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MA15 - Immunotherapy Prediction (ID 400)
- Event: WCLC 2016
- Type: Mini Oral Session
- Track: Chemotherapy/Targeted Therapy/Immunotherapy
- Presentations: 1
MA15.11 - Acquired Resistance Mechanisms to EGFR Kinase Inhibitors Alter PD-L1 Expression Status in Lung Cancer (ID 4652)
14:20 - 15:50 | Author(s): K. Ellison
Immunotherapies that target PD-1/PD-L1 exploit the primary roles of cytotoxic agents in lung cancers. However, tyrosine kinase inhibitors (TKIs) are still considered to be the first choice in lung cancer patients with EGFR mutations. Although immunotherapies may be applied as second line or later therapeutic approaches in these patients, after acquisition of resistance to EGFR-TKIs, it is unclear if acquired resistance mechanisms alter PD-L1 expression status that is employed as an important predictive biomarker for PD-1/PD-L1 targeting agents.
Lung cancer cell lines with EGFR mutations (HCC827, HCC4006, PC9, and H1975) and their isogenic descendants with acquired resistance to various EGFR-TKIs were examined in this study. The resistance mechanisms of descendants include T790M secondary mutation, MET gene amplification, epithelial to mesenchymal transition (EMT), and loss of amplified EGFR mutant allele. PD-L1 expression status was analyzed by immunohistochemistry (IHC) and immunoblotting. Effects of acquired resistance mechanisms on PD-L1 expression were also evaluated by shRNA mediated knockdown of candidate molecules, and co-localization analysis using fluorescent imaging. IFN-gamma was used to mimic immune cell attack. Published microarray data of cells with acquired resistance to EGFR-TKIs were also employed to evaluate our findings.
PD-L1 expression was upregulated in several resistant cells and correlated with EGFR activation. In addition, we found that the phosphorylation of EGFR tyrosine (Y) 992 site, but not Y845, Y1068, or Y1173, was correlated with increased expression of PD-L1. We also observed that TKI-resistant cells with marked E-cadherin downregulation (HCC4006 erlotinib resistant cells and H1975 osimertinib resistant cells), one of hallmarks of EMT, showed decreased expression of PD-L1. However, one cell line (853#10), displaying EMT-like phenotype but only slight E-cadherin downregulation, showed PD-L1 upregulation. Published microarray data from three TKI-resistant lines with EMT-like features also support the correlation of low E-cadherin and reduced PD-L1 expression. ShRNA mediated knockdown of E-cadherin decreased the expression of PD-L1 in parental cell lines. IFN-gamma treatment upregulated PD-L1 expression in both parental and in resistant cells with E-cadherin downregulation, however PD-L1 expression in resistant cells was still lower and localized mainly in the cytoplasm rather than the cell membrane.
We observed a dramatic change of PD-L1 expression status in lung cancers with EGFR mutation after acquisition of resistance to EGFR-TKIs, depending on the resistance mechanisms. These results support the importance of re-biopsy after acquisition of resistance to EGFR-TKIs, not only for the resistance mechanisms but also for the evaluation of PD-L1 expression status.
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