EP-2104R: A Fibrin-Specific Gadolinium-Based MRI Contrast Agent for Detection of Thrombus

• Published in: Journal of the American Chemical Society 2008-05, Vol.130 (18), p.6025-6039
• Main Authors: Overoye-Chan, Kirsten, Koerner, Steffi, Looby, Richard J, Kolodziej, Andrew F, Zech, Stephan G, Deng, Qing, Chasse, Jaclyn M, McMurry, Thomas J, Caravan, Peter
• Format: Article
• Language: English
• Subjects: Contrast Media - chemistry; Contrast Media - metabolism; Fibrin - chemistry; Fibrin - metabolism; Fibrinogen - chemistry; Fibrinogen - metabolism; Gadolinium - blood; Gadolinium - chemistry; Heterocyclic Compounds - blood; Heterocyclic Compounds - chemistry; Humans; Kinetics; Magnetic Resonance Angiography - methods; Nuclear Magnetic Resonance, Biomolecular - methods; Organometallic Compounds - blood; Organometallic Compounds - chemistry; Peptides - blood; Peptides - chemistry; Protein Binding; Substrate Specificity; Thermodynamics; Thrombosis - blood; Thrombosis - diagnosis
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja800834y

Thrombus (blood clot) is implicated in a number of life threatening diseases, e.g., heart attack, stroke, pulmonary embolism. EP-2104R is an MRI contrast agent designed to detect thrombus by binding to the protein fibrin, present in all thrombi. EP-2104R comprises an 11 amino acid peptide derivatized with 2 GdDOTA-like moieties at both the C- and N-terminus of the peptide (4 Gd in total). EP-2104R was synthesized by a mixture of solid phase and solution techniques. The La(III) analogue was characterized by and 1D and 2D NMR spectroscopy and was found to have the expected structure. EP-2104R was found to be significantly more inert to Gd(III) loss than commercial contrast agents. At the most extreme conditions tested (pH 3, 60 °C, 96 hrs), less than 10% of Gd was removed from EP-2104R by a challenge with a DTPA based ligand, while the commercial contrast agents equilibrated within minutes to hours. EP-2104R binds equally to two sites on human fibrin (K d = 1.7 ± 0.5 µM) and has a similar affinity to mouse, rat, rabbit, pig, and dog fibrin. EP-2104R has excellent specificity for fibrin over fibrinogen (over 100-fold) and for fibrin over serum albumin (over 1000-fold). The relaxivity of EP-2104R bound to fibrin at 37 °C and 1.4 T was 71.4 mM−1 s−1 per molecule of EP-2104R (17.4 per Gd), about 25 times higher than that of GdDOTA measured under the same conditions. Strong fibrin binding, fibrin selectivity, and high molecular relaxivity enable EP-2104R to detect blood clots in vivo.