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 microM. We investigated the cytotoxic mechanisms of various doxorubicin concentrations in MOLT-4 ALL-cells. Concentrations of up to 100 microM doxorubicin achieved similar cytotoxic effects in cultures of MOLT-4 cells, but acted via different mechanisms. Doxorubicin induced apoptosis (maximum effect at 1 microM), which was dependent on RNA synthesis and involved oxidative stress. Concentrations higher than 3 microM did not induce apoptosis, but significantly inhibited RNA synthesis. DNA strand breaks in MOLT-4 cells occurred in the presence of 1 to 5 microM 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 microM 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.