Abstract 2833: Epithelial cell adhesion molecule (EpCAM) is associated with prostate cancer progression and chemo-/radio-resistance in vitro and in vivo

Prostate cancer (CaP) is the most common cancer in males in Australia which caused more than 3000 deaths in 2015. EpCAM is a transmembrane protein that is expressed at low levels in a variety of human epithelial tissues, but overexpressed in most solid tumors. Our previous study indicated that EpCAM was strongly expressed in metastatic CaP cell lines, primary human CaP tissues and lymph node metastasis and is a biomarker involved in CaP progression, and chemo-/radio-resistance. However, the role of EpCAM in CaP progression and therapeutic resistance is still uncertain. The aim of this study was to investigate the role of EpCAM in CaP progression and chemo-/radio-resistance as well as underlying mechanisms in vitro and in vivo. Methods: EpCAM gene was knocked down (KD) in PC-3, DU145 and LNCaP CaP cell lines using shRNA. Proliferation assay, colony formation assay, docetaxel (DTX) and radiation dose-response assay were carried out to evaluate the effect of KD of EpCAM on proliferation and therapeutic response of CaP cells in vitro. Subcutaneous (s.c) and orthotopic CaP animal models were established using PC- 3-EpCAM-KD and PC-3-EpCAM-scramble (scr) control cells in NOD/SCID mice, to assess the effect of EpCAM on CaP tumourigenecity, chemotherapy (DTX) and radiation response. Signal transduction proteins in PI3K/Akt/mTOR signaling pathway, as well as proliferation, apoptotic and radiation response markers were evaluated by immunohistochemistry in xenografts. Results: KD of EpCAM reduced CaP proliferative potential and enhanced DTX and radiation sensitivity in three CaP cell lines. Both s.c and orthotopic EpCAM-KD xenografts displayed suppressed tumor growth and increased DTX and radiation responsiveness compared to EpCAM-scr control xenografts in NOD/SCID mice. Marked down-regulation of PI3K/Akt/mTOR pathway proteins (p-Akt and p-mTOR) and proliferation marker (Ki-67) and significant up-regulation of apoptotic (Caspase-3) and radiation (γ- H2AX) responses to chemo-/radio-therapies were found in EpCAM-KD xenografts, compared with control xenografts. In addition, Kaplan-Meier curve analysis demonstrated that KD of EpCAM improved median survival (MS) of tumor-bearing mice by 21.5 days compared with the control group (HR=26.94, CI95% 4.317-168.1, p=0.0004) and that KD of EpCAM improved MS of tumor-bearing mice which received docetaxel (50mg/kg, single dose, i.p.) by 11 days (HR=20.95, CI95% 3.599-121.9, p=0.0007), and radiotherapy (2Gy/day for 4 days) by 12 days (HR=11.00, CI95% 2.11-57.36, p=0.0044) compared with the control group, respectively. Conclusions: EpCAM plays an important role in CaP progression and chemo-/radio-resistance via PI3K/Akt/mTOR signaling pathway in vitro and in vivo and it is a promising therapeutic target for the treatment of CaP. EpCAM targeted therapy combined with chemo-/radio-therapy could be a novel modality for treatment-resistant CaP.