Background: The prototypical antiprogestin mifepristone exhibits potent growth inhibition activity towards ovarian cancer cells in vitro and in vivo. The aim of this research was to establish whether mifepristone is capable of inhibiting cell proliferation and inducing apoptotic cell death regardless of the degree of sensitivity ovarian cancer cells exhibit to cisplatin.

Repopulation of cancer cells that escape cytotoxic chemotherapy is a critical factor that negatively impacts treatment success. Thus, any strategy that prevents this phenomenon from occurring would be beneficial for the outcome of the treatment. One such strategy to inhibit tumor cell repopulation is the use of cytostatic compounds among courses of cytotoxic therapy. In this study, we tested the hypothesis that mifepristone, a steroid compound displaying a potent cytostatic effect in ovarian cancer as recently demonstrated in our laboratory (Clin Cancer Res 2007, 13, 3370-3379), should be efficacious to induce cytostasis and to prevent ovarian cancer repopulation if given in between rounds of cisplatin therapy. We established an in vitro approach in which OV2008 cisplatin-sensitive ovarian cancer cells were exposed to three rounds of a cytotoxic dose (20 μM) of cisplatin for 1 h, twelve days apart. Every four days the number of cells, their viability, and their distribution within the cell cycle were assessed by micro-cytometry using exclusion fluorochromes and propidium iodide, respectively. Further, the colony-forming capacity of the viable cells was evaluated along the experiment. Although cisplatin killed the vast majority of OV2008 cells, there were cells that escaped cisplatin toxicity and repopulated the culture. This phenomenon occurred each one of the three times the cells were challenged by cisplatin during the 36 days the study lasted. Post-cisplatin repopulation was evidenced by the increase in number and clonogenic capacity of the viable cells, the normalization in the distribution of cells within the different phases of the cell cycle (S, G1 and G2/M), and the concomitant reduction in sub-diploid DNA content (as marker of cytotoxicity). Instead, when the cells were exposed to cisplatin for 1 h, but 5, 10 or 20 μM mifepristone was present in the culture medium after removal of the platinum agent, both number of cells and their clonogenic capacity were reduced in a dose-related manner. Remarkably, the cultures exposed to cisplatin for 1 h followed by chronic exposure to 20 μM mifepristone did not have remaining viable cells to allow performing the clonogenic survival assay by day 12 of the study, suggesting an added lethality to the cytostatic effect of mifepristone. In conclusion, this study demonstrates that presence of cytostatic concentrations of mifepristone prevents the repopulation of ovarian cancer cells surviving the lethality of cisplatin, and further suggests mifepristone may potentiate cisplatin toxicity. The scheduling of mifepristone between courses of cisplatin-based therapy for human ovarian cancer has potential for improving treatment success. Supported by NIH grant CA121991.

Abstract. Repopulation of cancer cells escaping lethal chemotherapy is a critical factor hindering treatment success. One strategy to inhibit tumor cell repopulation is the use of cytostatic compounds between courses of lethal chemotherapy.In this study, we tested the hypothesis that mifepristone (MF), a steroid compound with demonstrated growth inhibition activity in ovarian cancer, should be efficacious in inducing cytostasis and preventing repopulation of ovarian cancer cells if given among rounds of cisplatin (CDDP) treatment. We established an in vitro approach wherein ovarian cancer cells with high (OV2008) or low (SK-OV-3) sensitivity to CDDP were exposed to 3 (OV2008) or 2 (SK-OV-3) rounds of lethal doses of CDDP for 1 h, 12 (OV2008) or 24 (SK-OV-3) days apart. Every 4 or 8 days cell number, cell viability, cell cycle traverse, and colony-forming capacity of viable cells was analyzed. Although CDDP killed the vast majority of cells, there were remnant cells escaping CDDP lethality and repopulating the culture, as evidenced by increased cell number, improved clonogenic capacity of viable cells, and normalization of DNA synthesis. Conversely, when cells were exposed to CDDP for 1 h, and 5, 10 or 20 μM MF was present in the culture medium after CDDP removal, the number, clonogenic capacity, and DNA synthesis ability of the cells were reduced in a dose-dependent manner. The blockage by MF of post-CDDP repopulation was accompanied by a remarkable increase in the percentage of cells expressing the cell death marker cleaved poly(ADP-ribose) polymerase and the mitotic marker phospho-histone H3, suggesting that MF also potentiated CDDP lethality and that the cells likely die due to mitotic failure. In summary, this is the first study reporting that presence of cytostatic concentrations of MF after courses of lethal doses of CDDP prevents repopulation of remnant ovarian cancer cells surviving CDDP treatment.

Faculty members from the University of South Dakota attended the Curriculum Reform Institute offered by the University of Wisconsin at Oshkosh, WI, during the summer of 2002 to design a course sequence for elementary education majors that better meets their needs for both content and pedagogy based on the science education standards. The special section of introductory biology that resulted from this workshop is designed to use laboratories and activities that either help students learn major concepts in the life sciences or model how to teach these concepts to their future K-8 students. This study describes how the active, hands-on learning opportunity for preservice teachers with its emphasis on both content and performance-based assessment was implemented in an introductory biology course for elementary education majors during the spring of 2004. During the initial offering of this course, student perceptions about what helped them to learn in the special section was compared with their nonscience major peers in the large lecture-intensive class that they would have taken. Each group of students completed early and late web-based surveys to assess their perceptions about learning during the courses. After the completion of the course, students in the special section appreciated how the relevance of science and conducting their own scientific experimentation helped them learn, enjoyed working and studying in small groups, valued diverse class time with very little lecture, were more confident in their abilities in science, and were more interested in discussing science with others. This course format is recommended for science classes for preservice teachers.