Virsik-Köpp, P., Hofman-Hüther, H., Rave-Fränk, M. and Schmidberger, H. The Effect of Wortmannin on Radiation-Induced Chromosome Aberration Formation in the Radioresistant Tumor Cell Line WiDr. Radiat. Res. 164, 148–156 (2005).

We analyzed the formation of radiation-induced chromosome aberrations in the cells of the radioresistant colon carcinoma cell line WiDr after treatment with wortmannin, an inhibitor of PI-3 kinases, including DNA-PK. Cells irradiated in G₀/G₁ phase with 200 kV X rays were treated with wortmannin before or after irradiation. Chromosome-type and chromatid-type aberrations were scored in metaphase cells by either Giemsa staining or FISH. Moreover, DNA-PK activity was measured in the absence and presence of wortmannin. In irradiated G₀/G₁-phase WiDr cells, only chromosome-type aberrations, including simple and complex exchanges and excess acentrics, were observed. After addition of 1 to 20 μM wortmannin, the formation of chromosome-type exchange aberrations was completely suppressed. The irradiated cells displayed exclusively chromatid-type aberrations including simple and complex chromatid exchanges and chromatid/isochromatid breaks. Whether the chromatid-type aberrations arise during G₀/G₁ as a result of homologous recombination processes coping with damaged DNA or whether DNA damage induced during G₀/G₁ phase persists until S and G₂ phase and is then processed by homologous recombination pathways must be investigated further.