Synergistic anticancer effect of glycolysis inhibition and oxidative phosphorylation suppression

Abstract

There is no effective therapy for melanoma, a malignant tumor of melanocytes with an increasing incidence. High energy demands of melanoma cells are predominantly satisfied by aerobic glycolysis. When glycolysis is suppressed, these metabolically plastic cells switch to oxidative phosphorylation. The aim of this study was to investigate the antimelanoma effects of simultaneous inhibition of glycolysis by 2-deoxy-D-glucose (2DG) and oxidative phosphorylation by rotenone (ROT). 2DG synergized with ROT in inducing death of B16 melanoma, but not primary mesenchymal cells. Combined treatment stimulated caspase activation, but not PARP cleavage and DNA fragmentation. Disintegration of plasma membrane and inability of caspase inhibitors and necrostatin to suppress toxicity of 2DG/ROT implied that combined treatment induced necrosis, rather than apoptosis and necroptosis. 2DG/ROT stimulated ATP depletion, mitochondrial superoxide production, and mitochondrial swelling, but not depolarization of mitochondria. 2DG/ROT-induced toxicity was suppressed by antioxidant α-tocopherol, but not mitochondrial depolarization inhibitor cyclosporine. Combined treatment induced the translocation of hexokinase II, a suppressor of voltage-dependent anion channel (VDAC) opening, and cytochrome c from mitochondria in the cytoplasm, while VDAC opening inhibitor DIDS suppressed 2DG/ROT toxicity. Our results suggest that 2DG/ROT treatment stimulates mitochondrial swelling, release of hexokinase II and subsequent opening of VDAC in the outer mitochondrial membrane. These events allow cytochrome c to exit and activate caspases, which are unable to stimulate PARP and consequent DNA fragmentation in the energy-depleted state. On the other hand, superoxide synthesized in mitochondria upon 2DG/ROT treatment also exits through VDAC and triggers energy-independent necrosis. Simultaneous inhibition of glycolysis and oxidative phosphorylation appears to be promising strategy for further development of novel anticancer therapeutics.