Abstract: Objective To determine the optimal concentration of c-erbB2 antisense probe labeled with superparamagnetic iron
oxide (SPIO) nanoparticles for in vivo tumor imaging in mice using magnetic resonance imaging (MRI). Methods Thirty BALB/c
mice bearing SK-Br-3 tumor were randomized into 5 groups to receive injections of different concentrations of SPIO-labeled
c-erbB2 antisense probe (containing 6.0, 9.0, 12.0, 15.0, or 18.0 mg Fe/kg). MRI was performed before and 6 h after the
injections, and the signal intensities of the tumor were compared among the groups. The tumor tissues were then dissected for
microscopic examination with HE and Prussian blue staining. Results The tumor-bearing mice all survived after injections of
the probe at doses of 6.0, 9.0 and 12.0 mg, but injections at higher doses (15.0 and 18.0 mg) caused death in some mice.
Injections of the probe at the doses of 12.0, 15.0 and 18.0 mg resulted in significant signal enhancement of the tumor (P<0.001)
to allow visual identification, but the changes showed no significant differences among the 3 groups (P>0.05). Pathological
examination revealed irregular structures of the tumor issue containing numerous heterogenous tumor cells aligned into
cancer nests; Prussian blue staining visualized scattered blue iron particles in the tumor issue, which was especially obvious in
mice injected with 12.0, 15.0 and 18.0 mg labeled probe. Conclusion Injection of 12.0 mg/kg SPIO-labeled c-erbB2 antisense
probe allows optimal tumor imaging in BALB/c mice using MRI.