Fig. 8. p53-dependent radiosensitization but p53-independent cell kill by STP. A, proliferation of E1A/ras-transformed p53-deficient cells was assessed 24 h after treatment with STP (20 nM) and IR (5 Gy) or both in combination. B, proliferation of the transformed p53-deficient cells after treatment with increasing doses of STP (0, 20, and 300 nM). C, caspase-3-like activity was determined 6 h after treatment in cytosolic extracts from p53-deficient cells using Ac-DEVD-pNA as a colorimetric caspase-3 substrate (CTL) 6 h after treatment with STP. D, formation of active caspase-3 was determined after STP treatment (300 nM) using an antibody recognizing the cleaved caspase-3 subunit.