Synthetic analogs of 1,4-anthracenedione (AQ code number), which block nucleoside transport, decrease macromolecule syntheses, induce cytochrome c release and apoptotic DNA fragmentation, and inhibit the proliferation of wild-type and multidrug resistant tumor cells in the nM range in vitro, rapidly cause the collapse of mitochondrial transmembrane potential in cell and cell-free systems. Because mitochondrial permeability transition (MPT) requires more than depolarization to occur, lead antitumor AQ8, AQ9 and AQ17 were shown to interact with isolated mitochondria to rapidly trigger large amplitude swelling and Ca²⁺ release, which are specific markers of MPT.

 ____________Compounds__ ______

   Code___Residues (R² = R³ = R⁴ = H)

   AQ8   R¹ = CH₃

   AQ9   R¹ = CH₂Br

  AQ17  R¹ = (1,3,4,6-tetra-O-acetyl-β-D-

  ____________glucosiminomethylene)_

The ability of AQ17 to induce mitochondrial swelling and Ca²⁺ release within 15 min is similar to that of classic MPT-inducing agents, such as alamethicin, atractyloside, phenylarsine oxide, arsenic trioxide and a 100 μM Ca²⁺ overload. AQ17 requires a priming concentration of 20 μM Ca²⁺ to trigger mitochondrial swelling and Ca²⁺ release and these ruthenium red-sensitive MPT events are inhibited by cyclosporin A, ADP and bongkrekic acid, which block components of the permeability transition pore (PTP), and by various ubiquinones, which interact with the quinone binding site of the PTP and raise the Ca²⁺ load required for PTP opening. Hence, antitumor AQs that target isolated mitochondria and trigger MPT might directly interact with components of the PTP to induce conformational changes that increase its Ca²⁺ sensitivity and transition from the closed to the open state.