Effects of PTS2 treatment on cancer cells viability. (A) Four cancer cell lines were treated with indicated doses of PTS2 for 36 h. Cell viability was determined by MTT assay. Untreated cells were expressed as 100%. Data are means ± S.D. from 3 independent experiments. *P < 0.05; **P < 0.01; ***P < 0.001 compared with untreated controls. (B) Cancer cells were incubated with 2.5 μg/ml of PTS2, harvested at indicated times, and counted. Results show cell numbers increase over time. Data are means ± S.D. from 3 independent experiments.