Effect of concentration on the cytotoxic mechanism of doxorubicin-apoptosis and oxidative DNA damage

Anthracycline derivatives such as doxorubicin are part of many chemotherapeutic regimens and reach peak plasma concentrations of 5 mu M. We investigated the cytotoxic mechanisms of various doxorubicin concentrations in MOLT-4 ALL-cells. Concentrations of up to 100 mu M doxorubicin achieved similar cytotoxic effects in cultures of MOLT-4 cells, but acted via different mechanisms. Doxorubicin induced apoptosis (maximum effect at 1 mu M), which was dependent on RNA synthesis and involved oxidative stress. Concentrations higher than 3 mu M did not induce apoptosis, but significantly inhibited RNA synthesis. DNA strand breaks in MOLT-4 cells occurred in the presence of 1 to 5 mu M doxorubicin to a similar extent, but showed a dose-dependence at higher concentrations. There was no GC/MS-detectable oxidation of DNA bases in apoptotic cells and only 1 out of 13 DNA base oxidation products, 8-hydroxyguanine, increased significantly in the presence of as much as 100 mu M doxorubicin. These results suggest that at pharmacologically relevant concentrations apoptosis and not oxidative DNA damage is the main killing mechanism of doxorubicin against ALL cells. (C) 1997 Academic Press