L8 - Therapeutic Strategies that target txn Flashcards
(30 cards)
What is a potential therapeutic for MYC but what is the problem?
siRNA or shRNA to deplete target
Hampered by problems of delivery and cellular uptake
What are small molecule drugs?
Small (400Da) cell permeable molecules
Structure must be well known
What are the targets of small molecule drugs but what is the problem with this?
Have small hydrophobic involutions involved in protein interactions
Problem - interactions between TFs often large flat and featureless
What do nutlins do?
Occupy p-53 binding pocket of MDM2 and prevent inactivation of p53
How have clinical trials for nutlins gone?
- Increased p53 and p21 confirming it reached its target
- All patients suffered haematological toxicity
What are stapled peptides>
Have a hydrocarbon crosslink conferring protease resistance and better stability
What is an example of a stapled peptide and how effective is it?
SAH-p53-8 (mimics p53 acitivation domain)
Suppress growth of MDMX driven tumour xenografts in mice
How do stapled peptides get into cells?
Too big to diffuse so requires pinocytosis
What is CX-5461
Cell permeable small molecule that selectively inhibits rRNA synthesis by pol1
What changes contribute to elevated rRNA txn by pol1 in cancers?
- RB binds UBF and prevents from recruiting SL1 and CBP (lost when RB inactivated)
- SL1 bound and repressed by p53 (p53 inactivated in cancers)
- Erk hyperactivated in cancers to phosphorylate and activate TIF-IA
- Increased MYC increases pol1 stimulation
How does CX-5461 work?
Inhibits pol1 txn complex assemply (blocks binding of SL1)
Sensitivity varies wildly between cell lines
How does CX-5461 induce p53?
- inhibits rRNA synth so lots of free ribosomal proteins
- MDM2 can be bound and inhibited by free ribosomal proteins (eg RPL11), releasing p53 from degradation
What happened to lymphoma cells treated with CX-5461?
Cells with WT p53 died at much lower doses
Suppressed growth of lymphomas in mice
Why is CV-5461 tolerated in mice when it should kill all cells (lack of rRNA)?
Normal mouse tissues make far more rRNA than necessary so that suppression does not trigger stress response or activae p53
What are HATs again? and what are they for?
histone acetyltransferases
recruitment is key mechanism of txn activation by p53 and acetylation stabilises p53 by inhibiting binding to MDM2
What do HDACIs do?
Inhibit HDACs to raise acetylation levels
How do HDACIs work?
Occupy HDAC active site blocking substrate with hydrozamic acid group chelating a catalytic Zn2+ - aliphatic linker joins with a capping group
Why is it unclear why HDACIs work?
Although HDAC inhibition promotes expression of p53 and targets,
MYC also recruits HATs and RB rcruits HDACs so HDACIs would be predicated to enhance MYC function and inhibit RB function
What is AML?
Acute myleloid leukaemia - disorder characterised by clonal expansion and accum of immature haematopoietic precursors
What is RAR?
Retinoic acid receptor
What is retinoic acid important for?
Activate metabolite of vit A
Important for cell differentiaition, embryonic development and adult haematopoiesis
Deficiency causes anemia
What is APL and what is characterised by?
Acute promyelocytic leukaemia
Chromsomal translocations that fuse RARa gene to PML gene
What are the internal symptoms of APL?
RXR/PML-RARa heterodimer binds many DNA sites - recruits HDACs and represses txn
How is arsenic used to treat APL?
Arsenic trioxide binds arsenic to PML/RARa and this attracts SUMO ligase Ubc9 which sumoylates and then ubiquitinated by RNF4 and degraded
