Thermodynamic stability and kinetic inertness of MS-325, a new blood pool agent for magnetic resonance imaging.
Stability constants were measured for complexes formed between a modified DTPA ligand and the metal ions Gd(III), Eu(III), Fe(III), Ca(II), Cu(II), and Zn(II) at 25 degrees C in 0.1 M NaClO4. The gadolinium complex of this ligand is MS-325, a novel blood pool contrast agent for magnetic resonance imaging currently undergoing clinical trials. Stability constants were determined by 4 different methods: direct pH titration, pH titration with competition by EDTA, competition with DTPA using an HPLC-MS detection system, and competition with Eu(III) by monitoring equilibrium by luminescence spectroscopy. The 1:1 stability constants, log beta101, are the following: Gd, 22.06 (23.2 in 0.1 M Me4NCl); Eu, 22.21; Fe, 26.66; Ca, 10.45; Cu, 21.3; Zn, 17.82. The exchange kinetics of the Gd complex, MS-325, with the radioactive tracer (152,154)Eu were studied at 25 degrees C in 0.1 M NaClO4. The exchange reaction has acid-dependent and acid-independent terms. The rate expression is given by the following: R = k(a)[GdL][H]2 + kb[GdL][Gd][H] + kc[GdL][Gd]. The rate constants were determined to be the following: k(a) = 1.84 x 10(6) M(-2) x min(-1), kb = 2.87 x 10(3) M(-2) x min(-1), kc = 3.72 x 10(-3) M(-1) x min(-1). MS-325 is 2-3 times more stable than GdDTPA at pH 7.4 and is 10-100 times more kinetically inert.
Caravan
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EPIX Medical, Inc., 71 Rogers Street, Cambridge, Massachusetts 02142-1118, USA.
Comuzzi
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Crooks
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McMurry
T J
TJ
Choppin
G R
GR
Woulfe
S R
SR
D002614:Chelating Agents / Q000737:chemistry; D003287:Contrast Media / Q000737:chemistry*; D003300:Copper / Q000737:chemistry; D004355:Drug Stability; D005063:Europium / Q000737:chemistry; D005290:Ferric Compounds / Q000737:chemistry; D005682:Gadolinium / Q000737:chemistry; D007700:Kinetics; D008279:Magnetic Resonance Imaging; D009942:Organometallic Compounds / Q000737:chemistry*; D011199:Potentiometry; D013816:Thermodynamics
D002614:Chelating Agents; D003287:Contrast Media; D005290:Ferric Compounds; D009942:Organometallic Compounds; D005063:Europium; D003300:Copper; D005682:Gadolinium; C109932:gadofosveset trisodium