Synergistic Inhibition of Mitochondrial Respiration by Anticancer Agent Erucylphosphohomocholine and Cyclosporin A

Abstract

Alkylphosphocholines are a new class of anticancer agents. The mechanisms by which these drugs display their antitumor activities are not known. In this work, we show that erucylphosphohomocholine, a new antineoplastic compound, significantly decreased ATP synthesis in isolated rat liver mitochondria at a concentration of 50 M or higher via permeabilization of the inner membrane. At a concentration of 25 M, it induced a moderate swelling of mitochondria, a slight decrease of the inner membrane potential, and an increase in state 4 respiration without an essential influence on state 3 respiration or the outer membrane permeability to cytochrome c. We found that cyclosporin A did not prevent mitochondrial swelling induced by 25-100 M erucylphosphohomocholine. Moreover, cyclosporin A induced a fast drop of the inner membrane potential in the presence of 25-50 M erucylphosphohomocholine that seems to be due to a strong synergistic inhibition of the respiratory activity. The ratio of uncoupled to state 3 respiration rates increased from 1.3 ؎ 0.1 with 25 M erucylphosphohomocholine and from 1.5 ؎ 0.1 with 1 M cyclosporin A to 4.5 ؎ 0.3 in the presence of both drugs. On the other hand, oligomycin or cyclosporin A protected certain cancer cell lines against erucylphosphohomocholine-induced apoptosis. This protection might be related to a prevention of cellular ATP hydrolysis by permeabilized mitochondria and to the inhibition of the classical permeability transition pore, respectively. Our findings provide new insight into the mechanisms by which these unusual alterations of mitochondria might be involved in anticancer activity of alkylphosphocholines.Alkylphosphocholines are a new class of antitumor agents, which target biomembranes and induce cancer cell apoptosis (1-3). Erucylphosphohomocholine (ErPC3), 2 one of the most effective alkylphosphocholines, has been shown to be a promising preclinical anticancer agent (4 -7). The precise mechanisms of antineoplastic activity of alkylphosphocholines are unknown. It has been found that they are working through p53-independent pathways (2, 8) involving mitochondrial alteration, cytochrome c release, and caspase-3 activation (9). Our previous studies have shown that the pro-apoptotic activity of ErPC3 is associated with an increased production of reactive oxygen species (10) and might be blocked by ligands of the peripheral-type benzodiazepine receptor (11), which is located in the outer membrane of mitochondria in close proximity to the voltage-dependent anion channel (12).In this work, we have found that in addition to pro-apoptotic activities, ErPC3 is also able to decrease ATP synthesis in isolated rat liver mitochondria. Our data showed that the ErPC3-mediated decrease of ATP synthesis involves a direct cyclosporin A (CsA)-insensitive permeabilization of the inner membrane. We have also discovered an unusual synergistic inhibition of ADP-dependent respiration of mitochondria in the presence of both CsA and ErPC3. The mechanism of this effect does not seem to be directly ...

The Translocator Protein Radioligand 18F-DPA-714 Monitors Antitumor Effect of Erufosine in a Rat 9L Intracranial Glioma Model

“…Induction of apoptosis was demonstrated by a significant increase in DNA degradation in 9L cells and caspase-3 activation. These results are in agreement with previously published reports demonstrating that ErPC3 has antineoplastic and apoptotic effects on glioblastoma cells (15,23,30).…”

“…Furthermore, TSPO has been closely associated with the mitochondrial permeability transition pore. In fact, using cyclosporine A, recent reports have described the blockage of the mitochondrial permeability transition pore complex countering ErPC3-induced apoptosis and decreasing tumor-infiltrating microglia/ macrophages (15,23,38). Therefore, interaction between ErPC3 and TSPO leading to the attraction of inflammatory cells is a plausible mechanism.…”

Potential involvement of F0F1-ATP(synth)ase and reactive oxygen species in apoptosis induction by the antineoplastic agent erucylphosphohomocholine in glioblastoma cell lines

“…To induce apoptosis and collapse of the mitochondrial membrane potential, human glioblastoma cells were treated with ErPC3 as described previously [7–9, 12, 13]. The involvement of ROS generation in ErPC3-induced cell death was studied by applying the ROS scavenger BHA as described previously [34].…”

“…Indeed, we were able to show that ErPC3 acts directly on mitochondria. In particular, ErPC3 induced swelling of isolated rat liver mitochondria and decreased ATP synthesis in a concentration-dependent manner via permeabilization of the inner mitochondrial membrane [13]. Since ErPC3 displays direct toxic effects on mitochondria, we concluded that ErPC3 (and its congener ErPC) target these organelles.…”

“…Mitochondria, as well as Apaf-1 and caspase-3, play major roles in ErPC- and ErPC3-induced apoptosis [7, 12, 13]. ErPC3 treatment was also found to result in mitochondrial membrane depolarization and cytochrome c release in intact glioma cells [7].…”