Heterogeneity is an omnipresent feature of mammalian cells in vitro and in vivo. It has been recently realized that even mouse and human embryonic stem cells under the best culture conditions are ...heterogeneous containing pluripotent as well as partially committed cells. Somatic stem cells in adult organs are also heterogeneous, containing many subpopulations of self-renewing cells with distinct regenerative capacity. The differentiated progeny of adult stem cells also retain significant developmental plasticity that can be induced by a wide variety of experimental approaches. Like normal stem cells, recent data suggest that cancer stem cells （CSCs） similarly display significant phenotypic and functional heterogeneity, and that the CSC progeny can manifest diverse plasticity. Here, I discuss CSC hetero- geneity and plasticity in the context of tumor development and progression, and by comparing with normal stem cell development. Appreciation of cancer cell plasticity entails a revision to the earlier concept that only the tumorigenic subset in the tumor needs to be targeted. By understanding the interrelationship between CSCs and their differentiated progeny, we can hope to develop better therapeutic regimens that can prevent the emergence of tumor cell variants that are able to found a new tumor and distant metastases.
Prostate cancer (PCa) is a prevalent malignancy that occurs primarily in old males. Prostate tumors in different patients manifest significant inter-patient heterogeneity with respect to ...histo-morphological presentations and molecular architecture. An individual patient tumor also harbors genetically distinct clones in which PCa cells display intra-tumor heterogeneity in molecular features and phenotypic marker expression. This inherent PCa cell heterogeneity, e.g., in the expression of androgen receptor (AR), constitutes a barrier to the long-term therapeutic efficacy of AR-targeting therapies. Furthermore, tumor progression as well as therapeutic treatments induce PCa cell plasticity such that AR-positive PCa cells may turn into AR-negative cells and prostate tumors may switch lineage identity from adenocarcinomas to neuroendocrine-like tumors. This induced PCa cell plasticity similarly confers resistance to AR-targeting and other therapies. In this review, I first discuss PCa from the perspective of an abnormal organ development and deregulated cellular differentiation, and discuss the luminal progenitor cells as the likely cells of origin for PCa. I then focus on intrinsic PCa cell heterogeneity in treatment-naïve tumors with the presence of prostate cancer stem cells (PCSCs). I further elaborate on PCa cell plasticity induced by genetic alterations and therapeutic interventions, and present potential strategies to therapeutically tackle PCa cell heterogeneity and plasticity. My discussions will make it clear that, to achieve enduring clinical efficacy, both intrinsic PCa cell heterogeneity and induced PCa cell plasticity need to be targeted with novel combinatorial approaches.
A tumor originates from a normal cell that has undergone tumorigenic transformation as a result of genetic mutations. This transformed cell is the cell-of-origin for the tumor. In contrast, an ...established clinical tumor is sustained by subpopulations of self-renewing cancer cells operationally called cancer stem cells (CSC) that can generate, intraclonally, both tumorigenic and nontumorigenic cells. Identifying and characterizing tumor cell-of-origin and CSCs should help elucidate tumor cell heterogeneity, which, in turn, should help understand tumor cell responses to clinical treatments, drug resistance, tumor relapse, and metastatic spread. Both tumor transplantation and lineage-tracing assays have been helpful in characterizing these cancer cell populations, although each system has its strengths and caveats. In this article, we briefly review and summarize advantages and limitations of both assays in support of a combinatorial approach to accurately define the roles of both cancer-initiating and cancer-propagating cells. As an aside, we also wish to clarify the definitions of cancer cell-of-origin and CSCs, which are often interchangeably used by mistake.
Androgen receptor (AR), a ligand-dependent nuclear transcription factor and a member of steroid hormone receptor family, plays an important role in prostate organogenesis by regulating epithelial ...differentiation and restricting cell proliferation. Although rarely mutated or amplified in treatment-naïve prostate cancer (PCa), AR signaling drives tumor growth and as a result, therapies that aim to inhibit AR signaling, called ARSIs (AR signaling inhibitors), have been in clinical use for >70 years. Unfortunately, the clinical efficacy of ARSIs is short-lived and the majority of treated patients develop castration-resistant PCa (CRPC). Numerous molecular mechanisms have been proposed for castration resistance; however, the cellular basis for CRPC emergence has remained obscure. One under-appreciated cellular mechanism for CRPC development is the AR heterogeneity that pre-exists in treatment-naive primary tumors, i.e., although most PCa cells express AR (i.e., AR+), there is always a population of PCa cells that express no/low AR (i.e., AR−/lo). Importantly, this AR heterogeneity becomes accentuated during ARSI treatment and highly prominent in established CRPC. Here, we provide a succinct summary of AR heterogeneity across the PCa continuum and discuss its impact on PCa response to treatments. While AR+ PCa cells/clones exhibit exquisite sensitivities to ARSIs, AR−/lo PCa cells/clones, which are greatly enriched in stem cell signaling pathways, display de novo resistance to ARSIs. Finally, we offer several potential combinatorial strategies, e.g., ARSIs with stem cell targeting therapeutics, to co-target both AR+ and AR−/lo PCa cells and metastatic clones.
•Discussed the dichotomous AR biological functions as a tumor suppressor vs. an oncogenic driver.•Presented an updated list of ‘AR-interacting’ proteins.•Focused on AR heterogeneity in subcellular localizations and expression levels.•Discussed the impact of AR heterogeneity on therapy response/resistance.•Highlighted several signaling pathways and offered potential therapeutic strategies in the AR−/lo PCa.
It is becoming increasingly clear that virtually all types of human cancers harbor a small population of stem-like cancer cells (i.e., cancer stem cells, CSCs). These CSCs preexist in primary tumors, ...can self-renew and are more tolerant of standard treatments, such as antimitotic and molecularly targeted agents, most of which preferentially eliminate differentiated and proliferating cancer cells. CSCs are therefore postulated as the root of therapy resistance, relapse and metastasis. Aside from surgery, radiation, and chemotherapy, immunotherapy is now established as the fourth pillar in the therapeutic armamentarium for patients with cancer, especially late-stage and advanced cancers. A better understanding of CSC immunological properties should lead to development of novel immunologic approaches targeting CSCs, which, in turn, may help prevent tumor recurrence and eliminate residual diseases. Here, with a focus on CSCs in solid tumors, we review CSC regulation programs and recent transcriptomics-based immunological profiling data specific to CSCs. By highlighting CSC antigens that could potentially be immunogenic, we further discuss how CSCs can be targeted immunologically.
Cancer stem cells (CSC), or cancer cells with stem cell properties, have been reported in many human tumors and are thought to be responsible for tumor initiation, therapy resistance, progression, ...relapse, and metastasis. Despite their potential clinical importance, how CSCs are regulated at the molecular level is not well understood. MicroRNAs (miRNA), small noncoding RNAs that play critical roles in normal stem cell functions during development, have emerged as important regulators of CSCs as well. In this review, we summarize the current major findings of miRNA regulation of various CSCs and discuss our recent findings that miR-34a suppresses prostate CSCs and metastasis by directly repressing CD44. This recent progress has important implications for understanding how CSCs are intricately regulated by networks of miRNAs and for developing novel mechanism-based miRNA therapeutics that specifically target CSCs.
It is increasingly appreciated that cancer cell heterogeneity and plasticity constitute major barriers to effective clinical treatments and long-term therapeutic efficacy. Research in the past two ...decades suggest that virtually all treatment-naive human cancers harbor subsets of cancer cells that possess many of the cardinal features of normal stem cells. Such stem-like cancer cells, operationally defined as cancer stem cells (CSCs), are frequently quiescent and dynamically change and evolve during tumor progression and therapeutic interventions. Intrinsic tumor cell heterogeneity is reflected in a different aspect in that tumors also harbor a population of slow-cycling cells (SCCs) that are not in the proliferative cell cycle and thus are intrinsically refractory to anti-mitotic drugs. In this Perspective, we focus our discussions on SCCs in cancer and on various methodologies that can be employed to enrich and purify SCCs, compare the similarities and differences between SCCs, CSCs and cancer cells undergoing EMT, and present evidence for the involvement of SCCs in surviving anti-neoplastic treatments, mediating tumor relapse, maintaining tumor dormancy and mediating metastatic dissemination. Our discussions make it clear that an in-depth understanding of the biological properties of SCCs in cancer will be instrumental to developing new therapeutic strategies to prevent tumor relapse and distant metastasis.
Cancer stem cells and radioresistance Rycaj, Kiera; Tang, Dean G.
International journal of radiation biology,
08/2014, Volume:
90, Issue:
8
Journal Article
Peer reviewed
Open access
Abstract
Purpose: Radiation therapy has made significant contributions to cancer treatment. However, despite continuous improvements, tumor recurrence and therapy resistance still occur in a high ...proportion of patients. One underlying reason for this radioresistance might be attributable to the presence of cancer stem cells (CSC). The purpose of this review is to discuss CSC-specific mechanisms that confer radiation resistance.
Conclusions: We focus our discussions on breast cancer and glioblastoma multiforme (GBM) and conclude that both CSC-intrinsic and CSC-extrinsic factors as well as adaptive responses in CSC caused by irradiation and microenvironmental changes all make contributions to CSC-mediated radioresistance. Our discussions emphasize CSC as novel therapeutic targets in order to potentiate radiotherapy efficacy.
The homeobox domain transcription factor NANOG, a key regulator of embryonic development and cellular reprogramming, has been reported to be broadly expressed in human cancers. Functional studies ...have provided strong evidence that NANOG possesses protumorigenic attributes. In addition to promoting self‐renewal and long‐term proliferative potential of stem‐like cancer cells, NANOG‐mediated oncogenic reprogramming may underlie clinical manifestations of malignant disease. In this review, we examine the molecular origin, expression, biological activities, and mechanisms of action of NANOG in various malignancies. We also consider clinical implications such as correlations between NANOG expression and cancer prognosis and/or response to therapy. We surmise that NANOG potentiates the molecular circuitry of tumorigenesis, and thus may represent a novel therapeutic target or biomarker for the diagnosis, prognosis, and treatment outcome of cancer. Finally, we present critical pending questions relating NANOG to cancer stem cells and tumor development. Stem Cells 2015;33:2381–2390
Prostate cancer (PCa) is heterogeneous, harboring phenotypically diverse cancer cell types. PCa cell heterogeneity is caused by genomic instability that leads to the clonal competition and evolution ...of the cancer genome and by epigenetic mechanisms that result in subclonal cellular differentiation. The process of tumor cell differentiation is initiated from a population of prostate cancer stem cells (PCSCs) that possess many phenotypic and functional properties of normal stem cells. Since the initial reports on PCSCs in 2005, there has been much effort to elucidate their biological properties, including unique metabolic characteristics. In this Review, we discuss the current methods for PCSC enrichment and analysis, the hallmarks of PCSC metabolism, and the role of PCSCs in tumor progression. Stem Cells 2018;36:1457–1474
Prostate cancer development is an evolutionary process that reflects an evolving of prostate cancer stem cells (PCSCs) possessing self‐renewal properties and genomic instability. Tumor metastases might be driven by the constantly evolving populations of PCSCs. This is evidenced by the fact that circulating tumor cells (CTCs) and disseminated tumor cells (DTCs) express many PCSC markers, and metastasis‐initiating cells (MICs) also share key PCSC features including ability to self‐renew, establish tumors and activate PCSC‐specific signaling pathways. In this review, we discuss the current methods for PCSC enrichment and analysis, the hallmarks of PCSC biology and the role of PCSCs in therapy resistance, tumor progression and metastases.
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