carcinogenesis Flashcards
angiogenesis: explain the basic mechanisms regulating angiogenesis, summarise the molecular mechanisms involved, explain the role of angiogenesis in health and disease, summarise the prospects for anti-angiogenic and pro-angiogenic therapies in cancer treatment
define angiogenesis
new blood vessel growth
3 physiological examples of angiogenesis
embryonic development, wound healing, menstrual cycle (uterine lining)
4 occurances when insufficient angiogenesis
baldness, MI (ischaemia), limb fractures, thrombosis
vascular malformations: 2 examples of angiodysplasia
hereditary haemorrhagic telangiectasia (HHT), Von Willebrand’s disease (VWD)
2 examples of cerebral malformations
arteriovenous malformation (AVM), cerebral cavernous malformation (CCM)
4 occurances when excessive angiogenesis
retinal disease, cancers, atherosclerosis, obesity
3 ways of new blood vessel formation
vasculogenesis (bone marrow progenitor cell), angiogenesis (sprouting in different angiogenic microenvironments), arteriogenesis (collateral growth)
stages of angiogenesis
EC receptor binding -> EC activation -> EC proliferation -> directional migration -> ECM remodelling -> tube formation -> loop formation -> vascular stabilisation
model of sprouting angiogenesis
selection of sprouting ECs -> sprout outgrowth and guidance -> sprout fusion and lumen formation -> perfusion and maturation
5 sprouting angiogenesis stages
tip/stalk cell selection -> tip cell navigation and stalk cell proliferation -> branching coordination -> stalk elongation, tip cell fusion, lumen formation -> perfusion and vessel maturation
angiogenesis balance: examples of inhibitors of angiogenesis
ECM, soluble factors or cell surface receptors; thrombospondin-1, statins
angiogenesis balance: examples of activators of angiogenesis (some essential, some required for modulation)
growth factors, soluble factors or cell surface receptors; VEGF (essential), FGF, PDGFB, EGF, LPA
angiogenesis balance: examples of things required for maturation and integrity of blood vessels
VE-cadherin, platelets, pathways (tissue or stimulus specific pathways)
what is a trigger for angiogenesis
hypoxia
what is HIF
hypoxia-inducible transcription factor, which controls regulation of gene expression by oxygen
what controls levels of HIF
pVHL (Von Hipper-Lindau) tumour suppressor gene
in absence of oxygen, what genes are coded for
pVHL doesn’t bind to HIF-a, so hypoxia-inducible genes are coded for, including VEGF
in presence of oxygen, what happens to HIF-a
pVHL binds to HIF-a, resulting in a proteasome destroying HIF-a
what does VEGF stand for
vascular endothelial growth factor
5 members of VEGF family
VEGF-A, VEGF-B, VEGF-C, VEGF-D, and placental growth factor (PlGF)
3 tyrosine kinase receptors of VEGF
VEGFR-1, VEGFR-2, VEGFR-3, and co-receptors neuropilin (Nrp1 and Nrp2)
what VEGFR is the major mediator of VEGF-dependent angiogenesis
VEGFR-2
how does VEGFR-2 mediate angiogenesis
activates signalling pathway that regulates endothelial cell migration, survival and proliferation, so is essential
2 sections of VEGFR
dimerisation/binding domain, tyrosine kinase domain
in sprouting angiogenesis, what leads the outgrowth of blood-vessel sprouts
specialised endothelial tip cells
where do specialised endothelial tip cells lead the outgrowth of blood-vessel sprouts towards
gradients of VEGF
what is tip cell selection based on
Notch signalling between adjacent endothelial cells at angiogenic front
what are Notch receptors and ligands
membrane-bound proteins that associate through their EC domains
what does the IC domain of Notch (NICD) do after Notch ligand binding
translocates to nucleus and binds to transcription factor RBP-J
what maintains quiescence in stable blood vessels
DII4 and Notch signalling
pathway by which tip cells are selected by VEGF/Notch signalling
VEGF activation increases expression of DII4 -> DII4 drives Notch signalling, which inhibits expression of VEGFR2 in adjacent cell -> DII4-expressing tip cells acquire a motile, invasive and sprouting phenotype -> adjacent cells (stalk cells) form base of emerging sprout, and proliferate to support sprout elongation
what proteins assist in migration (tip cell guidance and adhesion)
integrins
what cells are recruited for sprout outgrowth and guidance
myeloid cell recruitment
role of macrophages in vessel anastomosis
carve out tunnels in ECM, providing avenues for capillary infiltration (tissue-resident macrophages can be associated with angiogenic tip cells during anastomosis)
role of platelets in phyiological angiogenesis
vascular development and lymphangiogenesis, wound healing
what forms a barrier to ensure stabilisation and quiescence
VE-cadherin and Ang-1 (angiopoietin-1), pericyte maturation
where is VE-cadherin constitutively expressed
at junctions
3 things that VE-cadherin does
homophilic interactions mediate adhesion between endothelial cells, controls contact inhibition of cell growth, promotes survival of EC
what cells help stabilise neovessels by producing stabilising factor angiopoietin-1
mural cells (pericyte cells)
location of pericytes
go around blood vessels
location of Tie2 receptor
almost exclusive to endothelial cells
what are antagonistic ligands of Tie2 receptor, and where are they released from
Ang-1 (pericyte), Ang-2 (endothelial cell)
what 2 things does Ang-1 do upon Tie2 receptor binding
promotes vessel stability and inhibits inflammatory gene expression
what 3 things does Ang-2 do upon Tie2 receptor binding
antagonises Ang-1 signalling, promoting vascular instability and VEGF-dependent angiogenesis
when are Ang-2 plasma levels raised
during disease, including congestive heart failure, sepsis and chronic kidney disease
VEGF pathway vs angiopoetin-Tie2 pathway
VEGF pathway essential for driving angiogenesis, angiopoetin-Tie2 pathway required for modulation
what do small tumours (<1mm3) receieve oxygen and nutrients by
diffusion from host vasculature (no need for angiogenesis)
what do large tumours require to receive oxygen and nutrients
new vessel network, facilitating progressive growth
how do large tumours gain a new vessel network
secretes angiogenic factors (e.g. VEGF, angiopoietins), driven by hypoxia, that stimulate migration, proliferation and neovessel formation by endothelial cells in adjacent established vessels
what is the angiogenic switch and when can it occur
discrete step in tumour development when tumour requires angiogenesis; can occur at different stages in the tumour-progression pathway, depending on tumour nature and microenvironment
describe tumour blood vessel shape
irregularly shaped, dilated, tortous
describe tumour blood vessel organisation
not organised into definitive venules, arterioles and capillaries
why are tumour blood vessels leaky and haemorrhagic
excessive VEGF so platelet activation releasing pro-angiogenic factors, as well as angiostatic molecules
what cells are often loosely associated with tumour blood vessels
pericytes cells
what might some tumours recruit from the bone marrow for tumour blood vessels
endothelial progenitor cells
what do cancer-associated fibroblasts (CAFs) secrete
ECM containing pro-angiogenic growth factors (VEGFA, FGF2 etc.)
why do tumour blood vessels have poor organisation
don’t release all correct growth factors, pericytes are loosely associated (favouring leakage which is enhanced by angiopoietin 2), platelets release pro-angiogenic mediators (can be targeted)
2 agents which target VEGF
anti-VEGF antibodies, soluble VEGF receptors (e.g. VEGFR1)
agent which targets EC VEGFR
anti-VEGFR antibodies
agent which targets IC VEGFR
small-molecule VEGFR inhibitors
what is an anti-VEGF humanised MAb
avastin
side effects of avastin
GI perforation, hypertension, proteinuria, venous thrombosis, haemorrhgae, wound healing complications, limited efficacy as no overall quality of life or survival advantage vs chemotherapy alone (as no VEGF essential for normal endothelial cell angiogenesis)
3 modes of unconventional resistance by anti-angiogenic therapy in cancer
evasive resistance (adaption to circumvent specific angiogenic blockade), intrinsic or pre-existing indifference (vessel lining maybe less sensitive to VEGF inhibition), pericytes maybe less responsive to VEGF therapy
2 possible mechanisms of resistance to anti-angiogenic therapy
reduced blood supply and therefore reduces access by chemotherapeutic drugs, other angiogenic growth factors taking over
what is tumour cell vasculogenic mimicry (VM)
tumour cells “pretend” to be blood vessel cells; plasticity of aggressive cancer cells forming de novo vascular networks (malignant phenotype and poor clinical outcome)
problem of using sustained/aggressive anti-angiogenic therapy
may damage healthy vasculature leading to loss of vessels, creating vasculature resistant to further treatment and inadequate delivery of oxygen/drugs
how to do single cell RNASeq of tumour endothelium
tissue (tumour) -> isolate and sequence individual cells -> look at genes -> read counts -> compare gene expression profiles of single cells
purpose of single cell RNASeq
identify new molecular targets
4 challenges of finding better therapeutic strategies to inhibit angiogenesis in cancer due to in vitro research
tumours are complex 3D structures with unique microenvironments, in vitro studies grow as 2D monolayers (not 3D and with EC environment), tumours receive nutrients etc. through vasculature (not present in vitro), phenotype of tumour cells when cultured in 2D is different to 3D
function of a “tumour-on-a-chip” platform
development of a microphysiological system that incorporates human cells in a 3D extracellular matrix (ECM), supported by perfused human microvessels (reflect true tumour better), allowing better drug screening
when might anti-angiogenic therapies be used in other diseases
abnormal retina vascularisation (e.g. diabetic retinopathy, wet age-related macular degeneration)
when might pro-angiogenic therapies be used in other diseases
ischaemic diseases (e.g. MI, peripheral ischaemic disease)
what is age-related macular degeneration caused by, and symptom
abnormal growth of choroidal blood vessels, with leaky vessels causing oedema, and therefore causing visual impairment (main cause of blindness)
why is therapeutic angiogenesis used for coronary artery disease and peripheral artery disease
promotes neo-vascularisation to prevent ischaemic damage
