1. Positron Emission Tomography: Tool to Facilitate Drug Development and to Study Pharmacokinetics Robert B. Innis, MD, PhD Molecular Imaging Branch National Institute Mental Health

2. Outline of Talk 1.PET has high sensitivity and specificity 2.PET used in therapeutic drug development 3.Pharmacokinetic modeling of plasma concentration and tissue uptake can measure receptor density 4.Study drug distribution: “peripheral” benzodiazepine receptor 5.Study drug metabolism: inhibit defluorination

4. Positron Emission Tomography

5. PET vs. MRI PETMRI Spatial Resolution 2 – 6 mm<< 1 mm Sensitivity10 -12 M10 -4 M Temporal Resolution minutes<1 sec Radionuclide ( 11 C): high sensitivity Ligand (raclopride): high selectivity Radioligand [ 11 C]raclopride: high sensitivity & selectivity

6. Radioligand = Drug + Radioactivity 1.Drug administered at tracer doses a)No pharm effects b)Labels <1% receptors c)Labeled subset reflects entire population 2.Radioligand disposed like all drugs a)Metabolism & distribution 3.Radiation exposure

7. NIH Rodent PET Camera 18 F bone uptake rat Developed By: Mike Green & Jurgen Seidel

8. PET: Tool in Therapeutic Drug Development Determine dose and dosing interval Identify homogeneous group Biomarker for drug efficacy Monitor gene or stem cell therapy

9. Lazabemide blocks [ 11 C]deprenyl binding to monoamine-oxidase-B (MAO-B) Selegilene is more potent and longer acting than lazabemide

10. PET: Tool in Therapeutic Drug Development Determine dose and dosing interval Identify homogeneous group Biomarker for drug efficacy Monitor gene or stem cell therapy

11. Dopamine Transporter: Located on DA Terminals Removes DA from Synapse

12. SPECT Imaging of Dopamine Transporter in Caudate and Putamen of Human Brain

13. Healthy Parkinson Stage 1 123 I-β-CIT Dopamine Transporter SPECT: Decreased in Parkinson’s Disease

14. PET: Tool in Therapeutic Drug Development Determine dose and dosing interval Identify homogeneous group Biomarker for drug efficacy Monitor gene or stem cell therapy

15. Serial Dopamine Transporter Imaging in a Parkinson Patient Institute for Neurodegenerative Disorders

16. PET Imaging of Amyloid: Biomarker for Alzheimer’s Disease

17. PET: Tool in Therapeutic Drug Development Determine dose and dosing interval Identify homogeneous group Biomarker for drug efficacy Monitor gene or stem cell therapy

18. Viral vectors deliver gene that synthesizes dopamine (DA) Infuse virus into striatum (target cells) Target cells express the DA gene Gene Therapy Using Viral Vectors

19. Control Gene: Lac-Z postpre DA Synthesis Gene: AADC pre post PET Dopamine Imaging in Hemi-Parkinson Monkey: Monitors gene for DA synthesis in right striatum

20. NormalUnilateral Lesion Embryonic Stem Cells PET & MRI PET Imaging to Monitor Embryonic Stem Cell Treatment of “Parkinson Disease” in Rats

21. Outline of Talk 1.PET has high sensitivity and specificity 2.PET used in therapeutic drug development 3.Pharmacokinetic modeling: plasma concentration and tissue uptake 4.Study drug distribution: “peripheral” benzodiazepine receptor 5.Study drug metabolism: inhibit defluorination

22. AUC=32 AUC=16 Brain Drug Time Brain Uptake of [ 18 F]Fluoxetine: Measures Density of Serotonin Transporters & Affinity of Fluoxetine Patient Healthy

23. AUC=32 AUC=16 Brain Drug Time Brain Uptake of [ 18 F]Fluoxetine: Measures Density of Serotonin Transporters & Affinity of Fluoxetine PatientHealthy Inject Activity20 mCi10 mCi Patient Healthy

24. AUC=32 AUC=16 Brain Drug Time Brain Uptake of [ 18 F]Fluoxetine: Measures Density of Serotonin Transporters & Affinity of Fluoxetine PatientHealthy Inject Activity20 mCi Patient Healthy

25. AUC=32 AUC=16 Brain Drug Time Brain Uptake of [ 18 F]Fluoxetine: Measures Density of Serotonin Transporters & Affinity of Fluoxetine PatientHealthy Inject Activity20 mCi Weight50 kg100 kg Patient Healthy

26. AUC=32 AUC=16 Brain Drug Time Brain Uptake of [ 18 F]Fluoxetine: Measures Density of Serotonin Transporters & Affinity of Fluoxetine PatientHealthy Inject Activity20 mCi Weight100 kg Patient Healthy

27. AUC=32 AUC=16 Brain Drug Time Brain Uptake of [ 18 F]Fluoxetine: Measures Density of Serotonin Transporters PatientHealthy Inject Activity40 mCi20 mCi Weight100 kg Liver diseaseYesNo Patient Healthy

28. Binding Potential (BP) BP equals uptake in brain relative to how much activity is delivered in arterial plasma AUC=2 Plasma Drug Time Brain Drug AUC=16 Area Brain Curve Area Plasma Curve BP = 16 2 = 8

29. Brain Drug Time Binding Potential: Independent of Injected Dose * Double Plasma Input =>Double Brain Response AUC=32 AUC=16 BP 1st Time = 32 4 = 8 BP 2nd Time = 16 2 = 8 Plasma Drug AUC=2 AUC=4 *If ligand does not saturate receptors - i.e. if tracer doses used

30. What’s So difficult? Limited, noisy data. Plasma Parent Activity Brain Activity Time AUC = ?

31. Tissue uptake is proportional to density of receptors and the affinity of the drug Binding Potential

32. Plasma Brain K1K1 k2k2

33. Outline of Talk 1.PET has high sensitivity and specificity 2.PET used in therapeutic drug development 3.Pharmacokinetic modeling: plasma concentration and tissue uptake 4.Study drug distribution: “peripheral” benzodiazepine receptor 5.Study drug metabolism: inhibit defluorination

34. “Peripheral” Benzodiazepine Receptor 1.Mitochondrial protein highly expressed in macrophages and activated microglia 2.Exists in periphery and brain 3.Multiple potential functions: steroid synthesis, nucleotide transport 4.Distinct from typical benzodiazepine GABA A receptor in brain 5.Marker for cellular inflammation

35. Old and New PBR PET Ligands [ 11 C](R)-PK11195 IC 50 = 0.8 nM* ; cLogP = 5.3 [ 11 C]PBR28 IC 50 = 0.6 nM* ; cLogP = 3.0 New Ligand Aryloxyanilide Structure Higher specific receptor signal Lower lipophilicity

36. PBR Imaging in Cerebral Ischemia Cerebral ischemia (stroke) consists of a necrotic core surrounded by a penumbra with salvageable tissue. Penumbra accumulates a large number of activated microglia.

37. 21 9 5 1 2 4 14 (nCi/mg) B C A (%SUV) 0 300 100 200 [ 11 C]PBR28 PET summation image In vitro [ 3 H]PK11195 autoradiography Cresyl violet staining Contralateral Peri-ischemic area Central ischemic region Radioactivity accumulates in the peri-ischemic area and correlates with PBR receptor autoradiography.

38. 500 250 %SUV 0 [ 11 C]PBR28 Monkey Brain: Total Uptake Nonspecific Uptake: Preblocked with PK11195

39. [ 11 C]PBR01 Time-activity Curves Non-radiolabeled PBR01 1 mg/kg i.v. Baseline scanBlocking scan % standard uptake value (%SUV) 100 %SUV = Average of activity in the whole body High levels of specific binding

40. 2 min 25 min 115 min Brain Lungs Kidneys Heart Liver Gall bladder Urinary bladder Spleen Baseline Blocked PK11195 10 mg/kg Receptor Blockade Displaces from Lung & Kidney Drives More Radioligand to Brain

41. Brain Time Activity Curves 020406080100120 0 50 100 150 200 250 Front. ctx Thalamus White matter Time (min) Activity (%SUV) Lines are unconstrained 2-compartment fits Imaging Peripheral Type Benzodiazepine Receptors Using [ 11 C]PBR28 in Human PET average all frames

42. Subject #1 Subject #2 Total binding Non-specific binding [ 3 H]PK 11195 Receptor Autoradiography: Human Carotid Artery with Plaque

43. Outline of Talk 1.PET has high sensitivity and specificity 2.PET used in therapeutic drug development 3.Pharmacokinetic modeling: plasma concentration and tissue uptake 4.Study drug distribution: “peripheral” benzodiazepine receptor 5.Study drug metabolism: inhibit defluorination

44. [ 18 F]FCWAY: Defluorination Bone uptake: human skull at 2 h

45. [ 18 F]Fluoride Brain Skull Miconazole Inhibits Defluorination & Bone Uptake Temp Ctx Skull [ 18 F]FCWAY: Miconazole Baseline 15 mg/kg 30 mg/kg 60 mg/kg

46. Disulfiram: Decreases Skull Activity & Increases Brain Uptake Baseline Disulfiram Images at 2 h in same subject. Disulfiram 500 mg PO prior night

47. Disulfiram: Decreases skull uptake of fluoride & Increases brain uptake of [ 18 F]FCWAY Skull Temporal Cortex

48. Disulfiram: Decreases plasma fluoride & Increases plasma radiotracer [ 18 F]FCWAY [ 18 F]fluoride [ 18 F]FCWAY (parent tracer)

49. Summary of Talk 1.PET has high sensitivity and specificity 2.PET used in therapeutic drug development 3.Pharmacokinetic modeling: plasma concentration and tissue uptake 4.Study drug distribution: “peripheral” benzodiazepine receptor 5.Study drug metabolism: inhibit defluorination

52. Self-Assessment Quiz: True or False? Positron emission tomography (PET) studies involve the injection of a radioactively labeled drug that emits a particle called a positron. PET shows the location of radioactivity in a cross section (or tomograph) of the body. PET can be used to quantify the density of specific proteins in the body. Compartmental modeling of PET data typically uses measurements over time of 1) PET images of the target tissue and 2) concentrations of unchanged parent radioligand in plasma.