Overcoming Multidrug Resistance in Cancer Stem Cells. Biomed Res Int. 2015;2015:635745. [PMID: 26649310 PMCID: PMC4663294 DOI: 10.1155/2015/635745]

Dissecting the mechanism of temozolomide resistance and its association with the regulatory roles of intracellular reactive oxygen species in glioblastoma

Glioblastoma is the most common primary malignant brain tumor that is usually considered fatal even with treatment. This is often a result for tumor to develop resistance. Regarding the standard chemotherapy, the alkylating agent temozolomide is effective in disease control but the recurrence will still occur eventually. The mechanism of the resistance is various, and differs in terms of innate or acquired. To date, aberrations in O⁶-methylguanine-DNA methyltransferase are the clear factor that determines drug susceptibility. Alterations of the other DNA damage repair genes such as DNA mismatch repair genes are also known to affect the drug effect. Together these genes have roles in the innate resistance, but are not sufficient for explaining the mechanism leading to acquired resistance. Recent identification of specific cellular subsets with features of stem-like cells may have role in this process. The glioma stem-like cells are known for its superior ability in withstanding the drug-induced cytotoxicity, and giving the chance to repopulate the tumor. The mechanism is complicated to administrate cellular protection, such as the enhancing ability against reactive oxygen species and altering energy metabolism, the important steps to survive. In this review, we discuss the possible mechanism for these specific cellular subsets to evade cancer treatment, and the possible impact to the following treatment courses. In addition, we also discuss the possibility that can overcome this obstacle.

Thymoquinone inhibited vasculogenic capacity and promoted mesenchymal-epithelial transition of human breast cancer stem cells

Background

Vasculogenic mimicry (VM) is characterized by the formation of tubular structure inside the tumor stroma. It has been shown that a small fraction of cancer cells, namely cancer stem cells (CSCs), could stimulate the development of vascular units in the tumor niche, leading to enhanced metastasis to the remote sites. This study aimed to study the inhibitory effect of phytocompound, Thymoquinone (TQ), on human breast MDA-MB-231 cell line via monitoring Wnt/PI3K signaling pathway.

Methods

MDA-MB-231 CSCs were incubated with different concentrations of TQ for 48 h. The viability of CSCs was determined using the MTT assay. The combination of TQ and PI3K and Wnt3a inhibitors was examined in CSCs. By using the Matrigel assay, we measured the tubulogenesis capacity. The percent of CD24⁻ CSCs and Rhodamine 123 efflux capacity was studied using flow cytometry analysis. Protein levels of Akt, p-Akt, Wnt3a, vascular endothelial-cadherin (VE-cadherin), and matrix metalloproteinases-2 and -9 (MMP-2 and -9) were detected by western blotting.

Results

TQ decreased the viability of CSCs in a dose-dependent manner. The combination of TQ with PI3K and Wnt3a inhibitors reduced significantly the survival rate compared to the control group (p < 0.05). TQ could blunt the stimulatory effect of vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), fibroblast growth factor (FGF) on CSCs (p < 0.05). The vasculogenic capacity of CSCs was reduced after being-exposed to TQ (p < 0.05). Western blotting revealed the decrease of CSCs metastasis by suppressing MMP-2 and -9. The protein level of VE-cadherin was also diminished in TQ-treated CSCs as compared to the control cell (p < 0.05), indicating inhibition of mesenchymal-endothelial transition (MendT). TQ could suppress Wnt3a and PI3K, which coincided with the reduction of the p-Akt/Akt ratio. TQ had the potential to decrease the number of CD24⁻ CSCs and Rhodamine 123 efflux capacity after 48 h.

Conclusion

TQ could alter the vasculogenic capacity and mesenchymal-epithelial transition of human breast CSCs in vitro. Thus TQ together with anti-angiogenic therapies may be a novel therapeutic agent in the suppression of VM in breast cancer.

Simultaneously target of normal and stem cells-like gastric cancer cells via cisplatin and anti-CD133 CAR-T combination therapy

CD133 + cancer stem cells mediate chemoresistance in multiple aggressive cancers, and anti-CD133 chimeric antigen receptor T (CAR-T) cells are designed to selectively target cisplatin-resistant gastric cancer stem cells in this investigation. The relative CD133 expression was detected in gastric cancer patients before and after cisplatin treatment. Anti-CD133 CAR-T cells were incubated with cisplatin-exposed CD133⁺ BGC-823 cells to evaluate the killing efficacy. At the same time, the canonical T cell activation markers were assayed by fluorescence-activated cell sorting, and the functional cytokine profile was detected with enzyme-linked immunosorbent assays. In addition to the percentage of CD133 positive stem cell-like cells, the volume and weight of subcutaneous tumors in BGC-823, KATO III and MKN-28 xenograft models were measured to evaluate the anti-tumor activity of cisplatin and anti-CD133 CAR-T combination strategy. After cisplatin treatment, both human samples and BGC-823 cells showed up-regulated CD133 expression. Anti-CD133 CAR-T cells exhibited pronounced killing efficiency against cisplatin-exposed CD133⁺ BGC-823 cells with up-regulated activation markers and cytotoxicity cytokine production. Moreover, cisplatin and anti-CD133 CAR-T combination treatment inhibited tumor progression in three different xenograft models with diminished CD133 positive stem cell-like cell infiltration. These results indicate that cisplatin and anti-CD133 CAR-T combination strategy can simultaneously target normal and stem cell-like gastric cancer cells to improve the treatment outcome.

HDAC11 Regulates Glycolysis through the LKB1/AMPK Signaling Pathway to Maintain Hepatocellular Carcinoma Stemness

Hepatocellular carcinoma (HCC) contains a subset of cancer stem cells (CSC) that cause tumor recurrence, metastasis, and chemical resistance. Histone deacetylase 11 (HDAC11) mediates diverse immune functions and metabolism, yet little is known about its role in HCC CSCs. In this study, we report that HDAC11 is highly expressed in HCC and is closely related to disease prognosis. Depletion of HDAC11 in a conditional knockout mouse model reduced hepatocellular tumorigenesis and prolonged survival. Loss of HDAC11 increased transcription of LKB1 by promoting histone acetylation in its promoter region, thereby activating the AMPK signaling pathway and inhibiting the glycolysis pathway, which in turn leads to the suppression of cancer stemness and HCC progression. Furthermore, HDAC11 overexpression reduced HCC sensitivity to sorafenib. Collectively, these data propose HDAC11 as a new target for combination therapy in patients with kinase-resistant HCC. SIGNIFICANCE: This study finds that HDAC11 suppresses LKB1 expression in HCC to promote cancer stemness, progression, and sorafenib resistance, suggesting the potential of targeting HDAC11 to treat HCC and overcome kinase inhibitor resistance.

Drug resistance and Cancer stem cells

Therapy resistance is a major problem when treating cancer patients as cancer cells develop mechanisms that counteract the effect of therapeutic compounds, leading to fit and more aggressive clones that contribute to poor prognosis. Therapy resistance can be both intrinsic and/or acquired. These are multifactorial events, and some are related to factors including adaptations in cancer stem cells (CSCs), epithelial-mesenchymal transition (EMT), deregulation of key signaling pathways, drug efflux through ABC transporters, acquired mutations, evading apoptosis, and activation of DNA damage response among others. Among these factors, CSCs represent the major source of therapy resistance. CSCs are a subset of tumor cells that are capable of self-renewal and multilineage progenitor expansion that are known to be intrinsically resistant to anticancer treatments. Multiple clones of CSCs pre-exist, and some can adopt and expand easily to changes in the tumor microenvironment (TME) and/or in response to radio- and chemotherapy. A combination of both intrinsic and extrinsic factors contributes to CSC-mediated therapy resistance. In this review, we will focus on CSCs and therapy resistance as well as suggest strategies to eliminate CSCs and, therefore, overcome resistance. Video abstract.

A method to culture human alveolar rhabdomyosarcoma cell lines as rhabdospheres demonstrates an enrichment in stemness and Notch signaling

The development of three-dimensional cell culture techniques has allowed cancer researchers to study the stemness properties of cancer cells in in vitro culture. However, a method to grow PAX3-FOXO1 fusion-positive rhabdomyosarcoma (FP-RMS), an aggressive soft tissue sarcoma of childhood, has to date not been reported, hampering efforts to identify the dysregulated signaling pathways that underlie FP-RMS stemness. Here, we first examine the expression of canonical stem cell markers in human RMS tumors and cell lines. We then describe a method to grow FP-RMS cell lines as rhabdospheres and demonstrate that these spheres are enriched in expression of canonical stemness factors as well as Notch signaling components. Specifically, FP-RMS rhabdospheres have increased expression of SOX2, POU5F1 (OCT4), and NANOG, and several receptors and transcriptional regulators in the Notch signaling pathway. FP-RMS rhabdospheres also exhibit functional stemness characteristics including multipotency, increased tumorigenicity in vivo, and chemoresistance. This method provides a novel practical tool to support research into FP-RMS stemness and chemoresistance signaling mechanisms.

Summary: Here we report on a method to culture human PAX3-FOXO1 fusion-positive rhabdomyosarcoma cells in three dimensions, and use these rhabdospheres as a novel tool to study their stemness and chemoresistance signaling mechanisms.

Mesenchymal stem cells as a double-edged sword in tumor growth: focusing on MSC-derived cytokines

Mesenchymal stem cells (MSCs) show homing capacity towards tumor sites. Numerous reports indicate that they are involved in multiple tumor-promoting processes through several mechanisms, including immunosuppression; stimulation of angiogenesis; transition to cancer-associated fibroblasts; inhibition of cancer cell apoptosis; induction of epithelial-mesenchymal transition (EMT); and increase metastasis and chemoresistance. However, other studies have shown that MSCs suppress tumor growth by suppressing angiogenesis, incrementing inflammatory infiltration, apoptosis and cell cycle arrest, and inhibiting the AKT and Wnt signaling pathways. In this review, we discuss the supportive and suppressive impacts of MSCs on tumor progression and metastasis. We also discuss MSC-based therapeutic strategies for cancer based on their potential for homing to tumor sites.

Identification of potential therapeutic target of naringenin in breast cancer stem cells inhibition by bioinformatics and in vitro studies

Cancer therapy is a strategic measure in inhibiting breast cancer stem cell (BCSC) pathways. Naringenin, a citrus flavonoid, was found to increase breast cancer cells' sensitivity to chemotherapeutic agents. Bioinformatics study and 3D tumorsphere in vitro modeling in breast cancer (mammosphere) were used in this study, which aims to explore the potential therapeutic targets of naringenin (PTTNs) in inhibiting BCSCs. Bioinformatic analyses identified direct target proteins (DTPs), indirect target proteins (ITPs), naringenin-mediated proteins (NMPs), BCSC regulatory genes, and PTTNs. The PTTNs were further analyzed for gene ontology, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment, protein-protein interaction (PPI) networks, and hub protein selection. Mammospheres were cultured in serum-free media. The effects of naringenin were measured by MTT-based cytotoxicity, mammosphere forming potential (MFP), colony formation, scratch wound-healing assay, and flow cytometry-based cell cycle analyses and apoptosis assays. Gene expression analysis was performed using real-time quantitative polymerase chain reaction (q-RT PCR). Bioinformatics analysis revealed p53 and estrogen receptor alpha (ERα) as PTTNs, and KEGG pathway enrichment analysis revealed that TGF-ß and Wnt/ß-catenin pathways are regulated by PTTNs. Naringenin demonstrated cytotoxicity and inhibited mammosphere and colony formation, migration, and epithelial to mesenchymal transition in the mammosphere. The mRNA of tumor suppressors P53 and ERα were downregulated in the mammosphere, but were significantly upregulated upon naringenin treatment. By modulating the P53 and ERα mRNA, naringenin has the potential of inhibiting BCSCs. Further studies on the molecular mechanism and formulation of naringenin in BCSCs would be beneficial for its development as a BCSC-targeting drug.

Diltiazem potentiates the cytotoxicity of gemcitabine and 5-fluorouracil in PANC-1 human pancreatic cancer cells through inhibition of P-glycoprotein

AIM

Pancreatic cancer (PC) is one of the most aggressive tumors with dismal survival and a high death rate due to chemotherapeutic failure. P-glycoprotein (P-gp) plays a pivotal role in PC response to gemcitabine and 5-fluorouracil (5-FU). Diltiazem, a calcium channel blocker, is a P-gp inhibitor. In the current study, we investigated the hypothesis that targeting of P-gp by diltiazem can enhance the cytotoxicity of gemcitabine and 5-FU against human pancreatic cancer cells.

MAIN METHODS

The cytotoxic effect of diltiazem, gemcitabine, and 5-FU in single and combined forms against PANC-1 and AsPC-1 cells were assayed by MTT. Flow cytometric analysis was used for the determination of cell cycle, apoptosis, and stemness markers in PC cells. Besides, immunoblotting was used for assessment of Bax, caspase 3, cyclin D1, and P-gp expressions.

KEY FINDINGS

Diltiazem co-treatment, either with gemcitabine or 5-FU, synergistically reduced cell viability, induced apoptosis, and caused cell cycle arrest. In addition, diltiazem co-treatment decreased the expressions of stem cell markers CD24 and CD44, increased the expressions of Bax and cleaved caspase 3, enhanced DNA fragmentation, and attenuated cyclin D1 and P-gp expressions as compared to cells treated with either gemcitabine or 5-FU alone.

SIGNIFICANCE

Our findings suggest that diltiazem may be potential neoadjuvant therapy to enhance the response of PC to gemcitabine or 5-FU treatment.

Multidrug transporter MRP4/ABCC4 as a key determinant of pancreatic cancer aggressiveness

Recent findings show that MRP4 is critical for pancreatic ductal adenocarcinoma (PDAC) cell proliferation. Nevertheless, the significance of MRP4 protein levels and function in PDAC progression is still unclear. The aim of this study was to determine the role of MRP4 in PDAC tumor aggressiveness. Bioinformatic studies revealed that PDAC samples show higher MRP4 transcript levels compared to normal adjacent pancreatic tissue and circulating tumor cells express higher levels of MRP4 than primary tumors. Also, high levels of MRP4 are typical of high-grade PDAC cell lines and associate with an epithelial-mesenchymal phenotype. Moreover, PDAC patients with high levels of MRP4 depict dysregulation of pathways associated with migration, chemotaxis and cell adhesion. Silencing MRP4 in PANC1 cells reduced tumorigenicity and tumor growth and impaired cell migration. Transcriptomic analysis revealed that MRP4 silencing alters PANC1 gene expression, mainly dysregulating pathways related to cell-to-cell interactions and focal adhesion. Contrarily, MRP4 overexpression significantly increased BxPC-3 growth rate, produced a switch in the expression of EMT markers, and enhanced experimental metastatic incidence. Altogether, our results indicate that MRP4 is associated with a more aggressive phenotype in PDAC, boosting pancreatic tumorigenesis and metastatic capacity, which could finally determine a fast tumor progression in PDAC patients.

Advances in Therapeutic Targeting of Cancer Stem Cells within the Tumor Microenvironment: An Updated Review

Despite great strides being achieved in improving cancer patients' outcomes through better therapies and combinatorial treatment, several hurdles still remain due to therapy resistance, cancer recurrence and metastasis. Drug resistance culminating in relapse continues to be associated with fatal disease. The cancer stem cell theory posits that tumors are driven by specialized cancer cells called cancer stem cells (CSCs). CSCs are a subpopulation of cancer cells known to be resistant to therapy and cause metastasis. Whilst the debate on whether CSCs are the origins of the primary tumor rages on, CSCs have been further characterized in many cancers with data illustrating that CSCs display great abilities to self-renew, resist therapies due to enhanced epithelial to mesenchymal (EMT) properties, enhanced expression of ATP-binding cassette (ABC) membrane transporters, activation of several survival signaling pathways and increased immune evasion as well as DNA repair mechanisms. CSCs also display great heterogeneity with the consequential lack of specific CSC markers presenting a great challenge to their targeting. In this updated review we revisit CSCs within the tumor microenvironment (TME) and present novel treatment strategies targeting CSCs. These promising strategies include targeting CSCs-specific properties using small molecule inhibitors, immunotherapy, microRNA mediated inhibitors, epigenetic methods as well as targeting CSC niche-microenvironmental factors and differentiation. Lastly, we present recent clinical trials undertaken to try to turn the tide against cancer by targeting CSC-associated drug resistance and metastasis.

Role of Mitochondria in Cancer Stem Cell Resistance

Cancer stem cells (CSC) are associated with the mechanisms of chemoresistance to different cytotoxic drugs or radiotherapy, as well as with tumor relapse and a poor prognosis. Various studies have shown that mitochondria play a central role in these processes because of the ability of this organelle to modify cell metabolism, allowing survival and avoiding apoptosis clearance of cancer cells. Thus, the whole mitochondrial cycle, from its biogenesis to its death, either by mitophagy or by apoptosis, can be targeted by different drugs to reduce mitochondrial fitness, allowing for a restored or increased sensitivity to chemotherapeutic drugs. Once mitochondrial misbalance is induced by a specific drug in any of the processes of mitochondrial metabolism, two elements are commonly boosted: an increment in reactive nitrogen/oxygen species and, subsequently, activation of the intrinsic apoptotic pathway.

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.

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.

Cancer Stem Cells as a Potential Target to Overcome Multidrug Resistance

Multidrug resistance (MDR), which is a significant impediment to the success of cancer chemotherapy, is attributable to various defensive mechanisms in cancer. Initially, overexpression of ATP-binding cassette (ABC) transporters such as P-glycoprotein (P-gp) was considered the most important mechanism for drug resistance; hence, many investigators for a long time focused on the development of specific ABC transporter inhibitors. However, to date their efforts have failed to develop a clinically applicable drug, leaving only a number of problems. The concept of cancer stem cells (CSCs) has provided new directions for both cancer and MDR research. MDR is known to be one of the most important features of CSCs and thus plays a crucial role in cancer recurrence and exacerbation. Therefore, in recent years, research targeting CSCs has been increasing rapidly in search of an effective cancer treatment. Here, we review the drugs that have been studied and developed to overcome MDR and CSCs, and discuss the limitations and future perspectives.

Overexpression of DUSP6 enhances chemotherapy-resistance of ovarian epithelial cancer by regulating the ERK signaling pathway

Objective: DUSP6 is a negative regulator of the ERK signaling pathway and plays an important role in chemotherapy-resistance. Previously we showed that DUSP6 is overexpressed in ovarian cancer side population (SP) cells that possess cancer stem cell-like properties and are quiescent and chemotherapy-resistant. Here, we explore the effects of DUSP6 on chemotherapy-resistance by examining its regulation of the ERK signaling pathway and G0/G1 cell cycle arrest. Methods: mRNA and protein expression of DUSP6 and G0/G1 cell cycle checkpoint regulating proteins (CyclinD1, CyclinD3 and CyclinE2) was evaluated among ovarian cancer cell lines and tissue samples. Ovarian cancer cells were transiently transfected to overexpress DUSP6. After treatment with cisplatin, cell viability was measured by the MTS assay at 48 hours and the half maximal inhibitory concentration (IC50) for each cell line was calculated. Subcellular localization and cell cycle analysis were determined by using immunofluorescence and FACS, respectively. Results: SKOV3 and OVCAR8 SP cells were shown to express higher levels of DUSP6 and lower levels of CyclinD3 compared with non-SP (NSP) cells (P<0.001). Among 39 ovarian cancer tissue samples, expression of DUSP6 in the chemotherapy-resistant group (12 samples) was higher than in the chemotherapy-sensitive group (27 samples) (P<0.05). While a lower level of expression of CyclinD3 was seen in the chemotherapy-resistant group, it was not statistically different from the chemotherapy-sensitive group. HO8910 cells where shown to have higher IC50 to cisplatin than SKOV3 or OVCAR8 cells, and this correlated with higher levels of DUSP6 expression. Overexpression of DUSP6 in SKOV3 cells led to an increase in cisplatin IC50 values (P<0.05), and also markedly reduced the expression levels of phospho-ERK1/2 and CyclinD3 and to the predominance of cells in the G0/G1 phase. Conclusion: Our findings reveal an enhancement of chemotherapy-resistance and a predominance of cells in G1 cell cycle arrest in DUSP6-overexpressing ovarian cancer cells. This suggests that overexpression of DUSP6 promotes chemotherapy-resistance through the negative regulation of the ERK signaling pathway, increasing the G0/G1 phase ratio among ovarian cancer cells, and leading to cellular quiescence.

Bidirectional Crosstalk Between Cancer Stem Cells and Immune Cell Subsets

Cancer stem cells (CSCs), also known as tumor-initiating cells, are characterized by an increased capacity for self-renewal, multipotency, and tumor initiation. While CSCs represent only a small proportion of the tumor mass, they significantly account for metastatic dissemination and tumor recurrence, thus making them attractive targets for therapy. Due to their ability to sustain in dormancy, chemo- and radiotherapy often fail to eliminate cancer cells with stemness properties. Recent advances in the understanding of the tumor microenvironment (TME) illustrated the importance of the immune contexture, determining the response to therapy and clinical outcome of patients. In this context, CSCs exhibit special properties to escape the recognition by innate and adaptive immunity and shape the TME into an immunosuppressive, pro-tumorigenic landscape. As CSCs sculpt the immune contexture, the phenotype and functional properties of the tumor-infiltrating immune cells in turn influence the differentiation and phenotype of tumor cells. In this review, we summarize recent studies investigating main immunomodulatory properties of CSCs and their underlying molecular mechanisms as well as the impact of immune cells on cancer cells with stemness properties. A deeper understanding of this bidirectional crosstalk shaping the immunological landscape and determining therapeutic responses will facilitate the improvement of current treatment modalities and the design of innovative strategies to precisely target CSCs.

Research Progress on Chemical Constituents and Anticancer Pharmacological Activities of Euphorbia lunulata Bunge

Euphorbia lunulata Bunge (ELB) is a traditional Chinese medicine possessing the functions of expectoration, cough relief, asthma relief, detoxification, and itching relief. Modern pharmacological studies have showed that ELB exhibits a variety of activities, such as antitumor, antibacterial, and antioxidant activities. In particular, the anticancer activities of ELB have attracted much attention. In this review, we summarize the recent research progress on the chemical constituents and anticancer activities of ELB by searching the PubMed, Web of Science, and China National Knowledge Infrastructure databases. The results show that more than 151 components have been identified from extracts of ELB, including 73 terpenoids, 28 flavonoids, 8 phenylpropanoids, 7 steroids, 19 phenols, and 5 alkaloids. ELB has been shown to exhibit significant inhibitory effects on lung, cervical, gastric, breast, and liver cancers, and its anticancer effects are mainly manifested in the 3 aspects, including cell cycle arrest, cell apoptosis, and inhibition of the migration of cancer cells.

Nanotechnology approaches in the current therapy of skin cancer

Skin cancer is a high burden disease with a high impact on global health. Conventional therapies have several drawbacks; thus, the development of effective therapies is required. In this context, nanotechnology approaches are an attractive strategy for cancer therapy because they enable the efficient delivery of drugs and other bioactive molecules to target tissues with low toxic effects. In this review, nanotechnological tools for skin cancer will be summarized and discussed. First, pathology and conventional therapies will be presented, followed by the challenges of skin cancer therapy. Then, the main features of developing efficient nanosystems will be discussed, and next, the most commonly used nanoparticles (NPs) described in the literature for skin cancer therapy will be presented. Subsequently, the use of NPs to deliver chemotherapeutics, immune and vaccine molecules and nucleic acids will be reviewed and discussed as will the combination of physical methods and NPs. Finally, multifunctional delivery systems to codeliver anticancer therapeutic agents containing or not surface functionalization will be summarized.

CD34 cells in somatic, regenerative and cancer stem cells: Developmental biology, cell therapy, and omics big data perspective

The transmembrane phosphoglycoprotein protein CD34 has conventionally been regarded as a marker for hematopoietic progenitors. Its expression on these cells has been leveraged for cell therapy applications in various hematological disorders. More recently, the expression of CD34 has also been reported on cells of nonhematopoietic origin. The list includes somatic cells such as endothelial cells, fibrocytes and interstitial cells and regenerative stem cells such as corneal keratocytes, muscle satellite cells, and muscle-derived stem cells. Furthermore, its expression on some cancer stem cells (CSCs) has also been reported. Till date, the functional roles of this molecule have been implicated in a multitude of cellular processes including cell adhesion, signal transduction, and maintenance of progenitor phenotype. However, the complete understanding about this molecule including its developmental origins, its embryonic connection, and associated functions is far from complete. Here, we review our present understanding of the structure and putative functions of the CD34 molecule based upon our literature survey. We also probed various biological databases to retrieve data related to the expression and associated molecular functions of CD34. Such information, upon synthesis, is hence likely to provide the suitability of such cells for cell therapy. Moreover, we have also covered the existing cell therapy and speculated cell therapy applications of CD34⁺ cells isolated from various lineages. We have also attempted here to speculate the role(s) of CD34 on CSCs. Finally, we discuss number of large-scale proteomics and transcriptomics studies that have been performed using CD34⁺ cells.

SOX2 upregulates side population cells and enhances their chemoresistant ability by transactivating ABCC1 expression contributing to intrinsic resistance to paclitaxel in melanoma

Paclitaxel is the last choice for the treatment of advanced melanoma as a second-line chemotherapeutic agent, but there are still many cases of intrinsic resistance to paclitaxel in melanoma and the reasons that cause paclitaxel resistance remain unclear. Here, we identified that high expression of SRY-box transcription factor 2 (SOX2) and high ratio of side population (SP) cells reduced the sensitivity to paclitaxel in melanoma cells. The knockout and the induction of SOX2 completely depleted and significantly upregulated the ratios of melanoma SP cells, respectively. These data suggest that SOX2, a pluripotent transcription factor for inducing cancer stem cells in melanoma, is also sufficient and necessary for the induction of melanoma SP cells. ATP-binding cassette (ABC) subfamily C member 1 (ABCC1) is one of ABC transporters which causes SP cells to be resistance to chemotherapeutic agents by efficiently pumping drugs out of cells. The knockout and the induction of ABCC1 significantly increased and decreased the sensitivity of melanoma cells to paclitaxel. High expression of ABCC1 was identified in melanoma cell lines with high expression of SOX2 and in their SP cells. SOX2 was identified to induce ABCC1 transcription. Taken together, SOX2 upregulates SP cells and enhances their chemoresistant ability by increasing ABCC1 expression, which contributes to intrinsic resistance to paclitaxel in melanoma. Our findings will lead to new insights into melanoma biology and therapy resistance, and eventually to new therapeutic targets.

MDA-9/Syntenin (SDCBP) Is a Critical Regulator of Chemoresistance, Survival and Stemness in Prostate Cancer Stem Cells

Despite some progress, treating advanced prostate cancer remains a major clinical challenge. Recent studies have shown that prostate cancer can originate from undifferentiated, rare, stem cell-like populations within the heterogeneous tumor mass, which play seminal roles in tumor formation, maintenance of tumor homeostasis and initiation of metastases. These cells possess enhanced propensity toward chemoresistance and may serve as a prognostic factor for prostate cancer recurrence. Despite extensive studies, selective targeted therapies against these stem cell-like populations are limited and more detailed experiments are required to develop novel targeted therapeutics. We now show that MDA-9/Syntenin/SDCBP (MDA-9) is a critical regulator of survival, stemness and chemoresistance in prostate cancer stem cells (PCSCs). MDA-9 regulates the expression of multiple stem-regulatory genes and loss of MDA-9 causes a complete collapse of the stem-regulatory network in PCSCs. Loss of MDA-9 also sensitizes PCSCs to multiple chemotherapeutics with different modes of action, such as docetaxel and trichostatin-A, suggesting that MDA-9 may regulate multiple drug resistance. Mechanistically, MDA-9-mediated multiple drug resistance, stemness and survival are regulated in PCSCs through activation of STAT3. Activated STAT3 regulates chemoresistance in PCSCs through protective autophagy as well as regulation of MDR1 on the surface of the PCSCs. We now demonstrate that MDA-9 is a critical regulator of PCSC survival and stemness via exploiting the inter-connected STAT3 and c-myc pathways.

Characterization of Melanoma Cell Lines Resistant to Vemurafenib and Evaluation of Their Responsiveness to EGFR- and MET-Inhibitor Treatment

Constitutively active mutated BRAF kinase occurs in more than 40% of patients suffering from melanoma. To block its activity, a specific inhibitor, vemurafenib, is applied as a therapy. Unfortunately, patients develop resistance to this drug rather quickly. Previously, we demonstrated that pairs of inhibitors directed against EGFR (epidermal growth factor receptor) and MET (hepatocyte growth factor receptor) trigger a synergistic cytotoxic effect in human melanoma cells, and decrease their invasive abilities. In this study, we aimed to generate and characterize melanoma cells resistant to vemurafenib treatment, and then to evaluate the effectiveness of a previously developed therapy in this model. We showed that melanoma cells resistant to the BRAF inhibitor are characterized by a lower proliferation rate and they acquire a spindle-like shape. Using Western Blot, we also noticed increased levels of EGFR, MET, and selected markers of cancer stem cells in generated cell lines. Resistant cells also exhibited increased invasive abilities and elevated proteolytic activity, observed using scratch wound assays and gelatin zymography. Moreover, combination therapy reduced their viability, as measured with a colorimetric cytotoxicity test, and decreased invasiveness. The obtained results validate the application of combination therapy directed against EGFR and MET in melanoma cells resistant to treatment with inhibitors of mutated BRAF.

Molecular Mechanism of Matrine from Sophora alopecuroides in the Reversing Effect of Multi-Anticancer Drug Resistance in K562/ADR Cells

Multidrug resistance is the main obstacle to current chemotherapies. In this study, we evaluated the reversing effect of matrine, the principal alkaloid derived from Sophora alopecuroides, on chemoresistant leukemia K562/ADR cells. Matrine in a range of the nontoxic concentration was employed in the whole study. IC₅₀s of cancer medicines were tested using WST-8 assay. Drug export and apoptotic rates were examined using flow cytometry. The mRNA and protein expressions were quantified by quantitative real-time PCR and western blotting, respectively. Our data indicated that matrine had potent reversal properties augmenting cytotoxicity of cancer medicines on K562/ADR cells as well as apoptotic rates induced by doxorubicin. Moreover, matrine inhibited drug-exporting activity and expression of ATP-binding cassette subfamily B member 1 (ABCB1) on both mRNA and protein levels. That might result from inhibited NF-kappa B activation, which also led to restored intrinsic apoptosis. These findings suggest that matrine in the nontoxic concentration can suppress ABCB1 drug transport and facilitate the intrinsic apoptosis pathway through the inhibiting effect on NF-kappa B and has the potential to become an efficient sensitizer for anticancer drug resistance.

Bioactive lipids in cancer stem cells

Tumours are known to be a heterogeneous group of cells, which is why they are difficult to eradicate. One possible cause for this is the existence of slow-cycling cancer stem cells (CSCs) endowed with stem cell-like properties of self-renewal, which are responsible for resistance to chemotherapy and radiotherapy. In recent years, the role of lipid metabolism has garnered increasing attention in cancer. Specifically, the key roles of enzymes such as stearoyl-CoA desaturase-1 and 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase in CSCs, have gained particular interest. However, despite accumulating evidence on the role of proteins in controlling lipid metabolism, very little is known about the specific role played by lipid products in CSCs. This review highlights recent findings on the role of lipid metabolism in CSCs, focusing on the specific mechanism by which bioactive lipids regulate the fate of CSCs and their involvement in signal transduction pathways.

P-Glycoprotein and Breast Cancer Resistance Protein in Canine Inflammatory and Noninflammatory Grade III Mammary Carcinomas

P-glycoprotein (P-gp/ABCB1) and breast cancer resistance protein (BCRP/ABCG2) expression are frequently related to multidrug resistance (MDR) in neoplastic cells. Canine inflammatory and grade III noninflammatory mammary carcinomas (IMC and non-IMC) are aggressive tumors that could benefit from chemotherapy. This study describes the immunohistochemical detection of P-gp and BCRP in 20 IMCs and 18 non-IMCs from dogs that had not received chemotherapy. Our aim was to determine if P-gp and BCRP expression was related to the "inflammatory" phenotype, to establish a basis for future studies analyzing the response to chemotherapy in dogs with highly malignant mammary cancer. Immunolabeling was primarily membranous for P-gp with a more intense labeling in emboli, and immunolabeling was membranous and cytoplasmic for BCRP. P-gp was expressed in 17 of 20 (85%) IMCs compared to 7 of 18 (39%) non-IMCs (P = 0.006). BCRP was expressed within emboli in 15 of 19 (79%) emboli in IMC, 12 of 15 (80%) primary IMCs, and 12 of 18 (67%) non-IMCs, without statistically significant differences (P > .05). All IMCs and 67% of non-IMCs expressed at least 1 of the 2 transporters, and 63% (12/19) of IMCs and 39% (7/18) of non-IMCs expressed both P-gp and BCRP. P-gp and BCRP evaluation might help select patients for chemotherapy. P-gp, expressed in a significantly higher percentage of IMCs vs non-IMCs, might play a specific role in the chemoresistance of IMC.

GPR56 Drives Colorectal Tumor Growth and Promotes Drug Resistance through Upregulation of MDR1 Expression via a RhoA-Mediated Mechanism

Drug resistance continues to be a major obstacle of effective therapy for colorectal cancer, leading to tumor relapse or treatment failure. Cancer stem cells (CSC) or tumor-initiating cells are a subpopulation of tumor cells which retain the capacity for self-renewal and are suggested to be implicated in drug resistance. LGR5 is highly expressed in colorectal cancer and marks CSCs that drive tumor growth and metastasis. LGR5(⁺) CSCs cells were shown to interconvert with more drug-resistant LGR5(^-) cancer cells, and treatment with LGR5-targeted antibody-drug conjugates (ADC) eliminated LGR5(⁺) tumors, yet a fraction of LGR5(^-) tumors eventually recurred. Therefore, it is important to identify mechanisms associated with CSC plasticity and drug resistance in order to develop curative therapies. Here, we show that loss of LGR5 in colon cancer cells enhanced resistance to irinotecan and 5-fluorouracil and increased expression of adhesion G-protein-coupled receptor, GPR56. GPR56 expression was significantly higher in primary colon tumors versus matched normal tissues and correlated with poor survival outcome. GPR56 enhanced drug resistance through upregulation of MDR1 levels via a RhoA-mediated signaling mechanism. Loss of GPR56 led to suppression of tumor growth and increased sensitivity of cancer cells to chemotherapy and monomethyl auristatin E-linked anti-LGR5 ADCs, by reducing MDR1 levels. These findings suggest that upregulation of GPR56 may be a mechanism associated with CSC plasticity by which LGR5(^-) cancer cells acquire a more drug-resistant phenotype. IMPLICATIONS: Our findings suggest that targeting GPR56 may provide a new strategy for the treatment of colorectal cancer and combatting drug resistance.

An Updated Review of Oral Cancer Stem Cells and Their Stemness Regulation

Cancer stem cells (CSCs; also known as tumor-initiating cells) are a small population of cancer cells that retain characteristics similar to those of normal stem cells. CSCs are known to be responsible for metastasis, drug resistance, and cancer recurrence. Thus, controlling CSCs may provide an effective therapeutic intervention that inhibits tumor growth and aggressiveness. Despite the importance of targeting CSCs in cancer therapy, the detailed nature of oral CSCs remains underexplored. This article reviews the current understanding of oral CSCs, with emphasis on recent advances in novel signaling pathways involved in their stemness regulation.

Identification of MRP4/ABCC4 as a Target for Reducing the Proliferation of Pancreatic Ductal Adenocarcinoma Cells by Modulating the cAMP Efflux

Pancreatic cancer is one of the most lethal types of tumors with no effective therapy available; is currently the third leading cause of cancer in developed countries; and is predicted to become the second deadliest cancer in the United States by 2030. Due to the marginal benefits of current standard chemotherapy, the identification of new therapeutic targets is greatly required. Considering that cAMP pathway is commonly activated in pancreatic ductal adenocarcinoma (PDAC) and its premalignant lesions, we aim to investigate the multidrug resistance-associated protein 4 (MRP4)-dependent cAMP extrusion process as a cause of increased cell proliferation in human PDAC cell lines. Our results from in silico analysis indicate that MRP4 expression may influence PDAC patient outcome; thus, high MRP4 levels could be indicators of poor survival. In addition, we performed in vitro experiments and identified an association between higher MRP4 expression levels and more undifferentiated and malignant models of PDAC and cAMP extrusion capacity. We studied the antiproliferative effect and the overall cAMP response of three MRP4 inhibitors, probenecid, MK571, and ceefourin-1 in PDAC in vitro models. Moreover, MRP4-specific silencing in PANC-1 cells reduced cell proliferation (P < 0.05), whereas MRP4 overexpression in BxPC-3 cells significantly incremented their growth rate in culture (P < 0.05). MRP4 pharmacological inhibition or silencing abrogated cell proliferation through the activation of the cAMP/Epac/Rap1 signaling pathway. Also, extracellular cAMP reverted the antiproliferative effect of MRP4 blockade. Our data highlight the MRP4-dependent cAMP extrusion process as a key participant in cell proliferation, indicating that MRP4 could be an exploitable therapeutic target for PDAC. SIGNIFICANCE STATEMENT: ABCC4/MRP4 is the main transporter responsible for cAMP efflux. In this work, we show that MRP4 expression may influence PDAC patient outcome and identify an association between higher MRP4 expression levels and more undifferentiated and malignant in vitro models of PDAC. Findings prove the involvement of MRP4 in PDAC cell proliferation through a novel extracellular cAMP mitogenic pathway and further support MRP4 inhibition as a promising therapeutic strategy for PDAC treatment.

The multifaceted role of mesenchymal stem cells in cancer

Mesenchymal stem cells (MSCs) are multipotent stem cells derived from the mesoderm that give rise to several mesenchymal lineages, including osteoblasts, adipocytes, chondrocytes and myocytes. Their potent ability to home to tumors coupled with their differentiation potential and immunosuppressive function positions MSCs as key regulators of tumor fate. Here we review the existing knowledge on the involvement of MSCs in multiple tumor-promoting processes, including angiogenesis, epithelial-mesenchymal transition, metastasis, immunosuppression and therapy resistance. We also discuss the clinical potential of MSC-based therapy for cancer.

Potential effects of nicotine on glioblastoma and chemoradiotherapy: a review

Introduction: Glioblastoma multiforme (GBM) has a poor prognosis despite maximal surgical resection with subsequent multi-modal radiation and chemotherapy. Use of tobacco products following diagnosis and during the period of treatment for non-neural tumors detrimentally affects treatment and prognosis. Approximately, 16-28% of patients with glioblastoma continue to smoke after diagnosis and during treatment. The literature is sparse for information-pertaining effects of smoking and nicotine on GBM treatment and prognosis. Areas covered: This review discusses cellular pathways involved in GBM progression that might be affected by nicotine, as well as how nicotine may contribute to resistance to treatment. Similarities of GBM pathways to those in non-neural tumors are investigated for potential effects by nicotine. English language papers were identified using PubMed, Medline and Scopus databases using a combination of keywords including but not limited to the following: nicotine, vaping, tobacco, e-cigarettes, smoking, vaping AND glioblastoma or brain cancer OR/AND temozolomide, carmustine, methotrexate, procarbazine, lomustine, vincristine, and neural tumor cell lines. Expert opinion: Understanding the impact of nicotine on treatment and resistance to chemotherapeutics should allow physicians to educate their patients with GBM with evidence-based recommendations about the effects of continuing to use nicotine-containing products after diagnosis and during treatment.

Therapeutic targeting of gastrointestinal cancer stem cells

Gastrointestinal cancers remain a tremendous burden on society. Despite advances in therapy options, including chemotherapy and radiation, cancer mortality from recurrences and metastases occur frequently. Cancer stem cells (CSCs) drive disease recurrence and metastasis, as these cells are uniquely equipped to self-renew and evade therapy. Therefore, cancer eradication requires treatment strategies that target CSCs in addition to differentiated cancer cells. This review highlights current literature on therapies targeting CSCs in gastrointestinal cancer.

Rising horizon in circumventing multidrug resistance in chemotherapy with nanotechnology

Multidrug resistance (MDR) is one of the key barriers in chemotherapy, leading to the generation of insensitive cancer cells towards administered therapy. Genetic and epigenetic alterations of the cells are the consequences of MDR, resulted in drug resistivity, which reflects in impaired delivery of cytotoxic agents to the cancer site. Nanotechnology-based nanocarriers have shown immense shreds of evidence in overcoming these problems, where these promising tools handle desired dosage load of hydrophobic chemotherapeutics to facilitate designing of safe, controlled and effective delivery to specifically at tumor microenvironment. Therefore, encapsulating drugs within the nano-architecture have shown to enhance solubility, bioavailability, drug targeting, where co-administered P-gp inhibitors have additionally combat against developed MDR. Moreover, recent advancement in the stimuli-sensitive delivery of nanocarriers facilitates a tumor-targeted release of the chemotherapeutics to reduce the associated toxicities of chemotherapeutic agents in normal cells. The present article is focused on MDR development strategies in the cancer cell and different nanocarrier-based approaches in circumventing this hurdle to establish an effective therapy against deadliest cancer disease.

Re-establishing Apoptosis Competence in Bone Associated Cancers via Communicative Reprogramming Induced Through Notch Signaling Inhibition

Notch and its ligands on adjacent cells are key mediators of cellular communication during developmental choice in embryonic and adult tissues. This communication is frequently altered in the pathological interaction between cancer cells and healthy cells of the microenvironment due to the aberrant expression of tumor derived Notch receptors or ligands, that results in homotypic or heterotypic Notch signaling activation in tumor cells or surrounding stromal cells. A deadly consequence of this pathological communication is pharmacological resistance that results in patient's relapse. We will provide a survey of the role of Notch signaling in the bone marrow (BM), a microenvironment with a very high capacity to support several types of cancer, including primary cancers such as osteosarcoma or multiple myeloma and bone metastases from carcinomas. Moreover, in the BM niche several hematological malignancies maintain a reservoir of cancer stem cells, characterized by higher intrinsic drug resistance. Cell-cell communication in BM-tumor interaction triggers signaling pathways by direct contact and paracrine communication through soluble growth factors or extracellular vesicles, which can deliver specific molecules such as mRNAs, miRNAs, proteins, metabolites, etc. enabling tumor cells to reprogram the healthy cells of the microenvironment inducing them to support tumor growth. In this review we will explore how the dysregulated Notch activity contributes to tumor-mediated reprogramming of the BM niche and drug resistance, strengthening the rationale of a Notch-directed therapy to re-establish apoptosis competence in cancer.

Ovarian cancer stem cells: What progress have we made?

Ovarian cancer (OvCa) is the most lethal gynecological malignancy in the United States primarily due to lack of a reliable early diagnostic, high incidence of chemo-resistant recurrent disease as well as profuse tumor heterogeneity. Cancer stem cells (CSCs) continue to gain attention, as they are known to resist chemotherapy, self-renew and re-populate the bulk tumor with undifferentiated and differentiated cells. Moreover, CSCs appear to readily adapt to environmental, immunologic and pharmacologic cues. The plasticity and ability to inactivate or activate signaling pathways promoting their longevity has been, and continues to be, the challenge faced in developing successful CSC targeted therapies. Identifying and understanding unique ovarian CSC markers and the pathways they utilize could reveal new therapeutic opportunities that may offer alternative adjuvant treatment options. Herein, we will discuss the current state of ovarian CSC characterization, their contribution to disease resistance, recurrence and shed light on clinical trials that may target the CSC population.

Cancer stem cells: Road to therapeutic resistance and strategies to overcome resistance

Unlike other normal cells, a subpopulation of cells often termed as "stem cells" are long-lived and generate cellular progeny throughout life. Cancer stem cells (CSCs) are rare immortal cells within a tumor that can both self-renew by dividing and giving rise to many cell types that constitute the tumor. CSCs also have been shown to be involved in fundamental processes of cell proliferation and metastatic dissemination. CSCs are generally resistant to chemotherapy and radiotherapy, a subset of remaining CSCs after therapy can survive and promote cancer relapse and resistance to therapies. Understanding the biological characteristics of CSCs, the pathways leading to their sustainability and proliferation, and the CSCs role in drug resistance is crucial for establishing novel tumor diagnostic and therapeutic strategies. In this review, we address the pathways that regulate CSCs, the role of CSCs in the resistance to therapy, and strategies to overcome therapeutic resistance.

Comparative proteomics of side population cells derived from human hepatocellular carcinoma cell lines with varying metastatic potentials

Metastasis and recurrence following surgery are major reasons for the high mortality rate and poor prognosis associated with hepatocellular carcinoma (HCC). Cancer stem cells (CSCs) are thought to be able to cause cancer, and to be the primary cause of tumor recurrence and metastasis. The underlying mechanisms of the metastatic potential of CSCs is poorly understood. In the present study, side population (SP) cells were isolated from 4 HCC cell lines, and their self-renewal and migratory abilities were compared. The results demonstrate that SP cells from different cell lines exhibited similar self-renewal abilities but different metastatic potentials. Furthermore, the overall proteomes of the SP cells were systematically quantified. This revealed 11 and 19 differentially expressed proteins (DEPs), upregulated and downregulated, respectively, associated with increased metastatic potential. These proteins were involved in the 'regulation of mRNA processing' and 'cytoskeleton organization' biological processes. The majority of the proteins were involved in 'cell proliferation', 'migration' and 'invasion of cancer', and may promote HCC metastasis in a synergistic manner. The AKT and nuclear factor-κB signaling pathways may contribute to the regulation of HCC metastasis through regulating the DEPs in SP cells. To the best of our knowledge, the present study is the first to demonstrate the overall proteome difference among SP cells from the different HCC cell lines with different metastatic potentials. The present study provides novel information regarding the metastatic potential of CSCs, which will facilitate further investigation of the topic.

Induced PTF1a expression in pancreatic ductal adenocarcinoma cells activates acinar gene networks, reduces tumorigenic properties, and sensitizes cells to gemcitabine treatment

Pancreatic acinar cells synthesize, package, and secrete digestive enzymes into the duodenum to aid in nutrient absorption and meet metabolic demands. When exposed to cellular stresses and insults, acinar cells undergo a dedifferentiation process termed acinar-ductal metaplasia (ADM). ADM lesions with oncogenic mutations eventually give rise to pancreatic ductal adenocarcinoma (PDAC). In healthy pancreata, the basic helix-loop-helix (bHLH) factors MIST1 and PTF1a coordinate an acinar-specific transcription network that maintains the highly developed differentiation status of the cells, protecting the pancreas from undergoing a transformative process. However, when MIST1 and PTF1a gene expression is silenced, cells are more prone to progress to PDAC. In this study, we tested whether induced MIST1 or PTF1a expression in PDAC cells could (i) re-establish the transcriptional program of differentiated acinar cells and (ii) simultaneously reduce tumor cell properties. As predicted, PTF1a induced gene expression of digestive enzymes and acinar-specific transcription factors, while MIST1 induced gene expression of vesicle trafficking molecules as well as activation of unfolded protein response components, all of which are essential to handle the high protein production load that is characteristic of acinar cells. Importantly, induction of PTF1a in PDAC also influenced cancer-associated properties, leading to a decrease in cell proliferation, cancer stem cell numbers, and repression of key ATP-binding cassette efflux transporters resulting in heightened sensitivity to gemcitabine. Thus, activation of pancreatic bHLH transcription factors rescues the acinar gene program and decreases tumorigenic properties in pancreatic cancer cells, offering unique opportunities to develop novel therapeutic intervention strategies for this deadly disease.

Optimization Of Cancer Treatment Through Overcoming Drug Resistance

Cancer Drug resistance is a medical concern that requires extensive research and a thorough understanding in order to overcome. Remarkable achievements related to this field have been accomplished and further work is needed in order to optimize the cure for cancer and serve as the basis for precise medicine with few or no side effects.

Pharmacological targets of breast cancer stem cells: a review

Breast cancers contain small population of tumor-initiating cells called breast cancer stem cells (BCSCs), which are spared even after chemotherapy. Recently, BCSCs are implicated to be a cause of metastasis, tumor relapse, and therapy resistance in breast cancer. BCSCs have unique molecular mechanisms, which can be targeted to eliminate them. These include surface biomarkers, proteins involved in self-renewal pathways, drug efflux transporters, apoptotic/antiapoptotic proteins, autophagy, metabolism, and microenvironment regulation. The complex molecular mechanisms behind the survival of BCSCs and pharmacological targets for elimination of BCSCs are described in this review.

Euphorbia lunulata extract acts on multidrug resistant gastric cancer cells to inhibit cell proliferation, migration and invasion, arrest cell cycle progression, and induce apoptosis

ETHNOPHARMACOLOGICAL RELEVANCE

The milky sap or the aboveground part of the plant Euphorbia lunulata has long been used by Chinese people to treat noncancerous growths and cancerous ailments but the specific mode of action and the action mechanism remain to be elucidated.

AIM OF THE STUDY

To investigate the effects of Euphorbia lunulata extract on cell proliferation, migration, invasion, cell cycle progression, and apoptosis of multidrug resistant human gastric cancer cells; To study the mechanism of apoptosis induction by Euphorbia lunulata extract in multidrug resistant human gastric cancer cells.

MATERIALS AND METHODS

The aboveground part of fresh Euphorbia lunulata plant was extracted first with ethanol and then with n-hexane. The aseptic extract at varying concentrations was used to treat the multidrug resistant human gastric cancer SGC7901/ADR cells. After treatment, the inhibition of cell proliferation was examined by MTT assay. The inhibitions of cell migration and invasion were detected by Transwell method. The alteration of cell cycle progression was studied by flow cytometry. The morphological changes of cell nuclei were observed with fluorescence microscopy following Hoechst 33258 staining and the apoptotic indexes were calculated. The activation of caspase enzymes was analyzed by spectrophotometry. The sub-cellular distribution of cytochrome complex and the expression of Bax and Bcl-2 proteins were determined by Western blot.

RESULTS

The proliferation, migration, and invasion of SGC7901/ADR cells were significantly inhibited by Euphorbia lunulata extract, which showed time- and dose-dependent manners. Cell cycle was arrested in G2/M phase. Significant apoptotic morphological changes were observed in the nuclei of the treated cells, and apoptotic indexes were increased significantly; these changes were diminished when Z-VAD-FMK, a caspase inhibitor, was also presented. The activities of caspase-3, caspase-8, and caspase-9 were increased. The sub-cellular distribution of cytochrome complex was altered----reduced in the mitochondria and increased in the cytoplasm. The expression of Bax was upregulated, while that of Bcl-2 was downregulated.

CONCLUSION

Euphorbia lunulata extract inhibited the proliferation, migration, and invasion of SGC7901/ADR cells, arrested cell cycle progression, and induced cell apoptosis; the mechanism of apoptosis induction involved both the extrinsic and the intrinsic pathways.

Expression of genes and proteins of multidrug resistance in gastric cancer cells treated with resveratrol

Multidrug resistance (MDR) is a notable problem in the use of chemotherapy. Therefore, studies aimed at identifying substances capable of overcoming resistance of cancer cells are required. Examples of these compounds are polyphenols, including resveratrol, that exert a range of various biological activities. The aim of the present study was to demonstrate the effect of 3,5,4'-trihydroxy-trans-stilbene (resveratrol) on the expression of ATP binding cassette subfamily B member 1, Annexin A1 (ANXA1) and thioredoxin (TXN) genes, and the proteins encoded by these genes, which are associated with MDR. The experiments were performed in human gastric cancer cell lines EPG85-257RDB (RDB) and EPG85-257RNOV (RNOV), which are resistant to daunorubicin and mitoxantrone, respectively, in addition to EPG85-257P (control), which is sensitive to cytostatic drugs. Cells were treated with 30 or 50 µM resveratrol for 72 h and changes in the expression levels of the genes were analysed with the use of a reverse transcription-quantitative polymerase chain reaction. The cellular levels of P-glycoprotein (P-gp), ANXA1 and TXN were evaluated using immunofluorescence and western blot analysis. Resveratrol in both concentrations has been shown to have a statistically significant influence on expression of the mentioned genes, compared with untreated cells. In RDB cells, resveratrol reduced the expression level of all analyzed genes, compared with untreated cells. Similar results at the protein level were obtained for P-gp and TXN. In turn, in the RNOV cell line, resveratrol reduced TXN expression at mRNA and protein levels, compared with untreated cells. The results of the present study indicate that resveratrol may reduce the resistance of cancer cells by affecting the expression of a number of the genes and proteins associated with MDR.

Interaction between CD133 and PI3K-p85 promotes chemoresistance in gastric cancer cells

Chemoresistance in gastric cancer is the leading cause of tumor recurrence and poses a substantial therapeutic challenge. The stem cell biomarker CD133 has been implicated in drug resistance of tumor-initiating cells in a number of cancers including gastric cancer. Therefore, we investigated the molecular mechanism of CD133-associated multidrug resistance in gastric cancer cells. Using CD133 overexpressing and knockdown gastric cancer cell lines, we demonstrated that loss of CD133 significantly increased the growth inhibition of chemotherapeutic agents; whereas, overexpression significantly reduced growth inhibition. Furthermore, CD133 knockdown significantly reduced the enzymatic activity of phosphatidylinositol-3 kinase (PI3K) and the expression of P-glycoprotein (P-gp), B-cell lymphoma 2 (BCL2), and phosphorylated-protein kinase B (p-AKT), but elevated the expression of BCL2 associated X (BAX). Conversely, overexpression of CD133 significantly increased PI3K enzymatic activity, expression of P-gp, BCL2, and p-AKT, and decreased BAX expression. The PI3K/AKT inhibitor LY294002 mirrored the effects of loss of CD133; whereas, the PI3K/AKT activator epidermal growth factor reproduced the effects of CD133 overexpression. To identify the interaction between CD133 and PI3K, we used site-directed mutagenesis to mutate individual tyrosine residues of CD133. We found that binding between CD133 and p85, the regulatory subunit of PI3K, was significantly reduced when tyrosine 852 was mutated. In summary, we have demonstrated that CD133 activates the PI3K/AKT signal transduction pathway through direct interaction with PI3K-p85, resulting in multidrug resistance of gastric cancer cells. These results suggest that the interaction between CD133 and PI3K-p85 may offer a novel therapeutic target in multidrug resistant gastric cancer.

LSD1 activation promotes inducible EMT programs and modulates the tumour microenvironment in breast cancer

Complex regulatory networks control epithelial-to-mesenchymal transition (EMT) but the underlying epigenetic control is poorly understood. Lysine-specific demethylase 1 (LSD1) is a key histone demethylase that alters the epigenetic landscape. Here we explored the role of LSD1 in global epigenetic regulation of EMT, cancer stem cells (CSCs), the tumour microenvironment, and therapeutic resistance in breast cancer. LSD1 induced pan-genomic gene expression in networks implicated in EMT and selectively elicits gene expression programs in CSCs whilst repressing non-CSC programs. LSD1 phosphorylation at serine-111 (LSD1-s111p) by chromatin anchored protein kinase C-theta (PKC-θ), is critical for its demethylase and EMT promoting activity and LSD1-s111p is enriched in chemoresistant cells in vivo. LSD1 couples to PKC-θ on the mesenchymal gene epigenetic template promotes LSD1-mediated gene induction. In vivo, chemotherapy reduced tumour volume, and when combined with an LSD1 inhibitor, abrogated the mesenchymal signature and promoted an innate, M1 macrophage-like tumouricidal immune response. Circulating tumour cells (CTCs) from metastatic breast cancer (MBC) patients were enriched with LSD1 and pharmacological blockade of LSD1 suppressed the mesenchymal and stem-like signature in these patient-derived CTCs. Overall, LSD1 inhibition may serve as a promising epigenetic adjuvant therapy to subvert its pleiotropic roles in breast cancer progression and treatment resistance.

Bcl-2 Antiapoptotic Family Proteins and Chemoresistance in Cancer

Cancer is a daunting global problem confronting the world's population. The most frequent therapeutic approaches include surgery, chemotherapy, radiotherapy, and more recently immunotherapy. In the case of chemotherapy, patients ultimately develop resistance to both single and multiple chemotherapeutic agents, which can culminate in metastatic disease which is a major cause of patient death from solid tumors. Chemoresistance, a primary cause of treatment failure, is attributed to multiple factors including decreased drug accumulation, reduced drug-target interactions, increased populations of cancer stem cells, enhanced autophagy activity, and reduced apoptosis in cancer cells. Reprogramming tumor cells to undergo drug-induced apoptosis provides a promising and powerful strategy for treating resistant and recurrent neoplastic diseases. This can be achieved by downregulating dysregulated antiapoptotic factors or activation of proapoptotic factors in tumor cells. A major target of dysregulation in cancer cells that can occur during chemoresistance involves altered expression of Bcl-2 family members. Bcl-2 antiapoptotic molecules (Bcl-2, Bcl-xL, and Mcl-1) are frequently upregulated in acquired chemoresistant cancer cells, which block drug-induced apoptosis. We presently overview the potential role of Bcl-2 antiapoptotic proteins in the development of cancer chemoresistance and overview the clinical approaches that use Bcl-2 inhibitors to restore cell death in chemoresistant and recurrent tumors.

Nano-delivery system targeting to cancer stem cell cluster of differentiation biomarkers

Cancer stem cells (CSCs) are one of the most important origins of cancer progression and metastasis. CSCs have unique self-renewal properties and diverse cell membrane receptors that induced the resistance to the conventional chemotherapeutic agents. Therefore, the therapeutic removal of CSCs could result in the cancer cure with lack of recurrence and metastasis. In this regard, targeting CSCs in accordance to their specific biomarkers is a talented attitude in cancer therapy. Various CSCs surface biomarkers have been described, which some of them exhibited similarities on different cancer cell types, while the others are cancer specific and have just been reported on one or a few types of cancers. In this review, the importance of CSCs in cancer development and therapeutic response has been stated. Different CSCs cluster of differentiation (CD) biomarkers and their specific function and applications in the treatment of cancers have been discussed, Special attention has been made on targeted nano-delivery systems. In this regard, several examples have been illustrated concerning specific natural and artificial ligands against CSCs CD biomarkers that could be decorated on various nanoparticulated drug delivery systems to enhance therapeutic index of chemotherapeutic agents or anticancer gene therapy. The outlook of CSCs biomarkers discovery and therapeutic/diagnostic applications was discussed.

ABC Transporters in Cancer Stem Cells: Beyond Chemoresistance

The efficacy of chemotherapy is one of the main challenges in cancer treatment and one of the major obstacles to overcome in achieving lasting remission and a definitive cure in patients with cancer is the emergence of cancer resistance. Indeed, drug resistance is ultimately accountable for poor treatment outcomes and tumour relapse. There are various molecular mechanisms involved in multidrug resistance, such as the change in the activity of membrane transporters primarily belonging to the ATP binding cassette (ABC) transporter family. In addition, it has been proposed that this common feature could be attributed to a subpopulation of slow-cycling cancer stem cells (CSCs), endowed with enhanced tumorigenic potential and multidrug resistance. CSCs are characterized by the overexpression of specific surface markers that vary in different cancer cell types. Overexpression of ABC transporters has been reported in several cancers and more predominantly in CSCs. While the major focus on the role played by ABC transporters in cancer is polarized by their involvement in chemoresistance, emerging evidence supports a more active role of these proteins, in which they release specific bioactive molecules in the extracellular milieu. This review will outline our current understanding of the role played by ABC transporters in CSCs, how their expression is regulated and how they support the malignant metabolic phenotype. To summarize, we suggest that the increased expression of ABC transporters in CSCs may have precise functional roles and provide the opportunity to target, particularly these cells, by using specific ABC transporter inhibitors.