Hepatoma Synthesis in the Interaction of Daunorubicin with H-35 Rat Evidence for Inhibition of Growth Related to Compromised DNA

The H-35 rat hepatoma is relatively insensitive to the anthracycline antibiotic, daunorubicin (DNR), requiring 0.25 MMdaunorubicin for in hibition of cell proliferation by 50%. Studies were undertaken to inves tigate the basis for the apparent intrinsic resistance in this cell line. The relative insensitivity of the H-35 cells to DNR is not a function of metabolic inactivation of DNR to deoxyaglycone derivatives; after a 2-h incubation, less than 10% of drug is metabolized, exclusively by conver sion to daunorubicinol. The limited toxicity of DNR to the rat hepatoma may be explained, in part, by the absence of DNA strand breaks at daunorubicin concentrations up to l ¿IMwhile higher (supraclinical) DNR concentrations (5 and 10 MM) produce direct, "non-protein-associated" DNA strand breaks. Limited daunorubicin toxicity in this tumor cell line may also be related to the apparent absence of free radical-mediated cellular damage as the free radical scavengers dimethyl sulfoxide, catalase, mcthanul, and mannitol fail to reverse the inhibitory effect of l /IM DNR on cell proliferation. Daunorubicin does not induce leakage of the cytoplasmic enzyme, glutamic oxaloacetate transaminase, or diminish mitochondria) enzyme function. Conversely, while drug effects on RNA synthesis are small, and protein synthesis is minimally diminished, inhibition of cell proliferation corresponds closely with inhibition of DNA synthesis.