Therapeutic targeting of cancer stem cells

The Immune Privilege of Cancer Stem Cells: A Key to Understanding Tumor Immune Escape and Therapy Failure

Cancer stem cells (CSCs) are broadly considered immature, multipotent, tumorigenic cells within the tumor mass, endowed with the ability to self-renew and escape immune control. All these features contribute to place CSCs at the pinnacle of tumor aggressiveness and (immune) therapy resistance. The immune privileged status of CSCs is induced and preserved by various mechanisms that directly affect them (e.g., the downregulation of the major histocompatibility complex class I) and indirectly are induced in the host immune cells (e.g., activation of immune suppressive cells). Therefore, deeper insights into the immuno-biology of CSCs are essential in our pursuit to find new therapeutic opportunities that eradicate cancer (stem) cells. Here, we review and discuss the ability of CSCs to evade the innate and adaptive immune system, as we offer a view of the immunotherapeutic strategies adopted to potentiate and address specific subsets of (engineered) immune cells against CSCs.

What to Do for Increasing Cancer Burden on the African Continent? Accelerating Public Health Diagnostics Innovation for Prevention and Early Intervention on Cancers

No other place illustrates the increasing burden of cancer than in Africa and in particular, sub-Saharan Africa. Many of the individuals to be diagnosed with cancer will be in low-resource settings in the future due to, for example, an increase in populations and aging, and high co-morbidity with infections with viruses such as human immunodeficiency virus (HIV) and human papillomavirus (HPV), as well as the presence of infectious agents linked to cancer development. Due to lack of prevention and diagnostic innovation, patients present with advanced cancers, leading to poor survival and increased mortality. HIV infection-associated cancers such as B cell lymphomas, Kaposi's sarcoma, and HPV-associated cancers such as cervical cancer are particularly noteworthy in this context. Recent reports show that a host of other cancers are also associated with viral infection and these include lung, oral cavity, esophageal, and pharyngeal, hepatocellular carcinoma, and anal and vulvar cancers. This article examines the ways in which diagnostic innovation empowered by integrative biology and informed by public health priorities can improve cancer prevention or early intervention in Africa and beyond. In addition, I argue that because diagnostic biomarkers can often overlap with novel therapeutic targets, diagnostics research and development can have broader value for and impact on medical innovation.

Novel Therapeutics Against Breast Cancer Stem Cells by Targeting Surface Markers and Signaling Pathways

Background:

Breast cancer remains to be one of the deadliest forms of cancers, owing to the drug resistance and tumor relapse caused by breast cancer stem cells (BCSCs) despite notable advancements in radio-chemotherapies.

Objective:

To find out novel therapeutics against breast cancer stem cells by aiming surface markers and signaling pathways.

Methods:

A systematic literature search was conducted through various electronic databases including, Pubmed, Scopus, Google scholar using the keywords "BCSCs, surface markers, signaling pathways and therapeutic options against breast cancer stem cell. Articles selected for the purpose of this review were reviewed and extensively analyzed.

Results:

Novel therapeutic strategies include targeting BCSCs surface markers and aberrantly activated signaling pathways or targeting their components, which play critical roles in self-renewal and defense, have been shown to be significantly effective against breast cancer. In this review, we represent a number of ways against BCSCs surface markers and hyper-activated signaling pathways to target this highly malicious entity of breast cancer more effectively in order to make a feasible and useful strategy for successful breast cancer treatment. In addition, we discuss some characteristics of BCSCs in disease progression and therapy resistance.

Conclusion:

BCSCs involved in cancer pathogenesis, therapy resistance and cancer recurrence. Thus, it is suggested that a multi-dimensional therapeutic approach by targeting surface markers and aberrantly activated signaling pathways of BCSCs alone or in combination with each other could really be worthwhile in the treatment of breast cancer.

Breast cancer stem cells and the challenges of eradication: a review of novel therapies

Breast cancer is a heterogeneous disease that accounts for 30% of all cancers diagnosed in women and over half a million deaths per year. Cancer stem cells (CSCs) make up a small subpopulation of cells within a tumor, are capable of self-renewal and, are responsible for tumor initiation, formation, and recurrence. Breast CSCs (BCSCs) have been the subject of concentrated research as potential targets for breast cancer therapies. Cell surface markers CD44+/CD24- have been established as minimum biomarkers for BCSCs and the upregulation of CD44 expression has been linked to tumor formation in numerous cancers. Additionally, the deregulation of Notch, Wnt/Frizzled/β-catenin, Hippo, and Hedgehog signaling pathways is believed to be responsible for the formation of CSCs and lead to tumor formation. Tumor heterogeneity is a key feature of therapy resistance and a major challenge. CSCs are predominantly senescent and inherently immune to chemotherapy drugs which rely on an overactive cell cycle. Current therapeutic strategies include targeting CSC signaling pathways that play critical roles in self-renewal and defense. Anti-CD44 antibodies have been shown to induce terminal differentiation in CSCs resulting in a significant decrease in tumor metastasis. Additionally, targeting the tumor microenvironment has been shown to increase the effectiveness of chemotherapy drugs. In this review, we attempt to provide an overview of breast cancer, the stem of its cause, and novel therapies currently being explored.

Cigarette smoke stimulates the stemness of renal cancer stem cells via Sonic Hedgehog pathway

Cancer stem cells (CSCs) are essentially responsible for tumor initiation, growth, progression, metastasis and recurrence, and cigarette smoke (CS) is closely involved in the occurrence and development of kidney cancer. However, the effect of CS on renal CSCs has not been elucidated yet. In the present study, tumorsphere formation assay was used to enrich renal CSCs from 786-O and ACHN cells. We illustrated that CS effectively promoted renal CSCs stemness by enhancing tumorsphere formation, increasing the expression of renal CSCs markers (CD133, CD44, ALDHA1, Oct4, and Nanog) and elevating CD133+ cell population. Moreover, our results showed that CS triggered the activation of Sonic Hedgehog (SHH) pathway, while inhibition of SHH pathway dampened the promotive effects of CS on renal CSCs. Finally, higher levels of renal CSCs markers and SHH pathway-related proteins were observed in kidney cancer tissues from smokers than non-smoking cancer tissues. Taken together, these results demonstrated the important role of SHH pathway in regulating CS-induced renal CSCs stemness augment. Findings from this study could provide new insight into the molecular mechanisms of CS-elicited stemness of renal CSCs.

Overexpression of Large-Conductance Calcium-Activated Potassium Channels in Human Glioblastoma Stem-Like Cells and Their Role in Cell Migration

Glioblastomas (GBMs) are brain tumors characterized by diffuse invasion of cancer cells into the healthy brain parenchyma, and establishment of secondary foci. GBM cells abundantly express large-conductance, calcium-activated potassium (BK) channels that are thought to promote cell invasion. Recent evidence suggests that the GBM high invasive potential mainly originates from a pool of stem-like cells, but the expression and function of BK channels in this cell subpopulation have not been studied. We investigated the expression of BK channels in GBM stem-like cells using electrophysiological and immunochemical techniques, and assessed their involvement in the migratory process of this important cell subpopulation. In U87-MG cells, BK channel expression and function were markedly upregulated by growth conditions that enriched the culture in GBM stem-like cells (U87-NS). Cytofluorimetric analysis further confirmed the appearance of a cell subpopulation that co-expressed high levels of BK channels and CD133, as well as other stem cell markers. A similar association was also found in cells derived from freshly resected GBM biopsies. Finally, transwell migration tests showed that U87-NS cells migration was much more sensitive to BK channel block than U87-MG cells. Our data show that BK channels are highly expressed in GBM stem-like cells, and participate to their high migratory activity. J. Cell. Physiol. 232: 2478-2488, 2017. © 2016 Wiley Periodicals, Inc.

Improvements in Clinical Trials Information Will Improve the Reproductive Health and Fertility of Cancer Patients

There are a number of barriers that result in cancer patients not being referred for oncofertility care, which include knowledge about reproductive risks of antineoplastic agents. Without this information, clinicians do not always make recommendations for oncofertility care. The objective of this study was to describe the level of reproductive information and recommendations that clinicians have available in clinical trial protocols regarding oncofertility management and follow-up, and the information that patients may receive in clinical trials patient information sheets or consent forms. A literature review of the 71 antineoplastic drugs included in the 68 clinical trial protocols showed that 68% of the antineoplastic drugs had gonadotoxic animal data, 32% had gonadotoxic human data, 83% had teratogenic animal data, and 32% had teratogenic human data. When the clinical trial protocols were reviewed, only 22% of the protocols reported the teratogenic risks and 32% of the protocols reported the gonadotoxic risk. Only 56% of phase 3 protocols had gonadotoxic information and 13% of phase 3 protocols had teratogenic information. Nine percent of the protocols provided fertility preservation recommendations and 4% provided reproductive information in the follow-up and survivorship period. Twenty-six percent had a section in the clinical trials protocol, which identified oncofertility information easily. When gonadotoxic and teratogenic effects of treatment were known, they were not consistently included in the clinical trial protocols and the lack of data for new drugs was not reported. Very few protocols gave recommendations for oncofertility management and follow-up following the completion of cancer treatment. The research team proposes a number of recommendations that should be required for clinicians and pharmaceutical companies developing new trials.

Targeting self-renewal pathways in cancer stem cells: clinical implications for cancer therapy

Extensive cancer research in the past few decades has identified the existence of a rare subpopulation of stem cells in the grove of cancer cells. These cells are known as the cancer stem cells marked by the presence of surface biomarkers, multi-drug resistance pumps and deregulated self-renewal pathways (SRPs). They have a crucial role in provoking cancer cells leading to tumorigenesis and its progressive metastasis. Cancer stem cells (CSCs) are much alike to normal stem cells in their self-renewal mechanisms. However, deregulations in the SRPs are seen in CSCs, making them resistant to conventional chemotherapeutic agents resulting in the tumor recurrence. Current treatment strategies in cancer fail to detect and differentiate the CSCs from their non-tumorigenic progenies owing to absence of specific biomarkers. Now, it has become imperative to understand complex functional biology of CSCs, especially the signaling pathways to design improved treatment strategies to target them. It is hopeful that the SRPs in CSCs offer a promising target to alter their survival strategies and impede their tumorigenic potential. However, there are many perils associated with the direct targeting method by conventional therapeutic agents such as off targets, poor bioavailability and poor cellular distribution. Recent evidences have shown an increased use of small molecule antagonists directly to target these SRPs may lead to severe side-effects. An alternative to solve these issues could be an appropriate nanoformulation. Nanoformulations of these molecules could provide an added advantage for the selective targeting of the pathways especially Hedgehog, Wnt, Notch and B-cell-specific moloney murine leukemia virus integration site 1 in the CSCs while sparing the normal stem cells. Hence, to achieve this goal a complete understanding of the molecular pathways corroborate with the use of holistic nanosystem (nanomaterial inhibition molecule) could possibly be an encouraging direction for future cancer therapy.

Cancer stem cells: are they responsible for treatment failure?

Overcoming resistance to standard anticancer treatments represents a significant challenge. The interest regarding cancer stem cells, a cellular population that has the ability to self-renew and to propagate the tumor, was prompted by experimental evidence delineating the molecular mechanisms that are selectively activated in this cellular subset in order to survive chemotherapy. This has also stimulated combination strategies aimed at rendering cancer stem cells vulnerable to anticancer agents. Moreover, cancer stem cells offer a unique opportunity for modeling human cancers in mice, thus emerging as a powerful tool for testing novel drugs and combinations in a simulation of human disease. These novel animal models may lay the foundation for a new generation of clinical trials aimed at anticipating the benefit to patients of anticancer therapies.

The Hippo transducers TAZ and YAP in breast cancer: oncogenic activities and clinical implications

The Hippo signalling is emerging as a tumour suppressor pathway whose function is regulated by an intricate network of intracellular and extracellular cues. Defects in the signal cascade lead to the activation of the Hippo transducers TAZ and YAP. Compelling preclinical evidence showed that TAZ/YAP are often aberrantly engaged in breast cancer (BC), where their hyperactivation culminates into a variety of tumour-promoting functions such as epithelial-to-mesenchymal transition, cancer stem cell generation and therapeutic resistance. Having acquired a more thorough understanding in the biology of TAZ/YAP, and the molecular outputs they elicit, has prompted a first wave of exploratory, clinically-focused analyses aimed at providing initial hints on the prognostic/predictive significance of their expression. In this review, we discuss oncogenic activities linked with TAZ/YAP in BC, and we propose clinical strategies for investigating their role as biomarkers in the clinical setting. Finally, we address the therapeutic potential of TAZ/YAP targeting and the modalities that, in our opinion, should be pursued in order to further study the biological and clinical consequences of their inhibition.

Improving cancer therapy by targeting cancer stem cells: Directions, challenges, and clinical results

Cancer stem cells (CSC) are a rare cell population within a tumor characterized by the ability to form tumors following injection into an immunocompromised host. While the role of CSC has been clearly established in animal models, evidence of their clinical relevance has been harder to demonstrate. A number of markers, or combination thereof, have been used to detect and measure, although non-specifically, CSC in almost all human tumors. Several pathways have been identified as crucial for, but not necessarily unique to, CSC survival and proliferation, and novel agents have been designed to target such pathways. A number of such agents have entered early phase development. Further, drugs that have long been marketed for non-oncological indications have been redirected to oncology as they appear to affect one or more of such pathways. This article aims to review the available evidence on the clinical relevance of CSC from a drug development standpoint and the results of early phase clinical trials of agents interfering with the above pathways. It also discusses limitations of current clinical trial design and endpoints to demonstrate anti-CSC activity as well as possible strategies to overcome these limitations.

Deconstructing breast cancer cell biology and the mechanisms of multidrug resistance

Cancer complexity constantly challenges the way that clinicians manage breast cancer therapy. Tumor heterogeneity and intratumoral stroma characteristics allow cells with different phenotypes and deregulated apoptotic, proliferative and migration abilities to co-exist contributing to a disappointing therapeutic response. While new approaches are being associated with conventional chemotherapy, such as hormonal therapy or target monoclonal antibodies, recurrence and metastasization are still observed. Membrane transporters are the cell's first line of contact with anticancer drugs having a major role in multidrug resistance events. This structural-based activity enables the cell to be drug-resistant by decreasing drug intracellular concentration through an efflux-transport mechanism, mainly associated with overexpression of ATP-binding cassette (ABC) proteins. This review focuses on some of the important structural and biological properties of the malignant cell and tumor microenvironment, addressing the role of the membrane ABC transporters in therapeutic outcomes, and highlighting related molecular pathways that may represent meaningful target therapies.

Role of integrated cancer nanomedicine in overcoming drug resistance

Cancer remains a major killer of mankind. Failure of conventional chemotherapy has resulted in recurrence and development of virulent multi drug resistant (MDR) phenotypes adding to the complexity and diversity of this deadly disease. Apart from displaying classical physiological abnormalities and aberrant blood flow behavior, MDR cancers exhibit several distinctive features such as higher apoptotic threshold, aerobic glycolysis, regions of hypoxia, and elevated activity of drug-efflux transporters. MDR transporters play a pivotal role in protecting the cancer stem cells (CSCs) from chemotherapy. It is speculated that CSCs are instrumental in reviving tumors after the chemo and radiotherapy. In this regard, multifunctional nanoparticles that can integrate various key components such as drugs, genes, imaging agents and targeting ligands using unique delivery platforms would be more efficient in treating MDR cancers. This review presents some of the important principles involved in development of MDR and novel methods of treating cancers using multifunctional-targeted nanoparticles. Illustrative examples of nanoparticles engineered for drug/gene combination delivery and stimuli responsive nanoparticle systems for cancer therapy are also discussed.

Biological and clinical implications of cancer stem cells in primary brain tumors

Despite therapeutic advances, glioblastoma multiforme (GBM) remains a lethal disease. The infiltrative nature of this disease and the presence of a cellular population resistant to current medical treatments account for the poor prognosis of these patients. Growing evidence indicates the existence of a fraction of cancer cells sharing the functional properties of adult stem cells, including self-renewal and a greater ability to escape chemo-radiotherapy-induced death stimuli. Therefore, these cells are commonly defined as cancer stem cells (GBM-SCs). The initial GBM-SC concept has been challenged, and refined according to the emerging molecular taxonomy of GBM. This allowed to postulate the existence of multiple CSC types, each one driving a given molecular entity. Furthermore, it is becoming increasingly clear that GBM-SCs thrive through a dynamic and bidirectional interaction with the surrounding microenvironment. In this article, we discuss recent advances in GBM-SC biology, mechanisms through which these cells adapt to hostile conditions, pharmacological strategies for selectively killing GBM-SCs, and how novel CSC-associated endpoints have been investigated in the clinical setting.