Stem Cells in Cancer: A Review
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Transcript of Stem Cells in Cancer: A Review
Stem Cells in Cancer: A Review
Jovana J. GrbićSchultz Group Seminar
October 18, 2005
Stem Cells in Cancer: A Review
• Introduction and Background
– What is a stem cell? What is a cancer stem cell?– Epithelial cancer stem cell characteristics– How many insults could you take?– How do you know it’s the stem cells?– Therapeutic Implications– Where no scientist has gone before….
• Specific Case Studies:– Colorectal Cancer (CRC) and epithelial stem
cell renewal– Breast Cancer: mammary stem cells– AML/CML leukemias: leukemic stem cells
What is a Stem Cell? What is a Cancer Stem Cell?
• Fundamental homeostatic system for replacing terminally differentiated cells of the body due to senescence and injury
• Involves stages of division with decreasing reproductive capacity and increased commitment to differentiation
• Self-replication and progeny production
• Cancerous growth is abberant normal tissue homeostasis
Stem cell→committed progenitor→diff. cell
• Tumor stem cell model mimics normal tissue models
• Variations in tumor growth rates: variations in homeostatic mechanisms of SC regulation and preturbations in the niche microenvironment
• CSC’s arise from a multi-step process that parallels the slow development of cancer from normal tissues
Biochim Biophys Acta. 2005 Sep 25;1756(1):25-52
Nat Rev Cancer. 2005 Apr;5(4):275-84
How Many Insults Could You Take???
• I: Pretumor Progression– Mutational acquisition
(prenatal)– Additional mutations– Clonal expansion of stem cell
“niche”
• II: Patches– CSC ventures outside its niche– Present in phenotypically
normal epithelia
• III: Fields– Larger regions of clonal
outgrowth, may begin to manifest histologic atypia
Therapeutic Implications
• Multi-Drug Resistant Proteins– ABCG2 inhibitors, ABCG2
antibodies, stem cell inhibitors, immunotherapy
• Irradiation– Stem cells may be more
sensitive to irradiation
• Differentiation, apoptosis, and senscence
Where No Scientist Has Gone Before
• Identification of CSCs– Similar phenotype, slow cycling, constitute small percentage, BUT contain
many unique markers as well.
• Why can’t ablate with traditional chemotherapy?– Target rapidly dividing cells, overexpress a lot of ABC drug-transporters
• How do early epithelial CSCs migrate?– Form temporary migratory phenotype (i.e. wound healing, patches/fields)
• How are CSCs removed from a tumor population?– No mechanism as of yet for total progression from CSC to committed cell
lineage with loss of stem cell population
• Different cancers in the same organ:– Different malignant stem cells or different “packaging” of the same stem
cell?
Stem Cells in Cancer: A Review
• Introduction and Background
– What is a stem cell? What is a cancer stem cell?– Epithelial cancer stem cell characteristics– How many insults could you take?– How do you know it’s the stem cells?– Therapeutic Implications– Where no scientist has gone before….
• Specific Case Studies:– Colorectal Cancer (CRC) and epithelial stem cell
renewal– Breast Cancer: mammary stem cells– AML/CML leukemias: leukemic stem cells
Endothelial Gut Lining: Physiology and Stem Cell Renewal
Science. 2005 Mar 25;307(5717):1904-9
Colon epithelium
Canonical Wnt Signaling Maintains Crypt Progenitor Compartments
Cell. 2002 Oct 18;111(2):251-63Nat Genet. 1998 Aug;19(4):379-83
Wnt cascade is dominant force in controlling cell fate along crypt-villus axis:
~Staining for nuclear β-catenin mainly observed in crypts
~Tcf4 -/- mice lack proliferative compartments for maintaing progenitors
Intestinal Tumorigenesis:Mutational Wnt Pathway Activation
• Most molecular insights of CRC come from hereditary studies (5-10% of cases)
• Familial adenomatous polyposis (FAP): patients carry numerous polyps, invariably develop CRC around age 40
• Carry one mutant copy of APC– C-terminal truncation
• Inappropriate activation of intestinal TCF4—imposes proliferative phenotype in crypt epithelial cells
Cell. 2002 Oct 18;111(2):241-50
Science. 1997 Mar 21;275(5307):1784-7
Notch/bHLH Signaling
Science. 2005 Mar 25;307(5717):1904-9
• Important for regulating cell fate decisions/differentiation
• Most likely target is Hes family of bHLH proteins– Notch target genes control
intestinal homeostasis
• Hes1-/- mice contain increased secretory cells at the expense of absorptive enterocytes
Nat Genet. 2000 Jan;24(1):36-44.
CRC: Conclusions
• Crypt-villus unit represents one of the simplest self-renewing entities in mammalian biology
• Regulatory signaling pathways have emerged from embryonic development studies as a key in maintenance of this structure
• Transformation process probably manipulates key physiological regulators of normal intestinal epithelium as most efficial roadblocks towards cancer (not mutational changes in generic oncogenes or tumor suppressors)
Stem Cells in Cancer: A Review
• Introduction and Background
– What is a stem cell? What is a cancer stem cell?– Epithelial cancer stem cell characteristics– How many insults could you take?– How do you know it’s the stem cells?– Therapeutic Implications– Where no scientist has gone before….
• Specific Case Studies:– Colorectal Cancer (CRC) and epithelial stem cell
renewal– Breast Cancer: mammary stem cells– AML/CML leukemias: leukemic stem cells
• Most common malignant disease in Western women
• Despite advances, metastatic breast cancer remains a death sentence– Current treatment is limited by
emergence of therapy-resistant cells
– Early detection/treatment have drastically cut overall death rates
• Adequate predictions of metastatic invasion are KEY– 80% of women receive adjuvant
chemotherapy, only 40% need it
J Cell Sci. 2005 Aug 15;118(Pt 16):3585-94
Breast Cancer Background InfoMammary Arbor Architecture and
Cell Engineering
•Label-retention studies: 5-Br2-dU
•Cell-surface markers (Sca-1, CD49f)
•DNA-binding dyes: Hoechst efflux
•Hormone Receptor Status (ER, PR)
Signalling Pathways and Mammary Stem Cell Regulation
• Originally identified as a viral insertion in a MMTV-induced mammary tumor
• Stabilization of β-catenin in >50% breast cancer tumors (poor prognosis)
• Knockout mice lacking LEF/mice expressing Dickkopf (Wnt inhibitor) fail to develop mammary glands
• Wnt signaling plays a role in several human ovarian/breast cancer cell lines
• Important role in neoplastc mammary stem-cell-like progenitors– Expansion of Sca1+ progenitors in Wnt+
transgenic mice
– Did not observe such expansion in non-Wnt mediated tumor models
Wnt
Cancer Cell. 2004 Nov;6(5):497-506
Proc Natl Acad Sci U S A. 2003 Dec 23;100(26):15853-8
Signalling Pathways and Mammary Stem Cell Regulation
• Originally identified as a viral insertion in a MMTV-induced mammary tumor
• Stabilization of β-catenin in >50% breast cancer tumors (poor prognosis)
• Knockout mice lacking LEF/mice expressing Dickkopf (Wnt inhibitor) fail to develop mammary glands
• Wnt signaling plays a role in several human ovarian/breast cancer cell lines
• Important role in neoplastc mammary stem-cell-like progenitors– Expansion of Sca1+ progenitors in Wnt+
transgenic mice
– Did not observe such expansion in non-Wnt mediated tumor models
Wnt
Cancer Cell. 2004 Nov;6(5):497-506
Proc Natl Acad Sci U S A. 2003 Dec 23;100(26):15853-8 Keratin-6 staining
Signalling Pathways and Mammary Stem Cell Regulation-II
• Important in normal mammary development and identified as MMTV insertion site in mammary tumors
• Notch4 transgenic mice develop mammary tumors
• Role of Notch in formation of mammospheres:
• Important for normal development of virtually every organ system
• Pathway components shown to be OE in many cancer types (including breast)
• Majority of human breast cancers show uniform OE of PTCH1 and nuclear Gli1
• Cyclopamine confers growth inhibition of a subset of breast cancer cell lines in vivo
Notch Hedgehog
Breast Cancer Res. 2004;6(6):R605-15. Cancer Res. 2004 Sep 1;64(17):6071-4.
Identification and Isolation of Tumorigenic Breast Cancer Cells
PNAS U S A. 2003 Apr 1;100(7):3983-8
• Exponential increase in breast cancer with woman’s age
• Stem cells are an attractive target due to unlimited replicative potential
• Cell-surface markers used to identify/isolate subpopulation of tumorigenic cells– CD44+/CD24- cells show increased tumor formation
– As few as 100 cells can recapitulate human tumors
– CD44+/CD24- cells can be cultured indefinitely
Mammary Stem Cell Progression Model
CANCER!!!NORMAL TISSUE
Conclusion: Clinical ImplicationsProposed Future Breast
Cancer TreatmentKaplan-Meier Survival PlotBased on CD44 Expression
Histopathology. 2003 Jun;42(6):546-54
CD44+ breast tumor cells confer both lower rates of overall and disease-free survival
LESSONS FROM CURRENT TREATMENTS:
-Tumors can undergo accelerated repopulation between daily radiation doses (clonogenic assays)
-Tumor stem cells likely more resistant to both chemotherapy/radiation (repopulate from added stress of treatment)
-Treatment of Sca1+ mammary cells with taxol or radiation leads to increase in clonogens formed in matrigel
Stem Cells in Cancer: A Review
• Introduction and Background
– What is a stem cell? What is a cancer stem cell?– Epithelial cancer stem cell characteristics– How many insults could you take?– How do you know it’s the stem cells?– Therapeutic Implications– Where no scientist has gone before….
• Specific Case Studies:– Colorectal Cancer (CRC) and epithelial stem cell
renewal– Breast Cancer: mammary stem cells– AML/CML leukemias: leukemic stem cells
Hematopoiesis
Nat Rev Immunol. 2005 Jun;5(6):497-508
Hematopoietic system constantly generates specialized cell types from HSC progenitors:
The stem cell niche supports HSC regeneration/maintenance via stromal cells and osteoblasts
Earliest bifurcation is the multi-potent progenitor, which branches off into the common myeloid progenitor (E, M, MK, G) or common lymphoid progenitor
Lymphoid progenitors can branch into the pro-T-Cell or pro-B-Cell differentiation pathways depending on gene expression
Blood. 2005 Apr 1;105(7):2631-9.
Acute Myelogenous Leukemia Models
Nat Rev Cancer. 2005 Apr;5(4):311-21
Leukemias are myeloproliferative disorders that are clonal in nature
Earliest identified model for CSCs (LSC): only 1/1,000-5,000 cells could form colonies…massive cell injections in mice to replicate leukemias
LSCs express similar surface markers (CD34+/CD38-), telomerase levels, and are able to repopulate diverse cancer progenitors in mouse models
Stem cell pathway candidates for LSC transformation
NOD/SCID Mouse expansion of normal and neoplastic HSCs
Alternative HSC transformation model
Leuk Res. 2005 Sep 21 Epub
Polycomb group gene Bmi-1 determines the proliferative capacity of normal and leukemic stem cells
•Indispensable for generating AML in mice•Only 1% of Bmi-1 -/- cells could form colonies (>1010 cells) while 24% of Bmi-1+/+ cells did•Bmi-1 -/- weakly leukemogenic in vivo (transplants), but the effect is rescued by forced expression of Bmi-1 in these cells•From this data, we may construct more sophisticated models for LSC generation (i.e. cooperating genetic events, TLS-ERG)
Nature. 2003 May 15;423(6937):255-60.
Leukemia. 2005 Oct;19(10):1794-805
Chronic Myelogenous Leukemia
Nat Rev Cancer. 2005 Mar;5(3):172-83.
The Philadelphia Chromosome: t(9;22)(q34;q11)
Largely viewed as biphasic: Bcr-Abl translocation/expression in HSCs followed by expansion of CML-chronic phase granulocytes
Additional mutations (many discussed today) lead to blast phase CML: uncontrolled expansion of either myeloid (2/3) or lymphoid (1/3) blast cells
Gleevec
Therapeutic Directions
Nature. 2005 Jun 30;435(7046):1169-70
Nat Rev Cancer. 2005 Apr;5(4):311-21
Mathematical model of CML reoccurence post-Gleevec treatment:
S= LSC
P= Leukemic progenitors
D=differentiated LS
TD=terminally differentiated
Nature. 2005 Jun 30;435(7046):1267-70
Leukemic stem cells are NOT depleted by Gleevectreatment
Future cocktail therapies must address this problem