Abstract 1558: Therapeutic targeting of cell surface plectin induces anti-cancer immune response and pancreatic cancer regression

Background: Pancreatic ductal adenocarcinoma (PDA) is the 3rd deadliest cancer, diagnosed typically in advanced stages, with only an 8% 5-year survival rate, thus demonstrating the need for novel therapeutic approaches that significantly enhance chemo- and/or immune-therapy. Our team previously identified a promising functional target for cancer therapy in PDA, cell surface plectin 1 (CSP1) that is aberrantly expressed on PDA cells and thus a cell surface-associated biomarker of cancer. CSP1 expression first becomes apparent in high grade dysplasias, remaining high in early and advanced cancers and in metastases. Our first-in-human imaging trial in PDA patients using a CSP1-targeted imaging agent revealed that CSP is an available target and accessible for binding, a potentially a target for cancer therapy. We hypothesized that a monoclonal antibody (mAb) against CSP1 could lead to novel pancreatic cancer treatment options, thus, we developed a therapeutic mAb, e.g., ZB131, representing a first-in-class antibody selectively targeting CSP1. Methods: ZB131 is a humanized mAb targeted against human plectin 1 (rhSec8) that also binds murine CSP1. ZB131 affinity and its effect on cancer cells including proliferation, cytotoxicity, and migration were tested in vitro using saturation binding, SRB-based survival assays, flow cytometry, and migration assays on various pancreatic cell types and homeostatic “normal” controls. In vivo validation was performed using two nu/nu mouse models bearing subcutaneous MiaPACA2 or Yapc PDA cells, and a syngeneic KPC-derived tumor model to also evaluate immune responses to tumors treated with ZB131 or IgG control. Results: ZB131 exhibits high specificity and high affinity (0.4±0.1nM) to CSP1, and functionally induces G0 growth arrest followed by necrotic cell death of PDA cells in culture, and is synergistic with gemcitabine resulting in a 50-fold decrease in IC50. In vivo, in subcutaneous xenograft models, ZB131 monotherapy decreased PDA tumor volume 5-fold as compared to controls, and in combination with cisplatin resulted in sustained tumor reduction with greater than 85% tumor necrosis. In subcutaneous syngeneic PDA models, ZB131 induced complete tumor regression within 35 days mediated by an anti-tumor immune response as upon tumor rechallenge, full tumor regression was again achieved without additional ZB131 therapy. Leukocyte complexity analysis of regressing PDA tumors versus controls revealed an ~3-fold increase in effector and central memory T cells. Conclusion: CSP1 is a first in class anti-cancer target expressed on the cell surface of PDA, as well as other cancers including ovarian, esophageal and head neck. ZB131, an anti-CSP1 mAb, induces tumor cell intrinsic cell death, as well as a robust anti-tumor T cell response leading to complete tumor regression indicating the potential therapeutic efficacy of ZB131 in late-stage cancers. Citation Format: Julien Dimastromatteo, Amanda Poisonnier, Samantha Perez, Lisa Coussens, Kimberly Kelly. Therapeutic targeting of cell surface plectin induces anti-cancer immune response and pancreatic cancer regression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1558.