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Nanoscale Metal-Organic Frameworks (NMOFs): A new way to create better MRI Contrast Agents

(22.07.2010)


Background:
Magnetic resonance imaging (MRI) is a noninvasive technique based on the detection of nuclear spin reorientations in a magnetic field, which, however, is relatively insensitive and typically relies on large doses of administered contrast agents to distinguish adequately between normal and diseased tissues. Typically up to 3 g of Gd-based MRI contrast agents are applied which normally are excreted after a few hours with the urine of the patient. Such excretion however is heavily delayed in renail failure patients which than might be excluded from the use of some Gd-based agents due to potential side effects (NSF).

A new class of materials that appear promising in this quest were introduced in 2006 by Prof. Wenbin Lin of the University of North Carolina at Chapel Hill. Ever since, this emerging area has been growing rapidly as new materials with improved properties are discovered. Wenbin Lin and Joseph Della Rocca present the progress in this field in a Microreview published in the European Journal of Inorganic Chemistry (on-line in advance of print) July 7.

The new materials:








Fig.1: Generalized schematic of the synthesis of an
NMOF

 

Nanoscale Metal-Organic Frameworks (NMOFs) are combinations of metals and organic molecules on the nanoscale that provide unlimited possibilities for designing task-specific molecules. They are intrinsically biodegradable, and their high porosity makes them ideal for targeted delivery of entrapped agents. They can be specifically targeted to certain regions of the body. In addition to a wealth of applications in other fields, these properties make NMOFs also very suitable for use in biological systems and in particular as more effective contrast agents at lower doses. In addition to Gd carboxylate materials, NMOFs based on Fe, Mn, and Zn were investigated.

In order to enhance the stability, dispersibility, and biocompatibility of NMOFs for in-vivo applications, coatings such as amorphous silica, biocompatible polymers, and polyoxometalate-peptide hybrid spheres were used. Furthermore, some systems doped with lanthanides were studied as potential multimodal contrast agents.

The effectiveness of these agents has been demonstrated both in vivo and in vitro experiments. For example, iron carboxylate NMOFs modified with biocompatible polymers were used for imaging the liver and spleen of Wistar rats. Silica-coated, peptide-targeted Mn NMOFs were shown to be selectively taken up by a human colon cancer cell line in vitro. Finally, a versatile iron carboxylate system post-synthetically modified to contain a fluorophore or a chemotherapeutic showed strong fluorescence upon release from the framework and exhibited cytotoxicity comparable to cisplatin against colon cancer cells.


The original publication

Wen-bin Lin, Nanoscale Metal-Organic Frameworks: Magnetic Resonance Imaging Contrast Agents and Beyond, European Journal of Inorganic Chemistry, ahead of print, doi: 10.1002/ejic.201000496


Related News

 EVISA News, May 4, 2009: Gadolinium speciation analysis in search for the cause of nephrogenic systemic fibrosis (NSF)

 EVISA News, April 17, 2009: Gadolinium-based MRI contrast agents found intact in the outlet of a waste water treatment plant

 




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