5th Dec - Novel Drugs, Novel Uses for drugs and novel drug targets Flashcards
Why do we need novel drugs?
Most drugs don’t work in all patients
We need to enhance the specificity to reduce side effects
We need to enhance efficacy
There are still many untreatable diseases
What is pharmacological efficacy?
The ability of a ligand to evoke a response
What is clinical efficacy?
The ability of a drug to treat the disease
What percentage of current drug targets are enzymes?
41%
What percentage of current drug targets are GPCRs?
30%
What is the globally top selling drug and what does it target?
Adalimumab which is an antibody that binds TNFalpha treating rheumatoid arthritis
Roughly how many GPCRs are present in humans?
800
What are the clues to an orphan GPCRs ligand?
Tissue distribution
Structure
Screen with specific ligands
How is a GPCR deorphanised?
Using reverse pharmacology
- In silico GPCR identification
- Tissue Expression pattern and family tree analysis
- Expression in surrogate cell type
- Screen with synthetic ligand bank or biological extracts
- Cellular Assay
- Identify positive compounds
What is a ligand bank?
A bank of between 1-2 million synthetic compounds used by big Pharma to manipulate the receptor
What are possible sources of putative ligands for screening?
Tissue Extracts
Human haemofiltrate
Known and predicted ligand libraries
Synthetic ligands
Outline the general process of drug development
- Target identification via bioinformatics/expression profiling and validation by KO and OE to alter the cause of the disease
- Assay generation
- Lead finding
- Lead optimisation
- Development
5i. Non-clinical safety tests
5ii. Phase 1
5iii. Phase 2
5iv. Phase 3
5v. Phase 4
What is the approximate duration for drug development?
6-12 years
What is the probability of success of drug development?
<0.01%
What are the different assay systems used to screen drugs?
Monitoring coupling by [Ca2+i] response
cAMP assay
Assays of compound receptor interaction
Binding assays
Outline how calcium can be used to monitor coupling
Use Gq receptors, promiscuous G proteins or chimeric g proteins to elicit a calcium response. Then monitor the calcium response.
This can be done in a high throughput screen by using the fluorimetric imaging plate reader (FLIPR). Which can screen about 1536 compounds in seconds. Normally use a control which doesn’t express the receptor of interest which should show no response
How can a cAMP assay be used to find a successful ligand?
Both Gas and Gai directly affect cAMP levels.
In this process the G protein is fused to the receptor to make it more efficient at inhibiting/stimulating cAMP
cAMP levels are then monitored using Homogeneous time resolved fluorescence (HTRF) which uses FRET.
Anti-cAMP antibody has fluorophore which should cause cAMP’s fluorophore to fluoresce when bound to cAMP.
Then when new cAMP is produced, which is not labelled, it will displace the labelled cAMP –> loss of FRET as cAMP accumulates
How can you use beta arrestin to detect active receptors?
Fuse a small fragment of beta galactosidase to the GPCR tail. The larger fragment of beta galactosidase is fused to beta arrestin.
When the GPCR is activated and phosphorylated beta arrestin will bind.
Beta galactosidase is now active –> chemiluminescent signal
What is the advantage of the beta-galactosidase assay for receptor activation?
You do not need to know what the receptor couples to downstream
What are the advantages for binding assays in drug screening?
It doesn’t matter if the ligand is an agonist or antagonist
Independent of efficacy
Can detect allosteric modulators
Give an example of a drug which is a partial agonist, and because of this is beneficial
Buperomorphine is a partial agonist of the mu opiod receptor. It is used to treat heroine addiction as it out-competes heroine thus heroine will not have an effect but it does not elicit the response that heroine does
What would be the benefit of using a biased ligand at the mu opiod receptor to target the G-protein pathway and not the Beta arrestin pathway?
Would increase analgesic efficacy
Reduce GI dysfunction
Reduce respiratory suppression
What is TRV130?
A novel MOR G-protein biased ligand which has robust g protein signalling with similar efficacy to morphine but has far less beta arrestin recruitment
How was TRV130, the mu opiod receptor g protein biased ligand, discovered?
Analgesia studies in mice
Used human embryonic kidney cells to OE b-arrestin 2 and then performed the path hunter assay
Measured cAMP changes using HTRF
Internalisation assay
What is chronic heart failure?
When heart output does not match demands
What diseases attribute to chronic heart failure?
Coronary artery disease
hypertension
idiopathic dilated cardiomyopathy
alcoholic cardiomyopathy
What are the symptoms of chronic heart failure?
Fatigue Dyspnoea (breathlessness) Raised jugular venous pressure Pulmonary and peripheral oedema Left ventricular sytosolic dysfunction
What are the current treatments for chronic heart failure?
Diuretics - remove oedema
ACE inhibitors - cause vasodialtion
Beta blockers
Why could beta blockers used in the treatment of chronic heart failure?
Contrary to the hypothesis, in 1975 it was discovered that beta blockers actually reduced mortality in chronic heart failure as they have a protective effect when started on a low dose which slowly increases.
What is the mechanism behind beta blockers effect on chronic heart failure?
- Beta blocker e.g. carvedilol binds to beta adrenoceptor
- Increased sympathetic drive normally reduces the number of beta adrenoceptors in chronic heart failure, beta blockers counteract this by acting as inverse agonists
OR
- Ligand is biased i.e. certain beta blockers direct signalling down certain pathways. Believed that carevedilol can stimulate beta arrestin signalling whilst maintaining inverse efficacy for g protein pathway
