Elsevier

Academic Radiology

Volume 17, Issue 12, December 2010, Pages 1468-1476
Academic Radiology

Original investigation
Targeted Molecular Imaging of Antigen OC183B2 in Ovarian Cancers Using MR Molecular Probes

https://doi.org/10.1016/j.acra.2010.07.006Get rights and content

Rationale and Objectives

This study was designed to develop a novel magnetic resonance (MR) probe for the antigen OC183B2 in ovarian cancer cells and investigate its imaging features in vitro and in vivo.

Materials and Methods

Molecular probes were achieved through ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) conjugated to ovarian cancer monoclonal antibodies 183B2 (OCMab183B2) using a chemical method. In the control group, USPIOs were coupled with murine immunoglobulin G (mIgG) and conjugated the same way. Native polyacrylamide gel electrophoresis was used to evaluate the conjugation reaction. The cytotoxicity of the probe was measured using the methyl thiazolyl tetrazolium assay, and its cell-labeling efficiency was evaluated by Prussian blue staining. In vitro cell MR imaging was performed to evaluate the targeting of the probe to the cells. After that, the OCMab183B2 USPIOs and mIgG USPIOs were injected intravenously into nude mice implanted with ovarian cancer xenograft tumors, respectively. T2-weighted imaging and T2 mapping were then performed on a 3.0-T MR imaging system equipped with an animal birdcage coil at different times. Finally, the nude mice were sacrificed for histologic examination to confirm the imaging results.

Results

Native polyacrylamide gel electrophoresis displayed an optimal conjugation of USPIOs to OCMab183B2 and mIgG. Various blue-staining particles were found in the cells labeled with the molecular probe at different iron concentrations, and the density of particles was positively related to the iron concentration. Its labeling rate was 96.06%, which was higher than that of USPIOs (62.5%) at the same iron concentration (20 μg/mL). The methyl thiazolyl tetrazolium assay showed that there was no difference in cellular bioactivity between OCMab183B2 USPIO–labeled and nonlabeled cells (P > .05). In vitro cell MR imaging showed that there was an obvious decrease in signal intensity for the probe-labeled cells compared to mIgG USPIO–labeled cells. For in vivo MR imaging, distinct changes of signal intensities and T2 values of ovarian cancers were detected after the injection of OCMab183B2 USPIOs compared to mIgG USPIOs. The histologic analysis showed that iron depositions were visualized in the experimental group but not in the control group.

Conclusion

OCMab183B2 USPIO conjugates have the potential to be useful as OC183B2-targeted MR imaging agents for the early detection of ovarian cancers.

Section snippets

Cell Culture

The human ovarian cancer SKOV-3 cell line was obtained from American Type Culture Collection and maintained in the logarithmic phase at 37°C in 5% CO2 humidified air in RPMI-1640 medium supplemented with 10% bovine fetal serum, 2 mmol/L glutamine, penicillin (100 U/mL), and streptomycin (100 U/mL). The medium was changed every 2 to 3 days. All experiments were conducted in compliance with regulations of the Animal Welfare Committee of Peking University People’s Hospital.

Immunocytochemistry

Expression of OC183B2 in

Cell Culture

SKOV-3 cells were successfully cultured and harvested at their logarithmic phase during all the experiments. The cells took on a polygon shape, displayed higher nucleus/plasma ratios and good refraction, and showed an anchorage-dependent growth pattern under invert-phase contrast microscopy.

Expression of the Antigen OC183B2 in SKOV-3 Cells

Expression of the antigen OC183B2 in SKOV-3 cells was detected by immunocytochemistry analysis. The immunocytochemistry images revealed that OC183B2 was expressed in the cytoplasm and on the plasma membranes

Discussion

Extensive research aimed at developing efficient therapeutic strategies for ovarian carcinoma has not improved the mortality of ovarian carcinoma. Consequently, efforts are now focused on the early detection of ovarian carcinoma (18). Because of its capability to image some events at the cellular and subcellular levels, molecular MR imaging may offer the potential in the early detection of ovarian cancer. Our study has provided convincing evidence using in vivo mice models with regard to this

Conclusions

OCMab183B2 coupled to USPIO conjugates has demonstrated the potential to be useful as an OC183B2-targeted MR imaging contrast agent for monitoring ovarian cancers. Also, this work may provide a novel view for early detecting and differentiating tumors clinically.

Acknowledgments

We express our sincere appreciation to Professor Mingyuan Gao and his team at the Key Laboratory of Colloid, Interface Science and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, for preparations of PEG-coated nanoparticles and OCMab183B2 USPIOs MR probes.

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    This work was funded by grant 7092111 from the Beijing Nature Science Foundation (Beijing, China).

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