In vivo Off-Resonance Saturation Magnetic Resonance Imaging of αvβ3-Targeted Superparamagnetic Nanoparticles

Magnetic resonance imaging is a powerful clinical imaging technique that allows for noninvasive tomographic visualization of anatomic structures with high spatial resolution and soft tissue contrast. However, its application in molecular imaging of cancer has been limited by the lack of sensitivity and defection accuracy in depicting the biochemical expression of these diseases. Here, we combine an ultrasensitive design of superparamagnetic polymeric micelles (SPPM) and an off-resonance saturation (ORS) method to enhance the imaging efficacy of tumor biomarkers in vivo. SPPM nanoparticles encoded with cyclic(RGDfK) were able to target the alpha(v)beta(3)-expressing microvasculature in A549 non-small cell lung tumor xenografts in mice. ORS greatly improved tumor detection accuracy over the conventional T-2*-weighted method by its ability to turn "ON" the contrast of SPPM. This combination of ORS imaging with a tumor vasculature-targeted, ultrasensitive SPPM design offers new opportunities in molecular imaging of cancer. [Cancer Res 2009;69(4):1651-8]