Cancer and stem cells Flashcards
Where are all the precursors of the cell types of the body?
In the 3 germ layers
When do the pluripotent cells start differentiating?
During gastrulation
What happens to the stem cells when they leave the niche?
They begin to differentiate and give rise to more specialised cell types
Under the influence of pro-differentiation signals
What development does the cell cycle drive?
BOTH embryonic and postnatal development
What genes disrupt the cell cycle?
- Oncogenes: capable of transforming a normal cell –> cancer cell when ACTIVE
- TSG: restrict proliferation when active (mutations inactivate)
What are carcinogenic factors?
1) Chemical:
- Smoking
2) Parasites
3) Radiation:
- UV
- Ionising
4) Viruses:
- HPV
- HBV
What are carcinogenic factors capable of?
Activating oncogenes
Inhibiting TSGs
Describe the appearance of tumours
What does this mean?
Heterogeneous
Cells in the SAME tumour exhibit DIFFERENCES in terms of:
- Differentiation rate
- Proliferation rate
- Migratory and invasive capacity
- Size
- Therapeutic response
- Tumourgenicity
What is ‘intra-tumour heterogeneity’
Differences between cells in the same tumour
What is ‘inter-tumour heterogeneity’?
Differences between DIFFERENT tumours
How is the heterogeneity between tumours explained?
2 different models:
1) Stochastic
2) Cancer stem cell model
What is the stochastic model for cancer?
States that ALL tumour cells are EQUIPOTENT and can either differentiate or self-renew
Cells have unlimited proliferative capacity
ALL the cells of a tumour are tumour-initiating
All tumour cells are EQUALLY SUSCEPTIBLE to treatment (all have the same proliferative potential, all can be targeted by anti-proliferative drugs)
What does equipotent mean?
Equal capacity to differentiate
What are the problems with the stochastic model for cancer?
Tumours tend to RECUR after treatment, indicating:
- Not all cells are EQUALLY vulnerable to anti-proliferative treatments (some are differentially resistant to the drugs)
What is the cancer stem cell model for cancer?
States that only a SUBSET of tumour cells have the ability for long-term self renewal and therefore cancer formation
These cells give rise to COMMITTED progenitors with LIMITED proliferative potential that will eventually terminally differentiate
What does the cancer stem cell model form?
A hierarchy of differentiation:
- Tumour stays heterogenous
- Small reservoir os slowly proliferating CSCs
What are the therapeutic implications of the cancer stem cell model of cancer?
1) CSCs represent a very SMALL fraction of the cells in the tumour
2) If treat the cancer with drug that kills mainly proliferating cells - CSCs ESCAPE treatment
Why do CSCs escape the drug treatment that kills mainly proliferating cells?
CSCs are slowly proliferating/dormant
Resistant to the treatment
How can normal stem cells be functionally tested?
Ability for functional reconstruction
How can cancer stem cells be functionally tested?
Ability to initiate a tumour
What is the difference between the need for self-renewal in normal stem cells and cancer stem cells?
Normal - needed in order to maintain HOMEOSTASIS
Cancer - serves as a tool for TUMOUR GROWTH
What is the difference/similarities between the regulation of normal stem cells and cancer stem cells?
Similarities: Same signalling pathways (eg. Wnt)
Differences: Cancer - ELEVATED signalling
What are the different possibilities for a cancer cell to arise?
1) REPROGRAMMING event:
- One or more genetic/epigenetic transformation events that drive specialised cells (differentiated from stem cells) BACK into cancer stem cell entity
- Gives the cells capacity for self-renewal and differentiation
2) ONCOGENIC transformation:
- Normal stem cell transformed into a CSC that fuels tumour growth
- Through number of genetic/epigenetic transformations
Are the 2 mechanisms that can cause cancer mutually exclusive?
NO - they can happen in the SAME tumour
BUT, different cancers can be driven by one more than the other
What 2 features allow cancer stem cells to be characterised?
1) In VITRO potential (Establish cell lines that can self-renew and differentiate)
2) In VIVO potential (Ability to give rise to cancer following transplantation into animals)
What is acute myeloid leukaemia?
Blood cancer affecting the myeloid lineage
What do haemopotetic stem cells give rise to?
ALL blood cells
Where is the niche for haemopotetic stem cells?
In the bone marrow
How are haemopotetic stem cells characterised?
By the POSITIVE expression of CD34
By the NEGATIVE expression of CD38
What assay for testing HSCs ability?
- Take mice lacking the immune system and sub-lethally radiate the mouse to wipe of the HPC system
- -> eventually the mice DIE
BUT
- If transplant a SINGLE HSC into the mouse - can rescue the ENTIRE haematopoietic system
What happens to the Haemopoietic cell in leukemia?
- Undergoes ONE or MORE transformation events under the influence of genetic drivers
–> TRANSFORMED into a leukemic stem cell that has the ability to self-renew and differentiate
(With a biast differentiation to the myeloid lineage)
What happens if transplant a leukemic stem cell into an immunocompromised mouse with no HP system?
Generate BLOOD CANCERS in the mouse
What is glioblastoma?
An aggressive and invasive BRAIN CANCER
What is the treatment for glioblastoma?
- Surgical resection
- Radition
- Chemotherapy
As glioblastomas are heterogenous, what idea did this bring forward?
That they are driven by stem cells (cancer stem cell model)
In the stochastic model - all the cells are EQUAL (not driven by CSCs)
How can multi potent stem cells be captured in vitro?
- Dissociate the cells from a brain
- Plate the cells of laminin in the presence of cytokines: FGF2 and EGF
What are the undifferentiated markers for NS cells?
What are these cells negative for?
RC2
Negative for differentiation markers: GFAP (glia) and TUJ1 (neurons)
Can we isolate glioblastoma stem cells using the same methods as isolating NSCs?
Why?
Yes
As glioblastoma is driven by NS cells - NS cells are transformed into CSCs
Describe the glioblastoma stem cells are isolated
What does this produce?
Dissociate the cells from the glioblastoma and CULTURE them under the SAME conditions as the NSCs
(On laminin, in the presence of cytokines)
Produces self-renewing GBM colonies that express undifferentiated markers - Indicating the self-renewal stage
What are the undifferentiated markers of GBM colonies?
Nestin/Sox2
What happens if remove the self-renewal factors from the GBM colonies?
Forces the GBM stem cells to DIFFERENTIATE
What do the GBM glial cells express?
GFAP
What do the GBM neural precursors express?
Dcx
What is the difference between GBM cells and normal NSCs?
DIFFERENT tumours give rise to DIFFERENT GBM stem cell lines with DIFFERENT capacities for differentiation
What does the injection of undifferentiated GBM stem cells into the brain of mice cause?
GBM-like tumour
What can in vitro cancer cell systems be used for?
Example?
Drug screens - to identify suitable drugs to treat the tumours:
- Identify molecules that create/block a certain phenotype
Example:
- GBM and normal foetal NS cells - look similar when untreated
- Treat with INDATRALINE: selectively kills the GB cells through growth arrest, with a less severe effect on the NS cells
What are the 3 main approaches to study cancer?
1) Xenograft models - Inject tumour cells into a permissive environment (eg. kidney)
2) Cancer cell lines in the petri dish - form tumours
3) Genetically modified animals - Manipulated to over express oncogenes or TSG mutations
What are the limitations of using cell lines and animal models to study cancer?
What can be a solution to these problems?
- Failure to capture the TRANSITION from a normal to a tumourgenic phenotype in:
A traceable manner
In human context - Lack of mechanistic insight (mechanism that drives the process)
Solution:
- iPS cells
How can iPS be used to study cancer?
1) iPS from patients that carry the tumour
- iPS represents the early emrbyonic stem cells of these patients
2) Can introduce oncogenic mutation into the human pluripotent stem cell
These cells differentiate into the cell origin of the tumour:
- Can examine the phenotype and look for the hallmarks of cancer
What are the hallmarks of cancer?
- Sustained proliferation
- Impaired differentiation
- Formation of a cancer if transplant into a permissive environment
What is neuroblastoma?
Common solid tumour in infants/young children
Above the kidney, in the adrenal gland
Or
Around the spinal cord
Where does neuroblastoma originate from?
The neural crest
What do aggressive neuroblastomas express?
What is this?
High levels of the transcription factor MYCN
An oncogene
What does ectopic expression of MYCN in normal neural crest cells in the mouse cause?
Neuroblastoma-like tumours
Where do the neural crest cells come from?
The ECTODERM
What is the main marker of neural crest cells?
Sox10
How can the production of neural crest cells be mimicked using iPS cells in vitro?
Why do we want to do this?
Capture iPS cells in conditions that promote neural crest emergence in the neural tube (Wnt, BMP)
Want to do this in order to study neuroblastoma:
- Want to see what happens during the transformation from a neural crest into a neuroblast
- BUT, this can’t be seen in vitro
- May be able to instead, differentiate iPS cells –> neural crest and over express MYCN to get the neuroblastoma phenotype
What does the capture of iPS cells in conditions that promote neural crest emergence in the neural tube (Wnt, BMP) generate?
What happens if over express MYCN in these cells?
Cells that represent the neural crest and express Sox10
If over express MYCN:
- Higher colonic efficiency
- Differentiate faster compared to control
- If graft into a mouse –> form a tumour that represents human neuroblastoma
What method could be used to found the mechanism from the neural crest to transformed neuroblastoma cells?
- Differentiate iPS cells –> neural crest
- Over express MYCN –> get the neuroblastoma phenotype
What is ‘colonic efficiency’?
If take cells and re plate them - give rise to more colonies
