Lecture 18 - Rational Treatment of Cancer 2 Flashcards
Why is it difficult to target tumour suppressor genes?
- 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
Phenotype associated with tumour suppressor genes ??
Loss of heterozygosity
Example drug used to manipulate P53 levels
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
P53
Promotes pro apoptotic signalling
FACS analysis
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
What keeps P53 low ?
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
Nutlin 2
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
peptidominetic drugs
Design compounds that resembles aspects of the protein protein interaction site that is the functionally relevant thing in vivo and disrupt it
CDKs
are important tumour suppressor
What is required for Sphase genes ?
RB bind E2F TF which is essential for making S phase genes
What prevents going into S-phase??
Produce high levels of P21 prevents s phase – intereferes with phosphorylation and inactivation of RB
RAMU et al
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
Druggability!
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
How do you increase the impact of a drug ?
More of an impact if using catalyst- amplifier
Druggable
Druggable Lots of oncogenes- protein kinases Kinase oncogenes e.g. v-EGF-R,Abl Abl protein kinase Gleevec- success
Undruggable
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
Positives of Kinases as cancer drug targets
Many kinases are oncogenes
518 kinases in the genome
Very druggable due to ATP binding cleft
Negatives of kinases as cancer drug targets
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
Rational strategies – inhibitors of protein kinases
- Discourage proliferative signalling
- Exploit checkpoint vulnerability
Protein Kinases
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”
Erlotinib
Erlotinib (drug) specific to EGF-R > Success
Measure PK activity of target
> Use a compound library for hits that inhibit kinase (SCREEN) > improve basic structure
Followed with rational drug design- increase specificity and potency
Checkpoint kinase Inhibitor
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
Why target EGF-R?
- Overexpressed in large number of Carcinomas
- Oncogenic
Targeting EGF-R
Using Humanised Monoclonal antibody treatment
Alter codons so more consistent with human antibodies than mice
Problems of resistance
-Cetuximab
What forms of EGF-R mutation are Antibody based drugs unable to work on ??
Ligand - independent firing in the EGF-R mutant
oncogenes
Might work but triggering signalling pathways in the absence of appropriate extracellular cues
Targeted therapy
Need to know specific oncogenic mutation
Ovarian cancer
Ovarian cancer derivates resistance to treatment – significant complexity 20 different ways tumours resistance in one sub group
Complex
To distinguish who is going to benefit
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
Gleevec
- 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
What is the issue with tumours rapidly evolving ?
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
Rationale
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
