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S. Wu

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    MINI 02 - Immunotherapy (ID 92)

    • Event: WCLC 2015
    • Type: Mini Oral
    • Track: Biology, Pathology, and Molecular Testing
    • Presentations: 1
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      MINI02.09 - ERK Activation Mediates Increased PD-L1 Expression in KRAS Mutated Premalignant Human Bronchial Epithelial Cells (ID 1620)

      10:45 - 12:15  |  Author(s): S. Wu

      • Abstract
      • Presentation
      • Slides

      Immune checkpoint pathways including the PD-1/PD-L1 pathway are involved in tumor evasion from the immune system. Elevated PD-L1 expression in tumor cells inhibits tumor-infiltrating T cell function and may be associated with poor prognosis in lung cancer patients. There is increasing interest in developing immunotherapies that block the immunosuppressive effects of checkpoint pathways such as PD-L1, and identifying patients who may benefit from PD-L1 blockade. Activating KRAS mutations are common driver mutations in non-small cell lung carcinoma. Patients with mutated KRAS demonstrate less benefit from adjuvant chemotherapy and resistance to tyrosine kinase inhibitors. The effect of cancer cell driver mutations on immune checkpoint immune regulation is poorly understood. While recent clinical trials have suggested better response to PD-1 blockade in KRAS mutation subjects, it is unclear if this clinical finding is directly driven by KRAS regulating the PD-1/PD-L1 pathway with resultant improved efficacy to anti-PD-L1 immunotherapy or if the presence of a KRAS mutation is merely a surrogate marker of the overall mutational load and tumor immunogenicity. KRAS mutations are known to activate the RAF-MEK-ERK pathway. We hypothesize that KRAS mutation directly regulates the PD-1/PD-L1 pathway through ERK activation.

      Immortalized human bronchial epithelial cells (HBEC-vector control), KRAS–mutated (KRAS[v12]) HBEC cells (HBEC-KRAS), p53 knockdown HBEC cells (HBEC-p53), and p53 knockdown/KRAS mutated cells (HBEC-p53/KRAS) were used to assess mRNA and/or surface protein expression levels of immune checkpoints including Lag-3, Tim-3, PD-L1 and PD-L2 by real time-qPCR (RT-qPCR) and flow cytometry, respectively. HBEC-vector and HBEC-KRAS cells were treated with MEK (ERK kinase) inhibitor (PD0325901) at 1µM for 24hrs and evaluated for mRNA and surface protein expression of PD-L1. The premalignant HBEC cell lines were used instead of human lung cancer cell lines in order to assess the role of KRAS mutation in isolation without other mutations.

      PD-L1 and PD-L2 mRNA levels increased 2.4 fold (p<0.001) and 3.6 (p<0.001) fold in comparing HBEC-KRAS to HBEC-vector (wild-type) cells, while Lag-3 and Tim-3 mRNA expression levels were unchanged. Based on mean fluorescence intensity on flow cytometry, cell surface PD-L1 protein expression level was 2.2 and 1.6 fold higher in HBEC-KRAS and HBEC-p53/KRAS, respectively, compared to HBEC-vector cells. There was no increase in surface PD-L1 expression in HBEC-p53 cells compared to HBEC-vector control, suggesting that p53 mutation did not alter PD-L1 expression in HBEC-p53/KRAS cells. With MEK inhibition, PD-L1 mRNA levels decreased 10 and 11 fold in HBEC-vector and HBEC-KRAS cells, respectively. Analogously, PD-L1 surface protein levels were reduced 2.7 fold in HBEC-vector and HBEC-KRAS cells, respectively. These findings suggest that ERK activation mediates intrinsic expression and KRAS mutation mediates over-expression of PD-L1 mRNA and protein.

      Here, we demonstrate that PD-L1 expression is elevated in premalignant KRAS mutated human bronchial epithelial cells, and ERK activation mediates constitutive and KRAS mutation driven up-regulation of PD-L1 in these cells. Our findings suggest that KRAS mutation may directly regulate the PD-1/PD-L1 immune checkpoint pathway. Further understanding of KRAS driven molecular pathways that modulate immune checkpoints may elucidate therapeutic targets for potential combinational drugs to PD-L1 inhibition.

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