Sequential Salinomycin Treatment Results in Resistance Formation through Clonal Selection of Epithelial-Like Tumor Cells

Abstract

Acquiring therapy resistance is one of the major obstacles in the treatment of patients with cancer. The discovery of the cancer stem cell (CSC)–specific drug salinomycin raised hope for improved treatment options by targeting therapy-refractory CSCs and mesenchymal cancer cells. However, the occurrence of an acquired salinomycin resistance in tumor cells remains elusive. To study the formation of salinomycin resistance, mesenchymal breast cancer cells were sequentially treated with salinomycin in an in vitro cell culture assay, and the resulting differences in gene expression and salinomycin susceptibility were analyzed. We demonstrated that long-term salinomycin treatment of mesenchymal cancer cells resulted in salinomycin-resistant cells with elevated levels of epithelial markers, such as E-cadherin and miR-200c, a decreased migratory capability, and a higher susceptibility to the classic chemotherapeutic drug doxorubicin. The formation of salinomycin resistance through the acquisition of epithelial traits was further validated by inducing mesenchymal-epithelial transition through an overexpression of miR-200c. The transition from a mesenchymal to a more epithelial-like phenotype of salinomycin-treated tumor cells was moreover confirmed in vivo, using syngeneic and, for the first time, transgenic mouse tumor models. These results suggest that the acquisition of salinomycin resistance through the clonal selection of epithelial-like cancer cells could become exploited for improved cancer therapies by antagonizing the tumor-progressive effects of epithelial-mesenchymal transition.

Drug-adapted cancer cell lines as preclinical models of acquired resistance

“…Such models can be used to study processes that cannot be studied in cell lines. In this context, acquired resistance models have been established based on cell line-and patient-derived xenografts, organoids, and transgenic tumour models [115][116][117][118][119][120][121][122][123][124][125] . However, cell lines enable the establishment of a substantially larger number of models within a given timeframe and at a given cost, which is critical for studying the drug-induced heterogeneity.…”

Consecutive salinomycin treatment reduces doxorubicin resistance of breast tumor cells by diminishing drug efflux pump expression and activity

“…Unlike in several molecular evolution assays we performed with doxorubicin, the growth retardation here was only modest. A recent study by Kopp et al also showed that consecutive treatment of mesenchymal breast cancer cells with salinomycin resulted in resistance formation by mesenchymal to epithelial transition (MET) (27).…”

“…Cells (80% of confluency) were treated with salinomycin (Sigma-Aldrich, Germany) for 72 h as previously described (26). The concentration of salinomycin was 500 nM for the MCF-7 and BT-474 cells and 50 nM for the MDA-MB 231 and MDA-MB 436 cells as mesenchymal cells display increased sensitivity to salinomycin (16,27). Thereafter, the treatment medium was replaced with fresh medium and cells were grown until recovery (80% of confluency).…”

Influence of salinomycin treatment on division and movement of individual cancer cells cultured in normoxia or hypoxia evaluated with time-lapse digital holographic microscopy

“…A synergistic effect between salinomycin and conventional chemotherapeutic drugs that target cycling cells has been demonstrated 36,37 as well as the development of resistance to salinomycin. 38 …”