title: Resistance of ovarian carcinoma cells to docetaxel is XIAP dependent and reversible by phenoxodiol.
abstract: Although several pathways have been proposed to explain chemoresistance, all lead to some specific defect in the mechanism of apoptosis. The objective of this study was to characterize the molecular mechanisms of drug resistance to docetaxel in epithelial ovarian cancer cells (EOC) and the use of phenoxodiol as a chemosensitizer. Four established and 12 primary cultures of ovarian carcinoma cell lines (EOC) were treated with docetaxel (5-500 ng/ml) for 24 and/or 48 h. In all the studied cell lines, the best response was seen using 500 ng/ml of docetaxel. Sensitive cell lines were identified as those with IC50 < 100 ng/ml for 48 h while resistant cell lines were identified as those with IC50 > 100 ng/ml. The morphological features of apoptosis and the activation of caspases were seen only in the sensitive cell lines determined by Hoechst staining and Caspase Glo assay. Although X-linked inhibitor of apoptosis protein (XIAP) was expressed in all EOC cells, it was only inactivated in chemosensitive cells. We confirmed the role of XIAP in docetaxel resistance by downregulation of XIAP expression using RNA interference (RNAi) as well as by pretreatment with phenoxodiol. Our results indicate that 1) docetaxel induces its cytotoxic effect through the activation of apoptosis; 2) caspase activation relies on the removal of XIAP; and 3) phenoxodiol restores sensitivity in docetaxel-resistant EOC cells. We demonstrate that phenoxodiol, by interfering with XIAP activity, functions as a chemosensitizer to docetaxel and could provide a more effective treatment for refractory ovarian cancer.
authors.affiliation: Department of Obstetrics & Gynecology, Yale University School of Medicine, P.O. Box 208040, New Haven, CT 06520-8040, USA.
authors.forename: Eva
authors.initials: E
authors.lastname: Sapi
authors.forename: Ayesha B
authors.initials: AB
authors.lastname: Alvero
authors.forename: Wei
authors.initials: W
authors.lastname: Chen
authors.forename: David
authors.initials: D
authors.lastname: O'Malley
authors.forename: Xiao-Ying
authors.initials: XY
authors.lastname: Hao
authors.forename: Bambang
authors.initials: B
authors.lastname: Dwipoyono
authors.forename: Manish
authors.initials: M
authors.lastname: Garg
authors.forename: Marijke
authors.initials: M
authors.lastname: Kamsteeg
authors.forename: Thomas
authors.initials: T
authors.lastname: Rutherford
authors.forename: Gil
authors.initials: G
authors.lastname: Mor
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis; D002277:Carcinoma / Q000473:pathology*; D000077143:Docetaxel; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D005260:Female; D006801:Humans; D007529:Isoflavones / Q000494:pharmacology*; D010051:Ovarian Neoplasms / Q000473:pathology*; D011506:Proteins / Q000494:pharmacology*; D034622:RNA Interference; D043823:Taxoids / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D051636:X-Linked Inhibitor of Apoptosis Protein; D016335:Zinc Fingers
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D007529:Isoflavones; D011506:Proteins; D043823:Taxoids; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D000077143:Docetaxel; C471183:phenoxodiol