Pre-conditioning under hypoxia decreased cellular sensitivity to treatment, inducing DNA double-strand breaks.

<p>(A) Cellular viability after bleomycin treatment in HSC-2, with or without pre-conditioning under hypoxia, were assessed using the MTT assay. IC₅₀ value was calculated in order to compare cellular sensitivity to bleomycin. (B) Cellular viability after γ-ray irradiation in HSC-2, with or without pre-conditioning under hypoxia, were assessed with the MTT assay. HSC-2 cells were incubated under normoxic or hypoxic conditions for 24 hours before irradiation. After re-oxygenation, cells were irradiated with the indicated doses. After irradiation, the cells were cultured under normoxic conditions for 96 hours and cellular viabilities were evaluated with the MTT assay. Relative MTT tetrazolium reduction activities (relative viabilities) were calculated as the ratio to the value at 24 hours. Columns are the mean of three independent experiments; bars, SD. <i>P</i> values calculated with Student’s <i>t</i> test were: *, <i>P</i> < 0.05; **, <i>P</i> < 0.01.