Abstract 4909: Androgen targeted therapy induces ZEB1 expression and is associated with suppression of androgen signalling and therapy resistance

Abstract

Abstract Reactivation of the embryonic developmental pathway, epithelial-to-mesenchymal transition (EMT) is associated with prostate cancer (PCa) metastasis and therapy resistance. Recent evidence has demonstrated EMT is stimulated following androgen targeted therapy (ATT). In the present study we investigated the role of EMT transcription factor ZEB1 in ATT-driven EMT, PCa metastasis and drug resistance. Immunohistochemistry (IHC) staining of ZEB1 on tissue microarrays of primary tumors from clinical samples demonstrated ZEB1 expression correlated with increased tumor aggressiveness and Gleason score. Upon stratification of patient data (n=198), high ZEB1 protein expression correlated with a shorter time to biochemical recurrence (BCR). Furthermore, IHC staining of primary tumours from 148 treatment-naïve patients with and without metastasis demonstrated high ZEB1 levels and correlated to a reduced time to metastasis. To delineate the role of ZEB1 as a molecular driver of late-stage PCa, microarray analysis of an in vivo LNCaP progression model demonstrated ZEB1 levels increased following castration. Significantly, high ZEB1 levels were associated with patients who had undergone neoadjuvant hormone therapy with or without docetaxel and high ZEB1 levels were associated with a shorter time to BCR and metastasis. Inhibition of the androgen/androgen receptor (AR) axis in LNCaP cells using antiandrogen treatment or shRNA targeting AR resulted in upregulation of ZEB1 in LNCaP cells suggesting enhanced levels of ZEB1 may drive the early adaptive response of PCa after hormone therapy. Interestingly, in models where ZEB1 expression was elevated this was accompanied with repression of classical androgen-regulated genes suggesting ZEB1 is able to regulate the AR transcriptional pathway. We also investigated the role of ZEB1 in cancer invasion and chemoresistance. An inducible model of ZEB1 overexpression in LNCaP cells produced a robust EMT upon ZEB1 expression and was accompanied by an invasive phenotype in 3D cultures. ZEB1 overexpression also conferred resistance to docetaxel (IC50 of 8.17±2.45nM in ZEB1-expressing cells vs. 3.35±0.23nM in control cells) potentially as a result of a reduced apoptotic cell death response mediated by ZEB1. At suboptimal doses of docetaxel, the percentage of apoptotic cells (annexin-V+/propidium iodide-) decreased 4-fold when ZEB1 was expressed compared with control cells and was accompanied by a reduction in PARP cleavage and cleaved caspase-7 expression. In summary, we provide evidence that ZEB1 expression is increased in response to ATTs and correlates with disease progression, metastasis and therapy resistance. We also show ZEB1 is a transcriptional regulator of AR signalling in PCa, Together this provides the rationale to target ZEB1 for the development of novel therapies for the treatment of CRPC. Note: This abstract was not presented at the meeting. Citation Format: Katrina G. Sweeney, Nataly Stylianou, Gregor Tevz, Atefeh Taherianfard, Katrina Pirlo, Akanksha Upadhyaya, Ellca Ratther, Melanie Lehman, Martin Gleave, Jennifer Gunter, Elizabeth D. Williams, Colleen C. Nelson, Brett Hollier. Androgen targeted therapy induces ZEB1 expression and is associated with suppression of androgen signalling and therapy resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4909. doi:10.1158/1538-7445.AM2017-4909