Abstract 3261: Cellular effects of MEK inhibition in pancreatic cancer cell lines are not correlated with « classical » predictive markers of response to MEK inhibitors.
Authors: Neuzillet Cindy , Serova Maria , Tijeras-Raballand Annemilai , Astorgues-Xerri Lucile , Riveiro Maria E. , de Gramont Armand , Ruszniewski Philippe , Hammel Pascal , Faivre Sandrine , Raymond Eric 
Published: August 2014

Background: Deregulations of the Ras-Raf-MEK-ERK pathway, driven by K-RAS mutations (&gt;70%), are frequent in pancreatic adenocarcinoma (PAC). MEK inhibitors (MEKi) are currently under clinical evaluation in PAC. K-RAS and B-RAF mutations, epithelial-to-mesenchymal transition (EMT), PI3K-Akt-mTOR pathway activation, and pERK inhibition under treatment have been suggested as predictive markers for response to MEKi in various cancers, but remain unvalidated in PAC. This study aimed to compare the cellular effects of MEKi in a panel of PAC cell lines, according to their status for these “classical” predictive markers.

Materials and Methods: UO126, AZD6244, AS703026 and GSK1120212 are allosteric non-ATP competitive MEKi. Antiproliferative effects were evaluated by MTT assay. Cell cycle modifications were analyzed by flow cytometry. Protein expression was assessed by Western blot. Combinations were analyzed using the Chou-Talalay method.

Results: MIAPaCa-2, PANC-1 and Capan-1 were K-RAS mutated while BxPC-3 was wild-type. No activating mutations were found for B-RAF. MIAPaCa-2 and PANC-1 were mesenchymal (low E-cadherin/high vimentin) while Capan-1 and BxPC-3 were epithelial. PANC-1 exhibited high basal level of Akt, associated with high level of pAkt and downstream pP70S6K and pS6, suggesting basal activation of the pathway. MEKi exerted antiproliferative effects on PAC cell lines. UO126 and AZD6244 had low cytotoxic activity (72h-IC50=5.0-26.0μM) as compared to AS703026 and GSK1120212 (72h-IC50=0.009-0.65μM). Although both K-RAS mutated and mesenchymal, MIAPaCa-2 and PANC-1 exhibited very different response profile to MEKi: MIAPaCa-2 was the most sensitive (72h-IC50=0.009-13.7μM) and PANC-1 the most resistant (72h-IC50=33-61.3μM). These two cell lines were selected to compare the effects of UO126 (lowest activity) and GSK1120212 (highest activity). 24h-exposure to UO126 and GSK1120212 (30%) was observed after 48h of GSK1120212 in MIAPaCa-2, but not in PANC-1. Apoptosis induction was confirmed by PARP cleavage after 48h of GSK1120212 in MIAPaCa-2. The same pERK inhibition profile was observed in both cell lines with UO126 (partial&lt;5h) and GSK1120212 (complete, 72h). Moreover, MEKi induced an increase in pAkt in both cell lines. Co-treatment with MEKi and low-dose everolimus (mTOR inhibitor) for 72h was synergistic (CI&lt;1) in MIAPaCa-2 but not in PANC-1.

Conclusion: MEKi exerted their antiproliferative effects in PAC cells regardless of their K-RAS mutation and EMT status. There was no correlation between cellular effects and pERK inhibition. MEKi induced an activation of the Akt pathway. Dual MEK and mTOR inhibition had a synergistic effect in MIAPaCa-2 sensitive cells but not in PANC-1, suggesting that basal Akt pathway activation may be a factor of resistance to combined MEK/Akt pathway inhibition.

Citation Format: Cindy Neuzillet, Maria Serova, Annemilai Tijeras-Raballand, Lucile Astorgues-Xerri, Maria E. Riveiro, Armand de Gramont, Philippe Ruszniewski, Pascal Hammel, Sandrine Faivre, Eric Raymond. Cellular effects of MEK inhibition in pancreatic cancer cell lines are not correlated with « classical » predictive markers of response to MEK inhibitors. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3261. doi:10.1158/1538-7445.AM2013-3261