Figure 4.

Cross-resistance pattern and γ-radiation activity in HRS and HRSdx cells. (A) The resistance factor (RF) value is the ratio of the HRSdx IC₅₀ (KM-H2dx and HDLM-2dx) over the HRS IC₅₀ (KM-H2 and HDLM-2). RFs are reported in ascending order. RF < 1 indicates cross-sensitivity (CS), and RF ≥1 indicates cross-resistance (CR). An RF ranging from 1 to 2 indicates low CR, an RF from 2 to 5 indicates moderate CR, and an RF ≥ 5 indicates high CR. (B–D) Tumor cells were treated with γ-radiation (0–12 Gy). Then, cell viability, clonogenic growth, and cell cycle distribution were evaluated. (B) Cells were double-stained with Annexin-V-FITC and 7AAD and analyzed via flow cytometry. Bar charts show the percentage of viable cells (Annexin-V and 7AAD negative cells). (C) Clonogenic growth assay. Untreated and γ-radiation-treated cells were seeded in medium containing 0.8% methylcellulose and cultured for 14 days; aggregates with ≥40 cells were scored as colonies. Values (total number of colonies) are the mean ± SD of eight replicates. (D) Bar charts show the percentage of cells in each cell cycle phase, evaluated after propidium iodide staining and flow cytometry analysis. (E) Representative cytofluorimetric histograms of the cell cycle progression after γ-radiation treatment. Results are the mean ± SD of three independent experiments. * p < 0.05 HRSdx vs. parental HRS cells.