What can we learn from the identification of specific molecular abnormalities in malignant disease?

1
What can we learn from the identification of
specific molecular abnormalities in malignant
disease?

• Insights into normal cell biology
• Targets for diagnosis and follow-up
• Targets for rational drug design

2
Conventional cytotoxic drugs mainly act by
causing DNA damage and cell death
Studying the biology of cancer cells may provide
new targets for drug development
3
Signal transduction modules
Molecular links between changes in cell
environment and cellular responses
4
Signalling pathways control cell functions
Replicate
Move
Live/Die
5
Signal transduction modules
Molecular links between changes in cell
environment and cellular responses

• e.g.
• Erythropoietin and prevention of apoptosis in
• erythroid progenitors
• G-CSF and proliferation in myeloid progenitors

6
The hallmarks of cancer
Many of these features may result from
abnormalities in signalling components
(Hanahan Weinberg (2000) Cell 100, 57)
7
Ligand binding dimerizes receptor tyrosine
kinases resulting in their activation
Monomeric receptor
Dimeric receptor
No ligand
Ligand present
8
A number of signalling modules link growth factor
receptor binding to changes in cell function
PI3-kinase
Ras
STAT
MAPK
PKB
Activation of gene transcription
9
The Ras protein acts as a molecular switch in
response to changes in the external environment
of the cell
Growth factor
OFF
Ras.GDP
Exchange factor e.g. SOS
GTPase activating protein e.g. NF-1
Ras.GTP
ON
Proliferation Survival Movement
10
Recruitment of a Grb2-SOS complex to an activated
receptor tyrosine kinase mediates Ras activation
RAS
GDP
GTP
11
Examples of signalling pathway abnormalities in
haematological malignancy
Aberrant tyrosine kinase Bcr-Abl CML activity
Increased Ras activity point
mutation AML loss of NF1
12
(No Transcript)
13
(No Transcript)
14
The constitutive activity of the Bcr-Abl tyrosine
kinase bypasses the requirement for growth factors
Bcr-Abl
Ras
PI3-kinase
STAT
MAPK
PKB
Activation of gene transcription Increased
proliferation/survival
15
Examples of signalling pathway abnormalities in
haematological malignancy
Aberrant tyrosine kinase Bcr-Abl CML activity
Increased Ras activity point
mutation AML loss of NF1
16
AML
AML
Normal
17
Ras proteins are frequently activated by point
mutation in human cancers
OFF
Ras.GDP

• Carcinoma
• pancreas
• colon
• thyroid
• AML
• Myeloma

Exchange factor e.g. SOS
NF-1
MUTANT Ras.GTP
ON
Proliferation Survival Invasion
18
Loss of the NF-1 protein results in excessive Ras
activation
OFF
Ras.GDP

• Neurofibromatosis
• Myeloid leukaemias

Ras.GTP
ON
Proliferation Survival Invasion
19
Molecular targets in leukaemia therapy
Signal transduction pathways Dysregulated
kinases eg Bcr-Abl Mutant Ras proteins Apoptosis
pathways Bcl-2, NF-kappaB, p53 Differentiation
pathways Retinoic acid receptor Histone
deacetylases
20
Imatinib mesylate inhibits the activity of
Bcr-Abl by competing with ATP and is effective in
the treatment of CML
21
Addition of a farnesyl (C15) moiety is required
for Ras proteins to be active
F
Plasma membrane
Ras
-C-OMe
Farnesyl transferase
active
Ras
-CAAX
Cytoplasm
inactive
22
Targeting Ras proteins by inhibiting membrane
localisation
Plasma membrane
FT Inhibitors
Farnesyl transferase
Ras
-CAAX
Cytoplasm
inactive
23
The transcription factor NF-kB induces
transcription of pro-survival genes and is
constitutively activated in a variety of tumours
NIK
Degradation by proteasome
IKK1
IKK2
NEMO
P
IkB
NF-kB
NF-kB
Increased transcription eg Bcl-2
24
Inhibitors of proteasomal activity prevent NF-kB
activation by blocking IkB degradation
Proteasome inhibitor Eg PS-341
NIK
IKK1
IKK2
NEMO
P
IkB
NF-kB
IKK inhibitors
Reduced transcription
25
What can we learn from the identification of
specific molecular abnormalities in malignant
disease?

• Insights into normal cell biology
• Targets for diagnosis and follow-up
• Targets for rational drug design