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Applying An Understanding of
the Mechanisms of Action of
Estrogen and SERMs to Patient
and Treatment Selection in
Clinical Practice
Donald P. McDonnell, PhD
Professor of Pharmacology and Cancer Biology
Director of Graduate Studies, Pharmacology
Duke University Medical Center
Durham, North Carolina
The Estrogen Receptor Is a
Ligand-Dependent Transcription Factor
Nuclear Membrane
Cell Membrane
ERE
Altered
Cell
Function
5’
3’ mRNA
New
Protein
ERE= estrogen response element; mRNA= messenger RNA. Graphic courtesy of Donald P. McDonnell, PhD.
The Potential Fates of Agonist-activated ER
Genomic Actions
Non-genomic Actions
ER CoA
CoA ER
ER
ER
ERE
CoA ER
ER
ER
ER CoA
ER
ER
AP1
ER
MNAR
ER CoA
CoA ER
c-SRC
p50
ER = estrogen receptor; CoA = coactivator; AP = activator protein; MNAR = modulator of
nongenomic action of estrogen receptor; NF-kB = nuclear factor kB.
Reprinted from McDonnell DP. EJC Supplements. 2004;2:35, with permission from Elsevier.
p65
NF-B
X
A Simple Model to Explain
Estrogen Receptor Pharmacology
Agonist
ER
ER
Antagonist
ER = estrogen receptor.
Graphic courtesy of Donald P. McDonnell, PhD.
% Change in Spinal BMD
from Baseline
Clinical Validation of the
SERM Context
3
2
Placebo
Tamoxifen
1
0
-1
-2
-3
Baseline 3
6
12
18
24
Months
BMD = bone mineral density.
Love RR, et al. N Engl J Med. 1992;362:852. Copyright © 1992. Massachusetts Medical Society.
All rights reserved.
SERMs—A Historical Perspectivea
Lasofoxifene 1998
Arzoxifene 1998
Toremifene
1985
Tamoxifenb
1972
Droloxifene
Raloxifeneb
1983
GW5638
1994
Clomiphene
1962
1965
1970
1980
Empirical
discovery
aBased
Fulvestrantb
1992
on date of first publication; bFDA-approved.
1990
Bazedoxifene
2001
2000
Mechanism-based
discovery
Evolution of SERMs/ER Modulators
Bone
Uterus
Brain
Breast
(VMS)
++
++
++
++
Tamoxifen
+
+
–
–
Raloxifene
+
–
–
–
Bazedoxifene
+
–
–
–
TSEC
+
–
++
–
Estradiol
TSEC = tissue selective estrogen complex; VMS = vasomotor symptoms.
Graphic courtesy of Donald P. McDonnell, PhD.
+ = effect; – = no effect.
27-Hydroxycholesterol (27HC)

Produced primarily outside the entero-hepatic axis1

Most prevalent circulating oxysterol1

Inhibits estrogen action in the cardiovascular system1
CYP27A1
CYP7B1
HO
Cholic and Chenodeoxycholic acids
+ Propionic Acid
OH
HO
27HC
CYP7B1
Lithocholic acid
O
HO
Cholestenoic acid
CYP7B1
Acidic Pathway
Classic (Neutral)
Pathway
Cholesterol
Yamasaki Pathway
HO
Chenodeoxycholic
acid
1. Umetani M, et al. Nat Med. 2007;13:1185. Graphic courtesy of Carolyn D. DuSell, and Donald P. McDonnell, PhD.
Normalized Response
27HC Functions as an
ER Partial Agonist
90
80
70
60
50
40
30
20
10
0
E2
27HC
0.5nM E2 + 27HC
12
11
10
9
8
7
6
5
4
- Log [M ]
27HC = 27-hydroxycholesterol; ER = estrogen receptor; E2 = 17ß-estradiol
Reprinted from DuSell CD, et al. Mol Endocrinol. 2008;22:65, with permission from
The Endocrine Society.
27HC Activates Transcription of ER Target Genes
pS2
14
12
10
8
6
4
2
0
E2
27HC
11
10
9
8
7
6
12
Fold Induction
Fold Induction
PR
E2
27HC
10
8
6
4
2
0
5
11
10
12
E2
27HC
10
8
6
4
2
10
7
6
9
8
7
-Log [M]
5
E2
27HC
ERBB4
6
5
Fold Induction
Fold Induction
WISP2
11
8
-Log [M]
-Log [M]
0
9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
11
10
9
8
7
-Log [M]
Adapted from DuSell CD, et al. Mol Endrinol. 2008;22:65, with permission from The Endocrine Society.
6
5
Percent Survival
CYP7B1 Expression is Correlated with
Increased Survival In Breast Cancer
Disease-Free Years
DuSell CD, et al. Unpublished data. Graphic courtesy of Donald P. McDonnell, PhD.
Building the Case for 27HC as a
“Naturally” Occurring SERM

Circulates at levels high enough to activate ER1
– Range: 0.075 - 0.73 µM
– Males > Females

Elevated concentration (millimolar range) in
atherosclerotic lesions1,2

Attenuates the positive effect of estrogen on the
cardiovascular system1

Km of 27HC for its catabolic enzyme CYP7B1
(24 M)3 is greater than the Kd of 27HC for ER
(0.5 m)3
Km = Michaelis constant; Kd = dissociation constant.
1. Umetani M, et al. Nat Med. 2007;13:1185. 2. Brown AJ, et al. Atherosclerosis. 1999;142:1. 3. DuSell
CD, et al. Mol Endocrinol. 2008;22:65.
Factors That Influence the Molecular
Pharmacology of ER Ligands

Presence or absence of a coexpressed
progesterone receptor

Relative expression level of 2 estrogen
receptor (ER) subtypes

Impact of “estrogen” on structure of ER

Ability of differently conformed receptors
to interact with factors needed for activity
ER and PR Regulate Each Other
160
140
ER Activity
120
100
80
60
40
ER
20
ER + PR-A
0
Blank
10-11
10-10
10-9
10-8
10-7
10-6
Progesterone (M)
All samples treated with estradiol.
ER = estrogen receptor; PR = progesterone receptor.
Adapted from Wen DX, et al. Mol Cell Biol. 1994;14:8356, with permission from the American Society for Microbiology.
Factors That Influence the Molecular
Pharmacology of ER Ligands

Presence or absence of a coexpressed
progesterone receptor

Relative expression level of 2 estrogen
receptor (ER) subtypes

Impact of “estrogen” on structure of ER

Ability of differently conformed receptors
to interact with factors needed for activity
Primary Structure of ERα and ERβa
DNAbinding
domain
NH2
179
89
Ligand-binding
domain
38
251
142
18%
aNumbers
COOH
ERα
COOH
ERβ
AF-2
AF-1
NH2
43
84
28
248
28
97%
24%
58%
12%
Amino acid
homology
in boxes indicate number of amino acids.
Reprinted from Hall JM, et al. Mol Interv. 2005;5:343, with permission from The American Society
for Pharmacology and Experimental Therapeutics.
ERβ Is a Key Component of the Cellular
Processes That Regulate Cellular
Sensitivity to Agonists
Normalized Response
250
ERα
ERβ
ERα/ERβ
200
150
100
50
0
nh
12
11
9
8
10
-Log [M] E2
7
Reprinted from Hall JM, et al. Endocrinology. 1999;140:5566, with permission from
The Endocrine Society.
6
ERβ Agonists May Have Utility as
Treatment for Inflammatory Bowel Disease
3.5
Diarrhea
3
Stool Score
Vehicle
2.5
20 mg/kg
10 mg/kg
2
5 mg/kg
1 mg/kg
1.5
0.3 mg/kg
Normal
1
0.1 mg/kg
0.5
0
2
4
6
8
Day of Treatment
Reprinted from Harris HA, et al. Endocrinology. 2003;144:4241, with permission from
The Endocrine Society.
Factors That Influence the Molecular
Pharmacology of ER Ligands

Presence or absence of a coexpressed
progesterone receptor

Relative expression level of 2 ER subtypes

Impact of “estrogen” on structure of
estrogen receptor (ER)

Ability of differently conformed receptors
to interact with factors needed for activity
Crystallography Has Confirmed the Relationship
Between the Conformation of ER-ligand Complexes
and Their Biologic Activity
Graphic courtesy of Virginia Carnahan and
Donald P. McDonnell, PhD.
Color
Ligand
Green
IOS974/GW5638
Yellow
4-hydroxytamoxifen
Blue
Raloxifene
Different Compounds Induce
Different Structural Alterations Within
the Estrogen Receptors
Inactive
Pure
Antagonists
Fully Activated
SERMs
Adapted from McDonnell DP, et al. Mol Endocrinol. 1995;9:659, with permission from
The Endocrine Society.
Pure
Agonists
Factors That Influence the Molecular
Pharmacology of ER Ligands

Presence or absence of a coexpressed
progesterone receptor

Relative expression level of 2 estrogen
receptor (ER) subtypes

Impact of “estrogen” on structure of ER

Ability of differently conformed receptors
to interact with factors needed for activity
An Updated Model of Nuclear Receptor Pharmacology
CoR
CoR
Antagonist
NR
NRE
SNRMs
NRE
Agonist
CoA
CoA
CoR = corepressor; NRE = nuclear response element;
NR = nuclear receptor; SNRM = selective nuclear receptor
modulator; CoA = coactivator.
Graphic courtesy of Donald P. McDonnell, PhD.
NRE
X
Conclusions

Receptor conformation is determined by
the nature of the bound ligand

Differences in receptor conformation dictate
coactivator binding preferences

The biologic activity of different NR-cofactor
complexes is not equivalent

Screening for ligands which facilitate
specific NR-cofactor interactions allows
process/cell-specific modulators to be
developed