Abstract B57: MUC3A induces PD-L1 and reduces tyrosine kinase inhibitor effects functions in EGFR-mutant non-small cell lung cancer
Authors: Gong Yan , Luo Yuan , Peng Shan , Ma Shijing , Sun Yingming , Ren Jiangbo , Xie Conghua 
Published: March 2020

Abstract
Objective: Non-small cell lung cancer (NSCLC) patients with specific EGFR mutations benefited from the emergence of EGFR tyrosine kinase inhibitors (EGFR-TKIs). Unfortunately, almost all cases eventually recrudesced after a median of 10 months. Therapeutic antibodies blocking PD-L1 strikingly regressed NSCLC development. However, only 20% patients responded to the αPD-L1 therapy. EGFR activation was reported to induce PD-L1 expression in NSCLC. MUC3A is a transmembrane mucin with 2 EGF-like domains in the extracellular segment. This study 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 a 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 cells was detected by qRT-PCR and flow cytometry. Cell proliferation was assessed with CCK8. Cell apoptosis was examined by flow cytometry. Immunoblotting was used to identify molecular markers of signaling pathways. A 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: The 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 EGFR protein levels 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: Yan Gong, Yuan Luo, Shan Peng, Shijing Ma, Yingming Sun, Jiangbo Ren, Conghua Xie. MUC3A induces PD-L1 and reduces tyrosine kinase inhibitor effects functions in EGFR-mutant non-small cell lung cancer [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr B57.