Clonogenic survival assay. (A) Cells were treated with increasing concentrations of etoposide in the presence or absence of NU7026 (10 μM) for 16 hours. ▪ indicates etoposide alone; and □, etoposide + NU7026. (B) cells were treated with increasing concentrations of NU7026 in the presence or absence of etoposide (0.1 μM) for 16 hours. ▪ indicates NU7026 alone; and □, NU7026 + etoposide. Cells were then plated in soft agar for colony formation in the absence of drugs. Results are the means of 4 experiments ± SE.