Targeting GNAS mutant appendiceal adenocarcinoma.

Abstract

470 Background: Appendiceal cancers are rare, comprising just 0.5% of all intestinal neoplasia, preventing the systematic study of these tumors in randomized clinical trials. Given this absence of clinical data, no evidence-based guidelines exist regarding the best management of this disease and no drugs have been developed to specifically target appendiceal adenocarcinoma (AA). The G protein GNAS is the second most frequently mutated gene after KRAS in low-grade (49%) mucinous AA (52%), making it an attractive drug target in this orphan disease. Methods: Using CRISPR, GNAS was knocked out in KM12, SNU175 and SKCO1 gastric cell lines that harbor GNASR201C mutation. The mutant and KO pairs of cells were evaluated for their proliferation rate and ability to form colonies in a clonogenic assay. RNA sequencing of the mutant and knock out cells was performed to determine pathways potentially associated with the GNAS signaling pathway. The Sanger GDSC was used to identify drugs selectively lethal to GNAS mutant tumors. Results: KM12 cells knocked out for GNAS showed a 40% decrease in proliferation compared to the parent cells with mutant GNAS (p < 0.0001). GNAS knockout significantly reduced colony formation of all three mutant cell lines (KM12: 397 vs. 94, SNU175: 512 vs. 134, and SKCO1: 36 vs. 5, p = 0.0022). Analysis of four GNASR201C cell lines relative to matched controls identified IGF-1R, MEK and PKC as potential vulnerabilities. In vivo validation experiments are currently ongoing. Conclusions: Our findings suggest preliminarily that GNASR201C mutant cell lines are oncogene addicted to GNAS growth signal and could be targeted with inhibitor of GNAS or one of its downstream effectors.