Synergistic cytotoxicity between menadione and dicumarol vs. murine leukemia L1210

The water-soluble derivative of vitamin K, menadiol sodium bisulfite (K3), and the related anticoagulant dicumarol, inhibited growth of murine leukemia L1210 in liquid suspension culture. K3, but not dicumarol, cytotoxicity was abrogated by 1 mM cysteine. Isobolographic analysis of the effect of K3-dicumarol combinations, in the concentration ranges between 5 and 75 microM, on L1210 growth, indicated synergy between the two drugs. K3 (10 microM) caused a 3-fold stimulation of KCN-resistant O2 consumption by L1210 cells; addition of 50 microM dicumarol did not enhance KCN-resistant O2 consumption further, suggesting that K3-dicumarol synergy in L1210 was not due to dicumarol-mediated augmentation of K3-semiquinone-free radical formation. We examined the effect of dicumarol addition on L1210 cellular metabolites known to be affected by K3, i.e., glutathione, NADPH and ATP. Dicumarol prevented the elevation of the glutathione pool caused by less than or equal to 18 microM K3. K3-dicumarol combinations depleted the NADPH pool significantly, at concentrations of each which did not affect the NADPH pool. No synergistic effect on the ATP pool was observed. Thus, although the mechanism of K3-dicumarol synergy vs. leukemia remained unclear, it was possible that effects on the glutathione and/or NADPH pools contributed. We also investigated the effect of K3 and dicumarol on 45Ca++ transport by L1210 cells because of their effects on glutathione. Neither drug affected 45Ca++ influx or efflux rate constants. However, equilibrium 45Ca++ uptake was suppressed by K3 at concentrations lower than those which depleted glutathione.