P3.02b-047 Co-Activation of STAT3 and YAP1 Signaling Pathways Limits EGFR Inhibitor Response in Lung Cancer: Topic: EGFR Clinical

Abstract

EGFR tyrosine kinase inhibitors (TKIs) induce early activation of several signaling pathways. Interleukin-6 (IL-6) and signal transducer and activator of transcription 3 (STAT3) hyper-activation occur following EGFR TKI therapy in EGFR-mutant NSCLC cells. We explored the relevance of co-targeting EGFR, STAT3 and Src-YES-associated protein 1 (YAP1) signaling in EGFR-mutant NSCLC. We combined in vitro and in vivo approaches to explore whether concomitant activation of STAT3 and Src-YAP1 can limit the effectiveness of EGFR TKIs in EGFR-mutant NSCLC cells and xenograft models. In two cohorts of EGFR-mutant NSCLC patients, we examined messenger RNA (mRNA) gene expression within signaling pathways, leading to EGFR TKI resistance. Gefitinib suppressed EGFR, ERK1/2 and AKT phosphorylation but increased STAT3 phosphorylation (pSTAT3-Tyr705). In EGFR mutant cells, gefitinib plus TPCA-1 (STAT3 inhibitor) abolished pSTAT3-Tyr705 but not the YAP1 phosphorylation on tyrosine 357 by Src family kinases (SFKs). The triple combination of gefitinib, TPCA-1 and AZD0530 (SFK inhibitor) ablated both STAT3 and YAP1 phosphorylation and was highly synergistic, according to the combination index. In two EGFR mutant xenograft mouse models, the triple combination of gefitinib, TPCA-1 and AZD0530 markedly and safely suppressed tumor growth. High levels of STAT3 or YAP1 mRNA expression were associated with worse outcome to EGFR TKI in 64 EGFR-mutant NSCLC patients. Median progression-free survival (PFS) was 9.6 (95%CI, 5.9-14.1) and 18.4 months (95% CI, 8.8-30.2) for patients with high and low STAT3 mRNA, respectively (p<0.001), (HR for disease progression, 3.02; 95% CI, 1.54-5.93; p=0.0013). Median PFS was 9.6 (95% CI, 7.7-15.2) and 23.4 months (95%CI, 13.0-28.1) for patients with high and low YAP1 mRNA, respectively (p=0.005), (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 EGFR-mutant NSCLC patients treated with first-line EGFR TKI in the Department of Oncology of Shanghai Pulmonary Hospital. Our study reveals that STAT3 and Src-YAP1 signaling activation occurs following single EGFR TKI in EGFR-mutant NSCLC. STAT3 and YAP1 mRNA levels were significantly predictive of progression-free survival in the original as well as in the validation cohort of EGFR-mutant NSCLC patients. Co-targeting STAT3 and Src in combination with EGFR TKI could substantially improve survival.