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Bi/CNS 150
Lecture 29.5
Friday, December 7, 2012
“Inside-out” Actions for Psychiatric Drugs
Henry Lester
How do psychiatric drugs work?
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1. Statement of the problem: Antispychotics, Antidepressants, Bipolar drugs
2. Lessons from nAChRS; 3. Pharmacokinetics
4. Detailed hypotheses: Antipsychotic drugs SSRI Antidepressant drugs “Fast” NMDA blocker antidepressants
5. Tests of “inside-out” mechanisms for psychiatric drugs
Psychiatric drugs bind to classical targets within early exocytotic pathways: Therapeutic effects
Biological Psychiatry, Dec 2012 Henry A. Lester, Julie M. Miwa, and Rahul Srinivasan
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Eroom’s law applies especially to neural drugsScannell, Nature Revs Drug Disc. 2012
Contemporary ideas about psychiatric drugshave emphasized binding to
the classical targets at synapses. . .
“Inside-out” mechanisms emphasize binding to the same classical targets, but within the
endoplasmic reticulum and cis-Golgi
Some psychiatric drugs, their targets, logP values, and half lives
fluoxetine (Prozac)
serotonin transporter logP 3.4, 24-72 hr
clozapine (Clozaril)5-HT2A serotonin receptor, GPCR
logP 3.2, 8-12 hr
ketamine (“special K”)
NMDA glutamate receptor logP 2.2, 3-5 hr
chlorpromazine (Thorazine)
dopamine D2 receptor, GPCRlogP 5.2, 16-30 hr
nicotine acetylcholine receptor
logP 1.2, 0.5 -2 hr
recreational / abused / addictive
antipschizophrenic antidepressant
5logP = log (solubility in octanol / water)
BloodLungs
H+
Like most drugs, nicotine is a weak base.Its neutral form passes through 6 plasma membranes in ~ 20 s
logP = 1.1 = log (solubility in octanol / water) 6
NH+
N
N
N
N
N
CSF
Alveolar epithelium Brain capillary
AstrocyteEnd-feet
Endothelialcells
7Nucleus
UPRE
PlasmanACh
R
Nicotine in CSF
Classical Pathway:Channel activation & desensitization
→ Do neurons survive Despite stressors?
Unfolded protein response
membrane
COPII vesicleSec 13/31
Sar1
Sec24Sec23
ATF6
Golgi
PharmacologicalChaperoning→ upregulation
M3-M4 loop
H+ +
ERBiP
PERKIRE1
Clathrin
Secretory vesicle
COPII
Golgi complex
COPI
Early endosome
COPI
Lysosome
Ca2+
Na+
“Inside-out” Drug Action by Nicotine at α4β2 nAChRs
NH+
N
H+
N
N
Endoplasmic reticulum
nAChR
ATF6
IRE1
XBP1
eIF2α
PERK
ATF4
1. Agonist binding eventually favors stable, high-affinity states (a “chaperone”)
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channels
nicotine20 sec
Three possible results of nicotine-nAChR binding in the endoplasmic reticulum
“closed”
AC Highest affinity
Fre
e E
ne
rgy
Reaction Coordinate
“activated”
“desensitized”
Bound states with increasing affinityunbound
agonist
?
2. Nicotine binding at subunit interface favors assembled nAChRs (a “matchmaker”)
3. Nicotine may displace lynx, directing nAChRs toward cholesterol-poor domains (an “escort”)
nicotine
lynx
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R. L. Wiseman, C. M. Haynes, D. Ron Cell 2010
The three arms of the ER stress / unfolded protein response pathway
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During chronic exposure to nicotine, α4β2 nAChRs are selectively upregulated.
Pharmacological chaperoning is necessary but not sufficient for upregulation.
Other sequelae of chaperoning: changed stoichiometry, reduced ER stress and reduced UPR.
Upregulation proceeds similarly in clonal cells, rodent brains, and smokers’ brains.
Inside-out Pharmacology of Nicotine Effects at α4β2 nAChRs
Now we’re assessing gene expression in identified neurons chronically exposed to nicotine.
Inside-out pharmacology is a powerful concept for nearly all CNS drugs:They are all membrane-permeant weak bases.
The discovery criteria for psychiatric drugs lead to excellent intracellular chaperoning
1. High bioavailability implies high membrane permeationAll psychiatric drugs have logP > 2
2. Good stability in the body implies simple or little enzymatic breakdown.Half-life is ~ 1 day.
3. Good selectivity, few off-target effects imply high-affinity binding to the targetKd < 1 μM, often ~ 10 nM
a. “Chaperoning”: (i) Transporter ligands are
organic substratesions,or antagonists,
They favor two major binding states, “inward” vs “outward”.
(ii) GPCR ligands (see next slide): agonistsantagonistsallosteric modulators“inverse” agonists
b. “Matchmaking”:(i) Neurotransmitter transporters must homodimerize before leaving the ER(ii) GPCRs homo- and heterodimerize, in some cases required for ER export,
in some cases favored by ligands 11
Pharmacological chaperoning of GPCRs
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receptor mutant /WT drug class reference
adenosine A1 mutant agonists; antagonists (Malaga-Dieguez et al., 2010)
dopamine D4 bothtransported dopamine; quinpirole; antagonists
(Van Craenenbroeck et al., 2005
)gonadotropin-
releasing hormonemutant antagonists
(Conn and Ulloa-Aguirre, 2011
)
histamine H2 both agonist, inverse agonist (Alewijnse et al., 2000)
opsin mutant -- (Noorwez et al., 2008)
δ-opioid mutant antagonist (Leskela et al., 2012)
μ-opioid mutant agonists, antagonists (Chaipatikul et al., 2003)
melanin conc. hormone
mutant antagonist (Fan et al., 2005)
melanocortin-4 both antagonist, inverse agonist (Tao, 2010)vasopressin V1a both antagonist (Hawtin, 2006)
vasopressin V1b/V3 both antagonist (Robert et al., 2005)vasopressin V2 both antagonists (Wuller et al., 2004)
Enzyme or
channel
Transcription factors
Nucleus
Intracellular messenger
kinase cascade
Drug
+ In CSF
+
Endoplasmic reticulum
GolgiH+
ATF6,
CREB-H
IRE1
XBP1
p-eIF2α
PERK
ATF4
NucleusUPRE
Drug
+ in CSF
Transcription factors
ATF6
+ +
Neutral permeant drug
+
+ +
+
BiP
PERKIRE1
++
H+
ER
Golgi
β-arrestin
A. Inhibition of plasma membrane GPCR , and downstream effects
B. Intracellular pharmacological chaperoning of GPCR, and downstream effects
Most papers suggest . . . We suggest . . .
Two mechanisms for gene activation downstream from antipsychotic drugs
“Nearly” cell-autonomous actions of SSRI antidepressant treatment
Kellermann group 14
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Other diagrams
Samuels & Hen, Eur J. Neurosci, 2011
Adult Neurogenesis
Inside-out actions would occur here
Gene activation is too brief to account for the “therapeutic lag”
Axonal transport provides a natural delay in the “inside-out” mechanism.
Speed: ~ 1 mm / day.
Suggests that equivalent effects would require briefer delays in animals with shorter axons
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Marks et al, 1985
Dendritically localized events
Days of nicotine infusion
Mouse hippocampus
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How does acute ketamine produce antidepressant effects within 2 hr?
Monteggia & Duman groups suggest . . .
(1) involve BDNF synthesis & release, (2) occur in the dendrites,(3) require protein synthesis, (4) do not require gene activation.
The effects
NMDA Receptor
kinases↓
BDNFsecretion
BDNF mRNA
BDNF↑
Dendritic Golgi
Outside-in
Ca2++
Decreased Ca2+ flux
DendriticER
COPII
BDNF mRNA
p-eIF2α↓
pPERK↓
Escorting
BDNF secretion
BDNF↑
Inside-out
BiP
PERKIRE1
H+
+
ER
+ +
+
+ +
NMDA Receptor
NH2+
H3C
H+
O
Cl
NHH3C
O
Cl
We suggest . . .
“Acid trapping” of nicotine might1.keep nAChRs
desensitized untilthey are exocytosed;
2.serve as a reservoir for nicotine
Cell nACh
R membrane
Clathrin
Endoplasmic reticulum
nAChR
Secretory vesicle
COPII
Golgi complex
COPI
Early endosome
COPI
Lysosome
pH
5.2 100
6.0 30
6.7 3
6.3 20
6.5 10
7.2 1
nic+
nicCSF
Nicotine in CSF
NH+
N
H+
N
N
See detailed calculations for antipsychotics:Tischbirek et al, Neuron 2012
7.2 1 &
What knowledge do we need next?
As usual, we need cell biology & biochemistry
1. Reconstituted, cell-free systems for ER exit and retrieval
2.Better real-time markers for compartmentalized receptors and transportersa. Imaging mass spectrometryb. Plasma membrane binding only? Possible with impermeant derivativesc. ER binding only? More challenging, especially for antagonists.
3.Better measurements of pathway-specific gene activation (RNA-Seq)
4.Analyze newly synthesized proteins
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Polygenicthe disease occurs only if several genotypes are present together
Genetically Multifactorialseveral distinct genes (or sets of genotypes) can independently cause the disease
Partially penetrantnongenetic or epigenetic factors are required, or the disease is inherently stochastic
PolygenicGenetically Multifactorial
PartiallyPenetrant
Three concepts used in describing complex diseases such a schizophrenia
Contemporary ideas about psychiatric diseaseshave emphasized synaptic and signaling deficits . . .
“Inside-out” mechanisms emphasize that ~30% of a cell’s proteins enter the ER,
and additional nuclear and cytoplasmic proteins control their synthesis & trafficking.
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GABAergic “chandelier cell” in human cerebral cortex hasmany large axon terminals . . .
DeFelipe, Brain (1999) 122, 1807 (Cajal Institute, Madrid)
PyramidalCells
Ch terminals
~ 100 μm
Ch terminals
Ch axon
. . . and plentiful somatic ER
Jones, J. Comp. Neurol., 1984
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Bi/CNS 150
End of Lecture 29.5