7th Dec - Novel Drugs II Flashcards
Why were kinases originally believed to be bad drug targets?
Inhibitors generally compete with ATP (ATP is present at high concentrations in the cell)
Structurally similar active sites
Kinases are key in cellular function therefore inhibitors must be specific
Outline the course of CML
- Chronic Phase (5-6 years stabilisation)
- Excess myeloid cells that differentiate normally - Advanced Phase
- accumulation of molecular abnormalities, loss of capacity for terminal differentiation
- accelerated phase (6-9 months)
- blast crisis (3-6 months)
What is the philadelphia chromosome?
Common chromosomal translocation present in chronic phase CML patients
Truncation of 22 transferred to chromosome 9
Creates a chimeric protein of BCR-abl
When was the philadelphia chromosome discovered?
1973
What percentage of patients with CML carry the BCR-ABL protein?
95%
What does the BCR-ABL protein do?
It is a constitutively active tyrosine kinase, activating cell cycle enzymes and proteins speeding up mitosis and inhibiting DNA repair leading to genomic instability
Why is the BCR-ABL protein constitutively active?
The normal BCR protein couples with the Myr protein which acts as a latch keeping it in an inactive conformation. In BCR-ABL this latch doesn’t exist –> constitutive activation
What were the therapeutic options for CML before Gleevec?
Allogeneic stem cell transplantation
Interferon-alpha - slows down growth of malignant clones
Chemotherapy - targets all cell division
What was the cure rate of CML before Gleevec?
<20%
How does Gleevec work?
It binds to inactive BCR-ABL through H-bonding to T315 to block ATP binding
REMEMBER EVEN CONSTITUTIVELY ACTIVE PROTEINS ARE DYNAMIC THUS CONSTANTLY SWITCHING STATES
When was Gleevec approved?
2001
What were the results of the first clinical trials on gleevec?
98% of patients had massive reductions in white cells with minor side effects
Changes were rapid <1 week
What are the disadvantages of Gleevec?
It does not eliminate the BCR-ABL protein therefore must be treated long term
Less effective in blast phase and in Phildelphia chromosome positive acute lymphoblastic leukaemia
Some patients are resistant to gleevec
Why are some patients resistant to Gleevec?
Possibly due to Gleevec resistant BCR-ABL mutations which block Gleevec binding or generation of the inactive form
E.g. gatekeeper mutation t315 –> Ile
What is an alternative treatment for CML for gleevec resistant patients?
Pronatib-multikinase inhibitor which targets aurora kinase
What are the molecular targets of Gleevec other than BCR-ABL?
PDGF-R
c-Kit
What would be the clinical applications for targeting PDGF-R?
There is a constitutively active fusion protein (Tel-PDGF-R) in some leukaemias particularly glioblastomas
Autocrine loop involving PDGF in glioblastoma
What would be the clinical applications for targeting c-Kit?
It is an RTK for stem cell factor
Activating mutations for c-Kit are associated with a number of tumour types including gastrointestinal stromal tumours (GIST)
Could siRNA be used to treat CML?
Anti-bcr abl siRNA reduces bcr-abl mRNA in primary cells from CML patients and reduces BCR-ABL protein levels.
Induces apoptosis in K562 cell lines
What is muromonab?
An anti-cd3 drug used to prevent immune suppression in organ transplants and grafts
Give an example of an antibody targeted against a GPCR
HIV-1 gp120 interacts with CD4 causing a conformational change so it can now interact with the CCR5 causing receptor internalisation, thus CCR5 internalisation drags HIV into the cell.
Now there is an antibody which is targeted to CCR5 blocking the binding site preventing the entry of HIV into the cell, however unfortunately HIV is quite adaptive and can use other receptors to enter the cell
What is gene therapy?
The replacement of defective or missing genes to allow proteins with normal function
When was the first gene therapy trial and what for?
1990
A boy was given adenosine deaminase gene through a virus to treat ADA-SCID which led to temporary success however they developed leukaemia later
What is the first approved gene therapy?
Glybera for lipoprotein lipase defiency
