valinomycin and salinomycin

Salinomycin, isolated from Streptomyces albus, displays antimicrobial activity. Recently, a large-scale screening approach identified salinomycin and nigericin as selective apoptosis inducers of cancer stem cells. Growing evidence suggests that salinomycin is able to kill different types of non-stem tumor cells that usually display resistance to common therapeutic approaches, but the mechanism of action of this molecule is still poorly understood. Since salinomycin has been suggested to act as a K(+) ionophore, we explored its impact on mitochondrial bioenergetic performance at an early time point following drug application. In contrast to the K(+) ionophore valinomycin, salinomycin induced a rapid hyperpolarization. In addition, mitochondrial matrix acidification and a significant decrease of respiration were observed in intact mouse embryonic fibroblasts (MEFs) and in cancer stem cell-like HMLE cells within tens of minutes, while increased production of reactive oxygen species was not detected. By comparing the chemical structures and cellular effects of this drug with those of valinomycin (K(+) ionophore) and nigericin (K(+)/H(+) exchanger), we conclude that salinomycin mediates K(+)/H(+) exchange across the inner mitochondrial membrane. Compatible with its direct modulation of mitochondrial function, salinomycin was able to induce cell death also in Bax/Bak-less double-knockout MEF cells. Since at the concentration range used in most studies (around 10 μM) salinomycin exerts its effect at the level of mitochondria and alters bioenergetic performance, the specificity of its action on pathologic B cells isolated from patients with chronic lymphocytic leukemia (CLL) versus B cells from healthy subjects was investigated. Mesenchymal stromal cells (MSCs), proposed to mimic the tumor environment, attenuated the apoptotic effect of salinomycin on B-CLL cells. Apoptosis occurred to a significant extent in healthy B cells as well as in MSCs and human primary fibroblasts. The results indicate that salinomycin, when used above μM concentrations, exerts direct, mitochondrial effects, thus compromising cell survival.

Topics: Acid-Base Equilibrium; Animals; Antibiotics, Antineoplastic; Cell Respiration; Cell Survival; Drug Screening Assays, Antitumor; Fibroblasts; Humans; Jurkat Cells; Membrane Potential, Mitochondrial; Mice; Mitochondria; Nigericin; Oxygen Consumption; Pyrans; Valinomycin

Valinomycin and salinomycin-Na, 2 ionophorous antibiotics, exhibited in vitro antibabesial activities against Babesia gibsoni that infected normal canine erythrocytes containing low potassium (LK) and high sodium concentrations, i.e., LK erythrocytes, which completely lack Na,K-ATPase activity. The level of parasitemia of B. gibsoni was significantly decreased when the parasites were incubated in culture medium containing either 10(-1) ng/ml valinomycin or 10(2) ng/ml salinomycin-Na for 24 hr. Four-hour incubation in the culture medium containing 5 μg/ml salinomycin-Na led to the destruction of most parasites. In contrast, when the parasites infected canine erythrocytes containing high potassium (HK) and low sodium concentrations, i.e., HK erythrocytes, the in vitro antibabesial activities of both ionophorous antibiotics seemed to be weakened, apparently due to the protection by the host cells. Therefore, differential influences of ionophorous antibiotics on LK and HK erythrocytes were observed. In LK erythrocytes, the intracellular concentrations of potassium, sodium, and adenosine triphosphate (ATP) were not modified, and hemolysis was not observed after incubation in the medium containing each ionophorous antibiotic. These results suggested that these ionophorous antibiotics did not affect cells without Na,K-ATPase, and directly affected B. gibsoni. In HK erythrocytes, the ionophorous antibiotics increased the intracellular sodium concentration, and decreased the intracellular potassium and ATP concentrations, causing obvious hemolysis. Additionally, the decrease of the intracellular ATP concentration and the hemolysis in HK erythrocytes caused by valinomycin disappeared when the activity of Na,K-ATPase was inhibited by ouabain. These results indicate that modification of the intracellular cation concentrations by the ionophorous antibiotics led to the activation of Na,K-ATPase and increased consumption of intracellular ATP, and that the depletion of intracellular ATP resulted in hemolysis in HK erythrocytes. Moreover, the antibabesial activity of valinomycin disappeared when B. gibsoni in LK erythrocytes were incubated in culture media containing high potassium concentrations. This showed that the intracellular cation concentration in the parasites was not modified in those media and would remain the same.

Topics: Adenosine Triphosphate; Animals; Anti-Bacterial Agents; Babesia; Cells, Cultured; Culture Media; Dogs; Enzyme Inhibitors; Erythrocytes; Ionophores; Ouabain; Potassium; Pyrans; Sodium; Sodium-Potassium-Exchanging ATPase; Valinomycin

The effects of salinomycin on alkali cation transport and membrane functions in rat liver mitochondria have been investigated. After potassium uptake, stimulated by valinomycin or monazomycin in the presence of adenosine 5'-triphosphate, salinomycin caused rapid release of K(+) from mitochondria. Salinomycin reversed valinomycin- or monazomycin-induced oscillatory swelling of mitochondria preloaded with K(+), Rb(+), and Na(+) but was without effect on Li(+) or Cs(+) preloaded mitochondria. Salinomycin blocked the retention of K(+) more effectively than the retention of Rb(+) or Na(+). Salinomycin inhibited both coupled and uncoupled respiration with strict substrate specificity in medium of low but not in high K(+) concentration. The oxidation of glutamate, alpha-ketoglutarate, and malate plus pyruvate was inhibited by salinomycin, but that of beta-hydroxybutyrate or succinate was not significantly affected. Salinomycin inhibited adenosine triphosphatase activity of mitochondria induced by valinomycin or monazomycin in K(+) and Rb(+) medium without significantly affecting adenosine triphosphatase activity in Li(+), Na(+), or Cs(+) medium. Oxidative phosphorylation in mitochondria was inhibited by salinomycin but the inhibitory effect of salinomycin lacked the substrate specificity observed for respiration. It is proposed that salinomycin perturbs mitochondrial functions by acting as a mobile carrier for alkali cations through membranes.

Topics: Adenosine Triphosphatases; Animals; Anti-Bacterial Agents; Glycosides; In Vitro Techniques; Macrolides; Metals; Mitochondria, Liver; Oxidation-Reduction; Oxidative Phosphorylation; Oxygen Consumption; Potassium; Pyrans; Rats; Valinomycin