Calcium-Sensitive MRI Contrast Agents Based on Superparamagnetic Iron Oxide Nanoparticles and Calmodulin

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 103; no. 40; pp. 14707 - 14712
• Main Authors: Atanasijevic, Tatjana, Shusteff, Maxim, Fam, Peter, Jasanoff, Alan
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 03.10.2006; National Acad Sciences
• Subjects: Aggregation; Animals; Biological Sciences; Calcium; Calcium - metabolism; Calcium Signaling; Calmodulin - chemistry; Calmodulin - metabolism; Cattle; Contrast Media - chemistry; Dextrans; Ferrosoferric Oxide; Imaging; Iron - chemistry; Iron - metabolism; Iron oxides; Light; Magnetic resonance imaging; Magnetic Resonance Imaging - methods; Magnetite Nanoparticles; Microscopy, Atomic Force; Molecular imaging; Nanoparticles; Nanostructures - chemistry; NMR; Nuclear magnetic resonance; Oxides - chemistry; Oxides - metabolism; Protein Structure, Secondary; Proteins; Scattering, Radiation; Sensors; Signal transduction; Time Factors; Titration; Tracheoesophageal fistula
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0606749103

We describe a family of calcium indicators for magnetic resonance imaging (MRI), formed by combining a powerful iron oxide nanoparticle-based contrast mechanism with the versatile calciumsensing protein calmodulin and its targets. Calcium-dependent protein-protein interactions drive particle clustering and produce up to 5-fold changes in T2 relaxivity, an indication of the sensors' potency. A variant based on conjugates of wild-type calmodulin and the peptide M13 reports concentration changes near 1 μM$Ca^{2+}$, suitable for detection of elevated intracellular calcium levels. The midpoint and cooperativity of the response can be tuned by mutating the protein domains that actuate the sensor. Robust MRI signal changes are achieved even at nanomolar particle concentrations (<1 μM in calmodulin) that are unlikely to buffer calcium levels. When combined with technologies for cellular delivery of nanoparticulate agents, these sensors and their derivatives may be useful for functional molecular imaging of biological signaling networks in live, opaque specimens.