Lecture 8 (angiogenesis)

Question 1

What is angiogenesis

Answer 1

It is the formation of new blood vessels by sprouting growth from preexisting vessels.

Question 2

Why is angiogenesis a key process in tumour growth and metastasis?

Answer 2

-It provides the tumor with a nutrient supply and removes metabolic products via blood.
-If blood supply is deficient then tumors cannot grow and necrosis will occur.

Question 3

Angiogenic event sequence 1-4

Answer 3

1. HIF-1 induction
2. HIF-1 upregulates VEGF and MMPs
3. VEGF promotes endothelial cell proliferations and MMPs
4. Destruction of basement membrane/support matrix by MMPs

Question 4

Angiogenic event sequence 5-9

Answer 4

5. MMPs cause release of angiogenic growth factors held in matrix
   6.Migration and proliferation of endothelial cells
6. Expression of integrins by developing endothelium
   8.Capillary sprout formation
7. Vascularisation of tumour and formation of capillary loops

Question 5

what are the details of 1- HIF1 induction

Answer 5

-Normally HIF1 is degraded quickly.
-Low O2 (hypoxia) can lead to HIF1 activation.
-HIF-1 can also be upregulated by oncogenic signalling, e.g. EGFR, HER2, Akt.

Question 6

Ways HIF-1 can be activated:

Answer 6

-Occurs in transformed cells
-Oncogenic signals
-Loss of tumor suppressor function
-Dysregulation of HIF-1 degradation

Question 7

3- VEGF promotes endothelial cell proliferation and MMPs:

Answer 7

VEGF is released from cancer cells, enters the tissue surrounding the tumour, and moves towards endothelial cells thus VEGF induces MMPs from endothelium

Question 8

4- destruction of basement membrane by MMPs:

Answer 8

MMP1, MMP2, MMP7, and MMP9 all breakdown support and expose the endothelium

Question 9

5- MMPs cause release of angiogenic growth factors held in the matrix:

Answer 9

All the growth factors that were stuck in the matrix can now get through and reach the endothelial cells

Question 10

What is step 6 of the angiogenic sequence

Answer 10

It is the migration and proliferation of endothelial cells

Question 11

7- expression of integrins by developing endothelium:

Answer 11

Signaling via avb4 integrins lead to:
-Reduces p53 activity
-Reduces BAX
-Reduces p21 expression
-Increases BCL-2 expression

Question 12

8- capillary sprout formation:

Answer 12

Sprouting is led by the tip cell which can sense their environment to direct migration
-The canal is sculpted by apoptosis and finally there is basement membrane deposition

Question 13

9- vascularization of tumour and formation of capillary loops

Answer 13

This involves growth factors recruiting pericytes to support new blood vessels so the tumour now has access to blood supply, however this blood supply/capillary is chaotic which is a trademark of cancer and presents structures such as corkscrew vessels which are chaotic, unreliable, and leaky which can cause internal bleeding from the tumour

Question 14

Other blood vessel recruitment types in cancer besides sprouting angiogenesis

Answer 14

-Intussusception
-Vasculogenesis
-vessel co-option
-vessel mimicry
-trans-differentiation of cancer cells

Question 15

Intussusception blood vessel:

Answer 15

where a hole forms and the existing vessel splits in two

Question 16

Vasculogenesis:

Answer 16

Is where a new blood vessel is made from a stem cell

Question 17

Vessel co-option:

Answer 17

Where cancer cells grow along the existing blood vessel so it gets blood from that vessel due to close proximity.

Question 18

Vessel mimicry:

Answer 18

Where cancer cells form vessel like structures themselves

Question 19

Trans-differentiation of cancer cells:

Answer 19

The cancer cells can transform to act like a different type of cell ie. cancer stem-like cells can differentiate into endothelial cells

Question 20

What is VEGF and what does it do, what regulates its expression

Answer 20

-An angiogenic factor that is a secreted homodimeric glycoprotein.
-VEGF stimulates endothelial cell migration and proliferation.
-hypoxia and HIF-1 regulates its expression.
-there are numerous splice variants, 7 isoforms.

Question 21

VEGF receptors:

Answer 21

-VEGFR 1, 2, 3 (tyrosine kinase receptors)
-VEGFR 2 expression is the key mediator of VEGF-induced angiogenesis
-signalling activates NOS, Akt, STAT3, MAPKs

Question 22

What are angiopoietins

Answer 22

They are angiogenic factors
-Ang1 and Ang2
-Their receptors are Tie2-RTK

Question 23

Role of Ang1

Answer 23

Stabilizes vessels, endothelial cell survival signals, and maintains endothelial barrier

Question 24

Role of Ang2

Answer 24

-Destabilises vessels, mainly produced by endothelial cells, induced by VEGF, PDGFB, and IGF1, stored in granules and exocytosis is promoted by hypoxia
-Ang2 normally functions as an Ang1 antagonist, it promotes the dissociation of pericytes from pre-existing vessels and increases vascular permeability which facilitates the infiltration of proteases, cytokines, and angiogenic myeloid cells

Question 25

what are the anti-angiogenic factors and their roles

Answer 25

-angiostatin which inhibits bFGF-induced migration and proliferation (angiostatin is formed by MMPs cleaving plasminogen)
-endostatin which is internal fragment of collagen XVIII (18)
-IFNalpha and beta which suppress synthesis of bFGF and IL8
-thrombospondin1 which is secreted by different cell types, it inhibits endothelial cell growth and can cause autocrine FasL signalling

Question 26

How does anti-angiogenic drugs act on the tumour

Answer 26

-anti-angiogenic drugs don’t choke/suffocate a tumour but instead bring normal blood supply to the tumour to remove the chaos allowing them to be used in combination with immuno or chemotherapy.
-Used in treatment of breast, colorectal, ovarian, lung, gastric, and liver cancers

Question 27

Examples of anti-angiogenic drugs and how they work:

Answer 27

-Avastin (bevacizumab) which is a small monoclonal antibody specific against VEGF by binding to it and stopping VEGF signalling.
-Ramucirumab is more specific against VEGFR.
-Small molecule kinase inhibitors (dirty drugs, many targets-VEGFR, PDGFR, FGFR, c-KIT, can be useful but not specific so likely side effects)

Question 28

Recap: what are the key events of angiogenesis

Answer 28

9 events, key goal is to clear a path through the matrix then growth factors can begin growing

Question 29

Recap: how can angiogenesis be targeted

Answer 29

3 ways: through VEGF antibodies (against growth factors), VEGFR (against receptor), and kinase inhibitors