MODE OF ACTION OF BIOREDUCTIVE ALKYLATING AGENT, 2,3-BIS(CHLOROMETHYL)-1,4-NAPHTHOQUINONE

  • 1 January 1976
    • journal article
    • research article
    • Vol. 36  (11) , 4023-4031
Abstract
The bioreductive alkylating agent, 2,3-bis(chloromethyl)-1,4-naphthoquinone (CMNQ), was previously shown to inhibit the growth of Sarcoma 180 ascites cells in vivo. Evidence for the reductive activation of this agent via the mitochondrial respiratory chain was provided by CMNQ-induced oxidation of NADH; the interaction was on the substrate side of the site of rotenone inhibition. Consistent with the concept that reduction of CMNQ to a hydroquinone results in the generation of an alkylating species (i.e., a quinone methide) was the finding that radioactivity from [14C]CMNQ present in Sarcoma 180 ascites cells was associated with DNA, RNA and protein for a period of up to 72 h after exposure of tumor-bearing animals to this agent. Inhibition of the incorporation of [3H]thymidine, [3H]uridine and [14C]leucine into DNA, RNA and protein, respectively, of Sarcoma 180 ascites cells was produced by this agent, with DNA biosynthesis being the most susceptible. The inhibitory effect of CMNQ on the formation of DNA was, at least in part, the result of a prevention of the conversion of thymidine to its nucleotide forms. This action was due to a drug-induced decrease in intracellular levels of ATP, presumably resulting from uncoupling of oxidative phosphorylation by CMNQ and a partial loss of thymidine kinase activity in Sarcoma 180 cells, which did not appear to be due to direct inhibition of the enzyme by the drug. Although the primary event produced by CMNQ at the mitochondrial level appeared to be release of respiratory control, other effects on mitochondrial metabolism occurred. These included inhibition of NADH and succinoxidase activities, as previously demonstrated, and mitochondrial swelling, which suggested interaction of CMNQ with the inner mitochondrial membrane. These findings indicated a variety of biochemical lesions were associated with the antineoplastic activity of CMNQ and demonstrated a relationship between the effects of this drug on mitochondrial respiratory control and DNA biosynthesis.