Angiogenesis and Metastasis

Question 1

Continuous capillary

Answer 1

• Have tight occluding junctions that seal the spaces between endothelial cells
• All transport must take place across membranes

Question 2

Fenestered capillary

Answer 2

• Have perforations (fenestrations) through endothelial cells that allow exchange of small molecules with blood
• Example; endocrine organs, intestinal wall

Question 3

sinusoid capillary

Answer 3

• Have wide spaces between endothelial cells, large fenestrations, and a discontinuous basement membrane that allow for exchange of macromolecules and cells with tissues and blood
• Example; bone marrow, liver, spleen

Question 4

Tumors require access to circulation in order to grow and survive

Answer 4

• Cancer cells grow preferentially around blood vessels
o Tumor cells more than 0.2 mm away are non growing
o Further than that they die
• 0.2 mm is the distance oxygen can effectively diffuse
• Need oxygen and to shed waste and CO2

Question 5

Conditions as cells move further from vessels

Answer 5

• Higher lactate
• Lower pH
• Lower glucose
• Lower ATP
• Lower oxygen

Question 6

Angiogenesis is important in

Answer 6

• Embryonic development
• Implantation of the placenta
• Wound healing
• Many disease processeses
• Tumorigenesis

Question 7

Excessive angiogenesis

Answer 7

o	Blindness 
o	Rheumatoid arthritis
o	Cancer
o	AIDS complications
o	Psoriasis

Question 8

Insufficient angiogenesis

Answer 8

o	Stroke
o	Infertility
o	Heart disease
o	Ulcers
o	scleroderma

Question 9

VEGF and bFGF

Answer 9

• Receptors for these on the surfaces of endothelial cells
• Stimulate endothelial cell proliferation
• Tyrosine kinase receptors
• Transphosphorylation activates

Question 10

VEGF production in low oxygen

Answer 10

o HIF-1alpha is dephosphorylated

o Enters nucleus and along with HIF-1beta induces transcription of VEGF gene

Question 11

VEGF in normal oxygen

Answer 11

o HIF-1alpha is hydroxylated by proline hydroxylase
o Bound by pVHL and other proteins
o Tagged by ubiquitin and degraded by proteasome

Question 12

As tumor grows, capillaries increase

Answer 12

• Circulating endothelial cells from bone marrow are recruited to settle in the tumor stroma and differentiate
• Capillaries are also being assembled from endothelial cells present within the tumor stroma
• Other key players
o TGF-beta, EL-8, angiopoietin, angiogenin (1&2)

Question 13

angiogenesis in tumors

Answer 13

• Cell of vasculature
o Endothelial cells
o Pericytes
o Smooth muscle cells

• Nonvascular cells
o Neoplastic cells
o Supporting cells of the stroma

Question 14

Step 1 in angio

Answer 14

Stimulation of endothelial cells by angiogenic growth factors

• Basic fibroblast growth factor
o bFGF
• Vascular endothelial Growth factor
o VEGF

Question 15

Step 2 in angio

Answer 15

Degradation of the parental vessel basal lamina by activated endothelial cells to facilitate the formation of capillary sprout

• Secreted proteases
o Matrix metalloproteinases (MMPs)
o Plasminogen activator urokinase (uPA)
• MMPs are secreted to allow cells to migrate through the ECM

Question 16

step 3 in angio

Answer 16

endothelial cell migration and proliferation

• Regulation of cell migration
o Integrins
o Extracellular proteinases

Question 17

step 4 in angio

Answer 17

maturation of endothelial cells involving the formation of capillary tubes, reformation of the basal lamina and recruitment of pericytes

• Angiopoietin 1 (Ang 1)
• Platelet Derived Growth Factor (PDGF)

Question 18

angiogenic activators

Answer 18

o	VEGF-A
o	VEGF-B, C
o	FGF1 (aFGF)
o	FGF2 (bFGF)
o	Other FGFs

Question 19

angiogenic inhibitors

Answer 19

o	Thrombospondin-1, 2
o	Interferon alpha/beta
o	Angiostatin
o	Endostatin
o	Collagen IV fragments

Question 20

purpose of angiogenic switch

Answer 20

Tripping the angiogenic switch is essential for tumor expansion because many tumor cells populations initially lack the ability to attract blood vessels

Question 21

angiogenic switch

Answer 21

• angiogenesis is a component of the tumor phenotype that is activated during early pre-neoplastic stages
• Most tumors arise without angiogenic activity, exist in ‘dormant’ stage (carcinoma in situ) without vascularization
• become vascularized when subset of cells switches to angiogenic phenotype

Question 22

dormant lesion characteristics

Answer 22

o Proliferation rate is equal to apoptosis
o Angiogenic inducers are low
o Angiogenic inhibitor are high

Question 23

metastatic lesion characteristics

Answer 23

o Proliferation rate is greater than apoptosis rate
o Angiogenic inducers are high
o Angiogenic inhibitors are low

Question 24

Prevascular phase

Answer 24

• Angiogenic activity is absent or low
• Tumors remain small with volumes in a few cubic millimeters (prolif=apop)
• Tumors are generally thin or flat, stable, asymptomatic and rarely metastatic
• Micrometastases may have similar pre-vascular phase

Question 25

Vascular phase

Answer 25

* Characterized by tumors which have entered a phase of rapid growth, intensified invasion, increased metastatic potential * A bidirectional paracrine relationship between the tumor cells and endothelial cells is established. Endothelial- derived growth factors stimulate the growth of the tumor cells * Hypoxic areas of the tumor stimulate VEGF production and subsequent endothelial cell growth * Associated with increased appearance of symptoms. Bleeding, local edema, inappropriate hormonal activities, hypercoagulation states and cachexia

Question 26

Heterogeneity of angiogenic activity in tumors

Answer 26

* Neovascularization of a tumor usually originates is a subset of cells due to the presence of a mixture of angiogenic and non-angiogenic cells * Metastases derived from the angiogenic portion of the tumor are already angiogenic upon arrival at the target organ and therefore have an increased chance of becoming a detectable metastasis

Question 27

Possible advantage of using anti-angiogenic therapy

Answer 27

* Specificity may result in few side effects * Angiogenesis in adults is limited to reproductive tissues and wound healing * Structure of tumor vasculature is a barrier for traditional drug delivery (irregularly shaped, dilated, tortuous, dead ends) * Anti-angiogenesis therapies target accessible vessel endothelial cells * Drug resistance is reduced because endothelial cells are stable and have low mutation rates * In theory, should be applicable to all solid tumors regardless of origin since endothelial cells do not vary from one type to another

Question 28

Sequence of events in tumor metastasis

Answer 28

* Initial transformation event * Proliferation of transformed cells * Compromised nutritional supply to the tumor mass requiring the release of tumor angiogenesis factors * Endothelial cell expansion and reorganization * Local invasion and destruction of extracellular matrix components and parenchymal cells leading to migration of tumor cell aways from the primary tumor mas * Penetration of cancer cells through the blood vessel wall (intravasation) * Arrest of cancer cells in the lumen of small blood vessels or lymphatics * Reverse penetration of blood vessels * Organ colonization resulting in the formation of secondary tumor (metastases)

Question 29

Epithelial- mesenchymal transitions in cancer

Answer 29

* Cytoskeletal reorganization * Membrane reorganization * Increased growth * Increased motility * Take on more connective tissue properties and elements * Repress epithelial markers like: e-cadherin, u-cadherin, y-cadherin * Induce mesenchymal markers like: vimentin, fibronectin, n-cadherin

Question 30

Seed and soil model for preferred sites of metastasis

Answer 30

* Colonization of metastasized tumor cells is inefficient * Micrometastases often “seed” organs but most fail to grow into clinically observed tumors * Organs must provide a hospital environment (soil) for metastasized tumors to grow

Question 31

Factors that affect the location and efficiency of metastasis

Answer 31

* Chemokines in the specific tissue that attract the tumor cells to the site * The differentiation, development and growth conditions of the tissue (mitogens and growth factors) * The nature of the trafficking circulation (blood and lymphatic) systems in the specific organ