Circumvention of Adriamycin resistance: effect of 2-methyl-1,4-naphthoquinone (vitamin K 3) on drug cytotoxicity in sensitive and MDR P388 leukemia cells

Abstract

The effect of vitamin K 3 (2-methyl-1,4-naphthoquinone) on Adriamycin (ADR) induced growth inhibition of drug sensitive and multidrug resistant P388 leukemia cells was evaluated. Exposure to ADR concentrations of 100–5000 ng simultaneously with 1 μM vitamin K 3 elicited an enhanced inhibition of tumor cell survival. The effect of treatment with ADR alone, or in combination with vitamin K 3 on DNA and RNA biosynthesis in the sensitive and resistant tumor cells, was also assessed. DNA and RNA biosynthesis inhibition was increased in P388/S (the parental cell line) and P388/ADR cells (the ADR resistant cell line which exhibits the multidrug resistant (MDR) phenotype) exposed to ADR after pretreatment for 3 h with vitamin K 3. Concurrent administration in vivo of vitamin K 3 and ADR illustrated a therapeutically significant increase (P < 0.05) in the life span of sensitivie and resistant tumor cell bearing animals. Vitamin K 3 caused a depletion of the intracellular glutathione (GSH) levels in P388/S and P388/ADR leukemia cells but at concentrations greater than those that enhanced ADR cytotoxicity. Pretreatment of the tumor cells with 1 μM vitamin K 3 induced a 35–50% (P < 0.001) elevation in the intracellular ADR accumulation in MDR P388 leukemia cells, while such an effect was absent in P388/S tumor cells. DNA binding studies performed utilizing calf thymus DNA, indicated that vitamin K 3 enhanced the intercalation potential of ADR and also altered the equilibrium between the free and bound form of ADR in a cell free system. These factors and their possible effects on the potentiation of ADR cytotoxicity and the therapeutic significance of utilizing vitamin K 3 as an adjuvant in the chemotherapy of MDR tumors is discussed.