Objective: Cisplatin- and Taxol-induced apoptosis was studied in four human ovarian cancer cell lines to evaluate apoptosis as a measure of chemosensitivity.
Methods: In vitro sensitivities of OVCAR-3, SKOV-3, UL-1, and UL-2 cells to cisplatin or Taxol were determined by the sulforhodamine B assay. Induction of apoptosis was studied by DNA fragmentation following treatment with cisplatin and/or Taxol after 24- and 48-hr exposure. DNA fragmentation was further quantitated by the diphenylamine assay and the proportion of cells in the G1, G2/M, and S phase of the cell cycle was determined by flow cytometry. Presence of the p53 gene product was examined by Western blotting.
Results: The four cell lines represent various sensitivities to cisplatin and Taxol (LD50 range for cisplatin, 5-30 microg/ml; Taxol, 30-1000 nM). UL-2 represents a resistant cell line which was 10-30 times resistant to Taxol and 6 times resistant to cisplatin when compared to the others. Demonstration of apoptosis correlated with the sensitivity of the cell lines to both cisplatin and Taxol for OVCAR-3 and UL-2. DNA fragmentation of OVCAR-3 was uniformly present when treated with cisplatin or Taxol, at 24 or 48 hr. UL-2 demonstrated no apoptosis after 24 or 48 hr of treatment with either cisplatin or Taxol. When sequencing experiments were performed with cisplatin and Taxol, DNA fragmentation correlated with the cytotoxicity assays, except in UL-1 cells where no significant difference was observed in different interactions of cisplatin and Taxol. Pretreatment with Taxol generally resulted in enhanced cytotoxicity in a schedule-dependent manner, and increased fragmentation was demonstrated; cisplatin pretreatment consistently resulted in decreased fragmentation. Quantitation of the fragmented DNA correlated with that seen on gel electrophoresis. OVCAR-3 and UL-1 demonstrated the greatest change from baseline at 24 hr (3.8 and 3.7 times baseline, respectively), whereas UL-2 had little change from the baseline following treatment. G1 arrest occurred more readily in OVCAR-3 and SKOV-3 cells. UL-2 cells had very little change in the proportion of cells entering G1 arrest, but had a significant increase in the G2/M proportion. In OVCAR-3, UL-1, and UL-2 cells, we demonstrated the presence of an aberrantly expressed p53 gene product, while no p53 was detected in the SKOV-3 cells.
Conclusions: Our findings indicate that the ability to achieve significant cytotoxicity by cisplatin and Taxol may be directly related to the induction of apoptosis; however, cellular and genetic characteristics determine the eventual outcome of these treatments.