Tumour Biology Flashcards
What is metastasis?
It is a tumour deposit discontinuous with the primary tumour
Metastasis is a multifactorial process
Metastasis are the major cause of death from a malignant disease because of its difficulty to treat
Key properties of a metastatic cell
Detachment from the primary mass
Invasion of the ECM e.g. Basement membrane
Adhesion to endothelium
Extravasation
Avoidance of the immune system
Colonisation of and survival in secondary organ
What happens in detachment - loss of adhesion?
Adhesion molecules are downregulated in metastatic cancer cells
E-cadherin is common, indicating that loss of cell attachment is important for invasion.
Loss of adhesion is not just about cells detaching from each other what else happens with e-cadherins
When e-cadherin is lost beta-catenin is normally adhered too so when e-cadherins detaches it goes into the cytoplasm and is degraded in normal situations by the proteosome in combination with APC, when APC is mutated beta-catenin cannot be removed thus accumulates in the cytoplasm working in combination with transcription factors to induce EMT and cell cycle genes are influenced.
Loss of e cadherins and APC 2 genes cooperating to lead to proliferation and metastasis
What is required for tissues invasion?
Require degrading enzymes - matrix metalloproteinases required to degrade the ECM. They are normal enzymes involved in tissue remodelling.
May be secreted by tumour cells, but also by the strong which is important in tumour progression
How is the stroma abnormal in cancer
Contributes to the process of tumour invasion, tumour produces soluble factors to activate the stroma
Secreting the MMPs
Cells in stroma become activated - fibroblasts to secrete MMPs
MMPs allow the break down of the basement membrane which allows the stroma and tumour cells to interact
The tumour cells make up approximately 1% of the tumour mass.
What is the epitheilal-mesenchyme transition
This regulates invasion and metastasis
EMT is a normal process usually occurring during wound injury
Epithelial cells become spindle-like like mesenchyme
Migrates to site if damage
The reverts to epithelial morphology
This process is abnormally acquired by metastatic cells. And is used to acquire a secondary tumour site.
What regulates EMT?
Transcription factors,
Slug, snail, twist zeb1/2
Induced by TGF beta and RTK
What are the different kinds of invasion?
Ameboid - moment as a single cell in epithelia form
Mesenchymal after process of EMT
How does adhesion and extravasation occur?
As tumour cells enter small slow by size restriction and adhere through receptor ligand interactions
Travel in blood and lymph
Similar to inflammation - use identical ligand receptor adhere and extravasate like neutrophils
Outcome once colonised at secondary site
The outcome is not certain. It is dependent on the availability of growth factors and the environment to support the cells.
Patterns of metastatic spread is explained by?
Non random
Seed and soil hypothesis spread is governed the nature of the cancer cell (seed) and its new environment (soil)
Anatomical and mechanical routes - determine spread
E.g. Colorectal cancer going to the liver via the portal system .
New field: CTC
Circulating tumour cells, detect what is means for the future of the patient. Detect prognosis.
Acts in support of the seed hypothesis
What is the metastasis niche?
Tumour cells secrete factors which act systemically modifying the local environment and recruiting host immune cells, facilitating the appropriation of these sites for later colonisation
How does hypoxia drive invasions and metastasis?
Early in cancer development tumour cells are dependent on existing blood supply but as tumour gets bigger needs more nutrients
All cancers are hypoxic O2 is lower than required to sustain normal cells
Hypoxia initiates angiogenesis by HYPOXIA INDUCIBLE FACTOR -HIF
Normoxia - HIF interacts with pVHL causes degradation by ubiquitation.
In hypoxia - no interaction with pVHL. HIF alpha and HIF beta interact and induce gene expression of VEG for example.
Differences between cancerous vasculature and normal vasculature
Tumour vasculature is chaotic and leaky, not like normal vasculature, there are lots of holes to help with tumour migration facilitating survival and spread
They have partition lumen and multiple intercellular openings
Normal vessels: have a smooth cobblestone appearance.
Other mechanism tumours change to overcome the hypoxic environment
‘Glycolytic switch’
Alters the glucose metabolism from mainly by oxidative phosphorylation but to glycolysis predominantly. More anaerobic processes
Upregulate glucose intake more receptors and metabolism inc no glucose transporters and no of metabolites - super glucose user to feed cells energy requirements
This allows them to outcompete the other cells more uptakers. So they die less cells to compete with
Creates and acidic environment which other cells cannot survive so induces more cell death.
- micro natural selection
Characteristics of malignant tumours
Malignant cell growth
Metastasis
Glycolytic switch
Angiogenic switch
Malignancy is associated with loss of:
Density dependent inhibition of growth - once normal cells reach and finite density thy stop growing, cancer cells do not stop growing and divide a lot, a tumour that exhibits density dependent inhibition is benign
Contact inhibition of movement- normal cells move away from each other cancerous cells do not they cluster forming a tumour
Anchorage dependence - normal cells need contact with substratum for growth, cancer cells do not
Adhesion- normal cells are firmly adhered to each other and to their basement membrane, cancerous cells loss of adhesion to ECM and to other cells- mobile and can metastasise
Tumour development
Multi step Mutations occur leading to Apoptosis bypass Decrease in CAMs Cell cycle deregulation Increase motility and mobility
What type of tumour exhibits density dependent inhibition of growth
Benign tumour
A tumour which does not exhibit density dependent inhibition of growth is
A malignant tumour
Process of metastasis
The tumour invades beyond normal tissue boundaries - MMP to ECM
It detaches from primary tumour mass - down reg of CAMs
Tumour enters vascular or lymphatic endothelium
EMT travel
Slow down as vessels get smaller role along the vessel become attached and extravasates
Establishes itself in the new environment local tissue invasion and angiogenesis
EMT
Cancer cells abnormally acquire this process,
Normally cells involved in repair and the immune system can change from epithelial like to mesenchymal in order to travel to the area
Cancer cells acquire this process and use is migrate
It regulated by TGF and RTK acting in slug to decrease epithelial markers and increase mesenchymal ones
Process of detachment from cell membrane
Done regulation of CAMs
E cadherins common and spans the plasma membrane of adjacent cells and is attached to the cytoskeleton by beta catenin
When e cadherins is down regulated beta catenin is released into the cytoplasm
Normally degraded in combination with APC by the ubiquitin proteosome pathway
In a cell where APC is already mutated cannot be graded
Instead it binds to the TCF/LEF family of transcription factors which up regulate the transcription of c-Myc gene which controls the cell cycle
Over expression of Myc will increase the cell cycle
Lead to uncontrolled growth ?
Invasion
Degrade BM
Release of MMPs from the tumour cells and the stroma
Activated fibroblasts release MMPs
E.g. Breast tissue hard lump due to the activated fibroblasts
MMP used normally is tissue remodelling
Adhesion to endothelium
Tumour cells enter small capillaries slow down start to role on the surface of capillaries where there are selectins P,L,E which. Bind with tumour cells integrins and allow extravasation
Colonisation and survival in the secondary organ
Pattern of metastatic spread can be explained by
The growth factors of the environment
Breast cancer cells express CXCR4 metastasise in lungs due to expression of CXCL12
Also explained by anatomical location
Colorectal going to the liver by portal vein system
Surviving is the rate limiting step in metastasis and often prevents it
Glycolytic switch
Most cancers switch the energy generation mechanisms in the cell to glycolysis
As is faster and doesn’t require oxygen which may be difficult to get
The glycolytic switch is the upregulation of glucose transport mechanisms in the cell and the enzymes used in glycolysis
Due to cell size and number oxygen has become difficult to ascertain and use so by upregulating glucose acquisition and metabolism they can outcompete surrounding cells.
Cells in the centre of the tumour do not get much oxygen so they cause the switch within the cells to glycolysis so as more cells become hypoxic the most glycolysis is used
Which scan can be used to see cancer cells usage of oxygen
PET scans
What does glycolysis do to the surrounding environment
It causes it to become acidic
Due to lactic acid generation
As well as outcompeting surrounding cells for oxygen as glucose
The normal cells cannot function in the acidic environment whilst the cancerous cells are more resistant to it so can survive.
Angiogenesis
Growth of new capillaries
Normal process in embryogenesis and wound healing
Angiogenic stimuli is hypoxia
Needed in tumours otherwise the centres can become necrotic - too long a diffusion distance tumour produces - VEGF and FGF recruit endothelial progenitors and can cause existing blood vessels to proliferate
Some cases the tumour cell can transdifferentiate into endothelial cells
Vasculature not like normal it is chaotic and leaky (better for metastasis)
Some tumours are more angiogenic than others
Some tumours can be hypovascular and some hypervascular so can either not or can be treated with anti angiogenic mechanisms
Balance between pro and inhibitory angiogenic factors
