Figure 1.

Characterization of cisplatin resistance in head and neck cancer cell lines. A. IC₅₀ determination of cisplatin in UMSCC-17B, UMSCC-17B/CP, UMSCC-25 and UMSCC-25/CP. Cells were treated with cisplatin (0-100 μM) for 72 hours at 37°C. Representative results from at least three experiments for each of the two treatments are shown. Error bars represent standard error of mean of three wells (*, P < 0.05). B. Cisplatin induced caspase 3/7 activity in parental but not resistant cells. Cells were treated with cisplatin (20 μM) for 48 hours. Caspase 3/7 activity was evaluated following the protocol. The results are representative of three independent experiments (**, P < 0.01). C. Cisplatin induced caspase-3 cleavage in parental but not resistant cells. The indicated cells were treated with cisplatin (0-20 μM) for 24 hours and lysed and cleaved caspase 3 was measured by western blot. The results are representative of three independent experiments.