Drug Mechanism of action one Flashcards
Describe the structure of ligand gated ion channel receptors
Oligomeric assembly of subunits around a pore
Describe the strucure of GPCR
Monomeric structure of seven transmembrane domains
Describe the structure of tryosine kinase receptors
Single transmembrane helix with extracellular receptors and intergrated intracellular kinase (enzyme) domain
Describe the structure of nuclear receptor
Monomeric structure with seperate receptor and DNA binding domains
Describe the tyrosine kinase receptor
Extracellular receptor linked with an intracellular kinase domain (enzyme)
How do tyrosine kinase receptors work?
Ligand binds, Protein undergoes conformational change and autophosphorylates itself. The the intracellular kinase enzyme phosphorylate the tyrosine residues of intracellular target proteins
What ligands bind to tyrosine kinase receptors?
Cytokines, Growth hormones, Certain hormones
What is the example of tyrosine kinase receptor we look at?
Vascular Endothelial Growth Factor Receptors
What is the function of Vascular Endothelial Growth Factor Receptors?
Essential for angiogenesis during development, pregnancy (placenta), wound healing
When else is Vascular Endothelial Growth Factor Receptors important?
During pathophysiological conditions such as rheumatoid athritis and cancer, CV disease.
What is the specific Vascular Endothelial Growth Factor Receptors we look at?
VEGFR2
Though most tyrosine kinase receptors are monomeric structures in the case of VEGFR2 what has occured?
Dimerisation (two units together)
Describe the process that occurs when the ligand binds to VEGFR2
Ligand binds
Conformational change
Autophosphorylation of tyrosine residues and cytoplasmic domain.
This in turn can now phosphorylate (usually phosphorylation cascades) many target proteins mediating many biological processes such as:
Endothelial cell survivial Endothelial cell proliferation Endothelial cell migration NO and PGI2 production Increased vascular permeability
What are the resultant biological outcomes of VEGFR2 activation?
Endothelial cell survivial Endothelial cell proliferation Endothelial cell migration NO and PGI2 production Increased vascular permeability
With VEGFR2 describe the exact cascade that results in increased gene transcription
Receptor activation leads to autophosphorylation, then, phosphorylation of:
Phospholipase C Y (gamma)
Which hydrolyses PIP2 to DAG and IP3
DAG activates PKC (phosphorylates)
PKC (phosphorylates) Raf which Phosphorylates MEK which phosphorylates ERK
ERK activation leads to increased gene transcription
What drugs could target VEGF pathways?
Angiogensis inhibitors used in Cancer (watching for CV effects)
and
Angiogenesis stimulators used in Wound healing, Placental development etc.
Is the tyrosine kinase receptor pathway fast or slow?
Slow, it doesnt need to be fast as cell proliferation does not need to be isntantaneous
What sort of interactions does a ligand have with a receptor?
Van der waals
Hydrogen bonds
Ionic bonds
Covalent bonds
List the types of bonds ligands have with receptors from strongest to weakest
Van der waals (weakest)
Hydrogen bonds
Ionic bonds
Covalent bonds (essentially irreversible)
What is the affinity constant?
The affinity constant (Kd) is defined as the concentratioon of ligand present when the fractional occupany of receptors is 50%
What is affinity?
The affinity is the attraction a drug/molecule has for a specific receptor
Whats the relationship between Kd, Affinity and Fractional Occupany (FO)
The higher the affinity of a drug is the lower the concentration is for a given level of fractional occupany. This also means lower Kd value for a drug. I.e Less drug more binding.
What is the difference between affinity and biological response?
Affinity measures the concentration of a drug at a given receptor occupany.
Biological response measures concentration of a drug to produce a given response.
Why is a concentration response curve not reliable?
It is not strictly proportional,
- Considerable amplification may occur i.e low level of receptor occupany may cause full biological response
- Many factors downstream of receptor binding may interact to produce the final response
What can be determined from a concentration response curve?
EC50 (The 50% effective concentration fo a drug)
Emax (max effective concentration)
What is potency?
The EC50 of a agonist
Concentration that produces 50% of the maximal response
What is the relationship of potency and EC50?
The more potent a drug the lower the EC50
Does the EC50 describe the antagonist potency?
NO this is more complicated - however similar principles hold
What is the difference between Potency and Affinity?
Affinity is the measure of FO for a drug at a given concentration. Higher affinity means lower concentration of drug produces higher FO.
Potency is a measure of the drugs EC50. How much drug is required to produce 50% maximal effect.
Affinity doesnt = potency.
A drug may have high affinity but produce low biological response for that tissue. Or it may be very potent but have low affinity.
What is Efficacy?
The Ability of a drug to bind to a receptor and induce change in the receptors action. Measured by Emax.
Are receptors in a Off/on state?
No, some receptors have a basal level.
What is the result of having receptors at a basal level?
We have reverse agonists designed to turn off this basal level of activity
In relation to efficacy what are the three categories of drugs?
Agonist - positive efficacy, increases cellular response
Inverse agonist - negative efficacy, turns off cellular response.
Antagonist - Blocks receptors, keepings its basal cellular response.
What is an example in which an inverse agonist would be used?
Precocious puberty: The thyroid receptors are activated at a basal level with no ligand present at all, however we do not want their basal rate, so we use a inverse agonist to block them
Does an agonist produce the full response?
No, we grade agonism based on what we have observed today as the full response (moving target)
A partial agonist cannot induce full response even at maximal receptor occupancy. Only a full agonist can do so.
What is a partial agonist?
A drug that cannot induce full biological response even at full receptor occupancy
If you LOG the x axis of a concentration, FO/Response hyperbole the resulting graph is
Sigmoidal
What is the maximal effect of a drug determined by?
Efficacy and tissue properties
If the maximal effect of a drug is determined by tissue properties, what does this imply?
Drugs have different maximal response in different tissues
In terms of Affinity, Efficacy etc, how would an antagonist be described as?
They have affinity, but no efficacy. As it does not change the action of the receptor/ cellular response
How are antagonists defined?
How they bind to receptors
What are the categories of antagonism binding?
Reversible Competitive Antagonism
Irreversible Antagonism
What is reversible competitive antagonism?
Bind to the receptor in a reversible manner to compete directly with agonist binding.
What can be observed on a response concentration graph for agonist and reversible competitive antagonist binding?
As the concentration of reversible competitive antagonist increases, the concentration of agonist must increase to produce a full response.
I.e a maximal biological response can occur in the presence or reversible competitive antagonism providing the concentration of agonist is sufficient. It can out compete the antagonist.
How does a irreversible antagonist bind to a receptor?
Covalent bonding. New receptors must be formed to re-establish the previous level of function
On a concentration response curve for an agonist, in the presence of irreversible antagonist, what occurs?
The maximal response of the agonist is diminished.
However this tends only to occur at high levels of irreversible antagonist because of potency - how a little bit of drug can produce a large response, there is no need for full receptor occupancy.
Describe the equilibrium shift between receptors on and off in the presence of different drug efficacy..
No ligand = equilibrium favors receptors off
Full agonist = equilibrium strongly shifts to receptors on
Partial agonist = slight equilibrium to receptors on
Antagonist = no shift in equilibrium
Inverse agonist = shift in equilibrium to receptors off
Describe the difference between Affinity, Potency and Efficacy:
Affinity is a measure of a drugs FO at a given concentration
Potency is the EC50 of a drug. How much drug it takes to produce 50% of known maximal response
Efficacy is the ability of a drug to bind to a receptor and change its action. E max.
