Introduction: Most ovarian cancers are diagnosed in a late, incurable stage, which has prompted efforts towards earlier detection and more effective screening strategies. To be considered effective, screening must provide sufficient sensitivity and specificity to impact patient mortality while minimizing false positives. Magnetic relaxometry (MRX), which detects binding of targeted iron oxide nanoparticles (NPs) to cancer cells, offers the promise of improved sensitivity and specificity over conventional early detection modalities.

Methods: We investigated the sensitivity and specificity of MRX by scanning ovarian cancer cell samples containing 105, 106, and 107 cells incubated with a fixed amount (57 µg Fe3O4) of anti-HER2 antibody-conjugated, PEG-coated NPs or unconjugated, PEG-coated NPs (Senior Scientific LLC). To further evaluate specificity, we used cell lines with both high and low expression of HER2 (SKOV3 and HEY, respectively). To assess MRX under in vivo conditions, we subcutaneously injected 105, 106, and 107 anti-HER2 NP-labeled SKOV3 cells into nude mice (n = 9) and immediately performed MRX scanning. Prior to performing this study, we verified successful antibody-NP conjugation through an ELISA assay, which confirmed the presence of anti-HER2 antibody in NP pellets. Additionally, we performed flow cytometry to confirm a high level of specific binding between SKOV3 cells and anti-HER2-conjugated NPs.

Results: Our in vitro data revealed strong linearity between cell number and MRX signal for both SKOV3 and HEY cells incubated with anti-HER2 NPs (R2 = 0.99 and 1, respectively). Furthermore, there was little to no MRX signal for all cell samples incubated with unconjugated, PEG NPs regardless of cell number. The highest MRX signal was observed when 107 SKOV3 cells were incubated with anti-HER2 NPs, which was 2.1 ± 0.3 and 15.7 ± 1.4 times higher than when 107 Hey cells were incubated with anti-HER2 NPs or when 107 SKOV3 cells were incubated with unconjugated PEG NPs, respectively; significantly higher MRX signals (relative to the controls; p < .01) were also noted for samples containing 106 SKOV3 cells incubated with anti-HER2 NPs. When scanning live mice injected with 107 anti-HER2 NP-labeled SKOV3 cells, the MRX signal was significantly higher than the signal from the mice prior to the injection (p < .001). Additionally, MRX signal versus cell number in the injected mice was highly correlated (r = 0.99) with the MRX data from the corresponding cell sample scans.

Conclusion: MRX is sufficiently sensitive to detect 1 million cells in culture or 10 million cells in mice with a high level of specificity. Sensitivity may be improved by using nanoparticles coated with antibodies against antigens that are overexpressed by a larger fraction of ovarian cancers and will be the focus of future work.

Citation Format: Kelsey Mathieu, Zhen Lu, Hailing Yang, Lan Pang, Adam Kulp, John Hazle, Robert C. Bast. Feasibility of magnetic relaxometry for early ovarian cancer detection: preliminary evaluation of sensitivity and specificity in cell culture and in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1864. doi:10.1158/1538-7445.AM2017-1864