Caffeine-induced recovery from G2 block caused by neocarzinostatin

Caffeine was found to act as a stimulator of the recovery of HeLa-S3 cells from the G2 phase arrest induced by a cancer chemotherapeutic agent, neocarzinostatin (NCS). When the cells were incubated in the presence of caffeine after removal of NCS, the time required for the recovery of mitosis was dependent on the concentration of NCS and was markedly shortened by caffeine treatment in a concentration-dependent manner. When puromycin, a specific protein synthesis inhibitor, was added together with caffeine, a temporary recovery of mitosis was observed, followed by an irreversible arrest of mitosis, suggesting that the terminal point of action of NCS resides closer to the M phase than that of puromycin. These results indicate that the mechanism of NCS-induced G2 block is closely related to that of X-ray-induced G2 block.