Ultrasmall iron oxide nanoparticles (IONPs) have emerged as promising carriers for targeted metallodrug delivery in various tumors, including ovarian cancer. In particular, conjugation of IONPs with a Pt(IV) prodrug has been shown to enhance drug uptake, increase DNA platination, and reduce cell viability compared to free cisplatin [1]. However, little is known about how these nanocarriers influence the expression of key tumoral biomarkers or their effect on blood cells. Understanding these effects is essential for designing more effective targeted therapies that improve patient outcomes and reduce side effects. To study all these effects, we have employed an integrated analytical approach combining molecular biology assays with advanced mass spectrometry (MS) techniques. Single-cell inductively coupled plasma MS (SC-ICP-MS) enabled precise quantification of metallic nanoparticle uptake at the single-cell level [2], while mass cytometry (CyTOF) that simultaneously analyzes more than 40 markers, enabling the assessment of nanoparticle-induced changes in cells. 

Ovarian cancer (A2780) cells were treated for 24 hours with the Pt(IV)-IONP system and tested for intracellular Pt accumulation and and biomarker expression (human epidermal growth factor receptor 2, HER2, and transferrin receptor 1, TfR1) by SC-ICP-MS and CyTOF. Additionally, 191Ir and 193Ir were measured to assess cell viability (simultaneously in the case of CyTOF and sequentially in the case of ICP-MS). Initial results revealed that most A2780 cells were TfR1-positive, since this is highly expressed in most tumoral cell lines and about 75% of the cells were also HER-2 positive. Furthermore, all treated cells incorporated Pt via IONPs, and elemental single-cell analysis allowed for a detailed correlation of these parameters. However, after treatment with Pt-IONPs, the proportion of double-negative (HER2-/TfR1-) cells increased significantly, revealing a change on the biomarker expression upon drug incorporation. Slight Pt-IONP uptake was also observed in peripheral blood mononuclear cells (PBMCs), suggesting lower systemic interactions during drug transport. These findings highlight the need to further investigate the biodistribution of nanoparticle-based therapies to optimize their clinical efficacy. Overall, the combination of SC-ICP-MS and CyTOF technologies provides a powerful platform for profiling metallodrug uptake, biomarker modulation, and immune interactions, paving the way for more effective ovarian cancer therapies. 

References
[1] L. Gutiérrez-Romero, L. Rivas-García, C. Sánchez-González, J. Llopis, E. Blanco and M. Montes-Bayón, Pharmaceutics. Oct 2021, doi: 10.3390/pharmaceutics13101730.
[2] D. Turiel-Fernández, L. Gutiérrez-Romero, M. Corte-Rodriguez, J. Bettmer, and M. Montes-Bayón, Anal Chim Acta, vol. 1159, May 2021, doi: 10.1016/j.aca.2021.338356.