Lecture 23 Flashcards
How are monoclonal antibodies made for HER2
Immunise mice with HER2 and then isolate the spleen cells containing the antibody-producing B memory cells. These cells are fused with myeloma immortal cells. This creates an immortal cell line that will continue to make huge amounts of the antibody
What process can be used to determine the copy number of a gene that has been amplified in tumorigenesis
Fluorescent in situ hybridisation (FISH)
Different combinations of receptors stimulate different signalling pathways and can lead to cell proliferation, survival and a prevention of apoptosis, T or F
T
HER2 is a negative prognostic marker for several cancers, what is meant by this
Overexpression of HER2 correlates with poor survival rates of breast cancer patients
What are the different types of HER receptor
HER1, HER2, HER3 and HER4
On average, how many people will have cancer in their lifetime
1 in 3 to 1 in 4
Explain how immunoglobulins are humanised
The hypervariable domain involved in antigen binding is swapped into human antibodies. This enables the antibodies to be used in human patients without causing massive immune responses. It is achieved by cloning the murine heavy and light chain cDNA encoding 4D5 into the human IgG1 heavy chain and light chain plasmids. The humanised antibody is then made by transfecting Chinese Hamster Ovary (CHO) cells with light and heavy chain plasmids
What is unusual about the HER2 receptor
Unlike the other members of the HER receptor family, HER lacks the extracellular ligand binding domain. This means that it doesn’t require ligand binding to dimerise and hence is constitutively active
What is the most common type of cancer
Lung cancer
What causes HER proteins to become oncogenic
Overexpression or mutations
Up to what percentage of breast cancers are believed to be HER2 positive
0.25
What is the problem with using mice to produce HER2 antibodies
Murine antibodies are not well tolerated in humans, the immune response from these will kill
What are the three main causes of cancer
Physical carcinogen – UV and ionising radiation, chemical carcinogens – asbestos and tobacco smoke, biological carcinogens – infection from certain viruses, bacteria or parasites
Which conformations of HER receptor dimers signal the strongest and why
Homodimers don’t signal as strongly as heterodimers. The HER2:HER3 heterodimer signals the strongest as it activates both the Ras/MAPK pathway and the PI-3 Kinase pathway
How do the median survival rates of HER2 positive and HER2 negative breast cancers compare
HER2 positive – 3 years, HER2 negative – 6-7 years
What happens to the HER receptors (apart from HER2) following ligand binding
HER proteins undergo a conformational change upon ligand binding that is essential for dimerization and signalling. Once the ligand binds, the receptor can either homo or heterodimerise which stimulates the receptor to signal
What was the three different pieces of evidence for the use of the 4D5 monoclonal antibody in the treatment of HER2 positive breast cancer
4D5 binds to the extracellular domain of HER2 and leads to an inhibition of their proliferation. Injecting mice with the anti-HER2 monoclonal antibody supresses tumour growth in mice. Finally, injection of a radiolabelled 4D5 targets HER2 positive breast cancer cells in women
Outline the HER pathway of activation
Growth factor binding to a HER receptor allows dimerisation with other HER receptors. Dimerisation of the HER receptors allows for phosphorylation of the intracellular tyrosine kinase domain. This creates binding sites for signalling proteins such as PTEN PDK etc. This in-turn leads to the activation of PI-3 Kinase pathway which prevent the apoptosis of cancer cells. HER receptors can also signal through the activation of the MAP-K pathway to increase cancer cell proliferation
Describe Herceptin’s mechanism of action
Binds to extracellular domain of the HER2 receptor and inhibits the proliferation of human tumour cells through multiple mechanisms of action. Firstly, it blocks downstream signalling of HER2 receptor but it also marks cells for degradation by the immune system. Finally, it is believed to also exploit the internalisation of HER2 receptors
What family of receptors do the human epidermal growth factor receptors belong to
Receptor tyrosine kinases
HER proteins are tumour suppressor genes, T or F
F – they are proto-oncogenes
New versions of HER2 inhibitors also inhibit receptor dimerisation, T or F
T
What is unique about the HER3 receptor
The HER3 receptor has lost its intracellular tyrosine kinase domain and so cannot phosphorylate target proteins
Which mutant form of HER2 was first discovered in rats the promote cancer aetiology
Neu
What is the other name for the hypervariable domain involved in antigen recognition by immunoglobulins
Complementary determining region (CDR)
Normal breast tissue contains around 20,000 copies of the HER2 receptor, how many copies can be found in cancerous tissues
2 million copies – 10-fold increase
Herceptin is a monoclonal antibody used to target HER2 overexpression, what is meant by a monoclonal antibody
A massive population of antibodies derived from a single cell and that all specifically recognise a single epitope
Explain the serious complications that can occur because of Herceptin treatment
Because HER2 receptors are present in the heart, the inhibition as a result of Herceptin treatment can lead to decreased cardiac viability
What is the best way of using Herceptin to treat HER2 positive breast cancer
Combination with surgery, chemotherapy – 85% of patient’s cancer free for 5 years
How is the problem of immune response to foreign antibodies overcome
Humanisation
