Which pathways depend on signalling by receptor tyrosine kinase and how are these pathways activated?
MAPK pathway (proliferation) PI3K pathway (cell growth, proliferation, angiogenesis and metabolism)
Activation process:
- receptors bind to growth factors
- causes dimerisation of the receptor
- structural changes occur on the intracellular part
- tyrosine kinase becomes phosphorylated
- it reacts with adaptor proteins
- adaptor proteins activate the pathways
Which part of the receptor tyrosine kinase do monoclonal antibodies and small molecule tyrosine kinase inhibitors target?
Monoclonal antibodies: target extracellular/growth factor receptor ligand binding domain
Small molecule tyrosine inhibitors: target intracellular/tyrosine kinase domain
In the extracellular domain (of tyrosine kinase receptor), which regions are responsible for ligand binding and which are responsible for dimerisation?
1+3 bind to ligan
2+4 responsible for dimerisation
Give an example of a monoclonal antibody that stops tyrosine kinase signalling and describe how it works.
Cetuximab
Prevents the binding of ligand to the receptor
What type of cancer is cetuximab used in?
Metastatic colorectal cancer
How do antibodies access tumour cells?
- Tumour tissue has disorganised vasculature which is structurally weak
- Smooth muscle cells are reduced
- Links between endothelial cells are weakened
- -> makes blood vessels leaky (large molecules have access to malignant tissue)
- Tumour tissue generally does not have a lymphatic drainage system
- macromolecules are retained and can accumulate in solid tumours
Describe the nomenclature of mAbs.
*last syllable is always -mab
Next to last syllable:
- -u- = human (100%)
- -zu- = humanised (95%)
- -xi- = chimeric (65%)
- -o- = mouse; -a- = rat; -e- = hamster; -i- = primate
Previous syllable:
- -tu(m)- = for tumour in general
- -ma(r)- = breast; -pro- = prostate; -co(l)- = colon
- -ci(r)- = circulatory
Give examples of mAbs which target the following growth factor receptors:
- EGFR
- HER2 (ErB2)
- HER2/HER3
- VEGFR
- cetuximab and panitumumab
- trastuzumab
- pertuzumab
- bevacizumab
How do monoclonal antibodies work?
- Killing tumour directly:
- inhibit ligand binding
- signalling blocked
- apoptosis induced
- possible delivery of cytotoxic payload - Killing tumour cells via an immune-mediated mechanism:
- induction of phagocytosis
- complement dependent cytotoxicity (CDC)
- antibody dependent cell cytotoxicity (ADCC) - Vascular or stromal ablation
- VEGF antagonism
- Inhibit formation of new blood vessels
What % of women with HER2 +ve breast cancer will respond to Trastuzumab?
~20%
What is the recommended therapy for HER2 +ve metastatic or locally recurrent unresectable breast cancer?
Pertuzumab in combination with trastuzumab and docetaxel
What is the MOA of Trastuzumab?
- binds to domain IV on HER2
- suppresses ligand-dependent HER2 signalling
- prevents HER2 extracellular domain shedding
- identifies cells for antibody-dependent cell mediated cytotoxicity
What is the MOA of Pertuzumab?
- binds to domain II on HER2
- inhibits homo- and heterodimerisation
- suppresses ligand dependent HER2 signalling
- identifies cells for antibody-dependent cell mediated cytotoxicity
Why might women with HER2 +ve breast cancer be resistant to Trastuzumab treatment?
HER2 is ligand dependent and doesn’t need a growth factor in order to be activated
What is VEGF and what is its role?
Vascular Endothelial Growth Factor
- required for formation of new blood vessels
- one of the most unregulated antigens in cancer
- protects endothelial cells from death via activation of PKC pathway and up regulation of anti-apoptotic proteins such as Bcl-2
- activity is mediated by tyrosine kinase receptors (VEGFR1 and VEGFR2)
What drug can inhibit VEGF signalling?
Bevacizumab (Avastin) Inhibiting VEGF signalling: 1. block receptor binding 2. inhibit tumour growth and metastasis 3. deprive tumours of nutrient-providing blood vessels
How does trastuzumab emptansine (Kadcyla) work?
- drug gets into lysosome (receptor-mediated internalisation into cells)
- there is cleavage
- high concentration of an anti-mitotic drug inside cells
(anti-microtubule DNA - no new DNA formation - no tumour growth) - DM-1 catabolite binds to tubulin to cause mitotic arrest and cell death
What is the MOA of Tarceva (Erlotinib)?
Statically inhibits ATP binding by targeting the ATP binding site
- terminal phosphate is unable to phosphorylate tyrosine
What type of cancer is Tarceva/Erlotinib used for and what growth factor does it target?
Advanced stage NSCLC
Targets EGFR
What do small molecule tyrosine kinase inhibitors target?
target oncogene products such as:
- Bcr-Abl (chronic myeloid leukaemia)
- EGFR (NSCLC)
Describe the nomenclature of small molecule tyrosine kinase inhibitors.
- ib = inhibitory
- tinib = tyrosine kinase inhibitors
What is an activation loop?
Exon where ATP binds
Which mutations (and in which axons) are associated with drug resistance to erlotinib?
Exon 19: D761IY (>1%)
Exon 20: T790M (50%)
How many generations of EGFR tyrosine kinase inhibitors are there? Give examples for each.
1st generation (reversible)
- erlotinib
- gefitinib
2nd generation (irreversible) - afatinib
3rd generation (mutant-selective) - osimertinib
