Metal oxide nanoparticles as Metal oxide nanoparticles as contrast agents for magnetic contrast agents for magnetic

resonance imaging (MRI)resonance imaging (MRI)

Monday Seminar 21.3.2011

Jessica Rosenholm

Magnetic resonance imaging (MRI)Magnetic resonance imaging (MRI)

• Magnetic resonance imaging (MRI), or nuclear magnetic resonance imaging (NMRI), is primarily a medical imaging technique most commonly used in radiology to visualize the structure and function of the body

• MRI uses a powerful magnetic field to align the nuclear magnetization of (usually) hydrogen atoms in water

• Radiofrequency fields are used to systematically alter the alignment of this magnetization, causing the hydrogen nuclei to produce a rotating magnetic field detectable by the scanner

• MRI is one of the most powerful imaging techniques for living organisms as it provides images with excellent anatomical details based on soft-tissue contrast and functional information in a non-invasive and real-time monitoring manner

Source: Wikipedia

Clinical (relaxivity) contrast agentsClinical (relaxivity) contrast agents

• T1 contrast agents: Paramagnetic complexes; Gadolinium based e.g. Dotarem® (Gd-DOTA)

• spin – lattice/network relaxation, white white (bright contrast)

• Decrease T1

• T1: longitudinal relaxation time – mechanism due to interaction and energy exchanges between spins

• T2 contrast agents: Mangnetic nanoparticles; iron oxide based, e.g. ultrasmall superparamagnetic iron oxide (USPIO) or SPIOs• spin – spin relaxation, black (dark contrast)• Decrease T2 and T2*

• T2: transverse relaxation time – mechanism due to interactions and energy exchanges inside the spin system

2 classes approved by FDA:2 classes approved by FDA:

-To improve image quality, aquisition time, enlargements of detectable organs

- to target a specific area, tissue/cells (diagnostic radiology)

- for future challenges of cellular and molecular imaging associated with new therapeutic methods (therapeutic medicine)

White or dark contrast?White or dark contrast?

T1 and T2 MEMRI images obtained for the Mn complex schematically shown on the left. On the T1-weighted images, the contrast in the parenchyma is better at 24 h (b) while the contrast in the ventricle is maximal at 15 h (a) and gradually decreases after 48 h (c). The concentration of Mn2+ is minimal in the corpus callosum (a,b,d,e). The maximum concentration of Mn2+ is observed in the hippocampus region, the thalamus, and the cerebellum center (b,e).

Bertin et al. Bioconjugate Chem., 20, 760, 2009

T1

T2

15 h 72 h24 h

NB ! Manganese-enhanced MRI (MEMRI) which uses the Mn2+ ion as T1 contrast agent, is applicable to animals only owing to the toxicity of the Mn2+ despite the increasing appreciation of this technique in neuroscience research!

(chelate)

Microwave chemistry and the polyol processMicrowave chemistry and the polyol process

• Microwave chemistry widely applied in organic synthesis

• Also synthesis of nanoparticles and nanostructures whose growth is highly sensitive to the reaction conditions could benefit from the efficient and controlled heating provided by microwave irradiation

• ”Time is valuable” – synthesis takes a few min’s

• Environmentally friendly ”green” synthesis method

• Polyol reduction process frequently used and refined at Nano Biomedical Research Center (SJTU) used for synthesis of water-dispersible nanoparticles where glycols are used as reductant and metal salts as precursor

• At NBC used for preparing ultrasmall superparamagnetic iron oxides (USPIO) with controllable size with exceptionally good T1 and T2 relaxivity properties (normally only T2 for SPIOs)

MnO synthesis via the polyol processMnO synthesis via the polyol process

Pale-green synthesis solution after microwave reaction suggesting successful production of MnO (left). Right: TEM image of the same after purification. (Performed at SJTU during postdoc)

XRD for microwave digested MnO materialsXRD for microwave digested MnO materials

(20 min synthesis)

(PVP-stab. 20 min)

(PAA-stab. 20 min)

(30 min synthesis)

MRI images of agar and water suspensions MRI images of agar and water suspensions of MnOof MnO

Performed at Oulu University Hospital

Relaxivity measurements made by MRI in Oulu Relaxivity measurements made by MRI in Oulu Uni HospitalUni Hospital

To be done: corresponding measurements on the Bruker minispec at SJTU (in April)

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MnO for mesenchymal stem cell labeling MnO for mesenchymal stem cell labeling (Oulu)(Oulu)

Potential applications of nanotechnologies in stem cell research include:

1) Tracking of stem cell surface molecules and detailed examination of molecular motion without photobleaching

2) Noninvasive tracking of stem cells and progenitor cells transplanted in vivo

3) Stem cell delivery systems that enhance the survival of transplanted cells by releasing prosurvival biomolecules

4) Nanopatterned substrates that present covalently tethered biologically active molecules (adhesion sites, growth factors, and synthetic peptides) for stem cell differentiation and transplantation

5) Intracellular delivery of DNA, RNAi, proteins, peptides, and small drugs for stem cell differentiation.

As exogenous cell therapy undergoes rigorous testing in animal and human trials, it has become increasingly important to track the movement of transplanted cells to assess toxicity and therapeutic efficacy.

Current Nanotechnologies for Stem Cell Research. (A) Nanomaterials for stem cell labeling and tracking in vivo. Stem cells labeled by super-paramagnetic iron oxide nanoparticles or fluorescent quantum dots might be tracked by magnetic resonance imaging or cell imaging systems, respectively, either in vitro or in vivo. In most cases, stem cells are loaded with nanomaterials at concentrations that do not exert cytotoxic effects. (B) Many powerful strategies for the differentiation of stem cells require the delivery of bioactive molecules (e.g., plasmid DNA, siRNA, proteins, peptides, and small molecules) into the cytosolic or nuclear compartments of these cells. Polymeric nanocarriers, carbon nanotubes, and polyplexes are examples of nanomaterials used to deliver biomolecules within stem cells. In the case of polymeric nanocarriers and polyplexes, the material might degrade over time within the cell. (C) Nanoscale-engineered substrates and scaffolds to create biomimetic cellular environments. Stem cell adhesion to substrates or scaffolds with nanoscale resolution can cause clustering of cell integrins into focal adhesion complexes, and the concomitant activation of intracellular signaling cascades and guidance of stem cell behavior.

R. Langer et al. New Opportunities: The Use of Nanotechnologies to Manipulate and Track Stem Cells. Cell Stem Cell 2008.

Cellular uptake and toxicity of MnO particles (ÅA)

Strategies to Deliver Nanomaterials within Stem Cells.

Schematic representation of steps involved in cytosolic and nuclear delivery of nanomaterials into stem cells. Nanomaterials can enter the stem cell either by (i) receptor-mediated interactions or (ii) nonspecific internalization pathways. In both cases, the nanomaterials become entrapped within endosomes and are then released in the cytoplasm or trafficked to the acidic environments of lysosomes for degradation. Cytoplasm released nanomaterials might then be transported to the nucleus of the cell.

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Gd-doped particles for breast cancer Gd-doped particles for breast cancer diagnosis (TYKS)diagnosis (TYKS)

• Gadolinium(III) is an excellent relaxer. The free form of this ion is very toxic and thus the contrast agent is administered as chelate complexes with few water molecules directly coordinated

• Traditionally, the contrast agents used for in vivo MRI measurements are such small complexes, which distribute in the whole body and not only in the vicinity of the target site

• Present research thus aims at studying contrast agents that have a high potential for binding specifically to a certain tissue in the body

• Particles (TA-DAH!) can be internalized by cells their use as positive (T1) MRI contrast agents significantly prolongs the imaging time-frame, as the half-lives of currently commercially available Gd‐based contrast agents are extremely short (~30 sec ?)

• Tissue specificity (targeting) is desired in order to improve the clinical diagnostics and also because it is possible to reduce the dose, since the contrast agent would become concentrated near the target !!!

*

Control miceNo particles

MDA-MB-321 tumorsNano particles

MDA-MB-321 tumorsNano particles

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(MDA-MB-321 cells = breast cancer cells)

Remember :

Gd-doped particles for breast cancer Gd-doped particles for breast cancer diagnosis (TYKS)diagnosis (TYKS)

• DOTA chelated Gd3+ covalently bound to (targeted) nanoparticles

• Gadolinium (III) is highly paramagnetic and decreases water proton relaxation times via dipolar interactions, making it suitable as a contrast agent.

• We bind Gd to particles by using of 4,7,10-tetraazacyclododecane-1,4,7,10 tetraacetic acid (DOTA) chelate, which has a high binding constant to Gd

MR-images of Gd-DOTA-MSNPs taken at TYKS (Turku University Hospital)

Iron oxides and composites as contrast Iron oxides and composites as contrast agents (SJTU)agents (SJTU)

• Prof Gu’s group at SJTU is world-leading in producing magnetic particles with tunable properties for different purposes (have been commercialized, but not for MRI)

• Size scale : from single magnetite crystals to microparticles (see figure)• Currently studies are being made on how mesoporous silica coatings

affect the relaxivity of the magnetite nanoparticles (hmmm...secret? )• Next Shanghai trip will include an attempt to MR-image magnetite-

labeled cells

Mesoporous silica coatings of different thickness on different sizes of magnetite particles ranging from single crystals (left) to larger aggregates. Images and fabrication: Jixi Zhang, Med-X Institute, Shanghai Jiao Tong University.

Literature examples of MRI active iron Literature examples of MRI active iron oxidesoxides

• MRI is a very useful means of imaging of hard tissues

• Both ”white” (T1) and ”black” (T2) contrast can be achieved

• Coated SPIONs are often used, as the coating slows down the rate of oxidation process, which otherwise would lead to a decrease in the MRI signal

• Biocompatibility

V.I. Shubayev, T.R. Pisanic, S. Jin, Adv. Drug Delivery Rev. 61 (2009) 467–477

Literature examples : Time-Literature examples : Time-dependencydependency

Mouse liver T2-weighted TSE images at different time points before and after administration of Mn-SPIO micelles. “After injection” = 5 min after injection of micelles. The significant signal intensitymay assist in identifying small focal hepatic lesions, including tumor metastases.

Lu et al, Biomaterials 30 (2009) 2919

Literature examples : Targeting can greatly Literature examples : Targeting can greatly enhance contrastenhance contrast

MRI anatomical image of a mouse in the (A) coronal plane with the dotted line displaying the approximate location of the axial cross sections displayed in (C) and (D). Anatomical image in the (B) sagittal plane displaying the location of the 9L xenograft tumor. Change in R2 relaxation values for the tumor regions (superimposed over anatomical MR images) for mouse receiving (C) non-targeting PEG-coated iron oxide nanoparticles and (D) CTX-targeted PEG-coated iron oxide nanoparticles 3 h post nanoparticle injection.

C. Sun et al., Small 4 (2008) 372–379.

CTX-targeted iron oxide nanoparticles in 9L glioma flank xenografts

External collaborators

•MnO imaging and application : Roberto Blanco Sequeiros, Prof. Radiology, Oulu University Hospital ; Eveliina Lammentausta, PhD, Hospital Physicist

•Gd-MSNP imaging and application : Ronald J.H. Borra, MD; Medical Imaging Centre of Southwest Finland, Turku University Hospital, Turku, Finland (presently at Harvard …)

•SPION fabrication (and imaging) & MnO synthesis and characterization : Prof. Hongchen Gu, Wangchuan Xiao, Jixi Zhang, Nano Biomedical Research Center, Shanghai Jiao Tong University, P.R. China

•Cellular and animal studies : Cecilia Sahlgren, PhD; Veronika Mamaeva, MD; Turku Centre for Biotechnology and ÅA Dept of Biosciences

»MRI-mouse (...RIP)