Transcript Presentation 4 – Application Example – Can breast cancer be cured

PCR Application:
Can Breast Cancer
be Cured?
Normal, Healthy Cells
• Cells can change or differentiate
to become specialised according to
the tissue that they make up
• A healthy cell performs the correct functions
according to its type and specialised state
• This feature of cells is controlled by our DNA
Normal, Healthy Cells
Cell
adhesion
Cell division
Cell specialisation/differentiation
When things go wrong
Very common to get DNA
mutations
How does a healthy cell deal
with this?
Repair DNA
e.g. BRCA2
protein
Cell suicide –
removes cells
with badly
damaged DNA
Normal, Healthy Cells
DNA Mutations
Mutations are a change in the base nucleotide
sequence of our DNA
e.g. Deletion
ATGCGATATCGTT
G
e.g. Insertion
ATG C GAATG G C GA
Changes in the DNA sequence can change the
amino acid sequence of the protein.
DNA Mutations
• If a gene becomes mutated, cells can start to
lose control and become cancerous
• This can lead to the formation of a tumour
Reduced cell
adhesion cancer cells
lose their ability
to stick together
Uncontrollable
cell division
Cancer
Cells
No cell specialisation - cancer
cells lose their specialised features
Cancer cells arise from genetic mutations
Reduced cell
death - cancer
cells do not
always respond
to signals telling
them to die
Cancerous Cells
External Factors causing
genetic mutations
Physical Carcinogens
E.g. UV Radiation from sunlight
Biological Carcinogens
E.g. viruses such as HPV can create an opportunistic
environment for cancer
Chemical Carcinogens
E.g. Tobacco, alcohol
External Factors causing
genetic mutations
Inheritance of these genetic
mutations
Genotype
Genetic makeup of a cell – the set of alleles that a
person has.
Phenotype
The observable (way it looks) physical or biochemical
appearance of an organism. Determined by genotype
and environmental influences.
Example
TYPICAL FORM
(“WILD TYPE” - WT)
MUTANT FORM
Genotype Terminology
• Heterozygous – when the cells contains 2 different
alleles at a gene locus e.g. Bb
• Homozygous – when identical alleles of the gene
are present on both homologous chromosomes
e.g. BB or bb
Inherited Mutations
• The BRCA2 gene codes for a protein that repairs
DNA. Some people can inherit a BRCA2
mutation (Bb genotype for BRCA2)
• These people are more susceptible to
accumulating DNA damage and are
consequently at a higher risk of breast cancer
• Tumours arise from cells where Bb has
spontaneously mutated to become bb with time
(since this means that they have no BRCA2 in
these cells)
What Does Higher Risk of Breast
Cancer Mean?
• 12% of women without any inherited mutations
will develop breast cancer in their lives
• 45% of women with a harmful BRCA2 mutation
will develop breast cancer by 70 years of age
Managing Risk
Angelina Jolie has an inherited BRCA2 mutation and
elected to have her breasts removed as a preventative
measure
How did she know?
• A DNA sample would have been taken (from her blood or
saliva) and this sample would have been sent to a testing
laboratory
• Then the BRCA2 gene locus would have been amplified
by PCR and her genotype analysed by gel electrophoresis
Managing Risk
Other options;
• Enhanced screening – frequent mammograms
• Chemoprevention – possibly tamoxifen or
ralaxifene may help to reduce risk, but this has
not yet been proven
How can we kill cancer cells with
BRCA2 Mutations?
Cancer cell’s repair mechanisms cannot cope
Cancer cells commit suicide
(Healthy cells also commit suicide)
The Problem with mutated BRCA
• The mutation in the BRCA2 (bb) gene in tumour
cells is not enough to induce cell suicide
• So BRCA2 mutated cells do not respond very
well to chemotherapy or radiotherapy
• This is because other DNA repair mechanisms
exist in the body. The other major one is the
PARP pathway
Overcoming this Problem
• Treating cancers caused by BRCA2 mutations
by inhibiting the other DNA repair pathway:
Synthetic Lethality
Normal Cell
BRCA2
Mutant Cell
Normal Cell with
PARP inhibitor
drug
BRCA2 mutant
cell with PARP
inhibitor drug
DNA Damage – chemotherapy/radiotherapy
BRCA
BRCA
BRCA
BRCA
PARP
PARP
PARP
PARP
Cell
survives
Cell
survives
Cell
survives
Cell Death
Advantage of synthetic lethality– the person’s healthy
cells are not damaged – only their cancer cells
Normal Cell with
PARP inhibitor
drug
BRCA2 mutant
cell with PARP
inhibitor drug
DNA Damage
BRCA
BRCA
PARP
PARP
Cell
survives
Cell Death
Conventional chemotherapy and radiotherapy
both cause a lot of damage to healthy cells
Synthetic Lethality
+ Chemotherapy
or Radiotherapy
INHERITED MUTATION
+ PARP INHIBITOR
DRUG
NO BRCA2 + NO other
= CELL DEATH
mechanisms
of cancer cells
of DNA repair
Synthetic lethal treatments are currently being researched in
Cardiff University and elsewhere as a potential new therapy for
breast cancer
Your Task
Your PCR samples are from 4 individuals with or
without BRCA2 mutations
Your tasks are to:
1. GENOTYPE each sample
2. PHENOTYPE each sample