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A.T. Le

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    ORAL 21 - Biology - Moving Beyond the Oncogene to Oncogene-Modifying Genes (ID 118)

    • Event: WCLC 2015
    • Type: Oral Session
    • Track: Biology, Pathology, and Molecular Testing
    • Presentations: 1
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      ORAL21.01 - Adaptive Survival Signaling in Oncogenic Fusion Kinase Addicted NSCLC (ID 864)

      10:45 - 12:15  |  Author(s): A.T. Le

      • Abstract
      • Slides

      Gene fusions involving the proto-oncogenes ALK, ROS1, RET and NTRK1 are established or potential drug targets in cancer. Although targeted kinase inhibitors induce significant tumor shrinkage, complete patient responses are rare, and it is from that residual tumor burden that drug resistant clones eventually emerge. We have previously shown a role for WT EGFR signaling in ROS1+ cancer cells and their drug resistant derivatives. We hypothesized that EGFR performs a similar role in cancer cells harboring other gene fusions.

      Fusion oncogene NSCLC cell lines were treated as described and analyzed through immunoblot analyses or fixed onto chamber slides and assayed using kinase-adaptor proximity ligation assays (PLA). FFPE from NSCLC patients treated at the University of Colorado Hospital were also analyzed using kinase-adaptor PLAs. Nu/nu mice were injected with fusion oncogene positive NSCLC cell lines, treated as described, and volumes were measured 3x/week. FFPE tumors from mice were analyzed using various immunohistochemical markers or kinase-adaptor PLAs.

      Stimulation of NSCLC cells that harbor an oncogenic fusion with EGF not only increased downstream signaling, but also rapidly increased phosphorylation of the fusion kinase itself. Additionally, EGFR signaling can dictate the engagement of different downstream signaling effectors, diversifying the signaling and cell fate responses in certain cancer cells. Proximity ligation assays (PLA) were employed to visualize wild-type EGFR-GRB2 signaling complexes in NSCLC cells driven by an oncogenic fusion kinase. We observed two modes of EGFR-GRB2 complex formation, the first in unperturbed cells, and the second only when the fusion kinase was inhibited. The kinetics of the induction of EGFR-GRB2 signaling revealed EGFR can take over the signaling in these cells as quickly as 5 minutes, and this kinase inhibitor-induced rewiring can be reversed by simply washing out the drug, suggesting a preference for the fusion kinase in the signaling circuit of these cells. Analysis of fusion-positive patient samples acquired at the time of progressive disease from treatment with an oncogene targeted monotherapy revealed the presence of EGFR-GRB2 signaling complexes. Additional analyses of patient samples revealed evidence of potentially non-cell autonomous responses to these therapies that may enable the survival of cells that would otherwise be drug-sensitive. The combination of a fusion kinase inhibitor with anti-EGFR therapy provided superior blockage of EGFR and ALK signaling complexes, as well as improved reduction in tumor volume and prolonged survival in an ALK+ xenograft model.

      Collectively, these results demonstrate a previously unknown role for an unmutated kinase, EGFR, in modulating the oncogenic phenotype in cells addicted to oncogenic fusion kinases. The activation of the EGFR signaling pathway can quantitatively augment fusion kinase signaling, but also diversify it by regulating the engagement of alternate signaling effector proteins. This data provides evidence for a novel role for EGFR as an oncorequisite signaling partner in certain cancer cell populations that harbor an oncogenic fusion kinase. Combination therapy of a fusion kinase targeted inhibitor with anti-EGFR therapy may improve initial tumor cell killing, and delay or prevent the onset of drug resistance in these patient populations.

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