engleski

The effects of potassium ionophores on mitochondrial homeostasis in breast cancer stem cell model

Cancer stem cells (CSC) are a small population of tumor cells that can self-renew, have pluripotent capacity and are believed to be critical for tumor initiation, progression and metastasis, as well as for the treatment failure and disease relapse. Development of novel anticancer therapies that target CSC represents an apparent yet difficult to reach objective. Recently, a breast CSC model was established by inducing epithelial to mesenchymal transition (EMT) in immortalized human mammary epithelial cells (HMLE). Using this model, salinomycin (Sal) was identified to be selectively toxic against breast CSCs. The exact mechanism of the observed selectivity remains largely unknown. Salinomycin is a K+/H+ exchanger that can affect cation transport across different cellular membranes. It has been found recently that Sal induces rapid hyperpolarization of the inner mitochondrial membrane (IMM), similarly to another K+/H+ exchanger nigericin (Nig), but in contrast to the K+ ionophore valinomycin (Val). Also, when used above µM concentrations, Sal reduces respiration, causes matrix acidification and ATP depletion, thus compromising the cell survival. 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 disrupt potassium transport and modulate mitochondrial membrane potential and function. The main aim of our study was to test the early effects of various potassium ionophores: Sal, Nig, Val, along with proprietary crown ethers on the cancer stem cell model to elucidate their mechanisms of action, with the focus on mitochondrial membrane potential and function. Study was performed on an isogenic pair of HMLE cells (HMLE-pBp and HMLE-Twist), with latter displaying characteristics of cancer stem cells. We demonstrate that treatment with higher doses of Sal leads to increased level of reactive oxygen species (ROS) in both cell lines and increased basal respiration selectively in HMLE-Twist cell line. Total mitochondrial mass measured by NAO and Mitotracker DEEP RED FM was increased. Moreover, mitochondrial membrane potential was disrupted after the treatment with Sal in both cell lines, with the effect being more pronounced in HMLE-Twist cells. Several proprietary crown-ethers also show modulation of both plasma and mitochondrial membrane potential, which was confirmed by staining with different membrane potential dyes DiOC6(3), DiBAC4(3) and JC-1. In conclusion, we gained further insight into the mechanism of action and potential selectivity of potassium ionophores toward CSC. The current status of our ultimate aim to discover novel CSC- selective drugs will be discussed.

Cancer stem cells ; Salinomycin ; Potassium ionophores ; Crown ethers

nije evidentirano