BB3704 The Biology and Treatment of Cancer
Introduction
The hallmarks of cancer
- Self-sufficiency in growth signals
o Cancer cells are not dependent on normal growth factor signalling
o Acquired mutations during the development of cancer “short-circuit” growth factor
dependence
- Insensitivity to anti-growth signals
o Acquired mutations in tumour suppressor genes interfere with inhibitory signals.
- Tissue invasion & metastasis
o Normal cells maintain their location in the body
o Acquired mutations alter the activity of enzymes involved in cell invasion and those
proteins involved in cell-to-cell interaction
o Invasion and metastasis is the major cause of cancer death.
- Limitless replicative potential
o Normal cells display a finite number of division and senescence. Senescence is when
cells have reached their maximum amount of cell divisions
o Cancer cells maintain telomeres and divide continually
- Sustained angiogenesis
o Cancer cells can induce angiogenesis
- Evasion of immune response
- Evading apoptosis
o Normal cells are removed by apoptosis, e.g. after DNA damage. Cancer cells evade
apoptotic signals
Cancer as a genetic disease
- The key genes involved in cancer are
o Oncogene, e.g. growth inducer
Mutations in oncogenes are generally dominant mutations and cause
enhanced cell growth.
o Tumour suppressor gene, e.g. growth inhibitor
Clinical manifestations in tumour suppressor genes are caused by mutations
in both alleles → recessive
o DNA repair gene
DNA repair genes could be classified as tumour suppressor genes. The loss
of DNA repair genes increases the incidence of cancer
A mutation in one allele leads to the production of half of the DNA repair
genes → haplosufficient.
Li Fraumeni disease is when individuals have a mutation in their p53 gene.
They have a high incidence of different cancers.
Genes and mutations associated with cancer
- The retinoblastoma gene (pRB)
o Phosphorylation of RB is connected to the cell cycle. It is regulated by cyclins.
Mutation in RB changes the function of the gene.
o P16 is a tumour suppressor gene that has an impact on the function of RB.
o Too much production of a cyclin could lead to the overphosphorylation of RB.
o In tumour cells, the pRB pathway is frequently deregulated
Mutation is directly with the RB gene
Interaction with some form of oncoprotein
, o The point mutation of chromosomal deletions usually affects the pocket region of
pRB – necessary region of pRB activity. It is where other important transcription
factors bind to.
- P53
o Known as the “Guardian of the Genome”
o Four p53 proteins form a tetramer to become functional
o Is activated by DNA damage, oncogene activation and cell stress, such as hypoxia or
nucleotide depletion
o Reacts by cell cycle arrest, apoptosis, DNA repair or inhibition of angiogenesis
o Over 50% of cancers of different histological origin contain mutations in the p53
gene. It is the most commonly affected tumour suppressor gene in human cancer
o Inactivation of p53 results in a reduced ability of tumour suppression
o Mutations in p53 occurs in hotspots; between exons 5 and 9, and between codons
126 to 307
o Frequency and distribution of mutations differs in different tumour types
- One or more of these tumour suppressor genes is going to have to be inactivated for
carcinogenesis to occur:
o P53
o pRB
o P16
- Oncogenes
o Proto-oncogene
Normal cellular gene however, when altered by mutation it can contribute
to carcinogenesis
Proto-oncogene regulate cell growth and differentiation
Oncogenes:
Point mutation (Ras)
Gene amplification (myc)
Translocation (BCRabI)
Insertional mutagenesis (viral)
o There are various levels of oncogenic activation
Growth factors (overproduction)
Receptors (overproduction and change in structure)
o Intracellular cell signalling is often disrupted during cancer development.
Cancer as a multistep process
- Initiation
o Interaction of carcinogen with DNA. Exposure to carcinogens, e.g. UV light →
reversible i
- Promotion
o Selective growth advantage (free radicals) → reversible
- Progression
o Enhanced cell division (additional mutations) → reversible
- Malignant conversion
o Full blown cancer → malignant
DNA mutagenesis and carcinogenesis
- Radiation
o Gamma and X-rays → low linear energy transfer
o Particular radiation (protons, neutron, electrons) → high linear energy transfer
, - Non-ionising radiation (UV light)
o Dimers: covalent linkages between adjacent pyrimidines in DNA. Covalent linkages
are unbreakable.
100,000 genomes project
- Sequencing of 100,000 genomes from 70,000 individuals
- Aim
o Creation of new genomic medicine service for the NHS
o New diagnostics
o New treatments – individualised methods of treatment
, Discovery of tumour suppressor genes
Discovery
- The introduction of a virus into a cell added new genetic information. Therefore, it was
thought that carcinogenesis must be due to the gain of genetic information
- Biologists also believed that if malignancy was caused by somatic mutation, the nature of
malignancy implied that such mutations were dominant
o Barski & Cornefert (1962) fused a highly malignant mouse cell line with a mouse cell
line of lower malignancy → hybrid cell line retained the aggressive malignancy →
malignancy must be dominant
o Hybrids had fewer chromosomes that parent cells suggesting loss of genetic
information. Harris (1969) proposed that chromosome loss was central to
carcinogenesis
- Harris fused highly malignant Ehrlich tumour cells with mouse A9 cells which produced a few
tumours. He injected into mice and looked for development of tumours. Tumours developed
after a very long lag period compared to Ehrlich tumours. Those that did develop exhibited
chromosome loss → carcinogenesis was a recessive trait
Retinoblastoma
- Alfred Knudson studied children with eye tumours (retinoblastoma). He noticed two groups
of patients
o Familial form – early development of tumours with bilateral disease (both eyes)
o Sporadic form – late development and no family history with usually single eye
involvement
- For a tumour to develop, mutations were needed in a gene involved in this disease
(retinoblastoma gene). Normally, two copies of the gene are inherited, one from each
parent.
- In sporadic disease, mutations were needed in both copies. In familial disease, one mutated
copy is inherited from a parent, but mutation of both copies are needed for disease to
develop → more likely to develop retinoblastoma.
o Therefore, two hits are required for development of the disease → called Knudson’s
“two hit” hypothesis
o Two hit hypothesis – there must be two mutation sin order for cancer to be
initiated. One mutation taking out the first allele and another mutation taking out
the second allele.
- Loss of heterozygosity
The retinoblastoma gene
- The RB transcript is 5264bp long, encoded in 27 exons, located on chromosome 13q14 and
encodes a 105 kDa protein
- The pRB protein is constitutively expressed in most normal cycling cells.
- pRB is subject to phosphorylation during specific cell cycle phases
o Hypophosphorylated during early cell cycle
o Hyperphosphorylated as cells go into S-phase and DNA synthesis
- Principal role is to regulate transition from G1 into S-phase
- Signalling proteins such as cyclins and cyclin dependent kinases (CDKs) mediate and control
the phosphorylation of pRB. When cells begin cycling, cyclin D and cyclin E are induced in
association with CDK4 and CDK6. These complexes bind to and preferentially phosphorylate
pRB. A critical level of phosphorylation commits the cell to enter S-phase.
- The transcription factor E2F is inactive when bound to pRB. When pRB is phosphorylated,
E2F is released. Transcriptionally active E2F increases the activity of target genes required
Introduction
The hallmarks of cancer
- Self-sufficiency in growth signals
o Cancer cells are not dependent on normal growth factor signalling
o Acquired mutations during the development of cancer “short-circuit” growth factor
dependence
- Insensitivity to anti-growth signals
o Acquired mutations in tumour suppressor genes interfere with inhibitory signals.
- Tissue invasion & metastasis
o Normal cells maintain their location in the body
o Acquired mutations alter the activity of enzymes involved in cell invasion and those
proteins involved in cell-to-cell interaction
o Invasion and metastasis is the major cause of cancer death.
- Limitless replicative potential
o Normal cells display a finite number of division and senescence. Senescence is when
cells have reached their maximum amount of cell divisions
o Cancer cells maintain telomeres and divide continually
- Sustained angiogenesis
o Cancer cells can induce angiogenesis
- Evasion of immune response
- Evading apoptosis
o Normal cells are removed by apoptosis, e.g. after DNA damage. Cancer cells evade
apoptotic signals
Cancer as a genetic disease
- The key genes involved in cancer are
o Oncogene, e.g. growth inducer
Mutations in oncogenes are generally dominant mutations and cause
enhanced cell growth.
o Tumour suppressor gene, e.g. growth inhibitor
Clinical manifestations in tumour suppressor genes are caused by mutations
in both alleles → recessive
o DNA repair gene
DNA repair genes could be classified as tumour suppressor genes. The loss
of DNA repair genes increases the incidence of cancer
A mutation in one allele leads to the production of half of the DNA repair
genes → haplosufficient.
Li Fraumeni disease is when individuals have a mutation in their p53 gene.
They have a high incidence of different cancers.
Genes and mutations associated with cancer
- The retinoblastoma gene (pRB)
o Phosphorylation of RB is connected to the cell cycle. It is regulated by cyclins.
Mutation in RB changes the function of the gene.
o P16 is a tumour suppressor gene that has an impact on the function of RB.
o Too much production of a cyclin could lead to the overphosphorylation of RB.
o In tumour cells, the pRB pathway is frequently deregulated
Mutation is directly with the RB gene
Interaction with some form of oncoprotein
, o The point mutation of chromosomal deletions usually affects the pocket region of
pRB – necessary region of pRB activity. It is where other important transcription
factors bind to.
- P53
o Known as the “Guardian of the Genome”
o Four p53 proteins form a tetramer to become functional
o Is activated by DNA damage, oncogene activation and cell stress, such as hypoxia or
nucleotide depletion
o Reacts by cell cycle arrest, apoptosis, DNA repair or inhibition of angiogenesis
o Over 50% of cancers of different histological origin contain mutations in the p53
gene. It is the most commonly affected tumour suppressor gene in human cancer
o Inactivation of p53 results in a reduced ability of tumour suppression
o Mutations in p53 occurs in hotspots; between exons 5 and 9, and between codons
126 to 307
o Frequency and distribution of mutations differs in different tumour types
- One or more of these tumour suppressor genes is going to have to be inactivated for
carcinogenesis to occur:
o P53
o pRB
o P16
- Oncogenes
o Proto-oncogene
Normal cellular gene however, when altered by mutation it can contribute
to carcinogenesis
Proto-oncogene regulate cell growth and differentiation
Oncogenes:
Point mutation (Ras)
Gene amplification (myc)
Translocation (BCRabI)
Insertional mutagenesis (viral)
o There are various levels of oncogenic activation
Growth factors (overproduction)
Receptors (overproduction and change in structure)
o Intracellular cell signalling is often disrupted during cancer development.
Cancer as a multistep process
- Initiation
o Interaction of carcinogen with DNA. Exposure to carcinogens, e.g. UV light →
reversible i
- Promotion
o Selective growth advantage (free radicals) → reversible
- Progression
o Enhanced cell division (additional mutations) → reversible
- Malignant conversion
o Full blown cancer → malignant
DNA mutagenesis and carcinogenesis
- Radiation
o Gamma and X-rays → low linear energy transfer
o Particular radiation (protons, neutron, electrons) → high linear energy transfer
, - Non-ionising radiation (UV light)
o Dimers: covalent linkages between adjacent pyrimidines in DNA. Covalent linkages
are unbreakable.
100,000 genomes project
- Sequencing of 100,000 genomes from 70,000 individuals
- Aim
o Creation of new genomic medicine service for the NHS
o New diagnostics
o New treatments – individualised methods of treatment
, Discovery of tumour suppressor genes
Discovery
- The introduction of a virus into a cell added new genetic information. Therefore, it was
thought that carcinogenesis must be due to the gain of genetic information
- Biologists also believed that if malignancy was caused by somatic mutation, the nature of
malignancy implied that such mutations were dominant
o Barski & Cornefert (1962) fused a highly malignant mouse cell line with a mouse cell
line of lower malignancy → hybrid cell line retained the aggressive malignancy →
malignancy must be dominant
o Hybrids had fewer chromosomes that parent cells suggesting loss of genetic
information. Harris (1969) proposed that chromosome loss was central to
carcinogenesis
- Harris fused highly malignant Ehrlich tumour cells with mouse A9 cells which produced a few
tumours. He injected into mice and looked for development of tumours. Tumours developed
after a very long lag period compared to Ehrlich tumours. Those that did develop exhibited
chromosome loss → carcinogenesis was a recessive trait
Retinoblastoma
- Alfred Knudson studied children with eye tumours (retinoblastoma). He noticed two groups
of patients
o Familial form – early development of tumours with bilateral disease (both eyes)
o Sporadic form – late development and no family history with usually single eye
involvement
- For a tumour to develop, mutations were needed in a gene involved in this disease
(retinoblastoma gene). Normally, two copies of the gene are inherited, one from each
parent.
- In sporadic disease, mutations were needed in both copies. In familial disease, one mutated
copy is inherited from a parent, but mutation of both copies are needed for disease to
develop → more likely to develop retinoblastoma.
o Therefore, two hits are required for development of the disease → called Knudson’s
“two hit” hypothesis
o Two hit hypothesis – there must be two mutation sin order for cancer to be
initiated. One mutation taking out the first allele and another mutation taking out
the second allele.
- Loss of heterozygosity
The retinoblastoma gene
- The RB transcript is 5264bp long, encoded in 27 exons, located on chromosome 13q14 and
encodes a 105 kDa protein
- The pRB protein is constitutively expressed in most normal cycling cells.
- pRB is subject to phosphorylation during specific cell cycle phases
o Hypophosphorylated during early cell cycle
o Hyperphosphorylated as cells go into S-phase and DNA synthesis
- Principal role is to regulate transition from G1 into S-phase
- Signalling proteins such as cyclins and cyclin dependent kinases (CDKs) mediate and control
the phosphorylation of pRB. When cells begin cycling, cyclin D and cyclin E are induced in
association with CDK4 and CDK6. These complexes bind to and preferentially phosphorylate
pRB. A critical level of phosphorylation commits the cell to enter S-phase.
- The transcription factor E2F is inactive when bound to pRB. When pRB is phosphorylated,
E2F is released. Transcriptionally active E2F increases the activity of target genes required
