BACKGROUND: Dipyrithione (PTS2) is widely used as a bactericide and fungicide. 
Here, we investigated whether PTS2 has broad-spectrum antitumor activity by 
studying its cytotoxicity and proapoptotic effects in four cancer cell lines.
METHODS: We used MTT assays and trypan blue staining to test the viability of 
cancer cell lines. Hoechst 33258 and DAPI staining were used to observe cell 
apoptosis. Cell-cycle percentages were analyzed by flow cytometry. Apoptosis was 
assayed using caspase-3 and poly (ADP-ribose) polymerase (PARP) combined with 
Western blotting. Student's t-test was used for statistical analysis.
RESULTS: PTS2 inhibited proliferation in four cancer cell lines in a 
dose-dependent manner. Treated cells showed shrinkage, irregular fragments, 
condensed and dispersed blue fluorescent particles compared with control cells. 
PTS2 induced cycle-arrest and death. Cleavage of caspase-9, caspase-3, and PARP 
were detected in PTS2-treated cells. Antitumor activity of PTS2 was more 
effective against widely used cancer drugs and its precursor.
CONCLUSIONS: PTS2 appears to have novel cytotoxicity and potent broad-spectrum 
antitumor activity, which suggests its potential as the basis of an anticancer 
drug.