Suppression Of Antitumor Immune Responses Research Articles

Regulatory T Cells in Cancer

The immune system has evolved complex effector mechanisms to protect the host against a diversity of pathogenic organisms and regulatory adaptations that can curtail pathological sequelae of inflammatory events, prevent autoimmunity, and assist in tissue repair. Cancers, by virtue of their local manifestations of tissue dysfunction and destruction, inflammation, and genomic instability, can evoke these protective mechanisms, which support the progression of tumors and prevent their immune eradication. Central to these processes is a subset of CD4+T cells, known as regulatory T (Treg) cells, that express the X chromosome–linked transcription factor FOXP3. In addition to their critical role in controlling autoimmunity and suppressing inflammatory responses in diverse biological settings, Treg cells are ubiquitously present in the tumor microenvironment where they promote tumor development and progression by dampening antitumor immune responses. Furthermore, Treg cells can directly support the survival of transformed cells through the elaboration of growth factors and interacting with accessory cells in tumors such as fibroblasts and endothelial cells. Current insights into the biology of tumor-associated Treg cells have opened up opportunities for their selective targeting in cancer, with the goal of alleviating their suppression of antitumor immune responses while maintaining overall immune homeostasis.

Targeting of immunosuppressive myeloid cells from glioblastoma patients by modulation of size and surface charge of lipid nanocapsules

BackgroundMyeloid derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) are two of the major players involved in the inhibition of anti-tumor immune response in cancer patients, leading to poor prognosis. Selective targeting of myeloid cells has therefore become an attractive therapeutic strategy to relieve immunosuppression and, in this frame, we previously demonstrated that lipid nanocapsules (LNCs) loaded with lauroyl-modified gemcitabine efficiently target monocytic MDSCs in melanoma patients. In this study, we investigated the impact of the physico-chemical characteristics of LNCs, namely size and surface potential, towards immunosuppressive cell targeting. We exploited myeloid cells isolated from glioblastoma patients, which play a relevant role in the immunosuppression, to demonstrate that tailored nanosystems can target not only tumor cells but also tumor-promoting cells, thus constituting an efficient system that could be used to inhibit their function.ResultsThe incorporation of different LNC formulations with a size of 100 nm, carrying overall positive, neutral or negative charge, was evaluated on leukocytes and tumor-infiltrating cells freshly isolated from glioblastoma patients. We observed that the maximum LNC uptake was obtained in monocytes with neutral 100 nm LNCs, while positively charged 100 nm LNCs were more effective on macrophages and tumor cells, maintaining at low level the incorporation by T cells. The mechanism of uptake was elucidated, demonstrating that LNCs are incorporated mainly by caveolae-mediated endocytosis.ConclusionsWe demonstrated that LNCs can be directed towards immunosuppressive cells by simply modulating their size and charge thus providing a novel approach to exploit nanosystems for anticancer treatment in the frame of immunotherapy.

Sympathetic improvement of cancer vaccine efficacy

ABSTRACT The link between stress, other psychological factors and response to cancer, or even the cancer incidence and metastasis, is well established. The inhibition of β-Adrenergic receptors (β-AR) using β-blockers was demonstrated to have an inhibitory effect on cancer recurrence. Direct effects on the stress-induced suppression of anti-tumor immune responses were also shown. In a recent issue of Cancer Immunology Research, Daher and colleagues studied the molecular mechanism behind this protective effect in the context of cancer vaccination. They provided evidence that the β-AR signaling affected the priming of naïve CD8 + T cells in their myeloma model, rather than effector CD8 + T cells which downregulated the expression of β-AR after activation and became insensitive to such signaling. Blocking the β-adrenergic signaling during vaccination led to increased expansion and effector functions of antigen-specific CD8 + T cells and reduced tumor growth. This has implications for the clinical use of β-blockers as adjuvants to enhance cancer vaccination and other types of immunotherapy.

Abstract C132: Fusobacterium nucleatum in colorectal carcinoma and expression of multiple immune checkpoint molecules on T cells

Abstract Background: Fusobacterium nucleatum (Fn) appears to play a role in colorectal cancer carcinogenesis through suppression of antitumor immune response. This study aims to characterize immune-related signatures, including the expression of multiple immune checkpoint molecules in tumor-infiltrating T cells. Methods: We measured Fn DNA by quantitative PCR in a total of 155 colorectal cancer tissues. Gene expression profile was studied using microarray technology to determine the consensus molecular subtypes (CMS) and immune-related signatures using CIBERSORT and Gene Set Enrichment Analysis (GSEA), respectively. Expression of immune checkpoint molecules (PD-1, TIM-3, and TIGIT) on CD8+ cytotoxic T cells and the ratio of FOXP3-CD4-/FOXP3+CD4 were examined using multicolor flow cytometric analysis. Results: All patients had stage III disease underwent curative surgery. Fn infection was observed in 43% of patients and was associated with recurrence (Fisher’ exact test, P=0.002) and decreased overall survival (log-rank test, P<0.001). The distribution of CMS subtypes was CMS1/2/3/4/mixed (14%/24%/15%/27%/20%), which is comparable to previous data. Fn infection was associated with the platinum-resistant signature, hypoxia pathway, and stem cell pathways in the GSEA. Interestingly, Patients with Fn infection showed a trend toward enrichment in CMS4, mesenchymal subtype with the inflamed immune phenotype (9% vs. 17% with Fn-infection, P=0.24). The number of cytotoxic CD8+ T cells showed a trend toward decreased expression in patients with Fn infection. Furthermore, higher expression of inhibitory immune checkpoints (PD-1, P<0.01; TIM-3, P<0.05; TIGIT, P<0.05) was observed on CD8+ cytotoxic T cells of patients with Fn infection, compared to that of Fn negative cases. Besides, the regulatory FOXP3+CD4+ cells were increased in patients with Fn infection, supporting the suppressive role of Fn infection in the tumor immune microenvironment (P<0.05). Conclusions: The adverse prognostic impact of Fn infection depends on the suppression of T cell-mediated immune response by increased expression of inhibitory immune checkpoints on cytotoxic T cell and by increased regulatory T cells. Citation Format: Han Sang Kim, Wonkyu Kim, Chang Gon Kim, Jinseon Yoo, Soonmyung Paik, Eui-Cheol Shin, Tae-Min Kim, Hoguen Kim, Joong Bae Ahn. Fusobacterium nucleatum in colorectal carcinoma and expression of multiple immune checkpoint molecules on T cells [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C132. doi:10.1158/1535-7163.TARG-19-C132

Chemotherapy-Induced Tumor Cell Death at the Crossroads Between Immunogenicity and Immunotolerance: Focus on Acute Myeloid Leukemia.

In solid tumors and hematological malignancies, including acute myeloid leukemia, some chemotherapeutic agents, such as anthracyclines, have proven to activate an immune response via dendritic cell-based cross-priming of anti-tumor T lymphocytes. This process, known as immunogenic cell death, is characterized by a variety of tumor cell modifications, i.e., cell surface translocation of calreticulin, extracellular release of adenosine triphosphate and pro-inflammatory factors, such as high mobility group box 1 proteins. However, in addition to with immunogenic cell death, chemotherapy is known to induce inflammatory modifications within the tumor microenvironment, which may also elicit immunosuppressive pathways. In particular, DCs may be driven to acquire tolerogenic features, such as the overexpression of indoleamine 2,3-dioxygensase 1, which may ultimately hamper anti-tumor T-cells via the induction of T regulatory cells. The aim of this review is to summarize the current knowledge about the mechanisms and effects by which chemotherapy results in both activation and suppression of anti-tumor immune response. Indeed, a better understanding of the whole process underlying chemotherapy-induced alterations of the immunological tumor microenvironment has important clinical implications to fully exploit the immunogenic potential of anti-leukemia agents and tune their application.

PD-1+ regulatory T cells amplified by PD-1 blockade promote hyperprogression of cancer

PD-1 blockade is a cancer immunotherapy effective in various types of cancer. In a fraction of treated patients, however, it causes rapid cancer progression called hyperprogressive disease (HPD). With our observation of HPD in ∼10% of anti-PD-1 monoclonal antibody (mAb)-treated advanced gastric cancer (GC) patients, we explored how anti-PD-1 mAb caused HPD in these patients and how HPD could be treated and prevented. In the majority of GC patients, tumor-infiltrating FoxP3highCD45RA-CD4+ T cells [effector Treg (eTreg) cells], which were abundant and highly suppressive in tumors, expressed PD-1 at equivalent levels as tumor-infiltrating CD4+ or CD8+ effector/memory T cells and at much higher levels than circulating eTreg cells. Comparison of GC tissue samples before and after anti-PD-1 mAb therapy revealed that the treatment markedly increased tumor-infiltrating proliferative (Ki67+) eTreg cells in HPD patients, contrasting with their reduction in non-HPD patients. Functionally, circulating and tumor-infiltrating PD-1+ eTreg cells were highly activated, showing higher expression of CTLA-4 than PD-1- eTreg cells. PD-1 blockade significantly enhanced in vitro Treg cell suppressive activity. Similarly, in mice, genetic ablation or antibody-mediated blockade of PD-1 in Treg cells increased their proliferation and suppression of antitumor immune responses. Taken together, PD-1 blockade may facilitate the proliferation of highly suppressive PD-1+ eTreg cells in HPDs, resulting in inhibition of antitumor immunity. The presence of actively proliferating PD-1+ eTreg cells in tumors is therefore a reliable marker for HPD. Depletion of eTreg cells in tumor tissues would be effective in treating and preventing HPD in PD-1 blockade cancer immunotherapy.

Beta-Adrenergic Signaling in Tumor Immunology and Immunotherapy.

Communication between the nervous and immune systems is required for the body to regulate physiological homeostasis. Beta-adrenergic receptors expressed on immune cells mediate the modulation of immune response by neural activity. Activation of beta-adrenergic signaling results in suppression of antitumor immune response and limits the efficacy of cancer immunotherapy. Beta-adrenergic signaling is also involved in regulation of hematopoietic reconstitution, which is critical to the graft-versus-tumor (GVT) effect and to graft-versus-host disease (GVHD) following allogeneic hematopoietic cell transplantation (HCT). In this review, the function of beta-adrenergic signaling in mediating tumor immunosuppression will be highlighted. We will also discuss the implication of targeting beta-adrenergic signaling to improve the efficacy of cancer immunotherapy including the GVT effect, and to diminish the adverse effects including GVHD.

Notch and NF-κB: Coach and Players of Regulatory T-Cell Response in Cancer.

The Notch signaling pathway plays multiple roles in driving T-cell fate decisions, proliferation, and aberrant growth. NF-κB is a cell-context key player interconnected with Notch signaling either in physiological or in pathological conditions. This review focuses on how the multilayered crosstalk between different Notches and NF-κB subunits may converge on Foxp3 gene regulation and orchestrate CD4+ regulatory T (Treg) cell function, particularly in a tumor microenvironment. Notably, Treg cells may play a pivotal role in the inhibition of antitumor immune responses, possibly promoting tumor growth. A future challenge is represented by further dissection of both Notch and NF-κB pathways and consequences of their intersection in tumor-associated Treg biology. This may shed light on the molecular mechanisms regulating Treg cell expansion and migration to peripheral lymphoid organs thought to facilitate tumor development and still to be explored. In so doing, new opportunities for combined and/or more selective therapeutic approaches to improve anticancer immunity may be found.

Abstract LB-118: A conserved checkpoint molecule signature offers novel targets for tumor specific regulatory T cell manipulation

Abstract Regulatory T (Treg) cells play an important role in modulating the tumor microenvironment, leading to the suppression of anti-tumor immune responses. Tumor Tregs could be targeted by taking advantage of the differential expression of immune checkpoints on these cells as compared to other T cell subsets. While the elevated expression of checkpoints such as CTLA-4 on Tregs compared to conventional T cells is well-characterized, less is known about the collective landscape of Treg specific checkpoint expression specific in the tumor microenvironment. We identified a network of Treg-associated checkpoint markers including those previously associated with Treg function (CTLA4, ICOS) as well as several additional checkpoints (BTLA, LAG3, TIGIT, TNFRSF9) by characterizing the expression of 28 checkpoint molecules across 7,608 bulk tumor samples (31 tumor types) from TCGA. We then utilized whole transcriptome RNA sequencing of purified peripheral and tumor Treg cell populations across 4 different tumor types (glioblastoma multiforme, prostatic adenocarcinoma, urothelial transitional cell carcinoma, renal clear cell carcinoma) to characterize the Treg specific expression of checkpoint molecules. Peripheral and tumor Tregs demonstrate differential checkpoint expression landscapes, with tumor Tregs uniquely discriminated by collective expression of TNFRSF9 (4-1BB), HAVCR-2 (TIM-3), and LAG-3. This discriminatory signature was conserved across the 4 profiled tumor types, was associated with changes in Treg biology, and was confirmed in published data from three additional cancer cohorts (breast, colorectal, and non-small-cell-lung cancers). Furthermore, normalized TNFRSF9 expression in TCGA was also associated with a worse survival outcome, suggesting that elevated Treg TNFRSF9 expression may be a poor prognostic factor across a wide range of tumors. Taken together, these data highlight the potential of targeting TNFRSF9 expressing Tregs in the tumor as a novel immunotherapeutic approach for several types of cancer. Citation Format: Zachary T. Freeman, Daniel H. Hovleson, Alexander T. Pearson, Jingyi Zhai, Ali Ghasemzadeh, Thomas R. Nirschl, Hui Jiang, Scott A. Tomlins, Charles G. Drake. A conserved checkpoint molecule signature offers novel targets for tumor specific regulatory T cell manipulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-118.

Abstract 3783: Mitochondrial metabolism in tumor-associated macrophages: The role of MIF and tumor-derived lactate

Abstract Purpose: Within the tumor microenvironment, tumor-associated macrophages (TAMs) polarized to an "M2" phenotype promote angiogenesis, metastasis, and the suppression of anti-tumor immune responses. Previously, we have found that macrophage migration inhibitory factor (MIF) promotes lactate-enhanced M2-polarization, however the underlying mechanisms were not elucidated. As cancer cells that exhibit the Warburg Effect secrete copious amounts of lactate into the tumor microenvironment, highly glycolytic cancers may promote tumor progression by producing lactate to support an immunosuppressive tumor microenvironment. The goal of this study is to investigate the mechanism by which MIF and tumor-derived lactate support pro-tumorigenic M2-TAMs. Methods: Using primary bone marrow-derived macrophages (BMDMs), we explored the mechanisms of MIF and lactate-enhanced M2 polarization using metabolic inhibitors and gene expression assays. To investigate the role of MIF in mitochondrial metabolism, we conducted extracellular flux analysis to determine mitochondrial OCR and ECAR in macrophages polarized to an M0 and M2 phenotype. Results: Blocking mitochondrial pyruvate uptake reduces both M2 polarization and HIF1α stabilization. Blocking mitochondrial metabolism and respiration inhibits M2 polarization. MIF deficiency decreases mitochondrial OCR, NRF2 stability, and M2 polarization. Increasing CSN5 activity "rescues" the loss of M2 polarization with MIF deficiency. Conclusions: Tumor-derived lactate per se does not promote M2 polarization but instead requires subsequent metabolism to pyruvate. Additionally, we have identified that mitochondrial pyruvate metabolism is a previously undetermined requirement for M2 macrophages. Further, we have found a potential link between MIF and metabolism, where MIF likely regulates CSN5 activity and NRF2 stability to increase mitochondrial respiration. As inhibiting mitochondrial respiration blocks M2 polarization, MIF may promote lactate-enhanced M2 polarization by enhancing mitochondrial metabolism. Subsequent studies will be conducted to further investigate the metabolic pathways and mechanisms required for the mitochondrial metabolism of tumor-derived lactate in promoting M2-TAM polarization. Citation Format: Jordan Noe, Beatriz Rendon, Eun Jung Kim, Robert Mitchell. Mitochondrial metabolism in tumor-associated macrophages: The role of MIF and tumor-derived lactate [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3783.

MicroRNA 125a Regulates MHC-I Expression on Esophageal Adenocarcinoma Cells, Associated With Suppression of Antitumor Immune Response and Poor Outcomes of Patients

Immune checkpoint inhibition may affect growth or progression of highly aggressive cancers, such as esophageal adenocarcinoma (EAC). We investigated the regulation of expression of major histocompatibility complex, class 1 (MHC-I) proteins (encoded by HLA-A, HLA-B, and HLA-C) and the immune response to EACs in patient samples. We performed quantitative polymerase chain reaction array analyses of OE33 cells and OE19 cells, which express different levels of the ATP binding cassette subfamily B member 1 (TAP1) and TAP2, required for antigen presentation by MHC-I, to identify microRNAs (miRNAs) that regulate their expression. We performed luciferase assays to validate interactions between miRNAs and potential targets. We overexpressed candidate miRNAs in OE33, FLO-1, and OACP4 C cell lines and performed quantitative polymerase chain reaction, immunoblot, and flow cytometry analyses to identify changes in messenger RNA (mRNA) and protein expression; we studied the effects of cytotoxic T cells. We performed miRNA in situ hybridization, RNA-sequencing, and immunohistochemical analyses of tumor tissues from 51 untreated patients with EAC inthe Netherlands. Clinical and survival data were collected for patients, and EAC subtypes were determined. We found OE19 cells to have increased levels of 7 miRNAs. Of these, we found binding sites for miRNA 125a (MIR125a)-5p in the 3' untranslated region of the TAP2 mRNA and binding sites for MIR148a-3p in 3' untranslated regions of HLA-A, HLA-B, and HLA-C mRNAs. Overexpression of these miRNAs reduced expression of TAP2 in OE33, FLO-1, and OACP4 C cells, and reduced cell-surface levels of MHC-I. OE33 cells that expressed the viral peptide BZLF1 were killed by cytotoxic T cells, whereas OE33 that overexpressed MIR125a-5p or MIR 148a along with BZLF1 were not. In EAC and nontumor tissues, levels of MIR125a-5p correlated inversely with levels of TAP2 protein. High expression of TAP1 by EAC correlated with significantly shorter overall survival times of patients. EACs that expressed high levels of TAP1 and genes involved in antigen presentation also expressed high levels of genes that regulate the adaptive immune response, PD-L1, PD-L2, and IDO1; these EACs had a poor response to neoadjuvant chemoradiotherapy and associated with shorter overall survival times of patients. In studies of EAC cell lines andtumor tissues, we found increased levels of MIR125a-5p and MIR148a-3p to reduce levels of TAP2 and MHC-I, required for antigen presentation. High expression of MHC-I molecules by EAC correlated with markers of an adaptive immune response and significantly shorter overall survival times of patients.

RNAScope as a platform to detect IDO1 expression in tumor tissue sections.

116 RNAScope is a sensitive, specific platform to detect IDO1 expression in tumor tissue sections. M Pratta, M Rupar, P Waeltz, T Burn, G Hollis, M Covington, M Smith, and R Newton. Incyte Corp. Wilm. DE. Background: Indoleamine 2,3-Dioxygenase 1 (IDO1) catalyzes the primary and rate-limiting step in tryptophan catabolism to generate N-formyl-kynurenine (Kyn). Through a combination of local depletion of tryptophan and an increase in Kyn concentrations, IDO-1 activity can result in the suppression of antitumor immune responses. Because IDO-1 inhibitors are now in the clinic for treatment of multiple tumor types, immunohistological approaches are employed to demonstrate IDO1 expression in tumor biopsies. However, using a commercially available antibody to detect IDO1 by immunohistochemistry (IHC), the level of sensitivity was inadequate. Methods: In order to improve the sensitivity of IDO1 detection, we evaluated in situ hybridization (ISH) using RNAScope technology and digital quantitation by HALO analysis in collaboration with Advanced Cell Diagnostics (ACD). The technology was cross-validated using IDO1 qRT-PCR, Western blot, and activity analysis and compared with standard IHC. We initially evaluated IDO1 expression in HeLa cells stimulated with various concentrations of IFNγ, and then extended the observations using tissue sections from multiple tumor types. Results: In the HeLa cell model, IFNγ induced a time- and concentration-dependent increase of IDO1 at the mRNA, protein, and activity level. Although IDO1 was successfully detected in the HeLa cell samples by IHC, comparison of the platforms indicated IFNγ EC50 values were in strong agreement between RNAScope (193.8 pg/ml) and Western blot analysis (170.8 pg/ml), but was much higher by IHC analysis (2206 pg/ml). A strong positive correlation (*p < 0.0001) between RNAScope and Western blot analysis was observed, suggesting a highly coordinated induction of IDO1 by IFNγ at both the mRNA and protein levels. FFPE tumor tissue from melanoma, HNSCC, bladder, renal, ovarian, and lung cancers visualized by RNAScope all show varying levels of IDO1 expression. Conclusions: These data support the use of RNAScope for the analysis of IDO1 expression in clinical trials.

Head and Neck Carcinoma Immunotherapy: Facts and Hopes.

Cancer of the head and neck (HNC) is a heterogeneous disease of the upper aerodigestive tract, encompassing distinct histologic types, different anatomic sites, and human papillomavirus (HPV)-positive as well as HPV-negative cancers. Advanced/recurrent HNCs have poor prognosis with low survival rates. Tumor-mediated inhibition of antitumor immune responses and a high mutational burden are common features of HNCs. Both are responsible for the successful escape of these tumors from the host immune system. HNCs evolve numerous mechanisms of evasion from immune destruction. These mechanisms are linked to genetic aberrations, so that HNCs with a high mutational load are also highly immunosuppressive. The tumor microenvironment of these cancers is populated by immune cells that are dysfunctional, inhibitory cytokines, and exosomes carrying suppressive ligands. Dysfunctional immune cells in patients with recurrent/metastatic HNC can be made effective by the delivery of immunotherapies in combination with conventional treatments. With many promising immune-based strategies available, the future of immune therapies in HNC is encouraging, especially as methods for genetic profiling and mapping the immune landscape of the tumor are being integrated into a personalized approach. Efficiency of immune therapies is expected to rapidly improve with the possibility for patients' selection based on personal immunogenomic profiles. Noninvasive biomarkers of response to therapy will be emerging as a better understanding of the various molecular signals co-opted by the tumors is gained. The emerging role of immunotherapy as a potentially beneficial addition to standard treatments for recurrent/metastatic HNC offers hope to the patients for whom no other therapeutic options exist. Clin Cancer Res; 24(1); 6-13. ©2017 AACR.

Hypoxia-/HIF-1α-Driven Factors of the Tumor Microenvironment Impeding Antitumor Immune Responses and Promoting Malignant Progression.

The metabolic tumor microenvironment (TME) is characterized inter alia by critical oxygen depletion (hypoxia/anoxia), extracellular acidosis (pH ≤ 6.8), high lactate levels (up to 40mM in heterogeneously distributed areas), strongly elevated adenosine concentrations (10-100μM) and declining nutrient resources. These TME features are major drivers, e.g., for genetic instability, intratumor heterogeneity, malignant progression and development of resistance to conventional anticancer therapies. In this context, hypoxia-dependent (and non-hypoxic) HIF-1α activation plays a key role in orchestrating a multifaceted (local) suppression of innate and adaptive antitumor immune responses (and of immune-based tumor treatment). Besides the characteristic traits mentioned, the immune-suppressive actions can additionally be triggered by an (over-)expression of VEGF and activation of VEGFR, and externalisation of phosphatidylserine from the inner to the outer membrane leaflet of cells and exosomes. Altogether, and even individually, these features provide strong immune-suppressive signals. The downstream effects of an enhanced HIF-1α expression include (a) an activation of immune-suppressive effects (recruitment and stimulation of immune-suppressor cells [e.g., Treg, MDSC], secretion of immune-suppressive TH2-type cytokines), and (b) inhibition of antitumor immune responses (inhibition of immune cell actions [e.g., NK, NKT, CD4+, CD8+], inhibition of antigen-presenting cells [e.g., DC], reduced production of immune-stimulatory TH1-type cytokines).

76P - STAT3 inhibition reduces self-renewal in gastric cancer and promotes immune activation

Background: STAT3 (Signal Transducers and Activators of Transcription- 3) transcription factor participates in inflammation, suppression of anti-tumor immune responses, and also cancer cell proliferation invasion, and even maintenance of embryonic stem cells. In the present study we sought to evaluate the inhibition of STAT3 activation on self-renewal ability and immune modulation in gastric cancer. Methods: Human gastric cancer cell lines (MKN-45 and AGS), as well as patient samples were cultured in low attachment flasks and serum free media supplemented with bFGf, EGF and B27 until gastro-spheres appeared. Following characterization of the gastro-spheres, their effects on T cell response were evaluated by MLR assay as well as T cell culture. Finally the parental cells as well as spheres treated by Sttatic (an inhibitor of STAT3 activation) at IC50 and the self-renewal properties as well as T cell activation and differentiation was evaluated by different in vitro methods. Results: Gastro-Spheroids had higher potential of colony and sphere formation, higher ability of resistance to drugs, increased expression of genes involved in pluripotecy and EMT. So, spheroids were identified as structures enriched for CSCs. They have higher level of activated STAT3 at mRNA and Protein.STAT3 inhibition by Stattic decreased stemness properties including spheroid formation capacity and pluripotency gene expression of gastric cancer. Moreover, gastro-spheres demonstrated potent immunosuppressive effects on T lymphocyte proliferation, VEGF and TGF-β cytokine expression and regulatory T cell differentiation. Furthermore, STAT3 inhibition in cancer cells decreased immunosupression due to cancer cells and Th17/Treg shift towards Th17. Conclusions: The present findings could be useful in therapeutic processes directed at CSCs and give better understanding of tumor cross talk with its niche. However, in vivo investigation of anti-tumor and immunomodulatory effects of STAT3 inhibition is desirable. Legal entity responsible for the study: Royan Institute Ethical Committee Funding: None Disclosure: All authors have declared no conflicts of interest.

The Rac GTPase in Cancer: From Old Concepts to New Paradigms.

Rho family GTPases are critical regulators of cellular functions that play important roles in cancer progression. Aberrant activity of Rho small G-proteins, particularly Rac1 and their regulators, is a hallmark of cancer and contributes to the tumorigenic and metastatic phenotypes of cancer cells. This review examines the multiple mechanisms leading to Rac1 hyperactivation, particularly focusing on emerging paradigms that involve gain-of-function mutations in Rac and guanine nucleotide exchange factors, defects in Rac1 degradation, and mislocalization of Rac signaling components. The unexpected pro-oncogenic functions of Rac GTPase-activating proteins also challenged the dogma that these negative Rac regulators solely act as tumor suppressors. The potential contribution of Rac hyperactivation to resistance to anticancer agents, including targeted therapies, as well as to the suppression of antitumor immune response, highlights the critical need to develop therapeutic strategies to target the Rac pathway in a clinical setting. Cancer Res; 77(20); 5445-51. ©2017 AACR.

NF-κB c-Rel Is Crucial for the Regulatory T Cell Immune Checkpoint in Cancer

Regulatory Tcells (Tregs) play a pivotal role in the inhibition of anti-tumor immune responses. Understanding the mechanisms governing Treg homeostasis may therefore be important for development of effective tumor immunotherapy. We have recently demonstrated a key role for the canonical nuclear factor κB (NF-κB) subunits, p65 and c-Rel, in Treg identity and function. In this report, we show that NF-κB c-Rel ablation specifically impairs the generation and maintenance of the activated Treg (aTreg) subset, which is known to be enriched at sites of tumors. Using mouse models, we demonstrate that melanoma growth is drastically reduced in mice lacking c-Rel, but not p65, in Tregs. Moreover, chemical inhibition of c-Rel function delayed melanoma growth by impairing aTreg-mediated immunosuppression and potentiated the effects of anti-PD-1 immunotherapy. Our studies therefore establish inhibition of NF-κB c-Rel as a viable therapeutic approach for enhancing checkpoint-targeting immunotherapy protocols.

Human SLFN5 is a transcriptional co-repressor of STAT1-mediated interferon responses and promotes the malignant phenotype in glioblastoma.

We provide evidence that the IFN-regulated member of the Schlafen (SLFN) family of proteins, SLFN5, promotes the malignant phenotype in glioblastoma multiforme (GBM). Our studies indicate that SLFN5 expression promotes motility and invasiveness of GBM cells, and that high levels of SLFN5 expression correlate with high grade gliomas and shorter overall survival in patients suffering from GBM. In efforts to uncover the mechanism by which SLFN5 promotes GBM tumorigenesis, we found that this protein is a transcriptional co-repressor of STAT1. Type-I IFN treatment triggers the interaction of STAT1 with SLFN5, and the resulting complex negatively controls STAT1-mediated gene transcription via interferon stimulated response elements (ISRE). Thus, SLFN5 is both an IFN-stimulated response gene and a repressor of IFN-gene transcription, suggesting the existence of a negative-feedback regulatory loop that may account for suppression of antitumor immune responses in glioblastoma.

High-Risk Human Papillomavirus E7 Alters Host DNA Methylome and Represses HLA-E Expression in Human Keratinocytes

Human papillomavirus (HPV) infection distinctly alters methylation patterns in HPV-associated cancer. We have recently reported that HPV E7-dependent promoter hypermethylation leads to downregulation of the chemokine CXCL14 and suppression of antitumor immune responses. To investigate the extent of gene expression dysregulated by HPV E7-induced DNA methylation, we analyzed parallel global gene expression and DNA methylation using normal immortalized keratinocyte lines, NIKS, NIKS-16, NIKS-18, and NIKS-16∆E7. We show that expression of the MHC class I genes is downregulated in HPV-positive keratinocytes in an E7-dependent manner. Methylome analysis revealed hypermethylation at a distal CpG island (CGI) near the HLA-E gene in NIKS-16 cells compared to either NIKS cells or NIKS-16∆E7 cells, which lack E7 expression. The HLA-E CGI functions as an active promoter element which is dramatically repressed by DNA methylation. HLA-E protein expression on cell surface is downregulated by high-risk HPV16 and HPV18 E7 expression, but not by low-risk HPV6 and HPV11 E7 expression. Conversely, demethylation at the HLA-E CGI restores HLA-E protein expression in HPV-positive keratinocytes. Because HLA-E plays an important role in antiviral immunity by regulating natural killer and CD8+ T cells, epigenetic downregulation of HLA-E by high-risk HPV E7 may contribute to virus-induced immune evasion during HPV persistence.

Design, synthesis and optimization of bis-amide derivatives as CSF1R inhibitors

Signaling via the receptor tyrosine kinase CSF1R is thought to play an important role in recruitment and differentiation of tumor-associated macrophages (TAMs). TAMs play pro-tumorigenic roles, including the suppression of anti-tumor immune response, promotion of angiogenesis and tumor cell metastasis. Because of the role of this signaling pathway in the tumor microenvironment, several small molecule CSF1R kinase inhibitors are undergoing clinical evaluation for cancer therapy, either as a single agent or in combination with other cancer therapies, including immune checkpoint inhibitors. Herein we describe our lead optimization effort that resulted in the identification of a potent, cellular active and orally bioavailable bis-amide CSF1R inhibitor. Docking and biochemical analysis allowed the removal of a metabolically labile and poorly permeable methyl piperazine group from an early lead compound. Optimization led to improved metabolic stability and Caco2 permeability, which in turn resulted in good oral bioavailability in mice.