Lecture 6 - Angiogenesis and Metastasis Flashcards
What is Metastasis?
The ability of cancer cells to escape from the primary tumour via the blood and lymphatic system and to grow in a secondary site
What are the 4 clinical stages of cancer? (lung)
Stage I: Tumour 1-4cm. Disease has not spread outside of the lung
Stage II: Tumour is 3-7cm. Disease may be in lymph nodes or nearby tissues, but not in distant parts of the body
Stage III: Tumour is 3 cm to >7cm. Disease can be in >1 lymph nodes or nearby tissue, but not in distant parts of the body
Stage IV: Cancer has spear to distant parts of the body
What is the % of cancer mortality related to advanced metastatic disease?
90%
What percentage of cancers are diagnosed at stage III or IV?
45-46%
What are the stages in the metastatic cascade? (8)
- Primary tumour growth (proliferation)
- Angiogenesis
- Detachment and invasion into the surrounding tissue towards the vessels
- Intravasation into lymphatics/ capillaries
- Survival in the circulation
- Arrest in new/ secondary organ (small capillaries, adhesion to vessel wall)
- Extravasation into the secondary tissue
- Establishment of microenvironment
- death
- dormant
- proliferating
How do tumours overcome outgrowing their source of oxygen and nutrients?
- Change their metabolism (e.g. use fatty acids)
- Attract new blood vessels
- Co-opt existing blood vessels
What is angiogenesis?
The growth of new blood vessels
- formation, maturation and differentiation of blood vessels from pre-existing vessels.
What is an example of a time we would use angiogenesis not related to cancer in the body?
If you are wounded
What is tumour neo-angiogenesis?
the specific type of angiogenesis that occurs during tumour formation
- not programmed and depends on local signals
What condition drives neo-angiogenesis?
Hypoxia
What is HIF-1alpha?
hypoxia inducible factor 1 alpha is turned on by tumours in hypoxic conditions and is a transcription factor which leads to expression of VEGF (vascular endothelial growth factor)
Overview of MAPK cascade
Ras –> Raf –> MEK –> ERK –> Gene expression –> Cell Proliferation
What is VEGF and what does it do?
- vascular endothelial growth factor
- VEGF drives the growth of blood vessels
- VEGFR sits on endothelial cells
- tumour cells secrete the VEGF so that endothelial cells attracted towards the tumour
What are the receptors and ligands of the VEGF family?
Receptors - VEGFR 1,2,3
Ligands - VEGF A,B,C,D
What are the common pathways which VEGF signals through?
- MAPK
- PI3K/AKT
- PLC/PKC
- FAKL
What do the common pathways which VEGF induce lead to?
Proliferation, cell survival, migration
How is angiogenesis controlled normally?
- By an angiogenesis switch, as normally this process would be switched off when not needed in the body.
- Endogenous inhibitors inhibit the growth of blood vessels
What are the main characteristics of tumour angiogenesis?
- Disorganised vascular structure
- Low inter-endothelial cell junctions
- Low pericyte coverage
- Increased microvasculature permeability (leakiness)
- High interstitial fluid (IFP)
- High pressure, collapsing
What are some of the therapeutic strategies to inhibit angiogenesis?
- Inhibit production of angiogenic proteins
- Neutralise activators
- Stop blood vessels growing at the receptor stage
Name a small molecule inhibitor for anti-angiogenic therapy
Sorafenib
- inhibits MAPK but also inhibits VEGF receptors
- tyrosine kinase inhibitor
Name a monoclonal Ab for anti-angiogenic therapy and its mechanism of action
Bevacizumab
- antibodies against VEGFA so ligand can’t bind, neutralises VEGF-A
Why might some cancers respond better than others to Bevacizumab?
- If VEGF is the main cause of angiogenesis it will respond better than cancers where there are other contributing factors
What cancers typically respond better to Bevacizumab and what respond worse?
Better - Colorectal and Renal carcinoma
Worse - Malignant melanoma, pancreatic, breast, prostate
What are the resistant mechanisms cancer use against angiogenic therapies?
- Metabolic adaptation
- Re-vascularization by the expression of alternative angiogenic factors (e.g. bFGF, PDGF)
- Co-option of normal peritumoural blood vessels and vascular mimicry
- Blood flow alterations owing to vessel pruning and normalization can improve blood flow
What might your anti-angiogenic therapy actually end up doing to the cancer which you don’t want?
- May induces vascular regression
- which leads to intratumoral hypoxia
- selection of more invasive cancer cells
- which resistant to anti-angiogenic therapy.
What is it which tumours do to get into the surrounding tissues towards the vessels?
Change their phenotype via the epithelial to mesenchymal transition (EMT)
What are typical markers of epithelial cells?
- adherence junctions (E-cadherin)
- epithelial markers: E-cadherin, b-catenin
- cytokeratin expression
- epithelial cell polarisation
What are typical markers of mesenchymal cells?
- fibroblast-like shape
- increased motility an invasiveness
- secretion of proteases (MMPs)
- mesenchymal markers: N-cadherin, vimentin
What is MMP?
matrix metallo proteases
Secreted during the EMT to help degrade the matrix
What is the opposite of EMT which is important once tumours have got to their secondary site?
Mesenchymal to epithelial transitions MET
What is the main signalling pathway which activates EMT?
TGFbeta pathway
Overview of the TGFbeta pathway
- TGFbeta binds to the TGFbeta receptor which phosphorylates it
- Leads to phosphorylation of SMAD 2 and SMAD 3
- SMADs translocate to the nucleus acting as transcription factors leading to expression of ZEB1, SNAIL and TWIST
- These factors drive mesenchymal phenotype
What cells can secrete TGFb?
- Cancer cells
- Fibroblasts
- Epithelial cells
- Complex network of cells which contribute
What can stimulate the EMT?
Autocrine signalling can stimulate EMT.
Sectreted factors from the microenvironment act in a paracrine fashion to induce epithelial–mesenchymal transition (EMT).
What is the process of intravasation?
- Happens once cancer cells have migrated through to the tissues by blood vessels
- process of entering the blood vessel
- enter the circulation by transmigrating paracellularly through the endothelial cell (EC) junctions
- pass transcellularly through
What is the most important thing cancer cells have to do once they have made it into the blood vessels?
Survive
Why is it difficult for cancer cells to survive in the blood vessels?
- will encounter immune cells
- platelets
- bumping against the wall they will get damaged and die
What else can cancer cells die of in circulation?
Anoikis - death due to not being attached to something
How do cancer cells overcome Anoikis?
- Adaptation of metabolism to keep ATP production –> protein production
- Increase in survival signalling through other pathways
- Increase expression of pro-survival factors
What happens once cancer reach their secondary site?
- Adhesion molecules will mediate the adhesion of cancer cells to the secondary site
What are examples of adhesion molecules used by cancers at the secondary site?
Selectins (P-selectin, L-selectin)
CD44
Integrins
How might cancer cells die when they have reached their secondary site?
Tumour cells might get stuck trying to get out
They might adhere to different sites
What are the other ways other than in the blood which cancer cells can metastasis around the body?
- Transcoelomic spread
- Lymphatic spread
- Hematogenous spread
- Canalicular spread
What is the seed soil hypothesis?
- Most cancers don’t stop at the first environment they come to
- Provision of a fertile environment which supports the growth of the tumour cells is where they will stop
What must the secondary site have for the cancer to stop there?
- Compatible adhesion molecules on endothelial cells
- Appropriate growth factors and ECM
- Selective chemotaxis
- Physical features
What do some cancers do instead of settling and growing at their new secondary site:?
Establish dormancy - arrest of tumour growth in the primary or at a metastatic sites. Cells stay quiescent and do not divide until a favourable environment is present.
What affects the ways in which cancers metastasise?
- The cancer type
- The time of metastasis
- the route taken to metastasise
Breast cancer most common metastasis
Lung earlier on
What therapies are available to target metastatic disease?
- Not many effective ones
- But all the usuals may be used
What are we looking to do when targeting metastatic disease?
- Control further metastases
- Control the growth of both the primary and secondary tumours
- Relieve the symptoms experienced by the patient
What is Denosumab and what does it do?
- monoclonal antibody
- targets the receptor activator of nuclear factor-kappaB (RANK) ligand (a protein essential for osteoclast differentiation activity and survival)
- Loss of osteoclasts from the bone surface reduces bone turnover and bone loss in malignant and benign diseases
- In breast cancer, bone metastases are frequent – cancer treatment-induced bone loss (CTIBL) also occurs
How does cancer metastasise via Transcoelomic spread?
- Through body cavities
- e.g. penetrating peritoneal, pleural, pericardial or subarachnoid spaces
- ovarian tumours to liver surface
How does cancer metastasise via Lymphatic spread?
- via lymphatic system
- most common route for initial spread carcinomas
- e.g. breast cancer
How does cancer metastasise via Hematogenous spread?
- favoured route of sarcomas
- certain types of carcinomas tend to follow venous flow due to thinner walls of veins
- e.g. colorectal to liver via portal vein
How do cancers metastasise via Canalicular spread?
- favoured by carcinomas through a small passageway - e.g. bile ducts, urinary system, subarachnoid space
