7th Dec - Novel Drugs II

Question 1

Why were kinases originally believed to be bad drug targets?

Answer 1

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

Question 2

Outline the course of CML

Answer 2

1. Chronic Phase (5-6 years stabilisation)
   - Excess myeloid cells that differentiate normally
2. Advanced Phase
   - accumulation of molecular abnormalities, loss of capacity for terminal differentiation
   - accelerated phase (6-9 months)
   - blast crisis (3-6 months)

Question 3

What is the philadelphia chromosome?

Answer 3

Common chromosomal translocation present in chronic phase CML patients
Truncation of 22 transferred to chromosome 9
Creates a chimeric protein of BCR-abl

Question 4

When was the philadelphia chromosome discovered?

Answer 4

1973

Question 5

What percentage of patients with CML carry the BCR-ABL protein?

Answer 5

95%

Question 6

What does the BCR-ABL protein do?

Answer 6

It is a constitutively active tyrosine kinase, activating cell cycle enzymes and proteins speeding up mitosis and inhibiting DNA repair leading to genomic instability

Question 7

Why is the BCR-ABL protein constitutively active?

Answer 7

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

Question 8

What were the therapeutic options for CML before Gleevec?

Answer 8

Allogeneic stem cell transplantation
Interferon-alpha - slows down growth of malignant clones
Chemotherapy - targets all cell division

Question 9

What was the cure rate of CML before Gleevec?

Answer 9

<20%

Question 10

How does Gleevec work?

Answer 10

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

Question 11

When was Gleevec approved?

Answer 11

2001

Question 12

What were the results of the first clinical trials on gleevec?

Answer 12

98% of patients had massive reductions in white cells with minor side effects
Changes were rapid <1 week

Question 13

What are the disadvantages of Gleevec?

Answer 13

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

Question 14

Why are some patients resistant to Gleevec?

Answer 14

Possibly due to Gleevec resistant BCR-ABL mutations which block Gleevec binding or generation of the inactive form

E.g. gatekeeper mutation t315 –> Ile

Question 15

What is an alternative treatment for CML for gleevec resistant patients?

Answer 15

Pronatib-multikinase inhibitor which targets aurora kinase

Question 16

What are the molecular targets of Gleevec other than BCR-ABL?

Answer 16

PDGF-R

c-Kit

Question 17

What would be the clinical applications for targeting PDGF-R?

Answer 17

There is a constitutively active fusion protein (Tel-PDGF-R) in some leukaemias particularly glioblastomas
Autocrine loop involving PDGF in glioblastoma

Question 18

What would be the clinical applications for targeting c-Kit?

Answer 18

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)

Question 19

Could siRNA be used to treat CML?

Answer 19

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

Question 20

What is muromonab?

Answer 20

An anti-cd3 drug used to prevent immune suppression in organ transplants and grafts

Question 21

Give an example of an antibody targeted against a GPCR

Answer 21

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

Question 22

What is gene therapy?

Answer 22

The replacement of defective or missing genes to allow proteins with normal function

Question 23

When was the first gene therapy trial and what for?

Answer 23

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

Question 24

What is the first approved gene therapy?

Answer 24

Glybera for lipoprotein lipase defiency