The Notch Pathway as a Biomarker in Pancreatic Ductal Adenocarcinoma and its Potential Therapeutic Modulation

Pancreatic ductal adenocarcinoma (PDAC) is the 5th commonest cause of cancer related deaths in the UK and has a poor prognosis with 1-year survival of only 10%. Improved understanding of pancreatic carcinogenesis would allow identification of biomarkers to predict disease progression, prognosis, and allow targeting of novel therapeutics. The Notch pathway involves a group of transmembrane receptors, important in tissue development, which re-activate in a number of malignancies. Preliminary evidence suggests this occurs in PDAC. The aim of this study was to examine Notch pathway components as potential diagnostic and prognostic markers in PDAC, as well as a therapeutic target. Nuclear Notch-1, -3, -4 and their targets HES-1 and HEY-1 were up-regulated in a series of 42 resected PDAC compared to normal pancreas. Further up-regulation was seen when in advanced tumours. Nuclear Notch-3 and its target HEY-1 were associated with shortened survival following resection, with HEY-1 maintaining prognostic significance on multivariate analysis. Notch-1 siRNA knockdown resulted in reduction in viability, G1 arrest and induction of apoptosis, with Notch-3 knockdown resulting in reduction in viability, G2/M arrest and induction of apoptosis. Treatment with the gamma secretase inhibitor (GSI)-I resulted in greater inhibition than seen with combined Notch-1/3 knockdown. These effects however, were not confirmed in a murine xenograft model of PDAC using an alternative GSI, MRK-003. These findings may relate to poor pharmacological activity or reduced bioavailability of this particular agent in the mouse model. Using immunoprecipitation and mass spectrometry, a method was developed to detect a fragment of the Notch receptor in plasma of patients with PDAC. Although Notch-1 could not be detected, Notch-3 was detected in both controls and patients with PDAC, although at higher levels in the later. This may suggest a role as diagnostic biomarker.