Abstract:

Objective: To investigate the changes of signals in tumor tissue of the tumor-bearing nude mice after SPIO-shRNA molecular probe injection at different time points,and to clarify the mechanism and optimal scanning time of magnetic resonance imaging (MRI) by molecular probe in vivo. Methods: The injection dose of probe was 18 mg·kg^-1. A total of 30 BALB/c tumor-bearing nude mice were randomly divided into six groups(n=5). The mice in each group received MRI examination before and after injected with SPIO-shRNA molecular probe at different time points (12,24,27,30,and 36 h), and the changes of signal intensities in tumor tissue and controlateral muscle tissue of the nude mice were measured at different time points.Then the mice were sacrified after each examination,and the tumor and contralateral muscle tissues were obtained for HE and prussian blue staining, and the morphology of tumor tissue of the nude mice was observed under light microscope.Results: Compared with before injection,the signal intensities of T1WI in tumor tissue were increased at 12,24 and 27 h after injection of molecular probe(P<0.05),while the signal intensities of T2WI and T2*GRE were decreased at 12,24,27,30 and 36 h after injection of molecular probe(P < 0.05 or P < 0.01). The signal intensity of T2WI at 27 h after injection was the highest.However,the signal intensities of T2WI and T2*GRE at 27 h after injection were lower than those at 12,24,30, and 36 h(P<0.05). Compared with before injection,the signal intensity in contralteral muscle tissue of the nude mice at 24 h after injection was decreased(P<0.05). The HE staining results indicated that the structure of tumor tissue was abnormal and the unclear atypia was obvious.The prussian blue staining results showed that the blue-stained iron particles were distributed dispersedly at different time points, and the number of blue-stained iron particles was the most at 27 h after injection.Conclusion: The tumor tissue could be well labeled with the SPIO-shRNA molecular probes,and the optimal MRI scanning time is at 27 h after probe injection.

Key words: superparamagnetic iron oxide, molecular probe, magnetic resonance imaging, scanning time