Abstract 3310: N-cadherin promotes docetaxel resistance through upregulated TLR4 signaling in castration resistant prostate cancers

Abstract

Abstract Introduction: Docetaxel is a common therapeutic agent given to men with castration-resistant prostate cancer (CRPC). However, a number of patients show poor response or eventually develop resistance. Previously, different groups have suggested an association between chemoresistance and epithelial to mesenchimal transition (EMT) in certain advanced cancers. N-cadherin, a calcium-dependent cell-cell adhesion surface protein associated with EMT, is implicated in castration resistance and metastasis in prostate cancer. We have shown in previous studies that monoclonal antibodies raised against the extracellular domain of N-cadherin have potential therapeutic effects in castration-resistant tumor growth and metastasis. In this study, our objective is to determine the role of N-cadherin expression in chemoresistance and whether treatment with monoclonal antibodies restores chemosensitivity. Methods: Tissue microarrays of CRPC and high grade prostate cancer clinical samples were stained for TLR4. N-cadherin positive and negative cell lines were evaluated for sensitivity against docetaxel. N-cadherin and TLR4 were ectopically expressed in N-cadherin negative prostate cancer cells (LNCaP, VCaP). Docetaxel resistant cell lines (LNCaP-DocR and VCaP-DocR) were established through prolonged exposure to 10-20uM Docetaxel. For in vitro experiments, these models were used to evaluate cytotoxicity and apoptosis in the presence of docetaxel. N-cadherin expressing cell lines were treated with 2A9 monoclonal antibody (mAb), which was raised against the extracellular domain of N-cadherin, and by N-cadherin siRNA knockdown. For in vivo studies, N-cadherin positive xenografts were treated with 2A9 mAb and docetaxel, and tumor growth monitored over time. Results: Tissue microarray results showed significant TLR4 expression in CRPC samples (p < 0.005). In vitro studies showed TLR4 induction correlated with N-cadherin expression. This upregulation of N-cadherin and TLR4 expression promoted docetaxel resistance in CRPC by the activation of NF-kB signaling. Monoclonal antibodies against N-cadherin and TLR4 potentiated docetaxel induced cytotoxicity. Docetaxel resistant cells exhibited EMT phenotypes with increased invasion and castration resistant growth. Treatment with 2A9 antibody restored sensitivity to docetaxel. Combination therapy with 2A9 monoclonal antibody and docetaxel significantly affected tumor growth in N-cadherin positive CRPC xenograft models. Conclusions: These studies suggest that N-cadherin promotes TLR4-dependent docetaxel resistance in CRPC. Although further investigation will be needed, therapeutic targeting of N-cadherin with monoclonal antibodies in combination with therapeutic agents such as docetaxel may have significant clinical benefit. Citation Format: Tatsuya Shimomura, Evelyn Kono, Chau P. Tran, Joyce Yamashiro, Shu Lin, Sean Hyung-Kwon Lee, Zev A. Wainberg, Robert E. Reiter. N-cadherin promotes docetaxel resistance through upregulated TLR4 signaling in castration resistant prostate cancers. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3310. doi:10.1158/1538-7445.AM2014-3310