Lecture 4 - B cells and Cancer Flashcards
What are the hallmarks of cancer?
Hanahan & Weinberg’s Landmark Paper
- Proliferation in the absence of GFs
- Avoiding growth suppressors
- Avoid apoptosis
- Angiogenesis
- Immortality
- Metastasis
What features of B cells are a cancer risk?
- ‘Ignoring’ DNA damage
- Avoiding apoptosis
- Circulate around the body (metastasis)
- Rapid proliferation
- Long lived
What are the categories of malignancies of the immune system?
- Lymphomas: solid mass, lymphocytes
- Leukaemias: lymphocytes & leukocytes, in blood
- Myeloma: plasma cells in BM
What is the importance of non-Hodgkins lymphoma?
It is one of the most common cancers in men and women in Australia
What are the two types of lymphomas?
What differentiates them?
• Hodgkins:
Presence of Reed-Sterberg cell
• Non-Hodgkins
List some B cell lymphomas
- Burkitt lymphoma
- Diffuse large B-cell lymphoma
- Follicular lymphoma
- Hodgkins lymphoma
- non-Hodgkins lymphoma
Describe the growth rates of lymhomas
Can be either:
• Indolent
• Aggressive
What is the biggest risk factor for non-Hodgkins lymphoma?
Age:
• most people who get it are 60+
What is leukaemia?
- Malignancy that starts in blood forming tissue
* results in many cancerous cells entering circulation
What are some B cell leukaemias?
Whom do they affect?
- ALL: Acute lymphocytic leukaemia
• The very young and the elderly
• B cell precursor malignancy - CLL: Chronic lymphocytic leukaemia
• Men 50+
• Mature B cell malignancy
Which cells can become malignant in leukaemia?
- B cells
- T cells
- Myeloid cells
What is myeloma?
Malignancy of plasma cells
Describe the progression of myeloma
MGUS: asymtpomatic pre-malignant phase in which there is clonal cell proliferation
Found in 3% of over 50’s
Progresses in less than 1% of cases per year
How are B cell malignancies classified?
Physical observation: • Histology, Reed-Sternberg cell • Patient's condition • Karyotype • Flow cytometry
What is the Reed-Sternberg cell?
Mysterious but diagnostic cell seen in Hodgkins lymphoma
• has markers of both myeloid and lymphoid cells
What is an important diagnostic feature seen in multiple myeloma patients?
Increase concentrations and varied serum antibodies
• Clonal ‘paraproteins’
• Bruce Jones Proteins
What are clonal paraproteins?
Where are they found?
Abnormal Ig produced by excess clonal proliferation of B lymphocytes
They end up in the serum
What are Bence Jones Proteins?
Where are they found?
Free light chains
In blood and urine (because they are small enough to be filtered)
What are monoclonal antibodies (mAbs)?
These are antibodies that are all specific for a single epitope
The Abs are identical because they all come from identical B cells (i.e., they all come from the same clones)
What end organ damage occurs in multiple myeloma?
- Bone lesions and fractures
• Increased RANKL → stimulation of osteoclasts - Hypercalcemia
• Increased break down of bone - Renal insufficiency
• So much protein in serum - Anaemia
- Neutropaenia → infection
- Thrombocytopaenia → haemolytic tendency
What are current treatments for non-Hodgkins lymphoma?
- Chemotherapy
- Antibodies (Rituximab)
- Irradiation
- Bone marrow transplantation
Describe the features of Bortezemib
"Addresses the nature of the cell" • A treatment for Multiple Myeloma • A dipeptide molecule • inhibits the proteasome • Proteasome vital part of plasma cell machinery, as they are producing such large amounts of Ig
What is a proteasome?
A piece of cellular machinery that receives ubiquitin-marked proteins for digestion
Discuss bisphosphonates
Treatment for MM
- Inhibition of osteoclasts
- Reduced bone resorption
- Reduced growth
Addresses the symptoms of the cancer
Where is CD20 found?
On the surface of mature B cells
Describe the features of Rituximab
• Treatment for non-Hodgkins lymphoma
• A monoclonal anti-CD20 Ab
• Ab binds to the CD20 on mature B cells
• Leads to (transient) depletion of ALL B cells
(once off the drug, B cells come back slowly)
Where do malignant B cells congregate?
What is the effect of this?
The cells crowd the bone marrow
This disrupts all the other blood cells that are developing here
Effect:
• Cytopaenia Immunocompromise, frequent infection
• Anaemia, fatigue
• Thrombocytopaenia, haemorrhagic tendency
What is Bcl-2?
Describe its normal function, and how it could cause cancer
Cell survival protein
Normal function:
• Binds BH3-only to prevent it from triggering apoptosis
In cancer:
• Involved in translocations up against the Ig gene loci
• Over-expression
• BH3 can never out-compete Bcl-2 t trigger apoptosis
• Accumulation of cells with DNA damage
What is the down side of Bortezimib?
It does not selectively block proteasomes in plasma cells, rather affects all cells
Describe the heterogeneous nature of DLBCL
- Distinct types of the malignancy have been identified through gene expression profiling
- These various types are due to the different combination of mutations that have lead to the disease
Two categories:
• GC type
• ABC type
Describe ABT-263
- a treatment for B cell lymphomas
- This is a drug that binds Bcl-2 (displacing BH3-only)
- this allows the cell to undergo apoptosis
What is the most common B-cell leukaemia?
CLL: chronic lymphocytic leukaemia
What are some diagnostic criteria for MM?
(Multiple myeloma)
• >10% clonal plasma cells on bone marrow biopsy
• monoclonal antibodies in urine or serum
• end organ damage
What are some treatments of MM?
- Bortezimib
* Bisphosphonates
What is DLBCL?
Diffuse large B cell lymphoma
Describe differences in gene expression in ABC (activated B cells) and GC B cells
ABC: most genes are switched off
GC B: most genes are switched on
What are the two groups of DLBCL patients?
What treatment is appropriate for each respectively?
Low-clinical risk:
• Better survival rates
• GC type B cells
• Standard therapy + Rituximab
High clinical risk:
• Poor survival rates
• ABC type B cells
• Specific enzyme inhibitors targeting hyperactive pathways
What is BH3-only?
Describe its role in apoptosis
Molecule in the cell that triggers apoptosis
Function
- Cell stress
- Activation of BH3 only
- Activation of Bax and Bak
- Cyt c loss from mitochondria
- Formation of apoptosome
- Activation of caspases
- Apoptosis
Which molecule inhibits the action of BH3-only?
Bcl-2
Which drug binds Bcl-2?
What is the effect of this?
Which disease is it used for?
ABT-263
• Prevents Bcl-2 from inactivating BH3-only, which normally brings about apoptosis
• Thus, the cancerous cell is no longer immortal
Use to treat B cell lymphomas with overactive Bcl-2 such as:
• CLL
• Follicular lymphoma
What was the effect of ABT-199 in CLL patients?
Massive reduction in lymphocytes, killing all cancerous cells
Platelets unaffected to a large extent
List the functions of myc
- Drives proliferation
• Upregulation of cyclins - Regulates cell growth
• Enhances protein synthesis - Inhibits differentiation
- Strong proto-oncogene
What is Bcl-6?
Describe the processes it coordinates
- Inhibits DNA damage response
- Inhibits differentiation
- Inhibits apoptosis
What is the effect of myeloma cells on bone?
Malignant cells produce lots of RANK-L, which
• Increases osteoclast activity
Decreased OGP, which
• Decreases osteoblast activity
Increased resorption of bone, leaving it fragile
What is Bcl-x?
Cell survival protein
What is p53?
Detects DNA damage
What are cyclins?
Cell growth and proliferation regulators
What is the difference between oncogenes and proto-oncogenes?
Proto-oncogenes: normal cell function to do with growth and proliferation
Oncogene: inappropriately expressed proto-oncogene that causes the cell to proliferation uncontrollably
What one of the most important proto-oncogenes?
Which cancers can it lead to?
Myc
Burkitts Lymphoma, through translocation up against heavy chain locus
Describe the process leading to apoptosis when a cell experiences danger or damage
Which molecules can inhibit this?
→ Damage 1. BH3-only activated 2. Bax and Bak activation 3. Mitochondria release Cyt. c (Bax and Bak punch holes in mito membrane) 4. Formation of apoptosome 5. Activation of cytoplasmic caspases 6. Digestion of cell (apoptosis)
Bcl-2 can block BH3-only
Which mutation is commonly seen in Follicular lymphoma and CLL?
Over-expression of Bcl-2
Which molecule is vital for GC formation, as it inhibits apoptosis due to DNA damage in developing B cells?
Bcl-6
What is the relationship between Bcl-6 and p53?
Bcl-6 inhibits p53’s action of bringing about apoptosis
Which cancers commonly have Bcl-6 translocation?
DLBCL
What happens to Bcl-6 after CD40 signalling?
Down regulated so that the following can occur:
- Selection of high affinity Ig
- Elimination of DNA damaged cells, or those with low affinity Ig through apoptosis
How may Bcl-6 be turned into an oncogene?
- Translocation
• Up against Ig gene locus - Mutation of the repressor binding site in promoter
• Repressor can not bind - Mutations in ubiquitin binding site
• Ubiquitin can not bind
• Not targeted to proteasome
• Can not be degraded
→ Continued expression on Bcl-6
Give an example of a drug that ‘addresses the nature of the cell’
Bortezimib
• Malignant plasma cells (in MM) are producing a large amount of protein
• They rely on the proteasome to degrade miss-folded protein
• Bortezimib prevents the proteasome from properly functioning, so the plasma cells die
Which mutation commonly causes DLBCL?
Bcl-6 overexpression
Which mutation commonly causes CLL?
Bcl-2 overexpression
Which mutation commonly causes follicular lymphoma?
Bcl-2 over expression
Which cancer is Rituximab used for?
Non-Hodgkins lymphoma
Describe the risk-reward balance in B cells
Risk: development of cancers
Reward: very efficient way of protecting against microbes
Despite the risks, B cell cancers are rare, so these processes were not removed in evolution – the benefit outweighs the risk
How may chromosomal translocations be identified?
Classical / outdated:
• Karyotyping
• FISH
• Probe for myc
Now:
• Cancer genome sequencing
Describe the B cell cancer genome map
Based on new sequencing technologies, many of the common (and not so common) translocations that can lead to B cell cancers have been identified
Important loci:
• IgH, IgK, IgL
• Bcl2, Myc, Bcl6
These loci are fused together
Describe regulation of the cell cycle
Drivers:
• Cyclins
• Transiently expressed
• Phosphorylate Cdks
Brakes:
• p21, p15, p18
• Bind Cdks to inhibit their activity
Activated Cdks phosphorylate Rb
What is the general function of Bax and Bak?
Pro-apoptotic
Compare Ig content of blood in healthy individuals with those with MM
Normal:
• 10-15 mg/ml
• Heterogeneous
MM:
• 30 mg/ml
• Clonal
