PET i neuroscience nu och i framtiden Lars Farde Professor of - - PowerPoint PPT Presentation

Lars Farde

Professor of Psychiatry, Karolinska Institutet Chief scientist, AstraZeneca TSC at KI

PET i neuroscience – nu och i framtiden

Nuklearmedicinens dag, Malmö, 2014-09-17

PET- publications in MedLine (2010)

Number of publications

Oncology (total 2765 publ.) Neurology+psychiatry (total 3900 publ.) Immunology (total 1347 publ.) Hematology (total 322 publ.) Cardiology (total 576 publ.) Respiratory (total 724 publ.) Neurosurgery (total 998 publ.)

MedLine search ”positron emission tomography” AND ”[organ]”

Brain 31.13% Cancer 37.10% Lung 9.33% Kidney 1.72%

March 2013

As of today: Major applications of molecular imaging in drug discovery and development.

• Microdosing
• Drug occupancy at target of interest
• Biomarkers of pathophysiology

Microdosing

• Brain exposure is critical for CNS-drugs
• Low brain exposure - a significant reason for failure
• Taylor E.M. (2002) Clin. Pharmacokinet. 41:81-92.
• Can be controled for by PET-microdosing
• Injection IV of less than 1 microgram of labeled drug
• Primate study
• CNS drug (mGluR5)
• High brain exposure
• Primate study
• Drug for a peripheral target (CB1)
• Low brain exposure

Whole body PET-imaging 60 minutes after oral administration of an F-18 labeled drug.

High Low

….two hours later

High Low

Major applications of molecular imaging in drug discovery and development.

• Microdosing
• Drug occupancy at target of interest
• Biomarkers of pathophysiology

Haloperidol, 4 mg/d Control

11C]raclopride binding to D2-dopamine receptors

Farde et al, 1986

Raclopride is an original synthesis from former Astra in Södertälje

20 40 60 80 100 4 8 Dose; plasma concentration D2 receptor occupancy (%) Antipsychotic effect EPS

Suggested thresholds for antipsychotic effect and extrapyramidal side-effects (EPS)

Farde et al, Arch Gen Psych,1992, ”citation classique”

18/09/2014 Simon Cervenka 12

Drug target occupancy

A measurable link between pharmacokinetics and pharmacodynamics

Haloperidol, 4 mg/d Control

11C]raclopride binding to D2-dopamine receptors

Farde et al, 1986

Raclopride is an original synthesis from former Astra in Södertälje

The human genome

• About 20.500 protein-encoding genes

Clamp et al, PNAS, 2007

• A third of them are expressed in brain
• Accumulated portfolio of industry
• Binds to 473 proteins (Drews et al, 1996)

Examples of original radioligand development at Karolinska Institutet 1982-2010

Monkeys

• 160 radioligands examined

after radiolabelling Man

• 38 radioligands examined
• 16-18 validated and suitable

for applied studies world wide

• D2-dopamine
• [11C]raclopride (1985)
• [11C]FLB457 (1997)
• D1-dopamine
• [11C]SCH23390 (1985)
• [11C]NNC112 (1995)
• Dopamine transporter
• [11C]PE2I (2004)
• Serotonin transporter
• [11C]MADAM (2003)
• Serotonin 5HT2a
• [11C]MDL100907 (1997)
• Benzodiazepine
• [11C]Flumazenil (1986)
• [18F]Flumazenil (2006)
• Norepinephrine transporter
• [18F]FD2MeNER (2006)
• Serotonin 5HT1b
• [11C]AZ10419369 (2008)
• Amyloid Plaque
• [11C]AZD2184 (2008)
• [18F]AZD4694 (2009)

The global toolbox targets about 50 brain proteins

Haloperidol, 4 mg/d Control

11C]raclopride binding to D2-dopamine receptors

Farde et al, 1986

Scanditronix PC384-15B 384 detectors 8-11 mm FWHM

18 september 2014 Andrea Varrone 17

High Resolution Research Tomograph (2008)

• Dedicated for neuroimaging
• 120.000 detector elements
• Fully operational Jan 2008
• Highest resolution in series (2.0 mm)
• New reconstruction principle (PSF)

provides improved resolution (1.5 mm)

High resolution imaging of [11C]flumazenil binding to benzodiazepine receptors

[11C]flumazenil HR [11C]flumazenil HRRT [18F]flumazenil Autoradiography

GABAA receptors in vivo and in post-mortem human brain

From Fuchs and Flügge, Dialogues Clin Neurosci. 2004;6:171-183.

Monoaminergic innervation of the human brain

• The shared
• rganization may

reflect phylogenesis

• Implicated in

fundamental functions, i.e adaptation to environment, emotions etc

• Functions that are

impaired in major psychiatric disorders

PET imaging of brainstem nuclei:

18 September 2014 Martin Schain 21

**: p<0.01 ***: p<0.001

• High resolution PET imaging and WAPI enables

images with enough resoltion and contrast for identification of the small brainstem nuclei.

• The difference between HR and HRRT PET

systems (~30-40%) is attributable to their disparate resolutions, providing support for that the estimated values are realistic.

• The method allows for quantification of radioligand

binding in small brainstem structures

Major applications of molecular imaging in drug discovery and development.

• Microdosing
• Drug occupancy at target of interest
• Biomarkers of pathophysiology

[18F]FE-PE2I – a new selective radioligand for the dopamine transporter (DAT)

Sasaki et al, J Nucl Med

• Best in class of the more than 15 PET- and SPECT-ligands developed since 1989.
• Together with HRRT: Detailed mapping of regional DAT binding in PD

Varrone et al, 2011, Ito et al 2013

Control H&Y 1 H&Y 2 H&Y 1.5 BPND Parkinson

[18F]FE-PE2I binding to DAT in PD

Control PD H&Y 1

BPND Figure . A) Representative [18F]FE-PE2I parametric images of binding potential (BPND) in one control subject and one PD

• patient. B) [18F]FE-PE2I BPND values in different brain regions in controls and PD patients.

A B

↓ 33% p<0.05 ↓ 70% p<0.05 ↓ 35% p<0.05 ↓ 28% n.s.

Regional Dopamine Transporter binding in PD

Manuscript in prep, Varrone et al

Samantha Budd, 2008-11-05

Klunk et al, Annals of Neurol. 55, 2004

[11C]PIB - the first ligand for imaging of amyloid deposits in Alzheimers disease

[11C]PIB FDG

Control AD

27 18/09/2014 LF

Using rational design to design a second generation amyloid PET radioligands

Testing of 1,000’s compounds since 2003

AZD2184

11C- amyloid PET ligand

AZD4694

18F- amyloid PET ligand

[18F]AZD4694

[18F]AZD4694

• 10
• 9
• 8
• 7
• 6
• 5
• 4

[18F]AZD4694 showing amyloid deposits in Alzheimers Disease

18/09/2014 Simon Cervenka 29

Species differences

• Rule rather than exception !
• regional expression
• regional density

PET: 10MBq 18FDG, Resolution ~ 0.7 mm

CT

• Morphology with

high resolution

CT-PET

• Morphology with

high resolution

• Function with high

sensitivity

CT-PET-MR

• Morphology with high resolution
• Function with high sensitivity
• Added soft tissue contrast

Combined whole-body CT-PET-MR examination in vivo in mice using the nanoScan system (2012)

Human subjects µPET PET Molecular imaging Non-human primates Post mortem In vivo Rodents:

TG and WT

Post mortem brain studies

microdosing, occupancy, Longitudinal studies on disease biomarkers

PET

Autoradiography, immunohisto- chemistry, etc.

Translational molecular imaging

*all examples show raclopride binding to D2-dopamine receptors

[11C]raclopride binding to D2- dopamine receptors in the rat brain

Dorsal striatum Accumbens

<0.1µg 0.88µg 2.86µg

MRI

Häggkvist et al, manus in prep.

”Neuroinflammation”

Autoradiography in control brain in vitro (3H-PK11195) TSPO localisation in mitochondria

Doble et al 1987 Papadopoulos et al 2006

TSPO – marker for microglia

(The peripheral benzodiazepine receptor)

• The Translocator Protein (TSPO) serves as a marker for microglia (monocytes)
• Functions: Cholesterol transport, immunomodulation, protein import, apoptosis, cellular

respiration/oxidative stress

Microglia has been implied in the pathogenesis of: Multiple sclerosis Alzheimer´s disease Parkinson´s disease Depression Schizophrenia Stroke Epilepsy Amyotrophic lateral sclerosis Corticobasal degeneration Huntington´s disease HIV dementia Hepatic encephalopathy Glioma

Banati et al, 2002

PET radioligands for TSPO

• a marker for microglia

Reference radioligand [11C]PK11195 Ki = 4.5 nM, cLogP =5.3 Second generation radioligands [11C]DAA1106 [18F]FEDAA1106 [11C]DPA713 [11C]CLINME [11C]PBR28 Ki = 0.9 nM, cLogP =3.0

36

By courtesy of Bob Innis and Vic Pike, NIMH

[11C] PBR28 binding

38

High resolution imaging of [11C]PBR28 binding to TSPO in brain

• Control subject, summation images of radioactivity 9-90 minutes after i.v. bolus injection of 359

MBq [11C]PBR28

• High binding in lymphoid tissue in the neck region
• Lymphoid tissue is rich in macrophages

TSPO at baseline: effect of SNPs

• large interindividual variability in

binding affinity: a trimodal distribution

• f high-affinity binders (HABs), low-

affinity binder (LAB), and mixed-affinity binders (MABs).

• polymorphism (rs6971) located in exon

4 of the TSPO gene, results in a nonconservative amino-acid substitution from alanine to threonine (Ala147Thr) in the TSPO protein. predicts total distribution volume in human brains

39

Plasma-input based wavelet aided parametric images (PWAPI) overlaid in color on structural MRI in greyscale. PWAPI fitting Logan between 14-60 min

HAB MAB LAB

2 4 6 8 Volume of Distribution (ml/cm3)

[11C]PBR28 binding phenotype in relation to TSPO genotype

[11C]PK11195 binding to TSPO in PD

• PET- Striatum
• Increased TSPO signal in early (Ouchi et al 2005) and advanced PD (Gerhard et

al, 2006; Bartels et al 2010) Stable over up to 2 years (Gerhard et al)

• PET- Midbrain (Substantia nigra)
• Increased TSPO signal in early PD, (Ouchi et al, 2005); early and advanced

(Bartels et al 2010), No significant increase (Gerhard et al, 2006)

TSPO binding in PD using [11C]PK 11195

Gerhard et al. Neurobiol of Disease 2006;21:404–412

PD

Controls

• Increased binding in disease related regions
• No correlation with disease severity or

duration

MPO inhibition reduces oxidative stress, microglia activation and neurodegeneration – simplified model

MPO-mediated oxidative stress  ROS, RNS (e.g. HOCl, HOSCN, NO2)

Microglial activators:

e.g. cell debris, MMP’s (activated by MPO), nitrated α-synuclein aggregates (MPO involvement)

Neuronal death/damage

Nitrated α-synuclein  α-synuclein aggregation

DAT 

Microglial activation

(MPO localised to microglia in PD/MSA)

CD11b  CD68  TSPO 

Hypothesis: MPOi  reduction of oxidative stress  decreased α–synuclein aggregation, neuronal dysfunction / death and microglia activity  reduced PD pathology

Block et al. Nature Reviews Neuroscience 8, 57–69 (January 2007)

VT change in % at treatment with AZD3241, mean, n=18

44

Caudate Putamen Striatum Substantia nigra placebo AZD3241 placebo AZD3241 placebo AZD3241 placebo AZD3241

Jucaite et al, in prep

Acknowledgements

• Karolinska Institutet
• Christer Halldin
• Andrea Varrone
• Balazs Gulyas
• Simon Cervenka
• Sjoerd Finnemaa
• Anton Forsberg
• Karin Collste
• Akihiro Takano
• Katharina Varnäs
• Patrik Fazio
• Per Svenningson
• AstraZeneca TSC at KI
• Peter Johnström
• Aurelija Jucaite
• Zsolt Cselenyi
• Magnus Schou