Hyperthermic effects on cell killing in Dictyostelium discoideum amoebae treated with DNA-damaging agents

Hyperthermic effects on cell killing of amoeboid cells treated with DNA-damaging agents of Dictyostelium (D.) discoideum were studied. Though the amoeboid cells are usually cultured at 23°C, heat treatment at 30°C for 15 min immediately after UV irradiation markedly enhanced cell killing, while not observed in the case of heat treatment immediately before UV irradiation. Similar effects were observed in the case of heat treatment after treatment with 4-nitroquinoline 1-oxide, cis-platinum(II) di-amminedichloride or 8-methoxypsoralen photoaddition, while not observed when heat was applied before these treatments. On the contrary, little enhancement by heat treatment was observed even after treatment with N-methyl-N'-nitrc-N-nitrosoguanidine or methylmethanesulphonate. The hyperthermic mechanisms in D. discoideum are discussed, based on a diverse set of DNA lesions caused by chemicals and DNA repair mechanisms for them.