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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 34, Number 10
BKCSDE 34(10)
October 20, 2013 

Gadolinium Complexes of Bifunctional Diethylenetriaminepentaacetic Acid (DTPA)-bis(amides) as Copper Responsive Smart Magnetic Resonance Imaging Contrast Agents (MRI CAs)
Ki Soo Nam, Ji-Ae Park, Ki-Hye Jung, Yongmin Chang*, Tae-Jeong Kim*
Gd-DTPA(bisamides), Histidine, Aspartic acid, Copper sensor, Smart MRI CA
We present the synthesis and characterization of DTPA-bis(histidylamide) (1a), DTPA-bis(aspartamide) (1b), and their gadolinium complexes of the type [Gd(L)(H2O)] (2a: L = 1a; 2b: L = 1b). Thermodynamic stabilities and R1 relaxivities of 2a-b compare well with Omniscan®, a well-known commercial, extracellular (ECF) MRI CA which adopts the DTPA-bis(amide) framework for the chelate: R1 = 5.5 and 5.1 mM−1 for 2a and 2b, respectively. Addition of the Cu(II) ion to a solution containing 2b triggers relaxivity enhancement to raise R1 as high as 15.3 mM−1, which corresponds to a 300% enhancement. Such an increase levels off at the concentration beyond two equiv. of Cu(II), suggesting the formation of a trimetallic (Gd/Cu2) complex in situ. Such a relaxivity increase is almost negligible with Zn(II) and other endogenous ions such as Na(I), K(I), Mg(II), and Ca(II). In vivo MR images and the signal-to-noise ratio (SNR) obtained with an aqueous mixture of 2b and Cu(II) ion in an 1:2 ratio demonstrate the potentiality of 2 as a copper responsive MRI CA.
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