Effects of Cell Cycle Inhibitors on Cell Death of Human Cancer Cell Lines

Abstract

Genotoxic agents are known to cause cell death mostly by apoptosis in susceptible cells and this action plays an important role in tumor regression after chemotherapy. It has been thought that the apoptotic process may be associated with cell cycle. In the present study, the effect of aphidicolin and nocodazole, reversible cell cycle inhibitors, on the apoptosis or cell death induced by actinomycin D was studied in 3 cell lines. HeLa, SiHa and NIH／3T3 cells were treated with actinomycin D（100 nM）alone or in combination with cell cycle inhibitors for 20 hours; or presynchronized cells were treated with actinomycin D for 4 hours and further incubated for 20 hours in fresh medium. The synergistic effect of IBMX（5 or 10 μM）on the apoptosis or cell death induced by actinomycin D was also studied. The results were as follows; Majority of HeLa cells showed apoptotic changes after actinomycin D treatment. Aphidicolinor nocodazole blocked neither initiation nor progression of actinomycin D-induced apoptosis in HeLa cell. Aphidicolin pretreatment enhanced the actinomycin D-induced apoptosis of HeLa cells and cell death of SiHa cells and nocodazole pretreatment enhanced cell death of SiHa cells. IBMX moderately enhanced actinomycin D-induced cell death of NIH／3T3 and to less extent that of SiHa cells. These results show that neither initiation nor progression of actinomycin D-induced apoptosis or cell death can be blocked by cell cycle arrest, and that cAMP is partly responsible for actinomycin D-induced apoptosis in certain types of cells.