Targeting Activated Pathways in Doxorubicin-Resistant TNBC Alters Signaling, Survival and EMT: A Double-Edged Sword

Triple-negative breast cancer (TNBC) poses significant therapeutic challenges due to the limited availability of targeted treatment options and the development of resistance to chemotherapy, including doxorubicin (DOX). The objective of this study was to investigate the impact of inhibiting activated pathways in DOX-resistant TNBC and examine the effects on MAPK and PI3K/Akt signaling pathways, cell cycle regulation, and the regulators of the epithelial–mesenchymal transition (EMT) process. Continuous exposure of cells to increasing concentrations of DOX resulted in the selection of resistant cells that exhibited EMT characteristics. We assessed the expression levels of markers related to cell death, survival, mitophagy pathways and EMT using Western blotting and qPCR in both sensitive and resistant cells with activated-pathway inhibitor treatments. Additionally, we demonstrated differences in migration capacity between resistant and sensitive cells with or without inhibitor treatments. It was found that MEK inhibition was less effective than PI3K inhibition in both sensitive and resistant cells. Expression analyses clearly demonstrated that resistant cells exhibited more aggressive behavior, as indicated by EMT- and survival-related gene expressions. The combination of MEK and PI3K inhibitors was more effective in shutting down these signals in both cell types. The ability to induce EMT in DOX-resistant cells revealed that one form of resistance might combine with another, acting as a mediator for cellular switch. Although drug resistance and various inhibitors reduce the proliferative capacity of cells and related parameters, resistance contributes to the acquisition of metastatic characteristics.