Abstract A064: Hub protein analysis identifies CAD as a mediator for drug resistance in pancreatic cancer

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive disease with poor treatment options, emphasizing the need for novel therapeutic targets. Hub proteins have high connectivity (i.e., many interaction partners) and often act as central biological regulators. Here, we aimed to identify hub proteins with potential involvement in pancreatic cancer. We utilized multiOMIC data from laser-capture micro-dissected human PDAC epithelium (n = 32) and an integrative computational approach to query associations of identified candidate proteins with clinical outcomes in early (n = 186) and advanced PDAC patients (n = 253). Ultimately, we identified the pyrimidine biosynthesis regulator CAD (carbamoyl phosphate synthetase 2, aspartate transcarbamylase, dihydroorotase) as a potentially druggable target in pancreatic cancer. CAD expression was enriched in the malignant PDAC epithelium, and specifically within the basal-like tumour epithelial subtype. Tissue profiling through immunohistochemical staining of resectable PDAC patient samples (n = 165) found an increased proliferative index in samples with high CAD expression, assessed via KI67 positivity. To investigate the role of CAD in proliferation, PDAC cell lines with varying CAD expression were selected. siRNA-mediated knockdown of CAD demonstrated decreased cell proliferation of cell lines with inherently higher CAD expression. Furthermore, patients with higher tumour CAD expression showed poor response to modified FOLFIRINOX (mFFX) but not to Gemcitabine-nab-Paclitaxel treatment. Higher CAD expression was also associated with significantly worse overall survival in patients with advanced disease receiving chemo-treatment, suggesting CAD could influence the treatment response. Modelling this in vitro, first in the cell lines, CAD knockdown resulted in increased sensitivity to 5-Fluorouracil (5-FU) treatment. In preclinical patient-derived PDAC organoids (PDOs) models, we observed that a low-dose of a pharmacological CAD inhibitor increased the sensitivity to 5-FU in PDOs expressing high levels of CAD. Overall, our unbiased computational workflow identifies CAD as both a promising target for drug resistance towards mFFX in pancreatic cancer and a potential biomarker for patient treatment stratification.