Stromal Influences on Brain Tumor Formation and Growth

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Stromal Influences on Brain Tumor Formation and
Growth
Joshua B Rubin, M.D., Ph.D. Department of
Pediatrics Division of Pediatric
Hematology/Oncology Washington University School
of Medicine
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Somatic Mutation Theory of Carcinogenesis

• Cancer is derived from a single somatic cell that
  has acquired multiple DNA mutations.
• Assumptions
• In the absence of regulatory signals, metazoan
  cells in situ are quiescent.
• Cancer is a disease of proliferation

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Support for the Somatic Mutation Theory

• 1890 Hansemann notes mitotic abnormalities in
  cancer cells and postulates that some chromosomes
  might stimulate proliferation and others might
  block mitosis.
• 1914 Boveri observes that specific chromosomal
  abnormalities are associated with developmental
  anomalies in sea urchins and proposes that cancer
  might arise from somatic mutations.
• 1951 Armitage Doll postulate the multistage
  theory of cancer including somatic mutations,
  genomic rearrangements and changes in tissue
  interactions.
• 1960 Nowell Hungerford discover Philadelphia
  chromosome (922(BCRABL)). Soon afterward 814
  and 822 were described (MYCIg).
• 1971 Knudson explains the epidemiology of
  retinoblastoma in the two-hit hypothesis and
  this work yields the term anti-oncogene or tumor
  suppressor.
• 1976 Varmus discovers a cellular homologue (Src)
  to the transforming protein of Rous Sarcoma
  Virus, thus identifying the first oncogene.
• 1983 Cavenee showed second hit involved a gross
  chromosomal mechanism.

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Can SMT explain

• Stewart (1981) Injection of teratocarcinoma
  (TC) cells into mouse blastocyst generated normal
  tissues and those TC cells that became germ cells
  produced normal offspring.
• Martins-Green (1994) Integration of Rous sarcoma
  virus into chicken genome only produced tumors in
  the setting of inflammation.
• Sternlicht (1999) Expression of stromalysin-1 in
  mammary gland produced epithelial tumors.

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• Paget 1889 Tumor cells are like the seeds of
  plants, carried by the wind in all directions,
  but only able to live on congenial soil.

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Tissue organization field theory of carcinogenesis

• Boll (1890s), Waddington (1935) Cancer results
  from abnormal inductive interactions between
  tissues.
• Assumptions
• Metazoan cells proliferate in the absence of
  inhibitory signals.
• Cancer is a disease of tissue disorganization.

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Theoretical support for TOFT

• Inherited cancer predisposition syndromes often
  result in cancers in a tissue and age restricted
  fashion.
• The default state for unicellular organisms is
  proliferation. Almost complete homology between
  replicative machinery of yeast and human cells.
• During normal development organizing centers
  regulate growth and differentiation.

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What constitutes tumor stroma

• Vascular endothelial cells
• Fibroblasts
• Adipocytes
• Inflammatory cells (mast cells, phagocytes,
  microglia)
• Matrix

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Mammary gland carcinogenesis
Maffini et al.(2003) J Cell Sci 1171495-1502 21
days old-remove epithelial cells from mammary
glands 52 days old-NMU or vehicle injection 57
days old-NMU or vehicle treated EC transplant 9
month experiment
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Plexiform neurofibroma formation
Zhu et al. (2002) Science 296920-922 Nf1flox/flo
x or Nf1flox/- crossed or not with Krox20-Cre
transgenic mice
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Optic pathway glioma formation in NF1
Bajenaru et al. (2003) Cancer Research
638573-8577 Nf1flox/flox or Nf1flox/- crossed
or not with GFAP-Cre transgenic mice
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Additional experimental support for the TOFT

• 1982 DiBeradino Nuclei from Luckes frog renal
  carcinoma cells transplanted into enucleated,
  activated Ova produced normal tadpoles.
• 1999 Olumi Xenograft of normal prostatic
  epithelial cells (ECs) and myofibroblasts (CAFs)
  led to intraepithelial neoplasia while
  co-injection of immortalized, non-transformed ECs
  and CAFs led to malignancy.

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Pediatric brain tumors occur very early in life
and display lineage diversity
Hard to explain by SMT alone.
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Genetic Diseases Associated with Brain Tumors
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Kids Astrocytomas (astrocytes) Oligodendrogliomas
(oligodendrocytes) Meningiomas (?
Mesenchymal) Medulloblastoma, pineoblastoma
(neurons) Ependymoma (ependymal cells) Choroid
plexus carcinoma ( ? Endothelial)
Adults Astrocytomas (astrocytes) Oligodendroglioma
s (oligodendrocytes) Meningiomas (? Mesenchymal)
Primary Brain Tumor Histologies
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CXCR4 mediates a lineage independent, stromally
derived survival signal for brain tumors
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Human MB and GBM express CXCR4
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CXCL12 expression in tumor vasculature
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Xenograft Characterization
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Xenografts express CXCR4 and CXCL12
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AMD 3100 blocks the growth of intracranial
xenografts
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Could CXCR4 mediate a patterning effect in brain
tumor formation?
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Glioma formation in NF1

• NF1 loss is not sufficient for optic pathway
  glioma formation
• NF1 loss results in hyperactivation of RAS and
  is associated with decreased generation of cAMP.
• CXCR4 is G?i GPCR. CXCL12 binding results in
  activation of RAS and reduction in cAMP.
• Could CXCL12 provide an anatomically localized
  growth signal that promotes glioma formation in
  NF1?

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CXCL12 growth effects
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Cooperation between somatic mutation and stromal
factors is necessary for tumor growth
RTK
PI3K
RAS
PTEN loss
Akt Erk 1/2
p16 loss
P53 loss
Proliferation
Survival
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Targeting stroma
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Conclusions

• Carcinogenesis is not always a cell autonomous
  event.
• Abnormal epithelial-stromal interactions can
  promote tumorigenesis.
• Stromal elements represent novel therapeutic
  targets

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Thanks to
Washington University Nicole Warrington B. Mark
Woerner Lihua Yang Karen Gauvain Ashley
Ellis Robyn Klein David Gutmann Arie Perry Jason
Weber
Gary Bridger, AnorMed