Development of novel MUC1-C targeting antibody-drug conjugate for pancreatic cancer treatment.

e15025 Background: Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive forms of cancers, which is usually diagnosed in advanced stages and presents an abysmal 5-year survival rate of 3-10%. With late detection of metastasized/advanced disease, curative surgery is not an option for most patients. Accordingly, there is an urgent unmet need for development of therapeutics targeting the pancreatic cancer cells. MUC1 is one such cell surface antigen that is aberrantly overexpressed in most solid tumors including pancreatic cancer. In this study we report preclinical efficacy of pharmacological inhibition of MUC1 signaling by GO-203 and targeted delivery of toxin conjugated to novel MUC1-C antibodies (7B8 and 3D1) binding to the extra cellular domain (ECD) to the PDAC xenografts. Methods: Subjects from TCGA-PAAD were stratified into high (75 th percentile) and low (25 th percentile) MUC1-expressing cohorts. Differential expression was performed using DESeq2, followed by GSEA, and signaling network analysis using partial correlation networks, ARACNE, and BC3NET. Anti-MUC1 antibody-drug conjugates (ADCs) were generated by coupling monomethyl auristatin E (3D1-MMAE, 7B8-MMAE) via V-C-PAB linker and characterized for anti-tumor activity against pancreatic cancer cells including MIA PaCa-1, CAPAN2 and HAPF-II. Paired-end RNA-seq (50bp) was aligned and quantified to the Human Ensembl GRC38 reference using STAR aligner. Subcutaneous xenografts were obtained in nude mice by injecting 5X10 6 HPAF-II tumor cells. Results: Differential expression, pathway, and network analyses revealed consistent dysregulation of cancer survival-related processes, and P53-related pathways in the cohort with increased MUC1 expression. The ADCs (DAR of ~3.5) exhibited efficient internalization in cancer cells and associated apoptotic cell death (Kds = 2 - 5nM). Pharmacological inhibition of MUC1 signaling by GO-203 demonstrated reduction in canonical pathways including P53 and EMT. Treatment with 3D1-MMAE compared to both vehicle and GO-203 showed dysregulation of cellular metabolism pathways (cholesterol homeostasis, glycolysis) and exhibited several strong indicators of cellular stress including activation of unfolded protein response processes and mTorc1 signaling. Excellent tumor-suppressive effects of ADCs were observed in HPAF-II xenografts in nude mice. The 7.5 mg/kg (i.v., q7dx3), treatment showed complete tumor regression from 14th day (end of treatment) till the date of termination (Day 50). Doses up to 40 mg/kg were well tolerated by the mice and this anti-tumor efficacy was observed without any appreciable loss in body weight or adverse effects on tissues. Conclusions: Targeted delivery of MMAE toxin to the pancreatic cancer cells presents an exciting opportunity for a novel therapeutic intervention for the treatment of pancreatic cancer patients with MUC1 over expression in tumors.