Abstract 2626: Expression of human poliovirus receptor, an immune checkpoint biomarker in lung cancer

Abstract

Abstract Background: Recently, immune therapy has shown notable efficacy in melanoma, non-small-cell lung cancer (NSCLC), among others, indicating that the targeting of immune checkpoints may be a promising treatment for malignant tumors. The human Poliovirus Receptor (CD155), an immune checkpoint, has been found to be overexpressed on the membranes of various tumor cells including colorectal and ovarian carcinoma. Examining PVR’s expression in NSCLC could shine light on PVR’s potential role and its possible correlation to the prognosis and outcomes for NSCLC patients. Material and Methods: Gene expression data for lung cancer cell lines and tumor tissues was derived from the Cancer Cell Line Encyclopedia (CCLE [www.broadinstitute.org/ccle]) and the TCGA database (www.cbioportal.org), respectively. Immunohistochemistry (IHC) was performed on a Ventana Benchmark XT platform using an anti-PVR antibody (Cell Signaling #D3G7H at a 1:100 dilution). IHC staining was evaluated for a NSCLC Cell Line Tissue MicroArray (TMA) and a NSCLC patient cohort TMA. The H-score system was used to generate a semi-quantitative score, ranging from 0 to 300, that evaluates the intensity and prevalence of the staining on tumor cells. Patient data was analysed to uncover correlations between outcome and PVR expression in the NSCLC TMA cohort. Western blot analysis was performed to confirm antibody specificity and PVR expression levels in three NSCLC cell lines. Results: Analysis of mRNA expression data from CCLE and TCGA databases identified that PVR is highly expressed in lung cancer. Three lung cancer cell lines were chosen based on mRNA expression for this study: NCI-H211 (high), NCI-H1650 (moderate) and NCI-H187 (negative). Cell line data revealed that PVR demonstrated higher expression levels in lung cancer than other immune checkpoints, such as PD-L1, PD-L2, and Gal-9 among others. In addition, PVR expression was not correlated with other negative immune checkpoints including PD-L1 and Gal-9. Western blot analysis confirmed that the Cell Signaling antibody was specific to the PVR protein in NSCLC cell lines. IHC staining of NSCLC cell lines revealed that non-squamous NSCLC cell lines express higher levels of PVR than do squamous cell cell lines (p<0.0001, Fisher test). The prevalence of PVR in the NSCLC patient cohort was 68% (68/100) using a H-score cutoff of ≥ 7. Analysis revealed a lower positivity of 61.7% (37/60) in squamous carcinoma as compared to 77.5% (31/40) in non-squamous NSCLC. Analysis of the patient outcome data demonstrated that higher levels of PVR protein expression is correlated with poorer outcomes in patients with both squamous lung cancer and adenocarcinoma. Conclusions: PVR protein expression could potentially serve as a new immune checkpoint biomarker in lung cancer. This study demonstrates that high PVR protein levels predict poorer outcomes in lung cancer patients; suggesting that PVR may be an important target for future immune therapy. Citation Format: Camilla Koczara, Hui Yu, Kim Ellison, Christopher Rivard, Leslie Rozeboom, Daniel Chan, Kenichi Suda, Kristine Brovsky, Rafal Dziadziuszko, Fred Hirsch. Expression of human poliovirus receptor, an immune checkpoint biomarker in lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2626. doi:10.1158/1538-7445.AM2017-2626