Chemical Biology Perspectives on STING Agonists as Tumor Immunotherapy

γ-Butyrolactone Derivatives of MSA-2 are STING Prodrugs

STING agonists are potent enhancers of a pro-inflammatory response and, thus, potentially useful therapeutics. Unfortunately, many agonists developed to date require complex drug delivery formulations and often have poor water solubility, limiting their use for systemic administration. Here, we report the discovery and chemical characterization of lactones of MSA-2 as new STING prodrugs with enhanced properties. We show that these prodrugs form efficient inclusion complexes with tumor myeloid cell targeting cyclodextrin nanoparticles and propose a new mechanism of formation and hydrolysis.

A novel super-enhancer-related risk model for predicting prognosis and guiding personalized treatment in hepatocellular carcinoma

BACKGROUND

Our research endeavored to develop a robust predictive signature grounded in super-enhancer-related genes (SERGs), with the dual objectives of forecasting survival outcomes and evaluating the tumor immune microenvironment (TiME) in hepatocellular carcinoma (HCC).

METHODS

HCC RNA-sequencing data were retrieved from The Cancer Genome Atlas (TCGA), and 365 patients were randomly assigned to training or testing sets in 1:1 ratio. SERGs of HCC were downloaded from Super-Enhancer Database (SEdb). On the basis of training set, a SERGs signature was identified, and its prognostic value was confirmed by internal and external validation (GSE14520) sets. We subsequently examined the model for potential functional enrichment and the degree of tumor immune infiltration. Additionally, we carried out in vitro experiments to delve into the biological functions of CBX2 gene.

RESULTS

An SE-related prognostic model including CBX2, TPX2, EFNA3, DNASE1L3 and SOCS2 was established and validated. According to this risk model, patients in the high-risk group had a significantly worse prognosis, and their immune cell infiltration was significantly different from that of low-risk group. Moreover, the high-risk group exhibited a significant enrichment of tumor-associated pathological pathways. The SERGs signature can generally be utilized to screen HCC patients who are likely to respond to immunotherapy, as there is a positive correlation between the risk score and the Tumor Immune Dysfunction and Exclusion (TIDE) score. Furthermore, the downregulation of the CBX2 gene expression was found to inhibit HCC cell viability, migration, and cell cycle progression, while simultaneously promoting apoptosis.

CONCLUSIONS

We developed a novel HCC prognostic model utilizing SERGs, indicating that patients with high-risk score not only face a poorer prognosis but also may exhibit a diminished therapeutic response to immune checkpoint inhibitors (ICIs). This model is designed to tailor personalized treatment strategies to the individual needs of each patient, thereby improving the overall clinical outcomes for HCC patients. Furthermore, CBX2 is a promising candidate for therapeutic intervention in HCC.

Ultrasound -Induced Thermal Effect Enhances the Efficacy of Chemotherapy and Immunotherapy in Tumor Treatment

Background

The inadequate perfusion, frequently resulting from abnormal vascular configuration, gives rise to tumor hypoxia. The presence of this condition hinders the effective delivery of therapeutic drugs and the infiltration of immune cells into the tumor, thereby compromising the efficacy of treatments against tumors. The objective of this study is to exploit the thermal effect of ultrasound (US) in order to induce localized temperature elevation within the tumor, thereby facilitating vasodilation, augmenting drug delivery, and enhancing immune cell infiltration.

Methods

The selection of US parameters was based on intratumor temperature elevation and their impact on cell viability. Vasodilation and hypoxia improvement were investigated using enzyme-linked immunosorbent assay (ELISA) and immunofluorescence examination. The distribution and accumulation of commercial pegylated liposomal doxorubicin (PLD) and PD-L1 antibody (anti-PD-L1) in the tumor were analyzed through frozen section analysis, ELISA, and in vivo fluorescence imaging. The evaluation of tumor immune microenvironment was conducted using flow cytometry (FCM). The efficacy of US-enhanced chemotherapy in combination with immunotherapy was investigated by monitoring tumor growth and survival rate after various treatments.

Results

The US irradiation condition of 0.8 W/cm2 for 10 min effectively elevated the tumor temperature to approximately 40 °C without causing any cellular or tissue damage, and sufficiently induced vasodilation, thereby enhancing the distribution and delivery of PLD and anti-PD-L1 in US-treated tumors. Moreover, it effectively mitigated tumor hypoxia while significantly increasing M1-phenotype tumor-associated macrophages (TAMs) and CD8+ T cells, as well as decreasing M2-phenotype TAMs. By incorporating US irradiation, the therapeutic efficacy of PLD and anti-PD-L1 was substantially boosted, leading to effective suppression of tumor growth and prolonged survival in mice.

Conclusion

The application of US (0.8 W/cm2 for 10 min) can effectively induce vasodilation and enhance the delivery of PLD and anti-PD-L1 into tumors, thereby reshaping the immunosuppressive tumor microenvironment and optimizing therapeutic outcomes.

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.

The senescence journey in cancer immunoediting

Cancer progression is continuously controlled by the immune system which can identify and destroy nascent tumor cells or inhibit metastatic spreading. However, the immune system and its deregulated activity in the tumor microenvironment can also promote tumor progression favoring the outgrowth of cancers capable of escaping immune control, in a process termed cancer immunoediting. This process, which has been classified into three phases, i.e. "elimination", "equilibrium" and "escape", is influenced by several cancer- and microenvironment-dependent factors. Senescence is a cellular program primed by cells in response to different pathophysiological stimuli, which is based on long-lasting cell cycle arrest and the secretion of numerous bioactive and inflammatory molecules. Because of this, cellular senescence is a potent immunomodulatory factor promptly recruiting immune cells and actively promoting tissue remodeling. In the context of cancer, these functions can lead to both cancer immunosurveillance and immunosuppression. In this review, the authors will discuss the role of senescence in cancer immunoediting, highlighting its context- and timing-dependent effects on the different three phases, describing how senescent cells promote immune cell recruitment for cancer cell elimination or sustain tumor microenvironment inflammation for immune escape. A potential contribution of senescent cells in cancer dormancy, as a mechanism of therapy resistance and cancer relapse, will be discussed with the final objective to unravel the immunotherapeutic implications of senescence modulation in cancer.