Studies on the mechanism of chemosensitization by misonidazole in vitro.

Misonidazole (MISO) depletes intracellular glutathione and is more toxic in glutathione depleted cells. The depletion is time, temperature, drug concentration and cell line dependent. The role of glutathione depletion in the chemosensitization to alkylating agents obtained after hypoxic pretreatments with MISO was investigated using diethylmaleate (DEM), a thiol-removing agent with specificity for glutathione, to simulate the effects of MISO on intracellular glutathione levels. Melphalan cytotoxicity and binding to macromolecules were measured after pretreatments with MISO or DEM in vitro. From these studies we found that glutathione depletion could account for only a part of the chemosensitization to melphalan and that this component of sensitization was quantitatively related to an increased rate of melphalan binding. Assessments of DNA damage by the alkaline elution assay suggest that DNA strand breaks and DNA crosslinks are enhanced by sublethal pretreatments with MISO.