Abstract 5740: PD-L1 overexpression induced by oncogenicKRASandBRAFmutations through MAPK pathway activation in non-small cell lung cancer

Mutant KRAS and BRAF are important oncogenic drivers in non-small cell lung cancer (NSCLC), however, effective treatment strategies for most of these mutants have not been established. Immuno-oncology clinical trials have shown promising results of anti-programmed death 1 (PD-1) antibodies for a subset of NSCLC patients and tumor expression of programmed-death ligand 1 (PD-L1) is regarded as a predictive marker for anti-PD-1 therapy. We found that CD274 mRNA and PD-L1 protein expression were reduced in NSCLC lines by small interfering RNAs (siRNAs) targeting mutant KRAS, but not wild-type KRAS, and also by pharmacologic inhibitors of MEK and ERK. In addition, there was a positive correlation between CD274 expression and KRAS expression in NSCLC lines, and analyses of The Cancer Genome Atlas (TCGA) database revealed that NSCLCs with high KRAS expression exhibited higher levels of CD274 compared to the tumors with low KRAS expression among KRAS-mutant NSCLCs. Similarly, siRNA-mediated BRAF knockdown and inhibitors of BRAF and MEK reduced PD-L1 expression in BRAF-mutant NSCLC cells, suggesting that PD-L1 expression was also upregulated by oncogenic BRAF. Mechanistically, these results suggest that oncogenic KRAS and BRAF induce PD-L1 overexpression in NSCLCs by activation of the MEK-ERK pathway. For clinical translation, our results suggest that: 1. in NSCLCs the combination of KRAS and PD-L1 overexpression could be a surrogate predictive marker for anti-PD-1 treatment; and 2. that since the goal of checkpoint inhibitor immuno-oncology therapy is to inhibit the PD-L1 axis, that a combination of anti-PD-1 and targeted therapy to inhibit the MEK-ERK pathway could be beneficial. Citation Format: Yosuke Miura, Noriaki Sunaga, Pinjie Bao, Luc Girard, Yusuke Tsukagoshi, Tomomi Masuda, Norimitsu Kasahara, Reiko Sakurai, Kyoichi Kaira, Takeshi Hisada, John Minna, Masanobu Yamada. PD-L1 overexpression induced by oncogenic KRAS and BRAF mutations through MAPK pathway activation in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5740.