The Effect of Hyperthermia on the Cell Kinetics of Colon Cancer Cell Line

Viability of the Cells Accumulated in G2M Phase after Heating

Abstract

Perturbation of the cell cycle, particularly accumulation into the G2M phase occurs after hyperthermia. However, the viability of the G2M phased cells has not been examined. The effects of hyperthermia and hyperthermia combined with mitomycin C on the cytotoxity and cell kinetics of WiDr cells, human colon cancer cell line, were studied by clonogenic assay and flow cytometrical cell cycle analysis. Next, cells accumulated into the G2M phase after heating must be separated for evaluation of their clonogenic potential by the flow cytometrical cell sorting technic. The surviving fraction of WiDr cells decreased with the rise of heating temperature and the prolongation of heating time, especially at 44°C.
In flow cytometrical cell cycle analysis, accumulation into the G2M phase was observed after heating. In the 44°C group, accumulation into the G2M phase lasted for 48 hours after heating. In the cell cycle analysis of the cells heated in combination with mitomycin C, the proportion of G2M phased cells increased in comparison with the heating alone group. The surviving fraction of sorted GOG1 phased cells and G2M phased cells decreased with increasing temperature. The degree of reduction of the surviving fraction was marked in the G2M phased cells. The surviving fraction of the cells heated in combination with mitomycin C was markedly reduced in comparison with the cells heated alone. Consequently, the marked accumulation into the G2M phase resulting from hyperthermia shows the severity of damage of the cells, and these G2M phased cells were presumed to be the population of cells which were subject to lethal damage. The proportion of G2M phased cells after heating was considered to be a parameter of the anti-tumor effect and the sensitivity of hyperthermia.