In vitro detection of apoptosis using superparamagnetic iron oxide nanoparticles and molecular magnetic resonance imaging

Superparamagnetic iron oxide (SPIO) nanoparticles have the potential to greatly expand current anatomical imaging techniques, specifically MRI. SPIO nanoparticles targeted to phosphatidylserine (PS) have the potential to detect cell death in vitro. In this investigation, a method for detecting apoptosis was developed using annexin V for targeting SPIO nanoparticles to PS thus enabling us to detect different levels of cell death using a clinical MRI. The results demonstrated that the presence of MACS MicroBeads (annexin V-SPIO) leads to an increase in image contrast in the regions of large numbers of apoptotic cells. The relationship between the transverse relaxation rate (R2) and the level of apoptosis (ranging from 5-100%) was determined to be y = 1.945 + 0.187x -- 0.002x2 + 1.161E-5 x3 (R2 = 0.523) for cells tagged with annexin V-SPIO and y = 1.570 -- 0.013x + 1.918E-4x 2 -- 8.8680E-7x3 (R2 = 0.085) for cells untagged. Results show poor agreement with theoretical predictions but still offer potential improvement over previous efforts using SPECT imaging. The work presented here has implications for future studies of cancer treatment response and may one day help detect and quantify the levels of apoptosis in order to modify treatment according to specific patient needs.