cGAS and cancer therapy: a double-edged sword

The cGAS-STING-related signature affects the prognosis of colorectal cancer through its regulation of multiple immune cells

The cGAS-STING signaling pathway has emerged as a critical player in the immune response against cancer, including colorectal adenocarcinoma (COAD). Understanding the impact of this pathway on COAD at multiple omics levels is crucial for advancing cancer immunotherapy and precision medicine. This study aimed to investigate the relationship between cGAS-STING-related genes and COAD, analyzing gene mutations, copy number variations, DNA methylation, and gene expression to uncover the pathway's influence on COAD prognosis. Utilizing multi-omics sequencing data from TCGA and GEO databases, key core genes in the cGAS-STING pathway were identified and further validated through PCR and Western blot analysis. Mutations and copy number variations in the CASP8 and RIPK1 genes, differential DNA methylation patterns, and mRNA expression levels of specific genes were assessed to determine their impact on COAD prognosis. Validation through tissue samples highlighted NLRC3, CASP1, AIM2, and CXCL10 as core genes in the cGAS-STING pathway. Our findings demonstrate that mutations and copy number variations in CASP8 and RIPK1, differential DNA methylation patterns, and altered gene expression levels significantly influence the prognosis of COAD. The identification of core genes in the cGAS-STING pathway, particularly NLRC3, CASP1, AIM2, and CXCL10, has led to the development of a prognostic model predicting poor tumor outcomes through immune cell infiltration. This study provides valuable insights into the mechanisms of the cGAS-STING pathway in COAD and offers potential directions for future research in cancer immunotherapy and precision medicine.

cGAS/STING signaling pathway in gynecological malignancies: From molecular mechanisms to therapeutic values

Gynecological cancers, including cervical, ovarian, and endometrial malignancies, remain a significant global health burden, exacerbated by disparities in access to preventive measures such as HPV vaccination and routine screening. The cGAS/STING signaling pathway, a pivotal mechanism in innate immunity, detects cytosolic DNA from pathogens or cellular damage, triggering immune responses via type I interferons and inflammatory cytokines. This pathway's dual role in gynecological cancers, either promoting antitumor immunity or facilitating tumor immune evasion, makes it a compelling target for innovative therapies. The article outlines cGAS/STING's influence on tumor microenvironments, immune surveillance, and inflammation, with emphasis on molecular mechanisms driving cancer progression. It explores interactions between DNA damage response pathways and immune modulation, highlighting the impact of cGAS/STING activation or suppression in ovarian, cervical, and endometrial cancers. The therapeutic potential of STING agonists, PARP inhibitors, and targeted immunotherapies is reviewed, demonstrating how these approaches can boost immune responses, counteract chemotherapy resistance, and improve patient outcomes. The study also discusses strategies for leveraging cGAS/STING signaling to enhance the efficacy of immunotherapies and address tumor-mediated immune suppression, providing insights into future directions for personalized cancer treatments.

Regulation of cGAS-STING signalling and its diversity of cellular outcomes

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signalling pathway, which recognizes both pathogen DNA and host-derived DNA, has emerged as a crucial component of the innate immune system, having important roles in antimicrobial defence, inflammatory disease, ageing, autoimmunity and cancer. Recent work suggests that the regulation of cGAS-STING signalling is complex and sophisticated. In this Review, we describe recent insights from structural studies that have helped to elucidate the molecular mechanisms of the cGAS-STING signalling cascade and we discuss how the cGAS-STING pathway is regulated by both activating and inhibitory factors. Furthermore, we summarize the newly emerging understanding of crosstalk between cGAS-STING signalling and other signalling pathways and provide examples to highlight the wide variety of cellular processes in which cGAS-STING signalling is involved, including autophagy, metabolism, ageing, inflammation and tumorigenesis.

Enhancing Tumor-Specific immunity with SLdacA: A attenuated Salmonella-mediated c-di-AMP delivery system targeting the STING pathway

The STING agonist stimulates an anti-tumor immune response by activating T cells, but its limited tumor-targeting specificity poses risks of cytokine storms or autoimmune reactions. Conversely, attenuated Salmonella typhimurium △ppGpp (S.t△ppGpp) exhibits superior tumor-targeting specificity and potent anti-tumor immunogenicity. However, the anti-tumor effects of Salmonella carrying STING agonists remain underexplored. In this study, we engineered a strain called SLdacA, utilizing S.t△ppGpp as a carrier, to produce c-di-AMP. This engineered strain effectively enhances dendritic cell maturation and M1-type macrophage polarization by inducing type I interferon production, thereby recruiting and activating effector T cells against tumor progression. This process is regulated by the STING/type I interferon pathway. Our findings indicate that utilizing S.t△ppGpp as a delivery vehicle for STING agonists holds promise as a strategy for synergistic bacterial-mediated immunotherapy.

cGAS regulates metabolic reprogramming independently of STING pathway in colorectal cancer

BACKGROUND

Cyclic GMP-AMP synthase (cGAS) is widely acknowledged for detecting cytosolic chromatin fragments and triggering innate immune responses through the production of the second messenger cGAMP, which subsequently activates the adaptor protein STING. However, the role of cGAS in regulating metabolic reprogramming independently of STING activation has not yet been explored.

METHODS

Gene set enrichment pathway analysis (GSEA) based on TCGA transcriptomics, combined with Seahorse metabolic analysis of CRC cell lines and human normal colonic mucosa cell line FHC, was performed to profile the metabolic features in CRC. cGAS doxycycline- (dox) inducible knockout (iKO) CRC sublines were generated to investigate the role of cGAS in CRC. Transcriptome and proteome data from COAD cohorts were utilized to evaluate the RNA and protein expression levels of cGAS in COAD tissues and normal colon tissues. Overall survival information of patients with COAD was used to evaluate the prognostic value of cGAS expression. Colony formation assays were conducted to evaluate the clonogenicity of CRC cells under different situations. Flow cytometry detecting the signal of fluorogenic reactive oxygen species (ROS) probes was performed to evaluate the total cellular and mitochondrial oxidative stress level in CRC cells. A propidium iodide (PI) staining assay was used to evaluate the cell death level in CRC cells. Quantitative PCR (qPCR) was conducted to detect the RNA level of STING pathway downstream target genes. Mass spectrometry was used for the identification of novel binding partners of cGAS in CRC cells. Co-immunoprecipitation (co-IP) was conducted to confirm the interaction between cGAS and NDUFA4L2.

RESULTS

By integrating metabolic pathway analysis based on TCGA transcriptomics with Seahorse metabolic analysis of a panel CRC cell lines and the human normal colonic mucosa cell line FHC, we demonstrated that CRC cells exhibit typical characteristics of metabolic reprogramming, characterized by a shift from oxidative phosphorylation (OXPHOS) to glycolysis. We found that cGAS is critical for CRC cells to maintain this metabolic switch. Specifically, the suppression of cGAS through siRNA-mediated knockdown or doxycycline-inducible knockout reversed this metabolic switch, resulting in increased OXPHOS activity, elevated production of OXPHOS byproduct reactive oxygen species (ROS), and consequently caused oxidative stress. This disruption induced oxidative stress, ultimately resulting in cell death and reduced cell viability. Moreover, significant upregulation of cGAS in CRC tissues and cell lines and its association with poor prognosis in CRC patients was observed. Subsequently, we demonstrated that the role of cGAS in regulating metabolic reprogramming does not rely on the canonical cGAS-STING pathway. Co-immunoprecipitation combined with mass spectrometry identified NDUFA4L2 as a novel interactor of cGAS. Subsequent functional experiments, including mitochondrial respiration and oxidative stress assays, demonstrated that cGAS plays a crucial role in sustaining elevated levels of NDUFA4L2 protein expression. The increased expression of NDUFA4L2 is essential for cGAS-mediated regulation of metabolic reprogramming and cell survival in CRC cells.

CONCLUSION

cGAS regulates metabolic reprogramming and promotes cell survival in CRC cells through its interaction with NDUFA4L2, independently of the canonical cGAS-STING pathway.

Protein-protein interactions in cGAS-STING pathway: a medicinal chemistry perspective

Protein-protein interactions (PPIs) play pivotal roles in biological processes and are closely linked with human diseases. Research on small molecule inhibitors targeting PPIs provides valuable insights and guidance for novel drug development. The cGAS-STING pathway plays a crucial role in regulating human innate immunity and is implicated in various pathological conditions. Therefore, modulators of the cGAS-STING pathway have garnered extensive attention. Given that this pathway involves multiple PPIs, modulating PPIs associated with the cGAS-STING pathway has emerged as a promising strategy for modulating this pathway. In this review, we summarize an overview of recent advancements in medicinal chemistry insights into cGAS-STING PPI-based modulators and propose alternative strategies for further drug discovery based on the cGAS-STING pathway.

mTORC2-driven chromatin cGAS mediates chemoresistance through epigenetic reprogramming in colorectal cancer

Cyclic GMP-AMP synthase (cGAS), a cytosolic DNA sensor that initiates a STING-dependent innate immune response, binds tightly to chromatin, where its catalytic activity is inhibited; however, mechanisms underlying cGAS recruitment to chromatin and functions of chromatin-bound cGAS (ccGAS) remain unclear. Here we show that mTORC2-mediated phosphorylation of human cGAS serine 37 promotes its chromatin localization in colorectal cancer cells, regulating cell growth and drug resistance independently of STING. We discovered that ccGAS recruits the SWI/SNF complex at specific chromatin regions, modifying expression of genes linked to glutaminolysis and DNA replication. Although ccGAS depletion inhibited cell growth, it induced chemoresistance to fluorouracil treatment in vitro and in vivo. Moreover, blocking kidney-type glutaminase, a downstream ccGAS target, overcame chemoresistance caused by ccGAS loss. Thus, ccGAS coordinates colorectal cancer plasticity and acquired chemoresistance through epigenetic patterning. Targeting both mTORC2-ccGAS and glutaminase provides a promising strategy to eliminate quiescent resistant cancer cells.

Olaparib combined with CDK12-IN-3 to promote genomic instability and cell death in ovarian cancer

Large-scale phase III clinical trials of Olaparib have revealed benefits for ovarian cancer patients with BRCA gene mutations or homologous recombination deficiency (HRD). However, fewer than 50% of ovarian cancer patients have both BRCA mutations and HRD. Therefore, improving the effect of Olaparib in HR-proficient patients is of great clinical value. Here, a combination strategy comprising Olaparib and CDK12-IN-3 effectively inhibited the growth of HR-proficient ovarian cancer in cell line, patient-derived organoid (PDO), and mouse xenograft models. Furthermore, the combination strategy induced severe DNA double-strand break (DSB) formation, increased NHEJ activity in the G2 phase, and reduced HR activity in cancer cells. Mechanistically, the combination treatment impaired Ku80 poly(ADP-ribosyl)ation (PARylation) and phosphorylation, resulting in PARP1-Ku80 complex dissociation. After dissociation, Ku80 occupancy at DSBs and the resulting Ku80-primed NHEJ activity were increased. Owing to Ku80-mediated DNA end protection, MRE11 and Rad51 foci formation was inhibited after the combination treatment, suggesting that this treatment suppressed HR activity. Intriguingly, the combination strategy expedited cGAS nuclear relocalization, further suppressing HR and, conversely, increasing genomic instability. Moreover, the inhibitory effect on cell survival persisted after drug withdrawal. These findings provide a rationale for the clinical application of CDK12-IN-3 in combination with Olaparib.

Schisandrin C enhances type I IFN response activation to reduce tumor growth and sensitize chemotherapy through antitumor immunity

With the advancing comprehension of immunology, an increasing number of immunotherapies are being explored and implemented in the field of cancer treatment. The cGAS-STING pathway, a crucial element of the innate immune response, has been identified as pivotal in cancer immunotherapy. We evaluated the antitumor effects of Schisandra chinensis lignan component Schisandrin C (SC) in 4T1 and MC38 tumor-bearing mice, and studied the enhancing effects of SC on the cGAS-STING pathway and antitumor immunity through RNA sequencing, qRT-PCR, and flow cytometry. Our findings revealed that SC significantly inhibited tumor growth in models of both breast and colon cancer. This suppression of tumor growth was attributed to the activation of type I IFN response and the augmented presence of T cells and NK cells within the tumor. Additionally, SC markedly promoted the cGAS-STING pathway activation induced by cisplatin. In comparison to cisplatin monotherapy, the combined treatment of SC and cisplatin exhibited a greater inhibitory effect on tumor growth. The amplified chemotherapeutic efficacy was associated with an enhanced type I IFN response and strengthened antitumor immunity. SC was shown to reduce tumor growth and increase chemotherapy sensitivity by enhancing the type I IFN response activation and boosting antitumor immunity, which enriched the research into the antitumor immunity of S. chinensis and laid a theoretical basis for its application in combating breast and colon cancer.

cGAS Activation Accelerates the Progression of Autosomal Dominant Polycystic Kidney Disease

SIGNIFICANCE STATEMENT

The renal immune infiltrate observed in autosomal polycystic kidney disease contributes to the evolution of the disease. Elucidating the cellular mechanisms underlying the inflammatory response could help devise new therapeutic strategies. Here, we provide evidence for a mechanistic link between the deficiency polycystin-1 and mitochondrial homeostasis and the activation of the cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)/stimulator of the interferon genes (STING) pathway. Our data identify cGAS as an important mediator of renal cystogenesis and suggest that its inhibition may be useful to slow down the disease progression.

BACKGROUND

Immune cells significantly contribute to the progression of autosomal dominant polycystic kidney disease (ADPKD), the most common genetic disorder of the kidney caused by the dysregulation of the Pkd1 or Pkd2 genes. However, the mechanisms triggering the immune cells recruitment and activation are undefined.

METHODS

Immortalized murine collecting duct cell lines were used to dissect the molecular mechanism of cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) activation in the context of genotoxic stress induced by Pkd1 ablation. We used conditional Pkd1 and knockout cGas-/- genetic mouse models to confirm the role of cGAS/stimulator of the interferon genes (STING) pathway activation on the course of renal cystogenesis.

RESULTS

We show that Pkd1 -deficient renal tubular cells express high levels of cGAS, the main cellular sensor of cytosolic nucleic acid and a potent stimulator of proinflammatory cytokines. Loss of Pkd1 directly affects cGAS expression and nuclear translocation, as well as activation of the cGAS/STING pathway, which is reversed by cGAS knockdown or functional pharmacological inhibition. These events are tightly linked to the loss of mitochondrial structure integrity and genotoxic stress caused by Pkd1 depletion because they can be reverted by the potent antioxidant mitoquinone or by the re-expression of the polycystin-1 carboxyl terminal tail. The genetic inactivation of cGAS in a rapidly progressing ADPKD mouse model significantly reduces cystogenesis and preserves normal organ function.

CONCLUSIONS

Our findings indicate that the activation of the cGAS/STING pathway contributes to ADPKD cystogenesis through the control of the immune response associated with the loss of Pkd1 and suggest that targeting this pathway may slow disease progression.

At the Crossroads of the cGAS-cGAMP-STING Pathway and the DNA Damage Response: Implications for Cancer Progression and Treatment

The evolutionary conserved DNA-sensing cGAS-STING innate immunity pathway represents one of the most important cytosolic DNA-sensing systems that is activated in response to viral invasion and/or damage to the integrity of the nuclear envelope. The key outcome of this pathway is the production of interferon, which subsequently stimulates the transcription of hundreds of genes. In oncology, the situation is complex because this pathway may serve either anti- or pro-oncogenic roles, depending on context. The prevailing understanding is that when the innate immune response is activated by sensing cytosolic DNA, such as DNA released from ruptured micronuclei, it results in the production of interferon, which attracts cytotoxic cells to destroy tumors. However, in tumor cells that have adjusted to significant chromosomal instability, particularly in relapsed, treatment-resistant cancers, the cGAS-STING pathway often supports cancer progression, fostering the epithelial-to-mesenchymal transition (EMT). Here, we review this intricate pathway in terms of its association with cancer progression, giving special attention to pancreatic ductal adenocarcinoma and gliomas. As the development of new cGAS-STING-modulating small molecules and immunotherapies such as oncolytic viruses involves serious challenges, we highlight several recent fundamental discoveries, such as the proton-channeling function of STING. These discoveries may serve as guiding lights for potential pharmacological advancements.

Broadening Horizons: Exploring mtDAMPs as a Mechanism and Potential Intervention Target in Cardiovascular Diseases

Cardiovascular diseases (CVDs) have been recognized as the leading cause of premature mortality and morbidity worldwide despite significant advances in therapeutics. Inflammation is a key factor in CVD progression. Once stress stimulates cells, they release cellular compartments known as damage-associated molecular patterns (DAMPs). Mitochondria can release mitochondrial DAMPs (mtDAMPs) to initiate an immune response when stimulated with cellular stress. Investigating the molecular mechanisms underlying the DAMPs that regulate CVD progression is crucial for improving CVDs. Herein, we discuss the composition and mechanism of DAMPs, the significance of mtDAMPs in cellular inflammation, the presence of mtDAMPs in different types of cells, and the main signaling pathways associated with mtDAMPs. Based on this, we determined the role of DAMPs in CVDs and the effects of mtDAMP intervention on CVD progression. By offering a fresh perspective and comprehensive insights into the molecular mechanisms of DAMPs, this review seeks to provide important theoretical foundations for developing drugs targeting CVDs.

Targeting LYPLAL1-mediated cGAS depalmitoylation enhances the response to anti-tumor immunotherapy

Cyclic GMP-AMP synthase (cGAS) binds pathogenic and other cytoplasmic double-stranded DNA (dsDNA) to catalyze the synthesis of cyclic GMP-AMP (cGAMP), which serves as the secondary messenger to activate the STING pathway and innate immune responses. Emerging evidence suggests that activation of the cGAS pathway is crucial for anti-tumor immunity; however, no effective intervention method targeting cGAS is currently available. Here we report that cGAS is palmitoylated by ZDHHC9 at cysteines 404/405, which promotes the dimerization and activation of cGAS. We further identified that lysophospholipase-like 1 (LYPLAL1) depalmitoylates cGAS to compromise its normal function. As such, inhibition of LYPLAL1 significantly enhances cGAS-mediated innate immune response, elevates PD-L1 expression, and enhances anti-tumor response to PD-1 blockade. Our results therefore reveal that targeting LYPLAL1-mediated cGAS depalmitoylation contributes to cGAS activation, providing a potential strategy to augment the efficacy of anti-tumor immunotherapy.

Prognostic significance of STING expression in solid tumor: a systematic review and meta-analysis

Objective

Stimulator of interferon genes (STING) is a key regulator in initiating innate immune response from sensing cytosolic DNA. Recent studies have revealed that the cGAS-STING signaling pathway has a crucial role in tumor development and progression across cancer types. Herein, we conducted a meta-analysis to explore the relationship between the immunoexpression of STING and the survival outcome of patients in various solid tumors. Studies relevant to the subject were searched from PubMed, Embase, and Web of Science.

Results

Eleven studies including 2,345 patients were eligible for the analysis. STING expression in tumor cells was related to improved disease-free survival/recurrence-free survival (DFS/RFS) (HR = 0.656, 95% CI = 0.455-0.946, p = 0.024) but not with overall survival (OS) (HR = 0.779, 95% CI = 0.534-1.136, p = 0.194). STING expression in stromal cells, however, did not show significant correlation with DFS/RFS and OS (HR = 0.979, 95% CI = 0.565-1.697, p-value = 0.940 and HR = 1.295, 95% CI = 0.845-1.985, p = 0.235, respectively). In a subgroup analysis, STING expression in tumor cells was associated with better DFS (HR = 0.622, 95% CI = 0.428-0.903, p = 0.012). In tumor cells, favorable DFS/RFS were also related to studies from univariate analysis and the gastrointestinal system (HR = 0.667, 95% CI = 0.482-0.923, p = 0.015 and HR = 0.566, 95% CI = 0.330-0.971, p = 0.039).

Conclusions

STING expression in tumor cells is associated with favorable outcome in solid tumors.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, registration number: CRD42023427027.

Combination of IDO inhibitors and platinum(IV) prodrugs reverses low immune responses to enhance cancer chemotherapy and immunotherapy for osteosarcoma

In recent years, immune checkpoint blockades (ICBs) have made great progress in the treatment of cancer. However, most ICBs have not yet been observed to be satisfactory in the treatment of osteosarcoma. Herein, we designed composite nanoparticles (NP-Pt-IDOi) from a reactive oxygen species (ROS) sensitive amphiphilic polymer (PHPM) with thiol-ketal bonds in the main chain to encapsulate a Pt(IV) prodrug (Pt(IV)-C12) and an indoleamine-(2/3)-dioxygenase (IDO) inhibitor (IDOi, NLG919). Once NP-Pt-IDOi enter the cancer cells, the polymeric nanoparticles could dissociate due to the intracellular ROS, and release Pt(IV)-C12 and NLG919. Pt(IV)-C12 induces DNA damage and activates the cGAS-STING pathway, increasing infiltration of CD8+ T cells in the tumor microenvironment. In addition, NLG919 inhibits tryptophan metabolism and enhances CD8+ T cell activity, ultimately activating anti-tumor immunity and enhancing the anti-tumor effects of platinum-based drugs. NP-Pt-IDOi were shown to have superior anti-cancer activity in vitro and in vivo in mouse models of osteosarcoma, providing a new clinical paradigm for combining chemotherapy with immunotherapy for osteosarcoma.

Species-specific self-DNA detection mechanisms by mammalian cyclic GMP-AMP synthases

The mechanisms by which innate immune receptors mediate self-nonself discrimination are unclear. In this study, we found species-specific molecular determinants of self-DNA reactivity by cyclic guanosine monophosphate-adenosine monophosphate (GMP-AMP) synthase (cGAS). Human cGAS contained a catalytic domain that was intrinsically self-DNA reactive and stimulated interferon responses in diverse cell types. This reactivity was prevented by an upstream amino (N)-terminal domain. The cGAS proteins from several nonhuman primate species exhibited a similar pattern of self-DNA reactivity in cells, but chimpanzee cGAS was inactive even when its amino-terminal domain was deleted. In contrast, the N terminus of mouse cGAS promoted self-DNA reactivity. When expressed within tumors, only self-DNA-reactive cGAS proteins protected mice from tumor-induced lethality. In vitro studies of DNA- or chromatin-induced cGAS activation did not reveal species-specific activities that correlate with self-DNA reactivity observed in macrophages. Cell biological analysis revealed that self-DNA reactivity by human cGAS, but not mouse cGAS, correlated with localization to mitochondria. We found that epitope tag positions affected self-DNA reactivity in cells and that DNA present in cell lysates undermines the reliability of cGAS biochemical fractionations. These studies reveal species-specific diversity of cGAS functions, even within the primate lineage, and highlight experimental considerations for the study of this innate immune receptor.

Advances of MnO2 nanomaterials as novel agonists for the development of cGAS-STING-mediated therapeutics

As an essential micronutrient, manganese plays an important role in the physiological process and immune process. In recent decades, cGAS-STING pathway, which can congenitally recognize exogenous and endogenous DNA for activation, has been widely reported to play critical roles in the innate immunity against some important diseases, such as infections and tumor. Manganese ion (Mn²⁺) has been recently proved to specifically bind with cGAS and activate cGAS-STING pathway as a potential cGAS agonist, however, is significantly restricted by the low stability of Mn²⁺ for further medical application. As one of the most stable forms of manganese, manganese dioxide (MnO₂) nanomaterials have been reported to show multiple promising functions, such as drug delivery, anti-tumor and anti-infection activities. More importantly, MnO₂ nanomaterials are also found to be a potential candidate as cGAS agonist by transforming into Mn²⁺, which indicates their potential for cGAS-STING regulations in different diseased conditions. In this review, we introduced the methods for the preparation of MnO₂ nanomaterials as well as their biological activities. Moreover, we emphatically introduced the cGAS-STING pathway and discussed the detailed mechanisms of MnO₂ nanomaterials for cGAS activation by converting into Mn²⁺. And we also discussed the application of MnO₂ nanomaterials for disease treatment by regulating cGAS-STING pathway, which might benefit the future development of novel cGAS-STING targeted treatments based on MnO₂ nanoplatforms.

The emerging roles of TLR and cGAS signaling in tumorigenesis and progression of ovarian cancer

Ovarian cancer is fatal to women and has a high mortality rate. Although on-going efforts are never stopped in identifying diagnostic and intervention strategies, the disease is so far unable to be well managed. The most important reason for this is the complexity of pathogenesis for OC, and therefore, uncovering the essential molecular biomarkers accompanied with OC progression takes the privilege for OC remission. Inflammation has been reported to participate in the initiation and progression of OC. Both microenvironmental and tumor cell intrinsic inflammatory signals contribute to the malignancy of OC. Inflammation responses can be triggered by various kinds of stimulus, including endogenous damages and exogenous pathogens, which are initially recognized and orchestrated by a series of innate immune system related receptors, especially Toll like receptors, and cyclic GMP-AMP synthase. In this review, we will discuss the roles of innate immune system related receptors, including TLRs and cGAS, and responses both intrinsic and exogenetic in the development and treatment of OC.

Beta-Glucan from S. cerevisiae Protected AOM-Induced Colon Cancer in cGAS-Deficient Mice Partly through Dectin-1-Manipulated Macrophage Cell Energy

Although the impacts of Saccharomyces cerevisiae on cancers are mentioned, data on its use in mice with cyclic GMP-AMP synthase deficiency (cGAS-/-) are even rarer. Here, 12 weeks of oral administration of S. cerevisiae protected cGAS-/- mice from azoxymethane (AOM)-induced colon cancers, partly through dysbiosis attenuation (fecal microbiome analysis). In parallel, a daily intralesional injection of a whole glucan particle (WGP; the beta-glucan extracted from S. cerevisiae) attenuated the growth of subcutaneous tumor using MC38 (murine colon cancer cell line) in cGAS-/- mice. Interestingly, the incubation of fluorescent-stained MC38 with several subtypes of macrophages, including M1 (using Lipopolysaccharide; LPS), M2 (IL-4), and tumor-associated macrophages (TAM; using MC38 supernatant activation), could not further reduce the tumor burdens (fluorescent intensity) compared with M0 (control culture media). However, WGP enhanced tumoricidal activities (fluorescent intensity), the genes of M1 pro-inflammatory macrophage polarization (IL-1β and iNOS), and Dectin-1 expression and increased cell energy status (extracellular flux analysis) in M0, M2, and TAM. In M1, WGP could not increase tumoricidal activities, Dectin-1, and glycolysis activity, despite the upregulated IL-1β. In conclusion, S. cerevisiae inhibited the growth of colon cancers through dysbiosis attenuation and macrophage energy activation, partly through Dectin-1 stimulation. Our data support the use of S. cerevisiae for colon cancer protection.

Regulation of cGAS Activity and Downstream Signaling

Cyclic GMP-AMP synthase (cGAS) is a predominant and ubiquitously expressed cytosolic onfirmedDNA sensor that activates innate immune responses by producing a second messenger, cyclic GMP-AMP (cGAMP), and the stimulator of interferon genes (STING). cGAS contains a highly disordered N-terminus, which can sense genomic/chromatin DNA, while the C terminal of cGAS binds dsDNA liberated from various sources, including mitochondria, pathogens, and dead cells. Furthermore, cGAS cellular localization dictates its response to foreign versus self-DNA. Recent evidence has also highlighted the importance of dsDNA-induced post-translational modifications of cGAS in modulating inflammatory responses. This review summarizes and analyzes cGAS activity regulation based on structure, sub-cellular localization, post-translational mechanisms, and Ca²⁺ signaling. We also discussed the role of cGAS activation in different diseases and clinical outcomes.

Genetic variants involved in the cGAS-STING pathway predict outcome in patients with metastatic colorectal cancer: Data from FIRE-3 and TRIBE trials

BACKGROUND

The activation of stimulator of interferon genes (STING) was reported to enhance cetuximab-mediated natural killer cell activation and dendritic cell maturation. Polymorphisms in genes in the cyclic GMP-AMP synthase (cGAS)-STING pathway may affect innate immune response. Therefore, we hypothesised that genetic variants in the cGAS-STING pathway may predict the efficacy of cetuximab-based treatment in patients with metastatic colorectal cancer.

METHODS

Genomic DNA from blood samples of patients enrolled in FIRE-3 (cetuximab arm, n = 129; bevacizumab arm, n = 107) and TRIBE (bevacizumab arm, n = 215) was genotyped using the OncoArray-500K bead chip panel. Seven selected single nucleotide polymorphisms in 3 genes (cGAS, STING and interferon B1 (IFNB1)) were analysed for the association with overall survival and progression-free survival.

RESULTS

In the cetuximab cohort, patients with STING rs1131769 any T allele showed significantly shorter overall survival (36.3 versus 56.1 months) than carriers of C/C in both univariate [hazard ratio (HR) = 2.08; 95% confidence interval (CI): 1.06-4.07; P = 0.03] and multivariate (HR = 2.98; 95% CI: 1.35-6.6; P = 0.0085) analyses; patients carrying IFNB1 rs1051922 G/A and A/A genotype showed a significantly shorter progression-free survival than carriers of G/G allele in both univariate (G/A versus G/G, 10.2 versus 14.1 months, HR = 1.84; 95% CI 1.23-2.76; A/A versus G/G, 10.7 versus 14.1 months, HR = 2.19; 95% CI 0.97-4.96; P = 0.0077) and multivariate analyses (G/A versus G/G, HR = 2; 95% CI 1.22-3.3; A/A versus G/G, HR = 2.19, 95% CI 0.92-5.26, P = 0.02). These associations were not observed in the bevacizumab arm of FIRE-3 or TRIBE.

CONCLUSION

These results suggest for the first time that germline polymorphisms in STING and IFNB1 genes may predict the outcomes of cetuximab-based treatment in patients with metastatic colorectal cancer.