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Neoadjuvant immunochemotherapy (NAIC) achieves superior clinical benefits over neoadjuvant chemotherapy (NAC) in multiple types of human cancers, including gastric adenocarcinoma (GAC). However, it is poorly understood how the malignant epithelial cells and tumor immune microenvironment (TIME) might respond distinctly to NAIC and NAC that underlies therapeutic efficacy. Here treatment‐naive and paired tumor tissues from multiple centers were subjected to pathological, immunological, and transcriptomic analysis. NAIC demonstrated significantly increased rate of pathological complete response compared to NAC (pCR: 25% vs. 4%, p < 0.05). Interestingly, pretreatment intestinal subtype of Lauren's classification was predictive of pathologic regression following NAIC, but not NAC. A substantial portion of cancers underwent intestinal‐to‐diffuse transition, which occurred less following NAIC and correlated with treatment failure. Moreover, NAIC prevented reprogramming to an immunosuppressive TIME with less active fibroblasts and exhausted CD8+ T cells, and increased numbers of mature tertiary lymphoid structures. Mechanistically, activation of the tumor necrosis factor alpha (TNFα)/nuclear factor‐kappa B (NF‐κB) signaling pathway was associated with response to NAIC. Together, NAIC is superior to NAC for locally advanced GAC, likely due to reduced intestinal‐to‐diffuse conversion and reprogramming to an immuno‐active TIME. Modulation of the histological conversion and immunosuppressive TIME could be translatable approaches to improve neoadjuvant therapeutic efficacy. [ABSTRACT FROM AUTHOR]

Background: Aberrant activation of Wnt/β-catenin signaling by dysregulated post-translational protein modifications, especially ubiquitination is causally linked to cancer development and progression. Although Lys48-linked ubiquitination is known to regulate Wnt/β-catenin signaling, it remains largely obscure how other types of ubiquitination, such as linear ubiquitination governs its signaling activity. Methods: The expression and regulatory mechanism of linear ubiquitin chain assembly complex (LUBAC) on Wnt/β-catenin signaling was examined by immunoprecipitation, western blot and immunohistochemical staining. The ubiquitination status of β-catenin was detected by ubiquitination assay. The impacts of SHARPIN, a core component of LUBAC on malignant behaviors of gastric cancer cells were determined by various functional assays in vitro and in vivo. Results: Unlike a canonical role in promoting linear ubiquitination, SHARPIN specifically interacts with β-catenin to maintain its protein stability. Mechanistically, SHARPIN competes with the E3 ubiquitin ligase β-Trcp1 for β-catenin binding, thereby decreasing β-catenin ubiquitination levels to abolish its proteasomal degradation. Importantly, SHARPIN is required for invasiveness and malignant growth of gastric cancer cells in vitro and in vivo, a function that is largely dependent on its binding partner β-catenin. In line with these findings, elevated expression of SHARPIN in gastric cancer tissues is associated with disease malignancy and correlates with β-catenin expression levels. Conclusions: Our findings reveal a novel molecular link connecting linear ubiquitination machinery and Wnt/β-catenin signaling via SHARPIN-mediated stabilization of β-catenin. Targeting the linear ubiquitination-independent function of SHARPIN could be exploited to inhibit the hyperactive β-catenin signaling in a subset of human gastric cancers. [ABSTRACT FROM AUTHOR]

Purpose: Neoadjuvant immunochemotherapy (NAIC) markedly induces pathologic regression in locally advanced gastric adenocarcinoma. However, specific biomarkers are still lacking to effectively identify the beneficiary patients for NAIC., Patients and Methods: A prospective, single-arm, phase II study was conducted to treat locally advanced gastric adenocarcinoma with NAIC (NCT05515796). Correlation between clinicopathologic characteristics and neoadjuvant efficacy was investigated. Bulk RNA sequencing data from 104 samples (from 75 patients in two independent cohorts) and single-cell RNA sequencing data from 105 treatment-naïve gastric adenocarcinomas were comprehensively analyzed to decipher the association of epithelial and microenvironmental characteristics and clinical responses., Results: The prespecified primary endpoints were achieved: pathologic complete regression rate was 30%, major pathologic regression rate was 43%, and the regimen was well tolerated. Analysis of baseline clinical-pathologic parameters revealed the intestinal subtype of Lauren's classification as a key feature stratifying patients with increased sensitivity to NAIC. Mechanistically, an increased pool of DNA damage repair-active cancer cells and enrichment of CLEC9A+ dendritic cells in the tumor microenvironment were associated with enhanced responsiveness of the intestinal subtype gastric adenocarcinoma to NAIC. More importantly, an intestinal subtype-specific signature model was constructed by the machine learning algorithm NaiveBayes via integrating the transcriptomic features of both DNA damage repair-active cancer cells and CLEC9A+ dendritic cells, which accurately predicted the efficacy of NAIC in multiple independent gastric adenocarcinoma cohorts., Conclusions: Intestinal subtype is a histologic biomarker of enhanced sensitivity of gastric adenocarcinoma to NAIC. The intestinal subtype-specific signature model is applicable to guide NAIC for patients with locally advanced gastric adenocarcinoma., (©2024 American Association for Cancer Research.)