Akt/mTOR activation in cisplatin-resistant cells. (A) Cisplatin sensitivity. OV433 cells were chronically exposed to gradually increased concentrations of cisplatin starting from 0.1 to 0.8 µg/ml for over 6 months. Both parental (P) and cisplatin-resistant (CR) cells were treated with cisplatin (50 µM) for 24 h, and cisplatin sensitivity was determined by MTT assays. Data are representative of three independent experiments. **P < 0.001, statistically significant. (B) Activation of the Akt/mTOR pathway by cisplatin. OV433-P and -CR cells were treated with cisplatin (50 µM) for 24 h. Total protein was extracted, and the levels of PARP, phosphorylated Akt, mTOR, and p70S6 K were determined by Western blot analysis. Actin was used as a loading control.