Effect of APOs on tumor cell proliferation. Tumor cell lines LSA (A), PE-3T (B), EL-4 (C), and P815 (D) were incubated with 20 μmol/L concentration of APOs for 0 to 72 hours. The viable cell number was calculated as described in Fig 4. Means of cell numbers from experimental groups and the control ± SEM were plotted.