Lecture 18 - Rational Treatment of Cancer 2

Question 1

Why is it difficult to target tumour suppressor genes?

Answer 1

• Most drugs aim to inhibit by targeting active site of an enzyme
• Because tumour suppressors are MISSING in tumours It is DIFFICULT to enhance function

Question 2

Phenotype associated with tumour suppressor genes ??

Answer 2

Loss of heterozygosity

Question 3

Example drug used to manipulate P53 levels

Answer 3

Prima 1- reactivates mutant P53 by covalent binding to the core domain – induces a shape change so P53 modified to resemble WT
Promoting Pro-apoptotic signalling
- Restore by reconfiguring the shape of P53
- GOF drugs

Question 4

P53

Answer 4

Promotes pro apoptotic signalling

Question 5

FACS analysis

Answer 5

shows that when you treat cells expressing P53 with a glutamine mutation at position 248 cells dont apoptose
recognised by sug G1 populations in a FACs profile
in presence of Prima 1 apoptosis restored pro apoptotic signalling through using GOF small molecules

Question 6

What keeps P53 low ?

Answer 6

MDM2 protein ubiquitin ligase attaches ubiquitin to P53 and promotes its destruction – Keeps P53 levels low
MDM2 binds directly to P53
- possible to interfere with MDM2

Question 7

Nutlin 2

Answer 7

binds to MDM2 preventing binding of P53 results in stabilisation and accumulation of P53 and promotes apoptosis
-Not an enzyme inhibitor but inhibits the interaction between two proteins

Question 8

peptidominetic drugs

Answer 8

Design compounds that resembles aspects of the protein protein interaction site that is the functionally relevant thing in vivo and disrupt it

Question 9

CDKs

Answer 9

are important tumour suppressor

Question 10

What is required for Sphase genes ?

Answer 10

RB bind E2F TF which is essential for making S phase genes

Question 11

What prevents going into S-phase??

Answer 11

Produce high levels of P21 prevents s phase – intereferes with phosphorylation and inactivation of RB

Question 12

RAMU et al

Answer 12

Blocking proliferation of ovarian cancer cells
Usually use platinum based drugs but cancers get resistant quickly
Increasing expression levels of P27 in a conc dependent manner
Subsequent inhibition of Rb phosphorylation
Restoration of the Restriction Point

Question 13

Druggability!

Answer 13

A defined structure that specifically binds
an appropriate low molecular weight chemical entity
Usually a cavity that
• vulnerable to low mw compound
• Inhibition of function of the cavity
• Preferably disrupts catalytic activity ( which often involves
catalytic clefts)
• Provides lots of points of contact for drug
(more contact points = more potency and more specificity- lower conc of a drug to get the effect you want

Question 14

How do you increase the impact of a drug ?

Answer 14

More of an impact if using catalyst- amplifier

Question 15

Druggable

Answer 15

Druggable 
Lots of oncogenes- protein kinases 
Kinase oncogenes
e.g. v-EGF-R,Abl
Abl protein kinase
Gleevec- success

Question 16

Undruggable

Answer 16

Transcription factor oncogenes
e.g. myc and fos 
(only DNA binding cleft)
Myc over expressed in a lot of cancers
Need to increase specificity- get sequence specificity

Question 17

Positives of Kinases as cancer drug targets

Answer 17

Many kinases are oncogenes
518 kinases in the genome
Very druggable due to ATP binding cleft

Question 18

Negatives of kinases as cancer drug targets

Answer 18

most same as the positives

• Most kinases have a evolved from a common ancestor so binding sites all very similar
  e. g Similarity of a.a showed the EGFR was a kinase

Question 19

Rational strategies – inhibitors of protein kinases

Answer 19

• Discourage proliferative signalling

- Exploit checkpoint vulnerability

Question 20

Protein Kinases

Answer 20

Protein kinases originate from one phylogenic tree/ family
- can get specificity but very difficult
-High degree of specificity if you look carefully at residues around target site in the kinase – selectivity is key
In principle, CAREFUL examination of the ATP binding cleft
SHOULD allow “rational drug design”

Question 21

Erlotinib

Answer 21

Erlotinib (drug) specific to EGF-R > Success

Question 22

Measure PK activity of target

Answer 22

> Use a compound library for hits that inhibit kinase (SCREEN) > improve basic structure
Followed with rational drug design- increase specificity and potency

Question 23

Checkpoint kinase Inhibitor

Answer 23

Hit2
selective to the checkpoint kinase ChK among the others found by HTs
- synthesis of derivatives made to fill the ‘sugar pocket
- tweaking around this protein to increase potency

Question 24

Why target EGF-R?

Answer 24

• Overexpressed in large number of Carcinomas

- Oncogenic

Question 25

Targeting EGF-R

Answer 25

Using Humanised Monoclonal antibody treatment
Alter codons so more consistent with human antibodies than mice
Problems of resistance

-Cetuximab

Question 26

What forms of EGF-R mutation are Antibody based drugs unable to work on ??

Answer 26

Ligand - independent firing in the EGF-R mutant

Question 27

oncogenes

Answer 27

Might work but triggering signalling pathways in the absence of appropriate extracellular cues

Question 28

Targeted therapy

Answer 28

Need to know specific oncogenic mutation

Question 29

Ovarian cancer

Answer 29

Ovarian cancer derivates resistance to treatment – significant complexity 20 different ways tumours resistance in one sub group
Complex

Question 30

To distinguish who is going to benefit

Answer 30

to test hypothesis you need to do a clinical trial with every sub population to identify who is going to benefit from the treatment
- statistical power gets harder to prove as each subset population gets smaller and smaller

Question 31

Gleevec

Answer 31

• very affective drug
• conc dependent inhibition of ABL
  -One of 13 mutations that yields a resistant
  form of BCR-ABL that is catalytically active
  BCR- ABL fusion > oncogenic

Question 32

What is the issue with tumours rapidly evolving ?

Answer 32

Specific treatment - Natural selection pressure for evolution for something that is resistant
Need not only first but also second generation inhibitors that predict further mutations
- but also predictable- need to be one step ahead of evolution

Question 33

Rationale

Answer 33

Might want to switch between approaches or incorporate different treatments
May not be able to cure cancer but enable them to live to a ripe old age with cancer