W22 Pharmacology- Drug targets

Question 1

What is the General structure/features of catalytic receptors?

Answer 1

Made of protein
N terminal and C terminal

extracellular- binding site (ligand binding)
Dimerisation leads to…
autophosphorylation (Intracellular)… leads to activation of multiple downstream signalling (intracellular)

They undergo dimerization and autophosphorylation upon ligand binding

Question 2

What are Receptor Tyrosine Kinases?
Examples? (6)

Answer 2

High-affinity cell-surface receptors for growth factors (polypeptide), cytokines and hormones

Epidermal growth factor- EGF
Vascular endothelial growth factor-VEGF
Insulin
Neurotrophins
Insulin-like growth factor- IGF
Platelet-derived growth factor- PDGF & many others

Question 3

What does activation of RTK’s lead to?
What does hyperactivation of RTK’s lead to?

Answer 3

Activation leads to cell proliferation, differentiation, survival and metabolism

Hyperactivation leads to polyps, tumour and cancer

Question 4

Receptor Tyrosine Kinase (RTK)

Answer 4

Growth factor binding RTK, leads dimerization and autophosphorylation

One tyrosine kinase activate autophosphorylation of its partner and vice versa

Signalling proteins recruited to RTK

Signalling proteins contains SH2 domain to sense and bind specific RTK (specificity)

Question 5

Receptor Tyrosine Kinase (RTK)-contd

Answer 5

Some SH2 domain proteins are enzymes

They directly produce signals: e.g. phospholipase C- activation leads intracellular calcium release and PK C activation

Some SH2 domain proteins are adaptors

They link the RTK with the signalling protein
-e.g. Grb2 links between EGF receptor and SOS, a regulator of the Ras-MAP kinase pathway (will learn Ras-MAP kinase in details in the progressive years

Question 6

Receptor Tyrosine Kinase (RTK)- drugs

Answer 6

Very limited

Insulin: life saving drug (in PCL III, revisit insulin’s RTK signalling

Many neurotrophin analogues couldn’t pass through clinical trials (failures)

Monoclonal antibodies

Avastin (Bevacizumab): block tumour angiogenesis, by trapping VEGF
Herceptin (Trastuzamab): downregulate overexpressed EGF-HER-2 in breast cancer

Growth hormones act via RTK to modulate cell proliferation, differentiation, survival and others

Question 7

Where are Guanynyl cyclase receptors released from? (catalytic)

Answer 7

Limited membrane bound

e.g- Atrial natriuretic peptide
(recollect CVS lecture 5)

-released from atria, promotes vasodilation and urinary sodium excretion

GTP is converted to cyclic GMP

Question 8

Catalytic receptors:
Guanynyl cyclase receptors – Cytoplasmic:Nitric oxide

Answer 8

ANP and NO act on membrane bound and cytoplasmic guanynyl cyclase receptors

NO= endothelium-derived vasodilator factor (gasotransmitters)

Vascular smooth muscle:
1. NO stimulates cytoplasmic guanylyl cyclase
2. Elevation of intracellular [cGMP]
3. Activation of protein kinase G
4. Smooth muscle relaxation
5. PDE isoform breaks down cGMP

Question 9

Nuclear receptors

Answer 9

Receptors are also called transcription factors
They are intracellular and ligand binding and activate transcription of new proteins

Question 10

What are the most abundant ions in the body?

Answer 10

Cations: Na+, K+, Ca2+
Anions: Cl-, F-, PO4^3-

Question 11

What are the Key Features and Properties of an Ion Channel?

Answer 11

1. selective transmembrane pore
   (molecular sieve/filter)
   Charge & Size of the ions
   -sodium channel will not permit potassium ions
   -K+ channels more selective to K+ than Na+
2. Specific sensor for gating (open & close)
   - involves a conformational change
   -Types of sensors or molecular switch
   Membrane potential: Voltage-gated neurotransmitter binding: Ligand-gated Temp & stretch: mechanosensitive
3. Regulatory mechanisms
   -“inactivation” control (in built)
   - Abundance & location (e.g. post synaptic density)
   - Modulation (G proteins, 2nd messengers, protein kinases)

Question 12

General structure of Voltage-Gated Ion Channel

Answer 12

Can open and close
C and N terms inside the cell (intracellular)
P loop aligns to form a pore
6 transmembrane helices
4 subunits combined

Question 13

3 types of calcium channel?

Answer 13

T-type (transient)
L-Type- CVS
N-type- CNS

Question 14

T type calcium channel:

Answer 14

●Pacemaker, nerves
● Contraction, neurotransmitter release
●Drugs- Gabapentin, pregabalins (inhibit T-type calcium channel and neurotransmitter release)
●Drug use Epilepsy, neuropathic pain

Question 15

N type calcium channel

Answer 15

●Localisation ●Nerve terminus
●Function ●Neurotransmitter release
●Drugs -w-conotoxin (Zicotinide,
synthetic analogue)
●
●Drug use ●Chronic severe pain

Question 16

L-type calcium channel
(long-lasting)

Answer 16

●Localisation ●Nerve terminus
●Function ●Cardiac & smooth muscles
●Drugs Smooth muscle: dihydropyridines, such as nifedipine, amlodipine
Cardiac cells: phenyl alkyl amines, such as verapamil
Both: benzothiazepines, such as diltiazem
●Drug use ●Blood pressure, Arrhythmia, Angina, Stroke

Question 17

Features of Ligand-gated ion channels (nicotinic Ach receptor)
What do ligand-gated ion channels do?

Answer 17

5 subunits
Allows ion movement

• N & C terminus are located extracellularly
• Extracellular ligand binding site
• S2 transmembrane domain forms the pore lining
• 5 different subunits attach to form a pentamer
  e.g. nicotinic Ach receptor (2 a + b + d + e)- alpha units contain Ach binding pocket,
  i.e 2 Ach molecule binding required for receptor activation

Produce an ionotropic effect

Question 18

Examples of neurotransmitters and their channels:

Answer 18

Acetylcholine- Nicotinic AchR
ATP-P2X
5-HT- 5HT3
Glutamate (AMPA, NMDA, kainate)
GABA (GABAA receptors)

Question 19

What is a GCPR?

Answer 19

• G-protein coupled receptor
• Most common receptor in the genome
• Most neurotransmitters/hormones have one or - - More GCPR receptors
• Many in the mouth to signal taste
  Features= Specificity, sensitivity, fidelity

Question 20

What is the structure of GCPR

Answer 20

7 transmembrane spanning domains
Extracellular N terminus
Intracellular C terminus
3 ECL (extracellular loop), 3 ICL (intracellular loops)
They are in bundles in the cell membrane

Most GPCRs share a SIMILAR structure but DISTINCT amino acid sequences (specificity for ligand binding)

Question 21

GPCRs activate G proteins
What is a G-protein?

Answer 21

• guanine nucleotides bound proteins
• Heterotrimeric proteins (different three subtypes)
• Located intracellular, lipid anchors help to mobilise in intracellular membrane
• G alpha (Ga)- Binds to guanosine diphosphate (GDP) or guanosine triphosphate (GTP)

Question 22

What are the 3 types of G proteins?

Answer 22

G alpha, beta and gamma
G beta and G gamma mostly form a dimer=Gby

Question 23

G-protein cycle

Answer 23

1. When resting/inactive, Ga binds GDP and forms a complex with Gby
2. Upon ligand binding, GPCRs gets activated and catalyse exchange of GDP for GTP on Ga
3. Ga-GTP and Gby dissociate from each other and activate effector proteins
4. The GTPase activity of Ga converts bound GTP back to GDP
5. Ga-GDP reassociates with Gby, returns to inactive state
   (steps 1-5, G-protein cycle repeats several times)

Question 24

What are the different G alpha subunits?

Answer 24

Gsa, Gia, Gqa

Question 25

Gs alpha:
What is the effector?
What is the 2nd messenger?
What is the function?

Answer 25

Adenyl cyclase
cAMP
●Stimulatory
●(neurotransmitter release, smooth muscle relaxation)

Question 26

Gi alpha:
What is the effector?
What is the 2nd messenger?
What is the function?

Answer 26

Adenyl cyclase
cAMP
●Inhibitory
●(neurotransmitter release, smooth muscle contraction)

Question 27

Gq alpha
What is the effector?
What is the 2nd messenger?
What is the function?

Answer 27

Phospholipase C
Calcium
●Stimulatory
●(neurotransmitter release, smooth muscle contraction)

Question 28

What is the pharmacological target for
aspirin? (same for ibuprofen)

Answer 28

Enzyme- Cyclooxygenase (Cox-1)

COX1- Responsible for the production of inflammatory molecules in the body, mostly prostaglandin

Arachidonic acid bind to COX

Question 29

What are the 4 main drug targets?

Answer 29

Enzymes
Ion channels
Transporter ( carrier proteins)
Receptors

Question 30

What class is tyrosine kinase receptor?

Answer 30

Catalytic receptors

Question 31

What type of inhibitor is ibuprofen?
What type of inhibitor is aspirin?

Answer 31

Reversible, competitive
Irreversible non-competitive - Once it binds to the enzyme at allosteric site it stays there for some time.

Question 32

How is aspirin usually administered?

Answer 32

Orally so is absorbed in the GI tract

Low binding to plasma protein (ASA)
Acetylsalicylic acid is converted into salicylic acid in the plasma

Question 33

The VD of aspirin is 6L. What does this mean
about drug distribution in the body?

Answer 33

Vd > 40L= Drug accumulation in tissues
Vd< 10L= Drug restricted to plasma and interstitial fluid (largely) (Ideal so blood transports drug)

Volume of distribution= total amount of drug taken/ plasma concentration of drug (at a particular time)
Vd= Q/Cp

Average human- 40L body fluid 23L=Blood

Question 34

What is the half-life of a drug?
Why does Aspirin (ASA) half a shorter half life than Salicylic acid (SA)

Answer 34

The time at which the drug concentration has reduced by half.
It is still/not bound to a plasma protein **ASK SURESH

Question 35

The drug X increases liver enzyme activity, stimulates Y drug’s metabolism, and consequently lowers drug Y’s therapeutic effect. Which ONE of the following best describes the drugs X and Y interactions?

A. chemical antagonism
B. physiological antagonism
C. physical agonism
D. pharmacokinetic antagonism
E. surmountable antagonism