Cancer immunotherapy strategies that target the cGAS-STING pathway

Inactivated cGAS-STING Signaling Facilitates Endocrine Resistance by Forming a Positive Feedback Loop with AKT Kinase in ER+HER2- Breast Cancer

Endocrine-resistant ER+HER2- breast cancer (BC) is particularly aggressive and leads to poor clinical outcomes. Effective therapeutic strategies against endocrine-resistant BC remain elusive. Here, analysis of the RNA-sequencing data from ER+HER2- BC patients receiving neoadjuvant endocrine therapy and spatial transcriptomics analysis both show the downregulation of innate immune signaling sensing cytosolic DNA, which primarily occurs in endocrine-resistant BC cells, not immune cells. Indeed, compared with endocrine-sensitive BC cells, the activity of sensing cytosolic DNA through the cGAS-STING pathway is attenuated in endocrine-resistant BC cells. Screening of kinase inhibitor library show that this effect is mainly mediated by hyperactivation of AKT1 kinase, which binds to kinase domain of TBK1, preventing the formation of a trimeric complex TBK1/STING/IRF3. Notably, inactivation of cGAS-STING signaling forms a positive feedback loop with hyperactivated AKT1 to promote endocrine resistance, which is physiologically important and clinically relevant in patients with ER+HER2- BC. Blocking the positive feedback loop using the combination of an AKT1 inhibitor with a STING agonist results in the engagement of innate and adaptive immune signaling and impairs the growth of endocrine-resistant tumors in humanized mice models, providing a potential strategy for treating patients with endocrine-resistant BC.

Mesenchymal Stromal Cells Increase the Natural Killer Resistance of Circulating Tumor Cells via Intercellular Signaling of cGAS-STING-IFNβ-HLA

Circulating tumor cells (CTCs) shed from primary tumors must overcome the cytotoxicity of immune cells, particularly natural killer (NK) cells, to cause metastasis. The tumor microenvironment (TME) protects tumor cells from the cytotoxicity of immune cells, which is partially executed by cancer-associated mesenchymal stromal cells (MSCs). However, the mechanisms by which MSCs influence the NK resistance of CTCs remain poorly understood. This study demonstrates that MSCs enhance the NK resistance of cancer cells in a gap junction-dependent manner, thereby promoting the survival and metastatic seeding of CTCs in immunocompromised mice. Tumor cells crosstalk with MSCs through an intercellular cGAS-cGAMP-STING signaling loop, leading to increased production of interferon-β (IFNβ) by MSCs. IFNβ reversely enhances the type I IFN (IFN-I) signaling in tumor cells and hence the expression of human leukocyte antigen class I (HLA-I) on the cell surface, protecting the tumor cells from NK cytotoxicity. Disruption of this loop reverses NK sensitivity in tumor cells and decreases tumor metastasis. Moreover, there are positive correlations between IFN-I signaling, HLA-I expression, and NK tolerance in human tumor samples. Thus, the NK-resistant signaling loop between tumor cells and MSCs may serve as a novel therapeutic target.

Treg-derived TGF-β1 dampens cGAS-STING signaling to downregulate the expression of class I MHC complex in multiple myeloma

Multiple myeloma (MM) progression involves diminished tumor antigen presentation and an immunosuppressive microenvironment, characterized by diminished expression of major histocompatibility complexes (MHC) class I molecule and elevated programmed death ligand 1 (PDL1) in MM cells, along with an enriched population of regulatory T cells (Tregs). To investigate Treg's influence on MM cells, we established a co-culture system using Tregs from MM patients and the MM cell lines (MM.1S and SK-MM-1) in vitro and assessed the effects of intervening in the relevant pathways connecting Tregs and MM cells in vivo. In vitro, Tregs induced transforming growth factor beta-1 (TGF-β1) production, downregulated MHC I members, and increased PDL1 expression in MM cells. Treg-derived TGF-β1 suppressed the cGAS-STING pathway, contributing to the loss of MHC I molecule expression and PDL1 upregulation. Correspondingly, neutralizing TGF-β1 or activating the cGAS-STING pathway restored MHC I and PDL1 expression, effectively countering the pro-tumorigenic effect of Tregs on MM cells in vivo. These data elucidated how Tregs influence tumor antigen presentation and immunosuppressive signal in MM cells, potentially providing therapeutic strategies, such as neutralizing TGF-β1 or activating the cGAS-STING pathway, to address the immune escape and immunosuppressive dynamics in MM.

Interferons and interferon-related pathways in heart disease

Interferons (IFNs) and IFN-related pathways play key roles in the defence against microbial infection. However, these processes may also be activated during the pathogenesis of non-infectious diseases, where they may contribute to organ injury, or function in a compensatory manner. In this review, we explore the roles of IFNs and IFN-related pathways in heart disease. We consider the cardiac effects of type I IFNs and IFN-stimulated genes (ISGs); the emerging role of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway; the seemingly paradoxical effects of the type II IFN, IFN-γ; and the varied actions of the interferon regulatory factor (IRF) family of transcription factors. Recombinant IFNs and small molecule inhibitors of mediators of IFN receptor signaling are already employed in the clinic for the treatment of some autoimmune diseases, infections, and cancers. There has also been renewed interest in IFNs and IFN-related pathways because of their involvement in SARS-CoV-2 infection, and because of the relatively recent emergence of cGAS-STING as a pattern recognition receptor-activated pathway. Whether these advances will ultimately result in improvements in the care of those experiencing heart disease remains to be determined.

STING pathway as a cancer immunotherapy: Progress and challenges in activating anti-tumor immunity

The stimulator of the interferon genes (STING) signaling pathway plays a crucial role in innate immunity by detecting cytoplasmic DNA and initiating antiviral host defense mechanisms. The STING cascade is triggered when the enzyme cyclic GMP-AMP synthase (cGAS) binds cytosolic DNA and synthesizes the secondary messenger cGAMP. cGAMP activates the endoplasmic reticulum adaptor STING, leading to the activation of kinases TBK1 and IRF3 that induce interferon production. Secreted interferons establish an antiviral state in infected and adjacent cells. Beyond infections, aberrant DNA in cancer cells can also activate the STING pathway. Preclinical studies have shown that pharmacological STING agonists like cyclic dinucleotides elicit antitumor immunity when administered intratumorally by provoking innate and adaptive immunity. Combining STING agonists with immune checkpoint inhibitors may improve outcomes by overcoming tumor immunosuppression. First-generation STING agonists encountered challenges like poor pharmacokinetics, limited tumor specificity, and systemic toxicity. The development of the next-generation STING-targeted drugs to realize the full potential of engaging this pathway for cancer treatment can be a solution to overcome the current challenges, but further studies are required to determine optimal applications and combination regimens for the clinic. Notably, the controlled activation of STING is needed to preclude adverse effects. This review explores the mechanisms and effects of STING activation, its role in cancer immunotherapy, and current challenges.

Role of STING in the treatment of non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is a prevalent form of lung cancer. Patients with advanced NSCLC are currently being treated with various therapies, including traditional radiotherapy, chemotherapy, molecular targeted therapies and immunotherapy. However, a considerable proportion of advance patients who cannot benefit from them. Consequently, it is essential to identify a novel research target that offers an encouraging perspective. The stimulator of interferon genes (STING) has emerged as such a target. At present, it is confirmed that activating STING in NSCLC tumor cells can impede the proliferation and metastasis of dormant tumor cells. This review focuses on the role of STING in NSCLC treatment and the factors influencing its activation. Additionally, it explores the correlation between STING activation and diverse therapy modalities for NSCLC, such as radiotherapy, chemotherapy, molecular targeted therapies and immunotherapy. Furthermore, it proposes the prospect of innovative therapy methods involving nanoparticles, with the aim of using the features of STING to develop more strategies for NSCLC therapy.

The tumor microenvironment: shaping cancer progression and treatment response

The tumor microenvironment (TME) plays a crucial role in cancer progression and treatment response. It comprises a complex network of stromal cells, immune cells, extracellular matrix, and blood vessels, all of which interact with cancer cells and influence tumor behaviour. This review article provides an in-depth examination of the TME, focusing on stromal cells, blood vessels, signaling molecules, and ECM, along with commonly available therapeutic compounds that target these components. Moreover, we explore the TME as a novel strategy for discovering new anti-tumor drugs. The dynamic and adaptive nature of the TME offers opportunities for targeting specific cellular interactions and signaling pathways. We discuss emerging approaches, such as combination therapies that simultaneously target cancer cells and modulate the TME. Finally, we address the challenges and future prospects in targeting the TME. Overcoming drug resistance, improving drug delivery, and identifying new therapeutic targets within the TME are among the challenges discussed. We also highlight the potential of personalized medicine and the integration of emerging technologies, such as immunotherapy and nanotechnology, in TME-targeted therapies. This comprehensive review provides insights into the TME and its therapeutic implications. Understanding the TME's complexity and targeting its components offer promising avenues for the development of novel anti-tumor therapies and improved patient outcomes.

A novel self-assembled nucleobase-nanofiber platform of CDN to activate the STING pathway for synergistic cancer immunotherapy

2', 3'-cGAMP (CDN) as cGAS-STING pathway agonist is extensively used in tumor treatment. However, due to its negatively charged nature (containing two phosphate groups) and high hydrophilicity, CDN faces challenges in crossing cell membranes, resulting in reduced efficiency of its use. Additionally, CDN is susceptible to inactivation through phosphodiesterase hydrolysis. Therefore, the development of a new drug delivery system for CDN is necessary to prevent hydrolysis and enhance targeted accumulation in tumors, as well as improve cellular uptake for STING activation. In this study, we have developed peptide-polymer nanofibers (PEG-Q11) that incorporate thymine (T) and arginine (R) residues to facilitate complexation with CDN through the principles of Watson-Crick base pairing with thymine and favorable electrostatic interactions and bidentate hydrogen bonding with arginine side chains. The entrapment efficiency (EE) of PEG-Q11T3R4@CDN was found to be 51% higher than that of PEG-Q11@CDN. Due to its favorable biocompatibility, PEG-Q11T3R4@CDN was employed for immunotherapy in mouse CT26 tumors. In local tumor treatment, the administration of PEG-Q11T3R4@CDN at a low dose and through a single injection exhibited inhibitory effects. Furthermore, the local injection of PEG-Q11T3R4@CDN resulted in systemic therapeutic responses, effectively suppressing tumor metastasis by activating CD8 + T cells to target distant tumors. This research not only underscores the potential of PEG-Q11T3R4@CDN as an efficient therapeutic agent but also highlights its ability to achieve long-lasting systemic therapeutic outcomes following local treatment. Consequently, PEG-Q11T3R4@CDN represents a promising strategy for immunization.

Understanding nucleic acid sensing and its therapeutic applications

Nucleic acid sensing is involved in viral infections, immune response-related diseases, and therapeutics. Based on the composition of nucleic acids, nucleic acid sensors are defined as DNA or RNA sensors. Pathogen-associated nucleic acids are recognized by membrane-bound and intracellular receptors, known as pattern recognition receptors (PRRs), which induce innate immune-mediated antiviral responses. PRR activation is tightly regulated to eliminate infections and prevent abnormal or excessive immune responses. Nucleic acid sensing is an essential mechanism in tumor immunotherapy and gene therapies that target cancer and infectious diseases through genetically engineered immune cells or therapeutic nucleic acids. Nucleic acid sensing supports immune cells in priming desirable immune responses during tumor treatment. Recent studies have shown that nucleic acid sensing affects the efficiency of gene therapy by inhibiting translation. Suppression of innate immunity induced by nucleic acid sensing through small-molecule inhibitors, virus-derived proteins, and chemical modifications offers a potential therapeutic strategy. Herein, we review the mechanisms and regulation of nucleic acid sensing, specifically covering recent advances. Furthermore, we summarize and discuss recent research progress regarding the different effects of nucleic acid sensing on therapeutic efficacy. This study provides insights for the application of nucleic acid sensing in therapy.

STING-driven activation of T cells: relevance for the adoptive cell therapy of cancer

Adoptive cell therapy (ACT) can successfully treat hematopoietic cancers but lacks efficacy against solid tumors. This is due to insufficient T cell infiltration, high tumor heterogeneity, frequent antigen loss with subsequent tumor escape, and the immunosuppressive tumor microenvironment (TME). Alternative methods to boost the anticancer efficacy of adoptively transferred cells are actively pursued. Among adjuvants that are utilized to stimulate anticancer immune responses, ligands of the stimulator of interferon genes (STING) pathway have received increasing attention. STING activation can trigger dendritic cell (DC) activation and endogenous immune responses, thereby preventing tumor escape. Activation of the STING pathway in the context of ACT was accordingly associated with improved T cell trafficking and persistence in the TME combined with the reduced presence of immunosuppressive cells. Recent findings also suggest cell-intrinsic effects of STING ligands on T cells. Activation of the STING signaling pathway was in this regard shown to enhance effector functions of CD4+ and CD8+ T cells, suggesting that the STING signaling could be exploited to harness T cell anticancer functions. In this review, we will discuss how the STING signaling can be used to enhance the anticancer efficacy of ACT.

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.

Combination of a STING Agonist and Photothermal Therapy Using Chitosan Hydrogels for Cancer Immunotherapy

Cyclic dinucleotides (CDNs) are a promising class of immune agonists that trigger the stimulator of interferon genes (STING) to activate both innate and acquired immunity. However, the efficacy of CDNs is limited by drug delivery barriers. Therefore, we developed a combined immunotherapy strategy based on injectable reactive oxygen species (ROS)-responsive hydrogels, which sustainably release 5,6-dimethylxanthenone-4-acetic acid (DMXAA) as known as a STING agonist and indocyanine green (ICG) by utilizing a high level of ROS in the tumor microenvironment (TME). The STING agonist combined with photothermal therapy (PTT) can improve the biological efficacy of DMXAA, transform the immunosuppressive TME into an immunogenic and tumoricidal microenvironment, and completely kill tumor cells. In addition, this bioreactive gel can effectively leverage local ROS to facilitate the release of immunotherapy drugs, thereby enhancing the efficacy of combination therapy, improving the TME, inhibiting tumor growth, inducing memory immunity, and protecting against tumor rechallenge.

Impaired Integrated Stress Response and Mitochondrial Integrity Modulate Genotoxic Stress Impact and Lower the Threshold for Immune Signalling

Mitochondria-nucleus communication during stress dictates cellular fate with consequences on the etiopathology of multiple age-related diseases. Impaired mitochondrial quality control through loss of function of the mitochondrial protease HtrA2 associates with accumulation of damaged mitochondria and triggers the integrated stress response, implicating the transcription factor CHOP. Here we have employed a combined model of impaired mitochondria quality control, namely HtrA2 loss of function, and/or integrated stress response, namely CHOP loss of function, and genotoxicity to address the distinctive roles of these cellular components in modulating intracellular and intercellular responses. The genotoxic agents employed were cancer therapeutic agents such as irradiation with X-ray and protons or treatment with the radiomimetic bleomycin. The irradiation had an enhanced effect in inducing DNA damage in cells with CHOP loss of function, while the bleomycin treatment induced more DNA damage in all the transgenic cells as compared to the control. The genetic modifications impaired the transmission of DNA damage signalling intercellularly. Furthermore, we have dissected the signalling pathways modulated by irradiation in selected genotypes with RNA sequencing analysis. We identified that loss of HtrA2 and CHOP function, respectively, lowers the threshold where irradiation may induce the activation of innate immune responses via cGAS-STING; this may have a significant impact on decisions for combined therapeutic approaches for various diseases.