Pharmaceutical Chemistry Lecture on “PET Tracer Chemistry...
40
1 Slides are not to be reproduced without permission of author. Pharmaceutical Chemistry Lecture on “PET Tracer Chemistry and Imaging in Drug Discovery” Pharmaceutical Chemistry Lecture Pharmaceutical Chemistry Lecture on on “P ET Tracer Chemistry and Imaging in ET Tracer Chemistry and Imaging in Drug Discovery Drug Discovery” J&JPRD East – Research & Early Development J&JPRD East – Research & Early Development Dennis Hlasta March 19, 2008
Transcript of Pharmaceutical Chemistry Lecture on “PET Tracer Chemistry...
1Slides are not to be reproduced without permission of author.
Pharmaceutical Chemistry Lectureon
“PET Tracer Chemistry and Imaging in Drug Discovery”
Pharmaceutical Chemistry LecturePharmaceutical Chemistry Lectureonon
““PPET Tracer Chemistry and Imaging in ET Tracer Chemistry and Imaging in Drug DiscoveryDrug Discovery””
J&JPRDEast – Research & Early Development
J&JPRDEast – Research & Early Development
Dennis Hlasta
March 19, 2008
2Slides are not to be reproduced without permission of author.
New Drug Approvals New Drug Approvals –– Not Keeping Pace with Rising R&D SpendingNot Keeping Pace with Rising R&D Spending
0
15
30
45
60
1963 1968 1973 1978 1983 1988 1993 1998 2003
NC
E A
pp
rova
ls
0
20
40
R&
D E
xpen
ditu
res(B
illion
s of 2004$)
Source: Tufts CSDD Approved NCE Database, PhRMA, 2005
R&D Expenditures
New Drug Approvals
3Slides are not to be reproduced without permission of author.
Emerging DisciplinesEmerging Disciplines –– a Historical Perspectivea Historical Perspective-- that would “individually revolutionize” Drug Discoverythat would “individually revolutionize” Drug Discovery
• Computer Aided Drug Design
• Structure-Based Design
• Molecular Biology
• Genomics / Bioinformatics
• High-Throughput Screening
• Combinatorial Chemistry – Large 20-30K Libraries or Mixtures
– Diversity Enrichment Libraries
• Lab-on-a-Chip
4Slides are not to be reproduced without permission of author.
Comparison of Imaging MethodsComparison of Imaging Methods
Little metabolic information, No drug target information, Cost
Anatomy information,No Radiation,Soft Tissue information
Magnetic Resonance (MRI)
No metabolic information,No drug target information,Poor soft tissue contrast, Radiation Dose
Anatomy information, Bone density
Computed tomography(CT)
Radiation Dose,Cost
Metabolic informationDrug target info. - receptors
Positron emission tomography (PET)
ConsPros
5Slides are not to be reproduced without permission of author.
What is “functional molecular imaging”?What is “functional molecular imaging”?
CT scan
X-ray imaging
Diagnose this patient…
MRI scan
Images H-atom relaxation (water)
PET scan
Images the PET radionuclide location
6Slides are not to be reproduced without permission of author.
1818FDG PET brain scanFDG PET brain scan
• Radioactive analog of glucose
• Measures brain metabolism• Changes in metabolism
resulting from cognitive challenge or drug
PET scan
Images the PET radionuclide location
7Slides are not to be reproduced without permission of author.
What is “molecular imaging”?What is “molecular imaging”?
• Probing biological processes at the molecular level.
• Image these biological processes in 3D.
• Most drugs are designed for a specific molecular target.
• Molecular changes nearly always occur long before improved clinical symptoms.
8Slides are not to be reproduced without permission of author.
How do we do “functional molecular imaging”?How do we do “functional molecular imaging”?
• Use a PET scanner
• Measure the three-dimensional distribution of a radioactively-labeled compound in the body
• Non-Invasive
• Animal studies first, then translate to Human study.
• Depends critically on radiochemistry
9Slides are not to be reproduced without permission of author.
PositronEmissionTomography
10Slides are not to be reproduced without permission of author.
PositronEEEmissionmissionmissionTTTomographyomographyomography
Detects two gamma rays resulting from decay of positron - 511 keV
11Slides are not to be reproduced without permission of author.
PPPositronositronositronEmissionTTTomographyomographyomography
Photons emitted from inside subject - as opposed to
“transmission” where they are generated externally.
12Slides are not to be reproduced without permission of author.
PPPositronositronositronEEEmissionmissionmissionTomography
Generates three-dimensional maps of radioactivity
concentration - tomographic
13Slides are not to be reproduced without permission of author.
Clinical PET scanner
Animal PET scanner
PET ScannersPET Scanners
14Slides are not to be reproduced without permission of author.
[[1818F]F]--FFluorodeoxyglucoseluorodeoxyglucose ((1818FF--FDG)FDG)
• Glucose analog that is taken up by glucose-using cells and phosphorylated by hexokinase.
• Mitochondrial hexokinase is greatly elevated in rapidly-growing cells.
• Because the oxygen atom (which is replaced by F-18) is required for the next step in glucose metabolism, no further reaction occur on FDG.
• FDG is trapped in the cells.
• Results in intense radiolabelling of tissues with high glucose uptake.
• Imaging of Brain, Heart, and Tumors.
OHO
HO
OH18F
OH
Hamacher K. et al. J. Nucl. Med. 1986, 27, 235-238.
15Slides are not to be reproduced without permission of author.
1818FDG PET ImagesFDG PET Images
A typical PET image of the brain examination in transaxial view. Red areas show more accumulated radioactivity and blue areas show where low to no activity was accumulated.
18F-FDG whole body PET acquisition
http://en.wikipedia.org/wiki/Positron_emission_tomography
16Slides are not to be reproduced without permission of author.
FDG PET in Hodgkin's or nonFDG PET in Hodgkin's or non--Hodgkin's lymphomaHodgkin's lymphoma–– diagnosis and treatmentdiagnosis and treatment
http://www.petscan.org/frames_alzh.html
17Slides are not to be reproduced without permission of author.
Lung CancerLung Cancer
Clinical history: This patient was referred for assessment of a mass in the left lung.
Findings: There was high uptake of FDG consistent with lung cancer but no evidence of spread elsewhere. The mass was biopsied and shown to contain non-small cell lung cancer. The patient was treated with surgery.
Teaching points: PET/CT is used to determine the ‘stage’ of lung cancer (whether it has spread from the lung cancer elsewhere in the body). This helps to decide on the best treatment.
http://howpetworks.com/
18Slides are not to be reproduced without permission of author.
Alzheimer’s Disease DiagnosisAlzheimer’s Disease Diagnosis
• Early drug therapy to slow the loss of the patient's ability to function.• Future planning before loss of mental capacity.• Positive and accurate diagnosis of other dementing processes, chronic depression, and normal aging.• Help in the discovery and development of new therapies.
http://www.petscan.org/frames_alzh.html
axial
sagital
coronal
19Slides are not to be reproduced without permission of author.
How are PET Radionuclides Produced?How are PET Radionuclides Produced?
Radionuclide – An atom which is unstable, therefore undergoes radioactive decay
20Slides are not to be reproduced without permission of author.
Cyclotron Cyclotron –– produces PET Radionuclidesproduces PET Radionuclides
H218O 18F -
p
n
14N211C
O211CO2
18F t1/2 = 110 min
11C t1/2 = 20 minp
α
21Slides are not to be reproduced without permission of author.
What is Positron Emission Tomography?What is Positron Emission Tomography?
Where does the PET signal come from?Where does the PET signal come from?
22Slides are not to be reproduced without permission of author.
Matter Matter –– Antimatter ReactionAntimatter Reaction
• Warp core – USS Enterprise / Star Trek– Fictional power plant based on matter–antimatter
reaction.
– When matter and antimatter come into contact, they annihilate each other and release energy
– “dilithium crystals” are unreactive and regulate the reaction
– Deuterium is the matter and antideuterium is the antimatter.
• PET Imaging– PET radionuclide decays and release a positron
(antielectron).
– When the positron collides with an electron in a matter–antimatter reaction, they annihilate each other and energy is released as 2 gamma rays.
23Slides are not to be reproduced without permission of author.
γ1
γ1
γ2
γ2
Positron Emission Tomography (PET)Positron Emission Tomography (PET)
β+
positron
molecule in tissue
e-
β+
γ 2
γ 2annihilationevent
from radioactive ligand
[18F]-FDG
24Slides are not to be reproduced without permission of author.
Positron Emission TomographyPositron Emission Tomography
25Slides are not to be reproduced without permission of author.
How are PET Tracers Synthesized?How are PET Tracers Synthesized?
Tracer – molecule that is labeled with a radionuclide and used in molecular imaging. Given at extreme low dose levels in animal and human studies at 2-5 mCi or ~5 ug.
26Slides are not to be reproduced without permission of author.
PET Radiochemistry and CyclotronPET Radiochemistry and Cyclotron
• Cyclotron– F-18 & C-11 precursors
• Radiochemistry lab– Hot cells– Synthesis modules– QC analytical lab
Hot cellsHot cells
Synthesis modulesSynthesis modules
CyclotronCyclotron
27Slides are not to be reproduced without permission of author.
PET Tracer SelectionPET Tracer Selection
• Design drug molecules with C-11 and F-18 labeling in mind for future imaging studies.
N
11CH3O11CH3
11COOH 11CN
CH218F EWG18F
HNCH3
11CH3
28Slides are not to be reproduced without permission of author.
1111COCO22 ChemistryChemistry
11CO2
RNH11CH3
RO11CH3
RR'N11CH3
R11CH2I
R11CHO
11CH2O
11CH3I
R11CH2OH
RN11C(CH3)2
11CH3OH
R11COOH
(CH3)211CO
LiAlH4
MeLi
RNH2
RMgX
[H]
[O]RNH2
ROH
RR'NH
HILiAlH4
orHI
29Slides are not to be reproduced without permission of author.
Nucleophilic Displacements:• By far the largest body of F-18 fluorination experience is nucleophilic.• F– displacement of halogens on alkyl-halides• Tosylates, mesylates, triflates (most common pathway)
Nucleophilic Aromatic Substitution (SNAr):• Nucleophilic reactions with diazoniums don’t work well (Sandmeyer Rxn).• Substitution of activated aromatic nitro or iodide provides moderate yields in
uncomplicated structures.• Preferred method is substitution of EWG activated, aromatic-
trimethylammonium salts with fluoride.
OR 18F
R
K18F, K2CO3
Kryptofix 2.2.2S
CH3
OO
1818F ChemistryF Chemistry
Me3N
EWG
+ 18F
EWGK18F, K2CO3
Kryptofix 2.2.2
EWG = -SO2NH2; -COR; -CN; etc
30Slides are not to be reproduced without permission of author.
Examples of PET Tracer Syntheses Examples of PET Tracer Syntheses and Imagingand Imaging
31Slides are not to be reproduced without permission of author.
[[1818F]F]--FFluorodeoxyglucoseluorodeoxyglucose ((1818FDG)FDG)
K2CO3
OHO
HO18F
OH
OAcO
AcO
OAc
OAcO
AcO18F
OAcK18F
Kryptofix
2.2.2.
O
OAc
HCl
OAc OH
SO
CF3
O
H218O
Positron
CyclotronH2
18O / H18F K18FKryptofix
Kryptofix K18F
Hamacher K. et al. J. Nucl. Med. 1986, 27, 235-238.
O
N
O
OO
N
O
O
Kryptofix 2.2.2.
crown ether
32Slides are not to be reproduced without permission of author.
K18F - K222
DMSO
190 oC, 10 min
TFA
120 oC, 10 min
Horti AG, et al. J. Label Compds Radiopharm 1996, 28, 355-365.Horti AG, et al. J. Nucl. Med. 1997, 38, 1260-1265.
Ding YS, et al. Synapse 1996, 24, 403-407.Ding YS, et al. J. Label Compds Radiopharm 1997, 39, 828-832.
10% RCY, 50 min EOS
HN
N
Br HN
N
18F
K18F - K222
DMSO
120 oC, 10 min
NN
N NN
18F
55-65% RCY, 65 min EOS
HN
N
18F
(not isolated)
+OO OO
Nicotinic Nicotinic αα44ββ2 tracer 2 tracer –– Epibatidine an analgesic natural productEpibatidine an analgesic natural product
33Slides are not to be reproduced without permission of author.
Citalopram Citalopram –– Tracer for the Serotonin TransporterTracer for the Serotonin Transporter
J. Madsen, et al. Bioorg Med Chem 2003, 11, 3447-3456.
65-90% RCY, 45 min EOS>98% radiochemical purity
OBr
N
F
On-Bu3Sn
N
F
OH3
11C
N
F
Bu6Sn2Pd(PPh3)4
toluene, reflux,18 h, 55%
11CH3I
Pd2dba3:P(o-Tol)3
K2CO3, CuCl, DMF,
60 oC, 5 min
prep-HPLC
34Slides are not to be reproduced without permission of author.
Aprepitant Aprepitant –– NK1 Radiotracer [NK1 Radiotracer [1818F]SPAF]SPA--RQRQ
HO
N
NH
N
N NN
BOC
Ph
CF3O
N
NH
N
N NN
BOC
Ph
CF3
18F
18FCH2Br, CsCO3
DMF
70-80 oC
O
N
NH
NH
N NN
Ph
CF3
18F
TFA, CH2Cl2
RT
[18F]SPA-RQ
Bergstrom, Hargreaves, Burns, Goldberg, Sciberras et al Biol Psychiatry 2004, (55) 1007
35Slides are not to be reproduced without permission of author.
[11C]raclopride is a selective radiotracer for the D2 dopamine receptor
N
NN
F
O11CH3
O
ONH
OH
Cl
Cl
O
O
N
CH3
NS11CH3
H
[11C]flumazenil [11C]raclopride [11C]McN-5652
11C-labeled radiopharmaceuticals prepared via N-, O- and S-methylation reactions
Zhang et al. Nucl Med Biol 2002, 29, 233-241.
Wilson et al. Nucl Med Biol 2000, 27, 529-32Iwata et al. Appl Radio Isot 2001, 55, 17-22
11CH3
Alkylations with [Alkylations with [1111CC] MeI and [] MeI and [1111C ]MeOTfC ]MeOTf
36Slides are not to be reproduced without permission of author.
What value does a PET Tracer deliver?What value does a PET Tracer deliver?
• PET tracer used to quantitate the drug receptor occupancy.
• Allows a direct correlation of dose, receptor occupancy and therapeutic response.
• Key deliverable of a PET tracer is to set the dose for phase IIIhuman studies.
Dose
Therapeutic Response Adverse Events
Receptor Occupancy
37Slides are not to be reproduced without permission of author.
Imaging in drug discoveryImaging in drug discovery
• Proof of target– Is drug getting to target?
• Proof of mechanism– Is drug having an effect?
• Proof of efficacy– Is drug affecting disease?
38Slides are not to be reproduced without permission of author.
Impact of Molecular Imaging on Drug DevelopmentImpact of Molecular Imaging on Drug Development
• Improve selection of Development compounds
– Enhances the quality of molecules as well as enhances their probability of success.
• Eliminate failures early
• Can allow the early selection of the right clinical dose.
• People are heterogeneous, therefore finding the lowest dose of a drug that is effective for all is very difficult
• Find the right dose for clinical efficacy
– Optimizes the therapeutic index.
– Therapeutic index is the ratio of adverse event dosage to the lowest therapeutic dosage.
39Slides are not to be reproduced without permission of author.
Quotes by chemists . . . . Quotes by chemists . . . .
“People are growing up with no idea that science is actually different from political punditry, different from people spouting opinions. Science actually tells you things that are true, not just things that are somebody’s opinion, . . .”
Theodore Gray, Popular Science columnist (C&Enews, Nov. 26, 2007 p 50)
“It’s important to put our faces on chemistry and for us to feel proud to talk about what we do as chemists and how many alternative careers there are for chemistry.”
ACS President Catherine Hunt, (C&Enews, Dec. 17, 2007 p 36)
40Slides are not to be reproduced without permission of author.
BibliographyBibliographyMolecular Imaging:
1. R. J. Hargreaves “The Role of Molecular Imaging in Drug Discovery and Development.”Clinical Pharmacology & Therapeutics (Nature) 2008, 83, 349-353.
2. S. R. Meikle, F. J. Beekman, S. E. Rose “”Complementary molecular imaging technologies: High resolution SPECT, PET and MRI” Drug Discov Today: Technol. 2006, 3, 187-194.
PET Imaging:1. R. A. Frank, et al. J. Label Compds Radiopharm 2007, 50, 746-769.2. Gary J. Kelloff, et al. Clin Cancer Res 2005, 11, 7967-7985.3. http://howpetworks.com/4. http://www.petscan.org/frames_alzh.html5. http://depts.washington.edu/nucmed/IRL/pet_intro/toc.html6. http://en.wikipedia.org/wiki/Positron_emission_tomography
PET Radiochemistry:1. PET Chemistry: The Driving Force in Molecular Imaging (Ernst Schering Foundation
Symposium Proceedings), P.A. Schubiger, L. Lehmann, M. Friebe, Eds., Springer-Verlag: Berlin, Heidelberg, 2007.
2. Handbook of Radiopharmaceuticals: Radiochemistry and Applications, M. J. Welch, C. S. Redvanly, Eds., John Wiley & Sons: Chichester, UK., 2003.
3. Mason and Mathis Neuroimag Clin N Am 2003, 13, 671.4. H.D. Burns Annual Reports in Med Chem 2001, 36, 267.5. Lee and Farde TRENDS in Pharmacol Sci 2006, 27, 310.6. J. Wang and L Maurer Current Topics in Medicinal Chemistry 2005, 5, 1053-1075.
