Relation of the Antiproliferative Action of Methylglyoxal‐bis(guanylhydrazone) to the Natural Polyamines

Enzymic determinations of intracellular concentrations of methylglyoxal‐bis(guanylhydrazone), an anticancer drug which inhibits the synthesis of the polyamines spermidine and spermine, in cultured tumor cells revealed that the drug was remarkably effectively concentrated inside the cell. A concentration gradient across the cell membrane as great as 500–1000‐fold was formed in cells exposed to the drug for 1–2 days. An exposure of cultured Ehrlich ascites carcinoma cells to increasing concentrations of the drug indicated that the cells could tolerate intracellular concentrations up to 1 mM with only slight changes in their proliferation rate. Micromolar concentrations of spermidine or spermine, but not putrescine, effectively blocked the uptake of methylglyoxal‐bis(guanylhydrazone) and reduced the intracellular concentration of the drug below the levels required for growth inhibition. Analysis of cellular polyamine contents in Ehrlich ascites cells exposed to rising concentrations of methylglyoxal‐bis(guanylhydrazone) gave little support to the view that the drug‐induced growth inhibition was solely produced by an intracellular polyamine deprivation. Not only was the uptake of the drug inhibited in the presence of spermidine and spermine, but it was likewise washed out by polyamines from the cells that had been previously exposed to the drug and then transferred into drug‐free medium in the presence of polyamines. For the inhibition of methylglyoxal‐bis(guanylhydrazone) uptake by amines, three or more amino/imino groups were apparently required, since low concentrations of aliphatic diamines were either without any effect (short‐chain diamines) or only marginally prevented (long‐chain diamines) the uptake of the drug. High concentrations of Mg 2+ ions, however, markedly inhibited the transport of the drug into Ehrlich ascites tumor cells.