Gastric cancer (GC) represents a major health problem. HER2, when amplified, is the only validated druggable target. Adding trastuzumab, an anti HER2 monoclonal antibody, to first line chemotherapy improves overall survival. However, many patients do not benefit of this treatment due to some undiscovered mechanisms of primary resistance. Thus, we try to identify the role of PI3K and MAPKK pathways activation in a panel of HER2 positive gastric cancer cell lines (GCCL).
To evaluate primary resistance to anti HER2 treatment, we selected 3 HER2+ GCCL (SNU216, NCI-N87 and OE 19), and 2 negative (AGS and SNU 484). A somatic mutational analysis was conducted, (Oncocarta panel 1.0 by MassArray Sequenom) to better characterize our panel. Microsatellite instability (MSI) by PCR was also investigated. To assess sensitivity, cells were treated with two different anti HER2 drugs, trastuzumab and lapatinib. MTT assays were performed to identify IC50. A PI3K dual mTOR inhibitor (GSK 458) and a MEK inhibitor (Pimasertib) were also tested to explore the role of PI3K and MAPKK pathways in primary resistance. Protein expression by western blot (WB) at baseline and after treatment was done. FACS technology was performed to study changes in Apoptosis and Cell Cycle.
Baseline WB, confirmed the overexpression of HER2 in SNU216, NCI-N87 and OE19 cell lines, while AGS and SNU 484 resulted negative. Our cell lines have different mutational profiles. MSI was not detected. In MTT assays, our HER2+ GCCL were sensitive to anti HER2 drugs. At baseline, according with our WB evaluation, both PI3K and MAPKK pathways were activated in all cell lines studied. GSK 458 and Pimasertib were tested as single agents and in combination. An anti-proliferative effect of GSK 458 when combined with trastuzumab and lapatinib was detected. Apoptosis and Cell Cycle assays confirmed that inhibition of PI3K pathway, with GSK 458, added to anti HER2 drugs, was able to increase apoptosis and decrease the S phase of cell cycle. Inhibition of molecular targets was confirmed by post treatment WB.
Our experiments indicate that PI3K pathway have a role in primary resistance to anti HER2 agents in GCCL.
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All authors have declared no conflicts of interest.