Exam 2- Drug Target Interactions Part 2

Question 1

Biochemistry- A receptor

Answer 1

A molecule that transduces a signal

Question 2

5 classes of receptors

Answer 2

1. Nuclear Hormone Receptors
2. enzyme linked receptors
3. enzyme associated receptors
4. ligand gated ion channels
5. 2nd Messenger systems (GPCRs)

Question 3

Nuclear Hormone Receptors

Answer 3

act via intracellular receptors and the drug must cross the cell membrane

• effects can last for hours or days after drug is gone
• Beneficial and adverse effects last longer than drug elimination

Question 4

Example of Nuclear Hormone Receptors

Answer 4

• Growth hormones
• Steroids like glucocorticoids, sex steroids, thyroid hormones
  Most common MOA: binding to DNA via response elements

Question 5

Enzyme linked receptor

Answer 5

Large transmembrane proteins with extracellular ligand binding domains and intracellular enzyme domains
- common with trophic hormones like insulin

Question 6

Enzyme linked receptor signaling events

Answer 6

1. ligand binds extracellular domain
2. conformational change
3. dimerization (homo- or hetero-)
4. kinase domains together
5. phosphorylation event

Question 7

Example of Enzyme linked receptor

Answer 7

Receptor tyrosine kinase

Question 8

Ligand induced dimerization and phosphorylation

Answer 8

leads to variety of signaling events triggered
- further effects downstream events like
1. altering membrane permeability to ions
2. changes in gene expression
3. increased nutrient transport and more
intensity and duration of agonist-activation limited by receptor down-regulation

Question 9

Dimerization may vary

Answer 9

depending upon ligand or cell type

- doesn’t happen until ligand binding

Question 10

Intensity and duration of agonist-activation is limited by

Answer 10

receptor down regulation

• ligand binds, receptor endocytose and degraded
• New R synthesis takes time, limits drug efficacy

Question 11

Enzyme Associated Receptor

Answer 11

Mechanism of action is similar to kinase receptors, but, kinase activity is not intrinsic to the receptor - external molecule mediates phosphorylation
Ex. JAK/STAT pathway

Question 12

Cytokines

Answer 12

large class of molecules that mediate cell-cell communication, particularly involving the immune system

Question 13

For enzyme associated receptors Activity remains

Answer 13

as long as receptor is dimerized- even if ligand is gone

Question 14

Ligand-gated ion channel

Answer 14

1. ligand binds receptor, opens channel, ions flux down (electro)chemical gradients
   - Ion channels are not all the same multiple subtypes
   - the ligand binding site is on the extracellular surface
   - Effects are turned off immediately once ligand is gone

Question 15

Second Messenger Systems

Answer 15

• most complicated of the receptor systems
• lead to great signal amplification
• part of signal transduction pathways,
• GPCRs: signaling in 3 parts

Question 16

3 Parts of G protein Coupled Receptors

Answer 16

1. extracellular ligand binds to specific receptor
2. G-protein activated on cytoplasmic/intracellular surface (exchanges GDP for GTP)
3. G-protein changes activity of some effector like enzyme or ion channel

Question 17

G-proteins

Answer 17

family of proteins that function as molecular switch and an intermediate

• can be more than one per receptor
• bind and hydrolyze GTP, allows for tremendous signal amplification and increased longevity
• can be both stimulatory and inhibitory

Question 18

G-proteins are active while

Answer 18

bound to GTP

Question 19

G-proteins are inactive while

Answer 19

bound to GDP

Question 20

7TM

Answer 20

7 transmembrane loops

example of GPCR

Question 21

cAMP

Answer 21

Cyclic adenosine monophosphate

• made by adenylyl cyclase
• example of various second messengers

Question 22

cAMP what does it do

Answer 22

Mediates hormonal responses

• renal water conversation
• calcium homeostasis
• production of hormones
• smooth muscle relaxation (not skeletal muscle)

Question 23

Phosphoinisotol (IP3)

Answer 23

• example of 2nd messengers

- G-proteins stimulate phospholipase C which promotes the catabolism of membrane-bound PIP2 into DAG and IP3

Question 24

IP3 diffuses through

Answer 24

the cytoplasm, binds calmodulin and cascades further

Question 25

Gs proteins (Stimulatory)

Answer 25

Adenylyl cyclyase -> increased cAMP

Question 26

Gi1, Gi2, Gi3 effector

Answer 26

Adenylyl cyclyase -> decreased cAMP

Question 27

Gq effector | mACh, bomesin, 5-HT2

Answer 27

Phospholipase C-> increased IP3

Question 28

Steps of GPCR

Answer 28

1. Ligand binds to receptor 2. G-protein is released from the receptor 3. G-protein binds to the effector protein 4. Change in 2nd messenger 5. G-protein hydrolyzes GTP to GDP

Question 29

Nuclear hormone receptor response time

Answer 29

Slow (hours

Question 30

Nuclear hormone receptor - how the signal is transduced

Answer 30

``` Gene transcription (upregulation or downregulation) - induces a change in gene expression ```

Question 31

Nuclear hormone receptor - mechanism

Answer 31

Ligand binding results in conformational shift and binding to DNA response elements. Ligand must cross cell membrane

Question 32

Nuclear hormone receptor - Can the signal outlast the message?

Answer 32

Yes

Question 33

Ligand gated ion channel - how the signal is transduced

Answer 33

changes in ion transport

Question 34

Ligand gated ion channel - response time

Answer 34

Very rapid (milliseconds)

Question 35

Ligand gated ion channel - mechanism

Answer 35

Ligand opens or closes an ion channel. Typically extracellular binding of ligand

Question 36

Ligand gated ion channel - examples

Answer 36

Nerves, skeletal muscles

Question 37

Ligand gated ion channel - Can the signal outlast the message?

Answer 37

No

Question 38

Enzyme-coupled and enzyme-associated receptors - how the signal is transduced

Answer 38

Intracellular enzyme

Question 39

Enzyme-coupled and enzyme-associated receptors - response time

Answer 39

Moderate (minutes)

Question 40

Enzyme-coupled and enzyme-associated receptors - mechanism

Answer 40

Extracellular ligand binding results in intracellular enzymatic activity. Typically requires dimerization. Signal can be maintained after ligand leaves

Question 41

Enzyme-coupled and enzyme-associated receptors - examples

Answer 41

Response to cytokines, growth hormones

Question 42

Enzyme-coupled and enzyme-associated receptors - can the signal outlast the message?

Answer 42

Yes

Question 43

GPCR - how the signal is transduced

Answer 43

Second messenger (usually IP3 or cAMP)

Question 44

GPCR - response time

Answer 44

Rapid (seconds)

Question 45

GPCR - Mechanism

Answer 45

Extracellular binding to 7-TM results in activation of a GTP-binding protein. Activated G-protein goes on to activate some effector

Question 46

GPCR - Examples

Answer 46

Taste, smell, endocrine signals

Question 47

GPCR - can the signal outlast the messenger?

Answer 47

No

Question 48

Drug-Receptor complex formation leads to intracellular effector molecule phosphorylation

Answer 48

Receptor Dimerization and enzyme activation

Question 49

Which is a typical response to a G-protein activation?

Answer 49

- Activation of phospholipase C - activation and inhibition of adenylyl cyclase -NOT involved in inhibition of phospholipase C

Question 50

Membrane permeability of the ligand is most imporant for which type of receptor

Answer 50

Nuclear Hormone receptor bc it has to cross the cell membrane

Question 51

Which type of receptor frequently uses protein phosphorylation to tranduce its signal?

Answer 51

Enzyme linked receptor

Question 52

Within living systems, EC50 is

Answer 52

a measurement of a biological response of a compound

Question 53

The bigger the therapeutic window

Answer 53

the better and more safe we consider the drug to be

Question 54

A low EC50 means

Answer 54

high therapeutic window

Question 55

ED50

Answer 55

dose at which 50% of patient population exhibits specific effect - effective dose, 50% of population agonist activation

Question 56

TD50 and LD50

Answer 56

toxic and lethal doses for 1/2 the population TD is used more than LD TD50- measure of toxicity

Question 57

NOAEL

Answer 57

No observed adverse events level

Question 58

Drug selectivity confers

Answer 58

utility, clinically | selectivity is a major factor during drug development as target specific, or receptor specific binding

Question 59

Tied to the same R and effector

Answer 59

- on target toxicity - Usually a dose response, optimal dose to "fix" pathological condition - too much drug exaggerates E Ex: Diabetes type 1 use of insulin: if overdose -> hypoglycemic coma

Question 60

Mediated by the same R on different cells/tissues

Answer 60

- on target toxicity - same receptors exist on multiple cells, may differentiate Beneficial vs. Adverse R Ex: MOR in CNW vs. GI tract

Question 61

How to avoid/ mitigate for mediated on the same R

Answer 61

1. Use lowest effective dose 2. Effect pathology via administration of multiple drugs with different MOAs 3. Targeted delivery ( concentrate drug at R for benefit)

Question 62

Mediated by different R

Answer 62

- off-target toxicity - Drugs are selective not specific, so toxicities may be mediated by other receptor binding - Not always bad bc some new drugs/receptors have been discovered bc of these off target R bindings. - Its a problem and a potential opportunity

Question 63

Hypotension is an example of

Answer 63

on target toxicity