Objective: To investigate the feasibility of superparamagnetic iron oxide (SPIO)
nanoparticles (SPIO) as a magnetic resonance (MR) contrast agent to enhance tumor imaging in vivo.
Methods: Hydrophobic SPIO (oil-soluble SPIO; OSPIO) and hydrophilic SPIO (water-soluble SPIO;
WSPIO) were loaded in methoxy-poly(ethylene glycol)-block-poly(D,L-lactic acid) (PEG-PDLLA)
nanovesicles. Three groups of nude mice (n=12/group) xenografted with human colorectal carcinoma
(LoVo) cells were injected into the caudal vein with WSPIO, OSPIO-loaded nanovesicles, or WSPIO-loaded
nanovesicles. MRI scans were performed on all of the mice, and the relative T2 values were measured in the tumor and the
liver. The differences in these T2 values between the three groups were compared.
Results: The peak relative T2 values in the tumors detected by the OSPIO- or WSPIO-loaded contrast agents were reduced
by 10.12% and 11.40%, respectively. The relative T2 values in the WSPIO- and OSPIO-loaded polymeric nanovesicle
groups were more pronounced than the relative T2 value in the WSPIO group (P<0.05), but there was no significant
difference in the T2 value between the OSPIO- and WSPIO-loaded vesicle groups (P＞0.05). The greatest T2 value
decreases in the liver in the WSPIO, OSPIO-loaded and WSPIO-loaded vesicle groups were 32.85%, 52.77% and
56.89%, respectively. The decrease in the T2 values was more pronounced in the WSPIO- and OSPIO-loaded nanovesicle
groups than in the WSPIO group (P<0.05) and was more apparent in the WSPIO-loaded nanovesicle group than in the
OSPIO-loaded nanovesicle group (P<0.05).
Conclusion: SPIO-loaded polymeric nanovesicles generate significant T2WI signal intensity decreases in vivo and are
anticipated to be used as novel and effective contrast agents for tumor imaging.