Study: MR molecular probes show promise in early detection of ovarian cancers

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Ovarian cancer monoclonal antibodies coupled to ultrasmall superparamagnetic iron oxide nanoparticles conjugates have demonstrated the potential to be useful as an MR imaging contrast agent for early detection and differentiation of ovarian cancers, according to research published in the December issue of Academic Radiology.

In the study, Guangnan Quan, MD, from the department of radiology, Peking University People’s Hospital in Beijing, and colleagues attempted to couple ovarian cancer monoclonal antibodies 183B2 (OCMab183B2) to ultrasmall superparamagnetic iron oxide nanoparticles (USPIOs) and then investigate whether the complex could target ovarian cancer cells in vitro and in vivo as an MR molecular probe.

In the control group, USPIOs were coupled with murine immunoglobulin G (mIgG). Native polyacrylamide gel electrophoresis displayed an optimal conjugation of USPIOs to OCMab183B2 and mIgG, according to the researchers.

There was no difference in cellular bioactivity between OCMab183B2 USPIO-abeled and nonlabeled cells. The cytotoxicity of the probe was measured using the methyl thiazolyl tetrazolium assay.

In vitro cell MR imaging was performed to evaluate the targeting of the probe to the cells and the results showed that there was an obvious decrease in signal intensity for the probe-labeled cells compared to mIgG USPIO–labeled cells, according to Quan and colleagues.

After that, the OCMab183B2 USPIOs and mIgG USPIOs were injected intravenously into nude mice implanted with ovarian cancer xenograft tumors. T2-weighted imaging and T2 mapping were then performed on a 3T MR imaging system equipped with an animal birdcage coil at different times.

Quan and colleagues observed distinct changes of signal intensities, and T2 values of ovarian cancers were detected after the injection of OCMab183B2 USPIOs compared to mIgG USPIOs.

The authors also noted that a few limitations existed in the study. First, because of its large molecular weight and size, the probe would not easily pass through some barriers. This would make the process of targeting the probe to the tumor less efficient and also make it time-consuming. Next, the optimization of the coupling ratio between USPIOs and the antibody presented challenges. The ratio between antibody and USPIOs for coupling was 1:2. The more USPIOs that are added, the larger the molecular weight of the probe which not only makes the probe hard to diffuse but also harms the immunoreactivity of the antibody.

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