Abstract 2052: A novel antibody blocks anti-apoptotic activity of MUC1 in pancreatic cancer cell lines

Introduction: The third leading cause of cancer-related deaths in the United States is pancreatic cancer, >95% of which is Pancreatic Ductal Adenocarcinoma or PDAC. MUC1 is a transmembrane glycoprotein expressed on normal glandular epithelial cells. In PDAC, MUC1 is overexpressed and aberrantly glycosylated and is designated tumor associated MUC1 (tMUC1). Over 80% of human PDAC expresses tMUC1. In a NCI initiated study, out of 75 tumor antigens, MUC1 was ranked the second most targetable antigen. Furthermore, the 72 amino acid cytoplasmic tail of MUC1 (MUC1 CT) is reported to aid in oncogenic signaling leading to tumor progression and metastasis by blocking apoptosis. A novel monoclonal antibody, TAB004, has been developed specifically against tMUC1. TAB004 detects tMUC1 with a high rate of specificity and sensitivity and spares recognition of normal epithelial MUC1. HYPOTHESIS: Treatment with TAB004 curbs PDAC cell survival by blocking MUC1 CT associated oncogenic signaling and renders the cells more susceptible to standard chemotherapy drugs. Methods: Several human PDAC cell lines based on their tMUC1 expression were grown in media with heat-inactivated serum to ensure that it is devoid of complement proteins. Cells were treated with various concentrations of TAB004 antibody, control IgG, 5-FU, paclitaxel, or gemcitabine and the IC50 was determined using the MTT or SRB cell survival assays. Once IC50 was determined, cells were treated with combinations of TAB004 and the chemotherapy drugs. To determine apoptosis, treated cells were stained with Annexin V-FITC and PI, and analyzed by flow cytometer. tMUC1 expression and localization was determined by staining cells with TAB004.Cy5.5 and imaged by confocal microscopy. Data analysis was performed using GraphPad Prism 7.0 and a p value of Results: By itself, TAB004 treatment had minimal effect on most of the cell lines tested except for Capan2. The IC50 of TAB004 was ~400ugs/ml for Capan2. However, when combined with Gemcitabine, PTX, or 5-FU, TAB004 significantly increased anti-tumor efficacy of the drugs, especially 5-FU in Capan2, and 5-FU and gemcitabine, and PTX in BxPC3.MUC1. Annexin V-FITC and PI staining confirmed the MTT data in Capan2 cells. Fluorescent images showed that TAB004 internalizes in MUC1-positive PDAC cell lines but not in MUC1-negative cells. Conclusions: TAB004 has a dose-dependent, complement-independent growth-inhibitory effect on Capan2 cells (IC50 is ~400ug/ml). TAB 004 internalizes and activates apoptosis in Capan2 cells. The combination of TAB004 with chemotherapy drugs increases the efficacy of drug-induced killing of PDAC cells. Future studies will determine the mechanism of TAB004 induced apoptosis and sensitization of PDAC cells to drug-induced killing. Citation Format: Mukulika Bose, Pinku Mukherjee. A novel antibody blocks anti-apoptotic activity of MUC1 in pancreatic cancer cell lines [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 2052.