Role of the cGAS-STING pathway in regulating the tumor-immune microenvironment in dMMR/MSI colorectal cancer

Identification of CXCL13 as a Promising Biomarker for Immune Checkpoint Blockade Therapy and PARP Inhibitor Therapy in Ovarian Cancer

Ovarian cancer has poor response rates to immune checkpoint blockade (ICB) therapy, despite the use of genomic sequencing to identify molecular targets. Homologous recombination deficiency (HRD) is a conventional indicator of genomic instability (GI) and has been used as a marker for targeted therapies. Indicators reflecting HRD status have shown potential in predicting the efficacy of ICB treatment. Public databases, including TCGA, ICGC, and GEO, were used to obtain data. HRD scores, neoantigen load, and TMB were obtained from the TCGA cohort. Candidate biomarkers were validated in multiple databases, such as the Imvigor210 immunotherapy cohort and the open-source single-cell sequencing database. Immunohistochemistry was performed to further validate the results in independent cohorts. CXCL10, CXCL11, and CXCL13 were found to be significantly upregulated in HRD tumors and exhibited prognostic value. A comprehensive analysis of the tumor immune microenvironment (TIME) revealed that CXCL13 expression positively correlated with neoantigen load and immune cell infiltration. In addition, single-cell sequencing data and clinical trial results supported the utility of CXCL13 as a biomarker for ICB therapy. Not only does CXCL13 serve as a biomarker reflecting HRD status, but it also introduces a potentially novel perspective on prognostic biomarkers for ICB in ovarian cancer.

Cancer cell-extrinsic STING shapes immune-active microenvironment and predicts clinical outcome in gastric cancer

PURPOSE

The activation of cGAS-STING pathway can be triggered by cytosolic double-stranded DNA (dsDNA) in tumor and non-tumor compartments. We aim to assess the constitutive expression of dsDNA-cGAS-STING axis in different cellular contexts and compare their relative contribution to clinical outcomes.

METHODS

A cohort of 154 cases of patients with newly diagnosed gastric cancer were enrolled in this study to evaluate the histo-score of cytosolic dsDNA, cGAS, and STING via immunohistochemistry as well as the types and densities of tumor-infiltrating immune cells. Kaplan-Meier method, multivariable regression, and receiver operating characteristic curve were implemented to analyze the prognostic efficacy of dsDNA-cGAS-STING axis in distinct compartments.

RESULTS

The supra-normal concentration of cytosolic dsDNA correlated with the constitutive expression of cGAS-STING pathway in tumor compartments. In contrast to the lack of STING within cancer cells, the higher STING expression in non-tumor compartments indicated a transcellular cGAS-STING activation. Cancer cell-extrinsic STING was supported to potentiate nucleic acid immunity by sensing tumor-derived dsDNA fragments. Compartmental analyses also confirmed that the level of STING expressed in non-tumor cells was associated with the infiltration of protective immune cells, leading to the prolonged overall survival. Multivariate analysis further identified the independent prognostic value of cancer cell-extrinsic STING and its predictive accuracy could be significantly improved in combination with the immune cell infiltration.

CONCLUSIONS

Cancer cell-extrinsic STING facilitates the remodeling of immune-active tumor microenvironment and acts as an independent prognostic factor in gastric cancer.

Bidirectional regulation of the cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon gene pathway and its impact on hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) ranks as the fourth leading cause of cancer-related deaths in China, and the treatment options are limited. The cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) activates the stimulator of interferon gene (STING) signaling pathway as a crucial immune response pathway in the cytoplasm, which detects cytoplasmic DNA to regulate innate and adaptive immune responses. As a potential therapeutic target, cGAS-STING pathway markedly inhibits tumor cell proliferation and metastasis, with its activation being particularly relevant in HCC. However, prolonged pathway activation may lead to an immunosuppressive tumor microenvironment, which fostering the invasion or metastasis of liver tumor cells.

AIM

To investigate the dual-regulation mechanism of cGAS-STING in HCC.

METHODS

This review was conducted according to the PRISMA guidelines. The study conducted a comprehensive search for articles related to HCC on PubMed and Web of Science databases. Through rigorous screening and meticulous analysis of the retrieved literature, the research aimed to summarize and elucidate the impact of the cGAS-STING pathway on HCC tumors.

RESULTS

All authors collaboratively selected studies for inclusion, extracted data, and the initial search of online databases yielded 1445 studies. After removing duplicates, the remaining 964 records were screened. Ultimately, 55 articles met the inclusion criteria and were included in this review.

CONCLUSION

Acute inflammation can have a few inhibitory effects on cancer, while chronic inflammation generally promotes its progression. Extended cGAS-STING pathway activation will result in a suppressive tumor microenvironment.

Nanocarrier-mediated modulation of cGAS-STING signaling pathway to disrupt tumor microenvironment

The cGAS-STING signaling plays an important role in the immune response in a tumor microenvironment (TME) of triple-negative breast cancer (TNBC). The acute and controlled activation of cGAS-STING signaling results in tumor suppression, while chronic activation of cGAS-STING signaling results in immune-suppressive TME that could result in tumor survival. There is a need, therefore, to develop therapeutic strategies for harnessing tumor suppressive effects of cGAS-STING signaling while minimizing the risks associated with chronic activation. Combination therapies and nanocarriers-based delivery of cGAS-STING agonists have emerged as promising strategies in immunotherapy for controlled modulation of cGAS-STING signaling in cancer. These approaches aim to optimize the tumor suppressive effects of the cGAS-STING pathway while minimizing the challenges associated with modulators of cGAS-STING signaling. In the present review, we discuss recent advancements and strategies in combination therapies and nanocarrier-based delivery systems for effectively controlling cGAS-STING signaling in cancer immunotherapy. Further, we emphasized the significance of nanocarrier-based approaches for effective targeting of the cGAS-STING signaling, tackling resistance mechanisms, and overcoming key challenges like immune suppression, tumor heterogeneity, and off-target effects.

Poly (ADP-Ribose) Polymerase 1 Induces Cyclic GMP-AMP Synthase-stimulator of Interferon Genes Pathway Dysregulation to Promote Immune Escape of Colorectal Cancer Cells

Colorectal cancer (CRC) ranks third globally in cancer incidence and mortality, posing a significant human concern. Recent advancements in immunotherapy are noteworthy. This study explores immune modulation for CRC treatment. Initially targeting poly (ADP-ribose) polymerase 1 (PARP-1), a gene overexpressed in CRC tissues per The Cancer Genome Atlas, we examined its correlation with immune cell infiltration using the Tumor Immune Estimation Resource tool. Quantitative reverse transcription polymerase chain reaction assessed PARP-1 mRNA and inflammation-related gene expression in tumor tissues and cells. Assessing CD8 + T-cell proliferation and cytotoxicity towards HCT116 cells involved carboxyfluorescein diacetate succinimidyl ester and lactate dehydrogenase kits. Chemotaxis was gauged using a Transwell system in a CD8 + T-cell coculture setup, with immunofluorescence revealing cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING) levels in HCT116 cells. Enzyme-linked immunosorbent assay kits measured CD8 + T-cell cytokine secretion. The findings suggested that PARP-1 was overexpressed in CRC tissues and cells and this overexpression was positively correlated with Treg cell infiltration. Overexpression of PARP-1 could significantly reduce the proportion of cGAS and STING-positive cells in HCT116 cells, dampen the proliferation, tumor-killing capacity, and chemotaxis of CD8 + T cells, and inhibit the secretion of related cytokines. The introduction of STING agonists could reverse the effects caused by overexpressed PARP-1. In vivo experiments affirmed the independent anti-tumor effects of PARP-1 inhibitors and STING agonists, synergistically inhibiting tumor growth. Silencing PARP-1 in HCT116 cells potentially boosts CD8 + T-cell activity against these cells through the cGAS-STING pathway.

OPA3 inhibits the cGAS-STING pathway mediated by mtDNA stress to promote colorectal cancer progression

Colorectal cancer (CRC) is an extremely harmful malignant tumor. Optic atrophy 3 (OPA3) is highly expressed in multiple tumors, but its action in CRC is still unknown. This research aims to explore the role of OPA3 and its related molecular mechanisms for CRC. Firstly, we overexpressed and knocked down OPA3 to examine its effect on CRC cell (HT29 cell) growth. CRC cell viability, migration, invasion, and levels of proliferation markers and cell cycle-associated proteins were measured. Then, we treated cells with carbonyl cyanide m-chlorophenyl hydrazone (CCCP) to explore mitochondrial dysfunction and mtDNA stress in HT29 cells. Next, we overexpressed cGAS and STING to examine their correlation with OPA3. The results showed that OPA3 overexpression enhanced CRC cell viability, migration, invasion, and the levels of PCNA, Cyclin A2, and Cyclin B1. Knockdown of OPA3 had the opposite effects. Moreover, OPA3 knockdown facilitated mitochondrial dysfunction and mtDNA stress in CRC cells. OPA3 overexpression also inhibited CCCP-induced mitochondrial stress disorder. Additionally, OPA3 knockdown elevated the protein levels of p-STING and cGAS and the mRNA level of STING target genes. Furthermore, overexpression of either cGAS or STING partially alleviated the enhancement of HT29 cell proliferation, migration, and invasion mediated by OPA3 overexpression. In conclusion, OPA3 promotes CRC progression via inhibiting the cGAS-STING pathway, which is mediated by mtDNA stress. OPA3 may be a new potential target for CRC.

Identification of Prognosis Signature Based on cGAS-STING Pathway and Its Immunotherapeutic Significance in Lung Adenocarcinoma

Lung adenocarcinoma (LUAD) is a leading cause of cancer-related deaths worldwide, and there is an urgent need to develop personalized prognostic models for effective treatment strategies. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathways has been confirmed to engage in multiple cancer progression, prognosis, and immunotherapy benefits. However, the prognostic significance and immunotherapy response of cGAS-STING pathway-associated genes (CSPAGs) in LUAD remain unclear. Herein, we aimed to establish a CSPAG-based prognostic signature for LUAD patients. A total of 139 CSPAGs derived from the GSEA website were enrolled for subsequent analysis. Univariate Cox regression analysis shows that 22 of 139 CSPAGs were associated with LUAD prognosis. Lasso analysis identified 6 CSPAGs (IFNE, NFKB2, POL3RG, TRAF2, TICAM1 and NLRC3) as the most significant prognostic CSPAGs with the best model efficacy. The CSPAG signature classified LUAD patients into low-risk (LR) and high-risk (HR) groups. Kaplan-Meier analysis demonstrated that patients in the LR group had significantly better overall survival (OS) than those in the HR group (p < 0.05 represents statistical significance), indicating the predictive power of the CSPAG signature in LUAD prognosis. The receiver operating characteristic (ROC) curve analysis showed that the area under the curve (AUC) values for the CSPAG signature were higher than those for other well-established predictive factors, suggesting that the CSPAG signature had a higher predictive efficacy. The CSPAG nomogram incorporating clinical factors such as age, TNM status and the CSPAG risk score accurately predicted the OS of LUAD patients at 1, 3, and 5 years, indicating its potential clinical application in LUAD prognosis. Furthermore, we investigated the expression pattern of the 6 signature CSPAGs in different LUAD subpopulations with distinct clinical features. The CSPAG risk score was increased in the immune-high groups, suggesting a positive correlation between immune infiltration degree and CSPAG risk score. There was a heterogenicity of somatic mutation landscape between the two groups. The LR group had a strong immune cell activity, and most immune checkpoints were significantly expressed in the LR group, implying that this group benefited from immune checkpoint blockade (ICB) therapy. In addition, we verified the high predictive accuracy of the CSPAG signature in the GSE31210 and GSE203360 datasets. Taken together, this study established a CSPAG-based prognostic signature for LUAD patients with high predictive efficacy and clinical relevance. The association between CSPAGs and immune infiltration, and ICB therapy response, highlights the potential of the CSPAG signature as a personalized treatment strategy for LUAD patients.

Introducing Neoadjuvant Immunotherapy for Colorectal Cancer: Advancing the Frontier

OBJECTIVE

To give surgeons a review of the current and future use of neoadjuvant immunotherapy in patients with localized colorectal cancer (CRC).

BACKGROUND

Immunotherapy has revolutionized the standard of care in oncology and improved survival outcomes in several cancers. However, the applicability of immunotherapy is still an ongoing challenge. Some cancer types are less responsive to immunotherapy, and the heterogeneity in responses within cancer types is poorly understood. Clinical characteristics of the patient, the timing of immunotherapy in relation to surgery, diversities in the immune responses, clonal heterogeneity, different features of the tumor microenvironment, and genetic alterations are some factors among many that may influence the efficacy of immunotherapy.

RESULTS

In this narrative review, we describe the major types of immunotherapy used to treat localized CRC. Furthermore, we discuss the prediction of response to immunotherapy in relation to biomarkers and radiologic assessment. Finally, we consider the future perspectives of clinical implications and response patterns, as well as the potential and challenges of neoadjuvant immunotherapy in localized CRC.

CONCLUSIONS

Establishing mismatch repair (MMR) status at the time of diagnosis is central to the potential use of neoadjuvant immunotherapy, in particular immune checkpoint inhibitors, in localized CRC. To date, efficacy is primarily seen in patients with deficient MMR status and polymerase epsilon mutations, although a small group of patients with proficient MMR does respond. In conclusion, neoadjuvant immunotherapy shows promising complete response rates, which may open a future avenue of an organ-sparing watch-and-wait approach for a group of patients.

The role of cGAS-STING signaling pathway in colorectal cancer immunotherapy: Mechanism and progress

Colorectal cancer (CRC) is a common malignant tumor in the gastrointestinal tract, it is known as the "silent killer", which poses a serious threat to the lives of patients. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon gene (STING) signaling pathway responds to DNA by sensing, which plays an important role in anti-infection, autoimmune diseases and anti-tumor immunity. Recent studies have found that the activation of cGAS-STING pathway in CRC can induce the expression and secretion of type I interferon (IFN-I) and a variety of inflammatory factors, further activate anti-tumor CD8+ T cells, exert anti-tumor immune response, and inhibit the progression of CRC. Therefore, targeting the cGAS-STING pathway and developing drugs that can regulate the cGAS-STING pathway are of great significance for improving the therapeutic effect and prognosis of CRC patients. In this review, we introduce the cGAS-STING signaling pathway and the regulatory role of this signaling pathway in CRC immune microenvironment. In addition, we discussed the research progress of cGAS-STING pathway in CRC immunotherapy and the clinical research status of STING agonists developed against this pathway, emphasizing the clinical potential of CRC immunotherapy based on the cGAS-STING signaling pathway.

Genomic instability as a driver and suppressor of anti-tumor immunity

Genomic instability is a driver and accelerator of tumorigenesis and influences disease outcomes across cancer types. Although genomic instability has been associated with immune evasion and worsened disease prognosis, emerging evidence shows that genomic instability instigates pro-inflammatory signaling and enhances the immunogenicity of tumor cells, making them more susceptible to immune recognition. While this paradoxical role of genomic instability in cancer is complex and likely context-dependent, understanding it is essential for improving the success rates of cancer immunotherapy. In this review, we provide an overview of the underlying mechanisms that link genomic instability to pro-inflammatory signaling and increased immune surveillance in the context of cancer, as well as discuss how genomically unstable tumors evade the immune system. A better understanding of the molecular crosstalk between genomic instability, inflammatory signaling, and immune surveillance could guide the exploitation of immunotherapeutic vulnerabilities in cancer.

The relationship between tumor immunity and the cGAS-STING pathway in breast cancer: An immunohistochemical study

Breast cancer (BC) is classified into four major histological subtypes, namely luminal A, luminal B, HER2, and basal-like, and its treatment is based on these subtypes. The use of immune checkpoint inhibitors against BC depends on the expression of PD-1/PD-L1. Another tumor immune system-the cGAS-STING pathway-is a potential target for cancer immunotherapy. However, the status of the cGAS-STING pathway in BC has not been fully established. Therefore, we investigated the expression status of the cGAS-STING pathway and immune-related proteins in BC. We classified 111 BCs into six groups-29 hormone receptor-positive carcinomas, 12 HER2+ carcinomas (HER2), 8 luminal-HER2 carcinomas, 26 triple-negative breast carcinomas (TNBCs), 21 lobular carcinomas (LC), and 15 carcinomas with apocrine differentiation (CAD)-and investigated the relationship between BC and tumor immunity via the cGAS-STING pathway using histopathological and immunohistochemical methods. Expression of cGAS was high in CADs (100%) and low in TNBCs (35%); STING-positive lymphocytes were high in TNBC (85%, P = 0.0054). Expression of pSTAT3 was significantly high in patients with TNBC (≥10%, 88%). The proportion of PD-L1-positive tumor cells was higher in TNBCs (54%) than in other BCs (30%). SRGN expression was significantly higher in the TNBC group than in the other BC groups (58%). Tumor immune responses may differ among tumor subtypes. The cGAS-STING pathway may be functional in TNBC and CAD but not in LC. Therefore, targeting the cGAS-STING pathway might be useful in BC, particularly TNBC and CAD.

High levels of tumor cell-intrinsic STING signaling are associated with increased infiltration of CD8+ T cells in dMMR/MSI-H gastric cancer

Mismatch repair deficient (dMMR)/microsatellite instability-high (MSI-H) gastric cancer (GC) exhibits an immune-active tumor microenvironment (TME) compared to MMR proficient (pMMR)/microsatellite stable/Epstein-Barr virus-negative [EBV (-)] GC. The tumor cell-intrinsic cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway has been considered a key regulator of immune cell activation in the TME. However, its significance in regulating the immune-active TME in dMMR/MSI-H GC remains unclear. Here, we demonstrated that tumor cell-intrinsic cGAS-STING was highly expressed in dMMR GC compared to pMMR/EBV (-) GC. The expression of tumor cell-intrinsic STING was significantly and positively associated with the number of CD8+ tumor-infiltrating lymphocytes in GC. Analysis of TCGA datasets revealed that the expression of interferon-stimulated genes and STING downstream T-cell attracting chemokines was significantly higher in MSI-H GC compared to other subtypes of GC with EBV (-). These results suggest that tumor cell-intrinsic STING signaling plays a key role in activating immune cells in the dMMR/MSI-H GC TME and might serve as a novel biomarker predicting the efficacy of immunotherapy for GC treatment.

Interferon Gamma Induces Higher Neutrophil Extracellular Traps Leading to Tumor-Killing Activity in Microsatellite Stable Colorectal Cancer

Many patients with colorectal cancer do not respond to immune checkpoint blockade (ICB) therapy, highlighting the urgent need to understand tumor resistance mechanisms. Recently, the link between the IFNγ signaling pathway integrity and ICB resistance in the colorectal cancer tumor microenvironment has been revealed. The immunosuppressive microenvironment poses a significant challenge to antitumor immunity in colorectal cancer development. Tumor-associated neutrophils found in tumor tissues exhibit an immunosuppressive phenotype and are associated with colorectal cancer patient prognosis. Neutrophil extracellular traps (NET), DNA meshes containing cytotoxic enzymes released into the extracellular space, may be promising therapeutic targets in cancer. This study showed increased NETs in tumor tissues and peripheral neutrophils of high levels of microsatellite instability (MSI-H) patients with colorectal cancer compared with microsatellite stable (MSS) patients with colorectal cancer. IFNγ response genes were enriched in MSI-H patients with colorectal cancer compared with patients with MSS colorectal cancer. Co-culturing neutrophils with MSI-H colorectal cancer cell lines induced more NET formation and higher cellular apoptosis than MSS colorectal cancer cell lines. IFNγ treatment induced more NET formation and apoptosis in MSS colorectal cancer cell lines. Using subcutaneous or orthotopic CT-26 (MSS) tumor-bearing mice models, IFNγ reduced tumor size and enhanced PD-1 antibody-induced tumor-killing activity, accompanied by upregulated NETs and cellular apoptosis. These findings suggest that IFNγ could be a therapeutic strategy for MSS colorectal cancer.

Stimulator of Interferon Genes Protein (STING) Expression in Cancer Cells: A Tissue Microarray Study Evaluating More than 18,000 Tumors from 139 Different Tumor Entities

Stimulator of interferon genes protein (STING) activates the immune response in inflammatory cells. STING expression in cancer cells is less well characterized, but STING agonists are currently being evaluated as anticancer drugs. A tissue microarray containing 18,001 samples from 139 different tumor types was analyzed for STING by immunohistochemistry. STING-positive tumor cells were found in 130 (93.5%) of 139 tumor entities. The highest STING positivity rates occurred in squamous cell carcinomas (up to 96%); malignant mesothelioma (88.5%-95.7%); adenocarcinoma of the pancreas (94.9%), lung (90.3%), cervix (90.0%), colorectum (75.2%), and gallbladder (68.8%); and serous high-grade ovarian cancer (86.0%). High STING expression was linked to adverse phenotypes in breast cancer, clear cell renal cell carcinoma, colorectal adenocarcinoma, hepatocellular carcinoma, and papillary carcinoma of the thyroid (p < 0.05). In pTa urothelial carcinomas, STING expression was associated with low-grade carcinoma (p = 0.0002). Across all tumors, STING expression paralleled PD-L1 positivity of tumor and inflammatory cells (p < 0.0001 each) but was unrelated to the density of CD8+ lymphocytes. STING expression is variable across tumor types and may be related to aggressive tumor phenotype and PD-L1 positivity. The lack of relationship with tumor-infiltrating CD8+ lymphocytes argues against a significant IFN production by STING positive tumor cells.

Colorectal Cancer Immunotherapy: State of the Art and Future Directions

Cancer immunotherapy has become an indispensable mode of treatment for a multitude of solid tumor cancers. Colorectal cancer (CRC) has been one of the many cancer types to benefit from immunotherapy, especially in advanced disease where standard treatment fails to prevent recurrence or results in poor survival. The efficacy of immunotherapy in CRC has not been without challenge, as early clinical trials observed dismal responses in unselected CRC patients treated with checkpoint inhibitors. Many studies and clinical trials have since refined immunotherapies available for CRC, solidifying immunotherapy as a powerful asset for CRC treatment. This review article examines CRC immunotherapies, from their foundation, through emerging avenues for improvement, to future directions.

Integration of bulk RNA sequencing data and single-cell RNA sequencing analysis on the heterogeneity in patients with colorectal cancer

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway has emerged as a critical innate immune pathway that could virtually impact nearly all aspects of tumorigenesis including colorectal cancer. This work aimed to develop and validate molecular subtypes related to cGAS-STING pathways for colorectal cancer using Bulk RNA-seq and single-cell RNA-seq (scRNA-seq) data. Bulk RNA-seq data were acquired from The Cancer Genome Atlas dataset (training dataset) and Gene Expression Omnibus dataset (validation dataset). Univariate COX survival analysis was utilized to identify prognostic differentially expressed genes (DEGs) from 6 immune pathways related to cGAS-STING. ConsensusClusterPlus package was used to classify different subtypes based on DEGs. scRNA-seq data were used to validate differences in immune status between different subtypes. Two clusters with distinct prognosis were identified based on 27 DEGs. The six cGAS-STING-related pathways had different levels of significance between the two clusters. Clust1 had most number of amplified CNVs and clust2 had the most number of loss CNVs. TP53 was the top mutated gene of which missense mutations contributed the most of single-nucleotide variants. Immune score of clust1 was higher than that in clust2, as reflected in macrophages, T cells, and natural killer cells. Three unfavorable genes and 31 protection factors were screened between the two clusters in three datasets. ScRNA-seq data analysis demonstrated that macrophages were more enriched in clust1, and tumor cells and immune cells had close interaction. We classified two distinct subtypes with different prognosis, mutation landscape, and immune characteristics.

Short chain fatty acids prime colorectal cancer cells to activate antitumor immunity

Introduction

Colorectal cancer (CRC) is a leading cause of death worldwide and its growth can either be promoted or inhibited by the metabolic activities of intestinal microbiota. Short chain fatty acids (SCFAs) are microbial metabolites with potent immunoregulatory properties yet there is a poor understanding of how they directly regulate immune modulating pathways within the CRC cells.

Methods

We used engineered CRC cell lines, primary organoid cultures, orthotopic in vivo models, and patient CRC samples to investigate how SCFA treatment of CRC cells regulates their ability to activate CD8+ T cells.

Results

CRC cells treated with SCFAs induced much greater activation of CD8+ T cells than untreated CRC cells. CRCs exhibiting microsatellite instability (MSI) due to inactivation of DNA mismatch repair were much more sensitive to SCFAs and induced much greater CD8+ T cell activation than chromosomally instable (CIN) CRCs with intact DNA repair, indicating a subtype-dependent response to SCFAs. This was due to SCFA-induced DNA damage that triggered upregulation of chemokine, MHCI, and antigen processing or presenting genes. This response was further potentiated by a positive feedback loop between the stimulated CRC cells and activated CD8+ T cells in the tumor microenvironment. The initiating mechanism in the CRCs was inhibition of histone deacetylation by the SCFAs that triggered genetic instability and led to an overall upregulation of genes associated with SCFA signaling and chromatin regulation. Similar gene expression patterns were found in human MSI CRC samples and in orthotopically grown MSI CRCs independent of the amount of SCFA producing bacteria in the intestine.

Discussion

MSI CRCs are widely known to be more immunogenic than CIN CRCs and have a much better prognosis. Our findings indicate that a greater sensitivity to microbially produced SCFAs contributes to the successful activation of CD8+ T cells by MSI CRCs, thereby identifying a mechanism that could be therapeutically targeted to improve antitumor immunity in CIN CRCs.

The Impact of Tumor Cell-Intrinsic Expression of Cyclic GMP-AMP Synthase (cGAS)-Stimulator of Interferon Genes (STING) on the Infiltration of CD8+ T Cells and Clinical Outcomes in Mismatch Repair Proficient/Microsatellite Stable Colorectal Cancer

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway plays a crucial role in activating immune cells in the tumor microenvironment, thereby contributing to a more favorable response to immune checkpoint inhibitors (ICI) in colorectal cancer (CRC). However, the impact of the expression of cGAS-STING in tumor cells on the infiltration of CD8⁺ T cells and clinical outcomes in mismatch repair proficient/microsatellite stable (pMMR/MSS) CRC remains largely unknown. Our findings reveal that 56.8% of all pMMR CRC cases were cGAS-negative/STING-negative expressions (cGAS^-/STING^-) in tumor cells, whereas only 9.9% of all pMMR CRC showed cGAS-positive/STING-positive expression (cGAS⁺/STING⁺) in tumor cells. The frequency of cGAS⁺/STING⁺ cases was reduced in the advanced stages of pMMR/MSS CRC, and histone methylation might be involved in the down-regulation of STING expression in tumor cells. Since the expression level of cGAS-STING in tumor cells has been associated with the infiltration of CD8⁺ and/or CD4⁺ T cells and the frequency of recurrence in pMMR/MSS CRC, decreased expression of cGAS-STING in tumor cells might lead to poor immune cell infiltration and worse prognosis in most pMMR/MSS CRC patients. Our current findings provide a novel insight for the treatment of patients with pMMR/MSS CRC.

Activation of cGAS-STING Pathway Is Associated with MSI-H Stage IV Colorectal Cancer

Colorectal cancer is the second most common cause of cancer-related mortality in adults. Understanding colorectal tumorigenesis at both the cellular and molecular levels is crucial for developing effective treatment options. Forty-one biopsy samples from patients with metastatic CRC (mCRC) were collected at Split University Hospital in Croatia. A total of 41 patients (21 with microsatellite unstable tumours and 20 with microsatellite stable tumours) were randomly included in the study. Immunolabelling of cGAS and STING in metastatic CRC was performed and further complemented by histological classification, tumour grade, and KRAS, NRAS, and BRAF mutational status of mCRC. In bivariate analysis, elevated expression of cGAS and STING was positively associated with MSI-H colon cancer (Fisher's exact test, both p = 0.0203). Combined expression analysis of cGAS and STING showed a significantly higher percentage of patients with mCRC MSI-H with a fully or partially activated cGAS-STING signalling pathway (chi-square test, p = 0.0050). After adjusting for age, sex, and STING expression, increased cGAS expression remained significantly associated with MSI-H colon cancer in a multiple logistic regression model (β = 1.588, SE = ±0.799, p = 0.047). The cGAS-STING signalling axis represents a compelling new target for optimization of immune checkpoint inhibitor therapeutic approaches in patients with MSI-H stage IV CRC.

Cancer immunotherapy strategies that target the cGAS-STING pathway

Activation of the cGAS-STING pathway by cytoplasmic DNA induces the production of Type-1 interferons. Recent advances in research suggest that the cGAS-STING pathway is involved in different parts of the cancer-immunity cycle (CIC) to promote or suppress antitumor immune responses. Combination therapy of STING agonists has made certain progress in preclinical as well as clinical trials, but the selection of combination therapy regimens remains a challenge. In this review, we summarize the role of the cGAS-STING in all aspects of CIC, and focus on the combination immunotherapy strategies of STING agonists and current unsolved challenges.

STING pathway contributes to the prognosis of hepatocellular carcinoma and identification of prognostic gene signatures correlated to tumor microenvironment

Background

Hepatocellular carcinoma (HCC) is one of the most malignant solid tumors worldwide. Recent evidence shows that the stimulator of interferon genes (STING) pathway is essential for anti-tumor immunity via inducing the production of downstream inflammatory cytokines. However, its impact on the prognosis and tumor microenvironment of HCC was still limited known.

Methods

We obtained gene expression profiles of HCC from GEO, TCGA, and ICGC databases, and immune-related genes (IRGs) from the ImmPort database. Multivariate Cox regression was performed to identify independent prognostic factors. Nomogram was established to predict survival probability for individual patients. Kaplan–Meier curve was used to evaluate the survival difference. Afterward, ESTIMATE, TISCH, and TIMER databases were combined to assess the immune cell infiltration. Furthermore, the qPCR, western blotting, and immunohistochemistry were done to evaluate gene expression, and in vitro cell models were built to determine cell migratory ability.

Results

We found that gene markers of NLRC3, STING1, TBK1, TRIM21, and XRCC6 within STING pathway were independent prognostic factors in HCC patients. Underlying the finding, a predictive nomogram was constructed in TCGA-training cohort and further validated in TCGA-all and ICGC datasets, showing credible performance. Experimentally, up-regulated TBK1 promotes the ability of HCC cell migration. Next, the survival-related immune-related co-expressed gene signatures (IRCGS) (VAV1, RHOA, and ZC3HAV1) were determined in HCC cohorts and their expression was verified in human HCC cells and clinical samples. Furthermore, survival-related IRCGS was associated with the infiltration of various immune cell subtypes in HCC, the transcriptional expression of prominent immune checkpoints, and immunotherapeutic response.

Conclusion

Collectively, we constructed a novel prognostic nomogram model for predicting the survival probability of individual HCC patients. Moreover, an immune-related prognostic gene signature was determined. Both might function as potential therapeutic targets for HCC treatment in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02734-4.