P1.04-53 A High PD-L1 Expression in Non-Small Cell Lung Cancer Correlates with Expression of SPOP and CD8 Tumor-Infiltrating Lymphocytes

Abstract

Immunotherapy that targets PD 1 pathway has emerged as a novel treatment modality for malignant diseases. Clinical trials have reported durable responses and long-term remissions using PD-1/PD-L1. However, despite promising clinical results, checkpoint blockade therapies are only successful in a subset of patients. Thus, it is crucial to more fully understand the mechanisms behind immunotherapies. Recently, it has been reported that PD-L1 expression can be regulated at both transcriptional and post-transcriptional levels, including HIF-1, STAT3, NF-κB, AP-1, cyclin-dependent kinase 4 (CDK4) and speckle-type POZ protein (SPOP). In this study, we focused on the regulation of PD-L1 expression in lung cancer, and we investigated the association between the expression of PD-L1 and biomarkers in regard to clinical outcomes. We investigated CDK4, CDK6 and SPOP expression of lung cancer, and CD4 and CD8 expression of tumor-infiltrating lymphocytes (TILs) by immunohistochemistry of 52 patients with non-small cell lung cancers who had undertaken an operation or chemotherapy from May 2008 to December 2018 and analyzed PD-L1 expression (negative:<1%, low expression:1-49%, high expression: ≥50%). The staining intensity of CDK4, CDK6 and SPOP was scored as 0 (negative), 1 (weak), 2 (medium), and 3 (strong). Extent of staining was scored as 0 (0-10%), 1 (11-25%), 2 (26-50%), 3 (51-75%), and 4 (76-100%) according to the percentages of the positive staining areas in relation to the whole cancer area. For CD4+ and CD8+ cells, a number of stained cells were counted semi-quantitatively in high-powered fields (400x). A number of CD8+ cells in tumor tissue were scored as 0 (0-5 cells/HPF), 1 (6-10 cells/HPF), 2 (11-25 cells/HPF), 3 (26-50 cells/HPF), and 4 (51- cells/HPF). The observed protein expression levels and TILs counts were analyzed for correlation to PD-L1 expression and clinicopathological parameters. PD-L1 expression was observed in 33 (64%) patients of lung cancer, being low in 19 (37%) and high in 14 (27%). The positive rate of expression of SPOP was 42% in tumors with negative expression of DP-L1, 53% low expression and 14% high expression. That of CDK4, CDK6 and CD8 in tumor tissue was 79%, 79%, 57% and 53%, 63%, 43%, and 41%, 41%, 92%, respectively. The positive rate of SPOP of CDK4 positive group was significantly higher than that of CDK4 negative group (50% vs 7%, p=0.005). The positive rate of SPOP of high PD-L1 expression group was significantly lower than negative and low expression groups (14% vs 47%, p=0.03). CD8+ cell counts showed positive relation to PD-L1 expression. In previous report, CDK4/6 inhibitors treatment decreased SPOP protein abundance and elevated PD-L1 protein. Our data supported those findings that PD-L1 expression is regulated by CDK4 and SPOP. Then combination treatment with CDK4/6 inhibitors and PD-1/PD-L1 immune checkpoint blockade may have potential to enhance therapeutic efficacy for cancers.