DOE Animal Imaging Meeting May 20, 2004

Martin G. PomperJohns Hopkins University

Imaging Awake AnimalsImaging Awake Animals

Utility of small animal imaging

longitudinal studies – own control

fewer, readily available animals (rodents)

transgenic and other models of human disease

dedicated systems: no competition with clinic

more physiologically relevant milieu to study systems, e.g., protein-protein interaction, gene expression

Ben Tsui

Venu Raman

Ron Mease

SAIRP: structure

Current, active collaborators

Hyam Levitsky (oncology)T-C Wu (pathology)Bert Vogelstein (oncology)Richard Ambinder (oncology)John Laterra (oncology, KKI)Chi Dang (hematology)Edward Gabrielson (pathology)Kathleen Gabrielson (comparative med.)Manuel Hidalgo (oncology)Pete Pederson (biological chemistry)Kwamena Baidoo (SPH - radiochemistry)Tom Guilarte (SPH - toxicology)Srinivasa Raja (neurology)Jun Liu (pharmacology)Jin Zhang (pharmacology)Linzhao Cheng (ICE)Ron Rodriguez (urology)

Drew Weisenberger (Jefferson Natl. Labs)Carolyn Bertozzi (Univ. California, Berkeley)Stan Majewski (Jefferson Natl. Labs)Mark Williams (Univ. Virginia)Juri Gelovani (MD Anderson Cancer Center)Steve Michnick (Univ. of Montreal)Alan Kozikowski (Univ. Illinois, Chicago)AstraZenecaGlaxoWellcome

Inside Outside

New antibody-based imaging agents

Molecular target

[131I]anti-TEM7 tumor endothelium [125I]anti-claudin 4 pancreatic carcinoma [125I]anti-PSCA pancreatic carcinoma New cellular imaging agent

[125I]C. novyi spores C. novyi Conventional agents

[64Cu]ATSM hypoxia [64Cu]PTSM perfusion [18F]KF bone [15O]H2O perfusion [125I]anti-CD20 lymphocytes [131I]anti-CEA colon cancer [99m Tc]annexin V phosphatidyl serine (apoptosis) [125I]FIAU HSV1-TK [11C]raclopride * D2-dopamine receptors [11C]PK111 95* PBBR (inflammation) [11C]WIN 35,428 * dopamine transporters [11C]carfentanil * μ- opioid receptors [18 ]F fluorodeoxyglucose glucose metabolism * ( , , , )PET Center Dannals Ravert Mathews Smoot

Radiopharmaceutical synthesis: JHU SAIRP

Radiopharmaceutical synthesis: JHU SAIRP

New Receptor-based radiotracers

Molecular target

[11C]DCMC glutamate carboxypeptidase II [125I]ZJ-17 glutamate carboxypeptidase II [11C]GW7845 PPARγ [11 ]C AR - 26500R α7- nicotinic cholinergic receptor [11 ]C AR - 27159R α7- nicotinic cholinergic receptor [125 ]I AR- 26855R α7- nicotinic cholinergic receptor [125 ]I AR- 27184R α7- nicotinic cholinergic receptor [125 ]I phos-FLAG cell surface azidosugars [11 ]C paclitaxel P-glycoprotein ([18 ] 665017)F M α7- nicotinic cholinergic receptor ([18 ] )F FBnDCMC glutamate carboxy peptidase II

What is anesthesia?

change in bilayer properties (Meyer-Overton)

receptor-mediated phenomena:

inhibition of currents in excitatory ligand gated ion channels (LGICs)

excitation of inhibitory channels

receptor desensitization by neurotransmitters in membranes

Why anesthesia in imaging?

decrease motion artifact (especially for functional MR imaging)

decrease pain and stress?

Indications for awake imaging

avoid influence of anesthesia on: blood flow, metabolism, neural-vascular coupling

elucidate disease pathophysiology

drug/radiopharmaceutical development

mimic the human state

Effects of anesthesia: brain

blood flow/metabolism effects depend on the dose and type of anesthetic used

cerebrovascular reactivity to CO2 is perturbed by anesthetics

suppression of neural activity

how is global vs. regional CBF modulated by anesthetics?

species/strains have different sensitivities to anesthesia

Effects of anesthesia on cerebral blood flow

anesthetic effect on CBF

isoflurane ↑↑chlor al hydrate =α-chloralose ↓propofol ↓se vofl urane ↓pentobarbital ↓↓

Reversal of rCBF responses due to levodopa

(Hershey T, et al., Exp Neurol 2000;

166:342)

Magnitude vs. increment in functionalbrain imaging

(Shulman RG, et al. PNAS 1999; 96:3245)

Anesthetic and dosage effectOn rCBF in humans by SPM

(Kaisti K, et al. Anesthesiology2002; 96:1358)

Task

BrainElectricalResponse

fMRI Data

??

??

Isoflurane: increases rCBF but decreases metabolism

FDG in awake rats: state-of-the-art

(Kornblum, et al. Nat Med 2000; 18:655)

(Clin Pharm 2001; 41:64S)

Extracellular dopamine assessed with PET

TYROSINE

DA

DOPA

DA

DA

DA

MAO

DOPAC

DA

TYROSINE

DA

DOPA

DA

DA

DA

MAO

DOPAC

DA

DADA DA DA

DA

DADAmethylphenidate

CONHCH2

ClCl

O11CH3HO

NC2H5

H

[11C]raclopride

CONHCH2

ClCl

O11CH3HO

NC2H5

H

[11C]raclopride

RRRRRR

(Courtesy: Joanna Fowler, BNL)

Receptor occupancy: dose finding

generate time-activity curves (TACs) over ROIs, e.g., cortex and cerebellum

apply an appropriate model to the TAC data:

generate receptor occupancy (RO) from the model parameters using binding potentials estimated at baseline (BP0) and after administering drug (BPdrug):

RO% = 100 *

BP0 - BPdrug

BP0

Ca Cf Cbk2

K1 k3

k4

Anesthesia effects on receptor-basedimaging: dopaminergic transmission

augmentation of increased DA by cocaine or GBR12909 (DAT) by isoflurane

cocaine had no effect on 11C-raclopride (D2DR) binding in the awake state

Explanation: isoflurane enhances NO synthesis (induced by glu transmission and production of NOS) – NO facilitates uptake of DA transporter ligands by DAT

Conclusion: indirect effects between isoflurane and DAT inhibitors must be taken into account

(Tsukada H, et al., Brain Res 1999; 849:85)

decreased 11C-raclopride was demonstrated after amphetamine under ketamine but not under halothane

Explanation: halothane promotes conversion of D2 receptors to a low-affinity state (for DA)

Question: is 11C-raclopride binding a) increased under halothane, b) decreased under ketamine or c) both?

{Answer: need to do awake imaging study}

Anesthesia effects on receptor-basedimaging: dopaminergic transmission

(Ginovart N, et al., Neuropsychopharmacology 2002; 27:72)

11C-Raclopride for D2DR in rat striatum

Transaxial

Coronal

High specific activity study

Blocking study(1 mg/kg cold RAC)

0

50

100

150

200

250

300

350

400

450

500

0 10 20 30 40 50 60

StriatumCortex

time (min)A

vera

ge

cou

nts/

pixe

l

Time-activity curves from HSA studyTime-activity curves from HSA study

Time (min)

(Jae Sung Lee)

isoflurane and sevoflurane inhibit agonist binding to nAChRs

propafol reduces mAChR availability (by 11C-methyl-benztropine PET) to mediate unconsciousness

Anesthesia effects on receptor-basedimaging: other receptor systems

11C-NMPYB can measure increased endogenous brain ACh levels after phenserine (AChE inhibitor) treatment

Imaging AChE inhibition with small animalPET: a cautionary tale

(Ma B, et al., Nucl Med Biol 2004; 31:393)

Imaging AChE inhibition with small animalPET: a cautionary tale

The brain isn’t everything

(Toyama H, et al. Nucl Med Biol 2004; 31:251)

(Yang X-P, et al. Heart Circ Physiol 1999; 46:H1967-H1974)

echocardiography

ATLAS small animal PET

Conclusions

Anesthesia has varied and often inconsistent effects on physiology not only inherently, but also due to inter-institutional differences in administration.

Those effects are dose, species and strain dependent.

The mechanism of action of various anesthetics, not to mention the effects on physiology, are poorly characterized.

Awake animal, including small animal, imaging is feasible for a number of modalities and can eliminate this confound.

CA 92871