Abstract
Cellular signaling pathways involving mTOR, PI3K and ERK have dominated recent studies of breast cancer biology, and inhibitors of these pathways have formed a focus of numerous clinical trials. We have chosen trametinib, a drug targeting MEK in the ERK pathway, to address two questions. Firstly, does inhibition of a signaling pathway, as measured by protein phosphorylation, predict the antiproliferative activity of trametinib? Secondly, do inhibitors of the mTOR and PI3K pathways synergize with trametinib in their effects on cell proliferation? A panel of 30 human breast cancer cell lines was chosen to include lines that could be classified according to whether they were ER and PR positive, HER2 over-expressing, and “triple negative”. Everolimus (targeting mTOR), NVP-BEZ235 and GSK2126458 (both targeting PI3K/mTOR) were chosen for combination experiments. Inhibition of cell proliferation was measured by IC50 values and pathway utilization was measured by phosphorylation of signaling kinases. Overall, no correlation was found between trametinib IC50 values and inhibition of ERK signaling. Inhibition of ERK phosphorylation was observed at trametinib concentrations not affecting proliferation, and sensitivity of cell proliferation to trametinib was found in cell lines with low ERK phosphorylation. Evidence was found for synergy between trametinib and either everolimus, NVP-BEZ235 or GSK2126458, but this was cell line specific. The results have implications for the clinical application of PI3K/mTOR and MEK inhibitors.
Highlights
The MAPK (Mitogen activated protein kinase) pathway (RASRAF-MEK-ERK) and PI3K-AKT-mTOR pathways play dominant roles in regulating diverse cellular processes, including proliferation and survival, in breast cancer
We initially chose four breast cancer cell lines characterised by a diversity of activated signaling pathway and estrogen receptor (ER) expression: MCF-7 and T47D were ER+, SKBr3 was HER2+ and MDA-MB-231 was triple-negative
PI3K and MAPK pathway usage was analyzed by western blots (Figure 2A and B)
Summary
The MAPK (Mitogen activated protein kinase) pathway (RASRAF-MEK-ERK) and PI3K-AKT-mTOR pathways play dominant roles in regulating diverse cellular processes, including proliferation and survival, in breast cancer. These pathways have been identified as important for breast cancer behavior for a number of years [1,2] and interact strongly with the estrogen receptor (ER) pathway, as shown by cross-talk in the development of tamoxifen resistance in breast cancer [3,4]. The MAPK pathway is a validated therapeutic target in breast cancer, the mechanisms underlying the poor clinical response to MEK inhibition remain unclear. Activating mutations in PIK3CA, affecting the PI3K-AKT-mTOR pathway, are frequent in breast cancer [9] and raise the question of whether they alter the balance of pathway utilization
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
