The University of Hong Kong Gastric Cancer Drug Treatment Study

Targetable drivers governing to 5-fluorouracil and cisplatin (5FU+CDDP) resistance remain elusive due to the paucity of physiologically and therapeutically relevant models. Accordingly, we established 5FU+CDDP resistant intestinal subtype GC patient-derived organoid lines. JAK/STAT signaling and its downstream, adenosine deaminases acting on RNA 1 (ADAR1), are shown to be concomitantly upregulated in the resistant lines. ADAR1 was demonstrated to confer chemoresistance and self-renewal in an RNA editing-dependent manner. WES-seq coupled with RNA-seq identified enrichment of hyperedited lipid metabolism genes in the resistant lines. Mechanistically, ADAR1-mediated A-to-I editing on 3'UTR of stearoyl-CoA desaturase (SCD1) increased binding of KH domain-containing, RNA-binding, signal transduction-associated 1 (KHDRBS1), thereby augmenting SCD1 mRNA stability. Consequently, SCD1 facilitates lipid droplet formation to alleviate chemotherapy-induced ER stress and enhances self-renewal through increasing ß-catenin expression. Pharmacological inhibition of SCD1 abrogated chemoresistance and tumor-initiating cell frequency. Clinically, high proteomic level of ADAR1 and SCD1, or high SCD1 editing/ADAR1 mRNA signature score predicts a worse prognosis. Together, we unveiled a novel actionable target to circumvent chemoresistance.