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Pharm 507 > Receptor Pharm I > Flashcards

Receptor Pharm I Flashcards

1
Q

Target molecules for drugs

A

Receptors, enzymes, ion channels, transporters, proteins

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2
Q

Ligand

A

Endogenous or exogenous substance that binds to specific sites of target protein

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3
Q

Endogenous ligand examples

A

Neurotransmitters, hormones, growth factors, cytokines

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4
Q

Exogenous ligand examples

A

Drugs, toxins

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5
Q

How do exogenous ligands work?

A

Mimic the specific binding of the endogenous ligand

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6
Q

Types of exogenous ligands

A

Agonist - activate receptor and produces cellular response

Antagonist - blocks agonist from activating receptor

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7
Q

How do drugs interact with targets?

A

Receptor/ion channels - bind to same site as endogenous ligand to mimic or block it
Enzymes/transporters - bind the active/ligand binding site and inhibit catalytic/transport of protein

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8
Q

Drug + receptor = ??

A

Drug-receptor complex

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9
Q

Example of epinephrine and GPRC reaction

A

Epi(GPCR) -> AC -> cAMP -> PKA -> increase phosphorylation enzyme -> increased glycogen breakdown

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10
Q

Binding of drug to its receptor is reversible

A

Leads to “free” drug and “free” receptor

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11
Q

What does reversible drug binding lead to?

A

Competition among drugs and with endogenous ligands

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12
Q

Saturation

A 
Occupancy of all receptor sites by drugs
# of receptors is finite
Drug to occupy all receptors, adding more drug does nothing
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13
Q

Binding of drugs to receptors is ______; depends on the relative ______ the drug has for its receptor

A

Selective, affinity

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14
Q

Affinity determines…

A

Probability of a drug binding to a receptor site and duration of receptor occupancy

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15
Q

Structural points of attachment determine…

A

Receptor activation (agonists) or blockage (antagonists)

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16
Q

Selectivity is _____, not ______

A

Selectivity is relative, not absolute

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17
Q

Drug-Receptor Binding Equation

A

R + D RD

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18
Q

Drug-receptor binding obeys what law?

A

Law of mass action

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19
Q

Forward rate of constant for association

A

Kon

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20
Q

Reverse rate constant for dissociation

A

Koff

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21
Q

High affinity = ____ Koff

A

Low Koff

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22
Q

Low affinity = ___ Koff

A

High Koff

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23
Q

What is Koff used to determine?

A

Drug affinity

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24
Q

What is KD?

A

Equilibrium dissociation constant, units of concentration

Amount of drug needed to bind to receptor

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25
What is the dissociation constant equation?
KD = (Koff/Kon) = ([R][D])/[RD]
26
KD definition
Concentration of drug that occupies 50% of the receptors
27
High drug affinity yields ____ KD values
Low
28
Low drug affinity yields ____ KD values
High
29
Affinity equation
Affinity = 1/KD
30
Why is KD used?
To determine the amount of drug (concentration) needed to achieve a degree of receptor occupancy
31
Fractional receptor occupancy (FRO)
FRO = [D]/(KD + [D]
32
As drug concentration increased, receptor is saturated and FRO approaches __
1 (100% receptor occupancy)
33
Drug-receptor complex equation
[RD] = ([RT][D]/KD+[D])
34
Drug concentration vs receptor occupancy plot
Hyperbolic curve | Never actually reach 0 or 100
35
At KD, 50% of receptors are occupied…
1/10th KD yields 9% occupancy, 10x KD yields 91% occupancy
36
Fractional drug effect (E/Emax) is directly related to…
FRO
37
A low FRO yields ____, high FRO yields ____
Low effect, high effect
38
Binding and effect are NOT 1:1, this is due to…
Spare receptors
39
E/Emax proportional to FRO equation
(E/Emax) ~ ([D]/(EC50+[D])
40
EC50
Effective drug concentration that produces 50% of the response (half max effect)
41
Drug concentration vs effect graph
Sigmoidal curve
42
What is used to compare different drugs?
EC50
43
What kind of scale is a sigmoidal curve graph?
Semi-log
44
ED50
Dose required to produce 50% of maximal response
45
EC50 vs KD
EC50 substitutes for KD in drug effect equation, related but not identical
46
EC50 is usually < KD; why?
Spare receptors
47
What value is used to determine drug potency?
EC50
48
Amount of drug required to generate a given fractional effect is analogous to…
Affinity
49
EC50 value for high potency drug
Low
50
EC50 value for low potency drug
High
51
Does EC50 indicate drug efficacy?
Nope
52
Drug Efficacy
Magnitude of max effect drug is able to produce
53
What determines drug efficacy?
How well the drug activates the receptor when bound
54
Potency vs. Efficacy
Highly potent drugs can have low efficacy | Low potency drugs can have high efficacy (just need higher dose)
55
Does low efficacy mean the drug is clinically ineffective?
No
56
Signal amplification
Receptor signaling pathways that lead to intermediate and final responses
57
Outcome of a downstream amplification event
100% receptor binding is not required to generate 100% response
58
What direction does EC50 shift in the presence of spare receptors?
Left; EC50 < KD
59
Drug response _______ is often higher than its receptor ______.
Potency, affinity
60
Define spare receptors
More receptors than necessary
61
Direction shift with loss of spare receptors
Right
62
What happens with the agonist potency when receptors are lost
Decreases
63
Clinical significance of spare receptors
Low concentrations of endogenous ligands | Lower drug doses than what’s required for full receptor occupancy
64
Can cells lose some of their receptors but still generate full responses?
Yes, to a point
65
What causes receptor loss?
Diseases Chronic agonist administration (down-regulation) Irreversible antagonists
66
Clinically, what do you when receptors are lost?
Increase drug dose to achieve therapeutic effect

Pharm 507 (6 decks)

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