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D. Xia



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    MO20 - Preclinical Therapeutic Models II (ID 93)

    • Event: WCLC 2013
    • Type: Mini Oral Abstract Session
    • Track: Biology
    • Presentations: 1
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      MO20.02 - Proteomic analysis identifies baseline PI3K/Akt pathway activation and treatment-induced supppression of mTOR signaling as determinants of response to MEK inhibition (ID 2845)

      10:35 - 10:40  |  Author(s): D. Xia

      • Abstract
      • Presentation
      • Slides

      Background
      Inhibition of MEK is a promising treatment strategy for non-small cell lung cancer (NSCLC). MEK inhibitors are being investigated for KRAS mutant disease, but KRAS alone is not predictive of efficacy, and other predictors of response and resistance are not known. The downstream effects of MEK inhibition have not been fully described. Here, we report broad proteomic analysis of NSCLC cell lines before and after treatment with MEK inhibitor BAY86-9766.

      Methods
      We treated 109 NSCLC cell lines with BAY86-9766. Drug sensitivity was determined by CellTiter-Glo assay and cell lines were classified as sensitive or resistant based on whether their IC50 values were in the highest or lowest 1/3[rd] of those tested. Proteomic analysis for regular and phospho-proteins was performed by reverse phase protein array. Using paired t-tests, we compared pre- versus post-treatment protein levels in the overall group and between the sensitive vs. resistant cell lines.

      Results
      Increased activation of the PI3 kinase pathway at baseline correlated with resistance to MEK inhibition, with resistant cell lines showing higher baseline levels of pAkt (S437), pAkt (T308), pPDK1, and p4E-BP1 (S65), and lower baseline levels of PTEN (all p<0.05). Cell lines with increased MEK phosphorylation at baseline were more sensitive to MEK inhibition (p=0.048). BAY86-9766 was very effective at reducing pERK (p=1.65x10[-35]) but this modulation was not significantly different between sensitive and resistant cell lines (p=0.64). Increased phosphorylation of MEK was seen with treatment (1.66x10[-16]). mTOR signaling was suppressed by MEK inhibition, with decreased phospho-p70S6K, pS6 (S235/236), and pS6 (S240/S244) and increased eIF4E following treatment (all p<0.02). These effects were significantly more pronounced in sensitive vs resistant cell lines (all p<0.01). Higher levels of LKB1 total protein, pAMPK, and pTSC2 were also seen following treatment (all p<0.02).

      Conclusion
      We have performed broad proteomic analysis of NSCLC cell lines treated with MEK inhibitor BAY86-9766. Baseline activation of the PI3K/Akt pathway predicts for resistance to MEK inhibition. Sensitive cell lines, but not resistant cell lines, show suppression of mTOR activity with treatment with BAY86-9766. The effects of MEK inhibition of mTOR may be modulated by p90RSK through an LKB1 dependent pathway. This suggests a basis for combining targeted agents to overcome resistance, such as combinations of MEK inhibitors with PI3K inhibitors or mTOR inhibitors.

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