Inhibition of topoisomerase II in 32D.3(G) cells by hydroquinone is associated with cell death

Studies showing the inhibition of isolated human topoisomerase II (topo II) by benzene metabolites such as hydroquinone, coupled with the recognition that benzene-induced acute myelogenous leukemia bears a resemblance to second cancers caused by topo II inhibitors such as etoposide, suggested that topo II inhibition by hydroquinone might induce leukemogenic mutations. In these studies the inhibition of topo II by hydroquinone or etoposide was studied in parallel with the effects of these agents on differentiation, maturation and viability in murine bone marrow 32D.3(G) cells. Topoisomerase II of 32D.3(G) cells was inhibited by hydroquinone at concentrations of 5 micro M or higher and by etoposide at concentrations of 50 micro M or higher. At concentrations of either agent below those that inhibited topo II the cells responded normally to interleukin-3, which promoted proliferation, and to granulocyte colony-stimulating factor, which promoted differentiation and maturation. In dose ranges in which topo II was inhibited by either hydroquinone or etoposide, the cells became progressively less viable and cell counts decreased during the incubation period. Progressive inability to detect topo II protein by Western blot analysis as hydroquinone concentrations were increased suggested that either association of the probe with the enzyme was inhibited by hydroquinone or there was degradation of the protein as a function of hydroquinone-induced apoptosis.