Enhancement of cisplatin cytotoxicity in combination with herniarin in vitro.

Combinatorial chemotherapy is a valuable route, which can be conducted by different approaches. Use of cisplatin has been approved by the U.S. Food and Drug Administration for different kinds of cancers including bladder cancer. Herniarin is a member of simple coumarins, which are a group of common secondary metabolites in plants. In this study, the enhancing effects of herniarin on cisplatin cytotoxicity were investigated. Cytotoxicity of herniarin on transitional cell carcinoma (TCC) cells was first investigated in comparison with umbelliferone, the parent compound for a large number of coumarins including herniarin, by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. In order to test the effects of herniarin on cisplatin cytotoxicity, TCC cells were also treated with various combining concentrations of herniarin and cisplatin. In these experiments same amounts of dimethyl sulfoxide were used as controls. After 24, 48 and 72 h of treatments, the effects of herniarin on cisplatin cytotoxicity were evaluated by MTT assay. The level of chromatin condensation which represents the apoptotic morphology was also investigated by 4',6-diamidino-2-phenylindole (DAPI) staining. Results indicated that unlike umbelliferone, its methoxy analog, herniarin, had no significant cytotoxicity on TCC cells. On the other hand, the combination of 80 µg/mL herniarin with 5 µg/mL cisplatin, significantly enhanced the cytotoxicity of cisplatin. Furtheremore, DAPI staining revealed that combining concentrations of herniarin and cisplatin resulted in increased chromatin condensation in comparison with controls. This study is another confirmation for bioactivity of herniarin and shows that it might be a good candidate for further experiments investigating its mechanism of action.