Upstream and Downstream Co-inhibition of Mitogen-Activated Protein Kinase and PI3K/Akt/mTOR Pathways in Pancreatic Ductal Adenocarcinoma

Abstract

BACKGROUND: Extensive cross talk exists between PI3K/Akt/mTOR and mitogen-activated protein kinase (MAPK) pathways, and both are upregulated in pancreatic ductal adenocarcinoma (PDAC). Our previous study suggested that epidermal growth factor receptor inhibitor erlotinib which acts upstream of these pathways acts synergistically with PI3K inhibitors in PDAC. Horizontal combined blockade upstream and downstream of these two pathways is therefore explored. METHODS: Erlotinib paired with PI3K inhibitor (BYL719) was tested against erlotinib plus dual PI3K/mTOR inhibitor BEZ-235, and MEK inhibitor (PD98059) plus BEZ235, on five primary PDAC cell lines and on two pairs of parent and erlotinib-resistant (ER) cell lines. A range of in vitro assays including cell proliferation, Western blotting, migration, clonogenic, cell cycle, and apopotic assays was used to test for the efficacy of combined blockade. RESULTS: Dual downstream blockade of the MAPK and PAM pathways was more effective in attenuating downstream molecular signals. Synergy was demonstrated for erlotinib and BEZ235 and for PD-98059 and BEZ-235. This resulted in a trend of increased growth cell cycle arrest, apoptosis, cell proliferation, and colony and migration suppression. This combination showed more efficacy in cell lines with acquired resistance to erlotinib. CONCLUSIONS: The additional mTOR blockade provided by BEZ235 in combined blockade resulted in increased anticancer effect. The hypersensitivity of ER cell lines to additional mTOR blockade suggested PAM pathway oncogenic dependence via mTOR. Dual downstream combined blockade of MAPK and PAM pathways with MEK and PI3K/mTOR inhibitor appeared most effective and represents an attractive therapeutic strategy against pancreatic cancer and its associated drug resistance.

Noninvasive Bioluminescence Imaging of AKT Kinase Activity in Subcutaneous and Orthotopic NSCLC Xenografts: Correlation of AKT Activity with Tumor Growth Kinetics

“…Results show that there was a lack of apoptosis induction which corresponds also with the observation from other groups [37], [44]. Although apoptosis can be induced independently of caspase activation, resistance to TKIs like erlotinib may be caused by blocking apoptosis induction [45], [46]. Thus, successful induction of cancer cell death can be accomplished by combination therapies, for example, with HDAC inhibitors [37].…”

Phospho-Akt overexpression is prognostic and can be used to tailor the synergistic interaction of Akt inhibitors with gemcitabine in pancreatic cancer

“…Limited published preclinical research focusing on this issue in PDAC reported similar cytotoxic activity of perifosine in PANC-1, MIA PaCa-2, and AsPC-1 cells [55]. Sensitivity to perifosine in the PDAC cells also fell within the range of IC 50 values previously reported in PDAC cell lines and spheroids for other Akt inhibitors, such as NVP-BEZ-235 [56, 57]. …”

“…It is already known that in PDAC cells, dual PI3K-mTOR inhibition induces rapid overactivation of MAPK pathway through a PI3K-independent pathway [67], and that drug resistance may be overcome by inhibition of parallel oncogenic-dependent pathways, such as with the dual MEK and PI3K/mTOR blockade [57]. …”

Suppression of Tumor Growth and Muscle Wasting in a Transgenic Mouse Model of Pancreatic Cancer by the Novel Histone Deacetylase Inhibitor AR-42

“…Furthermore, mutations in Akt in addition to KRAS mutations may accelerate PDAC development [33]. Recently, targeting the PI3K/Akt pathway in combination with blockade of MAPK has been shown to increase cell cycle arrest and apoptosis in pancreatic cancer cell lines [34]. We previously reported that AR-42 induces dephosphorylation of Akt through release of PP1 from PP1-HDAC complexes independent of histone acetylation [19].…”