Stimulator Of Interferon Genes Ligand Research Articles

PiSTING: A Pocket-Independent Agonist Based on Multivalency-Driven STING Oligomerization.

The stimulator of interferon genes (STING) pathway is a potent therapeutic target for innate immunity. Despite the efforts to develop pocket-dependent small-molecule STING agonists that mimic the endogenous STING ligand, cyclic guanosine monophosphate-adenosine monophosphate (cGAMP), most of these agonists showed disappointing results in clinical trials owing to the limitations of the STING pocket. In this study, we developed novel pocket-independent STING-activating agonists (piSTINGs), which act through multivalency-driven oligomerization to activate STING. Additionally, a piSTING-adjuvanted vaccine elicited a significant antibody response and inhibited tumour growth in therapeutic models. Moreover, a piSTING-based vaccine combination with aPD-1 showed remarkable potential to enhance the effectiveness of immune checkpoint blockade (ICB) immunotherapy. In particular, piSTING can strengthen the impact of STING pathway in immunotherapy and accelerate the clinical translation of STING agonists.

PiSTING: A Pocket‐Independent Agonist Based on Multivalency‐Driven STING Oligomerization

The stimulator of interferon genes (STING) pathway is a potent therapeutic target for innate immunity. Despite the efforts to develop pocket‐dependent small‐molecule STING agonists that mimic the endogenous STING ligand, cyclic guanosine monophosphate–adenosine monophosphate (cGAMP), most of these agonists showed disappointing results in clinical trials owing to the limitations of the STING pocket. In this study, we developed novel pocket‐independent STING‐activating agonists (piSTINGs), which act through multivalency‐driven oligomerization to activate STING. Additionally, a piSTING‐adjuvanted vaccine elicited a significant antibody response and inhibited tumour growth in therapeutic models. Moreover, a piSTING‐based vaccine combination with aPD‐1 showed remarkable potential to enhance the effectiveness of immune checkpoint blockade (ICB) immunotherapy. In particular, piSTING can strengthen the impact of STING pathway in immunotherapy and accelerate the clinical translation of STING agonists.

The role of cGAMP via the STING pathway in modulating germinal center responses and CD4 T cell differentiation.

Germinal center (GC) responses are essential for establishing protective, long-lasting immunity through the differentiation of GC B cells (BGC) and plasma cells (BPC), along with the generation of antigen-specific antibodies. Among the various pathways influencing immune responses, the STING (Stimulator of Interferon Genes) pathway has emerged as significant, especially in innate immunity, and extends its influence to adaptive responses. In this study, we examined how the STING ligand cGAMP can modulate these key elements of the adaptive immune response, particularly in enhancing GC reactions and the differentiation of BGC, BPC, and follicular helper T cells (TFH). Employing in vivo models, we evaluated various antigens and the administration of cGAMP in Alum adjuvant, investigating the differentiation of BGC, BPC, and TFH cells, along with the production of antigen-specific antibodies. cGAMP enhances the differentiation of BGC and BPC, leading to increased antigen-specific antibody production. This effect is shown to be type I Interferon-dependent, with a substantial reduction in BPC frequency upon interferon (IFN)-β blockade. Additionally, cGAMP's influence on TFH differentiation varies over time, which may be critical for refining vaccine strategies. The findings elucidate a complex, antigen-specific influence of cGAMP on T and B cell responses, providing insights that could optimize vaccine efficacy.

Computational insights into the conformational transition of STING: Mechanistic, energetic considerations, and the influence of crucial mutations

STING (stimulator of interferon genes) is a crucial protein in the innate immune system's response to viral and bacterial infections. In this study, we investigated the mechanistic and energetic mechanism of the conformational transition process of STING activated by cGAMP binding. We found that the STING connector region undergoes an energetically unfavorable rotation during this process, which is compensated by the favorable interaction between cGAMP and the STING ligand binding domain. We further studied several disease-causing mutations and found that the V155 M mutation facilitates a smoother transition in the STING connector region. However, the V147L mutation exhibits unfavorable conformational transition energy, suggesting it may hinder STING activation pathway that relies on connector region rotation. Despite being labeled as hyperactive, the widespread prevalence of V147L/V147I mutations across species implies a neutral character, indicating complexity in its role. Overall, our analysis deepens the understanding of STING activation within the connector region, and targeting this region with compounds may provide an alternative approach to interfering with STING's function.

Tracing the STING exocytosis pathway during herpes viruses infection.

The STimulator of INterferon Genes (STING) constitutes a major DNA-sensing pathway that restricts HSV-1 infection in different models by activating type I interferon and pro-inflammatory responses. To counteract STING, HSV-1 has evolved numerous strategies including mechanisms to interfere with its oligomerization, post-translational modifications, and downstream signaling. Previously, we demonstrated that STING is packaged in extracellular vesicles (EVs) produced from HSV-1-infected cells. These EVs activated antiviral responses in uninfected recipient cells and suppressed a subsequent HSV-1 infection in a STING-dependent manner. Here, we provide information on the packaging of STING in EVs and its exocytosis. We found that STING exocytosis did not occur in CD63 knockdown cells supporting that STING follows the CD63 exocytosis pathway. Consistently, we found that STING co-localized with CD63 in cytoplasmic globular structures and exosomal STING and CD63 co-fractionated. Both golgicide A and brefeldin A prevented STING exocytosis during HSV-1 infection suggesting that STING trafficking through the Golgi is required. A STING ligand was insufficient for STING exocytosis, and downstream signaling through TBK1 was not required. However, STING palmitoylation and tethering to the ER by STIM1 were required for STING exocytosis. Finally, we found that HSV-1 replication/late gene expression triggered CD63 exocytosis that was required for STING exocytosis. Surprisingly, HSV-2 strain G did not trigger CD63 or STING exocytosis as opposed to VZV and HCMV. Also, EVs from HSV-1(F)- and HSV-2(G)-infected cells displayed differences in their ability to restrict these viruses. Overall, STING exocytosis is induced by certain viruses and shapes the microenvironment of infection.IMPORTANCEExtracellular vesicles (EVs) are released by all types of cells as they constitute a major mechanism of intercellular communication. The packaging of specific cargo in EVs and the pathway of exocytosis are not fully understood. STING is a sensor of a broad spectrum of pathogens and a key component of innate immunity. STING exocytosis during HSV-1 infection has been an intriguing observation, raising questions of whether this is a virus-induced process, the purpose it serves, and whether it is observed after infection with other viruses. Here, we have provided insights into the pathway of STING exocytosis and determined factors involved. STING exocytosis is a virus-induced process and not a response of the host to the infection. Besides HSV-1, other herpes viruses triggered STING exocytosis, but HSV-2(G) did not. HSV-1 EVs displayed different restriction capabilities compared with HSV-2(G) EVs. Overall, STING exocytosis is triggered by viruses to shape the microenvironment of infection.

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

Adoptive cell therapy (ACT) can successfully treat hema-topoietic 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 immunosup-pressive tumor microenvironment (TME). Alternative methods to boost the anticancer efficacy of adoptively transferred cells are ac-tively pursued. Among adjuvants that are utilized to stimulate anti-cancer 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 com-bined with the reduced presence of immunosuppressive cells. Re-cent 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, sug-gesting 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.

Elucidation of Protonation Cooperativity of a STING-Activating Polymer.

Stimuli-responsive nanomaterials have the potential to improve the performance and overcome existing barriers of conventional nanotherapeutics. Molecular cooperativity design in stimuli-responsive nanomedicine can amplify physiological signals, enabling a cooperative response for improved diagnostic and therapeutic precision. Previously, this work reported an ultra-pH-sensitive polymer, PEG-b-PC7A, that possesses innate immune activating properties by binding to the stimulator of interferon genes (STING) through polyvalent phase condensation. This interaction enhances STING activation and synergizes with the endogenous STING ligand for robust cancer immunotherapy. Despite its successes in innate immune activation, the fundamental physicochemical and pH-responsive properties of PC7A require further investigation. Here, this study elucidates the protonation cooperativity driven by the phase transition of PC7A copolymer. The highly cooperative system displays an "all-or-nothing" proton distribution between highly charged unimer (all) and neutral micelle (nothing) states without gradually protonated intermediates. The binary protonation behavior is further illustrated in pH-precision-controlled release of a representative anticancer drug, β-lapachone, by PC7A micelles over a noncooperative PE5A polymer. Furthermore, the bimodal distribution of protons is represented by a high Hill coefficient (nH >9), featuring strong positive cooperativity. This study highlights the nanoscale pH cooperativity of an immune activating polymer, providing insights into the physicochemical characterization and design parameters for future nanotherapeutics development.

Model for predicting age-dependent safety and immunomodulatory effects of STING ligands in non-human primates

Stimulator of interferon genes (STING) is a cytoplasmic dinucleotide sensor used as an immunomodulatory agent for cancer treatment. The efficacy of the STING ligand (STING-L) against various tumors has been evaluated in mouse models; however, its safety and efficacy in non-human primates have not been reported. We examined the effects of escalating doses of cyclic-di-adenosine monophosphate (c-di-AMP) or cyclic [G (3',5')pA (3',5'p] (3'-3'-cGAMP) administered intramuscularly or intravenously to cynomolgus macaques. Both ligands induced transient local and systemic inflammatory responses and systemic immunomodulatory responses, including the upregulation of interferon-α (IFN-α) and IFN-γ expression and the activation of multiple immunocompetent cell subsets. Better immunological responses were observed in animals that received c-di-AMP compared with those that received 3'-3'-cGAMP. Multi-parameter analysis using a dataset obtained before administering the ligands predicted the efficacy outcome partially. Importantly, the efficacy of these ligands was reduced in older macaques. We propose that 0.5mg/kg c-di-AMP via intramuscular administration should be the optimal starting point for clinical studies. Our study is the first to demonstrate the age-dependent safety and efficacy of STING-L in non-human primates and supports the potential of STING-L use as a direct immunomodulator invivo.

Integrative Strategy for Investigating the Interactions between STING and Small-Molecule Ligands.

Although small-molecule agonists of stimulator of interferon genes (STING) show significance in activating the immune system, the dynamic process involved in ligands activating STING remains unclear. Herein, we developed a biochemical strategy, integrating computer simulation and a biochemical engineering approach, to reveal the interaction mechanism between STING and 5,6-dimethylxanthenone-4-acetic acid (DMXAA), an agonist that activates the TANK binding kinase 1-interferon regulatory factor 3 signaling pathway. Specifically, inspired by an analysis of the STING-DMXAA crystal structure, we designed and synthesized DMXAA derivatives to investigate the STING-DMXAA binding model. We identified that the carboxyl moiety of DMXAA was a major pharmacophore responsive to STING activation. In particular, the loss of hydrogen bond interaction between the carboxylic acid of DMXAA and the side chain Thr262 of STING led to STING inhibition. DMXAA N-methyl amide derivative (DNHM) exhibited good inhibitor activity, inhibited STING-mediated interferon production in vitro and in vivo, and effectively attenuated STING-associated inflammatory diseases. Therefore, we provide a new insight into STING-ligand interactions, which may improve the understanding of STING biology.

Signal strength of STING activation determines cytokine plasticity and cell death in human monocytes

The cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) pathway is a cytosolic sensor of microbial and host-derived DNA and plays a key role in innate immunity. Activation of STING by cyclic dinucleotide (CDN) ligands in human monocytes induces a type I interferon response and production of pro-inflammatory cytokines associated with the induction of massive cell death. In this study we have re-evaluated the effect of signal strength of STING activation on the cytokine plasticity of human monocytes. CDN (2′3′c-GAMP) and non-CDN (diABZI, MSA-2) STING ligands in the range of EC50 concentrations (15 μM 2′3′c-GAMP, 100 nM diABZI, 25 μM MSA-2) induced IFN-β, IP-10, and large amounts of IL-1β and TNF-α, but no IL-10 or IL-19. Interestingly, LPS-induced production of IL-10 and IL-19 was abolished in the presence of diABZI or MSA-2, whereas IL-1β and TNF-α were not inhibited. Surprisingly, we observed that tenfold lower (MSA-2, i.e. 2.5 μM) or 100-fold lower (diABZI, i.e. 1 nM) concentrations strongly stimulated secretion of anti-inflammatory IL-10 and IL-19, but little of IL-1β and TNF-α. Induction of IL-10 was associated with up-regulation of PRDM1 (Blimp-1). While cytokine secretion stimulated by the higher concentrations was accompanied by apoptosis as shown by cleavage of caspase-3 and PARP-1, the low concentrations did not trigger overt cell death yet induced cleavage of gasdermin-D. Our results reveal a previously unrecognized plasticity of human monocytes in their signal strength-dependent production of pro- versus anti-inflammatory cytokines upon STING activation.

Recent progress on the activation of the cGAS-STING pathway and its regulation by biomolecular condensation.

The cyclic guanosine monophosphate (GMP)-adenosine monophosphate (AMP) synthetase (cGAS)-stimulator of interferon genes (STING) pathway, comprising the DNA sensor cGAS, the second messenger cyclic GMP-AMP (cGAMP), and the endoplasmic reticulum (ER) adaptor protein STING, detects cytoplasmic double-stranded DNA (dsDNA) to trigger type I-interferon responses for host defense against pathogens. Previous studies defined a model for the allosteric activation of cGAS by DNA-binding, but recent work reveals other layers of mechanisms to regulate cGAS activation such as the phase condensation and metal ions, especially the discovery of Mn2+ as a cGAS activator. Activation of the 2'3'-cGAMP sensor STING requires translocating from the ER to the Golgi apparatus. The sulfated glycosaminoglycans at the Golgi are found to be the second STING ligand promoting STING oligomerization and activation in addition to 2'3'-cGAMP, while surpassed levels of 2'3'-cGAMP induce ER-located STING to form a highly organized ER membranous condensate named STING phase-separator to restrain STING activation. Here, we summarize recent advances in the regulation of cGAS-STING activation and their implications in physiological or pathological conditions, particularly focusing on the emerging complexity of the regulation.

Control of STING Agonistic/Antagonistic Activity Using Amine-Skeleton-Based c-di-GMP Analogues.

Stimulator of Interferon Genes (STING) is a type of endoplasmic reticulum (ER)-membrane receptor. STING is activated by a ligand binding, which leads to an enhancement of the immune-system response. Therefore, a STING ligand can be used to regulate the immune system in therapeutic strategies. However, the natural (or native) STING ligand, cyclic-di-nucleotide (CDN), is unsuitable for pharmaceutical use because of its susceptibility to degradation by enzymes and its low cell-membrane permeability. In this study, we designed and synthesized CDN derivatives by replacing the sugar-phosphodiester moiety, which is responsible for various problems of natural CDNs, with an amine skeleton. As a result, we identified novel STING ligands that activate or inhibit STING. The cyclic ligand 7, with a cyclic amine structure containing two guanines, was found to have agonistic activity, whereas the linear ligand 12 showed antagonistic activity. In addition, these synthetic ligands were more chemically stable than the natural ligands.

SHR1032, a novel STING agonist, stimulates anti-tumor immunity and directly induces AML apoptosis

Stimulator of interferon genes (STING) activation induces type I interferons and pro-inflammatory cytokines which stimulate tumor antigen cross presentation and the adaptive immune responses against tumor. The first-generation of STING agonists, cyclic di-nucleotide (CDN), mimicked the endogenous STING ligand cyclic guanosine monophosphate adenosine monophosphate, and displayed limited clinical efficacy. Here we report the discovery of SHR1032, a novel small molecule non-CDN STING agonist. Compared to the clinical CDN STING agonist ADU-S100, SHR1032 has much higher activity in human cells with different STING haplotypes and robustly induces interferon β (IFNβ) production. When dosed intratumorally, SHR1032 induced strong anti-tumor effects in the MC38 murine syngeneic tumor model. Pharmacodynamic studies showed induction of IFNβ, tumor necrosis factor α (TNFα) and interleukin-6 (IL-6) in the tumors and, to a lower extent, in the plasma. More importantly, we found SHR1032 directly causes cell death in acute myeloid leukemia (AML) cells. In conclusion, our findings demonstrate that in addition to their established ability to boost anti-tumor immune responses, STING agonists can directly eradicate AML cells, and SHR1032 may present a new and promising therapeutic agent for cancer patients.

Stimulatory and inhibitory activity of STING ligands on tumor-reactive human gamma/delta T cells

ABSTRACT Ligands for Stimulator of Interferon Genes (STING) receptor are under investigation as adjuvants in cancer therapy. Multiple effects have been described, including induction of immunogenic cell death and enhancement of CD8 T-cell mediated anti-tumor immunity. However, the potential effects of STING ligands on activation and effector functions of tumor-reactive human γδ T cells have not yet been investigated. We observed that cyclic dinucleotide as well as novel non-dinucleotide STING ligands diABZI and MSA-2 co-stimulated cytokine induction in Vδ2 T cells within peripheral blood mononuclear cells but simultaneously inhibited their proliferative expansion in response to the aminobisphosphonate Zoledronate and to γδ T-cell specific phosphoantigen. In purified γδ T cells, STING ligands co-stimulated cytokine induction but required the presence of monocytes. STING ligands strongly stimulated IL-1β and TNF-α secretion in monocytes and co-stimulated cytokine induction in short-term expanded Vδ2 γδ T-cell lines. Simultaneously, massive cell death was triggered in both cell populations. Activation of STING as revealed by TBK1/IRF3 phosphorylation and IP-10 secretion varied among STING-expressing tumor cells. STING ligands modulated tumor cell killing by Vδ2 T cells as analyzed in Real-Time Cell Analyzer to variable degree, depending on the tumor target and time course kinetics. Our study reveals complex regulatory effects of STING ligands on human γδ T cells in vitro. These results help to define conditions where STING ligands might boost the efficacy of γδ T cell immunotherapy in vivo.

CD4 T cell-intrinsic STING signaling controls the differentiation and effector functions of TH1 and TH9 cells

BackgroundWhile stimulator of interferon genes (STING) activation in innate immune cells of the tumor microenvironment can result in CD8 T cell-dependent antitumor immunity, whether STING signaling affects CD4 T-cell responses...

Design, synthesis and biological evaluation studies of novel small molecule ENPP1 inhibitors for cancer immunotherapy

Ecto-nucleotide pyrophosphatase/phosphodiesterases 1 (ENPP1 or NPP1), is an attractive therapeutic target for various diseases, primarily cancer and mineralization disorders. The ecto-enzyme is located on the cell surface and has been implicated in the control of extracellular levels of nucleotide, nucleoside and (di) phosphate. Recently, it has emerged as a critical phosphodiesterase that hydrolyzes cyclic 2′3′- cGAMP, the endogenous ligand for STING (STimulator of INterferon Genes). STING plays an important role in innate immunity by activating type I interferon in response to cytosolic 2′3′-cGAMP. ENPP1 negatively regulates the STING pathway and hence its inhibition makes it an attractive therapeutic target for cancer immunotherapy. Herein, we describe the design, optimization and biological evaluation studies of a series of novel non-nucleotidic thioguanine based small molecule inhibitors of ENPP1. The lead compound 43 has shown good in vitro potency, stability in SGF/SIF/PBS, selectivity, ADME properties and pharmacokinetic profile and finally potent anti-tumor response in vivo. These compounds are a good starting point for the development of potentially effective cancer immunotherapy agents.

IMMU-53. STING-ING GLIOBLASTOMA WITH SPHERICAL NUCLEIC ACIDS

Abstract The Stimulator of Interferon Genes (STING) pathway represents a major innate immune sensing mechanism for tumor-derived DNA. Modified cyclic dinucleotides (CDNs) that mimic the endogenous STING ligand cGAMP are currently being explored in patients with solid tumors that are amenable to intratumoral delivery. Inadequate bioavailability and insufficient lipophilicity are limiting factors for clinical CDN development, in particular when consideration is given to systemic administration approaches. We have shown that the formulation of oligonucleotides into Spherical Nucleic Acid (SNA) nanostructures, i.e.,the presentation of oligonucleotides at high density on the surface of nanoparticle cores, lead to biochemical and biological properties that are radically different from those of linear oligonucleotides. First-generation brain-penetrant siRNA-based SNAs (NCT03020017, recurrent GBM) have recently completed early clinical trials. Here, we report the development of a STING-agonistic immunotherapy by targeting cGAS, the sensor of cytosolic dsDNA upstream of STING, with SNAs presenting dsDNA at high surface density. The strategy of using SNAs exploits the ability of cGAS to raise STING responses by delivering dsDNA and inducing the catalytic production of endogenous CDNs. SNA nanostructures carrying a 45bp IFN-simulating dsDNA oligonucleotide, the most commonly used and widely characterized cGAS activator, potently activated the cGAS-STING pathway in vitro and in vivo. In a poorly immunogenic and highly aggressive syngeneic mouse glioma model, in which tumours were well-established, only one dose of intranasal treatment with STING-SNAs decelerated tumour growth, improved survival and importantly, was well-tolerated. Our use of SNAs addresses the challenges of nucleic acid delivery to intracranial tumor sites via intranasal route, exploits the binding of dsDNA molecules on the SNA surface to enhance the formation of a dimeric cGAS:DNA complex and establishes cGAS-agonistic SNAs as a novel class of immune-stimulatory modalities for triggering innate immune responses against tumor.

Crucial role of stimulator of interferon genes-dependent signaling in house dust mite extract-induced IgE production

Stimulator of interferon genes (STING) is a DNA sensor that responds to pathogens and induces type I interferon production. Herein, the role of STING in house dust mite extract (HDM)-induced allergic asthma was investigated. C57BL/6 wild-type (WT) and Sting−/− mice were intratracheally sensitized with HDM, and the bronchoalveolar lavage fluid (BALF), sera, lungs, and mediastinal lymph nodes (MLNs) were analyzed. The total and HDM-specific serum IgE levels were lower in Sting−/− mice than in WT mice. B cell and IgE-positive B cell proportion in BALF and MLNs, respectively, was significantly lower in Sting−/− mice than in WT mice. Additionally, cyclic GMP-AMP, a STING ligand, augmented total and HDM-specific serum IgE levels and B cell proportion in BALF when applied in combination with HDM. To elucidate the role of STING in IgE production, follicular helper T (Tfh) cells, which are involved in B cell maturation, were investigated. Tfh cell proportion in MLNs decreased in Sting−/− mice, and IL-4 and IL-13 production by HDM-restimulated MLN cells from HDM-sensitized mice was decreased in Sting−/− mice compared with WT mice. Thus, STING plays an important role in the maturation and class switching of IgE-producing B cells in allergic inflammation via Tfh cells.

Prolonged activation of innate immune pathways by a polyvalent STING agonist

The stimulator of interferon genes (STING) is an endoplasmic reticulum transmembrane protein that is a target of therapeutics for infectious diseases and cancer. However, early-phase clinical trials of small-molecule STING agonists have shown limited antitumour efficacy and dose-limiting toxicity. Here, we show that a polyvalent STING agonist—a pH-sensitive polymer bearing a seven-membered ring with a tertiary amine (PC7A)—activates innate-immunity pathways through the polymer-induced formation of STING–PC7A condensates. In contrast to the natural STING ligand 2′,3′-cyclic-GMP-AMP (cGAMP), PC7A stimulates the prolonged production of pro-inflammatory cytokines by binding to a non-competitive STING surface site that is distinct from the cGAMP binding pocket. PC7A induces antitumour responses that are dependent on STING expression and CD8+ T-cell activity, and the combination of PC7A and cGAMP led to synergistic therapeutic outcomes (including the activation of cGAMP-resistant STING variants) in mice bearing subcutaneous tumours and in resected human tumours and lymph nodes. The activation of the STING pathway through polymer-induced STING condensation may offer new therapeutic opportunities.

Nanoparticle delivery improves the pharmacokinetic properties of cyclic dinucleotide STING agonists to open a therapeutic window for intravenous administration

The stimulator of interferon genes (STING) pathway plays an important role in the immune surveillance of cancer and, accordingly, agonists of STING signaling have recently emerged as promising therapeutics for remodeling of the immunosuppressive tumor microenvironment (TME) and enhancing response rates to immune checkpoint inhibitors. 2′3′-cyclic guanosine monophosphate–adenosine monophosphate (2′3′-cGAMP) is the endogenous ligand for STING, but is rapidly metabolized and poorly membrane permeable, restricting its use to intratumoral administration. Nanoencapsulation has been shown to allow for systemic administration of cGAMP and other cyclic dinucleotides (CDN), but little is known about how nanocarriers affect important pharmacological properties that impact the efficacy and safety of CDNs. Using STING-activating nanoparticles (STING-NPs) – a polymersome platform designed to enhance cGAMP delivery – we investigate the pharmacokinetic (PK)-pharmacodynamic (PD) relationships that underlie the ability of intravenously (i.v.) administered STING-NPs to induce STING activation and inhibit tumor growth. First, we demonstrate that nanoencapsulation improves the half-life of encapsulated cGAMP by 40-fold, allowing for sufficient accumulation of cGAMP in tumors and activation of the STING pathway in the TME as assessed by western blot analysis and gene expression profiling. Nanoparticle delivery also changes the biodistribution profile, resulting in increased cGAMP accumulation and STING activation in the liver and spleen, which we identify as dose limiting organs. As a consequence of STING activation in tumors, i.v. administered STING-NPs reprogram the TME towards a more immunogenic antitumor milieu, characterized by an influx of >20-fold more CD4+ and CD8+ T-cells. Consequently, STING-NPs increased response rates to αPD-L1 antibodies, resulting in significant improvements in median survival time in a B16-F10 melanoma model. Additionally, we confirmed STING-NP monotherapy in an additional melanoma (YUMM1.7) and breast adenocarcinoma (E0771) models leading to >50% and 80% reduction in tumor burden, respectively, and significant increases in median survival time. Collectively, this work provides an examination of the PK-PD relationship governing STING activation upon systemic delivery using STING-NPs, providing insight for future optimization for nanoparticle-based STING agonists and other immunomodulating nanomedicines.