Development of the pancreas and pancreatic cancer

Genome-wide DNA methylation analysis reveals molecular subtypes of pancreatic cancer

Pancreatic cancer (PC) is the fourth leading cause of cancer deaths in the United States with a five-year patient survival rate of only 6%. Early detection and treatment of this disease is hampered due to lack of reliable diagnostic and prognostic markers. Recent studies have shown that dynamic changes in the global DNA methylation and gene expression patterns play key roles in the PC development; hence, provide valuable insights for better understanding the initiation and progression of PC. In the current study, we used DNA methylation, gene expression, copy number, mutational and clinical data from pancreatic patients. We independently investigated the DNA methylation and differential gene expression profiles between normal and tumor samples and correlated methylation levels with gene expression patterns. We observed a total of ~23-thousand differentially methylated CpG sites (Δβ≥0.1) between normal and tumor samples, where majority of the CpG sites are hypermethylated in PC, and this phenomenon is more prominent in the 5′UTRs and promoter regions compared to the gene bodies. Differential methylation is observed in genes associated with the homeobox domain, cell division and differentiation, cytoskeleton, epigenetic regulation and development, pancreatic development and pancreatic signaling and pancreatic cancer core signaling pathways. Correlation analysis suggests that methylation in the promoter region and 5′UTR has mostly negative correlations with gene expression while gene body and 3′UTR associated methylation has positive correlations. Regulatory element analysis suggests that HOX cluster and histone core proteins are upstream regulators of hypomethylation, while SMAD4, STAT4, STAT5B and zinc finger proteins (ZNF) are upstream regulators of hypermethylation. Non-negative matrix factorization (NMF) clustering of differentially methylated sites generated three clusters in PCs suggesting the existence of distinct molecular subtypes. Cluster 1 and cluster 2 showed samples enriched with clinical phenotypes like neoplasm histological grade and pathologic T-stage T3, respectively, while cluster 3 showed the enrichment of samples with neoplasm histological grade G1. To the best of our knowledge, this is the first genome-scale methylome analysis of PC data from TCGA. Our clustering analysis provides a strong basis for future work on the molecular subtyping of epigenetic regulation in pancreatic cancer.

Blockade of delta-like ligand 4 signaling inhibits both growth and angiogenesis of pancreatic cancer

OBJECTIVES

The Notch signaling pathway is evolutionarily conserved and regulates cell-fate decisions in a variety of organ development. Previous studies have shown that delta-like ligand 4 (DLL4), one of transmembranous Notch ligands, is up-regulated at the site of tumor growth, especially of tumor angiogenesis. In this study, we examined the effects of the DLL4-Notch signaling on tumor angiogenesis using the neutralizing monoclonal antibodies against DLL4.

METHODS

The neutralizing monoclonal antibodies against murine DLL4 (HMD4-2) were newly established, and their effects on tumor growth and angiogenesis were evaluated using the mice subcutaneously implanted human pancreatic cancer cells (PK-1) in the dorsal flank area. To further assess the effects on tumor angiogenesis, PK-1 cells were implanted in skinfold chambers inserted on the dorsal area of the mice.

RESULTS

Treatment (intraperitoneally) with HMD4-2 suppressed the in vivo tumor growth with marked decrease of tumor vasculature and had no direct inhibitory effect on PK-1 cells in vitro. Real-time sequential analysis using the skinfold chamber model revealed the antiangiogenic effect of HMD4-2.

CONCLUSIONS

These results suggests that cell-to-cell interaction via DLL4-Notch signaling pathway has been implicated in tumor angiogenesis, and control of this pathway can be a new therapeutic approach to solid tumor.