Flotte’s Outline of
Neurosurgery
Research:
Basic Science and Experimental
Treatments
Genetics
(-) = tumor suppressor; (+) = oncogene
Cell cycle proteins
P53: chr17, G1 police (-); LGA >
GBM. Gain of function mutations lead to stable protein, prevents apoptosis
MDM2: inhibits p53(+)
P21: p53 induces to cause arrest(-)
P27/kip1: G1 inhibition(-)
P16/p15: inhibit CDK4/6(-)(genes
CDKN2A/B)
CDK4/CDK6: phosphorylate
RB(+)
RB: phopsphorylation releases E2F
allows G1>S (+)
P14ARF: alternative reading of CDKN2A;
RB independent arrest(-)
Growth Factors and Receptors
EDGFR: amplified or overexpressed in
primary GBM
PDGFR
DCC: lost in progression
PTEN(MMAC1): (-)
Migration
“Go or
Grow” hypothesis: cells postmitotic before migration.
4 medulloblastoma cells lines divided while migrating
(N7/03).
Factor
potency: SF/HGF > TGFα > FGF1.
Scatter Factor (SF)/ Hepatocyte
Growth Factor (HGF)
·
Receptor
is MET (c-Met oncogene product)
·
Potent
migratory factor
Ephrins
·
Cell-surface
bound
·
Bind
Eph receptor TKs
·
Regulate
axon guidance, neural crest migration
Matrix
metalloproteinase inhibitors: Marimastat, prinomastat
·
Gliomas
produce PDGF (A & B), EGF, TGFα, IGF-1.
·
Receptors
are tyrosine kinases
PDGF
·
PDGF-A,B,C,D
homodimers (AA, BB, CC, DD) or heterodimer (-AB)
·
Receptors: PDGFRα (binds
AA,BB,CC,AB), PDGFRß (binds BB,DD)
·
Overexpression
in LGA w/ p53 loss. Expressed in almost all oligodendrogliomas.
·
Simian
sarcoma virus is viral homologue of c-sis/PDGFB
·
Involved
in angiogenesis
EGF
·
EGFR
in ErbB family; also binds TGFά
o
Transmembrane
glycoprotein, intracellular TyK domain
·
Neurotrophic,
development, angiogenesis
·
EGFRvIII:
mutation in extracellular domain leads to constituitive activation
·
May
be due gene amplification, overexpression, autocrine/paracrine ligand stimulation,
or constitutive activation
·
EGFR
in gliomas
o
50% GBMs overexpressed/amplified (de novo GBM). 50%
of these cases have mutations
o
EGFR mutation can occur without overexpression of
wt-EGFR
o
EGFRvIII: most common mutant in GBM. Constitutive
autophosphorylation. Oncogenic transformation in absence of ligand
·
EGFR
Antagonists: N6/04
FGF
·
Acidic
FGF (aFGF), basic FGF (bFGF), and FGF-3 to -23
·
4
receptors, 1-4
·
Involved
in angiogenesis, neurotrophic
TGF-ß
·
Family:
BMPs, Mullerian inhibiting substance
·
Receptors:
I & II. Serine/Threonine kinases.
·
Released
by glioma cells in vivo & in vitro.
·
Inflammation,
wound healing, angiogenesis
TNFα
·
Inflammation, angiogenesis
·
Produced
by monocytes/macrophages
Receptor Tyrosine Kinases
·
600
protein kinases, 130 protein phosphatases. Kinases are commonly in oncogenic
pathways
·
Frequent
Alterations in Cancer:
–
Genomic
rearrangements (e.g. Bcr-Abl, EGFR)
–
Mutation
(e.g. Flt-3, c-Kit, c-Met)
–
Overexpression
(e.g. EGFR, VEGFR, c-Met)
·
Composed
of: Extracellular ligand-binding domain, membranous domain, intracellular
domain with intrinsic tyrosine kinase activity
·
Ras > Raf > Mek > MAPK
o
Most
RTKs. Needs assistance of scaffolding proteins.
o
Ras
inactiviating gene neurofibromin mutated in NF1;
·
PI-3
Kinase (PIP2 > PIP3) > PDK1/2 > Akt
o
Used
by EGFR
o
PTEN
inhibits PI3K
o
Akt
inhibits apoptosis, stimulates cell growth & proliferation
·
PLC-γ (PIP2 > IP3 & DAG)
o
Used
by EGFR
·
STATs
o
EGFR
activates STAT1,3, & 5
o
STAT1
proapoptotic, antimitotic; STAT3 antiapoptotic, promitotic
·
Mitogen-activated
protein kinase
·
Cause
DNA synthesis and cell division
·
RTK
inhibitors:
o
Herceptin,
HER-2 antibody (to extracellular domain). Approved for breast cancer – 15%
response rate.
Hesselager
N903
·
Inhibitors
of tyrosine kinase activity: Iressa, Tarceva – EGFR; Gleevec – PDGFR (in
clinical trials for GBM)
·
INK4A-ARF
locus codes for p16 & p14 suppressors. Deleted/ inactivated in 60% of GBM.
·
p53:
on Chr17
·
Rb:
inhibited by SV40 T antigen T121.
·
MYC:
transcription factor leading to cell proliferation, Amplified in some
medulloblastomas.
Ubiquitin-Proteosome
Pathway
Proteosome
inhibitor PS-341
Apoptosis
Telomerase
Ribonucleoprotein
enzyme that replicates telomeric DNA. Reactivated in some cancers, including
GBM.
hTERT:
human telomerase reverse transcriptase. May predict prognosis.
Sonic Hedgehog
Receptor:
Patched (PTCH)
Gli –
downstream effectors
Mutated in
minority of gliomas
·
Vasculogenesis:
new blood vessel formation (embryonic).
Angiogenesis: New branches formed
off existing vessels (tumors, etc)
·
Glioma
angiogenesis: VEGF (primary), SF/HGF, bFGF most important
·
Edema:
VEGF & angiopoietins
VEGF
·
endothelium
specific angiogenic factors.
·
5
homologues (B,C,D,E, and placenta growth factor PlGF).
·
Receptors:
VEGFR-1, VEGFR-2, neuropilin-1 (Nrp-1)
·
Promotes
NO synthesis, vascular permeability, proteases. May be responsible for edema.
·
VEGF
in gliomas:
o
VEGF is
expressed in human high-grade glioma but not in normal brain
o
VEGF receptors are expressed only on endothelial
cells
o
Increased
expression of VEGF, and VEGF receptors correlates with tumor vascularity and
malignancy grade in human gliomas
o
Upregulation
of VEGF is associated with areas of necrosis
o
High
proliferation rate of malignant glioma may lead to areas of necrosis and
hypoxia and result in increased expression of VEGF
Angiopoietins
·
Ang-1
to 4. Ligands for Tie-2, endothelium specific tyrosine kinase receptor.
Endostatin/angiostatin:
Inhibit angiogenesis
Also
thrombospondin 1 & 2, platelet factor-4
Therapy: VEGF antisense, Thalidomide:
inhibits endothelial cell proliferation, Fumagillin, angiostatin, endostatin,
COX2 inhibitors (Celecoxib), Topotecan (VEGF antagonist)
Angiogenesis
N12/03
Tumor Associated Antigens
·
Gliomas
have been shown to express several tumor associated antigens (TAAs): EGFRIII,
glycoprotein 240, tenascin, survivin, squamous cell carcinoma–associated
reactive antigen for cytotoxic T cells 1, α-2 chain of interleukin-13
receptor, and melanoma-associated antigens, such as tyrosinase,
tyrosinase-related protein 1 and 2, glycoprotein 100, melanoma antigen-1, and
melanoma antigen-3.
·
Identification
of a universally expressed glioma TAA has not been identified. Tumor cell
clones that do not express the particular, targeted TAA (anymore) escape from
the immune rejection and, thus, have an important proliferation advantage.
Types of Immunotherapy:
Cellular
·
Antigen
Presenting Cells (APCs) present antigens to T-cells via MHC
·
MHC
not detected in CNS
Cytokines
·
TNFά, IL-2, IL-4, INF-άßγ.
·
No
clear survival improvement when administered to GBM patients. IL-2 & INFά showed significant toxicity.
Adoptive
·
Intratumoral
injection of peripherally harvested lymphocytes or TILs (tumor infiltrating
lymphocytes), stimulated ex vivo with IL-2
·
No
definite survival benefit
·
Human,
non-MHC restricted, cytotoxic T-cell leukemic cell lines (TALL-104) – cytotoxic
against tumors, spares normal tissue
·
Stimulation
of autologous lymphocytes with patient’s tumor cells
Passive