Novel cytotoxic agents from an unexpected source: Bile acids and ovarian tumor apoptosis

Abstract

Objective Unique biologic activities have been identified for the 4 different bile acids: cholic acid (CA, chenodeoxycholic acid (CDCA), deoxycholic acid (DCA), and ursodeoxycholic acid (UDCA). The aim of this study was to examine and compare the effects of these 4 bile acids on the human ovarian cancer cell lines A2780 and A2780-CP-R(cisplatin-resistant) and to evaluate mechanisms of action. Methods Antiproliferative effects were determined by the cytotoxic MTT assay. Cells undergoing apoptosis were identified by morphologic analysis of cells stained using Diff-Quick and nuclear staining with DAPI and by quantitative nucleosome ELISA assay. Cells were lysed in buffer after 24 h of exposure to three different concentrations of bile acid (50 mM, 200 mM, and 400 mM) and protein concentrations were determined. Cell extracts containing 25 mg of protein were assayed for protein kinase C (PKC) enzyme activity. Results None of the bile acids stimulated proliferation of ovarian cancer cells. CA and UDCA had only minimal cytotoxic effect even at maximum concentrations. In contrast, DCA and CDCA administration resulted in statistically significant dose-dependent cytotoxicity in both platinum sensitive and platinum-resistant cell lines ( p < 0.05). Cells incubated with DCA and CDCA exhibited morphologic features characteristic of apoptosis. The quantitative nucleosome ELISA assay demonstrated over 10 times increased nucleosome levels after cells were treated for 24 h by DCA and CDCA at 200 mM and 400 mM as compared to CA or UDCA treatment and to untreated controls ( p < 0.01). All 4 bile acids reduced PKC activity at concentrations of 200 and 400 mM ( p < 0.01). Conclusions CDCA and DCA have significant cytotoxic activity in ovarian cancer cells via induction of apoptosis. The mechanism of apoptosis appears to be mediated by alternative kinases distinct from PKC. CDCA and DCA may have clinical utility in the treatment of ovarian cancer pending in vivo confirmation of activity especially in cisplatin-resistant disease.