Molecular Imaging. by Magnetic Resonance. Silvio Aime. University of Torino (Italy) Department of Chemistry IFM & Molecular Imaging Center

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1 Molecular Imaging by Magnetic Resonance Silvio Aime University of Torino (Italy) Department of Chemistry IFM & Molecular Imaging Center

2 Molecular Imaging In vivo characterization and quantitative measurement of biological process at cellular and molecular level Probe the molecular abnormalities at the basis of disease rather than imaging the end effects of a given pathology Combine new molecular agents with traditional imaging tools to create targeted, tailored therapies with the ability to simultaneously find, diagnose and treat disease The practice of Diagnostic Imaging in the era of Molecular Medicine ine

3 Molecular Imaging Enormous advances in molecular and cell biology techniques Direct imaging of these molecular changes seeking the marker Understanding the cellular and molecular mechanism of diseases Markers (targets)

4 the new frontier of Molecular Imaging Imaging Reporter Vector Target key-steps for molecular imaging procedures: choice of the target availability of high-affinity probes assessment of the biodistribution pattern of the probes use of amplification strategies use of sensitive, fast and high-resolution imaging technique

5 Imaging modalities: range of detection COMPUTED TOMOGRAPHY ULTRASOUNDS MRI PET, SPECT OPTICAL IMAGING Courtesy of H. Siebold, Siemens Medical Solutions

6 Magnetic Resonance Imaging (MRI) Non-invasive and safe technique Great spatial resolution (µm scale) Outstanding diagnostic capability MR sagittal image of human head A MR-image represents a map of the intensity of the 1 H-NMR signal of water protons

7 Magnetic Resonance Imaging (MRI) The contrast in the image may be markedly increased by using specific Contrast Agents (CA) which are chemicals able to alter significantly the relaxation rates of water protons Gd(III) chelates Iron Oxide particles METASTATIC LYMPH NODE IMAGING Metastatic Normal Without CA With Gd(III)-based CA

8 Gd(III) complexes: Targeting HSA The mechanism of action of angiographic CAs is based on their interaction with human serum albumin Gd(III) chelate Recognition Synthon O O P O - O MS325 (Epix) OH CO O O CONH H B22956/1 O - O N N Gd 3+ N O - O 3 Na + O O - - O O

9 Magnetic Resonance Angiography(MRA) rat head ( 2 T) without CA 5 min. after i.v. administration of extracellular CA 5 min. after i.v. administration of angiographic CA

10 Blood pool agent MRI coronary angiography

11 after HSA Fibrin Targeting Specificity for fibrin achieved by linking a probe to a peptide vector MR Contrast agent Fibrin binder Why Fibrin as Target? -Inflammation -Tumor growth and metastasis - Clot formation -Atherosclerosis 21

12 accumulation in the extravascular compartment of tumor O bladder pre P post 5 min seminal vescicle Prostate with in situ carcinoma non specific Q post 5 min R post 15 min specific Gd-loaded fibrin 25umol/Kg specific

13 Molecular Imaging by MRI Advantage: to exploit the superb spatial resolution of MRI Drawbacks: low sensitivity of NMR To develop more efficient CAs To increase the CA concentration at the target site Design of CAs endowed with very high relaxivities Accumulate a high number of CA units on the target

14 Nanosized carriers for MRI probes mean diameter nm Proteins (Apoferritin Virus capsides, ) Micelles Liposomes Micronized solid particles Nanoemulsions (PFCarbon) SW Carbon nanotubes Gd-loaded Zeolites

15 Gd(III)-based agents in Molecular Imaging: Targeting Cell Receptors Targeting of tumor cells overexpressing the Neural Cell Adhesion Molecule (NCAM) Pre-contrast NCAM SCID mice grafted with TEC (Tumor Endothelial Cells) isolated from human renal carcinoma and overexpressing NCAM TEC in Matrigel organizes in small vessels connected with mouse vasculature Cancer Res., h post-contrast

16 Paramagnetic Liposomes DOPC C3d peptide (targeting NCAM) Gd-complex Biotin or C3d doxorubicin ECK25 cells 8 Gd-complex R1obs s-1 cell pellets TARGETED LIPOSOME (with C3d) NON-TARGETED LIPOSOME CTRL A B C [Gd]mM

17 Innovative Theragnostic Nanosized Platforms Liposome Drug BNCT Targeting Vector Surface Modifier(s) MRI A new theragnostic perspective?

18 a straightforward route to the accumulation of Imaging Probes is through the intracellular entrapment Intracellular Entrapment of Imaging Probes: - Pinocytosis - via electroporation - Phagocytosis - via receptors - via receptor mediated Endocytosis - via transporting systems

19 Hepatospecific MRI contrast agents exploiting OATP Receptors on hepatocytes 0.1 mmol/kg Hepatotropic Gd-agent Patology: metastasis from colon cancer pre-contrast post-contrast - OOC - OOC CONH N N Gd 3+ N COO - OH COO - Gd(III) moles / mg prot. 3,0x10-8 2,5x10-8 2,0x10-8 1,5x10-8 1,0x10-8 5,0x C, 6h EPATOCYTES HTC - OOC COO - 0, [Gd-L] mm

20 Gd(III)-based agents in Molecular Imaging: Gd-DOTAC 6 GLN - 2 OC N Gd 3+ N COHN N N OC CO 2 Na + COHN CO 2 - O NH 2 Animal model Her-2/neu transgenic mice J. Med. Chem. 2006;49: PRE 72 h post prohance 72 h post Gd-DOTAC 6 GLN

21 Gd(III)-based agents in Molecular Imaging: Cell Labelling Pinocytosis Labelling of Cells in culture (stem cells, leucocytes, etc...) by incubation at high concentration (up to 100 mm) of well tolerated Gd(III) complexes Ex: labeling of Endothelial Progenitor Cells (EPC) with GdHPDO3A - CH 3 OOC N N OH Gd 3+ N N - OOC COO - Gd-HPDO3A Confocal Fluorescence Microscopy of EPCs labelled with EuHPDO3A The internalised imaging probe is confined in perinuclear endosomes

22 Gd(III)-based agents in Molecular Imaging: Cell Labelling In vivo MRI visualisation of Gd-labeled cells In-vivo T 1 weighted image of Gd-labelled EPCs dispersed into a subcutaneous matrigel plug seven days after the implantation MRM,2003 MRI visualisation of Human Pancreatic Islets labelled with Gd-HPDO3A and transplanted in the mouse liver NMR BioMed.,2007

23 Current status of MRI contrast agents Gd-based fibrin-targeting agent (visualisation of non-occlusive thrombi) 3D-Gd-MR Angiography MRI cell tracking experiment (Limph node targeting by tumor specific SPIO-labeled dendritic cells) Gd-enhanced MR images (Glioma) in vivo ph mapping of tumors