Effects of hyperthermia on the differentiation and growth of K562 erythroleukemic cell line

Several agents are known to induce differentiation in the human erythroleukemic cell line K562. In this work we have studied the ability of hyperthermia to induce differentiation in the K562 cell line. K562 cells were treated with hyperthermia in the range of 41–45 °C. Cell proliferation and the plating efficiency of heat treated cells along with their hemoglobin synthesis was measured and compared with controls. Hyperthermia severely inhibited the growth of K562 cells in the suspension culture in a time- and temperature-dependent manner. Sixty minutes of heating and 44 and 40 min of heating at 45 °C totally inhibited the growth of the cells. The number of clonogenic cells also decreased as a result of heat treatment. Extended periods of heating for more than 2 h at 41 °C resulted in thermal adaptation. Hyperthermia-induced hemoglobin synthesis by these cells, only at 42 and 43 °C. Maximum induction was observed after heat treatment for 80 min at 43 °C and 180 min at 42 °C. At lower temperature, although the fraction of surviving cells was high, but no signs of hemoglobin synthesis could be observed. At temperatures higher than 43 °C, the fraction of surviving cells decreased rapidly and also no signs of hemoglobin synthesis could be detected. At the two selective temperatures, hemoglobin synthesis started 4 days after heat treatment. The results showed that hyperthermia caused cytotoxicity and growth arrest and induced differentiation as judged by hemoglobin synthesis and reduced clonogenicity in this cell line. This is the first time that a physical agent has been shown to induce differentiation in erythroleukemic cell lines.