Molecular characterization of pancreatic cancers as seen in the SLUG gene revealing cancer progression.
Authors: Kawanishi Natsuko , Baca Yasmine , Xiu Joanne , Arai Hiroyuki , Wang Jingyan , Battaglin Francesca , Soni Shivani , Zhang Wu , Shields Anthony Frank , Goldberg Richard M. , Weinberg Benjamin Adam , Lou Emil , Sohal Davendra , Hall Michael J. , Seeber Andreas , Khushman Mohd , Lockhart A. Craig , Marshall John , Korn W. Michael , Lenz Heinz-Josef 
Published: January 2021

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Background: The SLUG gene plays an important role in EMT by repressing E-cadherin and promotes metastasis. Previous data suggest that overexpressed SLUG gene in pancreatic cancer (PC) showing a high frequency of metastasis and poor prognosis. As SLUG contribution to characteristics or metastatic features remains elusive, we clarified its functional roles in PC progression. Methods: A total of 2958 pancreatic tumors were analyzed using Whole Transcriptome sequencing, NextGen Sequencing (NGS) (NextSeq, 592 gene panel) or Whole Exome Sequencing (WES) (NovaSeq) (Caris Life Sciences, Phoenix, AZ). Microsatellite instability (MSI) status was tested by fragment analysis, immunohistochemistry (IHC) and NGS. PD-L1 expression was tested by IHC. Tumor mutational burden (TMB) was measured by counting all mutations found per tumor (a universal cutoff point of ≧10 mutations per MB). Immune cell fraction was calculated by quanTIseq (Finotello 2019, Genome Medicine). Results: A total of 1274 primary and 1684 metastatic pancreatic tumors were included for this study. They were divided equally into four classes in each group, according to their SLUG expression levels. Tumors in the highest quartile of SLUG expression (QH) showed significantly higher frequency in peritoneal-retroperitoneal-omentum metastasis (15.0%) compared to the lowest quartile (QL) (4.8%) (p = .0001). Similar trends were seen in the abdomen (6% vs 1%, p = .001) and bone (2.8% vs 0.0%, p = .005). However, liver (55.0% in QH vs 63.1% in QL) and lung (2.8% vs 14.1%) metastasis occurred most frequently in QL and the least frequently in QH (p = .0197 and p = .001, respectively). This data indicated that tumors with high SLUG gene expression levels tend to lead to disseminated metastasis, and with low expression levels, they tend to spread intravascularly. We detected significant differences among genetic mutations in ATM (5.7% in QL vs 1.8% in QH, p < 0.001) and APC (2.9% vs 0.5%, p < 0.001), and Wnt signaling expressions were higher in QL (4.6%) than QH (0.7%) (p < 0.001). Binary TMB-H and MSI-H tumors had higher frequencies in QL (2.7% and 2.1%) compared to QH (0.3% and 0.1%) (p < 0.001 in both). Contrastingly, PD-L1 expression levels were higher in QH (23.4%) compared to QL (11.0%) (p < 0.001) and had a linear relationship with the expression levels. The median values of the population of B cells, M1 and M2 macrophages were significantly higher in QH compared to QL, but those of myeloid dendritic and CD8+T cells conversely decrease as the SLUG expression increases. Conclusions: Our data indicated the SLUG expression level could determine the tumor characteristics in progression, especially the pattern of metastasis in PC, and it could possibly predict the prognosis and/or therapeutic effects. We also showed immune oncologic markers which have some relationships with SLUG expressions. Further investigation is warranted to better understand SLUG gene functions.