Angiogenesis is associated with an attenuated tumor microenvironment, aggressive biology, and worse survival in gastric cancer patients

Abstract

Angiogenesis is a cornerstone of cancer as it allows tumors to receive oxygen and nutrients. A high level of angiogenesis within a tumor may therefore be indicative of its aggressiveness. In this study, we examined this hypothesis in gastric cancer. Gene set variation analysis was used to measure the level of angiogenesis in tumors in 1,348 gastric cancer patients using the Hallmark_angiogenesis gene set to score tumor transcriptomes. As we predicted, there was a significant correlation between angiogenesis score and expression of angiogenesis-related genes. The score moderately correlated with abundance of vessel-related stromal cells, fibroblasts and chondrocytes in the tumor microenvironment (TME). Tumors with high score had low infiltration of T helper type 1 and 2 cells but a greater infiltration of M1 macrophages and dendritic cells. They also had enriched expression of gene sets for coagulation, hypoxia, epithelial mesenchymal transition (EMT), and TGF-β signaling. High angiogenesis score was significantly associated with advanced AJCC stage and higher T- but not N-parameters in the TNM staging system. Patients with a high score also had shorter survival. In conclusion, bulk tumor transcriptome-based quantification of tumor angiogenesis using a computational algorithm may serve to identify patients with worse survival in gastric cancer.

Keywords: Angiogenesis; EMT; GSVA; gastric cancer; gene set; prognostic biomarker; survival.

Figure 1

The angiogenesis score was associated with expressions of angiogenesis-related genes. Boxplots showing comparisons of the expression levels of (A) vascular endothelial growth factor (VEGF)-related genes, (B) endothelial cell marker-related genes; and (C) vascular stability-related genes, between low and high angiogenesis score groups in the TCGA and GSE84437 cohorts. We defined the VEGF-related genes as VEGFA, VEGFB, VEGFC, VEGFR1 (FLT1), VEGFR2 (KDR), VEGFR3 (FLT4), and PGF, and the endothelial cell marker-related genes as VWF, CD31 (PECAM1), and CD34, and vascular stability-related genes as ANGPT1, ANGPT2, TIE1, TIE2 (TEK), VE-cadherin (CDH5), JAM2 and Claudin5 (CLDN5).

Figure 2

The angiogenesis score was associated with fraction of stromal cells in gastric cancer. Correlation curve of the angiogenesis score with stromal cells, including endothelial cells, lymphatic- and microvascular-endothelial cells, pericytes, fibroblasts, and chondrocytes, were estimated using the xCell algorithm in the TCGA and GSE84437 cohorts. Spearman rank correlation was used in the analysis.

Figure 3

The angiogenesis score was associated with the fraction of immune cells in gastric cancer. Boxplots comparing immune cells including CD8⁺ T cells, CD4⁺ memory T cells, regulatory T cells, T helper cell type 1 (Th1), T helper cell type 2 (Th2) cells, M1 macrophages, M2 macrophages, and dendritic cells (DCs) by high and low angiogenesis score in TCGA and GSE84437 cohorts.

Figure 4

High angiogenesis score tumor groups enriched coagulation, epithelial mesenchymal transition (EMT), hypoxia, and transforming growth factor (TGF)-β signaling gene sets in the TCGA, GSE84437, and GSE26253 cohorts. Correlation curve of coagulation, epithelial mesenchymal transition (EMT), hypoxia, and TGF-β signaling gene sets with false discovery rate (FDR) and normalized enrichment score (NES) by gene set enrichment analysis.

Figure 5

The angiogenesis score was associated with clinical cancer aggressiveness. Boxplots of the angiogenesis score by (A) AJCC stage, T- and N-category in the TCGA, GSE26901, and GSE84437 cohorts. (B) Kaplan-Meier curves of OS in the TCGA (n = 368) and GSE84437 (n = 432) cohorts, and DFS in the GSE26253 (n = 432) cohort of angiogenesis score high (red) and low (blue) in gastric cancer. AJCC, American Joint Committee on Cancer; disease-free survival, DFS; overall survival, OS.