Pancreatic Ductal Adenocarcinoma (PDAC) is the most common type of pancreatic neoplasia,
accounting for more than 90% of all pancreatic cancer cases. Despite improvements in early diagnosis
and treatment, the 5-year survival rate has remained unvaried for many decades.
The aim of this PhD project was to elucidate the roles of two specific ion channels in the
pathophysiology of PDAC: voltage-gated sodium channel (VGSC) and the Ca2+- activated K+ channel
KCa3.1. Human pancreatic cell lines of different metastatic potential were used: HPDE (human
pancreatic ductal epithelial) cells, Panc-1, MiaPaCa-2, BxPC-3 and Capan-1 cells. VGSCs, typically
expressed in neuronal, ‘excitable’ cells, were also found earlier to be functional in several different
carcinomas, where they are linked to promotion of the metastatic potential. KCa3.1, which serves a
diversity of physiological roles such as cell-volume regulation in erythrocytes and migration in
macrophages and microglia, may also promote tumour invasiveness as shown for some tumours
including gliomas end endometrial cancer.
Initially, the expression of different VGSC subtypes (Nav1.1 - Nav1.7) was screened in PDAC
cell lines and abundant levels of mRNA and protein were found. However, whole-cell patch clamp
recordings detected a small inward current (~ 30 pA/pF) only in the 10% of MiaPaCa-2 cells, one of
the most aggressive cell lines available. Based on the PCR, western blot and patch clamp results
obtained, we hypothesized that epidermal growth factor receptor (EGFR) might suppress VGSC
expression to protect the Na+/H+ exchanger (NHE1), which has been proposed to serve a ’backbone’
function in driving PDAC metastasis by promoting extracellular acidosis. Indeed, when the EGFR
pathway was blocked pharmacologically (by AG1478 10 μM) an increased inward Na+ current was
detected by whole-cell patch clamp. Further experiments showed that a combination treatment of
AG1478 and TTX (tetrodotoxin) and cariporide (an NHE1 inhibitor) and TTX could reduce cell
migration further than treatments alone. This suggested that inhibition of the EGF-EGFR signalling
cascade increases VGSC activity and this promoted metastatic cell behaviours.
We also found that KCa3.1 channel was overexpressed at mRNA, protein and functional levels
in PDAC compared to control cells . We demonstrated both pharmacologically and by gene - silencing
approach that this channel regulated the migration and proliferation of MiaPaCa-2 cell line, revealing
its potential as another target for therapy, as it has been also suggested in other carcinomas (i.e.
endometrial cancer).
These results are discussed in their respective chapters. The Thesis ends with a General
Discussion chapter, where recent findings on the pathophysiology of PDAC are further highlighted in
relation to the findings of the thesis.