The inhibitor of oxidative phosphorylation, 2,4-dinitrophenol (DNP), abrogates etoposide cytotoxicity in murine leukemia L1210 cells without affecting the quantity of drug-induced DNA lesions. Cell cycle arrest and events associated with cell death were followed in etoposide treated L1210 cells under conditions in which DNP reduced cytotoxicity greater than 100-fold. Micronucleation, associated with mitotic catastrophe, and apoptotic internucleosomal degradation of DNA, were both inhibited by DNP co-treatment to an extent consistent with clonogenic survival. However, the ability of etoposide to cause cell cycle arrest was minimally affected by DNP. For the same proportion of cells arresting in G(2), DNP co-treatment profoundly reduced etoposide cytotoxicity, suggesting a separation between etoposide-induced G(2) arrest and cell death. At the same concentration used to treat L1210 cells, DNP was unable to abrogate etoposide cytotoxicity in HeLa, Chinese hamster ovary or HL60 cells. The relationship between ongoing macromolecular synthesis during etoposide treatment and clonogenic survival was further studied in L1210 and HeLa cells. In general, L1210 cells were more sensitive than HeLa cells to inhibition of macromolecular synthesis by DNP. A higher DNP concentration did partially block etoposide cytotoxicity in HeLa cells, in association with increased inhibition of macromolecular synthesis. It was not possible to attribute the reduced cytotoxicity of etoposide in HeLa cells to inhibition of DNA or RNA synthesis alone, because inhibitors with greater specificity (aphidicolin and DRB) had no effect on clonogenic survival. However, aphidicolin partially abrogated etoposide cytotoxicity in L1210 cells, although to a lesser extent than DNP. These data indicate that inhibition of DNA or RNA synthesis alone during etoposide exposure is insufficient to abrogate killing of HeLa cells, that inhibition of etoposide cytotoxicity in HeLa cells may require the additional inhibition of protein synthesis, and that the modulating effects of ongoing DNA synthesis on etoposide cytotoxicity are cell line dependent.

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