Apoptosis signaling in cancer stem cells

Modulation of Apoptotic, Cell Cycle, DNA Repair, and Senescence Pathways by Marine Algae Peptides in Cancer Therapy

Marine algae, encompassing both macroalgae and microalgae, have emerged as a promising and prolific source of bioactive compounds with potent anticancer properties. Despite their significant therapeutic potential, the clinical application of these peptides is hindered by challenges such as poor bioavailability and susceptibility to enzymatic degradation. To overcome these limitations, innovative delivery systems, particularly nanocarriers, have been explored. Nanocarriers, including liposomes, nanoparticles, and micelles, have demonstrated remarkable efficacy in enhancing the stability, solubility, and bioavailability of marine algal peptides, ensuring controlled release and prolonged therapeutic effects. Marine algal peptides encapsulated in nanocarriers significantly enhance bioavailability, ensuring more efficient absorption and utilization in the body. Preclinical studies have shown promising results, indicating that nanocarrier-based delivery systems can significantly improve the pharmacokinetic profiles and therapeutic outcomes of marine algal peptides. This review delves into the diverse anticancer mechanisms of marine algal peptides, which include inducing apoptosis, disrupting cell cycle progression, and inhibiting angiogenesis. Further research focused on optimizing nanocarrier formulations, conducting comprehensive clinical trials, and continued exploration of marine algal peptides holds great promise for developing innovative, effective, and sustainable cancer therapies.

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.

Translation of Precision Medicine Research Into Biomarker-Informed Care in Radiation Oncology

The reach of personalized medicine in radiation oncology has expanded greatly over the past few decades as technical precision has improved the delivery of radiation to each patient's unique anatomy. Yet, the consideration of biological heterogeneity between patients has largely not been translated to clinical care. There are innumerable promising advancements in the discovery and validation of biomarkers, which could be used to alter radiation therapy directly or indirectly. Directly, biomarker-informed care may alter treatment dose or identify patients who would benefit most from radiation therapy and who could safely avoid more aggressive care. Indirectly, a variety of biomarkers could assist with choosing the best radiosensitizing chemotherapies. The translation of these advancements into clinical practice will bring radiation oncology even further into the era of precision medicine, treating patients according to their unique anatomical and biological differences.

Ferroptosis: An emerging approach for targeting cancer stem cells and drug resistance

Resistance to chemotherapeutic agents remains a major challenge in the fierce battle against cancer. Cancer stem cells (CSCs) are a small population of cells in tumors that possesses the ability to self-renew, initiate tumors, and cause resistance to conventional anticancer agents. Targeting this population of cells was proven as a promising approach to eliminate cancer recurrence and improve the clinical outcome. CSCs are less susceptible to death by classical anticancer agents inducing apoptosis. CSCs can be eradicated by ferroptosis, which is a non-apoptotic-regulated mechanism of cell death. The induction of ferroptosis is an attractive strategy to eliminate tumors due to its ability to selectively target aggressive CSCs. The current review critically explored the crosstalk and regulatory pathways controlling ferroptosis, which can selectively induce CSCs death. In addition, successful chemotherapeutic agents that achieve better therapeutic outcomes through the induction of ferroptosis in CSCs were discussed to highlight their promising clinical impact.

miR-296-5p suppresses stem cell potency of hepatocellular carcinoma cells via regulating Brg1/Sall4 axis

Epithelial-mesenchymal transition (EMT), a pivotal event during cancer progression such as relapse and metastasis, is positively correlated with the stemness potency of tumor cells. Our previous study showed that miR-296-5p attenuated EMT program of hepatocellular carcinoma cells (HCC) through NRG1/ERBB2/ERBB3 signaling. In the present study, we uncovered that miR-296-5p was able to inhibit the stemness potency of HCC by decreasing the number and size of tumorspheres, downregulating the expression of CSC biomarkers and hampering the ability of tumorigenesis in NOD/SCID mice. Brahma-related gene-1 (Brg1), as the target protein of miR-296-5p detected by bioinformatics methods, activates a series of downstream cascades through directly binding to Sall4 promoter and enhancing Sall4 transcription. Importantly, the higher expressions of Brg1 and Sall4 in tumor tissues of HCC patients suggest poorer prognoses after surgical extraction. In conclusion, miR-296-5p exerts an inhibitory effect on stemness potency of HCC cells via Brg1/Sall4 axis.

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.

Marine anticancer drugs and their relevant targets: a treasure from the ocean

Marine organisms comprising animals and plants are wealthiest sources of bioactive compounds possessing various pharmacological properties specifically: free radical scavenging, antitumor, antimicrobial, analgesic, neuroprotective and immunomodulatory. Marine drugs provide an alternative source to meet the demand of effective, safe and low-cost drugs that are rising with the continuously growing world population. Cancer is one of the leading reasons of mortality in western nations in contrast to communicable diseases of developing nations. In spite of outstanding developments in cancer therapy in past three decades, there is still an insistent necessity for innovative drugs in the area of cancer biology, especially in the unexplored area of marine anticancer compounds. However, recent technological innovations in structure revelation, synthetic creation of new compounds and biological assays have made possible the isolation and clinical assessment of innumerable unique anticancer compounds from marine environment. This review provides an insight into the anticancer research so far conducted in the area of the marine natural products/synthetic derivatives, their possible molecular targets and the current challenges in the drug development. Graphical abstract.

ASPP2 enhances chemotherapeutic sensitivity through the down-regulation of XIAP expression in a p53 independent manner in hepatocellular carcinoma

Apoptosis stimulated protein of p53-2 (ASPP2) induces the transcription of p53-targeted genes to stimulates its pro-apoptosis function. The poor chemotherapeutic sensitivity is associated with the decreased ASPP2 expression in many human cancers. Here, multiple genes real-time RT-PCR array and western blotting analysis show that ASPP2 suppress the expression of X-linked inhibitor of apoptosis protein (XIAP), determinant of chemoresistance in cancer, in hepatocellular carcinoma (HCC) in a p53-independent manner. Further experiments with ASPP2-rAd and ASPP2-Lv confirmed that ASPP2 enhanced sensitivity of sorafenib to HCC via suppressing XIAP expression. XIAP mainly found on the cytoplasm and perinuclear areas of ASPP2 over-expressed HepG2 cells, while both cytoplasm and nucleus in ASPP2 shut down HepG2 cells. The association of poor sensitivity of sorafenib and XIAP expression was also found both in ASPP2 shut down and overexpress mice, where liver tissue with decreased or increased ASPP2 displayed less or more apoptosis, respectively. Finally, ASPP2 and XIAP expression analyzed in 43 hepatocellular carcinoma tumors and 44 adjacent normal tissues from 38 hepatocellular carcinoma patients for fully understand their expression within HCC patients. Compared with the tumor tissues, ASPP2 mRNA levels were increased, and XIAP levels decreased in the adjacent normal tissues. Taken together, XIAP suppressed ASPP2 increased tumor sensitivity to chemotherapy in a p53-independent manner, which was associated with chemotherapy resistance, suggesting that p53 activation and XIAP suppression were two independent ways that ASPP2 enhance the sensitivity of chemotherapy.

Foxn1 expression in keratinocytes is stimulated by hypoxia: further evidence of its role in skin wound healing

Recent studies have shown that the transcription factor Foxn1, which is expressed in keratinocytes, is involved in the skin wound healing process, yet how Foxn1 functions remains largely unknown. Our latest data indicate that Foxn1 drives skin healing via engagement in re-epithelization and the epithelial-mesenchymal transition (EMT) process. In the present study, 2D-DIGE proteomic profiling analysis of in vitro cultured keratinocytes transfected with adenoviral vector carrying Foxn1-GFP or GFP alone (control) revealed forty proteins with differential abundance between the compared groups. Among the proteins with Foxn1-dependent expression, several enable adaptation to hypoxia. Subsequent experiments revealed that hypoxic conditions (1% O₂) stimulate endogenous and exogenous (transfected Ad-Foxn1) Foxn1 expression in cultured keratinocytes. A proteomics analysis also identified proteins that can act as a factors controlling the balance between cell proliferation, differentiation and apoptosis in response to Foxn1. We also showed that in C57BL/6 keratinocytes, the stimulation of Foxn1 by hypoxia is accompanied by increases in Mmp-9 expression. These data corroborate the detected co-localization of Foxn1 and Mmp-9 expression in vivo in post-wounding skin samples of Foxn1::Egfp transgenic mice. Together, our data indicate that Foxn1 orchestrates cellular changes in keratinocytes in both physiological (self-renewal) and pathological (skin wound healing) contexts.

The developmental transcription factor IRF6 attenuates ABCG2 gene expression and distinctively reverses stemness phenotype in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC), which originates from the nasopharynx, is highly prevalent in Southern China and Southeast Asia, and more than 90% of all NPCs are non-keratinizing undifferentiated cells or poorly differentiated squamous cells. Cancer stem cells (CSCs) are capable of self-renewal and have differentiation potential. These properties form the basis of cancer initiation, development, and radiochemoresistance. However, the molecular mechanisms underlying NPC CSC maintenance remain poorly understood. Here, genomic expression profiling using our previously established monoclonal cellular and animal models revealed that interferon regulatory factor 6 (IRF6) was downregulated in highly metastatic NPC cells, cancer stem-like NPC cells and animal models. Functional assays revealed that elevated IRF6 expression suppressed cell proliferation, growth, CSCs properties and enhanced cell chemotherapeutic sensitivity. However, silencing IRF6 resulted in opposing effects. Moreover, we determined that as a tumor suppressor gene and transcription factor, IRF6 directly bound the upstream region of the ATP-binding cassette sub-family G member 2 (ABCG2) DNA element and suppressed target ABCG2 expression in NPC cells. Consistently, an inverse correlation was observed between the mRNA levels of IRF6 and ABCG2 in clinical NPC samples. With these results, we provide the first evidence that IRF6 directly targets the ABCG2 gene and selectively kills CSCs in NPC and that IRF6 may be a valuable tool for developing new CSC-targeted treatment strategies for undifferentiated NPC patients.

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.

CORRELATION BETWEEN INTRACELLULAR HEAT SHOCK PROTEIN 70 EXPRESSION AND CERVICAL LYMPH NODES ENLARGEMENT IN NASOPHARYNGEAL CARCINOMA

Tumor growth and metastasis in NPC patients suspected role of several molecular biomarkers that have been identified in tumor specimens of patients with NPC. Recent research states intracellular Hsp70 is a stress protein that is a main factor for the growth, invasion and metastasis of NPC. The purpose of this study is to analyze intracellular Hsp70 protein expression of NPC patients which correlate with staging of NPC as clinical manifestation. This study used cross sectional design. In this study, formalin-fixed paraffin-embedded biopsy specimens were obtained from 18 NPCs with all of histopathology and clinically divided into N0, N1, N2, N3. The expression of intracellular Hsp70 was obtained with immunohistochemistry using monoclonal antibody Anti Human Hsp70 antibodi from Santa Cruz Biotechnology, California, USA. Assessment of the staining was performed with Remmele methode by Histopathologies doctor Consultant. The Spearman’s test was used to determine the relationship between expression of intracellular Hsp70 protein and enlargement cervical nodul of NPC. Statistical significance was defined as p <0,05. There were 18 patients NPC patients that met the inclusion and exclusion criteria. Showed negative intracellular Hsp70 expression by 16,67% for all sample in which consist 1 patient of N0, 1 patient of N1, 1 patient of N2, 0 patient of N3. Followed by 27,78% mild positive intracellular Hsp70 expression which consist 0 patient of N0, 2 patients of N1, 0 patient of N2, 3 patients of N3. Followed by 44,44% moderate positive intracellular Hsp70 expression which consist 0 patient of N0, 0 patient of N1, 1 patient of N2, 9 patients of N3. Followed by 11,11% strongly positive intracellular Hsp70 expression which consist 0 patient of N0, 0 patient of N1, 0 patient of N2, 2 patients of N3. Spearman test results test scores p = 0.01 with a correlation coefficient 0.606. Correlation of intracellular Hsp70 protein expression with enlargement cervical nodul of lymphe (N0, N1, N2, N3) in patients with NPC showed significant (p<0.05). In conclusion, there was correlation between increase of the intacellular Hsp70 expression and enlargement cervical nodul of lymphe in nasopharyngeal carcinoma.

Expression levels of cleaved caspase-3 and caspase-3 in tumorigenesis and prognosis of oral tongue squamous cell carcinoma

Apoptosis plays a dual role in cancer development and malignancy. The role of apoptosis-related caspases in cancer remains controversial, particularly in oral tongue squamous cell carcinoma (OTSCC). In this study, we examined the protein levels of cleaved caspase-3, caspase-3, caspase-8, and caspase-9 on tissue microarrays consisting of samples from 246 OTSCC patients by immunohistochemistry. Wilcoxon signed-rank test indicated that the protein levels of cleaved caspase-3, caspase-3, caspase-8, and caspase-9 in tumor tissues were significantly higher compared to those in adjacent normal tissues (all p<0.001). The expression level of caspase-8 in tumors was elevated in patients with lymph node invasion. Moreover, positive expression of cleaved caspase-3 was associated with shorter disease-free survival (DFS) in OTSCC patients with moderate differentiation and lymph node invasion. Combination of either positive cleaved caspase-3 or higher caspase-3 expression or both was associated with poor DFS. Interestingly, stratification analysis showed that co-expression levels of positive cleaved caspase-3 or/and higher caspase-3 were associated with better disease-specific survival in patients with advanced stages of the disease, such as large tumor size and lymph node invasion, whereas it was associated with poor DFS in OTSCC patients with moderate cell differentiation and small tumor size. Taken together, cleaved caspase-3 and caspase-3/8/9 could be biomarkers for tumorigenesis in OTSCC patients. The co-expression level of cleaved caspase-3 and caspase-3 might be a prognostic biomarker for OTSCC patients, particular in those patients with certain tumor stages and cell differentiation status.

An Updated Review on Marine Anticancer Compounds: The Use of Virtual Screening for the Discovery of Small-Molecule Cancer Drugs

Marine secondary metabolites are a promising source of unexploited drugs that have a wide structural diversity and have shown a variety of biological activities. These compounds are produced in response to the harsh and competitive conditions that occur in the marine environment. Invertebrates are considered to be among the groups with the richest biodiversity. To date, a significant number of marine natural products (MNPs) have been established as antineoplastic drugs. This review gives an overview of MNPs, both in research or clinical stages, from diverse organisms that were reported as being active or potentially active in cancer treatment in the past seventeen years (from January 2000 until April 2017) and describes their putative mechanisms of action. The structural diversity of MNPs is also highlighted and compared with the small-molecule anticancer drugs in clinical use. In addition, this review examines the use of virtual screening for MNP-based drug discovery and reveals that classical approaches for the selection of drug candidates based on ADMET (absorption, distribution, metabolism, excretion, and toxicity) filtering may miss potential anticancer lead compounds. Finally, we introduce a novel and publically accessible chemical library of MNPs for virtual screening purposes.

Implementation of Nanoparticles in Cancer Therapy

Cancer is a wide group of diseases and generally characterized by uncontrolled proliferation of cells whose metabolic activities are disrupted. Conventionally, chemotherapy, radiotherapy, and surgery are used in the treatment of cancer. However, in theory, even a single cancer cell may trigger recurrence. Therefore, these treatments cannot provide high survival rate for deadly types. Identification of alternative methods in treatment of cancers is inevitable because of adverse effects of conventional methods. In the last few decades, nanotechnology developed by scientists working in different disciplines—physics, chemistry, and biology—offers great opportunities. It is providing elimination of both circulating tumor cells and solid cancer cells by targeting cancer cells. In this chapter, inadequate parts of conventional treatment methods, nanoparticle types used in new treatment methods of cancer, and targeting methods of nanoparticles are summarized; furthermore, recommendations of future are provided.

CD90 a potential cancer stem cell marker and a therapeutic target

Cancer Stem Cells (CSCs) have been recently identified and their role in carcinogenesis has been ascertained. CSCs have been correlated with high relapse in certain cancers, multiple drug resistance against chemotherapy and metastasis. Several markers such as CD133, CD24, CD44, EpCAM, and CD26 have been identified to isolate and characterize CSCs. None of these markers or their combinations are universal in nature and can be used to isolate CSCs from all types of cancer. CD90 is one such marker whose expression has been extensively studied in recent years. CD90+ cells have been isolated from several types of tumors and shown to exhibit cardinal properties of CSCs such as proliferation, differentiation, spheroid formation, metastasis and ability to form tumor xenograft in immunodeficient mice. It is also found to be co-expressed with several other CSC markers. CD90 is therefore, suggested as a candidate marker as well as a potential therapeutic target for elimination of CSCs.

Potential regulation of glioma through the induction of apoptosis signaling via Egl-9 family hypoxia-inducible factor 3

Glioma is an aggressive form of brain cancer that occurs following the abnormal proliferation of glial cells. Although glioma cannot spread to other organs, the morbidity and mortality rates of the disease are high, even following surgery, radiotherapy and chemotherapy. The function of Egl-9 family hypoxia-inducible factor 3 (Egln3) in cancer is controversial, and it is debated as to whether Egln3 positively or negatively regulates tumors. In the present study, a mouse model of low-grade glioma was successfully established. Through the use of immunohistochemical and western blot analyses, it was demonstrated that Egln3 expression in glioma tissue performed an important role in regulation by amplifying the signals for apoptosis, as determined by an increase in DNA fragments. Furthermore, Egln3 expression was inhibited by the administration of dimethyloxalylglycine, and the downregulated expression of Egln3 had marked effects on the regulation of glioma through apoptosis. The present study therefore provides evidence of an association between Egln3 expression and apoptosis in low-grade glioma.

The Progress and Prospects of Putative Biomarkers for Liver Cancer Stem Cells in Hepatocellular Carcinoma

Accumulating evidence suggests that hepatocellular carcinoma (HCC) is organized by liver cancer stem cells (LCSCs), which are a subset of cells with “stem-like” characteristics. Identification of the LCSCs is a fundamental and important problem in HCC research. LCSCs have been investigated by various stem cell biomarkers. There is still lack of consensus regarding the existence of a “global” marker for LCSCs in HCC. In this review article, we summarize the progress and prospects of putative biomarkers for LCSCs in the past decades, which is essential to develop future therapies targeting CSCs and to predict prognosis and curative effect of these therapies.

Monobenzyltin Complex C1 Induces Apoptosis in MCF-7 Breast Cancer Cells through the Intrinsic Signaling Pathway and through the Targeting of MCF-7-Derived Breast Cancer Stem Cells via the Wnt/β-Catenin Signaling Pathway

Monobenzyltin Schiff base complex, [N-(3,5-dichloro-2-oxidobenzylidene)-4-chlorobenzyhydrazidato](o-methylbenzyl)aquatin(IV) chloride, C1, is an organotin non-platinum metal-based agent. The present study was conducted to investigate its effects on MCF-7 cells with respect to the induction of apoptosis and its inhibitory effect against MCF-7 breast cancer stem cells. As determined in a previous study, compound C1 revealed strong antiproliferative activity on MCF-7 cells with an IC₅₀ value of 2.5 μg/mL. Annexin V/propidium iodide staining coupled with flow cytometry indicated the induction of apoptosis in treated cells. Compound C1 induced apoptosis in MCF-7 cells and was mediated through the intrinsic pathway with a reduction in mitochondrial membrane potential and mitochondrial cytochrome c release to cytosol. Complex C1 activated caspase 9 as a result of cytochrome c release. Subsequently, western blot and real time PCR revealed a significant increase in Bax and Bad expression and a significant decrease in the expression levels of Bcl2 and HSP70. Furthermore, a flow cytometric analysis showed that treatment with compound C1 caused a significant arrest of MCF-7 cells in G0/G1 phase. The inhibitory analysis of compound C1 against derived MCF-7 stem cells showed a significant reduction in the aldehyde dehydrogenase-positive cell population and a significant reduction in the population of MCF-7 cancer stem cells in primary, secondary, and tertiary mammospheres. Moreover, treatment with C1 down-regulated the Wnt/β-catenin self-renewal pathway. These findings indicate that complex C1 is a suppressive agent of MCF-7 cells that functions through the induction of apoptosis, cell cycle arrest, and the targeting of MCF-7-derived cancer stem cells. This work may lead to a better treatment strategy for the reduction of breast cancer recurrence.

Relationship between microvessel density and cancer stem cells in tumor angiogenesis: a meta-analysis

Aim: Several studies have shown that cancer stem cells (CSCs) promote tumor angiogenesis and are involved in tumor growth. A meta-analysis was conducted to evaluate the association between cancer stem cell markers expression and microvessel density (MVD). Methods: Relevant literature was identified from diverse databases. The Stata 12.0 and Review Manager 5.3 software were used to performed meta-analysis. Results: Sixteen studies investigating the correlation between CSCs and tumor angiogenesis were included in a total of 1409 cases. The result showed that positive CSC markers expression were associated with increased MVD count in human tumors and CSC-transplanted mouse tumor models (p < 0.0001). Conclusion: CSCs may be associated with angiogenesis during the growth and development of tumors.

Lgr5 expression is a valuable prognostic factor for colorectal cancer: evidence from a meta-analysis

Background

Lgr5 has recently been identified as a reliable biomarker of cancer stem cells (CSCs) in colorectal cancer (CRC); however, its prognostic value is still controversial.

Methods

We searched PubMed, Web of Science, and Wanfang databases with identical strategies to retrieve articles. We evaluated the impact of Lgr5 expression on survival of CRC patients through meta-analysis.

Results

A total of 12 studies comprising 2600 patients revealed that Lgr5 overexpression was negatively associated with overall survival (OS) (HR = 1.73, 95 % CI: 1.28–2.33; P = 0.00) and disease free survival (DFS) (HR = 2.89, 95 % CI: 1.89–4.44; P = 0.000) in CRC patients. Subgroup analysis suggested that Lgr5 overexpression was significantly associated with worse OS in subgroups with IHC as the method of Lgr5 assessment (HR = 2.01, 95 % CI: 1.39–2.89; P = 0.001), patients from Asia (HR = 1.81, 95 % CI: 1.27–2.58; P = 0.000), and NOS scores greater than 6 (HR = 2.12, 95 % CI: 1.41–3.19; P = 0.000). Furthermore, sensitivity analysis showed that the estimated HR ranged from 1.6 to 1.86 upon excluding one study sequentially from each analysis. In addition, Lgr5 overexpression was significantly associated with deep invasion of CRC (OR = 0.39, 95 % CI: 0.17–0.87; P = 0.002), lymphnode metastasis (OR = 0.45, 95 % CI: 0.26–0.76; P = 0.003), distant metastasis (OR = 0.37, 95 % CI: 0.22–0.62; P = 0.000), and AJCC stage (OR = 0.35, 95 % CI: 0.15–0.78; P = 0.01). However, Lgr5 overexpression was not correlated with tumor grade (OR = 0.75 95 % CI: 0.37–1.54; P = 0.433).

Conclusions

This study shows that Lgr5 can be a valuable and reliable prognostic factor of colorectal cancer progression.

Lgr5 expression is a valuable prognostic factor for colorectal cancer: evidence from a meta-analysis

Background

Lgr5 has recently been identified as a reliable biomarker of cancer stem cells (CSCs) in colorectal cancer (CRC); however, its prognostic value is still controversial.

Methods

We searched PubMed, Web of Science, and Wanfang databases with identical strategies to retrieve articles. We evaluated the impact of Lgr5 expression on survival of CRC patients through meta-analysis.

Results

A total of 12 studies comprising 2600 patients revealed that Lgr5 overexpression was negatively associated with overall survival (OS) (HR = 1.73, 95 % CI: 1.28–2.33; P = 0.00) and disease free survival (DFS) (HR = 2.89, 95 % CI: 1.89–4.44; P = 0.000) in CRC patients. Subgroup analysis suggested that Lgr5 overexpression was significantly associated with worse OS in subgroups with IHC as the method of Lgr5 assessment (HR = 2.01, 95 % CI: 1.39–2.89; P = 0.001), patients from Asia (HR = 1.81, 95 % CI: 1.27–2.58; P = 0.000), and NOS scores greater than 6 (HR = 2.12, 95 % CI: 1.41–3.19; P = 0.000). Furthermore, sensitivity analysis showed that the estimated HR ranged from 1.6 to 1.86 upon excluding one study sequentially from each analysis. In addition, Lgr5 overexpression was significantly associated with deep invasion of CRC (OR = 0.39, 95 % CI: 0.17–0.87; P = 0.002), lymphnode metastasis (OR = 0.45, 95 % CI: 0.26–0.76; P = 0.003), distant metastasis (OR = 0.37, 95 % CI: 0.22–0.62; P = 0.000), and AJCC stage (OR = 0.35, 95 % CI: 0.15–0.78; P = 0.01). However, Lgr5 overexpression was not correlated with tumor grade (OR = 0.75 95 % CI: 0.37–1.54; P = 0.433).

Conclusions

This study shows that Lgr5 can be a valuable and reliable prognostic factor of colorectal cancer progression.

Apoptotic and autophagic pathways with relevant small-molecule compounds, in cancer stem cells

Accumulating evidence demonstrates existence of cancer stem cells (CSCs), which are suspected of contributing to cancer cell self-renewal capacity and resistance to radiation and/or chemotherapy. Including evasion of apoptosis and autophagic cell death, CSCs have revealed abilities to resist cell death, making them appealing targets for cancer therapy. Recently, molecular mechanisms of apoptosis and of autophagy in CSCs have been gradually explored, comparing them in stem cells and in cancer cells; distinct expression of these systems in CSCs may elucidate how these cells exert their capacity of unlimited self-renewal and hierarchical differentiation. Due to their proposed ability to drive tumour initiation and progression, CSCs may be considered to be potentially useful pharmacological targets. Further, multiple compounds have been verified as triggering apoptosis and/or autophagy, suppressing tumour growth, thus providing new strategies for cancer therapy. In this review, we summarized regulation of apoptosis and autophagy in CSCs to elucidate how key proteins participate in control of survival and death; in addition, currently well-studied compounds that target CSC apoptosis and autophagy are selectively presented. With increasing attention to CSCs in cancer therapy, researchers are now trying to find responses to unsolved questions as unambiguous as possible, which may provide novel insight into future anti-cancer regimes.

Synthetic Glycosylated Ether Glycerolipids as Anticancer Agents

Glycosylated antitumor ether lipids (GAELs) are a class of synthetic antitumor ether lipids (AELs) with a sugar moiety in place of the phosphocholine found in the prototypical AEL, edelfosine. This chapter reviews the development of GAELs as antitumor agents. Studies on structure–activity relationships, mechanism of induction of cell death, metabolism, selectivity against cancer cells, toxicity, hemolysis and thrombogenic effects are discussed. The requirements for significant cytotoxic activity include a glycerol moiety, a cationic sugar other than mannose and an O- or C-glycosidic bond with either α- or β-configuration. Compounds with S- and N-glycosidic linkages are not very active. The most active GAEL to date, 1-O-hexadecyl-2-O-methyl-3-O-(2′-amino-2′-deoxy-α-d-galactopyranosyl)-sn-glycerol, displays greater in vitro activity than edelfosine, the AEL “gold standard”. The unique properties of GAELs as antitumor agents include their apoptotic-independent mechanism of inducing cell death and the ability to kill cancer stem cells. These characteristics of GAELs offer the potential for their development into chemotherapeutic agents to prevent the recurrence of tumors as well as for treatment against drug-resistant cancers.

Apoptosis inducing lead compounds isolated from marine organisms of potential relevance in cancer treatment

Apoptosis is a critical defense mechanism against the formation and progression of cancer and exhibits distinct morphological and biochemical traits. Targeting apoptotic pathways becomes an intriguing strategy for the development of chemotherapeutic agents particularly if the process is selective to cancer cells. Marine natural products have become important sources in the discovery of antitumour drugs, especially when recent technological and methodological advances have increased the scope of investigations of marine organisms. A high number of individual compounds from diverse organisms have induced apoptosis in several tumour cell lines via a number of mechanisms. Here, we review the effects of selected marine natural products and their synthetic derivatives on apoptosis signalling pathways in association with their pharmacological properties. Providing an outlook into the future, we also examine the factors that contribute to new discoveries and the difficulties associated with translating marine-derived compounds into clinical trials.

Distinctive effects of the cellular inhibitor of apoptosis protein c-IAP2 through stabilization by XIAP in glioblastoma multiforme cells

Inhibitor of apoptosis proteins (IAPs) are extensively involved in NFκB signaling pathways. Regulation of c-IAP2 turnover by other proteins was investigated in glioblastoma multiforme (GBM) cells in the present study. When overexpressed, X-linked IAP (XIAP) enhanced expression of ectopic c-IAP2, but not c-IAP1, and endogenous c-IAP2 levels were reduced once XIAP expression was silenced. TNFα stimulation substantially increased c-IAP2 expression, and this upregulation was impaired by suppression of XIAP. Similarly, when XIAP was limiting due to severe hypoxic conditions, c-IAP2 levels were downregulated. These data together indicate that XIAP is an important regulator responsible for stabilization of c-IAP2 levels under different conditions. Protein interactions occur through binding of BIR2 and BIR3 domains of c-IAP2 with the RING finger of XIAP. XIAP inhibition of c-IAP2 auto-degradation was dependent on this physical interaction, and it was independent of XIAP E3 ligase activity. Global c-IAP2 ubiquitination was not affected by XIAP, although c-IAP2 levels were significantly increased. A CARD-RING-containing fragment of c-IAP2 was found to target XIAP for proteasome-independent degradation, but it was unable to sensitize GBM cells to chemo-reagents. The XIAP-stabilized c-IAP2 was found to enhance IκB-α phosphorylation on serines 32 and 36, and to antagonize XIAP-induced increase in mature Smac and Bcl10. Taken together, our data identify a distinctive role of c-IAP2 as stabilizer of XIAP, which is likely involved in regulation of NFκB activation and apoptosis in GBM cells.

Side populations from cervical-cancer-derived cell lines have stem-cell-like properties

The target cells for the transforming mutations caused by high-risk human papillomavirus (HPV) infection could be the stem cells of the uterine cervical epithelium, generating particular cancer stem cells (CSCs). The aim of this study was to identify and characterize the CSCs from cervical-cancer-derived cell lines. The ability of SiHa, CaLo, and C-33A cell lines to efflux Hoechst 33342 was evaluated by flow cytometry and cells from the corresponding side populations (SPs) and nonside populations (NSPs) were analyzed for their cell-cycle status (pyronin Y) and their mRNA levels of ABC transporter family members (with qPCR). Specific markers (α6-integrin(bri)/CD71(dim), CK17) of normal epithelial stem cells were evaluated by flow cytometry. The biological properties of these cells were analyzed, including their colony heterogeneity, repopulation, and anchorage-independent colony formation. We identified SPs (around 3 %) in the SiHa and CaLo cell lines, more than 70 % of which were in G0 phase and strongly expressed ABC transporters (predominantly ABCG2 and ABCB1). The SP from CaLo cells showed an α6-integrin(bri)/CD(dim) pattern, whereas the SP from the SiHa cells showed an α6-integrin(-)/CD(dim) pattern. Recultured cells from the SPs of both cell lines generated both SPs and NSPs, and had higher clonogenic potential to form mainly holoclones and greater colony-forming efficiency under anchorage-independent growth conditions than the cells from the NSPs or total cell populations. Interestingly, we identified no SP in the HPV-uninfected C-33A cell line, and it did not express ABCG2 or other members of the ABC transporters (ABCB1, ABCC1, or ABCA3).

Nigericin selectively targets cancer stem cells in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is prevalent in southern China, northern Africa, and Alaska. The prognosis for NPC patients at early stage is good, while it is poor for patients at late stages. Cancer stem cells (CSCs) have been proposed to be associated with tumor initiation, relapse and metastasis, and the poor prognosis of NPC likely results from residual CSCs after therapy. Study on the therapy targeting CSCs in NPC remains poor, though it received intensive attentions in other cancers. Here, we used NPC cell lines with high and low proportion of CSCs as models to explore the effect of nigericin, an antibiotic, on CSCs. We found that nigericin could selectively target CSCs and sensitize CSCs in NPC to the widely used clinical drug cisplatin both in vitro and in vivo. Moreover, downregulation of the polycomb group protein Bmi-1 may contribute to the inhibitory effect of nigericin on CSCs. Furthermore, by using the in vitro NPC cell models, we found that nigericin could significantly decrease the migration and invasion abilities, which are known to be associated with CSCs. Taken together, our results suggest that nigericin can selectively target CSCs in NPC, which could be a candidate CSCs targeting drug for clinical evaluation.

Smac mimetics in combination with TRAIL selectively target cancer stem cells in nasopharyngeal carcinoma

Nasopharyngeal carcinoma is a common malignancy in Southern China. After radiotherapy and chemotherapy, a considerable proportion of patients with nasopharyngeal carcinoma suffered tumor relapse and metastasis. Cancer stem cells (CSC) have been shown with resistance against therapies and thus considered as the initiator of recurrence and metastasis in tumors, where the antiapoptotic property of CSCs play an important role. Smac/DIABLO is an inverse regulator for the inhibitors of apoptosis protein family (IAP), which have been involved in apoptosis. Here, the effects of Smac mimetics on the CSCs of nasopharyngeal carcinoma were studied both in vitro and in vivo, using two clones of nasopharyngeal carcinoma cell line CNE2 as models. We found that one of the clones, S18, had CSC-like properties and IAPs were overexpressed. The combination of Smac mimetics and TNF-related apoptosis-inducing ligand (TRAIL) can reduce the percentage of SP cells and inhibit the colony- and sphere-forming abilities of S18 cells, indicating their ability to attenuate the CSCs. Moreover, in a nasopharyngeal carcinoma xenograft model, the administration of Smac mimetics in combination with TRAIL also led to the elimination of nasopharyngeal carcinoma stem cells. Furthermore, the Smac mimetics in combination with TRAIL induced the degradation of cIAP1 and XIAP and thus induced apoptosis in vitro and in vivo. Taken together, our data show that Smac mimetics exerted an antitumor effect on nasopharyngeal carcinoma cancer stem cells, and this combination treatment should be considered as a promising strategy for the treatment of nasopharyngeal carcinoma.

Targeting cellular apoptotic pathway with peptides from marine organisms

Apoptosis is a critical defense mechanism against the formation and progression of cancer and exhibits distinct morphological and biochemical traits. Targeting apoptotic pathways becomes an intriguing strategy for the development of chemotherapeutic agents. Peptides from marine organisms have become important sources in the discovery of antitumor drugs, especially when modern technology makes it more and more feasible to collect organisms from seas. This primer summarizes several marine peptides, based on their effects on apoptotic signaling pathways, although most of these peptides have not yet been studied in depth for their mechanisms of action. Novel peptides that induce an apoptosis signal pathway are presented in association with their pharmacological properties.

Prognostic role of CD133 expression in colorectal cancer: a meta-analysis

Background

CD133 has been identified as a putative cancer stem cell marker in colorectal cancer (CRC). However, the clinical and prognostic significance of CD133 in CRC remains controversial.

Methods

Publications were identified which assessed the clinical or prognostic significance of CD133 in CRC up to October 2012. A meta-analysis was performed to clarify the association between CD133 expression and clinical outcomes.

Results

A total of 12 studies met the inclusion criteria, and comprised 3652 cases. Analysis of these data showed that CD133 was not significantly associated with the depth of CRC invasion (odds ratio [OR] = 1.44, 95% confidence interval [CI]: 0.77–2.68, Z = 1.15, P = 0.252) or tumor differentiation (OR = 0.63, 95% CI: 0.28–1.46, Z = −1.06, P = 0.286). Also, there was no statistically significant association of CD133 with lymph node metastasis (OR = 1.16, 95% CI: 0.87–1.54, Z = 1.05, P = 0.315) or lymphatic invasion (OR = 1.08, 95% CI: 0.81–1.43, Z = 0.53, P = 0.594). However, in identified studies, overexpression of CD133 was highly correlated with reduced overall survival (relative risk [RR] = 2.14, 95% CI: 1.45–3.17, Z = 3.81, P = 0.0001).

Conclusions

CD133 may play an important role in the progression of CRC, and overexpression of CD133 is closely related with poorer patient survival. If these findings are confirmed by well-designed prospective studies, CD133 may be a useful maker for clinical applications.

Targeting tumour-initiating cells with TRAIL based combination therapy ensures complete and lasting eradication of multiple myeloma tumours in vivo

Multiple myeloma (MM) remains an incurable disease despite improvements to available treatments and efforts to identify new drug targets. Consequently new approaches are urgently required. We have investigated the potential of native tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), in combination with doxorubicin, to induce apoptotic cell death in phenotypically distinct populations of myeloma cells in vitro and in vivo. The cytotoxic potential of TRAIL alone, and in combination with DOX, was assessed in vitro in purified CD138(+) and CD138(-) cells from the MM cell lines and samples from patients with MM. Mouse xenografts obtained by implanting CD138(-) MM cells were used to assess the efficacy of TRAIL, alone and in combination with DOX, in vivo. CD138(-) cells were shown to be more resistant to the cytotoxic activity of TRAIL than CD138(+) cells and have reduced expression of TRAIL death receptors. This resistance results in preferential killing of CD 138(+) cells during exposure of MM culture to TRAIL. Furthermore, prolonged exposure results in the appearance of TRAIL-resistant CD138(-) cells. However, when TRAIL is combined with doxorubicin, this results in complete eradication of MM cells in vivo. Most importantly, this treatment successfully eliminates CD138(-) cells implicated in tumour initiation and growth maintenance. These findings may explain the failure of current therapies and offer a promising new approach in the quest to cure MM and disseminated cancers.

Polymorphisms of the FAS and FASL genes and risk of breast cancer

FAS and its ligand FASL are crucial in apoptotic cell death. Loss of FAS and gain of aberrant FASL expression are common features of malignant transformation. This study was designed to investigate whether the functional polymorphisms of FAS -1377G/A (rs2234767) and FASL -844T/C (rs763110) affect the risk of developing breast cancer. Genotypes were analyzed by a polymerase chain reaction-restriction fragment length polymorphism assay in 436 breast cancer patients and 496 healthy controls. In this study, as compared to the wild-type homozygote and heterozygote, the distribution of the FAS -1377GG, GA and AA genotypes among breast cancer patients were significantly different from those among healthy controls (P=0.011), with the AA genotype being more prevalent among patients than the controls (P=0.003). Similarly, the frequencies of the FASL -844TT, TC and CC genotypes also significantly differed among breast cancer patients and healthy controls (P<0.001), with the CC genotype being significantly over-represented in breast cancer patients compared with the controls (P<0.001). In the unconditional logistic regression model following adjustment for age, the subjects carrying the FAS -1377AA genotype had a 1.75-fold increased risk [95% confidence interval (CI), 1.13-2.69] for development of breast cancer compared with patients carrying the GG genotype. Similarly, in the recessive model, the FASL -844CC genotype significantly increased the risk of breast cancer with an odds ratio (OR) of 1.92 (95% CI 1.46-2.54) compared with the TT or TT + TC genotypes. Our results suggest that functional polymorphisms in the death pathway genes FAS and FASL significantly contribute to the occurrence of breast cancer.

Antitumor peptides from marine organisms

The biodiversity of the marine environment and the associated chemical diversity constitute a practically unlimited resource of new antitumor agents in the field of the development of marine bioactive substances. In this review, the progress on studies of antitumor peptides from marine sources is provided. The biological properties and mechanisms of action of different marine peptides are described; information about their molecular diversity is also presented. Novel peptides that induce apoptosis signal pathway, affect the tubulin-microtubule equilibrium and inhibit angiogenesis are presented in association with their pharmacological properties. It is intended to provide useful information for further research in the fields of marine antitumor peptides.

Differentiation-inducing activity of hydroxycamptothecin on cancer stem-like cells derived from hepatocellular carcinoma

BACKGROUND

Hydroxycamptothecin (HCPT) is an anti-tumor agent that can induce differentiation in human cancer cells. Recent evidence indicates that side population (SP) cells possess characteristics of stem-like cells, and may be capable of initiating tumor growth.

AIMS

The present study investigated the differentiation of cancer stem-like cells derived from hepatocellular carcinoma.

METHODS AND RESULTS

Flow cytometry was used to isolated SP cells from HCC cell line (MHCC97 cells). These SP cells exhibit several stem-like cell characteristics that are distinct from the main population (MP) cells in vitro. After 3 days of induction with a low concentration of HCPT, the SP cells lost their capacity to proliferate and invade, and their tumorigenicity declined. Based on real-time quantitative RT-PCR, we also found that the expression of hepatocyte-specific markers such as α-fetoprotein, albumin, hepatocyte nuclear factor-4 and miR-122 gradually changed during the differentiation of SP cells.

CONCLUSIONS

Our data suggest that a low concentration of HCPT can induce hepatocyte-specific differentiation of cancer stem-like cells from MHCC97 cells, offering a possible therapeutic strategy for the treatment of human malignancies.

Immunotherapy of prostate cancer: should we be targeting stem cells and EMT?

Cancer stem cells have been implicated in a number of solid malignancies including prostate cancer. In the case of localised prostate cancer, patients are often treated with surgery (radical prostatectomy) and/or radiotherapy. However, disease recurrence is an issue in about 30% of patients, who will then go on to receive hormone ablation therapy. Hormone ablation therapy is often palliative in a vast proportion of individuals, and for hormone-refractory patients, there are several immunotherapies targeting a number of prostate tumour antigens which are currently in development. However, clinical responses in this setting are inconsistent, and it is believed that the failure to achieve full and permanent tumour eradication is due to a small, resistant population of cells known as 'cancer stem cells' (CSCs). The stochastic and clonal evolution models are among several models used to describe cancer development. The general consensus is that cancer may arise in any cell as a result of genetic mutations in oncogenes and tumour suppressor genes, which consequently result in uncontrolled cell growth. The cancer stem cell theory, however, challenges previous opinion and proposes that like normal tissues, tumours are hierarchical and only the rare subpopulation of cells at the top of the hierarchy possess the biological properties required to initiate tumourigenesis. Furthermore, where most cancer models infer that every cell within a tumour is equally malignant, i.e. equally capable of reconstituting new tumours, the cancer stem cell theory suggests that only the rare cancer stem cell component possess tumour-initiating capabilities. Hence, according to this model, cancer stem cells are implicated in both tumour initiation and progression. In recent years, the role of epithelial--mesenchymal transition (EMT) in the advancement of prostate cancer has become apparent. Therefore, CSCs and EMT are both likely to play critical roles in prostate cancer tumourigenesis. This review summarises the current immunotherapeutic strategies targeting prostate tumour antigens taking into account the need to consider treatments that target cancer stem cells and cells involved in epithelial--mesenchymal transition.

Colorectal cancer stem cells and cell death

Nowadays it is reported that, similarly to other solid tumors, colorectal cancer is sustained by a rare subset of cancer stem–like cells (CSCs), which survive conventional anticancer treatments, thanks to efficient mechanisms allowing escape from apoptosis, triggering tumor recurrence. To improve patient outcomes, conventional anticancer therapies have to be replaced with specific approaches targeting CSCs. In this review we provide strong support that BMP4 is an innovative therapeutic approach to prevent colon cancer growth increasing differentiation markers expression and apoptosis. Recent data suggest that in colorectal CSCs, protection from apoptosis is achieved by interleukin-4 (IL-4) autocrine production through upregulation of antiapoptotic mediators, including survivin. Consequently, IL-4 neutralization could deregulate survivin expression and localization inducing chemosensitivity of the colon CSCs pool.

Resistance to apoptosis-inducing stimuli in CD44+ head and neck squamous cell carcinoma cells

BACKGROUND

CD44 was identified previously as a surface marker in cancer stem cells (CSCs) of head and neck squamous cell carcinoma (HNSCC). Most cancer treatments have been linked to the activation of the apoptosis-signaling pathway; however, the resistance mechanisms to apoptosis in CSCs have not yet been fully elucidated.

METHODS

The sensitivity of CD44+ cells to diverse apoptosis-inducing stimuli was compared with that of CD44- cells. Furthermore, cell cycle changes and the expression of anti-apoptosis-related genes were examined using flow cytometry and real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

CD44+ cells were resistant to various apoptosis-inducing stimuli. Moreover, CD44+ cells showed a higher proportion of cells in G2/M phase of the cell cycle and upregulation of Bcl-2 and inhibitor of apoptosis (IAP) family genes compared with CD44- cells.

CONCLUSION

Treatment resistance in CSCs seems to be regulated by various mechanisms, and, therefore, additional treatment strategies to target CSCs are required in patients with HNSCC.

Bid and Bax are involved in granulosa cell apoptosis during follicular atresia in porcine ovaries

More than 99% of follicles undergo "atresia" during follicular development and growth. Follicular atresia is predominantly regulated by granulosa cell apoptosis. However, the intracellular signaling pathway of apoptosis in granulosa cells has not been revealed. In the present study, we examined changes in the expression of BH3-interacting domain death agonist (Bid) and Bcl-2-associated X protein (Bax), which are considered to promote the cell death ligand/receptor-mediated process in mitochondrion-dependent type II apoptosis, in porcine granulosa cells during atresia. Levels of mRNA and protein of Bid and Bax were determined by the reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting techniques, respectively. Levels of Bid and Bax mRNA and protein were markedly increased in granulosa cells of early atretic follicles compared with those of healthy follicles. In situ hybridization and immunohistochemical staining revealed that mRNA and protein of Bid and Bax were present in the granulosa cells, though only traces were found in healthy follicles; however, strong staining was noted in atretic follicles. These results indicate that Bid and Bax appear to be signal transduction factors in granulosa cells during follicular atresia and appear to play proapoptotic roles and confirm that the porcine granulosa cell is a mitochondrion-dependent type II apoptotic cell.

Targeting apoptosis pathways in cancer stem cells

There is a significant void in cancer biology with regard to the elucidation of the mechanisms that underlie tumor formation and progression. Recently, the existence of a hierarchy within cancer cell populations has been demonstrated experimentally for several tumor types. The identification of a tumor cell subset that is capable of self-renewal and, concurrently, generation into more differentiated progeny has engendered new perspectives toward selective targeting of tumors. Although the identification of the so-called "cancer stem cells" (CSCs) is a leap in the study of cancer ontogenesis, therapeutic targeting of such cells is plagued by significant difficulties. CSCs are able to evade the control mechanisms that regulate cell survival and proliferation. Apoptosis is one of the most critical and well-studied mechanisms, governing tissue development and homeostasis through a complex network of molecules that mediate death and survival signals. Escape from such a finely tuned death program is a prerequisite for any tumor-initiating cell. Thus, many compounds have been developed to target cancer cells and induce apoptosis directly or indirectly. Several TRAIL receptor agonists are in Phase I or II trials, and IAP inhibitors are undergoing clinical examination to exploit their ability to enhance ionizing radiation- and chemotherapy-induced apoptosis. Further, the EGF-R/Akt pro-survival signaling axis is one of the most frequently explored sources of targets for indirect apoptosis induction, as evidenced by the significant amount of molecules designed to target this pathway and have been approved by the FDA or are under clinical evaluation. Despite the promise of these magic bullets, the absence of reliable clinical models has considerably diminished the therapeutic potential of targeted therapies considerably. A more systematic molecular characterization of the tumor-initiating cell population in many tumors will allow us to refine the stimuli that force CSCs to die, thus accelerating the development of more effective treatment for cancer.

Cancer stem cells, models of study and implications of therapy resistance mechanisms

There is now compelling evidence for tumour initiating or cancer stem cells (CSCs) in human cancers. The current evidence of this CSC hypothesis, the CSC phenotype and methods of identification, culture and in vitro modelling will be presented, with an emphasis on prostate cancer. Inherent in the CSC hypothesis is their dual role, as a tumour-initiating cell, and as a source of treatment-resistant cells; the mechanisms behind therapeutic resistance will be discussed. Such resistance is a consequence of the unique CSC phenotype, which differs from the differentiated progeny, which make up the bulk of a tumour. It seems that to target the whole tumour, employing traditional therapies to target bulk populations alongside targeted CSC-specific drugs, provides the best hope of lasting treatment or even cure.

Stem cell characteristics of cell sub-populations in cell lines derived from head and neck cancers of Fanconi anemia patients

Increasing evidence indicates that cancer growth is driven by a sub-population of self-renewing cancer stem cells (CSCs) and that clinical problems of tumor recurrence after therapy may be related to differential resistance of CSCs to therapeutic elimination. Fanconi anemia (FA) is an autosomal recessive disorder associated with deficiencies of DNA repair and a greatly enhanced risk of hematopoietic malignancies and of head and neck squamous cell carcinoma (HNSCC). In FA patients, lack of DNA repair complicates therapies acting through DNA damage and alternative approaches, such as targeting signaling pathways associated with stem cell maintenance, might be of particular benefit. To assess effects of FA gene defects on the expression of stem cell properties, CSC patterns in cell lines derived from FA-related and sporadic HNSCC were compared. As for sporadic cell lines, FA cell lines showed colony morphologies associated with stem cell patterns. In all cell lines, cells with strong staining for CD44 (CD44(high) ) showed lower rates of apoptosis and a greater DNA damage induced block in the G2 phase of the cell cycle than CD44(low) cells. Mitomycin C, and UVB increased overall rates of apoptosis for both sporadic and FA cell lines, although FA cells tended to be more sensitive to apoptotic induction. Fluorescence activated cell sorting, immunohistochemistry, and QPCR indicated distinctly different patterns of gene expression of CD44(high) and CD44(low) cells in both sporadic and FA cell lines.

Targeting A20 decreases glioma stem cell survival and tumor growth

The A20 protein is a known inhibitor of apoptosis that here is shown to be a novel cancer stem cell-promoting factor associated with poor glioma patient survival.

Glioblastomas are deadly cancers that display a functional cellular hierarchy maintained by self-renewing glioblastoma stem cells (GSCs). GSCs are regulated by molecular pathways distinct from the bulk tumor that may be useful therapeutic targets. We determined that A20 (TNFAIP3), a regulator of cell survival and the NF-κB pathway, is overexpressed in GSCs relative to non-stem glioblastoma cells at both the mRNA and protein levels. To determine the functional significance of A20 in GSCs, we targeted A20 expression with lentiviral-mediated delivery of short hairpin RNA (shRNA). Inhibiting A20 expression decreased GSC growth and survival through mechanisms associated with decreased cell-cycle progression and decreased phosphorylation of p65/RelA. Elevated levels of A20 in GSCs contributed to apoptotic resistance: GSCs were less susceptible to TNFα-induced cell death than matched non-stem glioma cells, but A20 knockdown sensitized GSCs to TNFα-mediated apoptosis. The decreased survival of GSCs upon A20 knockdown contributed to the reduced ability of these cells to self-renew in primary and secondary neurosphere formation assays. The tumorigenic potential of GSCs was decreased with A20 targeting, resulting in increased survival of mice bearing human glioma xenografts. In silico analysis of a glioma patient genomic database indicates that A20 overexpression and amplification is inversely correlated with survival. Together these data indicate that A20 contributes to glioma maintenance through effects on the glioma stem cell subpopulation. Although inactivating mutations in A20 in lymphoma suggest A20 can act as a tumor suppressor, similar point mutations have not been identified through glioma genomic sequencing: in fact, our data suggest A20 may function as a tumor enhancer in glioma through promotion of GSC survival. A20 anticancer therapies should therefore be viewed with caution as effects will likely differ depending on the tumor type.

Glioblastomas are the most common and aggressive primary brain tumors in adults, with a median survival of only 12–15 months. Glioblastomas display a cellular hierarchy with a subset of cells having stem cell–like properties, including the capacity to self-renew and propagate tumors. Specific ablation of cancer stem cells is widely thought to be critical for effective and long-lasting treatment of cancers. We report the identification of the antiapoptotic protein A20 (which is also known as TNFAIP3) as a novel regulator of glioma stem cell survival. Glioma stem cells overexpress A20 relative to non-stem glioma cells, and this protects them from cell death, whereas depletion of A20 attenuates glioma stem cell survival and tumor growth. Interrogation of a molecular glioma database reveals that A20 levels correlate with decreased survival in patients. These data indicate that A20 is a tumor enhancer in the context of glioma, which importantly contrasts with its known function as a tumor suppressor in the context of lymphoma. Therefore, A20 may be a context-specific regulator of cancer stem cell survival and growth.