Modeling and analysis of PET studies with norepinephrine transporter (NET) ligands: The search for a reference

region

J Logan,Yu-Shin Ding, Kuo-Shyan Lin, Deborah Pareto, Joanna Fowler, Anat Biegon

Brookhaven National Laboratory

• Monoamine transporters remove neurotransmitters from synapse: SERT, DAT and NET

• Widespread distribution of NETs: thalamus, brain stem, cerebellum, frontal cortex,cingulate

• NET densities lower than DAT Bmax in basal ganglia

Problem:Many NET ligands exhibit a high and nonuniform (nonNET binding) which makes the identification of a reference region difficult.

The use of a reference region increases reproducibility of the outcome measure in test/retest studies

Why do we need a reference region?

NET tracers *(S,S)-[11C]-methyl reboxetine (SS-MRB)

(R,R)-[11C]-methyl reboxetine (RR-MRB)

[11C]-Nisoxetine (NIS)

(S,S)-[18F]fluororeboxetine (SS- FRB)

(R,R)-[18F]fluororeboxetine (RR- FRB)

Measured arterial input functions corrrected for metabolites

Methods:PET studies

Subjects (baboons): *Friendly, April, Chloe, Jess, Spicey

k6

NN

NETNS/FCp

K1

k2

k3

k4

k5

Model of NET ligand binding

2 1dROI k ROI K Cpdt

22 (1 )NN NET

kkBP BP

5 3

6 4

NN NETk kBP BPk k

1 2( / )(1 )NET NNDV K k Bp Bp

NET+ NN+NSCpK1

2k

wm occ bg tmp cng par cb fc mb thl

DV

0

2

4

6

8

10

12

14

thalamus (thl) 9.62 ± 2.53 cerebellum (cb) 6.89 ± 1.79 cingulate gyrus (cng) 6.32 ± 1.35 basal ganglia (bg) 5.58 ± 1.31 occipital cortex (occ) 5.40 ± 1.20 frontal cortex (fc) 5.05 ± 1.36

Average DV for (S,S)-[11C]-MRB Baseline (n=18, 6 baboons)

0 2 4 6 8 10 12 14 16 18 20

DV

2

4

6

8

10

12

14

16Friendly

AprilSpicey

Alecia

DaisyJess

thl

occ

Variation in DV between studies for thalamus and occipital cortex for SS-MRB

Study number

Why a reference region is needed

Blocking experiment to identify reference region

Experimental: PET studies with SS-MRB

(1)Baseline study

(2)Pretreat with cocaine (0.2, 0.4 or 0.8 mg/kg 5 minutes prior to the injection of the tracer

Cocaine is a non-selective inhibitor of DAT, SERT and NET

Reboxetine is a specific NET inhibitor with a high affinity and high selectivity

wm occ bg tmp cng par cb fc mb thl stm

% c

hg in

DV

with

Coc

-50

-40

-30

-20

-10

0

10

20

30

wm occ bg tmp cng par cb fc mb thl stm

% c

hg in

DV

with

Coc

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-40

-30

-20

-10

0

10

wm occ bg tmp cng par cb fc mb thl stm

% c

hg in

DV

with

coc

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-30

-20

-10

0

10

% Change in DV of (S,S)-MRB after Pretreatment with Cocaine

a. % chg in DV with 0.2 mg cocaine n=4 b. % chg in DV with 0.4 mg cocaine n=3

c. % chg in DV with 0.8 mg cocaine n=4

basal ganglia (bg), occipital cortx(occ), frontal cortx (fc) thalamus (thl), midbrain (mb), brainstem (stm),

DV ratio bg/occ (n= 18) 1.03 0.096 Friendly 1.19 0.07 Jess 1.05 0.05 April 0.99 0.06 Spicey 0.93 0.02

Using the composite REF the coefficient of variation (CV) for thl was reduced from 0.25 for the DV to 0.14 for the DVR

Smallest changes occurred in bg and occ for cocaine doses of .4 and .8 mg/kg

Observations

Reference region: (bg+occ)/2

Average DVR for (S,S)-[11C]-MRB Baseline (n=18)

REF=(occ+bg)/2

wm occ bg tmp cng par cb fc mb thl

DVR

0

1

2thl 1.76 ± 0.24 cb 1.28 ± 0.10 cng 1.16 ± 0.14 bg 1.01 ± 0.05 occ 0.98 ± 0.06 fc 0.92 ± 0.14

occ bg tmp cng par cb fc mb thl

DVR

0

1

2 SS mean (n = 7) RR mean (n = 2)

(SS RR) MRB SS MRB Pretreat with nisoxetine *

DVR for SS and RR MRB for “Friendly”

*nisoxetine binds a single class of saturable sites associated with NE uptake (Tejani-Butt, 1991)

occ bg tmp cng par cb fc mb thlD

VR0

1

2

Baseline Pretreat

occ bg tmp cng par cb fc mb thl

DV

0

1

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6

SS DV (n=5)RR DV (n=1)

occ bg tmp cng par cb fc mb thl

DVR

0

1

2

DVR SS (n=5)DVR RR (n=1)

Baseline DV and DVR for (S,S) and (R,R) [18F]-FRB

occ bg tmp cng par cb fc th

DV

0

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4

6

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10

12

occ bg tmp cng par cb fc thl

DVR

0

1

2

DV DVR (occ+bg)/2

Baseline DV and DVR for [11C]-NIS

1

2

1 S NNT T

KDV Bp Bpk

1

2

1 NNREF REF

KDV Bpk

Target Reference

(1 ) 1 /(1 )(1 )

NNNET NNT T

TNNREF REF

DV BpDVR Bp BpDV Bp

Summary(1)Large variation in DV of SS-MRB for a single baboon.

Reduced by using a reference region => a major source of variability is global, common to both regions and cancels in the ratio.

(2)The use of the avg of BG and OCC appeared to be better than either one alone to compensate for individual differences.

(3) NN binding varies with ligand. SS-MRB better than NIS or FRB. NIS pretreatment in SS MRB study did not appear to alter NN binding but reduced NET binding resulting in binding profile like the RR MRB cmpd

(4)Advantages of SS-MRB (a) Lower NN binding (b) Kinetics permit DV determination with 11C label 

Brookhaven Center for Translational Neuroimaging

Funded by DOE-OBER, NIH and ONDCP

David Alexoff, Karen Apelskog, Nicole Barbarich, Helene Benveniste,Anat Biegon, Elisabeth Caparelli, Pauline Carter, Stephen Dewey, Yu-Shin Ding, Congwu Du, Richard Ferrieri, Bernd Foerster, Joanna Fowler, John Gatley, Andrew Gifford, Rita Goldstein, Bud Jayne, Kun-eek Kil, Sunny Kim, Payton King, Nellie Klein, Aarti Kriplani, Kuo-Shyan Lin, Jean Logan, Jeming Ma, Doug Marsteller, Martine Mirrione, Lisa Muench, William Rooney, Colleen Shea, Wynne Schiffer, David Schlyer, Mike Schueller, Sepi Shokouhi, Dardo Tomasi, Frank Telang, Paul Vaska, Nora Volkow, Gene-Jack Wang, Donald Warner, Chris Wong, HaiTau Wu, Youwen Xu, Wei Zhu