Abstract 880: Activation of the Wnt pathway is associated with GNASR201 mutant appendiceal cancer in the peritoneum
Authors: Chowdhury Saikat , Ito Ichiaki , Pattalachinti Vinay K. , Shen John Paul 
Published: April 2023

Abstract
Background: Active mutations in the GNAS oncogene are frequent in appendiceal adenocarcinoma (AA) (~37%) and are also found less frequently in lung, colorectal, and endometrial cancers. Here, we performed differential gene expression analyses between GNASR201 and GNASWT AA tumors to understand critical downstream transcriptomic effects of the activation of GNAS.
Methods: Differential gene expression (DEG) studies between GNASR201C/H and GNASWT AA samples were studied in PDX (n=19) and clinical (n=14) cohorts. Tumor samples were surgically resected from AA patients at MD Anderson Cancer Center. Tumors were implanted in intraperitoneal (IP) (n=6, GNASR201C; n=7, GNASWT) and flank (n=3, GNASR201C; n=3, GNASWT) regions of NSG mice (n=19). RNA sequencing of tumor samples obtained from IP and flank was performed, and sequence reads of mouse and human tissues were classified by Xenome (v1.0.1-r). The clinical cohort (n=14) of AA patients was divided into GNASR201C/H (n=4) and GNASWT (n=10) groups for RNA-seq analysis. Reads were aligned with the human reference genome (GRCh38) by STAR aligner (v2.7.2b), and gene expressions were quantified by HTSeq (v0.11.0). DESeq2 (v1.30.1) was used for DGE studies between GNASR201C/H and GNASWT groups of both PDX and clinical cohorts. Gene sets enrichment analysis (GSEA) was conducted by the GSEA (v4.3.2) for each DGE study to identify gene sets significantly dysregulated in the human hallmark MSigDB (v2022) database.
Results: Gene expression profiles of GNASR201C/H and GNASWT tumors of both PDX (peritoneal and flank) and clinical cohorts formed distinct clusters in unsupervised clustering. After multiple hypothesis corrections, several genes were significantly up or downregulated in DGE studies of GNASR201C/H vs. GNASWT tumors in both PDX (~20%) and clinical cohorts (~0.5%). GSEA of peritoneal tumors identified that Wnt/Beta-catenin signaling was positively enriched (NES=1.14) in GNASR201C tumors than in GNASWT. Interestingly, positive enrichment of Wnt/Beta-catenin signal (NES=1.14) was also observed in GNASR201C metastatic AA patients in the clinical cohort. Our previous study showed that GNAS knock-out also decreased Wnt pathway activity in CRC cell lines, which aligns with the current observation of AA tumors. However, Wnt/Beta-catenin signaling was not enriched (NES=0.64) in GNASR201C mutant tumors grown in flanks of PDX models, suggesting that the peritoneal microenvironment may play a role in activating the Wnt pathway in GNASR201C AA tumors. Notch signaling was significantly enriched (NES=1.38) in GNASR201C/H AA patients but not in GNASR201C mutant IP and flank tumors.
Conclusions: Activation of Wnt signaling is associated with tumorigenesis of GNASR201C/H AA tumors. The peritoneal microenvironment may help to activate the Wnt pathway in this tumor group. PDX models could be used to study transcriptional activities of GNASR201 AA tumors.
Citation Format: Saikat Chowdhury, Ichiaki Ito, Vinay K. Pattalachinti, John Paul Shen. Activation of the Wnt pathway is associated with GNASR201 mutant appendiceal cancer in the peritoneum [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 880.