Background Although the tumor stroma in solid tumors like gastric cancer (GC) plays a crucial role in chemo-resistance, specific targets to inhibit the interaction between the stromal and cancer cells have not yet been utilized in clinical practice. The present study aims to determine whether cancer-associated fibroblasts (CAFs), a major component of the tumor stroma, confer chemotherapeutic resistance to GC cells, and to discover potential targets to improve chemo-response in GC. Methods To identify CAF-specific proteins and signal transduction pathways affecting chemo-resistance in GC cells, secretome and transcriptome analyses were performed. We evaluated the inhibiting effect of CAF-specific protein in in vivo and in vitro models and investigated the expression of CAF-specific protein in human GC tissues. Results Secretome and transcriptome data revealed that interleukin-6 (IL-6) is a CAF-specific secretory protein that protects GC cells via paracrine signaling. Furthermore, CAF-induced activation of the Janus kinase 1-signal transducer and activator of transcription 3 signal transduction pathway confers chemo-resistance in GC cells. CAF-mediated inhibition of chemotherapy-induced apoptosis was abrogated by the anti-IL-6 receptor monoclonal antibody tocilizumab in various experimental models. Clinical data revealed that IL-6 was prominently expressed in the stromal portion of GC tissues, and IL-6 upregulation in GC tissues was correlated with poor responsiveness to chemotherapy. Conclusions Our data provide plausible evidence for crosstalk between GC cells and CAFs, wherein IL-6 is a key contributor to chemoresistance. These findings suggest the potential therapeutic application of IL-6 inhibitors to enhance the responsiveness to chemotherapy in GC. Electronic supplementary material The online version of this article (10.1186/s12943-019-0972-8) contains supplementary material, which is available to authorized users.

Oncogenic RAS mutant (RASMUT) proteins have been considered undruggable via conventional antibody regimens owing to the intracellular location restricting conventional-antibody accessibility. Here, we report a pan-RAS–targeting IgG antibody, inRas37, which directly targets the intracellularly activated form of various RASMUT subtypes after tumor cell–specific internalization into the cytosol to block the interactions with effector proteins, thereby suppressing the downstream signaling. Systemic administration of inRas37 exerted a potent antitumor activity in a subset of RASMUT tumor xenografts in mice, but little efficacy in RASMUT tumors with concurrent downstream PI3K mutations, which were overcome by combination with a PI3K inhibitor. The YAP1 protein was up-regulated as an adaptive resistance-inducing response to inRas37 in RASMUT-dependent colorectal tumors; accordingly, a combination of inRas37 with a YAP1 inhibitor manifested synergistic antitumor effects in vitro and in vivo. Our study offers a promising pan-RAS–targeting antibody and the corresponding therapeutic strategy against RASMUT tumors.

Notwithstanding remarkable treatment success with anti‐PD‐1 monoclonal antibody, oncogenic mechanism of PD‐L1 regulation in gastric cancer (GC) remains poorly understood. We hypothesized that ARID1A might be related to tumor PD‐L1 expression in GC. We found that tumor PD‐L1 positivity was associated with loss of ARID1A and showed trend toward better survival of patients with various molecular subtypes of GC (experimental set, n = 273). Considering heterogeneous ARID1A expression, we validated this using whole tissue sections (n = 159) and found that loss of ARID1A was correlated with microsatellite instability‐high (MSI‐H), Epstein–Barr virus (EBV), and PD‐L1 positivity. Furthermore, for patients with MSI‐H tumors, the degree of PD‐L1 expression was significantly higher in ARID1A‐deficient tumors. After ARID1A knockdown in GC cell lines, total and membranous PD‐L1 protein, and PD‐L1 mRNA levels were increased based on Western blot, flow cytometry, and qRT‐PCR, respectively. With IFN‐γ treatment, PD‐L1 expression was significantly increased both in ARID1A‐deficient cancer cells and controls, but the increase was not more pronounced in the former. Loss of ARID1A increased PD‐L1 via activating AKT signaling, while LY294002 (PI3K inhibitor) decreased PD‐L1 levels. Furthermore, we found that 3 MSI‐H tumors showing highest expression of PD‐L1 had simultaneous KRAS mutation and loss of ARID1A, suggesting a possible synergistic role boosting PD‐L1. Our results strongly indicate that loss of ARID1A is tightly associated with high PD‐L1 expression in GC. These results would increase our understanding of the oncogenic mechanism of PD‐L1 regulation in GC, and also help to find the optimal candidates for immunotherapy.

Objective The aim of this study was to evaluate the prognostic significance of the intratumor stromal proportion in gastric signet ring cell (SRC) carcinomas. Background Cancer stroma, as exemplified by cancer-associated fibroblasts (CAFs), plays critical roles in cancer proliferation, invasion, and metastasis. Methods One hundred seventy-five SRC carcinoma cases were classified according to the intratumor desmoplastic stromal proportion to then analyze the clinicopathologic characteristics of stroma-rich cases. We also investigated the impact of CAFs on the migration as well as on the phenotypic changes of gastric SRC carcinomas in vitro.Furthermore, we performed RNA sequencing of a pair of CAFs and normal-tissue-associated fibroblasts. Results Stroma-rich SRC carcinomas (64 of 175 cases, 36.5%) were associated with female patients (P = 0.045), large tumor size (P = 0.007), higher T category (P \ 0.001), and the presence of perineural invasion (P = 0.018). Patients with stroma-rich SRC carcinomas had a significantly shorter disease-free survival (P \ 0.001) and overall survival (P \ 0.001). However, in a subgroup analysis, the prognostic significance of the stromal proportion correlated only with patients with T3/4 disease. From multivariate analysis, the high stromal proportion is an independent prognostic factor to predict worse disease-free survival (hazard ratio 2.288; P = 0.001) and overall survival (hazard ratio 2.503; P = 0.001). We found that CAFs enhanced the migratory abilities of cancer cells through the epithelial-mesenchymal transition, and RNA sequencing results confirmed these findings. Conclusions The intratumor stromal proportion could be a useful prognostic biomarker and a potential therapeutic target in gastric SRC carcinomas.

AKT1 signaling pathway is important for the regulation of protein synthesis and cell survival with implications in carcinogenesis. In this study, we explored the prognostic significance of AKT1 pathway in intrahepatic cholangiocarcinomas. We investigated the status of phosphatase and tensin homolog deleted on chromosome 10 (PTEN), phosphorylated (p) AKT1 (p-AKT1), p-mammalian target of rapamycin (p-MTOR), p-p70 ribosomal protein S6 kinase (p-RPS6KB2) and p-eukaryotic initiation factor 4E-binding protein-1 (p-EIF4EBP1) in 101 intrahepatic cholangiocarcinomas by immunohistochemistry. Western blot analysis was performed to verify the expression levels of p-AKT1 and p-MTOR. The relationship of protein expression with clinicopathological data and the correlations of protein expression levels were explored. The overexpression of p-AKT1, p-MTOR, and PTEN was associated with a better survival in patients with intrahepatic cholangiocarcinoma (P ¼ 0.0137, 0.0194, and 0.0337, respectively). In a multivariate analysis, PTEN was an independent prognostic factor, and p-AKT1 showed tendency (P ¼ 0.032 and 0.051, respectively). The overexpression of p-MTOR was correlated with well-to-moderately differentiated tumors (Po0.001) and tumors without metastasis (P ¼ 0.046). Expression levels of the AKT1 signaling pathway proteins in this study showed positive correlations with each other, except for PTEN. Aberrant expressions of p-AKT1 and p-MTOR in intrahepatic cholangiocarcinoma were associated with a favorable prognosis, possibly in a PTEN-independent manner. Our results indicate that dysregulation of the AKT1 pathway may have an important role in the development of intrahepatic cholangiocarcinoma, but not necessarily in the progression of the disease.