Abstract 4490: MUC3A induces PD-L1 and reduces tyrosine kinase inhibitor effects in EGFR-mutant non-small cell lung cancer
Authors: Luo Yuan , Ma Shijing , Sun Yingming , Peng Shan , Gong Yan , Xie Conghua 
Published: September 2020

Abstract
Objective: Lung cancer is one of the leading causes of cancer-related mortality in the world, and non-small cell lung cancer (NSCLC) accounts for approximately 85% of all lung cancers. With the emergence of epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs), the prognosis of adenocarcinoma patients with specific EGFR mutations has been significantly improved. Unfortunately, despite the success of EGFR-TKIs in NSCLC patients, almost all cases eventually recrudesce after a median of 10 months. Therapeutic antibodies blocking programmed death-ligand 1 (PD-L1) brought striking regression of NSCLC. However, only 20% patients response to the αPD-L1 therapy. Activation of EGFR signaling pathway was also reported to induce PD-L1 expression in NSCLC. MUC3A is a transmembrane mucin with 2 epidermal growth factor (EGF)-like domains in the extracellular segment. This work aimed to investigate the effects of MUC3A on PD-L1 expression and EGFR-TKIs sensitivity in EFGR-mutant NSCLC.
Methods: Expression levels of MUC3A and PD-L1 in tissue microarray of 92 patients' lung tumor samples were measured by immunohistochemistry. Data of lung cancer were downloaded from the TCGA database, and the correlation of PD-L1 expression between EGFR wild type and mutation in lung cancer patients was analyzed. H1975 and PC-9 cells were infected with lentiviral vectors to downregulate MUC3A. The expression pattern of PD-L1 in NSCLC cell lines was detected by qRT-PCR and flow cytometry. Cell proliferation was assessed with CCK-8. Cell apoptosis was examined by flow cytometry. Immunoblotting was used to identify molecular markers of signaling pathways. An xenograft nude mouse transplantation model was established to examine the effects of MUC3A and EGFR-TKIs on tumorigenesis in vivo. The expression levels of MUC3A, EGFR and PD-L1 in harvested tumors were measured by immunohistochemistry.
Results: Tissue microarray of 92 patients' lung tumor samples indicated that high levels of MUC3A were positively correlated with poor prognosis and PD-L1 expression. In the TCGA database, the levels of PD-L1 were independent of the protein levels of EGFR, but correlated with EGFR mutation. Our results showed that induction of PD-L1 by EGF stimulation was only detected in EGFR-mutated NSCLC cell lines, such as H1975 and PC-9, but not in H1299 and H460. Knockdown of MUC3A in H1975 and PC-9 reduced PD-L1 expression, as well as PI3K/Akt and MAPK pathways. In addition, MUC3A deficiency potentiated gefitinib and AZD-9291-induced growth inhibition in PC-9 and H1975 cells by downregulating proliferation and inducing apoptosis. More interestingly, knockdown of MUC3A decreased EGFR protein levels, but not mRNA levels. Our findings suggested that MUC3A deficiency improved EGFR-mutated NSCLC sensitivity to tyrosine kinase inhibitors via increasing EGFR protein stability and decreasing PD-L1 expression through PI3K/Akt and MAPK pathways. Mice inoculated with MUC3A deficiency tumor cells treated with AZD-9291 had the fastest tumor regression and delayed relapse.
Conclusions: The transmembrane mucin MUC3A increased EGFR stability. MUC3A induced PD-L1 and reduced tyrosine kinase inhibitor effects via EGFR modulation in NSCLC, suggesting potential implications for a novel immunotherapeutic approach.
Citation Format: Yuan Luo, Shijing Ma, Yingming Sun, Shan Peng, Yan Gong, Conghua Xie. MUC3A induces PD-L1 and reduces tyrosine kinase inhibitor effects in EGFR-mutant non-small cell lung cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4490.