Gadolinium-Loaded Viral Capsids as Magnetic Resonance Imaging Contrast Agents
Polymeric nanohybrid P22 virus capsids were used as templates for high density Gd3+ loading to explore magnetic field-dependent (0.5–7.0 T) proton relaxivity. The field-dependence of relaxivity by the spatially constrained Gd3+ in the capsids was similar when either the loading of the capsids or the concentration of capsids was varied. The ionic longitudinal relaxivity, r 1, decreased from 25–32 mM−1 s−1 at 0.5 T to 6–10 mM−1 s−1 at 7 T. The ionic transverse relaxivity, r 2, increased from 28–37 mM−1 s−1 at 0.5 T to 39–50 mM−1 s−1 at 7 T. The r 2/r 1 ratio increased linearly with increasing magnetic field from about 1 at 0.5 T, which is typical of T 1 contrast agents, to 5–8 at 7 T, which is approaching the ratios for T 2 contrast agents. Increases in electron paramagnetic resonance line widths at 80 and 150 K and higher microwave powers required for signal saturation indicate enhanced Gd3+ electron spin relaxation rates for the Gd3+-loaded capsids than for low concentration Gd3+. The largest r 2/r 1 at 7 T was for the highest cage loading, which suggests that Gd3+–Gd3+ interactions within the capsid enhance r 2 more than r 1.
KeywordsElectron Paramagnetic Resonance ATRP DTPA High Magnetic Field Magnetic Resonance Imaging Contrast Agent
This work was supported by an award from the American Heart Association (SQ) and was supported in part by a grant from the National Institutes of Health, NIBIB R01-EB012027 and by internal funding at the University of Denver. This work was partially supported by the US government, not protected by US copyright.
- 4.L. Helm, Future. Med. Chem. 2, 385–396 (2010)Google Scholar