Radiodiagnostické metody SPECT – single photon emission computer tomography PET – positron emission tomography Radiotherapy Jednofotonová emisní tomografie (SPECT) • g-emitující radioisotopy • rozlišení ~1 cm3 SPECT Izotopy pro SPECT Izotop Přeměna Poločas Zdroj 99mTc g 6 h generátor, 99Mo(b–)99mTc, 66 h 111In g 68 h cyklotron, 111Cd(p,n)111In 131I g, b– 8 d reaktor 153Sm g, b– 46 h reaktor 166Ho g, b– 26 h reaktor 177Lu g, b– 6.7 d reaktor http://upload.wikimedia.org/wikipedia/commons/b/b8/ECAT-Exact-HR--PET-Scanner.jpg PET PET •radioisotopes emitting positrons (b+-particles) •annihilation with electrons •two co-linear photons with an energy of 511 keV •detection of both photons at the same time •resolution about 1 mm3 •low energy à better resolution Izotopy pro PET Izotop Přeměna Poločas Zdroj 19F b+ 110 min cyklotron, 18O(p,n)18F 11C b+ 20 min cyklotron, 14N(p,a)11C 61Cu b+ 3.3 h cyklotron, 61Ni(p,n)61Cu 64Cu b+ 13 h cyklotron, 64Ni(p,n)64Cu 66Ga b+ 9.5 h cyklotron, 63Cu(a,ng)66Ga 68Ga b+ 68 min generátor, 68Ge(b–)68Ga, 288 d 86Y b+ 15 h cyklotron, 86Sr(p,n)86Y 110In b+ 69 min generátor, 110Sn(b–)110In, 4.11 d Každá minuta se počítá • Příprava izotopu • Izolace izotopu • Příprava radiofarmaka • Separace radiofarmaka • Analýza radiofarmaka • Doprava k pacientovi • Aplikace pacientovi • Dosažení žádané biodistribuce • Snímkování http://www.smw.ch/fileadmin/smw/images/SMW-2011-13272-Fig-04.jpg PET vs. SPECT [18F]-FDG-PET http://jnm.snmjournals.org/content/45/8/1309/F5.large.jpg 99mTc-MDP-SPECT Fused images •localization in tissues – combined techniques with CT or MRI •fused images – PET/CT, PET/MRI, SPECT/CT, SPECT/MRI •multimodal contrast agents • • http://www.intechopen.com/source/html/41157/media/image8.jpeg Radiotherapy •Leksell gamma knife •focuses the radiation from external sources into tumour •internal sources of radiation •short and defined radius of particles in tissue •a-emitters •b--emitters •g-emitters with low energy •emission of Auger electrons (EC isotopes) •selective deposition in tumors – half-lives in hours • http://upload.wikimedia.org/wikipedia/commons/thumb/2/2a/Elektroneneinfang_%282_Phasen%29.png/220px -Elektroneneinfang_%282_Phasen%29.png Radiotherapy Isotope Decay Half-life Source Mean range in tissue 64Cu b– 12.8 h cyclotron, 64Ni(p,n)64Cu 0.2 mm 67Cu b– 62 h cyclotron, 67Zn(n,p)67Cu 67Ga Auger 3.26 d cyclotron 89Sr b– 50.5 d reactor 90Y b– 64 h generator, 90Sr(b–)90Y 3.9 mm 111Ag b– 179 h cyclotron 1.1 mm 149Pm b– 2.2 d reactor 153Sm b– 1.9 d reactor 161Tb b– 166 h reactor 0.3 mm 166Ho b– 1.1 d reactor 177Lu b– 6.7 d reactor 186Re b– 90 h reactor 1.1 mm 188Re b– 17 h generator, 188W(b–)188Re 3.3 mm 212Pb b–/a 10.6 h/1.01h reactor 0.1 mm Radiotherapy Common criteria for radiopharmaceuticals §Selected molecule must be amenable to radiolabelling. Reaction must provide sufficient radiochemical yield, specific activity and must proceed in appropriate time, that means maximally 4, ideally less than 3 half-lives of radioisotope – also depends on half-life itself. Reaction must proceed under reasonable conditions because of automation of procedure in the case of clinical production. Procedure including yield must be reliable and reproducible. § §Biodistribution of a radiopharmaceutical must be related to the physiological response to enable measuring functionality of biochemical process under investigation. § §High affinity to the target leading to high contrast of a PET image. Interaction between radiopharmaceutical and biomolecules in target tissue must be the major mechanism. Also high specificity for target molecule is essential because interaction with similar targets leads to interference with desired radioactive signal detected by a PET camera. § §The lipophilicity (defined as usual partition coefficient between n-octanol and water – log P) that determines ability to cross cell membranes. §Optimal passage of lipid bilayers requires log P ~ 1.5 – 2. Higher log P values result in nonspecific binding caused by hydrophobic interactions with lipids and proteins. § §Certain properties as passage across the cell membrane or other barriers like blood brain barrier (BBB). Besides mentioned lipophilicity, also active transport of compounds must be taken in account, e.g. dopamine, serotonin and amino acids. Common criteria for radiopharmaceuticals In general, a low affinity to P-glycoprotein (P-gp) is a desirable property for most radiopharmaceuticals. P-gp is an ATP-dependent efflux pump naturally expressed in BBB. It can be over-expressed in tumours. P-gp transports compounds that have high affinity for the pump out of the cell and then radiotracers that have high affinity for P-gp show little accumulation in tissues like brain and tumour. Metabolism of a radiopharmaceutical is a very important point. Rapid metabolism is generally undesirable. Metabolites can then bind to other molecules or take part in other metabolic processes and result in non-specific accumulation of radioactivity. It is preferable to have the radioisotope in the part of molecule which reaches the target at first and after that is further metabolised. In some cases, metabolism of radiotracer is the mechanism underlying the accumulation of radioactivity in tissue. Clearance of non-specifically bound radioactivity by the time of measurement PET must be discriminated. This is relevant mainly for labelled macromolecules that slowly diffuse into cells and only small portion is bound to the target of interest. The unbound radiolabelled molecules must leave the cells again and be cleared from the circulation. Mutagenicity and toxicity, despite the radiophramaceutical is prepared under non-carrier added (NCA) conditions and small mass is administrated to the patient, must be tested. This differs in different countries according to the law. Usually toxicity tests on rodent species and Ames test for mutagenicity are performed at dosages much higher than those applied in PET studies. Preparation and administration RCY – RadioChemical Yield CA – Carrier Added NCA – Non-Carrier Added Targeting • vector – selectivity for imaged tissue: peptide, oligosacharide, etc. • chemically sensitive – labelling at mild conditions • include a biologically active molecule covalently linked to the complex • e.g. Progesterone receptor analogues (prostate cancer) Cocaine analogues (CNS diseases) Targeting Octreoscan – 111In –DTPA-Octreotide Targeting Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author Octreoscan imaging for neuroendocrine tumors. a) Coronal octreoscan image demonstrating radiotracer uptake in multiple liver metastases and a large pancreatic primary neuroendocrine carcinoma. (b) Coronal octreoscan fusion images with single photon emission tomography (SPECT) providing increased anatomic detail. (c) Axial octreoscan fusion images with SPECT. http://www.chemdrug.com/databases/dataimg/309/3081912.png http://cancergrace.org/wp-content/uploads/2007/01/pet-example-slide-final.jpg Technetium 99mTc • predicted by Mendeleev • first isolated 1938 • 20 isotopes (7 relatively stable) • used extensively (>90% of all diagnostic nuclear medicine) • t1/2 = 6 h • g-ray emission energy of 141 keV • versatile coordination chemistry • multiple oxidation states • easily generated from 99Mo (t1/2 = 66 h) • • • Rhenium •186Re, t1/2 = 90 h, available from reactor • 188Re, t1/2 = 17 h, available from 188W(b–)188Re generator • chemical properties similar to Terchnetium: diagnostic/therapeutic isotop-pair • Technetium 99mTc 99Mo/99mTc Generator • patented in 1958 • fission-produced 99Mo is processed and purified to anionic molybdate • loading on the positively charged alumina (Al2O3) column Technetium 99mTc Radionuklidový generátor Technetium 99mTc Počty elucí z generátoru 99mTc Chemistry • TcO4– most stable oxidation state, produced in generator, can not be complexed • insoluble TcO2 • reduction with ascorbic acid, FeCl2, NaBH4, Na2S2O4, SnCl2 – oxidation states IV, V – oxocation technecyl (disproportionation V à IV + VII) – oxidation states I, II, III (oxidation à IV) • stabilization of oxidation states with ligands • Technetium kit • reducing agent • coordinating ligand • antioxidants • buffers • lyophilized and sealed under inert atmosphere Technetium 99mTc Pharmacology • bio-distribution and targeting depends much on size and charge: –neutral – brain –cationic – hart –anionic – bones and kidney • so called technetium essential or first generation agent • targeting of other organs requires designer ligands: –must traverse the blood brain barrier –moderately lipophilic –neutral charge Technetium 99mTc Neutral complexes – brain imaging – oxidation states IV, V Technetium 99mTc Cationic complexes • hart imaging • uptake via Na-K ATPase pump as K+ mimics Technetium 99mTc Cardiolite SCAN_RESULTS.jpg D0509_Lant_cardiolite vials_0.jpg Cardiolite Each 5 mL vial contains a sterile, non-pyrogenic, lyophilized mixture of: •Tetrakis (2-methoxy isobutyl isonitrile) Copper (I) tetrafluoroborate – 1.0 mg •Sodium Citrate Dihydrate – 2.6 mg •L-Cysteine Hydrochloride Monohydrate – 1.0 mg •Mannitol – 20 mg •Stannous Chloride, Dihydrate, minimum (SnCl2•2H2O) – 0.025 mg Prior to lyophilization the pH is 5.3 to 5.9. The contents of the vial are lyophilized and stored under nitrogen. This drug is administered by intravenous injection for diagnostic use after reconstitution with sterile, non-pyrogenic, oxidant-free Sodium Pertechnetate 99mTc Injection. The pH of the reconstituted product is 5.5 (5.0 - 6.0). No bacteriostatic preservative is present. The precise structure of the technetium complex is 99mTc[MIBI]6+ where MIBI is 2-methoxy isobutyl isonitrile. Over 40 million people have received cardiac scans using Cardiolite. Technetium 99mTc Cardiolite has now been commercialized and is used to determine heart function and myocardial perfusion 201Tl is also used for heart imaging, but cardiolite is preferred Imaging agents in action myoview Myoview = tetrofosmin Technetium 99mTc Bone imaging • hydroxyapatite principal mineral component of bones Ca10(PO4)6(OH)2 • phosphate (PO43-) and pyrophosphate (P2O72-) bone seeking anions • diphosphonates give improved performance • • • • absorption via calcium coordination to phosphonate • stressed bone has higher calcium concentration • main use to detect cancer metastasis into bone jrdbody arthritic right ankle Technetium 99mTc Carbon 11C • half-life 20.40 min • decay mode: 99.8 % b+, 0.2 % EC • max b+ energy: 0.96 MeV • range in tissue: 0.96 mm • decay product: 11B Production • cyclotron-generated: mainly produced by the proton bombardment of 14N • 14N(p,a)11C nuclear reaction • target gas: 2% O2 in N2 à 11CO2 5% H2 in N2 à 11CH4 Carbon 11C Carbon 11C Palladium mediated reactions 11CH3I •methylation of N –, O –, S – compounds Carbon 11C Carbon 11C Carbon 11C Carbon 11C Carbon 11C Fluorine 18 F • half-life 109.7 min • decay mode: 96.9 % b+, 3.1 % EC • max b+ energy: 0.63 MeV • range in tissue: 0.54 mm • decay product: 18O Fluorine 18 F Production Fluorine 18 F Electrophilic 18F-Fluorination •reaction of highly polarized fluorine with an electron rich reactant, e.g., an aromatic system, an alkene, or a carbanion •starting with [18F]F2 – 50% RCY (molecule compsition 18F–19F) •other fluorination agents [18F]XeF2, [18F]AcOF Fluorine 18 F Nucleophilic 18F-Fluorination •[18F]fluoride •protonation at low pH •formation of ion pairs with cations – decrease of reactivity àphase transfer catalysis or use of crownethers and cryptands Nucleophilic Aliphatic Fluorination R–X + F– R–F + X– Nucleophilic Aromatic Fluorination Fluorine 18 F Prosthetic groups (PG) •labelled compound containing reactive moiety •fluoromethylation with [18F]FCH2I or [18F]FCH2Br •fluoroethylation with [18F]FCH2CH2X •other precursors Fluorine 18 F Prosthetic groups for biomolecules •enable labelling of peptides and proteins Amine reactive PGs Carboxylic acid reactive PGs Thiol reactive PGs Fluorine 18 F Prosthetic groups (PG) 18F-FDG: [18F]fluoro-2-deoxy-D-glucose – vyrábí se cyklotronicky v MOÚ • 1968, J. Pacák and M. Černý, Department of Organic Chemistry, UK • the most common PET tracer • distribution similar to glucose • can not be metabolized • accumulation in metabolically-active tissues Fluorine 18 F PET_anime Whole-body PET scan using 18F-FDG to show liver metastases of a colorectal tumor Fluorine 18 F Iodine isotopes Metalic nuclides (non-Tc, non-Re) Complex stability Thermodynamic stability • proton vs. metal competition •ligand basicity • • • stability constants • • Complex kinetics Formation kinetic • chemistry – high concentrations; NMR, UV-VIS • radiochemistry – low concentrations Kinetic inertness • in vitro experiments – transmetallation (Zn(II)) – decomplexation in acidic solutions – incubation in plood plasma Open-chain ligands •high thermodynamic stability •kinetically labile •fast complexation •applied in large excess Macrocyclic ligands •high thermodynamic stability •kinetically inert •slow complexation •variation of pendant arms – carboxylates, alcohol, amine, phosphorus derivatives – changes in stability, inertness, complexation rate, charge, lipophylicity Bifunctional chelators Thiourea bond http://upload.wikimedia.org/wikipedia/commons/c/c9/MITC-to-thiourea-2D.png • half-life 67.6 min • decay mode: 89 % b+, 11 % EC • max b+ energy: 1.90 MeV • range in tissue: 2.12 mm • decay product: 68Zn • Generator produced • source 68Ge (T1/2 = 271 d) • adsorbed on TiO2 or SnO2 • elution with HCl or citric acid • Chemistry • trivalent • hexacoordination • hard metal ion • precipitation of hydroxide at wide pH range • formation of tetrahydroxido complex at high pH Gallium 68Ga Ligands for 68Ga complexation Aminocarboxylates Hydroxybenzyl and hydroxypyridyl derivatives Thiol and amino-thiol chelates R = Gallium 68Ga Copper isotopes Isotope Decay Half-life Source 60Cu b+ 24 min cyclotron, 60Ni(p,n)60Cu 61Cu b+ 3.3 h cyclotron, 61Ni(p,n)61Cu 62Cu b+ 9.74 min generator, 62Zn(b–)62Cu, 9.3 h 64Cu b+ (61%), b– (39%) 12.8 h cyclotron, 64Ni(p,n)64Cu 67Cu b– 62 h cyclotron, 67Zn(n,p)67Cu • isotopes 60, 61, 62 and 64 – PET • isotopes 64 and 67 – SPECT and therapy • difficult production and isolation • Chemistry • divalent • hexacoordination • Jahn-Teller effect Ligands for copper complexation Open-chain ligands Copper isotopes Ligands for copper complexation Macrocyclic ligands Copper isotopes Sc, Y, In and Lanthanoides Decay Half-life Source Diagnotic isotopes 44Sc b+ 3.93 h generator, 44Ti(EC)44Sc, 59 y or cyclotron, 44Ca(p,n)44Sc 86Y b+ 14.7 h cyclotron, 86Sr(p,n)86Y 110In b+ 69.0 min generator, 110Sn(b–)110In, 4.11 d 111In g 68 h cyclotron, 111Cd(p,n)64In 134La b+ 6.70 min generator, 134Ce(b–)134La, 3.0 d 140Pr b+ 3.39 min generator, 140Nd(b–)140Pr, 3.3 d Therapeutic isotopes 90Y b– 64 h generator, 90Sr(b–)90Y, 28.8 y 149Pm b– 2.2 d reactor 153Sm b– 1.9 d reactor 161Tb b– 166 h reactor 166Ho b– 1.1 d reactor 177Lu b– 6.7 d reactor Sc, Y, In and Lanthanoides Chemistry • octa- or nona-coordination • octadentate ligands • hard metal ions luqboo! Radiochemical research Bisphosphonate-containing dota-amides •ligand synthesis and characterization •chemical complexation study •labelling (complexation of radionuclide) – pH, temperature, ligand concentration •affinity and stability study Labeling Affinity Radiochemical research Biodistribution of 177Lu-complexes in Lewis rat 24 h after injection Radiochemical research In vivo SPECT/CT visualization of 177Lu-complex 1 h p.i. 24 h p.i. potkan-LuBPAMD-1hP-600ugI potkan-LuBPAMD-24hPI-200ug 64Cu complex Radiochemical research PET/CT imaging of bone metastases with 68Ga-complex Figure-1_Fellner et al Ga-68 BPAMD Image of the Month (a) = coronal PET, (b) = sagittal PET/CT. For comparison (c) shows 18F-fluoride PET. University of Mainz, Zentral Klinik Bad Berka Radiochemical research Radiochemical research 68Ga-complex