Overcoming primary and acquired erlotinib resistance with epidermal growth factor receptor (EGFR) and phosphoinositide 3-kinase (PI3K) co-inhibition in pancreatic cancer

Abstract

PI3K/Akt is over-expressed in 50-70% of pancreatic ductal adenocarcinoma (PDAC). The hypothesis of this study is that PI3K and EGFR co-inhibition may be effective in PDAC with upregulated PI3K/Akt/mTOR (PAM) signaling. Five primary PDAC and two erlotinib acquired resistant (ER) cell lines with significantly over-expressed AKT2 gene, total Akt and pAkt, were used. Multiple inhibitors of the MAPK and PAM were tested alone or in combination by western blotting, cell proliferation, cell cycle, clonogenic, apoptosis, and migration assays. Erlotinib acted synergistically with PI3Kα inhibitor BYL in both ER cell lines (synergy index, SI=1.71 and 1.44 respectively). Treatment of ER cell lines by this dual blockade caused significant G1 cell cycle arrest (71%, P<0.001; 58%, P=0.003), inhibition of colony formation (69% and 72%, both P<0.001), and necrosis and apoptosis (75% and 53%, both P<0.001), more so compared to parent cell lines. In primary patient-derived tumor subrenal capsule (n=90) and subcutaneous (n=22) xenografts, Erlotinib plus BYL significantly reduced tumor volume (P=0.005). Strong pEGFR and pAkt immunostaining (2+/3+) was correlated with high response to erlotinib and low response to erlotinib plus BYL respectively. In conclusion, PDAC with increased expression of the PAM signaling were susceptible to PI3K/ EGFR co-inhibition suggesting oncogenic dependence. Erlotinib plus BYL should be considered for a clinical study in PDAC; further evaluation of pEGFR and pAkt expression as potential predictive biomarkers is warranted.