Assessing the role of STAT3 in DC differentiation and autologous DC immunotherapy in mouse models of GBM

Mechanisms of resistance to immune checkpoint inhibitors in melanoma: What we have to overcome?

Marching into the second decade after the approval of ipilimumab, it is clear that immune checkpoint inhibitors (ICIs) have dramatically improved the prognosis of melanoma. Although the current edge is already high, with a 4-year OS% of 77.9% for adjuvant nivolumab and a 6.5-year OS% of 49% for nivolumab/ipilimumab combination in the metastatic setting, a high proportion of patients with advanced melanoma have no benefit from immunotherapy, or experience an early disease relapse/progression in the first few months of treatment, surviving much less. Reasonably, the primary and acquired resistance to ICIs has entered into the focus of clinical research with positive (e.g., nivolumab and relatlimab combination) and negative feedbacks (e.g., nivolumab with pegylated-IL2, pembrolizumab with T-VEC, nivolumab with epacadostat, and combinatorial triplets of BRAF/MEK inhibitors with immunotherapy). Many intrinsic (intracellular or intra-tumoral) but also extrinsic (systematic) events are considered to be involved in the development of this resistance to ICIs: i) melanoma cell immunogenicity (e.g., tumor mutational burden, antigen-processing machinery and immunogenic cell death, neoantigen affinity and heterogeneity, genomic instability, melanoma dedifferentiation and phenotypic plasticity), ii) immune cell trafficking, T-cell priming, and cell death evasion, iii) melanoma neovascularization, cellular TME components(e.g., T_regs, CAFs) and extracellular matrix modulation, iv) metabolic antagonism in the TME(highly glycolytic status, upregulated CD39/CD73/adenosine pathway, iDO-dependent tryptophan catabolism), v) T-cell exhaustion and negative immune checkpoints, and vi) gut microbiota. In the present overview, we discuss how these parameters compromise the efficacy of ICIs, with an emphasis on the lessons learned by the latest melanoma studies; and in parallel, we describe the main ongoing approaches to overcome the resistance to immunotherapy. Summarizing this information will improve the understanding of how these complicated dynamics contribute to immune escape and will help to develop more effective strategies on how anti-tumor immunity can surpass existing barriers of ICI-refractory melanoma.

Roles of STAT3 in the pathogenesis and treatment of glioblastoma

Glioblastoma (GBM) is the most malignant of astrocytomas mainly involving the cerebral hemispheres and the cerebral cortex. It is one of the fatal and refractory solid tumors, with a 5-year survival rate of merely 5% among the adults. IL6/JAK/STAT3 is an important signaling pathway involved in the pathogenesis and progression of GBM. The expression of STAT3 in GBM tissues is substantially higher than that of normal brain cells. The abnormal activation of STAT3 renders the tumor microenvironment of GBM immunosuppression. Besides, blocking the STAT3 pathway can effectively inhibit the growth and metastasis of GBM. On this basis, inhibition of STAT3 may be a new therapeutic approach for GBM, and the combination of STAT3 targeted therapy and conventional therapies may improve the current status of GBM treatment. This review summarized the roles of STAT3 in the pathogenesis of GBM and the feasibility of STAT3 for GBM target therapy.

Resistance to durvalumab and durvalumab plus tremelimumab is associated with functional STK11 mutations in non-small-cell lung cancer patients and is reversed by STAT3 knockdown

Mutations in the STK11 (LKB1) gene regulate resistance to PD-1/PD-L1 blockade. This study evaluated this association in patients with nonsquamous non-small-cell lung cancer enrolled in three Phase 1/2 trials. STK11 mutations were associated with resistance to the anti-PD-L1 antibody durvalumab (alone/with the anti-CTLA-4 antibody tremelimumab) independently of KRAS mutational status, highlighting STK11 as a potential driver of resistance to checkpoint blockade. Retrospective assessments of tumor tissue, whole blood and serum revealed a unique immune phenotype in patients with STK11 mutations, with increased expression of markers associated with neutrophils (i.e. CXCL2, IL6), Th17 contexture (i.e. IL17A) and immune checkpoints. Associated changes were observed in the periphery. Reduction of STAT3 in the tumor microenvironment using an antisense oligonucleotide reversed immunotherapy resistance in preclinical STK11 knockout models. These results suggest that STK11 mutations may hinder response to checkpoint blockade through mechanisms including suppressive myeloid cell biology, which could be reversed by STAT3-targeted therapy.

Immunogenetics of glioblastoma: the future of personalized patient management

The prognosis of glioblastoma has changed little over the past two decades, with only minor improvements in length of overall survival through the addition of temozolomide (temodal) to standard of care and the recommended use of alternating electric field therapy (optune) to newly diagnosed patients. In an effort to define novel therapeutic targets across molecularly heterogeneous disease subgroups, researchers have begun to uncover the complex interplay between epigenetics, cell signaling, metabolism, and the immunosuppressive tumor microenvironment. Indeed, IDH mutations are now recognized as a defining differential factor not only influencing global hypermethylation and patient prognosis but also degree of immune infiltration within individual tumors. Likewise, next-generation sequencing has defined subgroup-specific transcriptional profiles that correlate with different mechanisms of immune evasion, including increased PD-L1 and CTLA-4 among mesenchymal tumors. Interestingly, sequencing of the T cell repertoire from numerous patient samples suggests that the correlation between mutational burden and enrichment of tumor-specific peptides may be less convincing than originally suspected. While this raises questions over the efficacy of dendritic cell or tumor-lysate vaccines and CAR-T therapies, these avenues continue to be explored. In addition to these active immunotherapies, inhibitors of molecular hubs with wide reaching effects, including STAT3, IDO, and TGF-β, are now in early-phase clinical trials. With the potential to block intrinsic biological properties of tumor growth and invasion while bolstering the immunogenic profile of the tumor microenvironment, these new targets represent a new direction for GBM therapies. In this review, we show the advances in molecular profiling and immunophenotyping of GBM, which may lead to the development of new personalized therapeutic strategies.

MIS416 as a siRNA Delivery System with the Ability to Target Antigen-Presenting Cells

MIS416 is a microparticulate formulation derived from propionibacterium acnes cell wall skeletons with intrinsic adjuvant activity. Conjugates of MIS416-SS-peptide containing a disulfide linkage facilitate the cytoplasmic delivery and release of peptides in antigen-presenting cells (APCs). We hypothesized that MIS416-siRNA (small interfering RNA) conjugates, containing a disulfide linkage between MIS416 and the siRNA, would allow cytoplasmic release of siRNA in APCs. MIS416-SS-siStat3 conjugates added to cell culture medium of monolayers of DCs in culture flasks successfully targeted Stat3 mRNA in DCs in vitro without transfection, downregulating Stat3 mRNA and protein levels. These results suggest that MIS416-SS-siRNA conjugates can be used as a novel siRNA delivery system for the knockdown of mRNA levels in APCs.

Jak Stat signaling and cancer: Opportunities, benefits and side effects of targeted inhibition

The effects of Jak Stat signaling and the persistent activation of Stat3 and Stat5 on tumor cell survival, proliferation and invasion have made the Jak Stat pathway a favorite target for drug development and cancer therapy. This notion was strengthened when additional biological functions of Stat signaling in cancer and their roles in the regulation of cytokine dependent inflammation and immunity in the tumor microenvironment were discovered. Stats act not only as transcriptional inducers, but affect gene expression via epigenetic modifications, induce epithelial mesenchymal transition, generate a pro-tumorigenic microenvironment, promote cancer stem cell self-renewal and differentiation, and help to establish the pre-metastatic niche formation. The effects of Jak Stat inhibition on the suppression of pro-inflammatory responses appears most promising and could become a strategy in the prevention of tumor progression. The direct and mediated mechanisms of Jak Stat signaling in and on tumors cells, the interactions with other signaling pathways and transcription factors and the targeting of the functionally crucial secondary modifications of Stat molecules suggest novel approaches to the future development of Jak Stat based cancer therapeutics.

Nutritional control of IL-23/Th17-mediated autoimmune disease through HO-1/STAT3 activation

The nutritional curcumin (CUR) is beneficial in cell-mediated autoimmune diseases. The molecular mechanisms underlying this food-mediated silencing of inflammatory immune responses are poorly understood. By investigating antigen-specific immune responses we found that dietary CUR impairs the differentiation of Th1/Th17 cells in vivo during encephalomyelitis and instead promoted Th2 cells. In contrast, feeding CUR had no inhibitory effect on ovalbumin-induced airway inflammation. Mechanistically, we found that CUR induces an anti-inflammatory phenotype in dendritic cells (DC) with enhanced STAT3 phosphorylation and suppressed expression of Il12b and Il23a. On the molecular level CUR readily induced NRF2-sensitive heme oxygenase 1 (HO-1) mRNA and protein in LPS-activated DC. HO-1 enhanced STAT3 phosphorylation, which enriched to Il12b and Il23a loci and negatively regulated their transcription. These findings demonstrate the underlying mechanism through which a nutritional can interfere with the immune response. CUR silences IL-23/Th17-mediated pathology by enhancing HO-1/STAT3 interaction in DC.

Bypassing STAT3-mediated inhibition of the transcriptional regulator ID2 improves the antitumor efficacy of dendritic cells

Despite the potent ability of dendritic cells (DCs) to stimulate lymphocyte responses and host immunity, granulocyte-macrophage colony-stimulating factor-derived DCs (GM-DCs) used as antitumor vaccines have demonstrated relatively modest success in cancer immunotherapy. We found that injecting GM-DCs into melanoma tumors in mice, or culturing GM-DCs with melanoma-secreted cytokines or melanoma-conditioned medium, rapidly suppressed DC-intrinsic expression of the gene encoding inhibitor of differentiation 2 (ID2), a transcriptional regulator. Melanoma-associated cytokines repressed Id2 transcription in murine DCs through the activation of signal transducer and activator of transcription 3 (STAT3). Enforced expression of ID2 in GM-DCs (ID2-GM-DCs) suppressed their production of the proinflammatory cytokine tumor necrosis factor-α (TNF-α). Vaccination with ID2-GM-DCs slowed the progression of melanoma tumors and enhanced animal survival, which was associated with an increased abundance of tumor-infiltrating interferon-γ-positive CD4(+) effector and CD8(+) cytotoxic T cells and a decreased number of tumor-infiltrating regulatory CD4(+) T cells. The efficacy of the ID2-GM-DC vaccine was improved by combinatorial treatment with a blocking antibody to programmed cell death protein-1 (PD-1), a current immunotherapy that overcomes suppressive immune checkpoint signaling. Collectively, our data reveal a previously unrecognized STAT3-mediated immunosuppressive mechanism in DCs and indicate that DC-intrinsic ID2 promotes tumor immunity by modulating tumor-associated CD4(+) T cell responses. Thus, inhibiting STAT3 or overexpressing ID2 selectively in DCs may improve the efficiency of DC vaccines in cancer therapy.

Synergistic anti-pancreatic cancer immunological effects by treatment with reduced expression in immortalized cells/dickkopf-3 protein and peripheral blood mononuclear cells

BACKGROUND AND AIM

Reduced expression in immortalized cells/dickkopf-3 (REIC/DKK3) is a reported tumor suppressor gene and has potential to become an innovative therapy for various cancers. We examined the antitumor immunological effects of human REIC/DKK3 protein against pancreatic cancer.

METHODS

Activation of extracellular signal-regulated kinases 1 and 2, mammalian target of rapamycin, and signal transducer and activator of transcription 3 by REIC/DKK3 protein was assessed in human peripheral blood mononuclear cells using immunoblotting. Pancreatic cancer cell lines (AsPC-1 and MIA Paca-2) were cocultured with peripheral blood mononuclear cells, and the anticancer effects of REIC/DKK3 protein were assessed using the methyl thiazole tetrazolium, cytotoxicity, and enzyme-linked immunospot assays. The antitumor immunological effects of the combined treatment with REIC/DKK3 protein and peripheral blood mononuclear cells were also assessed in a pancreatic cancer model using non-obese diabetic/severe combined immunodeficiency mice.

RESULTS

The REIC/DKK3 protein activated extracellular signal-regulated kinases 1 and 2, mammalian target of rapamycin, and signal transducer and activator of transcription 3 in peripheral blood mononuclear cells. REIC/DKK3 protein inhibited in vitro cancer cell viability and enhanced cytotoxicity when incubated with peripheral blood mononuclear cells. REIC/DKK3 protein induced significant production of interferon gamma from lymphocytes incubated with pancreatic cancer cells, indicating that CD8+ T cells were activated in the peripheral blood mononuclear cells when cocultured with AsPC-1 and MIA Paca-2 in the presence of REIC/DKK3 protein. Combined treatment with REIC/DKK3 protein and peripheral blood mononuclear cells produced in vivo anticancer immunostimulatory effects on pancreatic cancer cells.

CONCLUSIONS

The REIC/DKK3 protein and peripheral blood mononuclear cells synergistically enhanced anticancer immunological effects against pancreatic cancer cells. The observed immunomodulatory effect of combined treatment likely occurs in adenovirus-mediated REIC/DKK3 gene therapy and provides important clues to the therapeutic mechanisms involving immune cells.

Interleukin-6/STAT3 Pathway Signaling Drives an Inflammatory Phenotype in Group A Ependymoma

Ependymoma (EPN) in childhood is a brain tumor with substantial mortality. Inflammatory response has been identified as a molecular signature of high-risk Group A EPN. To better understand the biology of this phenotype and aid therapeutic development, transcriptomic data from Group A and B EPN patient tumor samples, and additional malignant and normal brain data, were analyzed to identify the mechanism underlying EPN Group A inflammation. Enrichment of IL6 and STAT3 pathway genes were found to distinguish Group A EPN from Group B EPN and other brain tumors, implicating an IL6 activation of STAT3 mechanism. EPN tumor cell growth was shown to be dependent on STAT3 activity, as demonstrated using shRNA knockdown and pharmacologic inhibition of STAT3 that blocked proliferation and induced apoptosis. The inflammatory factors secreted by EPN tumor cells were shown to reprogram myeloid cells, and this paracrine effect was characterized by a significant increase in pSTAT3 and IL8 secretion. Myeloid polarization was shown to be dependent on tumor secretion of IL6, and these effects could be reversed using IL6-neutralizing antibody or IL6 receptor-targeted therapeutic antibody tocilizumab. Polarized myeloid cell production of IL8 drove unpolarized myeloid cells to upregulate CD163 and to produce a number of proinflammatory cytokines. Collectively, these findings indicate that constitutive IL6/STAT3 pathway activation is important in driving tumor growth and inflammatory cross-talk with myeloid cells within the Group A EPN microenvironment. Effective design of Group A-targeted therapy for children with EPN may require reversal of this potentially immunosuppressive and protumor pathway.