Caspase-3 activation during apoptosis caused by glutathione–doxorubicin conjugate

Glutathione–doxorubicin (GSH–DXR) effectively induced apoptosis in rat hepatoma cells (AH66) at a lower concentration than DXR. After 24 h of drug treatment, DNA fragmentation of the cells was observed at the concentration of 1.0 μM DXR or 0.01 μM GSH–DXR. Increase in caspase-3 activity and DNA fragmentation were observed within 12 h and 15 h after treatment with either drug. Intracellular caspase-3 activity was increased in a dose-dependent manner after treatment with DXR or GSH–DXR, and caspase-3 activity correlated well with the ability to induce DNA fragmentation. When the cells were treated with either DXR or GSH–DXR for only 6 h, apoptotic DNA degradation and caspase-3 activation occurred 24 h after treatment. DNA fragmentation caused by these drugs was prevented completely by simultaneous treatment with the caspase-3 inhibitor, acetyl–Asp–Glu–Val–Asp-aldehyde (DEVD-CHO), at 10 μM. By contrast, DNA fragmentation was not prevented by the caspase-1 inhibitor, acetyl–Tyr–Val–Ala–Asp–aldehyde (YVAD-CHO), at the same concentration as DEVD-CHO, and caspase-1 was not activated at all by the treatment of AH66 cells with both DXR and GSH–DXR. These results demonstrate that DXR and GSH–DXR induce apoptotic DNA fragmentation via caspase-3 activation, but not via caspase-1 activation, and that GSH–DXR enhances the activation of caspase-3 approximately 100-fold more than DXR. Moreover, the findings suggested that an upstream apoptotic signal that can activate caspase-3 is induced within 6 h by treating AH66 cells with the drug. © 1999 Cancer Research Campaign