OBJECTIVETo 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).

METHODSThirty 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.

RESULTSThe 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 heterogeneous 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.

CONCLUSIONInjection of 12.0 mg/kg SPIO-labeled c-erbB2 antisense probe allows optimal tumor imaging in BALB/c mice using MRI.