13
1 JNPC http://www.journalofnasopharyngealcarcinoma.org/ e-ISSN 2312-0398 Published:2014-03 -20 DOI:10.15383/jnpc.6 Review Cancer Stem Cells in Nasopharyngeal Carcinoma: Current Evidence Fenggang Yu 1 , Kwok Seng Loh 2 1 Department of Otolaryngology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 2 Head & Neck Tumor Group, National Cancer Institute of Singapore, National University Health System (NUHS), Singapore Corresponding author: Fenggang Yu; E-mail: [email protected] Citation: Yu FG, Loh KS. Cancer stem cells in nasopharyngeal carcinoma: current evidence. J Nasopharyng Carcinoma, 2014, 1(6): e6. doi:10.15383/jnpc.6. Funding: This work was supported by a Grant from the National University Cancer Institute, Singapore (NCIS) Centre Grant to Dr. Loh and Dr. Yu. Competing interests: The authors have declared that no competing interests exist. Conflict of interest: None. Copyright: 2014 By the Editorial Department of Journal of Nasopharyngeal Carcinoma. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Abstract: Nasopharyngeal carcinoma (NPC) is highly prevalent in southern China and Southeast Asia. Cancer resistance to therapy, metastasis and disease recurrence are significant hurdles to successful treatment of NPC. Identifying mechanisms by which NPC is resistantiscritical to improving patient survival. Evidence gathered in the last decade suggests that tumor progression and recurrence may befuelled by cancer stem cells (CSCs). Understanding how CSCs contribute to the pathology of NPC will potentiallyaid the pursuit of novel therapies. In this review we summarize what major methods are currently used to identify CSCs in NPC and the challenges faced. Keywords: Nasopharyngeal carcinoma; Cancer stem cells Introduction In general,two models have been proposed to explain tumor growth and heterogeneity[1]. In the first model, all tumor cells are equipotent and a proportion of tumor cells stochastically proliferate to fuel tumor growth while other tumor cells differentiate. In the second model, tumors are hierarchically organized like normal tissues.Only a discrete fraction of cells with stem cell features (asymmetric division) is able to indefinitely sustain the malignant progeny through self-renewaland differentiation processes. Owing to the analogy to tissue-specific stem cells , thesesubset of cells are called cancer stem cells (CSCs) [2]. Thetheory of the CSCshas stirred much confusion and debate ever since, but it keeps generating excitement and optimism. Almost 200 years ago, the father of pathology, Rudolf Virchow, suggested that cancer cells arise from embryonic-like tissue[3], but it was not until 1994, in their pioneer work, have John Dick and colleagues demonstrated the hierarchy of the acute myeloid leukaemia malignant clone and defined the CSCs for the first time[4]. Following these papers, many other studies have shown that populations of cells presenting a higher ability to re-form the parental tumor on transplantation into immunodeficient mice can

Cancer Stem Cells in Nasopharyngeal Carcinoma

Embed Size (px)

DESCRIPTION

tht

Citation preview

Page 1: Cancer Stem Cells in Nasopharyngeal Carcinoma

1

JNPC ★ http://www.journalofnasopharyngealcarcinoma.org/ e-ISSN 2312-0398 Published:2014-03 -20 ★ DOI:10.15383/jnpc.6

Review

Cancer Stem Cells in Nasopharyngeal Carcinoma: Current Evidence

Fenggang Yu1, Kwok Seng Loh

2

1Department of Otolaryngology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore

2Head & Neck Tumor Group, National Cancer Institute of Singapore, National University Health System (NUHS), Singapore

Corresponding author: Fenggang Yu; E-mail: [email protected]

Citation: Yu FG, Loh KS. Cancer stem cells in nasopharyngeal carcinoma: current evidence. J Nasopharyng

Carcinoma, 2014, 1(6): e6. doi:10.15383/jnpc.6.

Funding: This work was supported by a Grant from the National University Cancer Institute, Singapore (NCIS)

Centre Grant to Dr. Loh and Dr. Yu.

Competing interests: The authors have declared that no competing interests exist.

Conflict of interest: None.

Copyright: 2014 By the Editorial Department of Journal of Nasopharyngeal Carcinoma. This is an open-access

article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use,

distribution, and reproduction in any medium, provided the original author and source are credited.

Abstract: Nasopharyngeal carcinoma (NPC) is highly prevalent in southern China and Southeast Asia. Cancer

resistance to therapy, metastasis and disease recurrence are significant hurdles to successful treatment of NPC.

Identifying mechanisms by which NPC is resistantiscritical to improving patient survival. Evidence gathered in the

last decade suggests that tumor progression and recurrence may befuelled by cancer stem cells (CSCs).

Understanding how CSCs contribute to the pathology of NPC will potentiallyaid the pursuit of novel therapies. In

this review we summarize what major methods are currently used to identify CSCs in NPC and the challenges faced.

Keywords: Nasopharyngeal carcinoma; Cancer stem cells

Introduction

In general,two models have been proposed to explain tumor

growth and heterogeneity[1]. In the first model, all tumor cells are

equipotent and a proportion of tumor cells stochastically

proliferate to fuel tumor growth while other tumor cells

differentiate. In the second model, tumors are hierarchically

organized like normal tissues.Only a discrete fraction of cells with

stem cell features (asymmetric division) is able to indefinitely

sustain the malignant progeny through self-renewaland

differentiation processes. Owing to the analogy to tissue-specific

stem cells , thesesubset of cells are called cancer stem cells

(CSCs) [2]. Thetheory of the CSCshas stirred much confusion

and debate ever since, but it keeps generating excitement and

optimism.

Almost 200 years ago, the father of pathology, Rudolf Virchow,

suggested that cancer cells arise from embryonic-like tissue[3],

but it was not until 1994, in their pioneer work, have John Dick

and colleagues demonstrated the hierarchy of the acute myeloid

leukaemia malignant clone and defined the CSCs for the first

time[4]. Following these papers, many other studies have shown

that populations of cells presenting a higher ability to re-form the

parental tumor on transplantation into immunodeficient mice can

Page 2: Cancer Stem Cells in Nasopharyngeal Carcinoma

2

JNPC ★ http://www.journalofnasopharyngealcarcinoma.org/ e-ISSN 2312-0398 Published:2014-03 -20 ★ DOI:10.15383/jnpc.6

be prospectively isolated from a great variety of solid tumors, such

as breast cancer[5], brain tumors[6], colorectal cancer[7,8], skin

squamous cell carcinoma (SCC)[9], head and neck cancer[10],

lung cancer[11], pancreatic cancer[12], prostate cancer[13] and

ovarian cancer[14]. Tumor cells presenting this higher tumor-

repopulating capacity have been referred to as CSCs, or as tumor-

initiating cells, but the best term to describe them is probably

tumor-propagating cells (TPCs).

Nasopharyngeal carcinoma (NPC) is a cancer arising from the

epithelial lining of the nasopharynx. It remains a serious health

problem in many parts of the world,although the worldwide

incidence is low. NPC is particularly endemic to regions in

southern China and South East Asia [15,16].In Singapore, it ranks

as the 3rdmost common cancer in Chinese adult males between

35to 60 years old. Uniquely, Epstein-Barr virus (EBV) is

consistently detected in undifferentiated NPC from these endemic

regions[17].Particularly among head and neck cancers of epithelial

origin, it is associated with the highest rateof locoregional

recurrence and distant metastasis [18,19] , resulting in a great

interest in studying this disease with the intention of developing a

better understanding of its biology and translating these findings

into improved therapeutic approaches. One of the major

mechanisms for recurrence of NPC has been suggested by the

CSCs proposition[20]. While information on CSCs hasbeen

advanced in a variety of cancers, data in NPC is just emerging. In

this paper, we will review the evidence for CSCs in NPC and the

future challenges ahead in elucidating this.

Discovery of NPC CSCs

Historically, the hematopoietic field has led the way in the

identification of stem cells and CSCs[4,21,22].The CSC-theory in

solid tumors was only validated relatively recently. Due to its

distinctive racial/ethnic and geographic distribution, studies of

CSCs in NPC are very scarce[23,24,25,26,27,28,29,30,31] (Table

1). Several important functional assays and surface markers have

been used to investigate the existence of cancer stem-like cells in

various NPC cell lines. Overall, those studies support the evidence

of a subpopulation of NPC cells that are more primitive,

proliferative, therapy resistant and tumorigenic in xenograft than

cells with alternative phenotypes, suggesting CSCs.

Table 1 Markers for CSCs in NPC

Marker Samples % Cells expressing markers Refs

BrdU EBV-NPC cell lines:SUNE-

1(5-8F, 6-10B) and TMNE

approximately 0.3% of label-retaining

cell (LRC) find in 3 kinds of NPC

xenografttumors

[23]

SP EBV- cell lines: CNE-2 about

2.6% of the total cells are SP cells

[24]

CD44

EBV- NPC cell line: SUNE-

1( 5-8F)

CD44+ cells occupied 52.5% of the total

cells

[25]

EBV+

NPC cell line:C666-1 CD44+ cells accounted for 45.3% of the

total cells.

[26]

EBV+ NPC cell line C666-1

cells

And

C666-1 Spheroids Primary

5.2861% of parental C666-1 cells are

CD44+

84.1461% C666-1 spheroids are CD44+

13.06% of NPC xenografts are CD44+

[27]

Page 3: Cancer Stem Cells in Nasopharyngeal Carcinoma

3

JNPC ★ http://www.journalofnasopharyngealcarcinoma.org/ e-ISSN 2312-0398 Published:2014-03 -20 ★ DOI:10.15383/jnpc.6

tumors

Xenografts

ALDH1

Tissue sections from NPC

patients

41 (39.0%) of 105 cases were defined as

having high-grade ALDH1 expression

[28]

EBV- NPC cell lines: 5-8F

and CNE2

1.96% of cells are ALDH1 positive [29]

C666-1 8.5% with high ALDH activity [30]

CD133

CNE2

primary culture

3.36±0.35% CD133+ cells

2.17% in primary cells

[31]

Label Retaining Cells (Lrcs)

Dye label–retaining technique can be used to identify normal

tissues that contain quiescent stem cells responsible for tissue

homeostasis. As CSCs can share properties with normal stem cells,

slow-cycling cells might also exist within a tumor. Their dormant

state might account for the relapse in cancer patients that can

occur years to decades after apparently successful treatment. In an

early study by Zhang et al.[23], the authors found there was about

0.3% of label retaining cells (LRC) in NPC cell lines and their

derived xenografttumors, a good indication that NPC contains

stem cells. However, what the lineage relationship of LRCs with

the rest of cells over time and their functions are lacking. This

question could be addressed further by isolation of live LRCs via

fluorescence-activated cell sorting(FACS)and applying them to

functional assays[32,33,34].

Side Population (SP)

The side population (SP) discrimination assay is based on the

differential potential of cells to efflux the Hoechst dye via the

ATP-binding cassette (ABC) family of transporter proteins

expressed within the cell membrane. SP assay has proven to be a

useful approach for the characterization and isolation of putative

stem cell and cancer stem cell populations, particularly in the

absence of specific markers. Wang et al.[24] demonstrated ∼2.6%

SP in CNE-2 line had cancer stem cell characteristics. These cells

were more resistant to chemotherapy and radiotherapy, and were

noted to have increased propensity to form tumors in vivo. The

presence, absence or change in SP has been used loosely as an

indicator of CSC activity across cell lines in some NPC drug

testing studies [35,36,37]. However, whether SP is a robust CSC

marker in all NPC cells should beconfirmedsystematically. Studies

in other cancers even argue that SP is neither necessary nor

sufficient for conferring a CSC phenotype, such as

glioblastomamultiforme (GBM)[38], thyroid cancer[39],

gastrointestinal cancers[40] and adrenocortical carcinoma[41].

Aldehyde Dehydrogenase (ALDH)

Another functional marker is aldehyde dehydrogenase 1 (ALDH1).

ALDH1 is normally responsible for maintaining cellular

homeostasis by detoxifying intracellular aldehydes through the

oxidation and conversion of retinol to retinoic acid. ALDH1 is

highly expressed in hematopoietic stem cells, as well as malignant

CSCs[42,43,44]. It has been used as a prognostic indicator of

metastases and poor survival[45]. Using EBVcell linesSUNE-1(5-

8F) and CNE2,Wu et al.[29] showed that ALDH1positive(1.96%)

cells had faster proliferation, higher clone formation,

migration,tumor formation in mice, greaterstemness gene

expression and SP cells.It correlated with TNM staging and

epithelial-mesenchymal transition (EMT) makers, proposed as

independent prognostic indicators. Using EBV+cell line C666-1,

Page 4: Cancer Stem Cells in Nasopharyngeal Carcinoma

4

JNPC ★ http://www.journalofnasopharyngealcarcinoma.org/ e-ISSN 2312-0398 Published:2014-03 -20 ★ DOI:10.15383/jnpc.6

our study[30] demonstrated ALDHHigh

(8.5%) cells possesscancer

stem-like traits: the cellsexhibited significantly greater ability to

proliferate, be clonogenic, resist chemotherapy drugs and radiation,

reconstitute a heterogeneous population,and express pluripotent

markers. Furthermore, subcutaneous injection of these cells into

immunodeficient nude mice resulted in a tendency of tumor

formation at a higher rate (not significant) as compared to cells

with lowALDHactivity. However, we did not find ALDHHigh

cells

are more migratory. Indeedwe showed almost all cells express

ALDH at variablelevels.There is no clear cut distinctionbetween

ALDH‘positive’ and ‘negative’ cells as Wu et al.[29] termed it.

The percentage is arbitrary and really depends on how stringent

one sets the gating. The discrepancy might be due to different

experimental conditions or the EBV status of the cell lines.Further

research by Luo et al. demonstrated that budding cells in the

invasive front of tumors with highlevel expression of ALDH1

correlated with aggressive tumor behaviour and poor patient

survival[28]. The authors speculated that they might possess the

invasive and metastatic properties of CSCs. Like in other

cancers[46,47], ALDHcould be a potential therapeutic target for

NPC CSCs as well.

CD44

CD44 is a cell surface receptor for the extracellular matrix

molecule hyaluronan. It influences cell behaviour by direct

signaling/structural roles or by acting as a co-receptor for receptor

tyrosine kinases[48]. CD44 alone or in combination with other

markers have been used successfully to enrich for CSCs in both

cell line and tumor samples[49]. Su et al.[25]reported that CD44+

cells in SUNE-1(5-8F)weremore proliferative, enriched for

stemness gene expression and more resistant to therapy.But in

vivo tumor imitation, one of the most important criteria for

CSCs,was not functionally addressed. In contrast, Janisiewicz et

al.[26] demonstrated CD44+ C666-1 cells exhibited a more robust

tumor-initiating capacity in the xenograft model. CD44+ cells

differentiated into CD44- cells, indicating a hierarchical

relationship. Patient tumors were heterogeneous for CD44 staining,

and a trend toward an association between CD44 expression and

clinical outcome was observed. Surprisingly, no corresponding

higher proliferation rates were seen in CD44+ population in vitro.

This is consistent with our finding that no difference was detected

for both populations incolony-forming efficiency [30]. This study

raises the question whether CD44- cells cannot survive in vivo or

they intrinsically cannot initiate tumors? In a more sophisticated

study by Lun et al.[28], spheroid culture of C666-1 was used to

enrich for CSCs initially and they found the spheroid cells had at

least 50 times higher tumorigenic potential than the unselected

cells. These cells expressed significantlyhigher level of multiple

stem cell markers (OCT4, NANOG, ALDH1, CD44 and CD133

CKIT, KLF4 and KLF5). Further work on CD44 showed that the

majority of spheroids cells are CD44+ and the CD44

+ cells were

resistant to chemotherapeutic agents and with higher spheroid

formation efficiency and exhibited stronger chemo resistance to

fluorouracil5-FU.CD44+cells could give rise to both CD44

+ and

CD44- cells, suggesting a hierarchical relationship. The

phenotypic heterogeneity also was observed in xenografts and

primary tumors. Serial transplantation is an important

measurement of long-term self-renewal ability of CSCs. The

authors reported spheroid cells could be serially engrafted into

nude mice, but no data has been shown in detail. Although

sphere-forming assays have been extensively used in many

cancers to assess clonogenicity, long-term renewal capacities and

multiline age differentiation, they must be interpreted with caution.

It is important to note that not only stem cells but also their transit-

amplifying progeny are able to form spheres and that, by contrast,

quiescent stem cells cannot form spheres. Thus sphere assays do

not allow for an accurate quantification of stem cell frequency in

vivo[50]. Even using the same protocol for culturing C666-1

spheres, we were unable to form decent passageblespheres from

the primary NPC cells. Does it mean there are actually no CSCs in

primary NPC cells orit is just an artificial adaption for C666-1 line

in long term in vitro cultures? It will be important to define to

what extent the ability of tumor cells to grow as spheres is directly

correlated with their ability to sustain tumor growth in vivo.

CD133

Page 5: Cancer Stem Cells in Nasopharyngeal Carcinoma

5

JNPC ★ http://www.journalofnasopharyngealcarcinoma.org/ e-ISSN 2312-0398 Published:2014-03 -20 ★ DOI:10.15383/jnpc.6

CD133 (also known as Prominin 1), a member of pentaspan

transmembrane glycoproteins, is expressed in hematopoietic stem

cells, endothelial progenitor cells, neuronal and glial stem cells. It

specifically localizes to cellular protrusions[51]. CD133 has

previously also been shown to be expressed in subpopulations of

cancer cells from brain, colon, lung, melanoma and other solid

tumors. This led to the assumption that CD133 expressing tumor

cells have stem cell or progenitor like properties and CD133 was

proposed as CSC marker[51]. Lun et al.[27]found that

1.90±0.84% of CD133+in C666-1 cells and completely absent in 2

of the xenografts (xeno-666 and xeno-2117). Consistently, we

only observed very rare C666-1 cells with faint cytoplasmic but

not surface staining of CD133.CD133 was barely detectable in

NPC primary cells or patient biopsies[30]. However, Zhuang et

al.[31] reported 3.36±0.35%CD133+ cells with CSCs

characteristics in CNE cell lines. Overall their study is descriptive.

For example, no significant difference was formed in thecell cycle

distribution between the CD133+ and CD133

- cells, but CD133

+

cells hadsignificantlyhigher proliferative index and had a greater

potential for in vivo tumor formation. The CD133 expression

dropped to zero at 21 days of culture. Whether CD133 is a marker

cannot be concluded from this study. Further extensive studies

with broader spectrum of cell lines, primary cells and

xenograftsareneeded.

Basically, the above studies have demonstrated that NPC cells are

heterogeneous and contain cancer stem-like cells. Based on these

limited publications, it is hard to say which marker works better

than the other to identify NPC CSCs. Even using the same cell

line and same marker [26,27], different results were obtained. The

exact reasons for the reported discrepancies across studies are not

clear. Possible explanations may include differences in techniques,

protocols and reagents such as antibodies. Additional sources of

confusion may mirror the inter/intra-tumor heterogeneity and

colon evolution. These studies highlight the need for

comprehensive analysis by using combinations of different

markers to identify potentially unique functional characteristics of

NPC CSCs. The gold standard of CSC identification continues to

be tumour initiation with serial transplantation in recipient mice,

but this may not be practical to NPC. It is very challenging and

will be discussed in the following section.

Unsolved Issues

Despite the useful data we obtained from the above studies, there

are still many unsolved issues:

Where Do The NPC Cscs Come From?

The stem cell characteristics of CSCs beg the question of the cell

type from which they are derived. Experimental evidence suggests

that CSCs arise either from normal stem cells that have become

cancerous through mutation, or from the transformed somatic cells

that have acquired the ability to self-renew. Lineage tracing in

experimental mouse models has strongly showed that Lgr5+

intestinal stem cells can initiate and maintain murine intestinal

adenomas[52,53]. In mouse models of skin cancer, hair follicle

bulge stem cells[54] can serve as target cells for transformation,

and CD34+ cells resembling their normal bulge stem cell

counterpart are capable of propagating the disease as a cancer

stem cell population[9]. In parallel, mouse models of breast cancer

and recent studies using human tumor samples demonstrate that

tumors can arise and be propagated from the transformation of

more differentiated luminal cells[55].

In NPC, EBV infection is detected in nearly all patients in the

endemic regions.Although the underlying mechanism of how EBV

contributes to cancer is not completely understood, emerging data

indicated that EBV latent membrane protein LMP1 and LMP2a

have transforming properties. Both proteins can activate a number

of signalling pathways such as NF-КB, STAT that trigger

morphological and phenotypic alterations in epithelial cells.

Significantly, they have been shown to induce EMT, increase the

cancer stem cell-like population and contribute to the onset of

metastases in NPC[56,57,58].

A major question surrounding NPC is that it is not known whether

or to what extent epithelial cells become infected when the host

first encounters EBV during primary infection. One hypothesis

Page 6: Cancer Stem Cells in Nasopharyngeal Carcinoma

6

JNPC ★ http://www.journalofnasopharyngealcarcinoma.org/ e-ISSN 2312-0398 Published:2014-03 -20 ★ DOI:10.15383/jnpc.6

isthat accumulation of genetic alterations renders cells more

permissive to latent EBV infection[59]. High frequencies of

chromosomal loss at 3p/9p are present in 80̴100% of

NPC[60,61,62], which is similar to the level of EBV infection.

This suggests that EBV infection may not be the initiating event in

NPC pathogenesis, but rather, occurs before the initiation of

invasive growth. Studies[63] indicate that undifferentiated

epithelial cells are more permissive than the terminally

differentiated cells for latent EBV infection and propagation.

Nasopharynx is lined by stratified squamous and respiratory type

epithelium. EBV infection of normal nasopharyngeal cells is rare.

EBV-infected epithelial cells are hardly detectable even in normal

nasopharyngeal biopsies from individuals who are at high risk of

developing NPC[64]. Basal cells in the epithelium of airway act as

stem cells with undifferentiated properties [65,66]. In addition to

their role in epithelial homeostasis, basal cells probably contribute

to disease susceptibility, initiation and progression. For example,

disruption of the normal balance between proliferation and

differentiation in airway basal cells can leadto basal cell

hyperplasia or epithelial hypoplasia[66,67]. Similarly, recent

studies demonstrated many cancers including prostate cancer, skin

basal cell carcinoma and basal-like breast cancer subtype are

originated in basal cells[68,69,70]. Consistently, we found almost

exclusively primary NPC cells are positive both for EBV and

basal cell marker p63(Figure 1). More importantly, like their

normal counterpart, these cells can be differentiated into goblet

cells and ciliated cells(unpublished data). The data suggest that

basal stem cells could bethe initiating and propagating cells of

NPC,although we cannot rule out NPC initiating cells of other

origin such as transformed somatic cells.

Figure 1.Primary cell culture of nasopharyngeal carcinoma (NPC). Primary NPC cells express EBV and basal cell markers revealed by immunohistochemistry with

antibodies against EBNA-1 and p63.

Are NPC Cscs Rare?

According to CSCs model, only a rare of population sits at the top

of the cellular hierarchy to drive the tumor progression. Indeed, in

many types of human tumors, CSCs have been shown to be rare,

with frequencies ranging from 0.0001 to 0.1% determined by the

capability of re-forming secondary tumors on transplantation into

immunodeficient mice[71,72]. By contrast, Morrison and

colleagues [73]demonstrated that the transplantation of melanoma

cells into more severely immunodeficientNOD scid IL2 receptor

gamma chain knockout mice (NSG) mice enhances the frequency

of CSCs by several orders of magnitude as compared to nonobese

diabetic/severe combined immunodeficient (NOD/SCID) mice.

Up to 27% of unselected melanoma cells from four different

patients were able to form xenografttumor, demonstrating that

CSCs are not always rare.Limiting-dilution transplants are

typically used to determine the frequency of CSCs. In available

published NPC studies,nude mice or NOD/SCID mice were

frequently used(Table1).For example, in the study by Lun et al.

injection of at least 1,000 C666-1spheroid cells occasionally

formed one tumor out of six nude mice [27]. In our own study [30],

at least 10000 ALDHHigh

C666-1 cells were necessary for tumor

formation in nude mice.Couldthe frequency of NPC CSCs be

underestimated? Almost all NPC cells wereectopically

transplanted into subcutaneous region, which does not mimic the

native environment and is suboptimal for engrafting[74,75]. This

can be seen from the experience ofxenografting either tissue

Page 7: Cancer Stem Cells in Nasopharyngeal Carcinoma

7

JNPC ★ http://www.journalofnasopharyngealcarcinoma.org/ e-ISSN 2312-0398 Published:2014-03 -20 ★ DOI:10.15383/jnpc.6

explants or dissociated primary cells. It is rarely a successful, even

though a large number of cells were transplanted.Orthotropic

models[74,75] have been reported but it is not clear why it has not

been extensively used. On top of that, primary cells may be more

accurate for localising CSCs frequency within primary tumorsthan

cell lines.Strikingly, we found more than 40% of primary NPC

cells highly express CD44 andALDH (unpublished data). More

studies using primary cells and orthotropic modelsinmore severely

immunodeficient NSG mice are required to assess whether the

lowfrequency of CSCs found in NPC is the consequence of

suboptimal assays rather than due to an intrinsic inability to be

propagated in immunodeficient mice.

Are NPC Cscsquiescent Or Fast Proliferating?

In many adult tissues[76,77,78], stem cells show a relative slow

turnover rate at homeostasis. For example, in the central nervous

system, the neural stem cells in the subventricular zone is a

relatively quiescent population with a cell cycle length up to 28

days, whereas the transit amplifying progenitors cells (TA) divide

rapidly with a cell cycle length of approximately 12 h)[79,80].In

melanoma, a subset of slow-cycling cells with doubling times

of >4 weeks within the rapidly proliferating main population is

essential for continuous tumor growth[81].However, in other adult

tissues—such as the small intestine—some cells with bona fide

stem cell activity remain in an actively dividing state[82].

Identification of CSCs has mostly been studied on the basis of

functional assays such as in vitro clonogenic assays, sphere

formation and tumorxenografting. It is important to note that all

these assays are measuresof proliferation. Do we deliberately

select for fast proliferating cells? Are these fast proliferating cells

true CSCs or just TA progenitors?If the original CSCs are

quiescent in vivo but are stimulated to divide in cultures

containingserum and saturated growth factors), we might be able

to capture the cells. Conversely, if they do not respond to in vitro

cultures (conditions are not adequate), we might miss the CSCs.

Mathematical modelling of the clonal fate data suggest that the

tumor is hierarchically organized similarto normal epidermis, but

CSCs divide rapidly instead of being mostly quiescent (like stem

cells) during normal homeostasis[83,84]. In contrast, Parada and

colleagues[85] used a genetic lineage ablation approach in a

mouse model of glioblastoma to identify a subset of glioma CSCs

marked by Nestin. It found that these cells are responsible for

sustaining long-term tumor growth and relapse through the

production of transient populations of highly proliferative cells,

but they themselves are quiescent. Another study demonstrated

that colon CSCs escape 5FU chemotherapy-induced cell death by

entering stemness and quiescence via the c-Yes/YAP axis[86]. As

NPC is a disease which can relapse (15%5̴8%) [87]and the

recurrent NPC is refectory to therapy, it is reasonable to think that

there might be some CSCs which are very quiescent and survive

the primary radiation and chemotherapy. To address this question,

the development of NPC animal models is necessary and lineage

tracing will be helpful to assess the fate of CSCs more directly

within their natural environment.

Is NPC Cscs Status Stable Or Has Plasticity?

CSCs can divide asymmetrically to self-renew and generate

differentiated cells.This forms the basis of a unidirectional

hierarchy of tumor. Like in most studies using cell lines,CSCs are

studied based on the assumption that it is a defined subpopulation

witha marker in a given cancer samples.This may over simplify

the complexity of the heterogeneity of in vivo tumors.Recent

research has identified unexpected plasticity of CSCs[81,88,89].

Chaffer et al.[89] found that certain degree of plasticity exist

within a breast cell population, which allows inter-conversion

between CSC and non-CSC states when driven by selective

pressures (including therapy) or clonal evolution, indicating

hierarchical models is not unidirectional rather bidirectional, not

stable rather dynamic. In intestinal tumors,LGR5- cells can give

rise to LGR5+tumor cells, supporting the idea that, when levels of

active β-catenin are increased, villus cells can reacquire CSC

properties by dedifferentiation[90].It has also been demonstrated

that cell surface markers could be dynamically and reversibly

expressed by tumorigenic cells[91].In Wang’s study[24]it was

Page 8: Cancer Stem Cells in Nasopharyngeal Carcinoma

8

JNPC ★ http://www.journalofnasopharyngealcarcinoma.org/ e-ISSN 2312-0398 Published:2014-03 -20 ★ DOI:10.15383/jnpc.6

found that Non-SP NPC cells can give rise to SP cells.We[30] also

found ALDHLow

NPC cells can regenerate ALDHHigh

cells , which

suggest the possibility of plasticity instead of technical limitation

of FACS.Adding yet another layer of complexity is the notion that

there may exist more than one distinct cancer stem-like state

within a tumor,because CSCs keep accumulatingdriver and

passenger epigenetic and genetic perturbations during theirclone

evolution andbranching[92,93]. As a result, phenotypic plasticity

superimposes on a multiplicity of pre-malignant and malignant

subclones, which makes a single or universal maker for CSCs

seems impossible.

Conclusion

Understanding how NPC CSCs contribute to initiation and

progression in tumors will undoubtedly lead to the identification

of novel targets. However, the complexity of CSCs in terms of

their heterogeneity and plasticity will make any one single marker

and drug unlikely to be efficient. An ideal strategy would be to

target boththe CSC andthe non-stem cells populations of tumor.

More importantly, the CSCs niche in which they are located is

acritical determinant of how they respond to a given treatment[94],

which strongly put forward the niche as an important and

inseparabletarget for novel therapies[95,96,97].Signaling

pathways that potentially kill or differentiate CSCs have been

increasingly identified, and experimentally or clinically

tested[92,98,99].

CSC study in NPC is still in its infancy. Using primary cells and

xenografts may be more disease relevant. Using orthotropic

models in more immunodeficent mice may be more accurate to

investigate CSCs frequency. Establishment of genetic lineage

tracing models may allow more direct trackingof CSCs in vivo.

Therapies targeting NPC CSCs began to emerge [35,36,37,100].

We anticipate that in the near future, successful targeting of CSCs

will significantly improve outcomes in NPC cancer patients and

impact patient management.

Conflict of interest

The authors have no other funding, financial relationships, or

conflicts of interest to disclose.

Declaration of The Source of Funding

This work was supported by a Grant from the National University

Cancer Institute, Singapore (NCIS) Centre Grant to Dr.Loh andDr.

Yu.

References:

1. L.V. Nguyen, R. Vanner, P. Dirks, C.J. Eaves, Cancer stem

cells: an evolving concept. Nature Reviews Cancer 12 (2012) 133-

143.

2. T. Reya, S.J. Morrison, M.F. Clarke, I.L. Weissman, Stem cells,

cancer, and cancer stem cells. Nature 414 (2001) 105-111.

3. K. Winter, Significance of young Rudolf Virchow in present

day thinking]. ZeitschriftfürärztlicheFortbildung 46 (1952) 522.

4. T. Lapidot, C. Sirard, J. Vormoor, B. Murdoch, T. Hoang, J.

Caceres-Cortes, M. Minden, B. Paterson, M.A. Caligiuri, J.E.

Dick, A cell initiating human acute myeloid leukaemia after

transplantation into SCID mice. (1994).

5. M. Al-Hajj, M.S. Wicha, A. Benito-Hernandez, S.J. Morrison,

M.F. Clarke, Prospective identification of tumorigenic breast

cancer cells. Proceedings of the National Academy of Sciences

100 (2003) 3983-3988.

6. S.K. Singh, C. Hawkins, I.D. Clarke, J.A. Squire, J. Bayani, T.

Hide, R.M. Henkelman, M.D. Cusimano, P.B. Dirks,

Identification of human brain tumor initiating cells. Nature 432

(2004) 396-401.

7. L. Ricci-Vitiani, D.G. Lombardi, E. Pilozzi, M. Biffoni, M.

Todaro, C. Peschle, R. De Maria, Identification and expansion of

human colon-cancer-initiating cells. Nature 445 (2006) 111-115.

C.A. O’Brien, A. Pollett, S. Gallinger, J.E. Dick, A human colon

cancer cell capable of initiating tumor growth in immunodeficient

mice. Nature 445 (2006) 106-110.

8. I. Malanchi, H. Peinado, D. Kassen, T. Hussenet, D. Metzger,

P. Chambon, M. Huber, D. Hohl, A. Cano, W. Birchmeier,

Cutaneous cancer stem cell maintenance is dependent on β-catenin

Page 9: Cancer Stem Cells in Nasopharyngeal Carcinoma

9

JNPC ★ http://www.journalofnasopharyngealcarcinoma.org/ e-ISSN 2312-0398 Published:2014-03 -20 ★ DOI:10.15383/jnpc.6

signalling. Nature 452 (2008) 650-653.

9. M. Prince, R. Sivanandan, A. Kaczorowski, G. Wolf, M.

Kaplan, P. Dalerba, I. Weissman, M. Clarke, L. Ailles,

Identification of a subpopulation of cells with cancer stem cell

properties in head and neck squamous cell carcinoma. Proceedings

of the National Academy of Sciences 104 (2007) 973-978.

10. A. Eramo, F. Lotti, G. Sette, E. Pilozzi, M. Biffoni, A. Di

Virgilio, C. Conticello, L. Ruco, C. Peschle, R. De Maria,

Identification and expansion of the tumorigenic lung cancer stem

cell population. Cell Death & Differentiation 15 (2007) 504-514.

11. A.T. Collins, P.A. Berry, C. Hyde, M.J. Stower, N.J. Maitland,

Prospective identification of tumorigenic prostate cancer stem

cells. Cancer Res 65 (2005) 10946-10951.

12. C. Li, D.G. Heidt, P. Dalerba, C.F. Burant, L. Zhang, V. Adsay,

M. Wicha, M.F. Clarke, D.M. Simeone, Identification of

pancreatic cancer stem cells. Cancer Res 67 (2007) 1030-1037.

13. M.D. Curley, V.A. Therrien, C.L. Cummings, P.A. Sergent,

C.R. Koulouris, A.M. Friel, D.J. Roberts, M.V. Seiden, D.T.

Scadden, B.R. Rueda, CD133 expression defines a tumor initiating

cell population in primary human ovarian cancer. Stem Cells 27

(2009) 2875-2883.

14. W. Ayadi, A. Khabir, B. Hadhri-Guiga, L. Fki, N. Toumi, W.

Siala, S. Charfi, A. Fendri, H. Makni, T. Boudawara, [North

African and Southeast Asian nasopharyngeal carcinomas: between

the resemblance and the dissemblance]. Bulletin du cancer 97

(2010) 475-482.

15. N. Toumi, M. Frikha, W. Siala, A. Khabir, H. Karray, T.

Boudawara, R.M. Gargouri, M. Ghorbel, J. Daoud, Juvenile

nasopharyngeal carcinoma: anatomoclinic, biologic, therapeutic

and evolutive aspects]. Bulletin du cancer 97 (2010) 427.

16. N. Raab-Traub, Epstein–Barr virus in the pathogenesis of NPC,

in, Seminars in cancer biology, Elsevier, 2002, pp. 431-441.

17. A.W. Lee, Y. Poon, W. Foo, S.C. Law, F.K. Cheung, D.K.

Chan, S.Y. Tung, M. Thaw, J.H. Ho, Retrospective analysis of

5037 patients with nasopharyngeal carcinoma treated during

1976–1985: overall survival and patterns of failure. International

Journal of Radiation Oncology Biology Physics 23 (1992) 261-

270.

18. C. Suárez, J.P. Rodrigo, A. Rinaldo, J.A. Langendijk, A.R.

Shaha, A. Ferlito, Current treatment options for recurrent

nasopharyngeal cancer. European Archives of Oto-Rhino-

Laryngology 267 (2010) 1811-1824.

19. C.A. O'Brien, A. Kreso, J.E. Dick, Cancer stem cells in solid

tumors: an overview, in, Seminars in radiation oncology, Elsevier,

2009, pp. 71-77.

20. J.E. Till, E.A. McCulloch, A direct measurement of the

radiation sensitivity of normal mouse bone marrow cells.

Radiation research 14 (1961) 213-222.

21. A.J. Becker, E.A. McCulloch, J.E. Till, Cytological

demonstration of the clonal nature of spleen colonies derived from

transplanted mouse marrow cells. (1963).

22. H.-B. Zhang, C.-P. Ren, X.-Y. Yang, L. Wang, H. Li, M. Zhao,

H. Yang, K.-T. Yao, Identification of label-retaining cells in

nasopharyngeal epithelia and nasopharyngeal carcinoma tissues.

Histochemistry and cell biology 127 (2007) 347-354.

23. J. Wang, L.P. Guo, L.Z. Chen, Y.X. Zeng, S.H. Lu,

Identification of cancer stem cell-like side population cells in

human nasopharyngeal carcinoma cell line. Cancer Res 67 (2007)

3716-3724.

24. J. Su, X.H. Xu, Q. Huang, M.Q. Lu, D.J. Li, F. Xue, F. Yi, J.H.

Ren, Y.P. Wu, Identification of cancer stem-like CD44+ cells in

human nasopharyngeal carcinoma cell line. Arch Med Res 42

(2011) 15-21.

25. A.M. Janisiewicz, J.H. Shin, O. Murillo‐Sauca, S. Kwok, Q.T.

Le, C. Kong, M.J. Kaplan, J.B. Sunwoo, CD44+ cells have cancer

stem cell–like properties in nasopharyngeal carcinoma, in,

International Forum of Allergy & Rhinology, Wiley Online

Library, 2012, pp. 465-470.

26. S.W. Lun, S.T. Cheung, P.F. Cheung, K.F. To, J.K. Woo, K.W.

Choy, C. Chow, C.C. Cheung, G.T. Chung, A.S. Cheng, C.W. Ko,

S.W. Tsao, P. Busson, M.H. Ng, K.W. Lo, CD44+ cancer stem-

like cells in EBV-associated nasopharyngeal carcinoma. PloS one

7 (2012) e52426.

27. W.R. Luo, F. Gao, S.Y. Li, K.T. Yao, Tumor budding and the

Page 10: Cancer Stem Cells in Nasopharyngeal Carcinoma

10

JNPC ★ http://www.journalofnasopharyngealcarcinoma.org/ e-ISSN 2312-0398 Published:2014-03 -20 ★ DOI:10.15383/jnpc.6

expression of cancer stem cell marker aldehyde dehydrogenase 1

in nasopharyngeal carcinoma. Histopathology 61 (2012) 1072-

1081.

28. A. Wu, W. Luo, Q. Zhang, Z. Yang, G. Zhang, S. Li, K. Yao,

Aldehyde dehydrogenase 1, a functional marker for identifying

cancer stem cells in human nasopharyngeal carcinoma. Cancer

letters 330 (2013) 181-189.

29. F. Yu, A.C.N. Sim, C. Li, Y. Li, X. Zhao, D.-Y. Wang, K.S.

Loh, Identification of a subpopulation of nasopharyngeal

carcinoma cells with cancer stem-like cell properties by high

aldehyde dehydrogenase activity. Laryngoscope (2013) n/a-n/a.

30. H.W. Zhuang, T.T. Mo, W.J. Hou, G.X. Xiong, X.L. Zhu, Q.L.

Fu, W.P. Wen, Biological characteristics of CD133(+) cells in

nasopharyngeal carcinoma. Oncol Rep 30 (2013) 57-63.

31. L.P. Deleyrolle, A. Harding, K. Cato, F.A. Siebzehnrubl, M.

Rahman, H. Azari, S. Olson, B. Gabrielli, G. Osborne, A. Vescovi,

Evidence for label-retaining tumor-initiating cells in human

glioblastoma. Brain 134 (2011) 1331-1343.

32. D. Hari, H.-W. Xin, K. Jaiswal, G. Wiegand, B.-K. Kim, C.

Ambe, D. Burka, T. Koizumi, S. Ray, S. Garfield, Isolation of live

label-retaining cells and cells undergoing asymmetric cell division

via nonrandom chromosomal cosegregation from human cancers.

Stem Cells Dev 20 (2011) 1649-1658.

33. H. Wei, C. Yan, X. Jiang, X. Song, L. Kong, H. Cao,

Identification of label-retaining cells in human gastric cancer

xenograft in nude mice. The Chinese-German Journal of Clinical

Oncology 12 (2013) 419-422.

34. S. Yu, R. Zhang, F. Liu, H. Wang, J. Wu, Y. Wang, Notch

inhibition suppresses nasopharyngeal carcinoma by depleting

cancer stem-like side population cells. Oncol Rep 28 (2012) 561-

566.

35. M.S. Wu, G.F. Wang, Z.Q. Zhao, Y. Liang, H.B. Wang, M.Y.

Wu, P. Min, L.Z. Chen, Q.S. Feng, J.X. Bei, Y.X. Zeng, D. Yang,

Smacmimetics in combination with TRAIL selectively target

cancer stem cells in nasopharyngeal carcinoma. Mol Cancer Ther

12 (2013) 1728-1737.

36. C.C. Deng, Y. Liang, M.S. Wu, F.T. Feng, W.R. Hu, L.Z.

Chen, Q.S. Feng, J.X. Bei, Y.X. Zeng, Nigericin selectively

targets cancer stem cells in nasopharyngeal carcinoma. Int J

Biochem Cell Biol 45 (2013) 1997-2006.

37. K.W. Broadley, M.K. Hunn, K.J. Farrand, K.M. Price, C.

Grasso, R.J. Miller, I.F. Hermans, M.J. McConnell, Side

population is not necessary or sufficient for a cancer stem cell

phenotype in glioblastomamultiforme. Stem Cells 29 (2011) 452-

461.

38. N. Mitsutake, A. Iwao, K. Nagai, H. Namba, A. Ohtsuru, V.

Saenko, S. Yamashita, Characterization of side population in

thyroid cancer cell lines: cancer stem-like cells are enriched partly

but not exclusively. Endocrinology 148 (2007) 1797-1803.

39. J. Burkert, W. Otto, N. Wright, Side populations of

gastrointestinal cancers are not enriched in stem cells. The Journal

of pathology 214 (2008) 564-573.

40. U.D. Lichtenauer, I. Shapiro, K. Geiger, M. Quinkler, M.

Fassnacht, R. Nitschke, K.-D. Rückauer, F. Beuschlein, Side

population does not define stem cell-like cancer cells in the

adrenocortical carcinoma cell line NCI h295R. Endocrinology 149

(2008) 1314-1322.

41. R.W. Storms, A.P. Trujillo, J.B. Springer, L. Shah, O.M.

Colvin, S.M. Ludeman, C. Smith, Isolation of primitive human

hematopoietic progenitors on the basis of aldehyde dehydrogenase

activity. Proceedings of the National Academy of Sciences 96

(1999) 9118.

42. D.J. Pearce, D. Taussig, C. Simpson, K. Allen, A.Z. Rohatiner,

T.A. Lister, D. Bonnet, Characterization of cells with a high

aldehyde dehydrogenase activity from cord blood and acute

myeloid leukemia samples. Stem Cells 23 (2005) 752-760.

43. C. Ginestier, M.H. Hur, E. Charafe-Jauffret, F. Monville, J.

Dutcher, M. Brown, J. Jacquemier, P. Viens, C.G. Kleer, S. Liu,

ALDH1 is a marker of normal and malignant human mammary

stem cells and a predictor of poor clinical outcome. Cell Stem Cell

1 (2007) 555-567.

44. E. Charafe-Jauffret, C. Ginestier, F. Iovino, C. Tarpin, M.

Diebel, B. Esterni, G. Houvenaeghel, J.-M. Extra, F. Bertucci, J.

Jacquemier, Aldehyde dehydrogenase 1–Positive cancer stem cells

Page 11: Cancer Stem Cells in Nasopharyngeal Carcinoma

11

JNPC ★ http://www.journalofnasopharyngealcarcinoma.org/ e-ISSN 2312-0398 Published:2014-03 -20 ★ DOI:10.15383/jnpc.6

mediate metastasis and poor clinical outcome in inflammatory

breast cancer. Clinical Cancer Research 16 (2010) 45-55.

45. Y. Luo, K. Dallaglio, Y. Chen, W.A. Robinson, S.E. Robinson,

M.D. McCarter, J. Wang, R. Gonzalez, D.C. Thompson, D.A.

Norris, ALDH1A isozymes are markers of human melanoma stem

cells and potential therapeutic targets. Stem Cells 30 (2012) 2100-

2113.

46. X. Mu, C. Isaac, T. Schott, J. Huard, K. Weiss, Rapamycin

inhibits ALDH activity, resistance to oxidative stress, and

metastatic potential in murine osteosarcoma cells. Sarcoma 2013

(2013).

47. H. Ponta, L. Sherman, P.A. Herrlich, CD44: from adhesion

molecules to signalling regulators. Nature Reviews Molecular Cell

Biology 4 (2003) 33-45.

48. M. Zöller, CD44: can a cancer-initiating cell profit from an

abundantly expressed molecule? Nature Reviews Cancer 11 (2011)

254-267.

49. E. Pastrana, V. Silva-Vargas, F. Doetsch, Eyes wide open: a

critical review of sphere-formation as an assay for stem cells. Cell

Stem Cell 8 (2011) 486-498.

50. Y. Welte, J. Adjaye, H.R. Lehrach, C.R. Regenbrecht, Cancer

stem cells in solid tumors: elusive or illusive? Cell communication

and signaling 8 (2010) 6.

51. N. Barker, R.A. Ridgway, J.H. van Es, M. van de Wetering, H.

Begthel, M. van den Born, E. Danenberg, A.R. Clarke, O.J.

Sansom, H. Clevers, Crypt stem cells as the cells-of-origin of

intestinal cancer. Nature 457 (2008) 608-611.

52. A.G. Schepers, H.J. Snippert, D.E. Stange, M. van den Born,

J.H. van Es, M. van de Wetering, H. Clevers, Lineage tracing

reveals Lgr5+ stem cell activity in mouse intestinal adenomas.

Science 337 (2012) 730-735.

53. G. Lapouge, K.K. Youssef, B. Vokaer, Y. Achouri, C.

Michaux, P.A. Sotiropoulou, C. Blanpain, Identifying the cellular

origin of squamous skin tumors. Proceedings of the National

Academy of Sciences 108 (2011) 7431-7436.

54. J. Kim, R. Villadsen, T. Sørlie, L. Fogh, S.Z. Grønlund, A.J.

Fridriksdottir, I. Kuhn, F. Rank, V.T. Wielenga, H. Solvang,

Tumor initiating but differentiated luminal-like breast cancer cells

are highly invasive in the absence of basal-like activity.

Proceedings of the National Academy of Sciences 109 (2012)

6124-6129.

55. Q.-L. Kong, L.-J. Hu, J.-Y. Cao, Y.-J. Huang, L.-H. Xu, Y.

Liang, D. Xiong, S. Guan, B.-H. Guo, H.-Q. Mai, Epstein-Barr

virus-encoded LMP2A induces an epithelial–mesenchymal

transition and increases the number of side population stem-like

cancer cells in nasopharyngeal carcinoma. PLoSPathog 6 (2010)

e1000940.

56. T. Yoshizaki, S. Kondo, N. Wakisaka, S. Murono, K. Endo, H.

Sugimoto, S. Nakanishi, A. Tsuji, M. Ito, Pathogenic role of

Epstein–Barr virus latent membrane protein-1 in the development

of nasopharyngeal carcinoma. Cancer letters 337 (2013) 1-7.

57. H. Zheng, L. Li, D. Hu, X. Deng, Y. Cao, Role of Epstein-Barr

virus encoded latent membrane protein 1 in the carcinogenesis of

nasopharyngeal carcinoma. Cell MolImmunol 4 (2007) 185-196.

58. K.-W. Lo, D.P. Huang, Genetic and epigenetic changes in

nasopharyngeal carcinoma, in, Seminars in cancer biology,

Elsevier, 2002, pp. 451-462.

59. A.S.C. Chan, K.F. To, K.W. Lo, K.F. Mak, W. Pak, B. Chiu,

M. Gary, M. Ding, X. Li, J.C.K. Lee, High frequency of

chromosome 3p deletion in histologically normal nasopharyngeal

epithelia from southern Chinese. Cancer Res 60 (2000) 5365-5370.

60. N. Wong, A.B. Hui, B. Fan, K.W. Lo, E. Pang, S.-F. Leung,

D.P. Huang, P.J. Johnson, Molecular cytogenetic characterization

of nasopharyngeal carcinoma cell lines and xenografts by

comparative genomic hybridization and spectral karyotyping.

Cancer genetics and cytogenetics 140 (2003) 124-132.

61. G. Niedobitek, N. Meru, H.J. Delecluse, Epstein‐Barr virus

infection and human malignancies. International journal of

experimental pathology 82 (2001) 149-170.

62. H. Näher, D. Petzoldt, [Epstein-Barr virus infection--a lympho-

and epitheliotropic infection]. Der Hautarzt,Zeitschrift fur

Dermatologie, Venerologie, undverwandteGebiete 43 (1992) 114-

119.

63. L.S. Young, A.B. Rickinson, Epstein–Barr virus: 40 years on.

Page 12: Cancer Stem Cells in Nasopharyngeal Carcinoma

12

JNPC ★ http://www.journalofnasopharyngealcarcinoma.org/ e-ISSN 2312-0398 Published:2014-03 -20 ★ DOI:10.15383/jnpc.6

Nature Reviews Cancer 4 (2004) 757-768.

64. X. Zhao, F. Yu, C. Li, Y. Li, S.-S. Chao, W.-S. Loh, X. Pan, L.

Shi, D.-Y. Wang, The use of nasal epithelial stem/progenitor cells

to produce functioning ciliated cells in vitro. American Journal of

Rhinology & Allergy 26 (2012) 345-350.

65. F. Yu, X. Zhao, C. Li, Y. Li, Y. Yan, L. Shi, B.R. Gordon, D.Y.

Wang, Airway stem cells: review of potential impact on

understanding of upper airway diseases. Laryngoscope 122 (2012)

1463-1469.

66. J.R. Rock, S.H. Randell, B.L. Hogan, Airway basal stem cells:

a perspective on their roles in epithelial homeostasis and

remodeling. Disease models & mechanisms 3 (2010) 545-556.

67. T. Stoyanova, A.R. Cooper, J.M. Drake, X. Liu, A.J.

Armstrong, K.J. Pienta, H. Zhang, D.B. Kohn, J. Huang, O.N.

Witte, Prostate cancer originating in basal cells progresses to

adenocarcinoma propagated by luminal-like cells. Proceedings of

the National Academy of Sciences 110 (2013) 20111-20116.

68. K.K. Youssef, G. Lapouge, K. Bouvrée, S. Rorive, S. Brohée,

O. Appelstein, J.-C. Larsimont, V. Sukumaran, B. Van de Sande,

D. Pucci, Adult interfolliculartumor-initiating cells are

reprogrammed into an embryonic hair follicle progenitor-like fate

during basal cell carcinoma initiation. Nature cell biology (2012).

69. B.T. Spike, D.D. Engle, J.C. Lin, S.K. Cheung, J. La, G.M.

Wahl, A mammary stem cell population identified and

characterized in late embryogenesis reveals similarities to human

breast cancer. Cell Stem Cell 10 (2012) 183-197.

70. B. Beck, C. Blanpain, Unravelling cancer stem cell potential.

Nature Reviews Cancer 13 (2013) 727-738.

71. T. Schatton, G.F. Murphy, N.Y. Frank, K. Yamaura, A.M.

Waaga-Gasser, M. Gasser, Q. Zhan, S. Jordan, L.M. Duncan, C.

Weishaupt, Identification of cells initiating human melanomas.

Nature 451 (2008) 345-349.

72. E. Quintana, M. Shackleton, M.S. Sabel, D.R. Fullen, T.M.

Johnson, S.J. Morrison, Efficient tumor formation by single

human melanoma cells. Nature 456 (2008) 593-598.

73. T. Liu, Y. Ding, W. Xie, Z. Li, X. Bai, X. Li, W. Fang, C. Ren,

S. Wang, R.M. Hoffman, An imageable metastatic treatment

model of nasopharyngeal carcinoma. Clinical Cancer Research 13

(2007) 3960-3967.

74. P.A. Smith, D. Merritt, L. Barr, D.A. Thorley-Lawson, An

Orthotopic Model of Metastatic Nasopharyngeal Carcinoma and

Its Application in Elucidating a Therapeutic Target That Inhibits

Metastasis. Genes & cancer 2 (2011) 1023-1033.

75. G. Cotsarelis, S.-Z. Cheng, G. Dong, T.-T. Sun, R.M. Lavker,

Existence of slow-cycling limbal epithelial basal cells that can be

preferentially stimulated to proliferate: implications on epithelial

stem cells. Cell 57 (1989) 201-209.

76. J.A. Nowak, L. Polak, H.A. Pasolli, E. Fuchs, Hair follicle

stem cells are specified and function in early skin morphogenesis.

Cell Stem Cell 3 (2008) 33-43.

77. F. Yu, C. M Morshead, Adult stem cells and bioengineering

strategies for the treatment of cerebral ischemic stroke. Current

stem cell research & therapy 6 (2011) 190-207.

78. C.M. Morshead, D. van der Kooy, Postmitotic death is the fate

of constitutively proliferating cells in the subependymal layer of

the adult mouse brain. The Journal of neuroscience 12 (1992) 249-

256.

79. C.M. Morshead, B.A. Reynolds, C.G. Craig, M.W. McBurney,

W.A. Staines, D. Morassutti, S. Weiss, D. van der Kooy, Neural

stem cells in the adult mammalian forebrain: a relatively quiescent

subpopulation of subependymal cells. Neuron 13 (1994) 1071-

1082.

80. A. Roesch, M. Fukunaga-Kalabis, E.C. Schmidt, S.E.

Zabierowski, P.A. Brafford, A. Vultur, D. Basu, P. Gimotty, T.

Vogt, M. Herlyn, A temporarily distinct subpopulation of slow-

cycling melanoma cells is required for continuous tumor growth.

Cell 141 (2010) 583-594.

81. B.D. Simons, H. Clevers, Strategies for homeostatic stem cell

self-renewal in adult tissues. Cell 145 (2011) 851-862.

82. D.P. Doupé, M.P. Alcolea, A. Roshan, G. Zhang, A.M. Klein,

B.D. Simons, P.H. Jones, A single progenitor population switches

behavior to maintain and repair esophageal epithelium. Science

337 (2012) 1091-1093.

83. G. Driessens, B. Beck, A. Caauwe, B.D. Simons, C. Blanpain,

Page 13: Cancer Stem Cells in Nasopharyngeal Carcinoma

13

JNPC ★ http://www.journalofnasopharyngealcarcinoma.org/ e-ISSN 2312-0398 Published:2014-03 -20 ★ DOI:10.15383/jnpc.6

Defining the mode of tumor growth by clonal analysis. Nature

(2012).

84. J. Chen, Y. Li, T.-S. Yu, R.M. McKay, D.K. Burns, S.G.

Kernie, L.F. Parada, A restricted cell population propagates

glioblastoma growth after chemotherapy. Nature 488 (2012) 522-

526.

85. Y. Touil, W. Igoudjil, M. Corvaisier, A.-F. Dessein, J.

Vandomme, D. Monte, L. Stechly, N. Skrypek, C. Langlois, G.

Grard, Colon cancer cells escape 5FU chemotherapy-induced cell

death by entering stemness and quiescence associated with the c-

Yes/YAP axis. Clinical cancer research: an official journal of the

American Association for Cancer Research (2013).

86. T. Xu, J. Tang, M. Gu, L. Liu, W. Wei, H. Yang, Recurrent

nasopharyngeal carcinoma: a clinical dilemma and challenge.

Current Oncology 20 (2013) e406.

87. P.B. Gupta, C.M. Fillmore, G. Jiang, S.D. Shapira, K. Tao, C.

Kuperwasser, E.S. Lander, Stochastic state transitions give rise to

phenotypic equilibrium in populations of cancer cells. Cell 146

(2011) 633-644.

88. C.L. Chaffer, I. Brueckmann, C. Scheel, A.J. Kaestli, P.A.

Wiggins, L.O. Rodrigues, M. Brooks, F. Reinhardt, Y. Su, K.

Polyak, Normal and neoplastic nonstem cells can spontaneously

convert to a stem-like state. Proceedings of the National Academy

of Sciences 108 (2011) 7950-7955.

89. K. Kemper, P.R. Prasetyanti, W. De Lau, H. Rodermond, H.

Clevers, J.P. Medema, Monoclonal antibodies against Lgr5

identify human colorectal cancer stem cells. Stem Cells 30 (2012)

2378-2386.

90. E. Quintana, M. Shackleton, H.R. Foster, D.R. Fullen, M.S.

Sabel, T.M. Johnson, S.J. Morrison, Phenotypic heterogeneity

among tumorigenic melanoma cells from patients that is reversible

and not hierarchically organized. Cancer cell 18 (2010) 510-523.

91. P. Valent, D. Bonnet, R. De Maria, T. Lapidot, M. Copland,

J.V. Melo, C. Chomienne, F. Ishikawa, J.J. Schuringa, G. Stassi,

Cancer stem cell definitions and terminology: the devil is in the

details. Nature Reviews Cancer (2012).

92. R. French, R. Clarkson, The Complex Nature of Breast Cancer

Stem-Like Cells: Heterogeneity and Plasticity. J Stem Cell Res

Ther S 7 (2012) 2.

93. S. Matsuda, T. Yan, A. Mizutani, T. Sota, Y. Hiramoto, M.

Prieto‐Vila, L. Chen, A. Satoh, T. Kudoh, T. Kasai, Cancer stem

cells maintain a hierarchy of differentiation by creating their niche.

International journal of cancer (2013).

94. M.Y. Konopleva, C.T. Jordan, Leukemia stem cells and

microenvironment: biology and therapeutic targeting. Journal of

Clinical Oncology 29 (2011) 591-599.

95. J.E. Visvader, G.J. Lindeman, Cancer stem cells: current status

and evolving complexities. Cell Stem Cell 10 (2012) 717-728.

96. R.J. Gillies, D. Verduzco, R.A. Gatenby, Evolutionary

dynamics of carcinogenesis and why targeted therapy does not

work. Nature Reviews Cancer 12 (2012) 487-493.

97. S. Vidal, V. Rodriguez-Bravo, M. Galsky, C. Cordon-Cardo, J.

Domingo-Domenech, Targeting cancer stem cells to suppress

acquired chemotherapy resistance. Oncogene (2013).

98. N. Takebe, P.J. Harris, R.Q. Warren, S.P. Ivy, Targeting cancer

stem cells by inhibiting Wnt, Notch, and Hedgehog pathways.

Nature Reviews Clinical Oncology 8 (2010) 97-106.

99. C.-H. Lin, P.-H. Hung, Y.-J. Chen, CD44 Is Associated with

the Aggressive Phenotype of Nasopharyngeal Carcinoma through

Redox Regulation. Int J MolSci 14 (2013)13266-13281.