Limitations of the cancer stem cell theory

Stem Cell Origin of Cancer: Clinical Implications for Cancer Immunity and Immunotherapy

A simple way to understand the immune system is to separate the self from non-self. If it is self, the immune system tolerates and spares. If it is non-self, the immune system attacks and destroys. Consequently, if cancer has a stem cell origin and is a stem cell disease, we have a serious problem and a major dilemma with immunotherapy. Because many refractory cancers are more self than non-self, immunotherapy may become an uphill battle and pyrrhic victory in cancer care. In this article, we elucidate cancer immunity. We demonstrate for whom, with what, as well as when and how to apply immunotherapy in cancer care. We illustrate that a stem cell theory of cancer affects our perspectives and narratives of cancer. Without a pertinent theory about cancer's origin and nature, we may unwittingly perform misdirected cancer research and prescribe misguided cancer treatments. In the ongoing saga of immunotherapy, we are at a critical juncture. Because of the allure and promises of immunotherapy, we will be treating more patients not immediately threatened by their cancer. They may have more to lose than to gain, if we have a misconception and if we are on a wrong mission with immunotherapy. According to the stem cell theory of cancer, we should be careful with immunotherapy. When we do not know or realize that cancer originates from a stem cell and has stem-ness capabilities, we may cause more harm than good in some patients and fail to separate the truth from the myth about immunotherapy in cancer care.

miR-26b regulates cell proliferation and apoptosis of CD117+CD44+ ovarian cancer stem cells by targeting PTEN

Ovarian cancer (OC) is the one of the most common cancer in women globally. However, it still represents the most dangerous gynecologic malignancy even with the advances in detection and therapeutics. Thus, there is an urgent need in finding more effective therapeutic options for OC patients including cancer stem cells (CSC). MicroRNAs (miRNAs) are small, endogenous, and non-coding RNAs that play critical roles in the progression of various types of tumor. Our aim of this study was to find the regulatory function of microRNA-26 (miRNA-26b) on the cell proliferation and apoptosis of ovarian CSCs. Our studies show that miR-26b is under-regulated in human CD117+CD44+ ovarian CSCs. The miR-26b overexpression inhibits the cell proliferation and promotes cell apoptosis. Moreover, phosphatase and tensin homolog (PTEN) is found to be a functional target of miR-26b. Moreover, PTEN overexpression reversed the effects of miR-26b on the cell proliferation and apoptosis. PTEN overexpression remarkably accelerated the cell proliferation, and inhibited cell apoptosis. These results indicate that miR-26b regulates cell proliferation and apoptosis of CD117+CD44+ ovarian CSCs by targeting PTEN.>.

The Cross Talk between Cancer Stem Cells/Cancer Initiating Cells and Tumor Microenvironment: The Missing Piece of the Puzzle for the Efficient Targeting of these Cells with Immunotherapy

Cancer Stem Cells/Cancer Initiating Cells (CSCs/CICs) is a rare sub-population within a tumor that is responsible for tumor formation, progression and resistance to therapies. The interaction between CSCs/CICs and tumor microenvironment (TME) can sustain “stemness” properties and promote their survival and plasticity. This cross-talk is also pivotal in regulating and modulating CSC/CIC properties. This review will provide an overview of the mechanisms underlying the mutual interaction between CSCs/CICs and TME. Particular focus will be dedicated to the immunological profile of CSCs/CICs and its role in orchestrating cancer immunosurveillance. Moreover, the available immunotherapy strategies that can target CSCs/CICs and of their possible implementation will be discussed. Overall, the dissection of the mechanisms regulating the CSC/CIC-TME interaction is warranted to understand the plasticity and immunoregulatory properties of stem-like tumor cells and to achieve complete eradications of tumors through the optimization of immunotherapy.

Effects and mechanism of RhoC downregulation in suppressing ovarian cancer stem cell proliferation, drug resistance, invasion and metastasis

Cancer stem cells are considered to be the root cause of tumor initiation, metastasis, recurrence and therapeutic resistance. Recent studies have reported that RhoC plays a critical role in regulating cancer stem cells; however, its function in ovarian cancer stem cells (OCSCs) remains unknown. The ovarian cancer cell line A2780, and the paclitaxel-resistant A2780 cell line (A2780-PTX) were obtained. A2780 cells were used to isolate and identify the highly invasive A2780-PM cells, and A2780-PTX cells were used to isolate and identify the highly drug-resistant and highly invasive A2780-PTX-PM cells by Transwell assay. MTT, Transwell and wound healing assays were used to compare the differences in cell proliferation, invasion and migration ability among the four cell lines. Immunofluorescence was used to detect the expression of stem cell markers CD117 and CD133. OCSCs were sorted by flow cytometry. Following si-RhoC transfection of the OCSCs, cell proliferation, drug resistance, invasion and migration ability and RhoC, CD117 and CD133 expression levels were assayed. RT-PCR was used to assess RhoC, CD117, CD133 and matrix metalloproteinase 9 (MMP9) mRNA expression levels. A2780-PM and A2780‑PTX-PM cells exhibited higher cell proliferation, drug resistance, and invasion and migration ability than the A2780 and A2780-PTX cell lines. Furthermore, CD133 and CD117 expression levels were higher in the A2780-PM and A2780‑PTX-PM cells than levels in the A2780 and A2780-PTX cells. Transfection of si-RhoC in OCSCs suppressed the proliferation, drug resistance, invasion, migration and CD117 and CD133 expression levels. Furthermore, the expression levels of RhoC, CD117, CD133, MDR1, and MMP9 mRNA were downregulated in the transfected population. Taken together, our results demonstrated that RhoC downregulation may inhibit the proliferation, drug resistance, invasion and migration of OCSCs, and RhoC may play an important role in the formation of OCSCs.

The role of Nanog expression in tamoxifen-resistant breast cancer cells

There is an accumulation of evidence that shows a significant role of cancer stem cells in tumor initiation, proliferation, relapse, and metastasis. Nanog is the most important core transcription marker of stem cells, known by its role in maintaining pluripotency, proliferation, and differentiation. Therefore, this study aimed to examine the role of Nanog in breast cancer cell tamoxifen resistance and its implications in breast cancer treatment. In this study, the expression of the three core transcription markers Nanog, Oct3/4, and Sox2 were quantitatively evaluated using flow cytometry. Then, small interfering RNA (siRNA) against human Nanog was transfected into tamoxifen-resistant breast cancer cells via Lipofectamine 2000. Nanog gene expression in the cells was detected using reverse transcription polymerase chain reaction (RT-PCR). The change in cell proliferation was evaluated using the tetrazolium bromide method. An enzyme-linked immunosorbent assay was used to detect apoptosis of the transfected cells alone and in combination with 4-hydroxytamoxifen. The results showed a high level expression of Nanog, Oct3/4, and Sox2 in MDA-MB-231 and MCF7/tamoxifen resistant cells compared with MCF7/wild-type. siRNA-mediated Nanog gene silencing can efficiently inhibit cell proliferation and induce apoptosis of tamoxifen-resistant breast cancer cells. This study provides a basis for further study of the role of Nanog in developing resistance to tamoxifen, its implication in breast cancer management, and as a new strategy to enhance response to endocrine therapy.

Towards dissecting molecular routes of intercellular communication in the tumour microenvironment: phenotypic plasticity of stem cell-associated markers in co-culture (carcinoma cell/fibroblast) systems

Increasing evidence attributes tumour fates to a small population of cells (cancer stem cells) capable of surviving therapeutic interventions. Investigation of their characteristics, especially in cross-talk with other cell types of the tumour microenvironment, can pave the way to innovative therapeutic concepts. The central issue of this study was to evaluate the impact of stroma on tumour cells with stem cell-like features in a squamous cell carcinoma model (FaDu). Six different types of experimental conditions were tested using distinct compositions of the culture system, and both morphologic and molecular features of the tumour cells were analysed. In detail, FaDu cells alone were used as a control, compared to tumour cells from co-culture, with squamous cell cancer-derived stromal fibroblasts or normal skin human fibroblasts, both in the direct and indirect (insert) systems, adding analysis of side population cells of FaDu culture. Measurements were taken on days 2, 7 and 9 of culture and immediately after preparation in the case of the side population. A panel of antibodies against keratins 8, 10, 19, stem cell markers CD29, CD44, CD133, as well as biotinylated adhesion/growth-regulatory galectin 1 served as a toolbox for phenotypic characterization. Co-culture with fibroblasts prepared from tumour stroma and with dermal fibroblasts affected marker presentation, maintaining an undifferentiated stage phenotypically related to stem cells. Side-population cells showed close relationship to cancer stem cells in these characteristics. In conclusion, normal and tumour stromal fibroblasts are capable of shifting the marker expression profile of FaDu cells to a stem cell-like phenotypic pattern in co-culture.

Cancer stem cell: implications in cancer biology and therapy with special reference to lung cancer

The cancer stem cell (CSC) theory is currently central to the field of cancer research, because it is not only a matter of academic interest but also crucial in cancer therapy. CSCs share a variety of biological properties with normal somatic stem cells in terms of self-renewal, the propagation of differentiated progeny, the expression of specific cell markers and stem cell genes, and the utilization of common signaling pathways and the stem cell niche. However, CSCs differ from normal stem cells in their tumorigenic activity. Thus, CSCs are also termed cancer initiating cells. In this paper, we briefly review hitherto described study results and refer to some excellent review articles to understand the basic properties of CSCs. In addition, we focus upon CSCs of lung cancers, since lung cancer is still increasing in incidence worldwide and remains the leading cause of cancer deaths. Understanding the properties of, and exploring cell markers and signaling pathways specific to, CSCs of lung cancers, will lead to progress in therapy, intervention, and improvement of the prognosis of patients with lung cancer. In the near future, the evaluation of CSCs may be a routine part of practical diagnostic pathology.