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Magnifying from inside: where a smart gadolinium unites chemistry, physics, and medicine

UW-Madison Chemistry Department. Magnifying from inside: where a smart gadolinium unites chemistry, physics, and medicine. Daria Fedyukina. Cavagnero Group. February 26, 2009. What is inside?. Brain exploration, circa 6500 BC. What is MRI? History of MRI.

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Magnifying from inside: where a smart gadolinium unites chemistry, physics, and medicine

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  1. UW-Madison Chemistry Department Magnifying from inside: where a smart gadolinium unites chemistry, physics, and medicine Daria Fedyukina Cavagnero Group February 26, 2009

  2. What is inside? Brain exploration, circa 6500 BC

  3. What is MRI? History of MRI Magnetic resonance imaging (MRI) is an non-invasive imaging technique used primarily in medical settings to produce high quality images of the inside of the human body. 1973 - Paul Lauterbur first demonstrated MRI 1975 - Richard Ernst magnetic resonance imaging using phase and frequency encoding 1977 - Raymond Damadian MRI of the whole body 2003 - Paul Lauterbur and Peter Mansfield The Nobel Prize in Physiology for work on the development of MRI . Clinical MRI scanner. Siemens AVANTO, 1.5T Beckmann, N. et al. NMR Biomed. 2007, 20, 154

  4. Advantages and Disadvantages of MRI Advantages of MRI: • noninvasiveness • using non-ionising radiation • high spatial resolution • soft-tissue discrimination (contrast) in any imaging plane. • morphological and functional information Disadvantages of MRI: Disadvantages of MRI: • Low sensitivity • Long scanning time • Cost How do scientists overcome weaknesses of MRI technique? Willmann, J.K., et al. Nature Reviews, 2008, 7, 591

  5. Content of the talk • Physics of MRI • Enhancing the contrast of MR image • Contrast Agents (CA) in MRI • Mechanism of CA action • Clinically approved CA • 3. Advances in CA for MRI • Extracellular CAs examples • Ca-sensitive CA • Fibrin-sensitive CA • Thiol-sensitive CA • CA for cell labeling • Intracellular CA

  6. Physics of MRI: NMR and MRI comparison • MRI is based on the principles of nuclear magnetic resonance. • MRI primarily images the NMR signal from the hydrogen nuclei. • Hydrogen nuclei are from water and fat. Fat H2O 1H NMR 1H NMR spectrum of Lipoma B MRI MRI of lipoma B in the brain Frund, R., et al. Frontiers in Bioscience, 1997, 2, 13

  7. Physics of MRI: Frequency encoding • MR signal itself does not possess any directional information • Magnetic field gradient is applied • The object in a magnetic field • Magnetic field gradient in +x direction • 1D 1H NMR spectrum is recorded Hornak, J.P. The Basics of MRI, online book, 2007 Mitchell, D.G. MRI Principles, Saunders Company press, 1999

  8. Physics of MRI: Phase encoding • A second spectrum is recorded with the gradient • at a 1o angle to the +x axis • The process is repeated over the 360 angles • The data are backprojected through space • to obtain an image Hornak, J.P. The Basics of MRI, online book, 2007 Mitchell, D.G. MRI Principles, Saunders Company press, 1999

  9. Physics of MRI: T1-weighted image • T1 relaxation • Efficiency of energy transfer from a spin to surroundings. • Property of a tissue. H2O – moves fast → long T1 relaxation times (~seconds) Fat – moves slower → short T1, relaxation times (~milliseconds) • T1-weighted image is based on the differences • in T1 relaxation times among tissues • Fat appears brighter than water • To increase intensity – decrease T1 • To improve the contrast – increase ΔT1 Brain with lipoma B Fat Frund, R., et al. Frontiers in Bioscience, 1997, 2, 13 Mitchell, D.G. MRI Principles, Saunders Company press, 1999 H2O

  10. Content of the talk • Physics of MRI • Enhancing the contrast of MR image • Contrast Agents (CA) in MRI • Mechanism of CA action • Clinically approved CA • 3. Advances in CA for MRI • Extracellular CAs examples • Ca-sensitive CA • Fibrin-sensitive CA • Thiol-sensitive CA • CA for cell labeling • Intracellular CA

  11. Contrast Agents: Introduction • Contrast Agents (CA) • paramagnetic or ferromagnetic substances • reduce relaxation times for water protons close to CAs Low density tissue of unknown morphology Before CA injection After CA injection • The overwhelming majority of CAs contain: • Gd(III) • Eight-dentate ligands like DTPA and DOTA Merbach, A.E. (ed.), The Chemistry of Contrast Agents in Medical Magnetic Resonance Imaging, John Wiley and Sons, 2001

  12. Contrast Agents in MRI: Gadolinium(III) Advantages of using Gd(III) in CA: • High electron spin quantum S = 7/2 Gd3+ [Xe]4f7 Gdeffeciently relaxes nearby protons • Low energy barrier between 8- and 9-coordinate states Fast exchange of relaxed water with the bulk water Disadvantages of using Gd(III) in CA: • High toxicity of free Gd3+ (LD50 ≈ 5 mg/kg) Caravan, P., Chem. Soc. Rev., 2006, 35, 512 Werner, E.J, et al., Angew. Chem. Int. Ed., 2008, 47, 8568

  13. Contrast Agents: DTPA and DOTA DTPA DOTA Diethylenetriaminepentaacetic acid N,N’,N”,N”’-tetrakis(carboxymethyl)- 1,4,7,10-tetraazacyclododecane Advantages of using DTPA/DOTA in CA: • Thermodynamically and kinetically stable complexes with Gd(III) • Highly hydrophilic → do not enter cells • Eight-dentate → 9th site is open for H2O • No intercalation groups → do not integrate into DNA • Relatively easy to synthesize → production in large scale Disadvantages of using DTPA/DOTA in CA: • CAs are not able to target disease states • Short circulation time (life time ~ 15 min) Roat-Malone, R.M., Bioinorganic Chemistry, Wiley-Interscience, 2002 Werner, E.J, et al., Angew. Chem. Int. Ed., 2008, 47, 8568

  14. Mechanism of CA action: Relaxivity Good Contrast Agent: • Paramagnetic ion must efficiently relax the water • Relaxed water must exchange rapidly with the bulk water Relaxivity: Commercial agents relaxivity: r1≈ 4 mM-1s-1 Requirement for robust clinical exam: ΔR1 ≥ 0.5 s-1 → [CA] ≥ 125 µM Goal – increase relaxivity of a CA Caravan, P., Chem. Soc. Rev., 2006, 35, 512 Bloembergen, N., Morgan, L.O., J. Chem. Phys., 1961, 34, 842

  15. Mechanism of CA action: What affects relaxivity? 1. Hydration number, q • High q: • favors relaxivity • destabilizes Gd(III) complex 2. Water exchange time, τm Decrease τm 3. Relaxation time of the bound water, T1m Usually T1m > τm. Often T1m limits the relaxivity. Decrease T1m Caravan, P., Chem. Soc. Rev., 2006, 35, 512 Bloembergen, N., Morgan, L.O., J. Chem. Phys., 1961, 34, 842

  16. Mechanism of CA action: What affects T1m? Correlation time: Rotational diffusion Electronic relaxation Water exchange Rotational diffusion dominates → Optimize τR For clinically used magnetic fields increase τR Use bulky ligands with isotropic rotation Bloembergen, N., Morgan, L.O., J. Chem. Phys., 1961, 34, 842 Bloembergen, N., J. Chem. Phys., 1957, 27, 572 Caravan, P., et al., Chem. Rev., 1999, 99, 2293

  17. Mechanism of CA action: summary • Factors leading to the increase in relaxivity: • Hydration number • low q – low relaxivity, • high q – high relaxivity BUT low stability • Water exchange time • low τm – high relaxivity • Rotational diffusion time • low τR – low relaxivity • optimized τR – high relaxivity • very high τR – low relaxivity

  18. Clinically approved CA: DTPA-based [Gd(DTPA)(H2O)]2- (NMG)22+ Magnevist: BSP, 1988 Blood vessel agent r1 = 3.8(0.5T) [Gd(DTPA-bmea)(H2O)] OptiMARK: Mallinckrodt Brain, spine, and liver agent r1 = 4.7 (0.5T) Uggeri, F., et al., Inorg. Chem., 1995, 34, 633

  19. Clinically approved CA: DOTA-based [Gd(DOTA)(H2O)]- (NMG)+ Dotarem: Guerbet Central nervous system Whole body imaging r1 = 3.6 (0.5T) [Gd(DO3A-butrol)(H2O)] Gadovist: BSP Central nervous system Can be taken in high doses r1 = 3.6 (0.5T) Weisman, G.R., Reed, D.P., J. Org. Chem., 1996, 61, 5186

  20. Synthesis of DTPA and its derivatives diethylenetriamine US Patent 4,859,451 US Patent 5,137,711 Frost, A.E. Nature, 1956, 178, 322

  21. Synthesis DOTA and its derivative Stetter, H. and Frank, W., Angew. Chem. Int. Ed. Engl., 1976, 15, 686 Gries, H. Topics in Current Chemistry, 2002, 221, pp. 1-24

  22. Content of the talk • Physics of MRI • Enhancing the contrast of MR image • Contrast Agents (CA) in MRI • Mechanism of CA action • Clinically approved CA • 3. Advances in CA for MRI • Extracellular CAs examples • Ca-sensitive CA • Fibrin-sensitive CA • Thiol-sensitive CA • CA for cell labeling • Intracellular CA

  23. Extracellular CAs: Ca2+ -sensitive Monitoring calcium dynamics in the brain Gd-DOPTRA • Sensitive to [Ca2+] and [Zn2+] • Insensitive to [Mg2+] • Higher q upon chelation • Bulky ligand with lowered • rotational diffusion rate • Relatively easy synthesis Free(-Ca2+) bound(+Ca2+) Dhingra, K., et al., Chem. Commun., 2008, 3444

  24. Extracellular CAs: Ca2+ -sensitive Major, J.L., et al. , PNAS,2007, 104, 13881

  25. Extracellular CAs: Fibrin-sensitive Thrombus Imaging Thrombus – a blood clot with [Fibrin] ≈ 10-100 µM Fibrin-binding Gd-DTPA-based CAs: • GdDTPA-GLPCDYYGTCLD (CA1) • (GdDTPA)4-(LPCDYYGTCBip·d)2 (CA2) d – D-Asp Bip – Biphenylalanine Nair, S.A., et al., Angew. Chem. Int. Ed., 2008, 47, 4918

  26. Extracellular CAs: Fibrin-sensitive Fibrin-binding Gd-DTPA-based CAs: GdDTPA-GLPCDYYGTCLD (CA1) (GdDTPA)4-(LPCDYYGTCBip·d)2 (CA2) CA1 CA2 K1 K2 Nair, S.A., et al., Angew. Chem. Int. Ed. 2008, 47, 4918

  27. Extracellular CAs: Fibrin-sensitive triethylenetetraamine derivative (GdDTPA)4-(L·P·C·D·Y·Y·G·T·C·Bip·d)2 Nair, S.A., et al., Angew. Chem. Int. Ed., 2008, 47, 4918 Overoye-Chan, K., et al., J. Am. Chem. Soc., 2008, 130, 6025

  28. Extracellular CAs: Thiol-sensitive + Digilio, G., et al., Chem. Commun., 2009, 893 Carrera, C., et al., Dalton Trans., 2007, 4980

  29. Contrast Agent for cell labeling Targeting exofacial protein thiols A – Buffer solution B – GdDO3A 2mM C – Cellular Pellet D – GdDO3AS-Act 1mM E – GdDO3AS-Act 2mM Gd-DO3AS-Act : • 3-fold relaxation enhancement upon binding • BUT • Partial internalization Digilio, G., et al., Chem. Commun., 2009, 893

  30. Intracellular CA: Macrophage imaging Fluorescein Apolipoprotein E derived lipopeptide Vucic, E., et al., J. Am. Chem. Soc., 2009, 131, 406

  31. Intracellular CA: Macrophage imaging CM MRI A P2fA2 Micelle forming Lipid Gd-DTPA-DSA Bilayer forming Lipid B High P2fA2 content High content of Gd-DTPA-DSA C • Highest relaxivity and uptake were found • for particles with 33% P2fA2 • At lower percent of P2fA2 • rotational diffusion is limiting • At higher percent of P2fA2 • water exchange is limiting A – untreated cells B – treated with 50% P2fA2 C – treated with 33% P2fA2 Vucic, E., et al., J. Am. Chem. Soc., 2009, 131, 406

  32. Summary • MRI is a state-of-the-art technique • excellent spatial resolution • poor sensitivity • Contrast Agents improve sensitivity of MRI • Majority of clinically used contrast agents are • Gd(III)- and DTPA/DOTA-based • Good Contrast Agents • increase relaxivity • target specific disease states • Significant progress in the field of targeted MRI • extracellular CA • intracellular CA

  33. Acknowledgements Practice Talk Attendees: Tianning Diao Chris Brown Chris Shaffer Jamie Ellis Kevin Williamson Olga Dykhno Shu Yao Prof. Silvia Cavagnero Cavagnero Group Ashok Sekhar Juana Du Sarah Weinreis Pavan Srinath Peter Culviner JayashreeNagesh James Gerken Thank you for attention!

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