1 chem e-120 harvard university extension school neurodegenerative disorders parkinson’s disease...
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CHEM E-120Harvard University Extension School
Neurodegenerative DisordersParkinson’s Disease
March 30, 2011
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Neurodegenerative DiseasesDue to physical degradation of components of the CNS
Parkinson’s - cell death of dopamine producing neurons in the basal ganglia
Alzheimer’s - neuronal cell death and dysfunction on areas of brain involved with memory and cognition
Huntington’s - neuronal death in cortex, basal ganglia, thalamus, and brainstem
Multiple Sclerosis - loss of the myelin (white matter) sheath on axonsneuroinflammatory disease
Amyotrophic Lateral Sclerosis (ALS, Lou Gehrig’s Disease) general loss of motor system neurons in the spinal cord, brain stem, and motor cortex
Cu-Zn superoxide dismutase (J. Med. Chem. 2010, 53, 1402–1406)
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Motor System
1. Corticospinal tract (formally pyramidal system)descends from the motor cortex terminating in the brainstem and spinal cordvoluntary movement
2. Basal ganglia tract (formally extrapyramidal system)ascend from midbrain cortexself-initiated movement movement sequencingamplitude and velocity of movementautomatic postural and reflex motor activity
Basal Ganglia System
Anatomically divided into 4 structures:a. striatum: caudate nucleus (cognition), putamen (motor), nucleus accumbensb. globus pallidusc. subthalamic nucleusd. substantia nigra
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Thalamus
Cortex
Cortex
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SN
SN Substantia nigra - extrapyramidal nigrostriatal pathwayGPi internal segment of globus pallidusGPe external segment of globus pallidus
striatum
GPi
GPe
excitoryinhibitory
direct pathway (remove brake)indirect pathway (brake)
subthalamicnucleus
Movement Control and Basal Ganglia – Normal Conditions
GPi and SN tonically active ( movement)
dopamine bindingto D1 and D5 excites direct
dopamine binding to D2, D3, D4 inhibits indirect
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Thalamus
Cortex
Cortex
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SN
SN Substantia nigra - extrapyramidal nigrostriatal pathwayGPi internal segment of globus pallidusGPe external segment of globus pallidus
striatum
GPi
GPe
excitoryinhibitory
direct pathway (remove brake)indirect pathway (brake)
subthalamicnucleus
Movement Control and Basal Ganglia – Parkinson’s Disease
GPi and SN tonically active ( movement)
lack of dopamine bindingto D1 and D5 inhibits direct
lack of dopamine binding to D2, D3, D4 disinhibits indirect
reduced
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Parkinson’s Disease
Characterized by neuronal cell death in the substantia nigra pars compacta (~1% cell loss/year nonparkinson’s individuals)
This leads to a substantial loss of neuronal dopamine in basal ganglia. About 80% of neuronal dopamine is in the basal ganglia.
Clinical onset of Parkinson’s noted when ~ 70% of striatal dopamine is lost. ~ 50 - 60% cell death
Loss of dopamine appears to reduce activity direct pathway increase activity indirect pathway
disruption of direct/indirect cycles
Degeneration of cholinergic, adrenergic, serotonergic systems
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Parkinson’s Disease
Effects ~ 1% of population with onset most likely at 55-65 years of age
Resting tremor of ~ 5 HzUnilateral or asymmetric onset of bradykinesia (abnormallyslow voluntary movements)RigidityPostural disturbance
FRONTLINE My Father, My Brother, and Me 2009http://video.mpbn.net/video/1082086931
OnsetMotorcomplications Resistant Symptoms Cognitive Decline
YEARS0
8 13 20 25
DEATH
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Current Drugs for Parkinson’s
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Monoamine Neurotransmitter Levels
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Dopamine
Norepheniphrine
Serotonin
Amg, amygdala; ACC, nucleus accumbens; AP, area postrema; Cer, cerebellum; CIC, cingular cortex; DMN, dorsal motor nucleus of the vagus nerve; EC, entorhinal cortex; FC, frontal cortex; GPe, external segment of globus pallidus; GPi, internal segment of globus pallidus; HI, hippocampus; HY, hypothalamus; LC, locus coeruleus; PU, putamen; Cau, caudate; SN, substantia nigra; PAL, pallidum; POG, parolfactory gyrus; PPN, pedunculopontine nucleus; RN, raphe nuclei; SI, substantia innominata; SC, spinal cord; STN, subthalamic nucleus; VTA, ventral tegmental area.
Nature Reviews Drug Discovery 2006, 5, 845
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Loss of dopamine transporter
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[123I]-β-CITDopaScan
Nature Reviews Drug Discovery 2006, 5, 8453/30/11 CHEM E-120
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Parkinsonism caused by MPTP
Uptake and accumulation in nigrostriatal dopaminergic neurons.
Phase 1 hydrolysis Phase 1 oxidation
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animal treated daily for 7 days with MPTP (30 mg/kg)PNAS 1985, 82, 2173
N
N
Paraquat
Dopamine Centered Medication Development
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Loss of dopamine
Clinical replacementof dopamine
L-DOPA
Prevention ofdopamine metabolism
MAO-B inhibitionCOMT inhibition
Substitution of dopamine
D2 type agonistsD1 type agonistsD3 agonistsDAT/Dopamine release
Current medications relieve symptoms but do not alterthe course of the disease
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L-DOPA
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Currently the medication of choiceProdrug of dopamine, dopamine cannot cross the BBB whereas L-DOPA is transported by aromatic amino acid transporters
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Blood-Brain Barrier (BBB)
A physical barrier that controls the movement of chemicals from extracellular fluid in the body (blood) into the extracellular fluid of the brain.
In the brain the endothelial cells in blood capillaries form a very tight junction that prevents many chemicals from passive diffusion across the capillary cell membrane into the brain.
Lipid-soluble substances can often diffuse across BBB
Active transporters exist in the capillary cell membraneglucoseamino acidshormones
Efflux transporters P-glycoprotein (P-gp)
MRPOrganic anion transporters (OAT3)
Transporters can be on blood side or CNS side of membranes.
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BBB in Capillary Cell
Nature Reviews Drug Discovery 2007, 6, 650
L-DOPA
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Dopa decarboxylase is a cytoplasmic (soluble) enzyme located throughout the body.
Higher levels outside the CNS that reduce levels of L-DOPA by metabolism before it reached the brain. Often requires dosage of 3-6 gms/day.
Adjunct therapy - peripherally active decarboxlyase inhibitorsSinemet – carbidopa (25mg) and levodopa (100mg) 2-3 times day
Clinical Aspects
Side effects usually due to peripherally generated dopamine“Wearing off” phenomenaIncreasing dosage can lead to dyskinesias – excessive and abnormal involuntary movementsOn/off phenomena Extended release form of Sinemet
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Metabolic Inhibition and Oxidative Stress
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Dopamine is readily oxidized to reactive intermediate
Consideration of MPTP suggests that metabolic stress may play a role on Parkinson’s Disease
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MAO-B Inhibitors
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Selective, irreversible inhibitor of MAO-B at <10mg/day. MAO-B predominate isoform in CNS.
Used in combination with L-DOPA. Proposed to increase dopamine levels and act as neuroprotective agent.
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Dopamine Agonists
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Used alone in early stage Parkinson’s and with L-DOPA in advanced stages
Striatum D1 >> D5 D2 > D3
D2 antagonists know to produce Parkinson-like effectsD1 partial agonists shown not to be effective
D2 agonists therefore of interestD3 agonists were found to posses efficacy
Efficacy of D1 activation appears less than D2 activation making D1 more susceptible to lower dopamine concentrations
Phenotype effects in knockout mice
D1 reduced agonist response, hyperlocomotionD2 Parkinsonian-like motor impairmentD3 HyperactivityD4 reduced locomotion, hypersensitivity to ethanol and stimulantsD5 reduced agonist induced locomotion, startle, and prepulse inhibition
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Ergot Akaloids – Dopamine Agonist
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Bromocriptine (Parlodel)1967
D1-type partial agonistD2-type full agonist5-HT agonist
Pergolide (Permax)
D1-type agonistD2-type full agonist5-HT agonist
Cabergoline(Dostinex)
Lisuride
Ki (nM)
D1 D2 D3
Dopamine 2729 146 69
Bromocriptine 120 4.9 30
Cabergoline 1462 1.6 1.3
Lisuride 57 1.2 1.1
Pergolide 447 37 0.863/30/11 CHEM E-120
D3 Agonists – Pramipexole (Mirapex)
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Approved in 1997
Bioisostere
Ki D2 = 7 nM D3 = 0.97 nM
Ki D2 = 1 nM D3 = 0.2 nM (agonist)
aminotetralinDual agonist effects at D3 and D2
D3 stimulation may potentiate direct pathwayD2 stimulation may attenuate indirect pathway
D3 is highly expressed in limbic system – some antidepressant effect
Potential antioxidant effect, Oxidation potential ~ 0.32 V vs 0.6 V dopamine water soluble, F = 90%
Journal of the Neurological Sciences 1999, 163, 25.
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D3 Agonists
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J. Med. Chem. 2005, 48, 5771-5779
occupation of a1 thought to beimportant for these compounds
a1 not fillednot important?
Ki D3 0.88 nM 5.3 nM 0.2 nM
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D3 Agonists
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high = ternary complex of ligand, receptor, and G-protein (agonist and antagonist binding)low = (antagonist binding)D2 long = 443 amino acids, postsynapticD2 short = 414 amino acids, presynaptic autoreceptor
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25SYNAPSE 61:1013–1018 (2007)
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J. Med. Chem. 2005, 48, 2493-2508
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D3 Agonists
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J. Med. Chem. 2008, 51, 5905
D3 Ki = 0.41 nMD2 330 nM
D1-like 13000 nM
8 compounds
D3 Ki = 0.78 nMD2 3.1 nMD1-like >100K nM
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D3 homology modelβ2 adrenergic
homology modelrhodopsin
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yawning in ratsis a measure ofD3 agonist activity
induction of hypothermiais an indicationof D2 agonist activity
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Therapeutics of Parkinson’s Disease and Other Movement Disorders Edited by Mark Hallett and Werner Poewe © 2008
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The adenosine A2a receptor is a member of the P1 GPCR family that modulates striatal output in the indirect basal ganglia pathway. Inhibition of adenosine A2a receptors produces motor stimulant effects.
Istradefylline (KW-6002) is an orally available, xanthine-based adenosine A2a receptor antagonist (Ki = 2.2 nM) that is in Phase III clinical trials for PD. It has shown positive benefit in reducing the tremor duration and general slowness/stiffness in advanced PD patients.
Adenosine A2a receptor antagonists
Attenuates MPTP-induced loss ofdopaminergic neurons.antioxidant effect?
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Ki (nM) A2a 2.2 22,000MAO-B 28,000 3.6 mM
O
N
O
S
NNH
NOHO
SYN-115
Synosia – Phase 3
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2011 10.4155/CLI.11.12 © 2011 Future Science Ltd