MTE23.02 Biomarker Characterization: Challenges and Perspectives

Abstract

Small molecule inhibitors are the current treatment for non-small-cell lung cancer (NSCLC), especially for tumors harboring an active mutation of epidermal growth factor receptor (EGFR). Approximately 90% of EGFR mutations are exon 19 deletions or exon 21 single-point L858R substitutions and are associated with sensitivity to EGFR tyrosine kinase inhibitors (EGFR TKIs), like gefitinib or erlotinib. However, less than 5% of EGFR-mutant NSCLC patients achieve a complete response to EGFR TKI and the overall median progression-free survival is no longer than 9-11 months. Accumulated studies report several mechanisms of early adaptive resistance that can occur as early as two hours after starting EGFR TKI therapy. The activation of signal transducer and activator of transcription 3 (STAT3) signaling is among these mechanisms of resistance. Furthermore, EGFR blockage enriches lung cancer stem cells through Notch3-dependent signaling pathway. We have previously demonstrated that NF-κB contributes to gefitinib resistance in EGFR-mutant NSCLC. The efficacy of EGFR tyrosine kinase inhibitors (TKIs) in EGFR-mutant non-small cell lung cancer (NSCLC) is jeopardized by the activation of signaling pathways. We examined the relevance of co-targeting EGFR, signal transducer and activator of transcription 3 (STAT3) and Src-YES-associated protein 1 (YAP1) signaling. We conducted clinical and preclinical studies of key components of signaling pathways limiting EGFR TKI efficacy in EGFR-mutant NSCLC. High levels of STAT3 or YAP1 mRNA expression were associated with worse outcome to EGFR TKI in two independent cohorts of EGFR-mutant NSCLC patients. In the initial cohort of 64 patients, median progression-free survival was shorter among the patients with high STAT3 than among those with low STAT3 (hazard ratio [HR] for disease progression, 3·02; 95% confidence interval [CI], 1·54-5·93; P=0·0013). Median progression-free survival was shorter among the patients with high YAP1 than among those with low YAP1 (HR for disease progression, 2·57; 95%CI, 1·30-5·09; P=0·0067). The results were similar in the validation cohort of 55 patients. We demonstrated that gefitinib augments STAT3 signaling in EGFR-mutant NSCLC cells. Gefitinib with TPCA-1 (STAT3 inhibitor) blocked STAT3, but not the YAP1 phosphorylation on tyrosine residue 357 by Src family kinases (SFKs) that occurs downstream of IL-6. The triple combination of gefitinib, TPCA-1 and AZD0530 (SFK inhibitor) ablated both STAT3 and YAP1 phosphorylation and markedly and safely suppressed tumor growth. Added value of our research: We found that EGFR TKI therapy activates STAT3 and that EGFR blockage enriches lung cancer stem cells with up-regulation of the YAP1 and Notch downstream effectors connective tissue growth factor (CTGF) and hairy-enhancer of split-1 (HES1), respectively. We sought to demonstrate that EGFR TKI treatment cannot abrogate STAT3 and Src-YAP1-Notch activation in EGFR-mutant NSCLC cell lines, leading us to examine whether the combination of gefitinib with compounds targeting STAT3 and Src, suppresses the mechanisms of resistance. Nine days after gefitinib treatment, STAT3 mRNA level was significantly increased, as well as the fraction of ALDH positive cells. TPCA-1, a compound that targets STAT3, increases sensitivity to gefitinib in PC-9 and H1975 cells; however, neither gefitinib nor TPCA-1 inhibits Src or YAP1. The addition of the Src inhibitor, saracatinib, to the doublet of gefitinib and TPCA-1, was highly synergistic and abrogated STAT3, and Src-YAP1-Notch signaling. Implications: Treatment with single EGFR TKI can no longer be considered adequate for patients with EGFR mutant NSCLC. Our findings ultimately suggest that a clinical trial evaluating the co-targeted inhibition of STAT3 and Src is warranted. As a result, STAT3 and YAP1 mRNA levels could become important predictive biomarkers. We searched PubMed for English language reports published up to December, 2015 using the terms “non-small-cell lung cancer”, “STAT3”, “interleukin-6”, “NF-κB”, “aldehyde-dehydrogenase (ALDH)”, “integrin-linked kinase (ILK)”, “glycoprotein 130 (gp130)”, “Src-homology 2 domain-containing phosphatase 2 (SHP2)”, “the complement C1r/C1s, Uegf, Bmp1 (CUB) domain-containing protein-1 (CDCP1)”, “AXL”, “ephrin type-A receptor-2 (EphA2)”, “Src family kinases (SFK)”, “YES-associated protein 1 (YAP1)”, “Notch”, “cell migration, invasion and metastases” and “STAT3 inhibitors”. STAT3, EGFR TKI, YAP1, NSCLC