Park, H. J., Lee, S. H., Chung, H., Rhee, Y. H., Lim, B. U., Ha, S. W., Griffin, R. J., Lee, H. S., Song, C. W. and Choi, E.;thK. Influence of Environmental pH on G₂-Phase Arrest Caused by Ionizing Radiation. Radiat. Res. 159, 86–93 (2003).

We investigated the effects of an acidic environment on the G₂/M-phase arrest, apoptosis, clonogenic death, and changes in cyclin B1-CDC2 kinase activity caused by a 4-Gy irradiation in RKO.C human colorectal cancer cells in vitro. The time to reach peak G₂/M-phase arrest after irradiation was delayed in pH 6.6 medium compared to that in pH 7.5 medium. Furthermore, the radiation-induced G₂/M-phase arrest decayed more slowly in pH 6.6 medium than in pH 7.5 medium. Finally, there was less radiation-induced apoptosis and clonogenic cell death in pH 6.6 medium than in pH 7.5 medium. It appeared that the prolongation of G₂-phase arrest after irradiation in the acidic environment allowed for greater repair of radiation-induced DNA damage, thereby decreasing the radiation-induced cell death. The prolongation of G₂-phase arrest after irradiation in the acidic pH environment appeared to be related at least in part to a prolongation of the phosphorylation of CDC2, which inhibited cyclin B1-CDC2 kinase activity.