Identification of a patient tissue-based phosphorylation site as a biomarker for epidermal growth factor receptor (EGFR) activity in non-small cell lung cancer.

Abstract

3143 Background: Non-small cell lung cancer (NSCLC) is a leading cause of cancer-related deaths globally. EGFR tyrosine kinase inhibitors (TKIs) have shown promise in treating NSCLC, yet resistance to these agents is common and current biomarkers rely on genetic data alone. Therefore, identifying reliable biomarkers to more comprehensively monitor EGFR activity and predict therapeutic responses is paramount. Here, we report an uncharacterized threonine phosphorylation site within core regulator of the EGFR pathway SHP2, that is strongly predictive of EGFR activity as defined by genetic mutation status that shows potential as a clinically relevant biomarker. Methods: Using DIA mass spectrometry phosphoproteomics, we could quantify >20,000 phosphosites from patient normal adjacent tumor (NAT) and primary tumor tissue. We further characterized these tissues using whole genome sequencing allowing us to define the mutational status of the EGFR. Statistical analysis was undertaken across all phospho-sites that identified a single uncharacterized phospho-site as a strong predictor of EGFR kinase activity. Finally, we generated monoclonal antibodies against the phospho-peptide and tested these in patient FFPE primary tumor tissue using immunohistochemistry to correlate phosphorylation levels with EGFR activation status. Results: Our results highlight how an individual phosphosite on SHP2 closely correlates with EGFR activity as defined by genetic mutation status in patient tissue. Interestingly, we further identify a group of patients who carry wild type EGFR yet have a phospho-signal potentially indicative of high EGFR activation without genetic aberration. These results were corroborated by a phospho-site specific antibody in FFPE tissue IHC, with strong signals observed in patients with an activating EGFR mutation (n=5), and complete absence of signal in patients harboring a wild type EGFR and no detectable mass spec signal (n=5). Conclusions: Our findings suggest that this uncharacterised SHP2 phosphosite may serve as a potent biomarker for EGFR activity in NSCLC. Further validation of the monoclonal antibodies as tools for this clinically relevant biomarker is required in larger patient cohorts to elucidate the role of the phosphosite in therapy response. This novel biomarker has the potential to guide therapeutic decision-making and contribute to personalized medicine strategies for NSCLC patients.