Survival fraction after exposure to various genotoxic agents. A) bleocin, B) cisplatin, C) mitomycin C, and D) camptothecin. Black square represents HeLa cells, white triangle indicates U87-MG cells, and black reverse triangle indicates U-CH1-N chordoma cell line. Cells were exposed to drugs at 37° for 1 hour. 2-4 independent experiments were carried out.