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Paramagnetic viral nanoparticles as potential high‐relaxivity magnetic resonance contrast agents
Author(s) -
Allen Mark,
Bulte Jeff W. M.,
Liepold Lars,
Basu Gautam,
Zywicke Holly A.,
Frank Joseph A.,
Young Mark,
Douglas Trevor
Publication year - 2005
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.20614
Subject(s) - nanoparticle , paramagnetism , rotational correlation time , dissociation constant , electron paramagnetic resonance , nuclear magnetic resonance , chemistry , metal , fluorescence , crystallography , materials science , nanotechnology , biochemistry , physics , receptor , organic chemistry , quantum mechanics
In order to compensate for the inherent high threshold of detectability of MR contrast agents, there has been an active interest in the development of paramagnetic nanoparticles incorporating high payloads of Gd 3+ with high molecular relaxivities. Toward this end, the protein cage of Cowpea chlorotic mottle virus (CCMV), having 180 metal binding sites, is being explored. In vivo CCMV binds Ca 2+ at specific metal binding sites; however, Gd 3+ can also bind at these sites. Using fluorescence resonance energy transfer we have characterized the binding affinity of Gd 3+ to the metal binding sites by competition experiments with Tb 3+ . The measured dissociation constant ( K d ) for Gd 3+ bound to the virus is 31 μM. The T 1 and T 2 relaxivities of solvent water protons in the presence of Gd 3+ ‐bound CCMV were 202 and 376 mM −1 s −1 , respectively, at 61 MHz Larmor frequency. The unusually high relaxivity values of the Gd 3+ –CCMV are largely a result of the nanoparticle virus size and the large number of Gd 3+ ions bound to the virus. These preliminary results should encourage further investigations into the use of viral protein cages as a new platform for MR contrast agents. Magn Reson Med, 2005. Published 2005 Wiley‐Liss, Inc.