title: Cisplatin inhibits paclitaxel-induced apoptosis in cisplatin-resistant ovarian cancer cell lines: possible explanation for failure of combination therapy.
abstract: Combination chemotherapy using paclitaxel with a platinum-based regimen is currently the standard first-line therapy for ovarian cancer after surgical cytoreduction. Whereas cisplatin-paclitaxel combination chemotherapy has shown significant efficacy over previous drug combinations in ovarian cancer, 20-30% of patients fail to respond to this combination. These patients are deemed cisplatin-paclitaxel resistant, although it is unclear whether the tumors are resistant to one or both drugs. Because the options available to ovarian cancer patients for second-line therapy are limited, and knowing that mechanistic differences exist between cisplatin and paclitaxel, we assessed the efficacy of combination drug therapy on cisplatin-resistant (cisplatinR) ovarian cancer cells. We found that paclitaxel induced apoptosis in cisplatinR cells as well as in the cisplatin-sensitive parental cell lines. In cisplatinR C-13 cells, the concomitant addition of cisplatin blocked paclitaxel-induced apoptosis as determined by DNA fragmentation assays, fluorescence microscopy, and flow cytometry. Paclitaxel-induced multimininucleation was also inhibited when the cells were exposed sequentially to paclitaxel and then cisplatin. Cisplatin did not block paclitaxel-induced stabilization of microtubules or prevent paclitaxel-induced loss of Bcl-2 expression in cisplatinR cells. Conversely, paclitaxel did not inhibit p53 protein accumulation by cisplatin. These results suggest that cisplatin blocks paclitaxel-induced apoptosis at a point downstream of Bcl-2 degradation and independent of microtubule stabilization. Our research shows that cisplatin can inhibit the effectiveness of paclitaxel in cispatinR cell lines. Therefore, the establishment of a clinical protocol to evaluate the efficacy of paclitaxel alone versus another second-line regimen in patients with cisplatin-paclitaxel-resistant ovarian cancer is warranted.
authors.affiliation: Department of Obstetrics and Gynecology, University of North Carolina, Chapel Hill 27599-7295, USA.
authors.forename: P L
authors.initials: PL
authors.lastname: Judson
authors.forename: J M
authors.initials: JM
authors.lastname: Watson
authors.forename: P A
authors.initials: PA
authors.lastname: Gehrig
authors.forename: W C
authors.initials: WC
authors.lastname: Fowler
authors.forename: J S
authors.initials: JS
authors.lastname: Haskill
mesh_terms: D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000008:administration & dosage / Q000037:antagonists & inhibitors*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects*; D002453:Cell Cycle / Q000187:drug effects; D002945:Cisplatin / Q000008:administration & dosage / Q000494:pharmacology*; D053938:DNA Fragmentation; D019008:Drug Resistance, Neoplasm; D005260:Female; D006801:Humans; D015162:Micronucleus Tests; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism; D009363:Neoplasm Proteins / Q000378:metabolism; D014411:Neoplastic Stem Cells / Q000187:drug effects / Q000473:pathology; D010051:Ovarian Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D017239:Paclitaxel / Q000008:administration & dosage / Q000037:antagonists & inhibitors*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D017211:Treatment Failure; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D000972:Antineoplastic Agents, Phytogenic; D009363:Neoplasm Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D017239:Paclitaxel; D002945:Cisplatin