Developing more sensitive methods of biomedical imaging that are effective with minimal amounts of contrast agents and side-effects is an important challenge in the early and accurate diagnosis of illnesses. Prof. Wenbin Lin of the University of North Carolina at Chapel Hill now reports about the possibilities provided by Nanoscale Metal-Organic Frameworks (NMOFs).
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, 24 (2010) 3725-3734.
DOI: 10.1002/ejic.201000496 
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