Nanoencapsulation of Ruthenium Complex Ru(ThySMet): A Strategy to Improve Selective Cytotoxicity against Breast Tumor Cells in 2D and 3D Culture Models

Background: Ruthenium complexes have shown promise in treating many cancers, including breast cancer. Previous studies of our group have demonstrated the potential of the trans- [Ru(PPh3)2(N,N-dimethylN′-thiophenylthioureato-k2O,S)(bipy)]PF6 complex, the Ru(ThySMet), in the treatment of breast tumor cancers, both in 2D and 3D culture systems. Additionally, this complex presented low toxicity when tested in vivo. Aims: Improve the Ru(ThySMet) activity by incorporating the complex into a microemulsion (ME) and testing its in vitro effects. Methods: The ME-incorporated Ru(ThySMet) complex, Ru(ThySMet)ME, was tested for its biological effects in two- (2D) and three-dimensional (3D) cultures using different types of breast cells, MDAMB- 231, MCF-10A, 4T1.13ch5T1, HMT-3522 and Balb/C 3T3 fibroblasts. Results: An increased selective cytotoxicity of the Ru(ThySMet)ME for tumor cells was found in 2D cell culture, compared with the original complex. This novel compound also changed the shape of tumor cells and inhibited cell migration with more specificity. Additional 3D cell culture tests using the non-neoplastic S1 and the triple-negative invasive T4-2 breast cells have shown that Ru(ThySMet)ME presented increased selective cytotoxicity for tumor cells compared with the 2D results. The morphology assay performed in 3D also revealed its ability to reduce the size of the 3D structures and increase the circularity in T4-2 cells. Conclusion: These results demonstrate that the Ru(ThySMet)ME is a promising strategy to increase its solubility, delivery, and bioaccumulation in target breast tumors.