W22 Pharmacology- Drug targets Flashcards
Catalytic & Nuclear Receptors Ion channels GCPR W31 Case studies
What is the General structure/features of catalytic receptors?
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
What are Receptor Tyrosine Kinases?
Examples? (6)
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
What does activation of RTK’s lead to?
What does hyperactivation of RTK’s lead to?
Activation leads to cell proliferation, differentiation, survival and metabolism
Hyperactivation leads to polyps, tumour and cancer
Receptor Tyrosine Kinase (RTK)
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)
Receptor Tyrosine Kinase (RTK)-contd
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
Receptor Tyrosine Kinase (RTK)- drugs
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
Where are Guanynyl cyclase receptors released from? (catalytic)
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
Catalytic receptors:
Guanynyl cyclase receptors – Cytoplasmic:Nitric oxide
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
Nuclear receptors
Receptors are also called transcription factors
They are intracellular and ligand binding and activate transcription of new proteins
What are the most abundant ions in the body?
Cations: Na+, K+, Ca2+
Anions: Cl-, F-, PO4^3-
What are the Key Features and Properties of an Ion Channel?
- 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+ - 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 - Regulatory mechanisms
-“inactivation” control (in built)
- Abundance & location (e.g. post synaptic density)
- Modulation (G proteins, 2nd messengers, protein kinases)
General structure of Voltage-Gated Ion Channel
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
3 types of calcium channel?
T-type (transient)
L-Type- CVS
N-type- CNS
T type calcium channel:
●Pacemaker, nerves
● Contraction, neurotransmitter release
●Drugs- Gabapentin, pregabalins (inhibit T-type calcium channel and neurotransmitter release)
●Drug use Epilepsy, neuropathic pain
N type calcium channel
●Localisation ●Nerve terminus
●Function ●Neurotransmitter release
●Drugs -w-conotoxin (Zicotinide,
synthetic analogue)
●
●Drug use ●Chronic severe pain
L-type calcium channel
(long-lasting)
●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
Features of Ligand-gated ion channels (nicotinic Ach receptor)
What do ligand-gated ion channels do?
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
Examples of neurotransmitters and their channels:
Acetylcholine- Nicotinic AchR
ATP-P2X
5-HT- 5HT3
Glutamate (AMPA, NMDA, kainate)
GABA (GABAA receptors)
What is a GCPR?
- 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
What is the structure of GCPR
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)
GPCRs activate G proteins
What is a G-protein?
- 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)
What are the 3 types of G proteins?
G alpha, beta and gamma
G beta and G gamma mostly form a dimer=Gby
G-protein cycle
- When resting/inactive, Ga binds GDP and forms a complex with Gby
- Upon ligand binding, GPCRs gets activated and catalyse exchange of GDP for GTP on Ga
- Ga-GTP and Gby dissociate from each other and activate effector proteins
- The GTPase activity of Ga converts bound GTP back to GDP
- Ga-GDP reassociates with Gby, returns to inactive state
(steps 1-5, G-protein cycle repeats several times)
What are the different G alpha subunits?
Gsa, Gia, Gqa
Gs alpha:
What is the effector?
What is the 2nd messenger?
What is the function?
Adenyl cyclase
cAMP
●Stimulatory
●(neurotransmitter release, smooth muscle relaxation)
Gi alpha:
What is the effector?
What is the 2nd messenger?
What is the function?
Adenyl cyclase
cAMP
●Inhibitory
●(neurotransmitter release, smooth muscle contraction)
Gq alpha
What is the effector?
What is the 2nd messenger?
What is the function?
Phospholipase C
Calcium
●Stimulatory
●(neurotransmitter release, smooth muscle contraction)
What is the pharmacological target for
aspirin? (same for ibuprofen)
Enzyme- Cyclooxygenase (Cox-1)
COX1- Responsible for the production of inflammatory molecules in the body, mostly prostaglandin
Arachidonic acid bind to COX
What are the 4 main drug targets?
Enzymes
Ion channels
Transporter ( carrier proteins)
Receptors
What class is tyrosine kinase receptor?
Catalytic receptors
What type of inhibitor is ibuprofen?
What type of inhibitor is aspirin?
Reversible, competitive
Irreversible non-competitive - Once it binds to the enzyme at allosteric site it stays there for some time.
How is aspirin usually administered?
Orally so is absorbed in the GI tract
Low binding to plasma protein (ASA)
Acetylsalicylic acid is converted into salicylic acid in the plasma
The VD of aspirin is 6L. What does this mean
about drug distribution in the body?
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
What is the half-life of a drug?
Why does Aspirin (ASA) half a shorter half life than Salicylic acid (SA)
The time at which the drug concentration has reduced by half.
It is still/not bound to a plasma protein **ASK SURESH
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
