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Cancer Stem Cells
What are Stem Cells?
Hematopoietic Stem Cell and Leukemia Stem Cells.
Mammary Stem Cell and Breast Cancer Cells
Cancer Stem Cells in Solid Tumors.
The Stem Cell Niche.
Implication of Cancer Stem Cells in Cancer Treatment.
Stem Cells
• Stem cells have two defining attributes:
– The capacity for self-renewal.
– The ability to differentiate into many different
cell types.
• Two most important classes of stem cells:
– Embryonic stem cells
– Adult stem cells
Totipotent, Pluripotent and Multipotent
A multipotent cell can give rise to multiple cell types, but
restricted to a single germ layer (e.g mesenchymal) or to a
specific sublineage (e.g. hamatopoietic lineage). Most adult
stem cells belong to this category.
A pluripotent cell is able to give rise to derivatives of all three
germ layers. (e.g. embryonic stem cell).
A totipotent cell can produce an entire organism—only a zygote
and a blastomere from a 2-cell stage embryo belongs to this
category.
Boundary of these definitions are often blurry.
Embryonic and Adult Stem Cells
totipotent
Loose definition
Strict definition pluripotent
Embryonic Stem (ES) Cells
• Derived from the inner cell mass of a blastocyst.
• A blastocyst is a hollow ball of cells formed 4-6
days after a human egg is fertilized.
Adult Stem Cells
• Many adult tissues have stem cells.
• The most well studied are the blood stem cell
(hematopoietic stem cell or HSC) and the neural
stem cell (NSC).
• Recently, it was discovered that an adult stem cell
from one tissue may act as a stem cell for another
tissue, i.e. blood to neural. (…but there are
controversies about the role of cell fusion in this
process).
Hematopoietic Stem Cell Lineage
Adult Stem Cells Have Been Found in Many Tissues
Skin Intestine
Identifying Adult Stem Cells by Genetically
Labeling Slow-Cycling Cells in Specific Tissues
Tumbar et al., Science 2004
Cancer Stem Cells
Adult or Embryonic Stem Cells that turn
malignant?
Malignant Cells that display ―stem-like‖
property?
Criteria for Cancer Stem Cells
Enriched for tumorigenic ability.
Enable serial propagation in vivo.
Regenerate phenotype diversity.
Beginning of the Cancer Stem Cell Concept
1937: Jacob Furth and Morton Kahn: a single
leukaemic cell was able to transmit the systemic
disease when transplanted into a mouse.
1960s: Robert Bruce and Hugo Van der Gaag: only a
small subset of primary cancer tissue was able to
proliferate in vivo.
Not every cell is able to proliferate to form a colony
in vitro or to give rise to a tumor when transplanted
in vivo.
Models to Explain the Inefficiency of Transplantation
Prospective identification of Cancer
Stem Cells
1994. John Dick described a reproducible way of
enriching cells with tumor-initiating activity and ruled
out the stochastic model.
AML-initiating cells were not only able to
differentiate and proliferate, but also had the
capacity to self-renew in vivo — a key attribute of
stem cells.
Bonnet, D and Dick, J, 1997
Early Evidence for Existence of
Leukemic Stem Cell
• AML blasts are biologically heterogenous population of cells :
– in vitro colony forming assays, majority of blasts have
little proliferative capacity.
– in vivo only small percentage of leukemic cells can form
spleen colonies.
• Leukemias are organized in hierarchical fashion:
– Maintained by a small population of cells that have stem
like qualities ie. leukemic stem cells (LSC’s).
– Ability for self renewal.
– Extensive proliferative capacity.
Stem Cell Model of Hematopoiesis
Development of NOD/SCID Model
(non-obese diabetes/severe combined immunodeficiency)
• A stem cell is defined functionally:
– Cell that can give rise to long term multilineage engraftment to
lethally irradiated mouse
• Direct evidence for the existence of human leukemic stem cells
relied on the development of NOD/SCID model.
- SCID: deficient in B and T- cells.
- NOD: Deficient in NK cells, macrophage and complement
activation.
• Both human hematopoietic stem cells and AML samples could be
xenografted into irradiated immunodeficient SCID or NOD/SCID
mice.
Prospective Isolation and Functional
Characterization of Leukemic Stem Cells
No
Engraftment
NOD/SCID
AML
NOD/SCID
Bonnet & Dick, Nat Med. 1997
Conclusions from John Dick Experiment
• AML samples contain cell that can initiate a leukemia-
like disease in NOD/SCID deficient mice.
– Frequency 0.2 – 100 per 106 cells
– Contained exclusively in CD34+/CD38- population (population
phenotypically similar to HSC).
• SL-IC (SCID Leukemia – Initiating Cell)
– These cells can differentiate in vivo to blasts phenotypically
and morphologically similar to original tumor, proliferative
capacity.
– Serially transplantable, ie. can self-renew.
Normal and Leukemic Human Hematopoietic Hierarchies
Biological Properties of LSC
• Most LSC have quiescent cell cycle status (G0)
– Decreased sensitivity to cell cycle dependent agents such as
Ara-C
• Express ABC transporters MDR1 and Bcrp1
– Responsible for drug efflux of anthracyclines
• Upregulate
– Death-associated protein kinase (DAPK)
– Interferon regulatory factor 1 (IRF-1)
– NF-κB
Therapeutic Implications of LSC
• Target cell surface markers
– DT IL-3
– Myelotarg
• Target LSC specific molecular
pathways
– MDR inhibitor
– Proteasome inhibitors /
NF-κB
• Combined therapy with ABC
transporter inhibitor and
chemotherapy?
Structure and Renewal Cycle of Mammary Gland
Three types of mammary
epithelial cells
Myoepithelial
Luminal
-Ductual
-Alveolar
Virgin Pre-lactating lactating Post-weaning
Stem Cell Hierarchy in Normal Mammary Gland
and Breast Cancer
Mammary Gland Breast Cancer
Generation of a functional mammary gland
from a single mammary stem cell
MaSC amplification in pre-maligant mammary
glands of MMTV-wnt transfenic animals
Shackleton M,….Visvader JE, Nature 2006
Isolation of Breast Cancer Initiating Cells
Al-Hajj…Michael Clarke, PNAS 2002
Tumorigenic Cells highly enriched in
CD44+CD24-/lowESA+ Cells
Tumorigenic Cells can Re-create Phenotypic
Diversity in Tumors
Hierarchy in normal brain and brain tumor
Identification of Cancer Stem Cells
from Solid Tumors
• FACS enrichment of side populations.
• Prospective purification using cell surface markers
followed by tumorigenic assays.
• At the current state, more an art than a science.
Identification of Cancer “Stem Cells” by
FACS Sorting of Side Populations
Side Population
MCF7
B104
C6 Glioma breast Hela
neuroblastoma
Cancer
Markers of Normal and Malignant Adult
Tissue Stem Cells
Organ Normal Tissue Cancer
Hematopoietic CD34+CD38-Thy1+
c-kit+IL-3Ra-
CD34+CD38-Thy1-
c-kit-IL-3Ra+
Breast Lin-Sca1low
CD24medCD49fhigh
CD44+CD24-/lowLineage-
OR Lin-CD29hiCD24+
Brain CD133+ CD133+
Lung Sca-1+CD34+
Skin CD20+
Prostate CD44+/a2b1hi/CD133+
Cancer Genes play an Essential Role in
Controlling Stem Cell Self-renewal
Signaling Pathways in Stem Cells and Cancer
Adult stem cells in tissue are thought
to reside in niches
What is Stem Cell Niche?
Microenvironmental cells that nurture stem cells and enable
them to maintain tissue homeostasis.
An appropriate spatiotemporal dialog occurs between stem and
niche cells in order to fulfull lifelong demands for
differentiated cells.
Niche cells provide a shelering environment that sequesters
stem cells from differentiation stimuli, apoptotic stimuli, and
other stimuli that would challenge stem cell reserves.
The niche also safeguards against excessive stem cell
production that could lead to cancer.
Maintaining a balance of stem cell quiescence and activity is a
hallmark of a functional niche.
Germline Stem Cell Niche in Flies
Stem Cell Niche in Intestine
Transit
amplifying
Moore and Lemischka, Science 2006
Stem Cell Niche in Hair Folicle
Moore and Lemischka, Science 2006
Stem Cell Niche in Bone Marrow
Moore and Lemischka, Science 2006
Cancer Stem Cell Niche?
Does cancer stem cell niche exist?
What are the signaling cross-talks between CSC and
their niches?
Diversity of niches for different type of cancer and
their metastases in different niches?
Can we model CSC niche in vitro?
Diverse CSCs and their niches in the same patient
initiate different metastasis, and responsible for
different sensitivity to treatments?
Stem Cells and Drug Resistance of Cancer
Therapeutic Implications of Cancer
Stem Cells
Remaining questions
Do all cancers have CSC?
What are the real (physiological) marker of CSC?
What genes/pathways gives the self-renewal ability to CSC? Difference in the
self-renewal mechanism between normal stem cells and CSC?
Common governing principle of all cancer stem cells?
Does CSC arise through mutations accrued in normal tissue stem cells or
whether stem-cell properties are acquired in more differentiated progenitor
cells?
How easily can non-CSC evolve to become CSC through ongoing genomic
instabilities in cancer cells?
What makes CSC resistant to traditional therapies, how to make them
susceptible?
Cancer Stem niche—does that determine metastasis tissue tropism?
Stemness = Metastasis Ability?
