1.3 Drug Targets

Question 1

What are the five targets for drug actions?

Answer 1

Receptors (Types 1-4)
Ion Channels
Enzymes
Transporters
Exceptions

Question 2

What are the four types of receptors?

Answer 2

Ligand gated ion channels (Type 1)
G-protein coupled receptors (Type 2)
Kinase linked receptors (Type 3)
Nuclear Receptors (Type 4)

Question 3

Describe Nuclear Receptors (Type 4)

Answer 3

An intracellular receptor. May be initially present in cytosol, then migrates to nucleus to have effect
Membrane permeable agonist.
Act by regulating gene expression
Delayed effect as it alters protein production
Long lasting effect due to low turnover of enzymes/proteins

Question 4

Give an example of a drug that acts at Nuclear Receptors (Type 4)

Answer 4

Prednisolone

Question 5

What is Prednisolone?

Answer 5

Inhibits cytokine gene expression
Used in Asthma
Acts at Kinase-Linked Receptor

Question 6

Describe Kinase-Linked Receptors (Type 3)

Answer 6

Transmembrane receptor that binds and activates a tyrosine kinase protein

Question 7

Give an example of a drug that acts at Kinase-Linked Receptors

Answer 7

Trastuzamab (Herceptin)

Question 8

What is Herceptin?

Answer 8

Monoclonal antibody against HER2. HER2 (human epidermal growth factor receptor) is over expressed in 25% of cancers. Binds to and prevents dimerisation of HER2 or agonist binding. Acts at Kinase-Linked Receptor

Question 9

Describe Ligand-Gated Ion Channels (Type 1)

Answer 9

Membrane bound ion channel whose ligand can either induce it to open or close. Very quick action.

Question 10

Give an example of a drug that acts at Ligand-Gated Ion Channels

Answer 10

Succinycholine
Pancuronium
Benzodiazepines

Question 11

What is Succinylcholine?

Answer 11

Nicotinic acetylcholine receptor agonist. Same mechanism of action as ACh. Keeps channel in open state –> desensitising it and preventing it from undergoing a new phase of contraction –> muscle relaxation.

Question 12

What is Pancuronium?

Answer 12

Nicotinic acetylcholine receptor antagonist. Binds to and prevents channel opening. Inhibits contraction –> muscle relaxant.

Question 13

What are Benzodiazepines?

Answer 13

Bind to modulatory site on GABAa receptor. Increased effect of GABA. Increased Cl permeability
Sedation and Anxiolytic

Question 14

Describe G-Protein coupled receptors (Type 2)

Answer 14

Transmembrane receptor. Stimulates G-protein binding which in turn modulates an intracellular second messenger.
Seven transmembrane helix
Responds quickly.
Can modulate enzyme or ion channel function.

Question 15

Give an example of a drug that acts at G-protein coupled receptors

Answer 15

Metaproterenol

Cetirizine

Question 16

What is Metaproterenol?

Answer 16

Beta2 adrenoceptor agonist. Bronchodilation. Obstructive airway disease, acute bronchospasm.

Question 17

Why is receptor selectivity important?

Answer 17

Limits side effects. Agonists of both beta1 and beta2 receptors will causes tachycardia and bronchodilation.