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Y. Fan



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    MO15 - Novel Genes and Pathways (ID 89)

    • Event: WCLC 2013
    • Type: Mini Oral Abstract Session
    • Track: Biology
    • Presentations: 1
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      MO15.02 - Impact of co-occurring genetic events on the signaling landscape of KRAS-mutant lung adenocarcinoma. (ID 2936)

      16:15 - 17:45  |  Author(s): Y. Fan

      • Abstract
      • Presentation
      • Slides

      Background
      Personalized medicine frameworks centered on identification and therapeutic targeting of dominant oncogenic driver mutations are rapidly becoming a standard of care in the clinical management of patients with lung adenocarcinoma. However, little is currently known about the nature and impact of co-occurring genetic events on signaling output downstream of initiating oncogenes. This lacuna in our understanding is particularly pertinent for the subgroup of KRAS-driven tumors, where mounting data point towards considerable heterogeneity in pathway activation and clinical response to targeted therapies. Here, we report a comprehensive analysis of genetic events that co-occur with or are mutually exclusive of mutant KRAS in a cohort of 230 lung adenocarcinomas and assess the impact of individual co-mutations on signaling streams using data derived from state of the art transcriptomic and (phospho)proteomic profiling of primary tumors.

      Methods
      An integrated analysis of 230 lung adenocarcinomas from The Cancer Genome Atlas (TCGA) consortium was performed using mutation (whole exome sequencing), transcriptomic (RNASeq), and proteomic (reverse phase protein array) datasets. Fischer’s exact test was applied to identify secondary mutations that occurred more frequently in either KRAS-mutant (n=68) or KRAS-wild-type (n=162) tumors and (phospho)protein markers that associated with each co-mutation. Genes with a mutation rate of ≥3% in the overall cohort were included in the analysis.

      Results
      Mutations in 18 genes were associated with KRAS mutational status in patient tumors (p≤0.01). Mutations in EGFR (p=0.0001), NF1 (p=0.001), and TP53 (p=0.001) were negatively correlated with the KRAS mutation. On the other hand, mutations in STK11 were significantly more frequent in the KRAS-mutant cohort (p=0.004), as were mutations in ATM (p=0.023) and MTOR (p=0.045). The most significant positive association involved mutations in ARHGEF11, a gene that encodes a Rho guanine nucleotide exchange factor (p=0.0004). Mutations in STK11 (29.4%) and TP53 (29.4%), the two most highly prevalent genetic events within the KRAS-mutant cohort were mutually exclusive. Unsupervised hierarchical clustering of transcriptomic and quantitative (phospho)proteomic profiles revealed separation of STK11-mutant tumors at the first branch of the cluster dendrogram, indicating activation of distinct signaling pathways downstream of this key tumor suppressor gene. Several less frequent genetic events had prominent and consistent effects on signaling output. We focused our attention on signaling via the MAPK pathway which may impact clinical sensitivity to MEK inhibitors, one of the most promising classes of targeted agents currently in clinical development for KRAS-mutant tumors. Preliminary analysis suggests that mutations in 3 individual genes can identify a subgroup of tumors (19% of the cohort) with profoundly suppressed MAPK signaling flux.

      Conclusion
      Analysis of recurrent secondary genetic events may define distinct and clinically relevant subsets of KRAS-mutant lung adenocarcinoma. Efforts to refine the sub-classification further and assess the impact of co-mutations on sensitivity to molecularly targeted agents are underway and updated results will be presented at the meeting.

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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)

      10:30 - 12:00  |  Author(s): Y. Fan

      • 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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    P1.01 - Poster Session 1 - Cancer Biology (ID 143)

    • Event: WCLC 2013
    • Type: Poster Session
    • Track: Biology
    • Presentations: 1
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      P1.01-003 - Targeting EMT in lung cancer: An integrated analysis of Axl and other mesenchymal targets in The Cancer Genome Atlas (TCGA) (ID 1991)

      09:30 - 16:30  |  Author(s): Y. Fan

      • Abstract

      Background
      We previously developed a 76-gene signature of epithelial-to-mesenchymal transition (EMT) that predicted resistance to EGFR and PI3K inhibition in non-small cell lung cancer (NSCLC). This analysis also identified Axl, a receptor tyrosine kinase, as a novel target for mesenchymal lung cancers. Here, we conducted an integrated molecular analysis of EMT in resected, treatment-naïve tumors from three clinical cohorts, including the Cancer Genome Atlas (TCGA) lung adenocarcinomas (LUAD) and squamous cell carcinomas (LUSC), with particular focus on Axl as a potential target in mesenchymal NSCLC.

      Methods
      Using our 76-gene EMT signature, TCGA patient tumors (230 LUAD, 178 LUSC) and a large MDACC cohort of resected tumors (n=279) were assigned an “EMT score.” Expression of >160 total and phosphoproteins were measured in the tumors by reverse phase protein array (RPPA). Proteomic profiles and other molecular markers (including mutation status, miRNA expression, and copy number) were correlated with EMT scores and Axl expression levels.

      Results
      The EMT score, derived from our EMT signature, identified NSCLC tumors with mesenchymal gene expression signatures (average 23% of tumors across all cohorts, range 14-34%). In both LUAD and LUSC, EMT scores were highly correlated with (1) expression levels of the miR200 family, a group of miRNAs previously known to regulate EMT (p-values <0.001 by Pearson correlation) and (2) levels of proteins central to EMT (e.g., E-cadherin, alpha-catenin, beta-catenin, claudin-7, fibronectin; p<0.001 for all). Mesenchymal tumors also had lower expression of TTF1 in LUAD (p=0.0002) and lower p63 in LUSC (p=0.003). Although pEGFR levels were higher in epithelial LUAD tumors (p=0.01), the frequency of EGFR mutations was not significantly higher in this group. EMT score was not associated with smoking status. Consistent with our previous findings in cell lines and patients with advanced NSCLC (BATTLE trial), protein expression of the receptor tyrosine kinase Axl was significantly higher in tumors with mesenchymal signatures (high EMT scores) and with low E-cadherin protein expression (p<0.005 for both). The inverse correlation between tumor E-cadherin and Axl expression was confirmed in an independent group of NSCLC cases by immunohistochemistry. Although a small number of Axl mutations were observed (<3% of tumors), few occurred in the kinase domain and their biological significance is unknown. Other potential therapeutic targets expressed at higher levels in mesenchymal lung cancers included PKC-alpha, NFKB, and FGFR1.

      Conclusion
      The EMT gene expression signature performed well in the TCGA LUAD, TCGA LUSC, and MDACC cohorts, correlating strongly with established markers of EMT on other data platforms (miRNA and protein). We observed strong protein expression of the receptor tyrosine kinase Axl (as well as other targets) among mesenchymal tumors, supporting further investigation of AXL as a potential EMT target and into the mechanism of its overexpression in NSCLC.