherapeutic agents and the existence of powerful antioxidant and DNA damage repair mechanisms. The distinctive characteristics of CSCs make them ideal targets for clinical therapeutic approaches, and the identification of efficient and specific CSCs biomarkers is of utmost importance. Aldehyde dehydrogenases (ALDHs) comprise a wide superfamily of metabolic enzymes that, over the last years, have gained increasing attention due to their association with stem-related features in a wide panel of hematopoietic malignancies and solid cancers. Aldehyde dehydrogenase 1B1 (ALDH1B1) is an isoform that has been characterized as a marker of colon cancer progression, while various studies suggest its importance in additional malignancies. Here, we review the basic concepts related to CSCs and discuss the potential role of ALDH1B1 in cancer development and its contribution to the CSC phenotype.

Targeting cancer stem cells and signalling pathways through phytochemicals: A promising approach against colorectal cancer

BACKGROUND

Cancer stem cells (CSCs) are strongly associated with high tumourigenicity, chemotherapy or radiotherapy resistance, and metastasis and recurrence, particularly in colorectal cancer (CRC). Therefore, targeting CSCs may be a promising approach. Recently, discovery and research on phytochemicals that effectively target colorectal CSCs have been gaining popularity because of their broad safety profile and multi-target and multi-pathway modes of action.

PURPOSE

This review aimed to elucidate and summarise the effects and mechanisms of phytochemicals with potential anti-CSC agents that could contribute to the better management of CRC.

METHODS

We reviewed PubMed, EMBASE, Web of Science, Ovid, ScienceDirect and China National Knowledge Infrastructure databases from the original publication date to March 2022 to review the mechanisms by which phytochemicals inhibit CRC progression by targeting CSCs and their key signalling pathways. Phytochemicals were classified and summarised based on the mechanisms of action.

RESULTS

We observed that phytochemicals could affect the biological properties of colorectal CSCs. Phytochemicals significantly inhibit self-renewal, migration, invasion, colony formation, and chemoresistance and induce apoptosis and differentiation of CSCs by regulating the Wnt/β-catenin pathway (e.g., diallyl trisulfide and genistein), the phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin pathway (e.g., caffeic acid and piperlongumine), the neurogenic locus notch homolog protein pathway (e.g., honokiol, quercetin, and α-mangostin), the Janus kinase-signal transducer and activator of transcription pathway (e.g., curcumin, morin, and ursolic acid), and other key signalling pathways. It is worth noting that several phytochemicals, such as resveratrol, silibinin, evodiamine, and thymoquinone, highlight multi-target and multi-pathway effects in restraining the malignant biological behaviour of CSCs.

CONCLUSIONS

This review demonstrates the potential of targeted therapies for colorectal CSCs using phytochemicals. Phytochemicals could serve as novel therapeutic agents for CRC and aid in drug development.

Andrographolide suppresses the malignancy of triple-negative breast cancer by reducing THOC1-promoted cancer stem cell characteristics

Triple-negative breast cancers (TNBCs) are difficult to cure and currently lack of effective treatment strategies. Cancer stem cells (CSCs) are highly associated with the poor clinical outcome of TNBCs. Thoc1 is a core component of the THO complex (THOC) that regulates the elongation, processing and nuclear export of mRNA. The function of thoc1 in TNBC and whether Thoc1 serves as a drug target are poorly understood. In this study, we demonstrated that thoc1 expression is elevated in TNBC cell lines and human TNBC patient tissues. Knockdown of thoc1 decreased cancer stem cell populations, reduced mammosphere formation, impaired THOC function, and downregulated the expression of stemness-related proteins. Moreover, the thoc1-knockdown 4T1 cells showed less lung metastasis in an orthotopic breast cancer mouse model. Overexpression of Thoc1 promoted TNBC malignancy and the mRNA export of stemness-related genes. Furthermore, treatment of TNBC cells with the natural compound andrographolide reduced the expression of Thoc1 expression, impaired homeostasis of THOC, suppressed CSC properties, and delayed tumor growth in a 4T1-implanted orthotopic mouse model. Andrographolide also reduced the activity of NF-κB, an upstream transcriptional regulator of Thoc1. Notably, thoc1 overexpression attenuates andrographolide-suppressed cellular proliferation. Altogether, our results demonstrate that THOC1 promotes cancer stem cell characteristics of TNBC, and andrographolide is a potential natural compound for eliminating CSCs of TNBCs by downregulating the NF-κB-thoc1 axis.

Natural compounds as a potential modifier of stem cells renewal: Comparative analysis

Cancer stem cells (CSCs) are indispensable for development, progression, drug resistance, and tumor metastasis. Current cancer-directed interventions target targeting rapidly dividing cancer cells and slow dividing CSCs, which are the root cause of cancer origin and recurrence. The most promising targets include several self-renewal pathways involved in the maintenance and renewal of CSCs, such as the Wnt/β-Catenin, Sonic Hedgehog, Notch, Hippo, Autophagy, and Ferroptosis. In view of safety, natural compounds are coming to the front line of treatment modalities for modifying various signaling pathways simultaneously involved in maintaining CSCs. Therefore, targeting CSCs with natural compounds is a promising approach to treating various types of cancers. In view of this, here we provide a comprehensive update on the current status of natural compounds that effectively tune key self-renewal pathways of CSCs. In addition, we highlighted surface expression markers in several types of cancer. We also emphasize how natural compounds target these self-renewal pathways to reduce therapy resistance and cancer recurrence properties of CSCs, hence providing valuable cancer therapeutic strategies. The inclusion of nutraceuticals is believed to enhance the therapeutic efficacy of current cancer-directed interventions significantly.

Bench to Bedside: New Therapeutic Approaches with Extracellular Vesicles and Engineered Biomaterials for Targeting Therapeutic Resistance of Cancer Stem Cells

Cancer has recently been the second leading cause of death worldwide, trailing only cardiovascular disease. Cancer stem cells (CSCs), represented as tumor-initiating cells (TICs), are mainly liable for chemoresistance and disease relapse due to their self-renewal capability and differentiating capacity into different types of tumor cells. The intricate molecular mechanism is necessary to elucidate CSC's chemoresistance properties and cancer recurrence. Establishing efficient strategies for CSC maintenance and enrichment is essential to elucidate the mechanisms and properties of CSCs and CSC-related therapeutic measures. Current approaches are insufficient to mimic the in vivo chemical and physical conditions for the maintenance and growth of CSC and yield unreliable research results. Biomaterials are now widely used for simulating the bone marrow microenvironment. Biomaterial-based three-dimensional (3D) approaches for the enrichment of CSC provide an excellent promise for future drug discovery and elucidation of molecular mechanisms. In the future, the biomaterial-based model will contribute to a more operative and predictive CSC model for cancer therapy. Design strategies for materials, physicochemical cues, and morphology will offer a new direction for future modification and new methods for studying the CSC microenvironment and its chemoresistance property. This review highlights the critical roles of the microenvironmental cues that regulate CSC function and endow them with drug resistance properties. This review also explores the latest advancement and challenges in biomaterial-based scaffold structure for therapeutic approaches against CSC chemoresistance. Since the recent entry of extracellular vesicles (EVs), cell-derived nanostructures, have opened new avenues of investigation into this field, which, together with other more conventionally studied signaling pathways, play an important role in cell-to-cell communication. Thus, this review further explores the subject of EVs in-depth. This review also discusses possible future biomaterial and biomaterial-EV-based models that could be used to study the tumor microenvironment (TME) and will provide possible therapeutic approaches. Finally, this review concludes with potential perspectives and conclusions in this area.

Macrophage induced ERK-TGF-β1 signaling in MCF7 breast cancer cells result in reversible cancer stem cell plasticity and epithelial mesenchymal transition

BACKGROUND

Breast cancer is a heterogenous disease composed of multiple clonal populations and the mechanism by which the tumor microenvironment induces cancer stem cell plasticity is not fully understood.

METHODS

MCF7 breast cancer cells were treated with macrophage conditioned medium (MɸCM). PD98059 and SB431542 were used for ERK and TGF-βR inhibition respectively. Epithelial-mesenchymal transition (EMT) and cancer stem cell markers (CSC) were studied using qRT-PCR and flowcytometry. SCID mice were used for animal experiments.

RESULTS

MɸCM- induced ERK/TGF-β1 signaling led to enrichment of CSC and EMT in MCF7 cells and mammospheres. These effects were abrogated by both MEK inhibitor PD98059 (TGF-β1 synthesis) and SB431542 (TGF-β1 signaling). The increase in CSC was both hybrid (ALDH1⁺) and mesenchymal (CD44⁺ CD24^- cells). Increase in hybrid E/M state was at a single cell level as confirmed by the increase in both claudin-1 (E) and vimentin (M). This did not have any growth advantage in SCID mice and monitoring of CSC and EMT markers before and after growth in SCID mice indicated reversal of these markers in tumor cells recovered from mice. Removal of MɸCM and neutralization of TNF-α, IL-6 and IL-1β in MɸCM abrogated ERK phosphorylation, TGF-β and CSC enrichment indicating the requirement of continuous signaling for maintenance.

CONCLUSIONS

ERK signaling plays an important role in MɸCM- induced EMT and CSC plasticity which is completely reversible upon withdrawal of signals.

GENERAL SIGNIFICANCE

Our experimental observations support the semi-independent nature of EMT-stemness connection which is very dynamic and reversible depending on the microenvironment.

The synergistic anticancer effect of salinomycin combined with cabazitaxel in CD44+ prostate cancer cells by downregulating wnt, NF-κB and AKT signaling

BACKGROUND

Tumor-initiating or cancer stem cells (CSCs) reduce the effectiveness of conventional therapy. Thus, it is crucial to eliminate CSCs while killing bulky cancer cells using a combination of conventional chemotherapy and anti-CSC drugs. Salinomycin is a selective inhibitor against CSCs and shows promise in combination applications. The aim of the study was to examine the efficacy of co-administered cabazitaxel and salinomycin on the survival of prostate cancer cells and CSCs.

METHODS AND RESULTS

CD44 + stem cells were isolated from human PC3 prostate cancer cells by using magnetic activated cell sorting. The cells were concomitantly exposed to salinomycin and cabazitaxel, and the cell survival was determined by MTT test. Apoptosis was assessed by image-based cytometer, and cell migration was evaluated by wound healing assay. The expression of target mRNA and protein were assessed by RT-qPCR and Western blot, respectively. Combination index (CI) analysis showed that simultaneous administration of salinomycin and cabazitaxel was able to exert strong synergistic effect on CD44 + subpopulation (CI = 0.33), but no synergism was observed in PC3 cells. The combination of the two agents significantly increased Bax, cytochrome c, caspase-3 and - 8 mRNA expression in CD44 + CSCs, causing apoptosis. The applied therapy strategy strongly inhibited the phosphorylation of Akt, protein expression of Akt1, NF-κB and Wnt.

CONCLUSIONS

In conclusion, our data suggest that combining salinomycin with cabazitaxel shows promise as a prostate cancer treatment approach that can target CSCs.

TRG16, targeted by miR-765, inhibits breast cancer stem cell-like properties via regulating the NF-κB pathway

Previous studies reported that cancer stem cells (CSCs) might be responsible for drug resistance and cancer progression. Transformation-Related Gene 16 Protein (TRG16), a pseudokinase, was reported to be a suppressor in some types of cancer and its overexpression impaired hepatocellular carcinoma cell stemness. However, the function of TRG16 in BC remains unclear. We found that TRG16 expression was significantly downregulated in BC tissues compared with adjacent tissues (n = 40; P < 0.001) and BC patients with lower expression of TRG16 had a worse prognosis. Forced expression of TRG16 inhibited BC stem cell-like properties as evidenced by decreased CD44-positive cells (CSC marker), reduced mammosphere quantity, and downregulated Nanog, aldehyde dehydrogenase, octamer-binding transcription factor 4, and SRY-box transcription factor 2 expression (CSC markers). Moreover, TRG16 overexpression inhibited self-renewal and invasion capabilities of BC cells in vitro as well as tumor growth in vivo but increased cisplatin sensitivity. However, TRG16 silencing had the opposite effects. Further mechanistic studies revealed that TRG16 was targeted and negatively regulated by miR-765, a facilitator of BC progression. TRG16 could suppress the activation of the NF-κB pathway in BC cells, which is a positive pathway in BC progression and contributes to the maintenance of cancer cell stemness. In conclusion, the results above demonstrate that TRG16, negatively regulated by miR-765, may inhibit the BC progression by regulating BC stem cell-like properties and this inhibition may be mediated by the NF-κB pathway. Our findings indicate that TRG16 may be a potential therapeutic targetable node for BC. TRG16, negatively regulated by miR-765, may inhibit the BC progression through regulating BC stem cell-like properties and this inhibition may be mediated by the NF-κB pathway.

Novel therapeutics and drug-delivery approaches in the modulation of glioblastoma stem cell resistance

Glioblastoma (GBM) is a deadly malignancy with a poor prognosis. An important factor contributing to GBM recurrence is high resistance of GBM cancer stem cells (GSCs). While temozolomide (TMZ), has been shown to consistently extend survival, GSCs grow resistant to TMZ through upregulation of DNA damage repair mechanisms and avoidance of apoptosis. Since a single-drug approach has failed to significantly alter prognosis in the past 15 years, unique approaches such as multidrug combination therapy together with distinctive targeted drug-delivery approaches against cancer stem cells are needed. In this review, a rationale for multidrug therapy using a targeted nanotechnology approach that preferentially target GSCs is proposed with discussion and examples of drugs, nanomedicine delivery systems, and targeting moieties.

Drug resistance in cancer therapy: the Pandora's Box of cancer stem cells

Drug resistance is the main culprit of failure in cancer therapy that may lead to cancer relapse. This resistance mostly originates from rare, but impactful presence of cancer stem cells (CSCs). Ability to self-renewal and differentiation into heterogeneous cancer cells, and harboring morphologically and phenotypically distinct cells are prominent features of CSCs. Also, CSCs substantially contribute to metastatic dissemination. They possess several mechanisms that help them to survive even after exposure to chemotherapy drugs. Although chemotherapy is able to destroy the bulk of tumor cells, CSCs are left almost intact, and make tumor entity resistant to treatment. Eradication of a tumor mass needs complete removal of tumor cells as well as CSCs. Therefore, it is important to elucidate key features underlying drug resistance raised by CSCs in order to apply effective treatment strategies. However, the challenging point that threatens safety and specificity of chemotherapy is the common characteristics between CSCs and normal peers such as signaling pathways and markers. In the present study, we tried to present a comprehensive appraisal on CSCs, mechanisms of their drug resistance, and recent therapeutic methods targeting this type of noxious cells.

Juglone and KPT6566 Suppress the Tumorigenic Potential of CD44+CD133+ Tumor-Initiating Caco-2 Cells In Vitro and In Vivo

Pin1, a cis/trans isomerase of peptidyl-prolyl peptide bonds, plays a crucial role in the pathogenesis of many human cancers. Although chemical inhibitors of Pin1 show potent antitumor therapeutic properties against various cancers, their effect on colorectal cancer, especially colorectal tumor-initiating cells, remains unknown. Here, we investigated the effect of Juglone and KPT6566 on Caco-2 cells and tumor-initiating Caco-2 cells. Juglone and KPT6566 inhibited cell growth and colony formation, and induced apoptosis of Caco-2 cells. We also found that Juglone and KPT6566 downregulated expression of G1-phase-specific cyclins and cyclin-dependent kinases in a time-dependent manner, consistent with suppression of Caco-2 cell proliferation and colony formation. Although tumor-initiating cells are thought to be responsible for resistance to traditional chemotherapeutic drugs, our experiments demonstrate that Juglone or KPT6566 kill both tumor-initiating and non-tumor-initiating Caco-2 cells with equal or similar efficacy. Finally, when CD44⁺CD133⁺ tumor-initiating Caco-2 cells were injected into NSG mice, Juglone or KPT6566 led to a meaningful reduction in tumor volume and mass compared with tumors isolated from mice that received control treatment. Overall, these results indicate that chemical Pin1 inhibitors may be a valuable therapeutic option against colorectal tumor-initiating cancer cells.

Heme Oxygenase-1 Has a Greater Effect on Melanoma Stem Cell Properties Than the Expression of Melanoma-Initiating Cell Markers

Melanoma-initiating cells (MICs) contribute to the tumorigenicity and heterogeneity of melanoma. MICs are identified by surface and functional markers and have been shown to display cancer stem cell (CSC) properties. However, the existence of MICs that follow the hierarchical CSC model has been questioned by studies showing that single unselected melanoma cells are highly tumorigenic in xenotransplantation assays. Herein, we characterize cells expressing MIC markers (CD20, CD24, CD133, Sca-1, ABCB1, ABCB5, ALDH^high) in the B16-F10 murine melanoma cell line. We use flow cytometric phenotyping, single-cell sorting followed by in vitro clonogenic assays, and syngeneic in vivo serial transplantation assays to demonstrate that the expression of MIC markers does not select CSC-like cells in this cell line. Previously, our group showed that heme-degrading enzyme heme oxygenase-1 (HO-1) can be upregulated in melanoma and increase its aggressiveness. Here, we show that HO-1 activity is important for non-adherent growth of melanoma and HO-1 overexpression enhances the vasculogenic mimicry potential, which can be considered protumorigenic activity. However, HO-1 overexpression decreases clone formation in vitro and serial tumor initiation in vivo. Thus, HO-1 plays a dual role in melanoma, improving the progression of growing tumors but reducing the risk of melanoma initiation.

Identification, Culture and Targeting of Cancer Stem Cells

Chemoresistance, tumor progression, and metastasis are features that are frequently seen in cancer that have been associated with cancer stem cells (CSCs). These cells are a promising target in the future of cancer therapy but remain largely unknown. Deregulation of pathways that govern stemness in non-tumorigenic stem cells (SCs), such as Notch, Wnt, and Hedgehog pathways, has been described in CSC pathogenesis, but it is necessary to conduct further studies to discover potential new therapeutic targets. In addition, some markers for the identification and characterization of CSCs have been suggested, but the search for specific CSC markers in many cancer types is still under development. In addition, methods for CSC cultivation are also under development, with great heterogeneity existing in the protocols used. This review focuses on the most recent aspects of the identification, characterization, cultivation, and targeting of human CSCs, highlighting the advances achieved in the clinical implementation of therapies targeting CSCs and remarking those potential areas where more research is still required.

Metabolic Features of Tumor Dormancy: Possible Therapeutic Strategies

Simple Summary

Tumor recurrence still represents a major clinical challenge for cancer patients. Cancer cells may undergo a dormant state for long times before re-emerging. Both intracellular- and extracellular-driven pathways are involved in maintaining the dormant state and the subsequent awakening, with a mechanism that is still mostly unknown. In this scenario, cancer metabolism is emerging as a critical driver of tumor progression and dissemination and have gained increasing attention in cancer research. This review focuses on the metabolic adaptations characterizing the dormant phenotype and supporting tumor re-growth. Deciphering the metabolic adaptation sustaining tumor dormancy may pave the way for novel therapeutic approaches to prevent tumor recurrence based on combined metabolic drugs.

Abstract

Tumor relapse represents one of the main obstacles to cancer treatment. Many patients experience cancer relapse even decades from the primary tumor eradication, developing more aggressive and metastatic disease. This phenomenon is associated with the emergence of dormant cancer cells, characterized by cell cycle arrest and largely insensitive to conventional anti-cancer therapies. These rare and elusive cells may regain proliferative abilities upon the induction of cell-intrinsic and extrinsic factors, thus fueling tumor re-growth and metastasis formation. The molecular mechanisms underlying the maintenance of resistant dormant cells and their awakening are intriguing but, currently, still largely unknown. However, increasing evidence recently underlined a strong dependency of cell cycle progression to metabolic adaptations of cancer cells. Even if dormant cells are frequently characterized by a general metabolic slowdown and an increased ability to cope with oxidative stress, different factors, such as extracellular matrix composition, stromal cells influence, and nutrient availability, may dictate specific changes in dormant cells, finally resulting in tumor relapse. The main topic of this review is deciphering the role of the metabolic pathways involved in tumor cells dormancy to provide new strategies for selectively targeting these cells to prevent fatal recurrence and maximize therapeutic benefit.

Reduction in O-glycome induces differentially glycosylated CD44 to promote stemness and metastasis in pancreatic cancer

Aberrant protein glycosylation has been shown to have a significant contribution in aggressive cancer, including pancreatic cancer (PC). Emerging evidence has implicated the involvement of cancer stem cells (CSCs) in PC aggressiveness; however, the contribution of glycosylation on self-renewal properties and maintenance of CSC is understudied. Here, using several in vitro and in vivo models lacking C1GALT1 expression, we identified the role of aberrant O-glycosylation in stemness properties and aggressive PC metastasis. A loss in C1GALT1 was found to result in the truncation of O-glycosylation on several glycoproteins with an enrichment of Tn carbohydrate antigen. Mapping of Tn-bearing glycoproteins in C1GALT1 KO cells identified significant Tn enrichment on CSC glycoprotein CD44. Notably, a loss of C1GALT1 in PC cells was found to enhance CSC features (side population-SP, ALDH1+, and tumorspheres) and self-renewal markers NANOG, SOX9, and KLF4. Furthermore, a loss of CD44 in existing C1GALT1 KO cells decreased NANOG expression and CSC features. We determined that O-glycosylation of CD44 activates ERK/NF-kB signaling, which results in increased NANOG expression in PC cells that facilitated the alteration of CSC features, suggesting that NANOG is essential for PC stemness. Finally, we identified that loss of C1GALT1 expression was found to augment tumorigenic and metastatic potential, while an additional loss of CD44 in these cells reversed the effects. Overall, our results identified that truncation of O-glycans on CD44 increases NANOG activation that mediates increased CSC activation.

Role of T-box genes in cancer, epithelial-mesenchymal transition, and cancer stem cells

Sharing a common DNA binding motif called T-box, transcription factor T-box gene family controls embryonic development and is also involved in cancer progression and metastasis. Cancer metastasis shows therapy resistance and involves complex processes. Among them, epithelial-mesenchymal transition (EMT) triggers cancer cell invasiveness and the acquisition of stemness of cancer cells, called cancer stem cells (CSCs). CSCs are a small fraction of tumor bulk and are capable of self-renewal and tumorsphere formation. Recent progress has highlighted the critical roles of T-box genes in cancer progression, EMT, and CSC function, and such regulatory functions of T-box genes have emerged as potential therapeutic candidates for cancer. Herein we summarize the current understanding of the regulatory mechanisms of T-box genes in cancer, EMT, and CSCs, and discuss the implications of targeting T-box genes as anticancer therapeutics.

Repurposing of Anticancer Stem Cell Drugs in Brain Tumors

Brain tumors in adults may be infrequent when compared with other cancer etiologies, but they remain one of the deadliest with bleak survival rates. Current treatment modalities encompass surgical resection, chemotherapy, and radiotherapy. However, increasing resistance rates are being witnessed, and this has been attributed, in part, to cancer stem cells (CSCs). CSCs are a subpopulation of cancer cells that reside within the tumor bulk and have the capacity for self-renewal and can differentiate and proliferate into multiple cell lineages. Studying those CSCs enables an increasing understanding of carcinogenesis, and targeting CSCs may overcome existing treatment resistance. One approach to weaponize new drugs is to target these CSCs through drug repurposing which entails using drugs, which are Food and Drug Administration-approved and safe for one defined disease, for a new indication. This approach serves to save both time and money that would otherwise be spent in designing a totally new therapy. In this review, we will illustrate drug repurposing strategies that have been used in brain tumors and then further elaborate on how these approaches, specifically those that target the resident CSCs, can help take the field of drug repurposing to a new level.

Long Non-Coding RNAs (lncRNAs) in Response and Resistance to Cancer Immunosurveillance and Immunotherapy

Long non-coding RNAs (lncRNAs) are critical regulatory elements in cellular functions in states of both normalcy and disease, including cancer. LncRNAs can influence not only tumorigenesis but also cancer features such as metastasis, angiogenesis and resistance to chemo-and immune-mediated apoptotic signals. Several lncRNAs have been demonstrated to control directly or indirectly the number, type and activities of distinct immune cell populations of adaptive and innate immunities within and without the tumor microenvironment. The disruption of lncRNA expression in both cancer and immune cells may reflect alterations in tumor responses to cancer immunosurveillance and immunotherapy, thus providing new insights into lncRNA biomarker-based prognostic and therapeutic cancer assessment. Here we present an overview on lncRNAs’ functions and underlying molecular mechanisms related to cancer immunity and conventional immunotherapy, with the expectation that any elucidations may lead to a better understanding and management of cancer immune escape and response to current and future immunotherapeutics.

Cancer Cell Fusion and Post-Hybrid Selection Process (PHSP)

Fusion of cancer cells either with other cancer cells (homotypic fusion) in local vicinity of the tumor tissue or with other cell types (e.g., macrophages, cancer-associated fibroblasts (CAFs), mesenchymal stromal-/stem-like cells (MSC)) (heterotypic fusion) represents a rare event. Accordingly, the clinical relevance of cancer-cell fusion events appears questionable. However, enhanced tumor growth and/or development of certain metastases can originate from cancer-cell fusion. Formation of hybrid cells after cancer-cell fusion requires a post-hybrid selection process (PHSP) to cope with genomic instability of the parental nuclei and reorganize survival and metabolic functionality. The present review dissects mechanisms that contribute to a PHSP and resulting functional alterations of the cancer hybrids. Based upon new properties of cancer hybrid cells, the arising clinical consequences of the subsequent tumor heterogeneity after cancer-cell fusion represent a major therapeutic challenge. However, cellular partners during cancer-cell fusion such as MSC within the tumor microenvironment or MSC-derived exosomes may provide a suitable vehicle to specifically address and deliver anti-tumor cargo to cancer cells.

Role of the bone marrow microenvironment in drug resistance of hematological malignances

The unique features of the tumor microenvironment (TME) govern the biological properties of many cancers, including hematological malignancies. TME factors can trigger invasion, and protect against drug cytotoxicity by inhibiting apoptosis and activating specific signaling pathways (e.g. NF-ΚB). TME remodeling is facilitated due to the high self-renewal ability of the bone marrow. Progressing tumor cells can alter some extracellular matrix (ECM) components which act as a barrier to drug penetration in the TME. The initial progression of the cell cycle is controlled by the MAPK pathway (Raf/MEK/ERK) and Hippo pathway, while the final phase is regulated by the PI3K/Akt /mTOR and WNT pathways. In this review we summarize the main signaling pathways involved in drug resistance (DR) and some mechanisms by which DR can occur in the bone marrow. The relationship between autophagy, endoplasmic reticulum stress, and cellular signaling pathways in DR and apoptosis are covered in relation to the TME.

Translocation of intracellular CD24 constitutes a triggering event for drug resistance in breast cancer

The capacity of tumor cells to shift dynamically between different states could be responsible for chemoresistance and has been commonly linked to the acquisition of stem cell properties. Here, we have evaluated the phenotype switching associated with drug resistance in breast cancer cell lines and cell lineage obtained from Brazilian patients. We have highlighted the role of the cancer stem cell marker CD24 in the dynamics of cell plasticity and the acquirement of drug resistance. We showed that the translocation of CD24 from cytosol to cell membrane is a triggering event for the phenotype change of breast tumor cells exposed to drug stress. Here, we provide evidence that the phenotype switching is due to the presence of a cytosolic pool of CD24. Importantly, the cellular localization of CD24 was correlated with the changes in the dynamics of p38 MAPK activation. A strong and continuous phosphorylation of the p38 MAPK led to the overexpression of Bcl-2 after treatment in persistent cells presenting high density of CD24 on cell membrane. This phenotype enabled the cells to enter in slow-down of cell cycle, after which several weeks later, the dormant cells proliferated again. Importantly, the use of a p38 activity inhibitor sensitized cells to drug treatment and avoided chemoresistance.

Multiple strategies with the synergistic approach for addressing colorectal cancer

Cancer treatment is improving widely over time, but finding a proper defender to beat them seems like a distant dream. The quest for identification and discovery of drugs with an effective action is still a vital work. The role of a membrane protein called P-glycoprotein, which functions as garbage chute that efflux the waste, xenobiotics, and toxins out of the cancer cells acts as a major reason behind the therapeutic failure of most chemotherapeutic drugs. In this review, we mainly focused on a multiple strategies by employing 5-Fluorouracil, curcumin, and lipids in Nano formulation for the possible treatment of colorectal cancer and its metastasis. Eventually, multidrug resistance and angiogenesis can be altered and it would be helpful in colorectal cancer targeting.We have depicted the possible way for the depletion of colorectal cancer cells without disturbing the normal cells. The concept of focusing on multiple pathways for marking the colorectal cancer cells could help in activating one among the pathways if the other one fails. The activity of the 5-Fluorouracil can be enhanced with the help of curcumin which acts as a chemosensitizer, chemotherapeutic agent, and even for altering the resistance. As we eat to survive, so do the cancer cells. The cancer cells utilize the energy source to stay alive and survive. Fatty acids can be used as the energy source and this concept can be employed for targeting the colorectal cancer cells and also for altering the resistant part.

Conjugation of Natural Triterpenic Acids with Delocalized Lipophilic Cations: Selective Targeting Cancer Cell Mitochondria

Currently, a new line of research on mitochondria-targeted anticancer drugs is actively developing in the field of biomedicine and medicinal chemistry. The distinguishing features of this universal target for anticancer agents include presence of mitochondria in the overwhelming majority, if not all types of transformed cells, crucial importance of these cytoplasmic organelles in energy production, regulation of cell death pathways, as well as generation of reactive oxygen species and maintenance of calcium homeostasis. Hence, mitochondriotropic anticancer mitocan agents, acting through mitochondrial destabilization, have good prospects in cancer therapy. Available natural pentacyclic triterpenoids are considered promising scaffolds for development of new mitochondria-targeted anticancer agents. These secondary metabolites affect the mitochondria of tumor cells and initiate formation of reactive oxygen species. The present paper focuses on the latest research outcomes of synthesis and study of cytotoxic activity of conjugates of pentacyclic triterpenoids with some mitochondria-targeted cationic lipophilic molecules and highlights the advantages of applying them as novel mitocan agents compared to their prototype natural triterpenic acids.

Differential Prognosis and Response of Denovo vs. Secondary Muscle-Invasive Bladder Cancer: An Updated Systematic Review and Meta-Analysis

Simple Summary

Bladder cancer is one of the leading causes of death worldwide. About 75% of patients initially present with non-muscle-invasive disease, while the rest presents with primary muscle-invasive disease. Up to a third of non-muscle-invasive bladder cancers progresses into secondary muscle-invasive bladder cancer. Little is known about clinical outcomes after upfront neoadjuvant cisplatin-based chemotherapy and subsequent radical cystectomy for secondary muscle-invasive bladder cancer compared to primary muscle-invasive bladder cancer. Here, we systematically reviewed the current literature evaluate oncological outcomes between primary and secondary muscle-invasive bladder cancer.

Abstract

To evaluate oncological outcomes of primary versus secondary muscle-invasive bladder cancer treated with radical cystectomy. Medline, Embase, Scopus and Cochrane Library were searched for eligible studies. Hazard ratios for overall survival (OS), cancer specific survival (CSS) and progression free survival (PFS) were calculated using survival data extracted from Kaplan-Meier curves. A total of 16 studies with 5270 patients were included. Pooled analysis showed similar 5-year and 10-year OS (HR 1, p = 0.96 and HR 1, p = 0.14) and CSS (HR 1.02, p = 0.85 and HR 0.99, p = 0.93) between primMIBC and secMIBC. Subgroup analyses according to starting point of follow-up and second-look transurethral resection revealed similar results. Subgroup analyses of studies in which neoadjuvant chemotherapy was administered demonstrated significantly worse 5-year CSS (HR 1.5, p = 0.04) but not 10-year CSS (HR 1.36, p = 0.13) in patients with secMIBC. Patients with secMIBC had significantly worse PFS at 5-year (HR 1.41, p = 0.002) but not at 10-year follow-up (HR 1.25, p = 0.34). This review found comparable oncologic outcomes between primMIBC and secMIBC patients treated with RC regarding OS and CSS. Subgroup analysis showed worse 5-year CSS but not 10-year CSS for neoadjuvant chemotherapy in the secMIBC group. Prospective clinical trials incorporating molecular markers, that allow precise risk stratification of secMIBC and further research uncovering underlying molecular and clinical drivers of the heterogeneous group of secMIBC is needed.

STAT3-induced HLA-F-AS1 promotes cell proliferation and stemness characteristics in triple negative breast cancer cells by upregulating TRABD

Breast cancer (BC) is one of the most common malignances and is a leading cause of cancer-related deaths in women globally. Triple negative breast cancer (TNBC) is a common subtype of BC. Emerging evidence has indicated the crucial roles of long noncoding RNAs (lncRNAs) in the tumorigenesis of TNBC. Our aim was to explore the role and regulatory mechanism of lncRNA HLA-F antisense RNA 1 (HLA-F-AS1) in TNBC cells. Cell counting kit-8 (CCK-8) assay, colony formation assay, flow cytometry analysis and western blot analysis were used to measure HLA-F-AS1-mediated cellular behaviors in TNBC. Xenograft tumor assay was applied to assess biological function of HLA-F-AS1 in vivo. Luciferase reporter assay and RNA pull down assay were used to verify the binding ability between molecules. Our findings demonstrated that HLA-F-AS1 expression was significantly upregulated in TNBC tissues and cells, and high level of HLA-F-AS1 indicated the poor prognosis of patients with TNBC. HLA-F-AS1 promoted TNBC progression by facilitating cell proliferation and stemness maintenance and inhibiting cell cycle arrest at G0/G1 stage and apoptosis in vitro as well as inducing tumor growth in vivo. HLA-F-AS1. In addition, signal transducer and activator of transcription 3 (STAT3) transcriptionally induced HLA-F-AS1 upregulation in TNBC cells via interacting with HLA-F-AS1 promoter. Moreover, HLA-F-AS1 acted as the molecular sponge of microRNA 541-3p (miR-541-3p) to elevate TRABD (TraB domain containing) expression in TNBC cells. Rescue experiments confirmed that the decrease of cell proliferation and stemness characteristics under silenced HLA-F-AS1 was rescued by TRABD overexpression in TNBC cells. In conclusion, STAT3-induced HLA-F-AS1 facilitates cell proliferation and stemness characteristics in TNBC by miR-541-3p-dependent upregulation of TRABD, which might provide a potential novel direction for the treatment of TNBC.

CD44+ cells determine fenofibrate-induced microevolution of drug-resistance in prostate cancer cell populations

Combinations of metabolic blockers (incl. fenofibrate) with chemotherapeutic drugs interfere with the drug-resistance of prostate cancer cells. However, their effect on cancer stem cells-dependent microevolution of prostate cancer malignancy remains unaddressed. Here, we hypothesize that the combined docetaxel/fenofibrate treatment prompts the selective expansion of cancer stem cells that affects the microevolution of their progenies. Accordingly, we adapted a combined in vitro/in vivo approach to identify biological and therapeutic consequences of this process. Minute subpopulations of docetaxel-resistant CD133high and/or CD44high cancer stem cell-like (SCL) cells were found in prostate cancer DU145 and PC3 cell populations. When pretreated with docetaxel, they readily differentiated into docetaxel-resistant CD44negative "bulk" cells, thus accounting for the microevolution of drug-resistant cell lineages. Combined docetaxel/fenofibrate treatment induced the generation of poly(morpho)nuclear giant cells and drug-resistant CD44high SCL cells. However, the CD44negative offspring of docetaxel- and docetaxel/fenofibrate-treated SCLs remained relatively sensitive to the combined treatment, while retaining enhanced resistance to docetaxel. Long-term propagation of drug-resistant SCL-derived lineages in the absence of docetaxel/fenofibrate resulted in their reverse microevolution toward the drug-sensitivity and invasive phenotype. Consequently, prostate tumors were able to recover from the combined docetaxel/fenofibrate stress after the initial arrest of their expansion in vivo. In conclusion, we have confirmed the potential of fenofibrate for the metronomic treatment of drug-resistant prostate tumors. However, docetaxel/fenofibrate-induced selective expansion of hyper-resistant CD44high SCL prostate cells and their "bulk" progenies prompts the microevolution of prostate tumor drug-resistance. This process can limit the implementation of metabolic chemotherapy in prostate cancer treatment.

Counteracting Chemoresistance with Metformin in Breast Cancers: Targeting Cancer Stem Cells

Despite the leaps and bounds in achieving success in the management and treatment of breast cancers through surgery, chemotherapy, and radiotherapy, breast cancer remains the most frequently occurring cancer in women and the most common cause of cancer-related deaths among women. Systemic therapeutic approaches, such as chemotherapy, although beneficial in treating and curing breast cancer subjects with localized breast tumors, tend to fail in metastatic cases of the disease due to (a) an acquired resistance to the chemotherapeutic drug and (b) the development of intrinsic resistance to therapy. The existence of cancer stem cells (CSCs) plays a crucial role in both acquired and intrinsic chemoresistance. CSCs are less abundant than terminally differentiated cancer cells and confer chemoresistance through a unique altered metabolism and capability to evade the immune response system. Furthermore, CSCs possess active DNA repair systems, transporters that support multidrug resistance (MDR), advanced detoxification processes, and the ability to self-renew and differentiate into tumor progenitor cells, thereby supporting cancer invasion, metastasis, and recurrence/relapse. Hence, current research is focusing on targeting CSCs to overcome resistance and improve the efficacy of the treatment and management of breast cancer. Studies revealed that metformin (1, 1-dimethylbiguanide), a widely used anti-hyperglycemic agent, sensitizes tumor response to various chemotherapeutic drugs. Metformin selectively targets CSCs and improves the hypoxic microenvironment, suppresses the tumor metastasis and inflammation, as well as regulates the metabolic programming, induces apoptosis, and reverses epithelial-mesenchymal transition and MDR. Here, we discuss cancer (breast cancer) and chemoresistance, the molecular mechanisms of chemoresistance in breast cancers, and metformin as a chemo-sensitizing/re-sensitizing agent, with a particular focus on breast CSCs as a critical contributing factor to acquired and intrinsic chemoresistance. The review outlines the prospects and directions for a better understanding and re-purposing of metformin as an anti-cancer/chemo-sensitizing drug in the treatment of breast cancer. It intends to provide a rationale for the use of metformin as a combinatory therapy in a clinical setting.

The cellular origins of cancer with particular reference to the gastrointestinal tract

Stem cells or their closely related committed progenitor cells are the likely founder cells of most neoplasms. In the continually renewing and hierarchically organized epithelia of the oesophagus, stomach and intestine, homeostatic stem cells are located at the beginning of the cell flux, in the basal layer of the oesophagus, the isthmic region of gastric oxyntic glands and at the bottom of gastric pyloric-antral glands and colonic crypts. The introduction of mutant oncogenes such as Kras^G12D or loss of Tp53 or Apc to specific cell types expressing the likes of Lgr5 and Mist1 can be readily accomplished in genetically engineered mouse models to initiate tumorigenesis. Other origins of cancer are discussed including 'reserve' stem cells that may be activated by damage or through disruption of morphogen gradients along the crypt axis. In the liver and pancreas, with little cell turnover and no obvious stem cell markers, the importance of regenerative hyperplasia associated with chronic inflammation to tumour initiation is vividly apparent, though inflammatory conditions in the renewing populations are also permissive for tumour induction. In the liver, hepatocytes, biliary epithelial cells and hepatic progenitor cells are embryologically related, and all can give rise to hepatocellular carcinoma and cholangiocarcinoma. In the exocrine pancreas, both acinar and ductal cells can give rise to pancreatic ductal adenocarcinoma (PDAC), although the preceding preneoplastic states are quite different: acinar-ductal metaplasia gives rise to pancreatic intraepithelial neoplasia culminating in PDAC, while ducts give rise to PDAC via. mucinous cell metaplasia that may have a polyclonal origin.

Mechanisms of cancer stem cell therapy

Cancer stem cells (CSCs) are responsible for carcinogenesis and tumorigenesis and are involved in drug and radiation resistance, metastasis, tumor relapse and initiation. Remarkably, they have other abilities such as inheritance of self-renewal and de-differentiation. Hence, targeting CSCs is considered a potential anti-cancer therapeutic strategy. Recent advances in the identification of biomarkers to recognize CSCs and the development of new techniques to evaluate tumorigenic and carcinogenic roles of CSCs are instrumental to this approach. Elucidation of signaling pathways that regulate CSCs colony progression and drug resistance are critical in establishing effective targeted therapies. CSCs play a central key role in immunomodulation, immune evasion and effector immunity, which alters immune system balancing. These include mTOR, SHH, NOTCH and Wnt/β-catering in cancer progression. In this review article, we discuss the importance of these CSCs pathways in cancer therapy.

Cancer Stem Cells in Soft-Tissue Sarcomas

Soft tissue sarcomas (STS) are a rare group of mesenchymal solid tumors with heterogeneous genetic profiles and clinical features. Systemic chemotherapy is the backbone treatment for advanced STS; however, STS frequently acquire resistance to standard therapies, which highlights the need to improve treatments and identify novel therapeutic targets. Increases in the knowledge of the molecular pathways that drive sarcomas have brought to light different molecular alterations that cause tumor initiation and progression. These findings have triggered a breakthrough of targeted therapies that are being assessed in clinical trials. Cancer stem cells (CSCs) exhibit mesenchymal stem cell (MSC) features and represent a subpopulation of tumor cells that play an important role in tumor progression, chemotherapy resistance, recurrence and metastasis. In fact, CSCs phenotypes have been identified in sarcomas, allied to drug resistance and tumorigenesis. Herein, we will review the published evidence of CSCs in STS, discussing the molecular characteristic of CSCs, the commonly used isolation techniques and the new possibilities of targeting CSCs as a way to improve STS treatment and consequently patient outcome.

Analysis of influencing factors of no/low response to preoperative concurrent chemoradiotherapy in locally advanced rectal cancer

The aim of this study is to investigate the influencing factors associated with no/low response to preoperative concurrent chemoradiotherapy (CCRT) for locally advanced rectal cancer (LARC) patients. A total of 79 patients were included in this prospective study. Fifteen factors that might affect the resistance to CCRT were included in this logistic regression analysis, these factors include the general clinical data of patients, the expression status of tumor stem cell marker CD44v6 and the volumetric imaging parameters of primary tumor lesions. We found that the no/low response status to preoperative CCRT was positively correlated with the real tumor volume (RTV), the total surface area of tumor (TSA), and CD44v6 expression, whereas negatively correlated with the tumor compactness (TC). According to the results of logistic regression analysis, two formulas that could predict whether or not no/low response to preoperative CCRT were established. The Area Under Curve (AUC) of the two formulas and those significant measurement data (RTV, TC, TSA) were 0.900, 0.858, 0.771, 0.754, 0.859, the sensitivity were 95.8%, 79.17%, 62.50%, 95.83%, 62.5%, the specificity were 70.9%, 74.55%, 83.64%,47.27%, 96.36%, the positive predictive values were 58.96%, 57.58%, 62.51%,44.23%, 88.23%, the negative predictive values were 97.48%, 89.13%, 83.64%, 96.29%, and 85.48%, respectively.

Different Camptothecin Sensitivities in Subpopulations of Colon Cancer Cells Correlate with Expression of Different Phospho-Isoforms of Topoisomerase I with Different Activities

The heterogeneity of tumor cells and the potential existence of rare cells with reduced chemotherapeutic response is expected to play a pivotal role in the development of drug resistant cancers. Herein, we utilized the colon cancer cell lines, Caco2 and DLD1, to investigate heterogeneity of topoisomerase 1 (TOP1) activity in different cell subpopulations, and the consequences for the chemotherapeutic response towards the TOP1 targeting drug, camptothecin. The cell lines consisted of two subpopulations: one (the stem-cell-like cells) divided asymmetrically, was camptothecin resistant, had a differently phosphorylated TOP1 and a lower Casein Kinase II (CKII) activity than the camptothecin sensitive non-stem-cell-like cells. The tumor suppressor p14ARF had a different effect in the two cell subpopulations. In the stem-cell-like cells, p14ARF suppressed TOP1 activity and downregulation of this factor increased the sensitivity towards camptothecin. It had the opposite effect in non-stem-cell-like cells. Since it is only the stem-cell-like cells that have tumorigenic activity our results point towards new considerations for future cancer therapy. Moreover, the data underscore the importance of considering cell-to-cell variations in the analysis of molecular processes in cell lines.

Senescence-Associated Pro-inflammatory Cytokines and Tumor Cell Plasticity

The well-recognized cell phenotypic heterogeneity in tumors is a great challenge for cancer treatment. Dynamic interconversion and movement within a spectrum of different cell phenotypes (cellular plasticity) with the acquisition of specific cell functions is a fascinating biological puzzle, that represent an additional difficulty for cancer treatment and novel therapies development. The understanding of the molecular mechanisms responsible for moving or stabilizing tumor cells within this spectrum of variable states constitutes a valuable tool to overcome these challenges. In particular, cell transitions between epithelial and mesenchymal phenotypes (EMT-MET) and de-and trans-differentiation processes are relevant, since it has been shown that they confer invasiveness, drug resistance, and metastatic ability, due to the simultaneous acquisition of stem-like cell properties. Multiple drivers participate in these cell conversions events. In particular, cellular senescence and senescence-associated soluble factors have been shown to unveil stem-like cell properties and cell plasticity. By modulating gradually the composition of their secretome and the time of exposure, senescent cells may have differential effect not only on tumor cells but also on surrounding cells. Intriguingly, tumor cells that scape from senescence acquire stem-like cell properties and aggressiveness. The reinforcement of senescence and inflammation by soluble factors and the participation of immune cells may provide a dynamic milieu having varied effects on cell transitions, reprogramming, plasticity, stemness and therefore heterogeneity. This will confer different epithelial/mesenchymal traits (hybrid phenotype) and stem-like cell properties, combinations of which, in a particular cell context, could be responsible for different cellular functions during cancer progression (survival, migration, invasion, colonization or proliferation). Additionally, cooperative behavior between cell subpopulations with different phenotypes/stemness functions could also modulate their cellular plasticity. Here, we will discuss the role of senescence and senescence-associated pro-inflammatory cytokines on the induction of cellular plasticity, their effect role in establishing particular states within this spectrum of cell phenotypes and how this is accompanied by stem-like cell properties that, as the epithelial transitions, may also have a continuum of characteristics providing tumor cells with functional adaptability specifically useful in the different stages of carcinogenesis.

Calcium Channels as Novel Therapeutic Targets for Ovarian Cancer Stem Cells

Drug resistance in epithelial ovarian cancer (EOC) is reportedly attributed to the existence of cancer stem cells (CSC), because in most cancers, CSCs still remain after chemotherapy. To overcome this limitation, novel therapeutic strategies are required to prevent cancer recurrence and chemotherapy-resistant cancers by targeting cancer stem cells (CSCs). We screened an FDA-approved compound library and found four voltage-gated calcium channel blockers (manidipine, lacidipine, benidipine, and lomerizine) that target ovarian CSCs. Four calcium channel blockers (CCBs) decreased sphere formation, viability, and proliferation, and induced apoptosis in ovarian CSCs. CCBs destroyed stemness and inhibited the AKT and ERK signaling pathway in ovarian CSCs. Among calcium channel subunit genes, three L- and T-type calcium channel genes were overexpressed in ovarian CSCs, and downregulation of calcium channel genes reduced the stem-cell-like properties of ovarian CSCs. Expressions of these three genes are negatively correlated with the survival rate of patient groups. In combination therapy with cisplatin, synergistic effect was shown in inhibiting the viability and proliferation of ovarian CSCs. Moreover, combinatorial usage of manidipine and paclitaxel showed enhanced effect in ovarian CSCs xenograft mouse models. Our results suggested that four CCBs may be potential therapeutic drugs for preventing ovarian cancer recurrence.

Association of SOX2, OCT4 and WNT5A Expression in Oral Epithelial Dysplasia and Oral Squamous Cell Carcinoma: An Immunohistochemical Study

The cancer stem cells deliver uncontrolled proliferative capacity within the tumor imparting to increasing size while epithelial mesenchymal transition adds to the invasive potential. Studies using specific markers elucidating the role of these phenomena may bring advancement in the targeted therapy of tumor. SOX2 and OCT4 are two among few stem cell markers indicative of proliferative potential and WNT5A is an epithelial mesenchymal transition marker indicative of invasive potential. We aimed to determine the association between expression of SOX2, OCT4 and WNT5A in oral epithelial dysplasia, oral squamous cell carcinoma and normal oral mucosa. 20 cases of oral squamous cell carcinoma, 20 cases of oral epithelial dysplasia (leukoplakia with dysplasia) and 25 normal oral mucosa tissues specimens were immunohistochemically stained to assess SOX2, OCT4 and WNT5A expression. SOX2 expression was higher in oral squamous cell carcinoma than in oral epithelial dysplasia and very low in normal oral mucosa. OCT4 was very low in oral squamous cell carcinoma and oral epithelial dysplasia when compared to SOX2, while negative in normal tissues. Co-expression of SOX2 and OCT4 showed statistically non-significant difference for tumor proliferation. WNT5A expression was found to be increasing from normal oral mucosa to oral epithelial dysplasia and oral squamous cell carcinoma. In conformity with present study, SOX2 itself can act as a potential marker for proliferation in tumor cells while OCT4 has non-significant role in regulation of tumor behavior in oral squamous cell carcinoma as well as in oral epithelial dysplasia. WNT5A can be a putative marker in studying invasive potential of oral squamous cell carcinoma.

Lichen Secondary Metabolite Physciosporin Decreases the Stemness Potential of Colorectal Cancer Cells

Secondary metabolites of lichens are promising bioresources for candidate anti-cancer drugs. Accordingly, several approaches have been proposed for screening these molecules for novel anti-cancer lead compounds. In this study, we found that a non-toxic concentration of physciosporin, a compound isolated from Pseudocyphellaria granulata, significantly decreased colony formation on soft agar and spheroid formation by CSC221 cancer stem-like cells. Physciosporin also decreased spheroid formation in other colorectal cancer cell lines, including DLD1, Caco2, and HT29. Aldehyde dehydrogenase-1 (ALDH1), the most important cancer stem marker, was sharply downregulated at both the protein and mRNA level following treatment with physciosporin. Physciosporin also decreased the transcriptional activity of the glioma-associated oncogene homolog zinc finger protein (Gli), as well as the Hes1 and CSL promoters, in reporter assays. Moreover, the drug significantly suppressed spheroid formation in CSC221 cells overexpressing Gli1/2 or EN1 (an S2-cleaved but membrane-tethered form of human Notch1) but did not suppress spheroid formation in cells overexpressing both Gli1/2 and ∆EN1, suggesting that physciosporin suppresses colon cancer cell stemness through the Sonic hedgehog and Notch signaling pathways. Together, these results demonstrate for the first time that physciosporin is a potent inhibitor of colorectal cancer cell stemness.

Therapeutic Strategies Targeting Cancer Stem Cells and Their Microenvironment

Cancer stem cells (CSCs) have been demonstrated in a variety of tumors and are thought to act as a clonogenic core for the genesis of new tumor growth. This small subpopulation of cancer cells has been proposed to help drive tumorigenesis, metastasis, recurrence and conventional therapy resistance. CSCs show self-renewal and flexible clonogenic properties and help define specific tumor microenvironments (TME). The interaction between CSCs and TME is thought to function as a dynamic support system that fosters the generation and maintenance of CSCs. Investigation of the interaction between CSCs and the TME is shedding light on the biologic mechanisms underlying the process of tumor malignancy, metastasis, and therapy resistance. We summarize recent advances in CSC biology and their environment, and discuss the challenges and future strategies for targeting this biology as a new therapeutic approach.