The Protective Effect of Venetoclax on the Calcium-Induced Mitochondrial Pore and ROS Production as a New Possible Factor Contributing to Drug Resistance.
Recent data show that there are direct relationships between mitochondrial activity, cancer progression, and chemoresistance. Venetoclax (Ven) is a mitochondria-targeted chemotherapeutic drug, which facilitates apoptosis by selectively inhibiting the antiapoptotic protein Bcl-2. Ven exhibits a dual effect, affecting not only mitochondria but also the cell drug resistance system. There is also evidence indicating that cancer cells develop resistance to Ven, which is mediated by the upregulation of antiapoptotic proteins, simultaneous activation of multiple signaling pathways, an alteration in the cellular and mitochondrial metabolism, and other defensive mechanisms. The influence of Ven on the opening of the mitochondrial permeability transition pore (mPTP), a key event in the induction of mitochondria-dependent cell death, has not been previously studied.
The effect of Ven on calcium-induced mPTP opening, respiration, and reactive oxygen species (ROS) production was examined in isolated rat liver mitochondria, using cation-selective electrodes, as well as fluorescent and chemiluminescent methods.
Ven was found to have a protective effect against the Ca2+-induced mPTP opening, increasing the threshold calcium concentrations and the calcium load that activate pore opening. A comparison with the known mPTP inhibitors ADP, bongkrekic acid (BA), cyclosporine A (Cs), oligomycin, used separately and in combination with Ven, showed a similarity of the effect of Ven (at a concentration of 50 µM) to the effect of BA (20 µM). The effects of both were prevented by carboxyatractyloside (CATR). Also, the protective effect of Ven, as well as that of BA, was completely eliminated by 2-thenoyltrifluoroacetone (TTFA), an inhibitor of the ubiquinone-binding site of succinate dehydrogenase complex at low concentrations (5 µM and 50 µM under the oxidation of succinate and NAD-dependent substrates, respectively). Simultaneously, Ven decreased the ROS production induced by TTFA under the same conditions.
Ven shows two protective activities, namely, the inhibition of mPTP opening and the suppression of ROS production in mitochondria, which may be additional causes of the development of drug resistance. The results of the TTFA test are consistent with the data on the dependence of Ven resistance on the state of the respiratory chain.
The effect of Ven on calcium-induced mPTP opening, respiration, and reactive oxygen species (ROS) production was examined in isolated rat liver mitochondria, using cation-selective electrodes, as well as fluorescent and chemiluminescent methods.
Ven was found to have a protective effect against the Ca2+-induced mPTP opening, increasing the threshold calcium concentrations and the calcium load that activate pore opening. A comparison with the known mPTP inhibitors ADP, bongkrekic acid (BA), cyclosporine A (Cs), oligomycin, used separately and in combination with Ven, showed a similarity of the effect of Ven (at a concentration of 50 µM) to the effect of BA (20 µM). The effects of both were prevented by carboxyatractyloside (CATR). Also, the protective effect of Ven, as well as that of BA, was completely eliminated by 2-thenoyltrifluoroacetone (TTFA), an inhibitor of the ubiquinone-binding site of succinate dehydrogenase complex at low concentrations (5 µM and 50 µM under the oxidation of succinate and NAD-dependent substrates, respectively). Simultaneously, Ven decreased the ROS production induced by TTFA under the same conditions.
Ven shows two protective activities, namely, the inhibition of mPTP opening and the suppression of ROS production in mitochondria, which may be additional causes of the development of drug resistance. The results of the TTFA test are consistent with the data on the dependence of Ven resistance on the state of the respiratory chain.