Analysis of events associated with cell cycle arrest at g₂ phase and cell death induced by cisplatin

DNA is the accepted target for cisplatin, but recent evidence has shed doubt on DNA synthesis as the critical process. L1210/0 cells incubated for 2 hours with cisplatin progress to the G₂ phase of the cell cycle and are arrested there for several days. They then either progress in the cell cycle or die. In cells that eventually die, total transcription, polyadenylated [poly(A)⁺] RNA synthesis, and protein synthesis were markedly inhibited only after 48 hours. Nicotinamide adenine dinucleotide (NAD) and adenosine triphosphate (ATP) levels decreased after 3 days. Cell membrane integrity was lost after 4 days. These results demonstrate that cells can be lethally damaged, yet continue to undergo apparently normal metabolic activities for several days. In a previous study, DNA double-strand breaks were detected after 1 day. We now show that by 2 days, breaks are visible as fragmentation in the nucleosome spacer regions of chromatin. This type of damage is consistent with cell death occurring by the process of apoptosis. Cell shrinkage and morphology were also consistent with this type of cell death. The slow cell death reported here appears to occur at the G₂/M transition and may involve events that normally occur at this stage of the cell cycle. These results demonstrate the importance of DNA degradation as an early and possibly essential step in cell death. [J Natl Cancer Inst 82: 749-755, 1990]