Lecture 2: Drug-receptor Interactions Flashcards
Nature of drug receptors
-most are proteins
-regulatory, transport, structural proteins
-enzymes
Quantitative Aspects of DR interactions
-determine relationship between dose and effect
-responsibile for selectivity of drug action
Selectivity of drug action
-size, shape, charge of drug molecule
-changes in structure can affect receptor binding
-mediate actions of agonists and antagonists
Agonist
-drug that binds to receptor and stimulate response
antagonist
-drug that binds to receptor without altering receptor function (stimulating response)
-alter interaction of receptor with another drug
Assessing DR interactions
- receptor binding/target engagement
- Functional Assays
receptor binding/target engagement
-use biochemical or biophysical approach to assessing
-typically measures static event not function
Functional Assays
-assessing signaling events associated with receptor activity
-ion influx/second messenger/gene regulation/substrate change
concentration-effect
-response to low concentrations of drug increase proportionally
-dose increase = response decrease
-certain concentrations reached where response can no longer increase
Concentration-Effect Relationship
linear curve or semi log (s curve)
10-90 = 3 log rule
SLIDE 36 v important
Affinity
-ability of drug to interact with receptor
-Kd
-determinant of potency
-one drug can have different ones for different receptors
Kd
-measure affinity
-dissociation constant
high affinity
-tight binding
-low Kd value
Law of Mass action
-effect of drug directly proportional to amount of DR complex formed
D + R -ka and kd-> DR –> effect
rate of association
-Kon[D][R]
-first part of graph increasing until 100% bound
rate of dissociation
Koff [DR]
-last part of graph, decrease in % bound
equilibrium
Kon[D][R] = Koff[DR]
or [D][R]/[DR] = KD
when KD = [D]
-drug occupies half the receptors
[R] = [DR]
relationship between occupied receptor B (DR) and [D]
B = (D*Bmax(R total))/(D+KD)
-essentially michaelis menten equation
Law of mass action assumptions made
-binding reversible
-D and R only exist as free and bound
-all receptors have same affinity for D and are independent
Bmax
total number of receptors on given cell or tissue
-half this value = KD
Radio/labeled receptor binding
-fluorescent marker added to ligand
-receptor + ligand and then filtered
Saturation binding analysis
-requires labeled ligand
-not useful for HTS
-use of heterologous competition assays for profiling (assumes test drugs compete for same sight as labeled ligand)
Heterologous competition binding
receptor + ligand + test and then filter
Pharmacological profiling
-IC50
-Ki
-relative affinity
IC50
determined from experimental data
Ki
-indirect measure of affinity (KD)
-cheng-prusoff equation
Cheng-Prusoff equation
Ki = IC50/[1+L/KD]
MATH AND GRAPH
GOFIWHEF
