Anti-metastatic functions of type 1 interferons: Foundation for the adjuvant therapy of cancer

Molecular and cellular factors determining the functional pleiotropy of cytokines

Cytokines are soluble factors vital for mammalian physiology. Cytokines elicit highly pleiotropic activities, characterized by their ability to induce a wide spectrum of functional responses in a diverse range of cell subsets, which makes their study very challenging. Cytokines activate signalling via receptor dimerization/oligomerization, triggering activation of the JAK (Janus kinase)/STAT (signal transducer and activator of transcription) signalling pathway. Given the strong crosstalk and shared usage of key components of cytokine signalling pathways, a long-standing question in the field pertains to how functional diversity is achieved by cytokines. Here, we discuss how biophysical - for example, ligand-receptor binding affinity and topology - and cellular - for example, receptor, JAK and STAT protein levels, endosomal compartment - parameters contribute to the modulation and diversification of cytokine responses. We review how these parameters ultimately converge into a common mechanism to fine-tune cytokine signalling that involves the control of the number of Tyr residues phosphorylated in the receptor intracellular domain upon cytokine stimulation. This results in different kinetics of STAT activation, and induction of specific gene expression programs, ensuring the generation of functional diversity by cytokines using a limited set of signalling intermediaries. We describe how these first principles of cytokine signalling have been exploited using protein engineering to design cytokine variants with more specific and less toxic responses for immunotherapy.

Genetic Influences in Cancer-Associated Myositis

Idiopathic inflammatory myopathies (IIMs) comprise a heterogeneous group of rare immune-mediated disorders that primarily affect muscles but also lead to dysfunction in other organs. Five different clinical subphenotypes of IIM have been distinguished: dermatomyositis, polymyositis, inclusion body myositis, antisynthetase syndrome, and immune-mediated necrotizing myopathy. Excess mortality and morbidity associated with IIM are largely attributed to comorbidities, particularly cancer. The risk of malignancy is not equally distributed among IIM groups and is particularly high among patients with dermatomyositis. The cancer risk peaks around 3 years on either side of the IIM diagnosis and remains elevated even 10 years after the onset of the disease. Lung, colorectal, and ovarian neoplasms typically arise before the onset of IIM, whereas melanoma, cervical, oropharyngeal, and nonmelanoma skin cancers usually develop after IIM diagnosis. Given the close temporal proximity between IIM diagnosis and the emergence of malignancy, it has been proposed that IIM could be a consequence rather than a cause of cancer, a process known as a paramalignant phenomenon. Thus, a separate group of IIMs related to paramalignant phenomenon has been distinguished, known as cancer-associated myositis (CAM). Although the relationship between IIM and cancer is widely recognized, the pathophysiology of CAM remains elusive. Given that genetic factors play a role in the development of IIM, dissection of the molecular mechanisms shared between IIM and cancer presents an opportunity to examine the role of autoimmunity in cancer development and progression. In this review, the evidence supporting the contribution of genetics to CAM will be discussed.

Serine-arginine splicing factor 2 promotes oesophageal cancer progression by regulating alternative splicing of interferon regulatory factor 3

OBJECTIVE

Often, alternative splicing is used by cancer cells to produce or increase proteins that promote growth and survival through alternative splicing. Although RNA-binding proteins are known to regulate alternative splicing events associated with tumorigenesis, their role in oesophageal cancer (EC) has rarely been explored.

METHODS

We analysed the expression pattern of several relatively well characterized splicing regulators on 183 samples from TCGA cohort of oesophageal cancer; the effectiveness of the knockdown of SRSF2 was subsequently verified by immunoblotting; we measured the ability of cells treated with lenti-sh-SRSF2/lenti-sh2-SRSF2 to invade through an extracellular matrix coating by transwell invasion assay; using RNA-seq data to identify its potential target genes; we performed qRT-PCR to detect the changes of exon 2 usage in lenti-sh-SRSF2 transduced KYSE30 cells to determine the possible effect of SRSF2 on splicing regulation of IRF3; RNA Electrophoretic mobility shift assay (RNA-EMSA) was performed by the incubation of purified SRSF2 protein and biotinylated RNA probes; we performed luciferase assay to confirm the effect of SRSF2 on IFN1 promoter activity.

RESULTS

We found upregulation of SRSF2 is correlated with the development of EC; Knock-down of SRSF2 inhibits EC cell proliferation, migration, and invasion; SRSF2 regulates the splicing pattern of IRF3 in EC cells; SRSF2 interacts with exon 2 of IRF3 to regulate its exclusion; SRSF2 inhibits the transcription of IFN1 in EC cells.

CONCLUSION

This study identified a novel regulatory axis involved in EC from the various aspects of splicing regulation.

The duality of STAT2 mediated type I interferon signaling in the tumor microenvironment and chemoresistance

The tumor microenvironment consists of tumor cells, extracellular matrix, blood vessels, and non-tumor cells such as fibroblasts and immune cells. Crosstalk among components of this cellular ecosystem can transform non-malignant cells and promote tumor invasion and metastasis. Evidence is accumulating that the transcription factor STAT2, a downstream effector of type I interferon (IFN-I) signaling, can either inhibit or promote tumorigenesis depending on the unique environment presented by each type of cancer. STAT2 has long been associated with the canonical JAK/STAT pathway involved in various biological processes including reshaping of the tumor microenvironment and in antitumor immunity. This dichotomous tendency of STAT2 to both inhibit and worsen tumor formation makes the protein a curious, and yet relatively ill-defined player in many cancer pathways involving IFN-I. In this review, we discuss the role of STAT2 in contributing to either a tumorigenic or anti-tumorigenic microenvironment as well as chemoresistance.

MACHETE identifies interferon-encompassing chromosome 9p21.3 deletions as mediators of immune evasion and metastasis

The most prominent homozygous deletions in cancer affect chromosome 9p21.3 and eliminate CDKN2A/B tumor suppressors, disabling a cell-intrinsic barrier to tumorigenesis. Half of 9p21.3 deletions, however, also encompass a type I interferon (IFN) gene cluster; the consequences of this co-deletion remain unexplored. To functionally dissect 9p21.3 and other large genomic deletions, we developed a flexible deletion engineering strategy, MACHETE (molecular alteration of chromosomes with engineered tandem elements). Applying MACHETE to a syngeneic mouse model of pancreatic cancer, we found that co-deletion of the IFN cluster promoted immune evasion, metastasis and immunotherapy resistance. Mechanistically, IFN co-deletion disrupted type I IFN signaling in the tumor microenvironment, leading to marked changes in infiltrating immune cells and escape from CD8+ T-cell surveillance, effects largely driven by the poorly understood interferon epsilon. These results reveal a chromosomal deletion that disables both cell-intrinsic and cell-extrinsic tumor suppression and provide a framework for interrogating large deletions in cancer and beyond.

Immunosuppressive lncRNA LINC00624 promotes tumor progression and therapy resistance through ADAR1 stabilization

BACKGROUND

Despite the success of HER2-targeted therapy in achieving prolonged survival in approximately 50% of treated individuals, treatment resistance is still an important challenge for HER2+ breast cancer (BC) patients. The influence of both adaptive and innate immune responses on the therapeutic outcomes of HER2+BC patients has been extensively demonstrated.

METHODS

Long non-coding RNAs expressed in non-pathological complete response (pCR) HER2 positive BC were screened and validated by RNA-seq. Survival analysis were made by Kaplan-Meier method. Cell death assay and proliferation assay were performed to confirm the phenotype of LINC00624. RT-qPCR and western blot were used to assay the IFN response. Xenograft mouse model were used for in vivo confirmation of anti-neu treatment resistance. RNA pull-down and immunoblot were used to confirm the interaction of ADAR1 and LINC00624. ADAR1 recombinant protein were purified from baculovirus expression system. B16-OVA cells were used to study antigen presentation both in vitro and in vivo. Flow cytometry was used to determine the tumor infiltrated immune cells of xenograft model. Antisense oligonucleotides (ASOs) were used for in vivo treatment.

RESULTS

In this study, we found that LINC00624 blocked the antitumor effect of HER2- targeted therapy both in vitro and in vivo by inhibiting type I interferon (IFN) pathway activation. The double-stranded RNA-like structure of LINC00624 can bind and be edited by the adenosine (A) to inosine (I) RNA-editing enzyme adenosine deaminase RNA specific 1 (ADAR1), and this editing has been shown to release the growth inhibition and attenuate the innate immune response caused by the IFN response. Notably, LINC00624 promoted the stabilization of ADAR1 by inhibiting its ubiquitination-induced degradation triggered by β-TrCP. In contrast, LINC00624 inhibited major histocompatibility complex (MHC) class I antigen presentation and limited CD8+T cell infiltration in the cancer microenvironment, resulting in immune checkpoint blockade inhibition and anti-HER2 treatment resistance mediated through ADAR1.

CONCLUSIONS

In summary, these results suggest that LINC00624 is a cancer immunosuppressive lncRNA and targeting LINC00624 through ASOs in tumors expressing high levels of LINC00624 has great therapeutic potential in future clinical applications.

Metastatic triple negative breast cancer adapts its metabolism to destination tissues while retaining key metabolic signatures

Despite recent therapeutic progress in cancer treatment, the metastatic establishment of cancers at distant organs remains the major cause of mortality in patients with solid tumors. The past decade has brought several advances in the understanding of metabolic phenotypes of tumors that are different from their adjacent nonmalignant tissues. Just recently, attention has been drawn to the fact that metastasizing tumor cells can display dynamic metabolic changes to survive in their changing microenvironment during the metastatic cascade. Here, we perform a comprehensive investigation of the extent of adaptation of metastatic triple negative breast cancer (TNBC) cells to their new microenvironment in the distant tissues. This study could reveal new therapeutic windows for developing more effective treatments of metastatic tumors.

Triple negative breast cancer (TNBC) metastases are assumed to exhibit similar functions in different organs as in the original primary tumor. However, studies of metastasis are often limited to a comparison of metastatic tumors with primary tumors of their origin, and little is known about the adaptation to the local environment of the metastatic sites. We therefore used transcriptomic data and metabolic network analyses to investigate whether metastatic tumors adapt their metabolism to the metastatic site and found that metastatic tumors adopt a metabolic signature with some similarity to primary tumors of their destinations. The extent of adaptation, however, varies across different organs, and metastatic tumors retain metabolic signatures associated with TNBC. Our findings suggest that a combination of anti-metastatic approaches and metabolic inhibitors selected specifically for different metastatic sites, rather than solely targeting TNBC primary tumors, may constitute a more effective treatment approach.

Antiviral Responses in Cancer: Boosting Antitumor Immunity Through Activation of Interferon Pathway in the Tumor Microenvironment

In recent years, it became apparent that cancers either associated with viral infections or aberrantly expressing endogenous retroviral elements (EREs) are more immunogenic, exhibiting an intense intra-tumor immune cell infiltration characterized by a robust cytolytic apparatus. On the other hand, epigenetic regulation of EREs is crucial to maintain steady-state conditions and cell homeostasis. In line with this, epigenetic disruptions within steady-state cells can lead to cancer development and trigger the release of EREs into the cytoplasmic compartment. As such, detection of viral molecules by intracellular innate immune sensors leads to the production of type I and type III interferons that act to induce an antiviral state, thus restraining viral replication. This knowledge has recently gained momentum due to the possibility of triggering intratumoral activation of interferon responses, which could be used as an adjuvant to elicit strong anti-tumor immune responses that ultimately lead to a cascade of cytokine production. Accordingly, several therapeutic approaches are currently being tested using this rationale to improve responses to cancer immunotherapies. In this review, we discuss the immune mechanisms operating in viral infections, show evidence that exogenous viruses and endogenous retroviruses in cancer may enhance tumor immunogenicity, dissect the epigenetic control of EREs, and point to interferon pathway activation in the tumor milieu as a promising molecular predictive marker and immunotherapy target. Finally, we briefly discuss current strategies to modulate these responses within tumor tissues, including the clinical use of innate immune receptor agonists and DNA demethylating agents.

Antitumor activity of novel POLA1-HDAC11 dual inhibitors

Hybrid molecules targeting simultaneously DNA polymerase α (POLA1) and histone deacetylases (HDACs) were designed and synthesized to exploit a potential synergy of action. Among a library of screened molecules, MIR002 and GEM144 showed antiproliferative activity at nanomolar concentrations on a panel of human solid and haematological cancer cell lines. In vitro functional assays confirmed that these molecules inhibited POLA1 primer extension activity, as well as HDAC11. Molecular docking studies also supported these findings. Mechanistically, MIR002 and GEM144 induced acetylation of p53, activation of p21, G1/S cell cycle arrest, and apoptosis. Oral administration of these inhibitors confirmed their antitumor activity in in vivo models. In human non-small cancer cell (H460) xenografted in nude mice MIR002 at 50 mg/kg, Bid (qd × 5 × 3w) inhibited tumor growth (TGI = 61%). More interestingly, in POLA1 inhibitor resistant cells (H460-R9A), the in vivo combination of MIR002 with cisplatin showed an additive antitumor effect with complete disappearance of tumor masses in two animals at the end of the treatment. Moreover, in two human orthotopic malignant pleural mesothelioma xenografts (MM473 and MM487), oral treatments with MIR002 and GEM144 confirmed their significant antitumor activity (TGI = 72-77%). Consistently with recent results that have shown an inverse correlation between POLA1 expression and type I interferon levels, MIR002 significantly upregulated interferon-α in immunocompetent mice.

Induction of interferon signaling and allograft inflammatory factor 1 in macrophages in a mouse model of breast cancer metastases

Background: Metastatic breast cancer cells recruit macrophages (metastasis-associated macrophages, or MAMs) to facilitate their seeding, survival and outgrowth. However, a comprehensive understanding of the gene expression program in MAMs and how this program contributes to metastasis remain elusive. Methods: We compared the transcriptomes of MAMs recruited to lung metastases and resident alveolar macrophages (RAMs) and identified a large variety of differentially expressed genes and their associated signaling pathways. Some of the changes were validated using qRT-PCR and immunofluorescence. To probe the functional relevance to metastatic growth, a gene-targeting mouse model of female mice in the C57BL6/J background was used to study allograft inflammatory factor 1 (AIF1, also known as ionized calcium-binding adapter molecule 1 or IBA1). Results: Interferon signaling is one of the most activated pathways in MAMs, with strong upregulation of multiple components of the pathway and a significant enrichment for the gene signatures of interferon-alpha-treated human macrophages. Aif1, an interferon-responsive gene that regulates multiple macrophage activities, was robustly induced in MAMs. Aif1 deficiency in MAMs, however, did not affect development of lung metastases, suggesting that AIF1 indicates MAM activation but is dispensable for regulating metastasis. Conclusions: The drastically different gene expression profile of MAMs as compared to RAMs suggests an important role in promoting metastatic growth. Dissection of the underlying mechanisms and functional validation of potential targets in the profile may provide novel therapeutic strategies for the treatment of metastatic diseases.

Extracellular vesicles in cancer progression

Cancer cells release a variety of factors that contribute to the alteration of proximal and distal tissues to promote metastasis. Recent studies have demonstrated that aggressive cancer cells release extracellular vesicles with higher protein content and in excess than extracellular vesicles isolated from patients with less aggressive disease or healthy individuals. We found that melanoma tumor-derived extracellular vesicles (TEV) downregulate type I interferon receptor subunit 1 (IFNAR1), suppress expression of the interferon stimulated gene cholesterol 25-hydroxylase (CH25H). Loss of CH25H is observed in the leukocytes from melanoma patients, which correlated with metastasis and poor survival. Similarly, mice also exhibit loss of IFNAR1 following TEV administration. Moreover, loss of CH25H increased TEV uptake and TEV-induced pre metastatic niche and lung metastasis. Use of the anti-hypertensive drug, reserpine, mimicked the effects of the CH25H product 25-hydroxycholesterol to suppress TEV uptake and TEV-mediated tumor growth, pre-metastatic niche formation, and lung metastasis. These results suggest the importance of CH25H in suppressing TEV mediate cancer progression and importance of developing strategies to suppress TEV uptake and TEV-mediated disease progression.

Induction of interferon signaling and allograft inflammatory factor 1 in macrophages in a mouse model of breast cancer metastases

Background: Metastatic breast cancer cells recruit macrophages (metastasis-associated macrophages, or MAMs) to facilitate their seeding, survival and outgrowth. However, a comprehensive understanding of the gene expression program in MAMs and how this program contributes to metastasis remain elusive. Methods: We compared the transcriptomes of MAMs recruited to lung metastases and resident alveolar macrophages (RAMs) and identified a large variety of differentially expressed genes and their associated signaling pathways. Some of the changes were validated using qRT-PCR and immunofluorescence. To probe the functional relevance to metastatic growth, a gene-targeting mouse model of female mice in the C57BL6/J background was used to study allograft inflammatory factor 1 (AIF1, also known as ionized calcium-binding adapter molecule 1 or IBA1). Results: Interferon signaling is one of the most activated pathways in MAMs, with strong upregulation of multiple components of the pathway and a significant enrichment for the gene signatures of interferon-alpha-treated human macrophages. Aif1, an interferon-responsive gene that regulates multiple macrophage activities, was robustly induced in MAMs. Aif1 deficiency in MAMs, however, did not affect development of lung metastases, suggesting that AIF1 indicates MAM activation but is dispensable for regulating metastasis. Conclusions: The drastically different gene expression profile of MAMs as compared to RAMs suggests an important role in promoting metastatic growth. Dissection of the underlying mechanisms and functional validation of potential targets in the profile may provide novel therapeutic strategies for the treatment of metastatic diseases.

MAP3K7 and CHD1 Are Novel Mediators of Resistance to Oncolytic Vesicular Stomatitis Virus in Prostate Cancer Cells

A key principle of oncolytic viral therapy is that many cancers develop defects in their antiviral responses, making them more susceptible to virus infection. However, some cancers display resistance to viral infection. Many of these resistant cancers constitutively express interferon-stimulated genes (ISGs). The goal of these experiments was to determine the role of two tumor suppressor genes, MAP3K7 and CHD1, in viral resistance and ISG expression in PC3 prostate cancer cells resistant to oncolytic vesicular stomatitis virus (VSV). MAP3K7 and CHD1 are often co-deleted in aggressive prostate cancers. Silencing expression of MAP3K7 and CHD1 in PC3 cells increased susceptibility to the matrix (M) gene mutant M51R-VSV, as shown by increased expression of viral genes, increased yield of progeny virus, and reduction of tumor growth in nude mice. Silencing MAP3K7 alone had a greater effect on virus susceptibility than did silencing CHD1. Silencing MAP3K7 and CHD1 decreased constitutive expression of ISG mRNAs and proteins, whereas silencing MAP3K7 alone decreased expression of ISG proteins, but actually increased expression of ISG mRNAs. These results suggest a role for the protein product of MAP3K7, transforming growth factor β-activated kinase 1 (TAK1), in regulating translation of ISG mRNAs and a role of CHD1 in maintaining the transcription of ISGs.

Combining Radiation Therapy With Interferons: Back to the Future

Radiation therapy has been linked to the induction of an intratumoral type I interferon (IFN) response, which positively affects the response to treatment. This has spiked the interest to combine radiation therapy with IFN-based treatment. Interestingly, this combination treatment has been considered previously, since preclinical studies demonstrated a radiosensitizing effect of interferons. As a result, multiple clinical trials have been performed combining radiation therapy with interferons in different tumor types. Although potential benefit has been suggested, the outcomes of the trials are diverse and challenging to interpret. In addition, increased grade ≥3 toxicity frequently resulted in a negative recommendation regarding the combination therapy. The latter appears premature because many studies were small and several aspects of the combination treatment have not yet been sufficiently explored to justify such a definite conclusion. This review summarizes the available literature on this combination therapy, with a focus on IFN-α and IFN-β. Based on preclinical studies and clinical trials, we evaluated the potential opportunities and describe the current challenges. In addition, we identify several issues that should be addressed to fully exploit the potential benefit of this combinatorial treatment approach.

Interferons α and β in cancer: therapeutic opportunities from new insights

Over the past decade, preclinical and clinical research have confirmed the essential role of interferons for effective host immunological responses to malignant cells. Type I interferons (IFNα and IFNβ) directly regulate transcription of >100 downstream genes, which results in a myriad of direct (on cancer cells) and indirect (through immune effector cells and vasculature) effects on the tumour. New insights into endogenous and exogenous activation of type I interferons in the tumour and its microenvironment have given impetus to drug discovery and patient evaluation of interferon-directed strategies. When combined with prior observations or with other effective modalities for cancer treatment, modulation of the interferon system could contribute to further reductions in cancer morbidity and mortality. This Review discusses new interferon-directed therapeutic opportunities, ranging from cyclic dinucleotides to genome methylation inhibitors, angiogenesis inhibitors, chemoradiation, complexes with neoantigen-targeted monoclonal antibodies, combinations with other emerging therapeutic interventions and associations of interferon-stimulated gene expression with patient prognosis - all of which are strategies that have or will soon enter translational clinical evaluation.

Serum proteomic analysis of melanoma patients with immunohistochemical profiling of primary melanomas and cultured cells: Pilot study

The steadily increasing incidence of malignant melanoma (MM) and its aggressive behaviour makes this tumour an attractive cancer research topic. The tumour microenvironment is being increasingly recognised as a key factor in cancer biology, with an impact on proliferation, invasion, angiogenesis and metastatic spread, as well as acquired therapy resistance. Multiple bioactive molecules playing cooperative roles promote the chronic inflammatory milieu in tumours, making inflammation a hallmark of cancer. This specific inflammatory setting is evident in the affected tissue. However, certain mediators can leak into the systemic circulation and affect the whole organism. The present study analysed the complex inflammatory response in the sera of patients with MM of various stages. Multiplexed proteomic analysis (Luminex Corporation) of 31 serum proteins was employed. These targets were observed in immunohistochemical profiles of primary tumours from the same patients. Furthermore, these proteins were analysed in MM cell lines and the principal cell population of the melanoma microenvironment, cancer‑associated fibroblasts. Growth factors such as hepatocyte growth factor, granulocyte‑colony stimulating factor and vascular endothelial growth factor, chemokines RANTES and interleukin (IL)‑8, and cytokines IL‑6, interferon‑α and IL‑1 receptor antagonist significantly differed in these patients compared with the healthy controls. Taken together, the results presented here depict the inflammatory landscape that is altered in melanoma patients, and highlight potentially relevant targets for therapy improvement.

My journey from tyrosine phosphorylation inhibitors to targeted immune therapy as strategies to combat cancer

Since the 1980s there has been a drive toward personalized targeted therapy for cancer. "Targeted cancer therapy" originally focused on inhibiting essential tumor survival factors, primarily protein tyrosine kinases. The complexity and rapid mutability of tumors, however, enable them to develop resistance to tyrosine kinase inhibitors (TKIs), even when these are multitargeted or applied in combination. This has led to the development of targeted cancer immunotherapy, to enhance immune surveillance against the tumor. In this paper, we provide a personal view of the development of targeted therapy, from TKIs to targeted immunotherapy.

The PKR-Like Endoplasmic Reticulum Kinase Promotes the Dissemination of Myc-Induced Leukemic Cells

Hyperactive oncogenic Myc stimulates protein synthesis that induces the unfolded protein response, which requires the function of the eukaryotic translation initiation factor 2-alpha kinase 3, also known as protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK). Activated PERK acts to limit mRNA translation, enable proper protein folding, and restore the homeostasis in the endoplasmic reticulum. Given that Myc activation contributes to many types of lymphoid and myeloid human leukemias, we used a mouse model to examine the importance of PERK in development and progression of Myc-induced leukemias. We found that genetic ablation of Perk does not suppress the generation of the leukemic cells in the bone marrow. However, the cell-autonomous Perk deficiency restricts the dissemination of leukemic cells into peripheral blood, lymph nodes, and vital peripheral organs. Whereas the loss of the IFNAR1 chain of type I IFN receptor stimulated leukemia, Perk ablation did not stabilize IFNAR1, suggesting that PERK stimulates the leukemic cells' dissemination in an IFNAR1-independent manner. We discuss the rationale for using PERK inhibitors against Myc-driven leukemias. IMPLICATIONS: The role of PERK in dissemination of Myc-induced leukemic cells demonstrated in this study argues for the use of PERK inhibitors against leukemia progression.

STAT5 expression correlates with recurrence and survival in melanoma patients treated with interferon-α

Interferons (IFN) have a direct growth-inhibiting effect on tumor cells through Janus kinase-dependent activation of the transcription factor signal transducer and activator of transcription (STAT1). In vitro, signaling through STAT5 has been demonstrated to counteract this effect and lead to IFN resistance of melanoma cell lines. In 32 patients treated with IFN-α in an adjuvant setting, we investigated paraffin-embedded tumor tissue from primary melanomas and melanoma metastases for expression of STAT3 and STAT5, by immunohistochemistry, and for expression of phosphorylated signaling transduction activating transcription factor (pSTAT)3 and pSTAT5, by immunofluorescence. Tumor cell expression levels of these proteins were correlated with patient characteristics and clinical outcomes. The patient cohort consisted of 12 (37.5%) patients at AJCC stage I/II (primary melanoma) and 20 (62.5%) at stage III/IV (metastatic melanoma). Recurrence was observed for 25 (78.1%) either during or after IFN-α therapy. χ Correlation of staining intensities with clinical data revealed association of pSTAT3 and STAT5 expression with sex (P=0.003 and 0.016, respectively) and of STAT3 with tumor stage (P=0.019). Recurrence of melanoma was found to be associated with high STAT5 expression (P=0.017). Multivariable regression analysis revealed STAT5 expression as an independent factor for predicting progression-free survival (P<0.0001) and overall survival (P=0.022). In summary, high expression of STAT5 correlated with melanoma recurrence and survival of patients treated with IFN-α in the adjuvant setting. Recently, it has been suggested that mutations of Janus kinases are involved in resistance to immune checkpoint blocker treatments implying a possible role of STAT5 for immune checkpoint resistance.

STING agonist therapy in combination with PD-1 immune checkpoint blockade enhances response to carboplatin chemotherapy in high-grade serous ovarian cancer

Background

High-grade serous carcinoma (HGSC) of the ovary is predominantly diagnosed at late stages and primarily treated with debulking surgery followed by platinum/taxane-based chemotherapy. Although certain patients benefit significantly from currently used chemotherapy, there are patients who either do not respond or have an inadequate duration of response. We previously showed that tumours from chemoresistant patients have an immunosuppressed pre-existing tumour immune microenvironment with decreased expression of Type I Interferon (IFN1) genes.

Methods

Efficacy of a ‘STimulator of INterferon Genes’ agonist was evaluated in combination with carboplatin chemotherapy and PD-1 immune checkpoint blockade therapy in the ID8-Trp53^−/− immunocompetent murine model of HGSC.

Results

Treatment with STING agonist led to decreased ascites accumulation and decreased tumour burden. Survival of mice treated with a combination of carboplatin, STING agonist and anti-PD-1 antibody was the longest. Tumour immune transcriptomic profiling revealed higher IFN response, antigen presentation and MHC II genes in tumours from STING agonist-treated mice compared to vehicle controls. Flow cytometry analysis revealed significantly higher intra-tumoural PD-1⁺ and CD69⁺CD62L⁻, CD8⁺ T cells in STING agonist-treated mice.

Conclusions

These findings will enable rational design of clinical trials aimed at combinatorial approaches to improve chemotherapy response and survival in HGSC patients.

Suppression of Transposable Elements in Leukemic Stem Cells

Genomic transposable elements (TEs) comprise nearly half of the human genome. The expression of TEs is considered potentially hazardous, as it can lead to insertional mutagenesis and genomic instability. However, recent studies have revealed that TEs are involved in immune-mediated cell clearance. Hypomethylating agents can increase the expression of TEs in cancer cells, inducing ‘viral mimicry’, causing interferon signalling and cancer cell killing. To investigate the role of TEs in the pathogenesis of acute myeloid leukaemia (AML), we studied TE expression in several cell fractions of AML while tracking its development (pre-leukemic haematopoietic stem cells, leukemic stem cells [LSCs], and leukemic blasts). LSCs, which are resistant to chemotherapy and serve as reservoirs for relapse, showed significant suppression of TEs and interferon pathways. Similarly, high-risk cases of myelodysplastic syndrome (MDS) showed far greater suppression of TEs than low-risk cases. We propose TE suppression as a mechanism for immune escape in AML and MDS. Repression of TEs co-occurred with the upregulation of several genes known to modulate TE expression, such as RNA helicases and autophagy genes. Thus, we have identified potential pathways that can be targeted to activate cancer immunogenicity via TEs in AML and MDS.

A Novel Agonist of the TRIF Pathway Induces a Cellular State Refractory to Replication of Zika, Chikungunya, and Dengue Viruses

The ongoing concurrent outbreaks of Zika, Chikungunya, and dengue viruses in Latin America and the Caribbean highlight the need for development of broad-spectrum antiviral treatments. The type I interferon (IFN) system has evolved in vertebrates to generate tissue responses that actively block replication of multiple known and potentially zoonotic viruses. As such, its control and activation through pharmacological agents may represent a novel therapeutic strategy for simultaneously impairing growth of multiple virus types and rendering host populations resistant to virus spread. In light of this strategy's potential, we undertook a screen to identify novel interferon-activating small molecules. Here, we describe 1-(2-fluorophenyl)-2-(5-isopropyl-1,3,4-thiadiazol-2-yl)-1,2-dihydrochromeno[2,3-c]pyrrole-3,9-dione, which we termed AV-C. Treatment of human cells with AV-C activates innate and interferon-associated responses that strongly inhibit replication of Zika, Chikungunya, and dengue viruses. By utilizing genome editing, we investigated the host proteins essential to AV-C-induced cellular states. This showed that the compound requires a TRIF-dependent signaling cascade that culminates in IFN regulatory factor 3 (IRF3)-dependent expression and secretion of type I interferon to elicit antiviral responses. The other canonical IRF3-terminal adaptor proteins STING and IPS-1/MAVS were dispensable for AV-C-induced phenotypes. However, our work revealed an important inhibitory role for IPS-1/MAVS, but not TRIF, in flavivirus replication, implying that TRIF-directed viral evasion may not occur. Additionally, we show that in response to AV-C, primary human peripheral blood mononuclear cells secrete proinflammatory cytokines that are linked with establishment of adaptive immunity to viral pathogens. Ultimately, synthetic innate immune activators such as AV-C may serve multiple therapeutic purposes, including direct antimicrobial responses and facilitation of pathogen-directed adaptive immunity.IMPORTANCE The type I interferon system is part of the innate immune response that has evolved in vertebrates as a first line of broad-spectrum immunological defense against an unknowable diversity of microbial, especially viral, pathogens. Here, we characterize a novel small molecule that artificially activates this response and in so doing generates a cellular state antagonistic to growth of currently emerging viruses: Zika virus, Chikungunya virus, and dengue virus. We also show that this molecule is capable of eliciting cellular responses that are predictive of establishment of adaptive immunity. As such, this agent may represent a powerful and multipronged therapeutic tool to combat emerging and other viral diseases.