Transcript Slide 1

Genetics of brain tumours
Dr Keith Giles
Laboratory for Cancer Medicine,
Western Australian Institute for Medical Research,
School of Medicine and Pharmacology,
University of Western Australia
[email protected]
Overview
1. Glioblastoma - the most common & lethal form of
adult primary brain tumour
2. What we know about the molecular biology of
glioblastoma
3. Targeted therapy of glioblastoma
4. New advances in understanding glioblastoma
genetics
5. Research into microRNAs and glioblastoma
Glioblastoma
• Most common & lethal primary brain tumour in adults
• Highly resistant to therapy (surgery, radiation therapy
& chemotherapy)
• Disease recurrence is common following surgery
• Life expectancy of glioblastoma multiforme patients
(GBM; Grade IV) is ~14 months
• Urgent need for new treatment options
Molecular biology
organism
organ
cell
molecules:
DNA, RNA,
proteins
What cells make up a tumour?
How genes cause disease
DNA
(genes)
Disease
RNA
Protein
Structure &
function of cells
Genetic basis of cancer
Cancers originate as the result of hereditary or
accumulated changes (mutations) in genes that
control critical processes in cells
DNA
GAC TAAT C G G
sequence
GACTAGTCGG
Normal gene
Single base change
GAC TAAC CAT C G G
Insertion
GACTCGG
Deletion
Genetic basis of cancer
Mutations can activate oncogenes or silence
tumour suppressor genes
tumour suppressor
genes (good)
oncogenes
(bad)
Genetic basis of cancer
There is increased or decreased expression of specific
genes in cancer
Normal cell
Cancer cell
Gene A
Gene A
Gene B
Gene B
Genetic basis of cancer
These changes (mutations) can be studied in the
laboratory using sophisticated genetic analysis
methods
The hallmarks of cancer
How does glioblastoma arise?
Molecular development of glioblastoma
1.
Two main pathways by which glioblastomas
develop (primary vs secondary)
2.
Primary and secondary glioblastomas can
arise via different mutations
3.
Mutations between primary or secondary
glioblastomas can differ
Increased EGFR expression and
signaling in glioblastoma
normal
cell
glioblastoma
cell
growth
growth
How can understanding the genetics of
cancer cells (glioblastoma)
help us to develop new treatments for
the disease?
Understand what has “gone wrong”
in glioblastoma cells
Design a drug to correct what has
“gone wrong”
Targeted cancer therapy
Find & understand mutation/alteration that drives
cancer cell growth (choosing the ‘right’ target)
Design & develop drug that specifically targets
this mutation/alteration
Normal cells lack the mutation & should be
relatively unaffected; side effects should be
minimised
Gleevec & chronic myelogenous
leukaemia (CML)
(TIME magazine,
May 2001)
(Tyrosine
kinase
Inhibitor)
Is there a ‘gleevec’ for
glioblastoma?
Not yet
There may never be
one drug that works on
all glioblastomas
Why?
Heterogeneity
(no single mutation causes all
glioblastomas)
Redundancy
(a glioblastoma is not dependent on
one mutation; other mutations can
compensate)
growth
Resistance
(by targeting one mutation, new
mutations can arise that allow
glioblastoma cells to escape this
targeting)
Case study of a targeted
glioblastoma drug
Erlotinib (Tarceva)
(A small molecule tyrosine kinase
inhibitor of the epidermal growth factor
receptor [EGFR])
Epidermal growth factor receptor
(EGFR) as a therapeutic target in glioblastoma
Tyrosine kinase
inhibitor (erlotinib)
PI3K/Akt
ERK1/2
The rationale for using erlotinib to treat
glioblastoma
• About half of glioblastomas have high expression
of EGFR
• Blocking EGFR should block glioblastoma growth
& invasion
• Promising results in other cancer with high
expression of EGFR (eg. lung)
• Small molecule tyrosine kinase inhibitor (TKI) crosses blood-brain barrier
Erlotinib and glioblastoma
• Unfortunately, few patients (~10-20%) respond to
erlotinib and survival benefit is small
• Need to identify what determines whether a
patient will respond/not respond to erlotinib
• Combine erlotinib with other treatments
(chemotherapy, other targeted agents, radiation
therapy) to improve responses and increase patient
survival
Mutations downstream of EGFR render
glioblastoma cells resistant to erlotinib
Tyrosine kinase
inhibitor (erlotinib)
PI3K/Akt
ERK1/2
New advances in
understanding of
glioblastoma
Brain tumour stem cells
• Cancer stem cell hypothesis: tumours are dependent on a small
population of cancer stem cells that are distinct from the more
abundant tumour cells.
• Cancer stem cells are highly resistant to conventional cancer
therapies
• Express specific cell surface markers (eg. CD133).
• Molecular characterisation has identified possible drug targets
for brain tumour stem cells.
Targeting brain tumour stem cells
The Cancer Genome Project
• Human Genome Project: database of a complete genome of a
normal human
• Cancer Genome Project: established in 2006; to characterise
>10,000 tumours at a molecular level from at least 20 tumour
types (incl. glioblastoma) by 2015.
• Will identify many more mutations responsible for
glioblastomas - new treatment targets?
• Made possible by rapid development of high throughput
techniques - researchers can screen millions of DNA bases
quickly and cheaply. This has only been feasible in the last few
years.
The Cancer Genome Project
• Some achievements to date in understanding glioblastoma:
(1) Discovery that patients with an unmethylated version of
MGMT gene respond better to temozolomide. Patient selection?
(2) Discovery that a subset of glioblastoma patients that live an
average of three years have different gene mutations to regular
glioblastoma patients. What do these do?
(3) Identification of at least four glioblastoma subtypes, based on
their DNA signatures. Survival, response to aggressive
chemotherapy & radiotherapy differed according to subtype.
microRNAs and
glioblastoma
microRNAs (miRNAs)
• miRNAs are short, endogenous, non-coding RNAs
- >900 miRNAs, many are conserved, cell & tissue-specific expression
• miRNAs negatively-regulate gene expression
- bind to specific target mRNAs, predicted to regulate 1/3 of all genes
• miRNAs have important functions in normal cells
- development, differentiation, angiogenesis, proliferation, apoptosis
• miRNA expression is altered in disease states
- cancer - oncogenes & tumour suppressor genes
microRNAs block expression of
specific target genes
DNA
RNA
protein
microRNA
microRNA expression is altered in
cancer cells vs normal cells
• Cancer miRNA “signature” - classify tumours
• Biomarkers?
Strategies to use microRNAs as therapeutics
A
B
A role for microRNAs in glioblastoma?
Normal cell
Glioblastoma cell
MicroRNA 1
high
low
MicroRNA 2
low
high
MicroRNA 3
low
low
Levels of miR-7 microRNA are significantly
reduced in glioblastoma patient tissues vs
normal brain
miR-7 expression (relative to U44 snRNA)
1.2
1
0.8
0.6
0.4
0.2
0
Culture of glioblastoma cell lines in the
laboratory
glioblastoma tumour
glioblastoma cell line
• Study gene mutations/alterations
• Study new treatments
Levels of miR-7 microRNA are significantly
reduced in glioblastoma tumour cell lines vs
normal brain
Glioblastoma cell lines can be transfected
with microRNA
microRNA (eg. miR-7)
glioblastoma cell line
• Determine effects on other genes involved
in glioblastoma (eg. EGFR)
• Measure effects on glioblastoma cell growth
EGFR protein expression is decreased by
miR-7 microRNA in human cancer cell lines
(Webster et al 2009 JBC)
miR-7 microRNA reduces glioblastoma
cell growth
Summary
• Glioblastomas are different & often arise via different
mutations. This might explain why they can respond
differently to treatment.
• First generation of targeted agents have yielded
disappointing results, but research can explain why this
has been the case and improvements made to future drug
design.
• Understanding all of the important mutations in
glioblastoma (eg. via large scale research efforts such as
the Cancer Genome Project) should allow the
development of new drugs that are effective in patients
with the correct mutation.
More work is needed
but progress is being made…
“I’ve been treating glioblastoma for about 22 years. I’ve
taken care of more than 20,000 patients. The kinds of
things we’ve seen in the clinic in the last four years
blows away anything I saw in the previous 18 years of
my career.”
Howard Fine, MD - Chief, Neuro-oncology, Centre for Cancer
Research, National National Cancer Institute, commenting in
Jan 2010 on a report estimating that the percentage of
glioblastoma patients who survive two years from diagnosis has
more than tripled in the last five years as a result of new
treatment regimens.
Acknowledgements
Rebecca Webster, Priscilla Zhang, Karina Price,
Michael Epis, Andrew Barker, Felicity Kalinowski
The Leedman Lab
Western Australian Institute for Medical Research
Terry Johns (Monash), Kerrie McDonald (Lowy),
Greg Goodall (Hanson), John Mattick (UQ)
Cancer Council WA & Pearl Bethel Allan Research
Grant Endowment
National Health and Medical Research Council
miRNAs may act as tumour suppressors
or oncogenes
microRNAs block expression of target genes
• miRNAs bind to specific target mRNAs, regulate 1/3 of all genes
• One miRNA can have 100’s of mRNA targets
Glioblastomas arise from glial cells
• Glioblastomas are a group of low-grade and high-grade brain
tumours that originate from glia (Greek for ‘glue’)
• Normally, glial cells (eg. astrocytes) provide support to
neurons (nerve cells): nutrients, mechanical support,
development, immune function
• Genetic alterations occur in glial cells
glioblastoma