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Focal Adhesion Kinase Silencing Augments Docetaxel-Mediated Apoptosis in Ovarian Cancer Cells

Authors' Affiliations: Departments of ¹ Gynecologic Oncology and ² Cancer Biology, University of Texas M.D. Anderson Cancer Center, Houston, Texas; ³ Department of Psychology, University of Iowa, Iowa City, Iowa: and ⁴ Department of Cell and Developmental Biology and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina

Requests for reprints: Anil K. Sood, Departments of Gynecologic Oncology and Cancer Biology, University of Texas M.D. Anderson Cancer Center, 1155 Herman Pressler, Unit 1362, Houston, TX 77030. Phone: 713-745-5266; Fax: 713-792-7586; E-mail: asood{at}mdanderson.org.

Objective: Docetaxel causes cell death through induction of apoptosis; however, cell death characteristics for docetaxel have not yet been fully elucidated. We examined the role of focal adhesion kinase (FAK) cleavage in docetaxel-mediated apoptosis.

Methods: FAK degradation after treatment with docetaxel was determined in both taxane-sensitive (HeyA8 and SKOV3) and taxane-resistant (HeyA8-MDR and SKOV3-TR) ovarian cancer cell lines by Western blot analysis. Cell growth was determined with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. FAK-targeting small interfering RNA (siRNA) was used to decrease FAK expression. Apoptosis and caspase activity were determined using commercially available kits.

Results: SKOV3 and HeyA8 cell lines were both sensitive to docetaxel (IC₅₀ levels, 1-6.2 nmol/L), whereas the SKOV3-TR and HeyA8-MDR cells were resistant (IC₅₀ 250 nmol/L for both). Docetaxel induced high rates of apoptosis in SKOV3 and HeyA8 cells (84% and 66% apoptosis, respectively) but minimal apoptosis (5-8%) in SKOV3-TR and HeyA8-MDR cells. Similarly, FAK was cleaved in SKOV3 and HeyA8 cells in response to docetaxel treatment but unchanged in the resistant cells. Caspase-3 and caspase-8 activity also increased significantly in docetaxel-treated SKOV3 and HeyA8 cells but not in the taxane-resistant cells. DEVD-fmk (caspase-3 blocker) was able to block both FAK cleavage and apoptosis mediated by docetaxel in SKOV3 and HeyA8 cells. FAK siRNA transfection resulted in 70% to 90% decrease in FAK levels in all cell lines within 72 hours. FAK silencing augmented docetaxel-mediated growth inhibition (5- to 8-fold increase) and apoptosis in both of the taxane-sensitive and taxane-resistant cell lines.

Conclusions: Docetaxel induces FAK cleavage, mediated through activation of caspase-3, in taxane-sensitive ovarian cancer cells but not in taxane-resistant cells. The absence of FAK degradation may contribute to cell survival in taxane-resistant cells. FAK silencing promotes the in vitro efficacy of docetaxel in both taxane-sensitive and taxane-resistant cell lines and may serve as a novel therapeutic approach.

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