Abstract 1728: Targeting hedgehog reverses taxane resistance by Gli-dependent and independent mechanisms in ovarian cancer

Abstract Objective: Recent studies have implicated hedgehog signaling in the formation and continued growth of a variety of malignancies, including ovarian cancer. Several inhibitors of the hedgehog pathway have been identified that block the activity of the Smoothened (Smo) receptor. The goal of this study was to determine the in vitro and in vivo effects of Smo antagonists alone and in combination with chemotherapy in ovarian cancer. Methods: Expression of hedgehog signaling components (Smo, Gli1 and Gli2) was assessed in 3 pairs of parental and chemotherapy-resistant ovarian cancer cell lines (A2780ip2/A2780cp20, SKOV3ip1/SKOV3TRip2, HeyA8/HeyA8MDR) using Western blot and qPCR. Cell lines were exposed to increasing concentrations of two different Smo antagonists (Cyclopamine, LDE225) alone and in combination with carboplatin, paclitaxel, adriamycin, and topotecan. Selective knockdown of Smo, Gli1 and Gli2 was achieved using siRNA constructs. Cell viability was assessed by MTT assay and PARP cleavage was used as an indicator of apoptosis. SKOV3TRip2 orthotopic xenografts were treated with vehicle, LDE225, paclitaxel or combination therapy for 5 weeks. Tumor weight for each treatment group was measured and compared using student's t-test. Results: Expression of Smo and Gli1 was high in A2780ip2/A2780cp20, moderate in SKOV3ip2/SKOV3TRip2 and low/absent in HeyA8/HeyA8MDR. Gli2 was high in SKOV3ip2/SKOV3TRip2, moderate in A2780ip2/A2780cp20 and low in HeyA8/HeyA8MDR. Response to cyclopamine and LDE225 varied among the cell lines examined with IC50s ranging from 7.5 to >20 µM. Both agents sensitized chemotherapy-resistant cell lines to paclitaxel (5- to 26-fold, including Smo[low]/Gli1[neg] HeyA8MDR), but not to carboplatin, adriamycin, or topotecan. Selective knockdown of Gli1 and Gli2 resulted in taxane sensitization only in Gli1/2-high A2780cp20 cells (2- to 8-fold). A decrease in acetyl-α-tubulin confirmed microtubule-specific effects of Smo targeting, supporting the taxane specificity of this effect. In vivo, SKOV3TRip2 xenografts treated with LDE225 or paclitaxel alone had slightly less tumor burden than the control group (reduced by 28.1%, p=0.42 and 32.0%, p=0.40, respectively). Those treated with combined LDE225 and paclitaxel, however, had significantly less tumor burden than those treated with vehicle (70.5% reduction, p=0.015). Conclusions: Targeting the hedgehog pathway decreases cell viability and increases taxane sensitivity in taxane-resistant ovarian cancer models. Interestingly, these effects were noted even in cells with little constitutive hedgehog activity. This suggests both Gli-dependent and -independent mechanisms contribute to taxane resistance, expanding the potential use of hedgehog inhibitors to all taxane-resistant tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1728. doi:10.1158/1538-7445.AM2011-1728