MYC expression correlates with PD-L1 expression in non-small cell lung cancer
Introduction
Lung cancer is a major public health issue worldwide, with a high prevalence and high mortality [1]. Throughout the era of platinum-based doublet chemotherapy, target agents have been widely used [2]. However, in cases where a treatment target cannot be identified and patients have resistance to the target agent, new breakthroughs are needed.
The tumor microenvironment interacts with cancer cells by modulating programmed death-1 receptor −1 (PD-1) and the ligand PD-L1 pathways. Expression of PD-L1 on cancer cells leads to evasion from the immune response, permitting cancer progression and metastasis [3], [4]. Immunotherapy for lung cancer had entered a golden era with the development of immune checkpoint inhibitors that interfere with cytotoxic T lymphocyte antigen-4 (CTLA-4), PD-1 and its ligand PD-L1. A number of immune checkpoint inhibitors are under development based on biological findings. The PD-1 inhibitors nivolumab and pembrolizumab have received FDA approval for lung cancer treatment [5], [7].
Demand for biomarkers for predicting therapeutic outcomes of these drugs is high. Biomarkers developed to date [5] are: (1) PD-L1 expression in cancer cells; (2) tumor microenvironment/immune effector cells (with PD-L1 expression in the tumor microenvironment, PD-L2 expression in tumor cells and infiltrating immune cells, CD8 and T-cell and effector functional markers, and gene expression of CTLA4 and CX3CL1); (3) gene alteration and phenotypic alteration of tumor cells such as tumor mutational load, oncogene mutation, and epithelial mesenchymal transition; and (4) clinicopathological biomarkers such as squamous cell histology and smoking history. In lung cancer, PD-L1 is a therapeutic target of immune checkpoint inhibitors and is used as a biomarker to predict therapeutic response. However, its usefulness as a therapeutic biomarker is challenged because of: (1) differences in antibodies and staining platforms from different companies; (2) instability of PD-L1 antigenicity; and (3) different reading criteria among researchers for predicting therapeutic responses. These issues suggest an urgent need for effective surrogate markers for predicting response to immune checkpoint inhibitors.
MYC, located on chromosome 8q24.21, is a regulator gene that regulates the expression of approximately 15% of human genes by recruiting histone acetyltransferases and binding enhancer box sequences (E-boxes) [6], [7]. Malfunction of MYC, including MYC translocation involved in the development of Burkitt lymphoma, is found in cervix, colon, breast, stomach, and lung cancer[8], [9], [10]. MYC overexpression is observed in 41% of non-small cell lung cancer (NSCLC) and associated with loss of cell differentiation [9]. In addition to its classic function, MYC seems be involved in preventing immune cells from attacking tumor cells by inducing PD-L1 and CD47 expression [11]. Using cancer cells and mouse models, Casey et al. showed that (1) suppression of MYC in mouse and human tumor cells causes a reduction in the levels of PD-L1 mRNA and protein (2) MYC directly binds to the promoters of the PD-L1 genes (3) MYC inactivation in mouse tumors down-regulates PDL1 expression and enhances the anti-tumor immune response [11]. This finding suggests that when combined with PD-L1 expression, MYC and PD-L1 double-positive lung cancer patients may exhibit unique clinical characteristics. MYC could be a surrogate biomarker for response prediction for therapy with immune checkpoint inhibitors.
To explore this possibility, we investigated the correlation of MYC and PD-L1 expression using human lung cancer tissue and evaluated the clinical implications of MYC and PD-L1 double positivity in lung cancer tissues.
Section snippets
Materials and methods
2.1 Cell lines, plasmids, and antibodies. Lung cancer cells were obtained from ATCC (Manassas, VA, USA) or the Korean Cell Line Bank (Seoul, Korea). pcDNA3-cMYC was a gift from Wafik El-Deiry (Addgene plasmid #16011) and pcDNA3 was the negative control [12]. Anti-PD-L1 (22C3) was obtained from DAKO and anti-cMYC antibody (Y69) was from Abcam® (ab32072). Unless otherwise stated, antibodies were from Cell Signaling Technology (Danvers, MA, USA).
2.2 Study population. The study used 84 lung cancer
Results
3.1 Relationship of PD-L1 and MYC in lung cancer cells. To examine the relationship between PD-1 and MYC expression, we investigated the relationship between the expression of the two proteins in unstimulated NSCLC cell lines using immunoblots. Among the eight cell lines tested, 5 showed distinct MYC expression, 2 showed no expression and 1 showed faint expression. No significant relationship was observed between the expression of the two proteins based on estimated correlation between the
Discussion
Since the expression of PD-L1 in the tumor tissues is not only a target for immune checkpoint inhibitors but also a major biomarker for predicting therapeutic responses, there is a growing interest in the molecules that regulate the expression of PD-L1 [5]. Recent in vitro study by Casey et al. amplified interest in MYC by showing that MYC directly binds to the promoters of PD-L1 and CD47, induces their expression, and plays critical roles in immune escape [11].
The loss of control of MYC
Conclusions
In conclusion, MYC expression significantly correlated with PD-L1 expression and NSCLC patients with MYC-PD-L1 double-positive samples showed poor clinical outcomes. These findings suggested that it is worth evaluating the usefulness of MYC expression as a surrogate marker of treatment response assessment to immune checkpoint inhibitor therapy. Additional prospective clinical studies may be needed to identify NSCLC patients with PD-L1-MYC double-positive samples who may benefit from currently
Conflict of interest
The authors declare that they have no competing interests.
Acknowledgements
This study was supported by a faculty research grant of Yonsei University College of Medicine 6-2015-0152 awarded to EY KIM. The funding source has not played any role in the planning and execution of this study. There was no writing assistance for the preparation of this manuscript.
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