Frizzled-1 amplification promotes fibrosis in the gastric tumor microenvironment through the activation of fibroblasts via the SLIT2/ROBO1 axis.

[BACKGROUND] A fibrotic tumor microenvironment (TME) promotes tumor progression by the interactions between tumor cells and cancer-associated fibroblasts (CAFs) in the extracellular matrix (ECM), which enhance tumor cell survival and growth, and by suppressing antitumor immunity. However, how characteristic gene expression and amplification in cancer cells drive the formation of a fibrotic TME in patients with gastric cancer (GC) is unclear.

[METHODS] We performed genomic and transcriptomic analyses via datasets from The Cancer Genome Atlas and the Asian Cancer Research Group to identify amplified and overexpressed genes associated with the presence of a fibrotic TME in tumors. Syngeneic mouse models of GC and multiplexed immunohistochemistry (IHC) were used to validate the findings of the transcriptomic analysis and investigate the underlying mechanisms.

[RESULTS] The Frizzled class receptor 1 (FZD1) gene was frequently amplified and highly expressed in GC patients with fibrotic tumors, and FZD1 expression was related to a poor prognosis. The overexpression of Fzd1 in murine GC tumor cells was significantly associated with enhanced tumor fibrosis and growth and reduced infiltration of CD3 lymphocytes and CD8 T cells into tumors. SLIT2 secretion was increased in Fzd1-overexpressing tumor cells via the canonical WNT-β-catenin pathway, and SLIT2 activated CAFs to produce more ECM through the SLIT2‒ROBO1 axis.

[CONCLUSIONS] This study highlights the potential of FZD1 as a biomarker for predicting fibrotic status in patients with GC and the SLIT2‒ROBO1 axis as a therapeutic target to reverse a fibrotic and immunosuppressive TME.