Modulation of cytotoxicity of menadione sodium bisulfite versus leukemia L1210 by the acid-soluble thiol pool

Abstract

We investigated the mechanism of antitumor activity of the water-soluble derivative of menadione, menadione sodium bisulfite (vitamin K3), versus murine leukemia L1210. Vitamin K3, in concentrations greater than 27 microM, caused time- and concentration-dependent depletion of the acid-soluble thiol (GSH) pool. Maximal GSH depletion to 15% of control occurred at 45 microM vitamin K3. Vitamin K3-mediated GSH depletion and vitamin K3-mediated growth inhibition were abrogated by coincubation with 1 mM cysteine or 1 mM reduced glutathione but not by 1 mM ascorbic acid or 180 microM alpha-tocopherol. Low concentrations of vitamin K3 (9-27 microM) elevated both the GSH pool and the total glutathione pool, the latter to a greater degree. Vitamin K3 also caused an increased rate of superoxide anion generation by L1210, maximal at 45 microM vitamin K3 (300% of control), and a concentration-dependent depletion of the reduced nicotinamide adenine dinucleotide phosphate (NADPH) and total nicotinamide adenine dinucleotide phosphate (NADP) pools. Forty-fifty % depletion of the NADPH pool occurred after exposure to 27 microM vitamin K3 and 100% occurred at 36 microM vitamin K3; 27 microM vitamin K3 is a nontoxic concentration of vitamin K3. Loss of NADPH and total NADP was prevented by coincubation with 1 mM cysteine but not by coincubation with ascorbic acid or alpha-tocopherol. We conclude that tumor cell growth inhibition by vitamin K3 is modulated by acid-soluble thiols and may be caused by GSH pool and/or NADPH depletion. Toleration of partial NADPH depletion by L1210 cells may indicate that a threshold level of NADPH loss of greater than 50% is necessary for toxicity. NADPH depletion may be a toxic effect common to quinone drugs. Equitoxic concentrations of vitamin K3, phylloquinone, lapachol, dichlorolapachol, and doxorubicin caused L1210 NADPH pools to deplete to 30 +/- 10 (SD), 60 +/- 10, 60 +/- 11, and 80 +/- 12% of control, respectively. In contrast, GSH depletion may not be a common mechanism of toxicity. Of these quinones, only vitamin K3 caused significant GSH depletion when studied in equitoxic concentrations.