Nanoparticle's Encapsulation As a Marker for Leading Cells in Collective Migration of Breast Cancer Cells

PURPOSE In 2020, there were 2.3 million women diagnosed with breast cancer. Deaths related to cancer occur due to metastasis. In most types of solid tumors, spreading happens through collective migration, guided by “cellular leaders.” Previously, we have shown that 100-200 nm nanoparticles encapsulated more efficiently by cells with high metastatic potential (MP) than by cells with low MP. The aim of the current research is to quantitatively compare the encapsulation ability between metastatic cells that act as leaders during migration, and peripheral cells. METHODS We used Wound Healing Assay to study collective migration in two cell lines: MCF7 and MDA-MB-231 (low and high MP respectively). Firstly, we conducted calibration experiments to find the “optimal time”, when the cells reach the maximal speed during wound closure. Further, the cells were incubated with 200nm fluorescent nanoparticles for one hour prior to the determined “optimal time”. Digital images were acquired using fluorescent microscopy and Fiji software. Colocalization of nanoparticles was calculated using Pearson coefficient. Statistical differences were performed using ANOVA. RESULTS The highest wound closure rate for low MP cells was reached in 2.6 hours and for high MP cells in 3.9 (8 and 11% of wound area closure respectively). The coefficients of nanoparticle encapsulation were 0.063±0.005 and 0.046±0.004 at the edge of the wound and at peripheral area, respectively, for cells with high MP 0.039±0.003 and 0.027±0.002 for low MP. We observed a significant difference in encapsulation efficiency between leading and peripheral cells for both, high and low MP cells (p<0.013). CONCLUSION We have found the “optimal time” of wound closure, with the increased migration activity for each tested cell type. We have demonstrated that encapsulation efficiency of leading cells is significantly higher than for peripheral cells. Therefore, nanoparticles encapsulation can be used as a potential marker for most aggressive and invasive, leading cells in collective migration of breast cancer cells.