Sunday June 30, 2019 from 07:30 to 09:00
Investigating a novel recombinant antibody to attenuate prostate cancer progression by targeting cell surface GRP78
Ali Al-Hashimi1, Kevin Won 1, Elizabeth Pham 2, Natalie Mariano2, Julie Bailis2, Richard Austin1, Bobby Shayegan1.
1Department of Surgery and Medicine , McMaster University , Hamilton, ON, Canada; 2Department of Research , Amgen, South San Francisco , CA, United States
Introduction: Tissue factor (TF), a procoagulant protein, drives prostate cancer (PCa) tumour progression via activation of GRP78 on the cell surface (cs). In PCa, GRP78 is an endoplasmic reticulum-resident chaperone that localizes to the cell surface, where it functions as a signaling molecule with antigenic properties. PCa patients produce autoantibodies (AutoAbs) against the N-terminus of GRP78 that act as a potent driver of tumour growth via upregulation of TF activity and prosurvival pathways. Here, we describe a recombinant anti-GRP78 antibody (AEP8587) that competes with the binding of AutoAbs to csGRP78, decreases TF activation, and may act as a novel therapeutic antibody with anti-tumour activity.
Methods: Changes in TF activity or survival were evaluated in vitro in the PCa cell line DU145 following treatment with anti-GRP78 AutoAbs or co-treatment with either enoxaparin, a low molecular weight heparin (LMWH), or AEP8587. Protein expression of TF and UPR markers was determined using western blotting and qRT-PCR. TF activity was determined using a real-time continuous assay. AutoAbs were purified from PCa patients (St. Joseph’s Healthcare Hamilton).
Results: Pre-prostatectomy PCa patients display high levels of anti-GRP78 AutoAbs (~60 µg/ml), compared to healthy controls (~5 µg/ml). Here, we show that anti-GRP78 AutoAb increases TF activation in vitro and leads to increased tumour progression in a DU145 xenograft model. In contrast, we show a co-treatment of anti-GRP78 AutoAb with either enoxaparin or AEP8587 completely abolishes the AutoAb-mediated increase in TF activity in vitro. Enoxaparin or AEP8587 co-treatment reversed the AutoAb effect on increased UPR markers.
Conclusions: We have identified anti-GRP78 AutoAb as a driver of PCa progression. Our results indicate that a recombinant antibody, AEP8587, can bind to csGRP78 and prevent the binding of anti-GRP78 AutoAbs. This represents a potential novel means to manage PCa progression.