engleski

Modulation of Multiple Drug Resistance by Proprietary Potassium Ionophores in Breast Cancer Stem Cell Model

Cancer stem cells (CSCs) represent a subpopulation of cancer cells responsible for tumor formation, relapse and metastasis. These cells share properties of embryonic stem cells like pluripotency and self-renewal. CSCs exhibit resistance to a whole range of drugs with different cellular targets, via phenomenon called multiple drug resistance (MDR). Mechanisms of MDR include enhanced survival pathways and increased activation of drug efflux pumps, P-gp and ABCG2. Also, CSC resistance to therapy is related to enhanced reactive oxygen species (ROS) defense capability. Recently, breast CSC model established by Weinberg group enabled screening of a large library of compounds for selectivity against CSCs. The most selective compound identified was salinomycin, a natural potassium ionophore. Salinomycin can act as P-gp inhibitor and this feature has been attributed to its selectivity towards CSC. Based on the above mentioned studies and anticancer activity of crown-ethers that act as K+ ionophores (previously published by our group), we hypothesized that these compounds could show selectivity towards breast CSCs by modulation of MDR. Therefore, the aim of this study was to identify CSC selective drugs and to elucidate their mechanisms of action, with the focus on their strategies to overcome MDR: P-gp inhibition as well as abrogation of ROS defense. We used the breast CSC model, which consists of two isogenic epithelial breast cell lines HMLEshGFP and HMLEshEcad, with latter showing markers of CSC. In addition, we used breast cancer cell lines with different degree of differentiation/invasiveness, SUM159 and MCF7, and a multidrug resistance cell model, A2780 and A2780/Adr. The use of these cell lines enabled us to examine effects of compounds on cell viability and P-gp activity. Abrogation of ROS defense was evaluated by compounds’ ability to induce ROS levels in CSCs, which are known to posses stable low levels of basal ROS. The compounds’ toxicity evaluated by MTT and xCELLigence system showed toxicity of several compounds on HMLEshEcad and SUM159 cells. The most promising compounds exhibited inhibition of P-gp activity evaluated by Rhodamine 123 efflux assay. In addition, ROS levels upon treatment with crown ethers, measured by both flow cytometry and fluorometry, showed an increase over time in several cell lines. To conclude, proprietary crown ether compounds modulate MDR in breast CSCs via inhibition of P- gp and induction of ROS.

Breast cancer stem cells ; MDR ; Potassium Ionophores

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