STING expression and response to treatment with STING ligands in premalignant and malignant disease

STINGing Defenses: Unmasking the Mechanisms of DNA Oncovirus-Mediated Immune Escape

DNA oncoviruses represent an intriguing subject due to their involvement in oncogenesis. These viruses have evolved mechanisms to manipulate the host immune response, facilitating their persistence and actively contributing to carcinogenic processes. This paper describes the complex interactions between DNA oncoviruses and the innate immune system, with a particular emphasis on the cGAS-STING pathway. Exploring these interactions highlights that DNA oncoviruses strategically target and subvert this pathway, exploiting its vulnerabilities for their own survival and proliferation within the host. Understanding these interactions lays the foundation for identifying potential therapeutic interventions. Herein, we sought to contribute to the ongoing efforts in advancing our understanding of the innate immune system in oncoviral pathogenesis.

Differential Regulation of the STING Pathway in Human Papillomavirus-Positive and -Negative Head and Neck Cancers

Squamous cell carcinomas, which arise from the cells that line the mucosal surfaces of the head and neck, represent the most common type of head and neck cancers (HNSCC). Human papillomavirus (HPV) infection has been strongly associated with the development of oropharyngeal cancers, which are cancers that occur in the back of the throat, including the tonsils and base of the tongue. HNSCCs with and without HPV infection have distinct pathology, with HPV-positive patients having higher levels of immune infiltration, activation in the tumor microenvironment and better response to radiation and chemotherapy. It is, however, unclear whether HPV infection in HNSCCs has the potential to activate innate-immune sensing pathways and if these cancers possess intrinsic immunogenicity associated with HPV infection. Here we investigate the innate immune stimulator of interferon genes (STING) pathway and immune responses to STING activation in HNSCCs and uncover fundamental differences in the regulation of this pathway in cell lines versus primary human clinical specimens. We show that while STING is differentially expressed in HPV-positive and -negative HNSCC cell lines, they exhibit a gross functional defect in signaling through this pathway. However, STING activation in immune cell populations generated immune signatures predicted to elicit useful tumoricidal mechanisms. In contrast, IHC analysis of human tissue microarrays revealed enhanced STING expression in HPV-related tumors and high intratumoral expression of STING correlated with increased survival.

SIGNIFICANCE

STING is an important innate immune sensor of cytosolic DNA, inducing essential antiviral and antitumoral responses. This research shows that STING expression is enhanced in HPV-positive HNSCC patient tissue, with high intratumoral STING expression correlating with increased survival. In addition, STING activation in immune cell populations augmented antitumoral effects against HNSCCs, suggesting patients may benefit from the use of STING agonists in combination with traditional therapies.

The cGAS/STING/IFN-1 Response in Squamous Head and Neck Cancer Cells after Genotoxic Challenges and Abrogation of the ATR-Chk1 and Fanconi Anemia Axis

Locally advanced head and neck squamous cell carcinomas (HNSCC) are often refractory to platinum-based radiochemotherapy and new immuno-oncological strategies. To stimulate immunogenic antitumor responses in HNSCC patients, we investigated the cGAS/STING/IFN-1 signaling pathway after genotoxic treatments and concomitant abrogation of the DNA damage response (DDR). For this purpose, FaDu and UM-SCC1 cells were exposed to X-rays or cisplatin and treated with an ATR or Chk1 inhibitor, or by Fanconi anemia gene A knockout (FANCA ko). We assessed clonogenic survival, cell cycle regulation, micronuclei, free cytosolic double-stranded DNA, and the protein expression and activity of the cGAS/STING/IFN-1 pathway and related players. Cell survival, regulation of G2/M arrest, and formation of rupture-prone cGAS-positive micronuclei after genotoxic treatments were most affected by ATR inhibition and FANCA ko. In UM-SCC-1 cells only, 8 Gy X-rays promoted IFN-1 expression unaltered by abrogation of the DDR or concomitant increased TREX1 expression. At a higher dose of 20 Gy, this effect was observed only for concurrent Chk1- or ATR-inhibition. FANCA ko or cisplatin treatment was ineffective in this regard. Our observations open new perspectives for the enhancement of cGAS/STING/IFN-1-mediated antitumor immune response in HNSCC by hypofractionated or stereotactic radiotherapy concepts in multimodal settings with immuno-oncological strategies.

ICI-based therapies: A new strategy for oral potentially malignant disorders

Oral potentially malignant disorders (OPMDs) are linked with an escalated risk of developing cancers, particularly oral squamous cell carcinoma (OSCC). Since prevailing therapies cannot effectively forestall the exacerbation and recurrence of OPMDs, halting their malignant progression is paramount. The immune checkpoint serves as a cardinal regulator of the immune response and the primary cause of adaptive immunological resistance. Although the exact mechanism remains elusive, elevated expression of multiple immune checkpoints in OPMDs and OSCC relative to healthy oral mucosa has been ascertained. This review delves into the immunosuppressive microenvironment of OPMDs, the expression of diverse immune checkpoints such as programmed death receptor-1 (PD-1) and programmed death receptor-1 ligand (PD-L1) in OPMDs, and the potential application of corresponding inhibitors. In addition, synergistic strategies incorporating combined immune checkpoint inhibitors, such as cGAS-STING, costimulatory molecules, cancer vaccines, and hydrogels, are discussed to gain a more comprehensive understanding of the role and application of immune checkpoint inhibitors (ICIs) in oral carcinogenesis.

The role of dendritic cells in radiation-induced immune responses

Dendritic cells perform critical functions in bridging innate and adaptive immunity. Their ability to sense adjuvant signals in their environment, migrate on maturation, and cross-present cell-associated antigens enables these cells to carry antigen from tissue sites to lymph nodes, and thereby prime naïve T cells that cannot enter tissues. Despite being an infrequent cell type in tumors, we discuss how dendritic cells impact the immune environment of tumors and their response to cancer therapies. We review how radiation therapy of tumors can impact dendritic cells, through transfer of cell associated antigens to dendritic cells and the release of endogenous adjuvants, resulting in increased antigen presentation in the tumor-draining lymph nodes. We explore how tumor specific factors can result in negative regulation of dendritic cell function in the tumor, and the impact of direct radiation exposure to dendritic cells in the treatment field. These data suggest an important role for dendritic cell subpopulations in activating new T cell responses and boosting existing T cell responses to tumor associated antigens in tumor draining lymph nodes following radiation therapy. It further justifies a focus on the needs of the lymph node T cells to improve systemic anti-immunity following radiation therapy.

Prognostic Significance of STING Immunoexpression in Relation to HPV16 Infection in Patients with Squamous Cell Carcinomas of Oral Cavity and Oropharynx

Infection with HPV16 in cancers of the oral cavity (OCSCC) and oropharynx (OPSCC) is, today, an important etiological and prognostic factor. Patients with HPV-positive OPSCC have a better prognosis than uninfected patients. However, in over 40% of these patients, cancer progression is noticed. Their identification is particularly important due to the ongoing clinical trials regarding the possibility of de-escalation of anticancer treatment in patients with HPV-positive OPSCC. Some studies suggest that there is possibility to differentiate prognosis of HPV16-positive patients by STING (Stimulator of Interferon Genes) immunoexpression. The aim of the present study was to analyze the influence of STING immunoexpression on overall (OS) and disease-free survival (DFS) of patients with HPV16-positive and -negative OCSCC and OPSCC. The study was performed in a group of 87 patients with OCSCC and OPSCC for which in our earlier study active HPV16 infection was assessed by P16 expression followed by HPV DNA detection. To analyze STING immunoexpression in tumor area (THS) and in adjacent stromal tissues (SHS) H score (HS) was applied. In the subgroup with HPV16, active infection patients with tumors with THS had significantly better DFS (p = 0.047) than those without THS. In this subgroup, TSH did not significantly influence OS, and SHS did not significantly correlate with OS and DFS. In the subgroup of patients without active HPV16 infection, THS and SHS also did not significantly influence patients' survival. Presented results indicated prognostic potential of tumor STING immunoexpression in patients with active HPV16 infection in cancers of oral cavity and oropharynx.

Potential role of cGAS/STING pathway in regulating cancer progression

The activation of innate immune response after the engagement of dsDNA is an evolutionarily preserved sophisticated strategy against invading microbial pathogens. cGAS has been identified as one of the major dsDNA sensor present in the cytoplasm which catalyzes the synthesis of a cyclic dinucleotide 2'3'cGAMP, as the secondary messenger that binds and activates the downstream stimulator of interferon (IFN) genes (STING) for subsequent production of type 1 IFNs and other inflammatory genes. Recent progress in the mechanical understanding of cGAS/STING signalling has unveiled its intricate role in tumor progression and metastasis. In this review, we specifically focus on new developments concerning the role of cGAS/STING signalling in regulating antitumorigenesis and tumorigenesis.

Nucleic Acid Sensing in the Tumor Vasculature

Endothelial cells form a powerful interface between tissues and immune cells. In fact, one of the underappreciated roles of endothelial cells is to orchestrate immune attention to specific sites. Tumor endothelial cells have a unique ability to dampen immune responses and thereby maintain an immunosuppressive microenvironment. Recent approaches to trigger immune responses in cancers have focused on activating nucleic acid sensors, such as cGAS-STING, in combination with immunotherapies. In this review, we present a case for targeting nucleic acid-sensing pathways within the tumor vasculature to invigorate tumor-immune responses. We introduce two specific nucleic acid sensors-the DNA sensor TREX1 and the RNA sensor RIG-I-and discuss their functional roles in the vasculature. Finally, we present perspectives on how these nucleic acid sensors in the tumor endothelium can be targeted in an antiangiogenic and immune activation context. We believe understanding the role of nucleic acid-sensing in the tumor vasculature can enhance our ability to design more effective therapies targeting the tumor microenvironment by co-opting both vascular and immune cell types.

Stimulator of interferon response cGAMP interactor overcomes ERBB2-mediated apatinib resistance in head and neck squamous cell carcinoma

PURPOSE

Apatinib resistance is the main obstacle to the effective treatment of advanced head and neck squamous cell carcinoma (HNSCC). This study aimed to evaluate the function of Erb-B2 receptor tyrosine kinase 2 (ERBB2) and stimulator of interferon response cGAMP interactor (STING) in apatinib resistance in HNSCC.

METHOD

The Cancer Genome Atlas database of HNSCC was used to analyze the relationship between vascular endothelial growth factor receptor 2 (VEGFR2) expression and prognosis. An apatinib resistant (AR) HNSCC cell line was constructed based on the CAL27 cell line. RNA sequencing was performed to explore the differentially expressed mRNAs. Quantitative real-time reverse transcription PCR (qRT-PCR) and western blotting were used to evaluate the expression and phosphorylation level VEGFR2, ERBB2, STING, and related proteins. Apatinib resistance was evaluated by colony formation and cell viability assays. A mouse subcutaneous tumor formation model was established to evaluate the efficiency of combination treatment and vascularization was evaluated by assessing CD31 immunofluorescence.

RESULT

The expression of VEGFR2 was high in tumor of patients with HNSCC. Western blotting and qRT-PCR revealed that in AR cells, ERBB2 expression was high, whereas the expression of STING was low. Targeted treatment of ERBB2 using lapatinib could attenuate apatinib resistance. Further research confirmed that overexpressing STING could decrease ERBB2 expression.

CONCLUSION

STING could sensitize AR cells to apatinib by decreasing ERBB2 expression. The combination of lapatinib or a STING agonist with apatinib ameliorated acquired apatinib resistance in a synergistic manner.

Combined STING levels and CD103+ T cell infiltration have significant prognostic implications for patients with cervical cancer

Activation of STimulator of INterferon Genes (STING) is important for induction of anti-tumor immunity. A dysfunctional STING pathway is observed in multiple cancer types and associates with poor prognosis and inferior response to immunotherapy. However, the association between STING and prognosis in virally induced cancers such as HPV-positive cervical cancer remains unknown. Here, we investigated the prognostic value of STING protein levels in cervical cancer using tumor tissue microarrays of two patient groups, primarily treated with surgery (n = 251) or radio(chemo)therapy (n = 255). We also studied CD103, an integrin that marks tumor-reactive cytotoxic T cells that reside in tumor epithelium and that is reported to associate with improved prognosis. Notably, we found that a high level of STING protein was an independent prognostic factor for improved survival in both the surgery and radio(chemo)therapy group. High infiltration of CD103+ T cells was associated with improved survival in the radio(chemo)therapy group. The combination of STING levels and CD103+ T cell infiltration is strongly associated with improved prognosis. We conclude that combining the prognostic values of STING and CD103 may improve the risk stratification of cervical cancer patients, independent from established clinical prognostic parameters.

STINGing Viral Tumors: What We Know from Head and Neck Cancers

It has now become increasingly clear that viruses, which may not be directly oncogenic, can affect the biology of tumors as well as immune behavior against tumors. This has led to a fundamental question: Should tumors associated with viral infection be considered distinct from those without? Typically, viruses activate the host innate immune responses by stimulating pathogen recognition receptors and DNA-sensing pathways, including the stimulator of interferon genes (STING) pathway. However, regulation of the STING pathway in a virus-associated tumor microenvironment is poorly understood. Human papillomavirus (HPV) infection within a subset of head and neck squamous cell carcinomas (HNSCC) promotes a unique etiology and clinical outcome. For reasons currently not well understood, patients with HPV⁺ tumors have a better outcome in terms of both overall survival and reduced risk of recurrence compared with HPV^- HNSCC. This observation may reflect a greater intrinsic immunogenicity associated with HPV infection, pertaining to innate immune system pathways activated following recognition of viral nucleotides. Here we discuss how HNSCC provides a unique model to study the STING pathway in the context of viral-induced tumor type as well as recent advances in our understanding of this pathway in HSNCC.

Defining Immunogenic and Radioimmunogenic Tumors

In the cancer literature tumors are inconsistently labeled as ‘immunogenic’, and experimental results are occasionally dismissed since they are only tested in known ‘responsive’ tumor models. The definition of immunogenicity has moved from its classical definition based on the rejection of secondary tumors to a more nebulous definition based on immune infiltrates and response to immunotherapy interventions. This review discusses the basis behind tumor immunogenicity and the variation between tumor models, then moves to discuss how these principles apply to the response to radiation therapy. In this way we can identify radioimmunogenic tumor models that are particularly responsive to immunotherapy only when combined with radiation, and identify the interventions that can convert unresponsive tumors so that they can also respond to these treatments.

HPV16 drives cancer immune escape via NLRX1-mediated degradation of STING

The incidence of human papillomavirus-positive (HPV+) head and neck squamous cell carcinoma (HNSCC) has surpassed that of cervical cancer and is projected to increase rapidly until 2060. The coevolution of HPV with transforming epithelial cells leads to the shutdown of host immune detection. Targeting proximal viral nucleic acid-sensing machinery is an evolutionarily conserved strategy among viruses to enable immune evasion. However, E7 from the dominant HPV subtype 16 in HNSCC shares low homology with HPV18 E7, which was shown to inhibit the STING DNA-sensing pathway. The mechanisms by which HPV16 suppresses STING remain unknown. Recently, we characterized the role of the STING/type I interferon (IFN-I) pathway in maintaining immunogenicity of HNSCC in mouse models. Here we extended those findings into the clinical domain using tissue microarrays and machine learning-enhanced profiling of STING signatures with immune subsets. We additionally showed that HPV16 E7 uses mechanisms distinct from those used by HPV18 E7 to antagonize the STING pathway. We identified NLRX1 as a critical intermediary partner to facilitate HPV16 E7-potentiated STING turnover. The depletion of NLRX1 resulted in significantly improved IFN-I-dependent T cell infiltration profiles and tumor control. Overall, we discovered a unique HPV16 viral strategy to thwart host innate immune detection that can be further exploited to restore cancer immunogenicity.

cGAS-STING signaling in cancer immunity and immunotherapy

Recent studies have shown that the innate immune cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway may play an important role in antitumor immunity. Additionally, the cGAS-STING pathway promotes the senescence of cancer cells, induces apoptosis of cancer cells, and increases the protective effect of cytotoxic T cells and natural killer cell-mediated cytotoxicity. We believe that the combination of the cGAS-STING signaling pathway with other therapeutic methods provides a new perspective from which to overcome obstacles in the application of this review. Further, we highlight the antitumor mechanism of the cGAS-STING signaling pathway and the latest advances in monotherapy and combination therapy with related agonists.

Leukoplakia and Immunology: New Chemoprevention Landscapes?

Oral potentially malignant disorders (OPMDs) comprise a range of clinical-pathological alterations frequently characterized by an architectural and cytological derangements upon histological analysis. Among them, oral leukoplakia is the most common type of these disorders. This work aims to analyze the possible use of drugs such as immunochemopreventive agents for OPMDs. Chemoprevention is the use of synthetic or natural compounds for the reversal, suppression, or prevention of a premalignant lesion conversion to malignant form. Experimental and in vivo data offer us the promise of molecular prevention through immunomodulation; however, currently, there is no evidence for the efficacy of these drugs in the chemoprevention action. Alternative ways to deliver drugs, combined use of molecules with complementary antitumor activities, diet influence, and better definition of individual risk factors must also be considered to reduce toxicity, improve compliance to the protocol treatment and offer a better individualized prevention. In addition, we must carefully reconsider the mode of action of many traditional cancer chemoprevention agents on the immune system, such as enhancing immunosurveillance and reversing the immune evasion. Several studies emphasize the concept of green chemoprevention as an alternative approach to accent healthy lifestyle changes in order to decrease the incidence of HNSCC.

Loss of HPV type 16 E7 restores cGAS-STING responses in human papilloma virus-positive oropharyngeal squamous cell carcinomas cells

Human papilloma viruses (HPV) are the main culprit in cervical and oropharyngeal cancers. HPV positive (+) cancers are regarded as 'oncogene addicted', displaying an absolute requirement for the continued expression of the oncogenes for their viability owing their survival, and thus making these genes salient targets for developing specific therapeutic agents. There is a strong association between HPV and oropharyngeal squamous cell carcinomas (OPSCC), a subset of head and neck cancers (HNCs). Alarmingly, HPV-associated OPSCC are on the rise globally, and the number of cases of HPV + OPSCCs surpasses that of cervical cancer in the USA. Here, we show that major HPV oncogenes, E6 and E7, are essential for the survival of HPV positive (+) OPSCCs, making these oncogenes salient targets for HPV-driven OPSCCs. HPV E7 is known to interact with STING, a component of the viral DNA-sensing cGAS-STING machinery which activates a pro-typical anti-viral type I interferon (IFN) response. Our recent work showed that E7 from HPV type 16 is responsible for the blockade of cGAS-STING responses in HPV + OPSCC cells. In this study, we show that CRISPR/Cas9-mediated loss of E7 from HPV + OPSCC cells, SCC2 and SCC104, restored cGAS-STING responses. Future work could involve HPV oncogene targeting leading to HPV + OPSCC tumour regression and that the combined use of STING agonists would induce favourable tumour clearance by activating appropriate anti-tumour responses.

cGAS-STING pathway in oncogenesis and cancer therapeutics

The host innate immunity offers the first line of defense against infection. However, recent evidence shows that the host innate immunity is also critical in sensing the presence of cytoplasmic DNA derived from genomic instability events, such as DNA damage and defective cell cycle progression. This is achieved through the cyclic GMP-AMP synthase (cGAS)/Stimulator of interferon (IFN) genes (STING) pathway. Here we discuss recent insights into the regulation of this pathway in cancer immunosurveillance, and the downstream signaling cascades that coordinate immune cell recruitment to the tumor microenvironment to destroy transformed cells through cellular senescence or cell death programs. Its central role in immunosurveillance positions the cGAS-STING pathway as an attractive anti-cancer immunotherapeutic drug target for chemical agonists or vaccine adjuvants and suggests a key node to be targeted in a synthetic lethal approach. We also discuss adaptive mechanisms used by cancer cells to circumvent cGAS-STING signaling and present evidence linking chronic cGAS-STING activation to inflammation-induced carcinogenesis, cautioning against the use of activating the cGAS-STING pathway as an anti-tumor immunotherapy. A deeper mechanistic understanding of the cGAS-STING pathway will aid in the identification of potentially efficacious anti-cancer therapeutic targets.

Immunotherapy for Head and Neck Cancer

The immune system has a vital role in the development, establishment, and progression of head and neck squamous cell carcinoma (HNSCC). Immune evasion of cancer cells leads to progression of HNSCC. An understanding of this mechanism provides the basis for improved therapies and outcomes for patients. Through the tumor's influence on the microenvironment, the immune system can be exploited to promote metastasis, angiogenesis, and growth. This article provides an overview of the interaction between immune infiltrating cells in the tumor microenvironment, and the immunologic principles related to HNSCC. Current immunotherapeutic strategies and emerging results from ongoing clinical trials are presented.

Magnitude of Therapeutic STING Activation Determines CD8+ T Cell-Mediated Anti-tumor Immunity

Intratumoral (IT) STING activation results in tumor regression in preclinical models, yet factors dictating the balance between innate and adaptive anti-tumor immunity are unclear. Here, clinical candidate STING agonist ADU-S100 (S100) is used in an IT dosing regimen optimized for adaptive immunity to uncover requirements for a T cell-driven response compatible with checkpoint inhibitors (CPIs). In contrast to high-dose tumor ablative regimens that result in systemic S100 distribution, low-dose immunogenic regimens induce local activation of tumor-specific CD8⁺ effector T cells that are responsible for durable anti-tumor immunity and can be enhanced with CPIs. Both hematopoietic cell STING expression and signaling through IFNAR are required for tumor-specific T cell activation, and in the context of optimized T cell responses, TNFα is dispensable for tumor control. In a poorly immunogenic model, S100 combined with CPIs generates a survival benefit and durable protection. These results provide fundamental mechanistic insights into STING-induced anti-tumor immunity.

The Common Costimulatory and Coinhibitory Signaling Molecules in Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinomas (HNSCCs) are closely linked with immunosuppression, accompanied by complex immune cell functional activities. The abnormal competition between costimulatory and coinhibitory signal molecules plays an important role in the malignant progression of HNSCC. This review will summarize the features of costimulatory molecules (including CD137, OX40 as well as CD40) and coinhibitory molecules (including CTLA-4, PD-1, LAG3, and TIM3), analyze the underlying mechanism behind these molecules' regulation of the progression of HNSCC, and introduce the clinic application. Vaccines, such as those targeting STING while working synergistically with monoclonal antibodies, are also discussed. A deep understanding of the tumor immune landscape will help find new and improved tumor immunotherapy for HNSCC.

STING activation reprograms tumor vasculatures and synergizes with VEGFR2 blockade

The stimulator of interferon genes (STING) signaling pathway is a critical link between innate and adaptive immunity, and induces anti-tumor immune responses. STING is expressed in vasculatures, but its role in tumor angiogenesis has not been elucidated. Here we investigated STING-induced tumor vascular remodeling and the potential of STING-based combination immunotherapy. Endothelial STING expression was correlated with enhanced T-cell infiltration and prolonged survival in human colon and breast cancer. Intratumoral STING activation with STING agonists (cGAMP or RR-CDA) normalized tumor vasculatures in implanted and spontaneous cancers, but not in STING-deficient mice. These were mediated by upregulation of type I/II interferon genes and vascular stabilizing genes (e.g., Angpt1, Pdgfrb, and Col4a). STING in non-hematopoietic cells is as important as STING in hematopoietic cells to induce a maximal therapeutic efficacy of exogenous STING agonist. Vascular normalizing effects of STING agonists were dependent on type I interferon signaling and CD8+ T cells. Notably, STING-based immunotherapy was maximally effective when combined with VEGFR2 blockade and/or immune checkpoint blockade (αPD-1 or αCTLA-4), leading to complete regression of immunotherapy-resistant tumors. Our data show that intratumoral STING activation can normalize tumor vasculature and the tumor microenvironment, providing a rationale for combining STING-based immunotherapy and anti-angiogenic therapy.

DNA released from neutrophil extracellular traps (NETs) activates pancreatic stellate cells and enhances pancreatic tumor growth

Neutrophil extracellular trap (NET) formation results in the expulsion of granulocyte proteins and DNA into the extracellular space. This process is mediated by the enzyme peptidyl arginine deiminase 4 (PADI4) and translocation of elastase to the nucleus. NET formation, marked by increased levels of extracellular DNA, promotes pancreatic cancer proliferation and metastasis. Mice deficient in Padi4 demonstrate decreased pancreatic tumor growth, associated with a reduction in circulating extracellular DNA levels, diminished pancreatic stromal activation and improved survival in murine orthotopic pancreatic adenocarcinoma. Transplantation of Padi4-/- bone marrow into genetically engineered mice with Kras driven pancreatic adenocarcinoma (Pdx1-Cre:KrasG12D/+, KC mice) limits the frequency of invasive cancers when compared with syngeneic controls. DNA from neutrophils activates pancreatic stellate cells that form dense, fibrous stroma which can promote and enable tumor proliferation. DNase treatment diminishes murine tumor growth and stromal activation to reverse the effect of NETs within the tumor microenvironment. Furthermore, deletion of the receptor for advanced glycation end products (RAGE) in pancreatic stellate cells abrogates the effects of DNA in promoting stellate cell proliferation and decreases tumor growth. Circulating neutrophil-derived DNA correlates with the stage in patients with pancreatic ductal adenocarcinoma, confirming the role of NETs in human pancreatic cancer. These findings support further investigation into targeting of NETs, PADI4 and extracellular DNA as a potential treatment strategy in patients with pancreatic cancer. Trial Registration: This study reports correlative data from a clinical trial registered with clinicaltrials.gov, NCT01978184 (November 7, 2013).

cGAS-STING responses are dampened in high-risk HPV type 16 positive head and neck squamous cell carcinoma cells

Head and neck cancers (HNCs) are a major health problem and a leading cause of morbidity and mortality worldwide. More than 90% of these tumours are head and neck squamous cell carcinomas (HNSCCs). Amongst the common risk factors for HNCs (tobacco and alcohol use), there is a strong association of human papillomavirus (HPV) with HNSCCs. HPV type 16 (HPV 16), the major high-risk HPV type, is most commonly associated with HPV-driven HNSCCs. The promiscuous nature of the major HPV oncogene, E7, allows its interaction with a myriad of host proteins including STING, a component of the viral DNA-sensing cyclic GMP-AMP synthase (cGAS) - stimulator of interferon genes (STING) machinery. Sensing of viral DNA by the cGAS-STING machinery results in a type I interferon (IFN)-mediated anti-viral response. Amelioration of IFN responses resulting from the direct blockade of STING by E7 was first demonstrated in high-risk HPV type 18 (HPV 18) positive (+) cervical squamous cell carcinoma (CESC) cells. However, the role of E7 from HPV 16 (HPV 16E7) in antagonising cGAS-STING responses have not been investigated, let alone in the context of HNSCCs. Here, we show that HPV 16E7+, but not HPV 16E7 negative (-), HNSCC cells respond poorly to cGAS-STING activation stimulus. We further confirm that this inhibition occurred via the highly conserved LXCXE motif in 16E7. This finding contributes to the better understanding of role of high-risk HPV E7 in blocking cGAS-STING pathway, especially in the context of HNSCCs.

Immunotherapy for Head and Neck Cancer

The immune system has a vital role in the development, establishment, and progression of head and neck squamous cell carcinoma (HNSCC). Immune evasion of cancer cells leads to progression of HNSCC. An understanding of this mechanism provides the basis for improved therapies and outcomes for patients. Through the tumor's influence on the microenvironment, the immune system can be exploited to promote metastasis, angiogenesis, and growth. This article provides an overview of the interaction between immune infiltrating cells in the tumor microenvironment, and the immunologic principles related to HNSCC. Current immunotherapeutic strategies and emerging results from ongoing clinical trials are presented.

Roles of the cGAS-STING Pathway in Cancer Immunosurveillance and Immunotherapy

Cyclic GMP-AMP synthase (cGAS) is a cytosolic DNA sensor that initiates innate immune responses. DNA-bound cGAS produces cyclic GMP-AMP (cGAMP), which activates stimulator of interferon genes (STING) to induce inflammatory cytokines and other immune mediators. cGAS detects DNA without sequence specificity and responds to both cytosolic foreign DNA from pathogens and self-DNA leaked into the cytosol due to genome instability or cellular damage. Because of the diverse sources of cytosolic DNA, the cGAS-STING pathway plays a critical role during infection, autoimmune diseases, and senescence. Moreover, cGAS detects tumor-derived DNA and stimulates endogenous antitumor immunity. Thus, the cGAS-STING pathway is a promising target for cancer immunotherapy. Here, we review the role of the cGAS-STING pathway in various diseases and highlight various approaches targeting the cGAS-STING pathway for cancer therapy.

Activating the Nucleic Acid-Sensing Machinery for Anticancer Immunity

Nucleic acid sensing pathways have likely evolved as part of a broad pathogen sensing strategy intended to discriminate infectious agents and initiate appropriate innate and adaptive controls. However, in the absence of infectious agents, nucleic acid sensing pathways have been shown to play positive and negative roles in regulating tumorigenesis, tumor progression and metastatic spread. Understanding the normal biology behind these pathways and how they are regulated in malignant cells and in the tumor immune environment can help us devise strategies to exploit nucleic acid sensing to manipulate anti-cancer immunity.

Evaluation of Explant Responses to STING Ligands: Personalized Immunosurgical Therapy for Head and Neck Squamous Cell Carcinoma

Surgeons have unique in situ access to tumors enabling them to apply immunotherapies to resection margins as a means to prevent local recurrence. Here, we developed a surgical approach to deliver stimulator of interferon genes (STING) ligands to the site of a purposeful partial tumor resection using a gel-based biomaterial. In a range of head and neck squamous cell carcinoma (HNSCC) murine tumor models, we demonstrate that although control-treated tumors recur locally, tumors treated with STING-loaded biomaterials are cured. The mechanism of tumor control required activation of STING and induction of type I IFN in host cells, not cancer cells, and resulted in CD8 T-cell-mediated cure of residual cancer cells. In addition, we used a novel tumor explant assay to screen individual murine and human HNSCC tumor responses to therapies ex vivo We then utilized this information to personalize the biomaterial and immunotherapy applied to previously unresponsive tumors in mice. These data demonstrate that explant assays identify the diversity of tumor-specific responses to STING ligands and establish the utility of the explant assay to personalize immunotherapies according to the local response.Significance: Delivery of immunotherapy directly to resection sites via a gel-based biomaterial prevents locoregional recurrence of head and neck squamous cell carcinoma. Cancer Res; 78(21); 6308-19. ©2018 AACR.

Correction: STING expression and response to treatment with STING ligands in premalignant and malignant disease

[This corrects the article DOI: 10.1371/journal.pone.0187532.].