Immunotherapy with STING and TLR9 agonists promotes synergistic therapeutic efficacy with suppressed cancer-associated fibroblasts in colon carcinoma

STING Agonists and How to Reach Their Full Potential in Cancer Immunotherapy

As cancer continues to rank among the leading causes of death, the demand for novel treatments has never been higher. Immunotherapy shows promise, yet many solid tumors such as pancreatic cancer or glioblastoma remain resistant. In these, the "cold" tumor microenvironment with low immune cell infiltration and inactive anti-tumoral immune cells leads to increased tumor resistance to these drugs. This resistance has driven the development of several drug candidates, including stimulators of interferon genes (STING) agonists to reprogram the immune system to fight off tumors. Preclinical studies demonstrated that STING agonists can trigger the cancer immunity cycle and increase type I interferon secretion and T cell activation, which subsequently induces tumor regression. Despite promising preclinical data, biological and physical challenges persist in translating the success of STING agonists into clinical trials. Nonetheless, novel combination strategies are emerging, investigating the combination of these agonists with other immunotherapies, presenting encouraging preclinical results. This review will examine these potential combination strategies for STING agonists and assess the benefits and challenges of employing them in cancer immunotherapy.

Potential therapeutic strategies for colitis and colon cancer: bidirectional targeting STING pathway

The cyclic-GMP-AMP synthase (cGAS)-stimulator of interferon gene (STING) pathway has emerged as a promising therapeutic target for colitis and colon cancers. Notably, inhibiting STING may mitigate the progression of colitis, whereas activating STING can enhance anti-tumor immune responses against colon cancer. This duality suggests that the development of STING agonists and inhibitors possesses significant clinical translational potential. In this review, we provide a comprehensive overview of STING inhibitors/agonists that have been systematically evaluated in the contexts of colitis and colon cancer and their specific molecular mechanisms. Other well-characterized STING inhibitors/agonists may also hold considerable promise for the treatment of these conditions, although efficacy validation remain necessary. Additionally, we delve into the latest advances concerning STING oligomerization, degradation and phase separation-dependent self-regulation, proposing potential druggable targets that could inspire the development of novel STING agonists or inhibitors. In Summary, targeting STING appears to be a promising strategy for the treatment of colitis and colon cancer.

Cytosolic bacterial pathogens activate TLR pathways in tumors that synergistically enhance STING agonist cancer therapies

Intracellular bacterial pathogens are distinctive tools for fighting cancer, as they can proliferate in tumors and deliver therapeutic payloads to the eukaryotic cytosol. Cytosol-dwelling bacteria have undergone extensive preclinical and clinical testing, yet the mechanisms of activating innate immunity in tumors are unclear. We report that phylogenetically distinct cytosolic pathogens, including Listeria, Rickettsia, and Burkholderia species, elicited anti-tumor responses in poorly immunogenic melanoma and lymphoma in mice. Although the bacteria required cytosolic access, anti-tumor responses were largely independent of the cytosolic sensors cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING), but instead required Toll-like receptor (TLR) signaling. Combining pathogens with STING agonists elicited profound, synergistic anti-tumor effects with complete responses in >80% of mice. Small molecule TLR agonists also synergistically enhanced STING agonists. The responses required RAG2 but not interferons, and cured mice developed immunity to cancer rechallenge requiring CD8+ T cells. These studies provide a framework for enhancing microbial and small molecule innate agonists for cancer, via co-activating STING and TLRs.

Immunoconjugates as an Efficient Platform for Drug Delivery: A Resurgence of Natural Products in Targeted Antitumor Therapy

The present review provides a detailed and comprehensive discussion on antibody-drug conjugates (ADCs) as an evolving new modality in the current therapeutic landscape of malignant diseases. The principle concepts of targeted delivery of highly toxic agents forsaken as stand-alone drugs are examined in detail, along with the biochemical and technological tools for their successful implementation. An extensive analysis of ADCs' major components is conducted in parallel with their function and impact on the stability, efficacy, safety, and resistance profiles of the immunoconjugates. The scope of the article covers the major classes of currently validated natural compounds used as payloads, with an emphasis on their structural and mechanistic features, natural origin, and distribution. Future perspectives in ADCs' design are thoroughly explored, addressing their inherent or emerging challenges and limitations. The survey also provides a comprehensive overview of the molecular rationale for active tumor targeting of ADC-based platforms, exploring the cellular biology and clinical relevance of validated tumor markers used as a "homing" mechanism in both hematological and solid tumor malignancies.

From Structure to Function: How Prebiotic Diversity Shapes Gut Integrity and Immune Balance

The microbiota stability, diversity, and composition are pillars for an efficient and beneficial symbiotic relationship between its host and itself. Microbial dysbiosis, a condition where a homeostatic bacterial community is disturbed by acute or chronic events, is a predisposition for many diseases, including local and systemic inflammation that leads to metabolic syndrome, diabetes, and some types of cancers. Classical dysbiosis occurs in the large intestine. During this period, pathogenic strains can multiply, taking advantage of the compromised environment. This overgrowth triggers an exaggerated inflammatory response from the human immune system due to the weakened integrity of the intestinal barrier. Such inflammation can also directly influence higher polyp formation and/or tumorigenesis. Prebiotics can be instrumental in preventing or correcting dysbiosis. Prebiotics are molecules capable of serving as substrates for fermentation processes by gut microorganisms. This can promote returning the intestinal environment to homeostasis. Effective prebiotics are generally specific oligo- and polysaccharides, such as FOS or inulin. However, the direct effects of prebiotics on intestinal epithelial and immune cells must also be taken into consideration. This interaction happens with diverse prebiotic nondigestible carbohydrates, and they can inhibit or decrease the inflammatory response. The present work aims to elucidate and describe the different types of prebiotics, their influence, and their functionalities for health, primarily focusing on their ability to reduce and control inflammation in the intestinal epithelial barrier, gut, and systemic environments.

Cooperative tumor inhibition by CpG-oligodeoxynucleotide and cyclic dinucleotide in head and neck cancer involves T helper cytokine and macrophage phenotype reprogramming

Head and neck cancer ranks as the sixth most common cancer worldwide, highlighting the critical need for the development of new therapies to enhance treatment efficacy. The activation of innate immune receptors given their potent immune stimulatory properties aid in the eradication of cancer cells. In this study, we investigated the immune mechanism and anti-tumor function of a Toll-like receptor 9 (TLR9) agonist, CpG-oligodeoxynucleotide-2722 (CpG-2722), in combination with cyclic dinucleotides, which are agonists of stimulator of interferon genes (STING). Our results revealed that CpG-2722 stimulation increased the expression of Th1 pro-inflammatory cytokines. Stimulation by STING agonists exhibited lower expression of Th1 cytokines but higher expression of Th2 cytokines compared to CpG-2722. However, the combination of these two agonists significantly enhanced Th1 cytokines while reducing Th2 cytokines. Moreover, in vivo experiment showed that both CpG-2722 and 2'3'-c-di-AMP suppressed head and neck tumor growth, with their combination proving more effective than the use of these agonists alone. The combined treatment cooperatively promoted the production of Th1 cytokines and type I interferons, while suppressing Th2 cytokines in the tumors as observed in vitro. Additionally, it led to the accumulation of M1 macrophages, dendritic cells, and T cells, shaping a favorable tumor microenvironment for T cell-mediated tumor killing. The anti-tumor activity of the CpG-2722 and 2'3'-c-di-AMP combination depends on the macrophage presence but does not directly activate M1 macrophage polarization, instead working through a reprogrammed cytokine profile. Furthermore, this combination shows a cooperative anti-tumor activity with anti-PD-1 in treating head and neck tumors. Overall, these findings highlight a Th response and macrophage phenotype reprograming involved functional mechanism underlying the cooperative activity of the combination of TLR9 and STING agonists in the immunotherapy of head and neck cancer.

DNA sensing of dendritic cells in cancer immunotherapy

Dendritic cells (DCs) are involved in the initiation and maintenance of immune responses against malignant cells by recognizing conserved pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs) through pattern recognition receptors (PRRs). According to recent studies, tumor cell-derived DNA molecules act as DAMPs and are recognized by DNA sensors in DCs. Once identified by sensors in DCs, these DNA molecules trigger multiple signaling cascades to promote various cytokines secretion, including type I IFN, and then to induce DCs mediated antitumor immunity. As one of the potential attractive strategies for cancer therapy, various agonists targeting DNA sensors are extensively explored including the combination with other cancer immunotherapies or the direct usage as major components of cancer vaccines. Moreover, this review highlights different mechanisms through which tumor-derived DNA initiates DCs activation and the mechanisms through which the tumor microenvironment regulates DNA sensing of DCs to promote tumor immune escape. The contributions of chemotherapy, radiotherapy, and checkpoint inhibitors in tumor therapy to the DNA sensing of DCs are also discussed. Finally, recent clinical progress in tumor therapy utilizing agonist-targeted DNA sensors is summarized. Indeed, understanding more about DNA sensing in DCs will help to understand more about tumor immunotherapy and improve the efficacy of DC-targeted treatment in cancer.

Harnessing the cGAS-STING pathway to potentiate radiation therapy: current approaches and future directions

In this review, we cover the current understanding of how radiation therapy, which uses ionizing radiation to kill cancer cells, mediates an anti-tumor immune response through the cGAS-STING pathway, and how STING agonists might potentiate this. We examine how cGAS-STING signaling mediates the release of inflammatory cytokines in response to nuclear and mitochondrial DNA entering the cytoplasm. The significance of this in the context of cancer is explored, such as in response to cell-damaging therapies and genomic instability. The contribution of the immune and non-immune cells in the tumor microenvironment is considered. This review also discusses the burgeoning understanding of STING signaling that is independent of inflammatory cytokine release and the various mechanisms by which cancer cells can evade STING signaling. We review the available data on how ionizing radiation stimulates cGAS-STING signaling as well as how STING agonists may potentiate the anti-tumor immune response induced by ionizing radiation. There is also discussion of how novel radiation modalities may affect cGAS-STING signaling. We conclude with a discussion of ongoing and planned clinical trials combining radiation therapy with STING agonists, and provide insights to consider when planning future clinical trials combining these treatments.

Cytosolic bacterial pathogens activate TLR pathways in tumors that synergistically enhance STING agonist cancer therapies

Bacterial pathogens that invade the eukaryotic cytosol are distinctive tools for fighting cancer, as they preferentially target tumors and can deliver cancer antigens to MHC-I. Cytosolic bacterial pathogens have undergone extensive preclinical development and human clinical trials, yet the molecular mechanisms by which they are detected by innate immunity in tumors is unclear. We report that intratumoral delivery of phylogenetically distinct cytosolic pathogens, including Listeria, Rickettsia, and Burkholderia species, elicited anti-tumor responses in established, poorly immunogenic melanoma and lymphoma in mice. We were surprised to observe that although the bacteria required entry to the cytosol, the anti-tumor responses were largely independent of the cytosolic sensors cGAS/STING and instead required TLR signaling. Combining pathogens with TLR agonists did not enhance anti-tumor efficacy, while combinations with STING agonists elicited profound, synergistic anti-tumor effects with complete responses in >80% of mice after a single dose. Small molecule TLR agonists also synergistically enhanced the anti-tumor activity of STING agonists. The anti-tumor effects were diminished in Rag2-deficient mice and upon CD8 T cell depletion. Mice cured from combination therapy developed immunity to cancer rechallenge that was superior to STING agonist monotherapy. Together, these data provide a framework for enhancing the efficacy of microbial cancer therapies and small molecule innate immune agonists, via the co-activation of STING and TLRs.