Lecture

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Lecture 13 Angiogenesis and tumor growth
Axiom 13 Take the initiative to get involved.
Be a positive role-model in a young persons
life.
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Tumors require the continuing formation of new
blood vessels

• Supply oxygen and nutrients
• Supply endocrine and paracrine growth-enabling
  factors

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According to some recent research, Americas high
divorce rate is creating a population of young
hypertensives.
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Microvascular endothelial cells that line
capillary blood vessels are situated very close
to normal tissue cells such as epithelial cells
in the gut mucosa
Tumor cells form multiple layers around a
capillary Ergo most distant tumor cells are
oxygen deprived

• Islet cells of pancreas, fat cells and muscle
  cells are similarly arranged.
• Liver cells arranged around a central capillary
• Epithelial cells in crypts (100 um distance from
  vessel)

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THM 1

• Tumor cell survival is dependent on the health
  and proliferation of endothelial cells in
  surrounding blood vessels.

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How Does Radiation Therapy Work? (e.g. what is
the molecular basis for cell death)

• Yes, there is a link between tumor growth and
  growth of healthy tissue.

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Old View

• Radiation causes breaks in DNA, cell undergoes
  apoptosis.
• Side effects in GI syndrome (Gut)
• due to apoptosis of healthy epithelial cells
• in mucosa

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New data suggesting that radiation kills stem
cells indirectly.

• Death of epithelial stem cells in gut may be a
  secondary event resulting form the demise of the
  endothelial cells on which they depend.
• (Richard Kolesnick Science 29313 July, 2001
  MSKCC)

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What is the molecular mechanism of endothelial
cell death?

• Irradiation of microvascular endothelial cells
  generates ceramide an apoptotic signalling
  molecule.

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Effects of radiotherapy on intestinal mucosa and
bone marrow
Small intestine mucosa

• Note bFGF doesnt protect bone marrow!
• Why? Guess which tissue doesnt have receptors
  for bFGF?

Loss of villi
Science 29313 July, 2001 MSKCC
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Can microvasculature be protected from gut
irradiation?

• Yes, Systemic administration of (basic Fibroblast
  Growth Factor (bFGF)- an endothelial cell
  mitogen.
• What else can you do? What about inhibition of
  enzyme that makes ceramide? (sphingomyelinase)

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Effects of radiotherapy on intestinal mucosa and
bone marrow
Small intestine mucosa
Loss of villi
Why doesnt bFGF protect bone marrow?
Gray (Gy) unit of radiation
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Some tumors are more resistant to radiotherapy
than others

• Hodgkins lymphoma very sensitive
• Glioblastoma radioresistant
• Improve therapeutic index of radiation by
• deprotecting (combination therapy) the tumor or
• protecting normal tissue (bFGF).

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Is apoptosis in healthy and diseased cells
related?

• Yes The molecular details of healthy tissue
  death following radiotherapy is similar to the
  way in which tumor growth is inhibited by
  endothelial cell blockers
• ANTIANGIOGENIC THERAPY
• 200 biotech and big pharma companies are
  pursuing angiogenesis research

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Inhibition of angiogenesis can retard
experimental tumor growth and metastasis
Fig. 16.20 Angiogenesis and tumor growth
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If tumor growth is limited by rate of oxygen
diffusion to 200 um, how can a tumor grow to be
several inches?

• Tumors release bFGF (endothelial mitogen)
• VEGF (Vascular Endothelial Growth factor)
• Ergo tumor cells stimulate their life support
  system!

100-200 um
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Tumor vasculature actively supports cell
proliferation!

• Endothelial cells protect tumor cells by
  releasing at least 20 growth and survival factors

• e.g. heparin-binding epithelial growth factor
• interleukin

(e.g. acute wound healing, chronic wounds from
diabetes, arteriosclerosis, venous ulcers,
pressure sores)
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Tumor growth is dependent on angiogenesis

• Ergo, tumor vasculature is an attractive target
  for cancer therapy

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Anti-angiogenic drugs

• Endostatin generated by proteolysis of a larger
  extracellular protein-- collagen XVIII
• Works by binding to tropomyosin in endothelial
  cells! JBC 276pp.25190-25196, 2001
• Lowers VEGF levels, most successful in sarcomas
  and melanomas
• Angiostatin generated by proteolysis of a larger
  extracellular protein plasminogen
• 2-methoxyestradiol Panzem

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This is not a magic bullet?Problems

• Repeated injections
• Prolonged treatment
• Transmission of toxins and infectious particles
• High cost of manufacturing large amounts of
  protein molecules
• Alternative strategies!

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Joki et al., Nature Biotechnology 1935-39 2001

• Genetically engineer kidney epithelial cells to
  express endostatin, then encapsulate the cells
  in sodium alginate containing 1,4-b-D-mannuronic
  and a-L guluronic residues
• The mixture of alginate and cells solidifies into
  beads, spheroids, that contain immobilized cells
  in and artificial extracellular matrix that
  allows free exchange of proteins, nutrients, and
  oxygen between encapsulated cells and the host.
• The alginate beads protect the encapsulated cells
  from tissue rejection
• Beads are resistant to enzymatic digestion

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Joki et al., Nature Biotechnology 1935-39 2001

• Endostatin cell factories reduce tumor growth by
  gt70
• Increase in intratumoral apoptosis
• Increase in large necrotic areas near tumor
• But tumor is still present!
• Encapsulated cells remain alive for up to 4
  months. If they cut off vascular nutrition, how
  do they stay alive?
• Unable to prevent growth of nascent or small
  tumors, but did delay tumor growth

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How can the efficacy be improved?

• More beads?
• Beads with different cells?
• Different endostatin expression vectors?
• Increase inhibitor levels
• Combining implantation of anti-angiogenic cells
  factories with another therapeutic
  strategychemotherapy?

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Fig. 16.21 Response of a solid tumor to
treatment with angiogenesis inhibitors.
Tumor is not ameliorated!
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Diagram illustrates tumor progression from a
hyperplastic, premalignant stage through the
'angiogenic switch' to an invasive, metastatic
cancer

• Tumorstroma communication during tumor
  progression.. The colored arrows indicate lines
  of communication between tumor cells and
  surrounding stromal components of the tumor,
  including fibroblasts, endothelial cells,
  inflammatory cells and structural matrix
  components. The gold arrows may be representative
  of the contribution of matrix metalloproteinases,
  which represent a greater proportion of the
  communication signals in early, as compared to
  later stages of tumor progression.

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End Review of first 2 topics
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