Conjugation of toll-like receptor-7 agonist to gastric cancer antigen MG7-Ag exerts antitumor effects

The Multifaceted Functionality of Plasmacytoid Dendritic Cells in Gastrointestinal Cancers: A Potential Therapeutic Target?

Gastrointestinal (GI) tumors pose a significant global health burden, necessitating the exploration of novel therapeutic approaches. Plasmacytoid dendritic cells (pDCs) play a crucial role in tumor immunity, exhibiting both anti-tumor and pro-tumor effects. This review aims to summarize the role of pDCs in different types of GI tumors and assess their potential as therapeutic targets. In gastric cancer, hepatocellular carcinoma, and intrahepatic cholangiocarcinoma, increased infiltration of pDCs was associated with a worse outcome, whereas in esophageal cancer, pancreatic cancer, and colorectal cancer, pDC infiltration improved the outcome. Initial animal studies of gastric cancer and hepatocellular carcinoma showed that pDCs could be a successful therapeutic target. In conclusion, pDCs play a multifaceted role in GI tumors, influencing both anti-tumor immunity and tumor progression. Further research is needed to optimize their clinical application and explore combinatorial approaches.

The Latest Approach of Immunotherapy with Endosomal TLR Agonists Improving NK Cell Function: An Overview

Toll-like receptors (TLRs) are the most well-defined pattern recognition receptors (PRR) of several cell types recognizing pathogens and triggering innate immunity. TLRs are also expressed on tumor cells and tumor microenvironment (TME) cells, including natural killer (NK) cells. Cell surface TLRs primarily recognize extracellular ligands from bacteria and fungi, while endosomal TLRs recognize microbial DNA or RNA. TLR engagement activates intracellular pathways leading to the activation of transcription factors regulating gene expression of several inflammatory molecules. Endosomal TLR agonists may be considered as new immunotherapeutic adjuvants for dendritic cell (DC) vaccines able to improve anti-tumor immunity and cancer patient outcomes. The literature suggests that endosomal TLR agonists modify TME on murine models and human cancer (clinical trials), providing evidence that locally infused endosomal TLR agonists may delay tumor growth and induce tumor regression. Recently, our group demonstrated that CD56^bright NK cell subset is selectively responsive to TLR8 engagement. Thus, TLR8 agonists (loaded or not to nanoparticles or other carriers) can be considered a novel strategy able to promote anti-tumor immunity. TLR8 agonists can be used to activate and expand in vitro circulating or intra-tumoral NK cells to be adoptively transferred into patients.

Targeting toll-like receptor 7/8 for immunotherapy: recent advances and prospectives

Toll-like receptors (TLRs) are a large family of proteins that are expressed in immune cells and various tumor cells. TLR7/8 are located in the intracellular endosomes, participate in tumor immune surveillance and play different roles in tumor growth. Activation of TLRs 7 and 8 triggers induction of a Th1 type innate immune response in the highly sophisticated process of innate immunity signaling with the recent research advances involving the small molecule activation of TLR 7 and 8. The wide range of expression and clinical significance of TLR7/TLR8 in different kinds of cancers have been extensively explored. TLR7/TLR8 can be used as novel diagnostic biomarkers, progression and prognostic indicators, and immunotherapeutic targets for various tumors. Although the mechanism of action of TLR7/8 in cancer immunotherapy is still incomplete, TLRs on T cells are involved in the regulation of T cell function and serve as co-stimulatory molecules and activate T cell immunity. TLR agonists can activate T cell-mediated antitumor responses with both innate and adaptive immune responses to improve tumor therapy. Recently, novel drugs of TLR7 or TLR8 agonists with different scaffolds have been developed. These agonists lead to the induction of certain cytokines and chemokines that can be applied to the treatment of some diseases and can be used as good adjutants for vaccines. Furthermore, TLR7/8 agonists as potential therapeutics for tumor-targeted immunotherapy have been developed. In this review, we summarize the recent advances in the development of immunotherapy strategies targeting TLR7/8 in patients with various cancers and chronic hepatitis B.

Roles of Plasmacytoid Dendritic Cells in Gastric Cancer

Gastric cancer (GC) is the fifth most common neoplasm and the third most deadly cancer in humans worldwide. Helicobacter pylori infection is the most important causative factor of gastric carcinogenesis, and activates host innate and adaptive immune responses. As key constituents of the tumor immune microenvironment, plasmacytoid dendritic cells (pDCs) are increasingly attracting attention owing to their potential roles in immunosuppression. We recently reported that pDCs have vital roles in the development of immunosuppression in GC. Clarifying the contribution of pDCs to the development and progression of GC may lead to improvements in cancer therapy. In this review, we summarize current knowledge regarding immune modulation in GC, especially the roles of pDCs in GC carcinogenesis and treatment strategies.

Bacterial Translocation in Gastrointestinal Cancers and Cancer Treatment

In recent years, there has been increasing evidence that gut microbiota is associated with the onset and exacerbation of various diseases, such as gastrointestinal cancer. For instance, it is well known that local inflammation of the intestinal tract in colorectal cancer that is caused by the increased number of Fusobacterium, due to changes in the intestinal bacterial flora, is involved in carcinogenesis. In contrast, gut bacteria or their products, pathogen-associated molecular patterns, not only cause intestinal inflammation but also invade the bloodstream through dysbiosis and gut barrier dysfunction, thereby leading to systemic inflammation, namely bacterial translocation. The involvement of bacterial translocation in the carcinogenesis of gastrointestinal cancers and their prognosis is increasingly being recognized. The Toll-like receptor signaling pathways plays an important role in the carcinogenesis of such cancers. In addition, bacterial translocation influences the treatment of cancers such as surgery and chemotherapy. In this review, we outline the concept of bacterial translocation, summarize the current knowledge on the relationship between gut bacteria and gastrointestinal cancer, and provide future perspectives of this field.

Inhibitory Effect of Immunologically Activated Mesenchymal Stem Cells on Lung Cancer Cell Growth and Metastasis

Background: Mesenchymal stem cells (MSCs) could inhibit the proliferation of lung cancer cells. The authors' study aimed to investigate the effects of immunologically activated human umbilical cord (HUC)-MSCs on A549 lung cancer cells. Materials and Methods: HUC-MSCs were separated from the umbilical cord using the adherence method. Surface markers of HUC-MSCs were detected by flow cytometry for MSC identification. Imiquimod (TLR7 agonist) was incubated with HUC-MSCs for immune activation, and the expression of MSC-specific markers and immune inflammatory molecules was measured by quantitative real-time polymerase chain reaction. HUC A549 cells were cocultured with HUC-MSCs treated with imiquimod, siTLR7 (small interfering RNA for TLR7) or TLR7 overexpression, and then cell viability, proliferation, migration, and invasion, and the expression of phosphatidylinositol-3-kinase (PI3K)/Akt and NF-κB was investigated using MTT assay, clone formation assay, transwell assay, and western blot, respectively. Results: HUC-MSCs were identified as positive for CD73, CD105, CD44, CD29, and CD90. Expression of MSC markers was inhibited, while those of immune inflammatory molecules expression except IL-6 (interleukin-6) was enhanced after MSCs were immunologically activated by imiquimod. After being cocultured with HUC-MSCs treated with imiquimod or overexpressed TLR7, cell viability, proliferation, and metastasis, and the phosphorylation of P65 and AKT in A549 cells were decreased, but apoptosis was increased, while siTLR7 showed the opposite effect HUC. Conclusions: Immunologically activated HUC-MSCs inhibited the growth and metastasis, yet, promoted the apoptosis of A549 lung cancer cells via regulating the PI3K/Akt and NF-κB pathways.

TLRs as a Promise Target Along With Immune Checkpoint Against Gastric Cancer

Gastric cancer (GC) is one of the most common cancers in the world, and the incidence of gastric cancer in Asia appears to increase in recent years. Although there is a lot of improvement in treatment approaches, the prognosis of GC is poor. So it is urgent to search for a novel and more effective treatment to improve the survival rate of patients. Both innate immunity and adaptive immunity are important in cancer. In the innate immune system, pattern recognition receptors (PRRs) activate immune responses by recognizing pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Toll-like receptors (TLRs) are a class of pattern recognition receptors (PRRs). Many studies have reported that TLRs are involved in the occurrence, development, and treatment of GC. Therefore, TLRs are potential targets for immunotherapy to gastric cancer. However, gastric cancer is a heterogeneous disorder, and TLRs function in GC is complex. TLRs agonists can be potentially used not only as therapeutic agents to treat gastric cancer but also as adjuvants in conjunction with other immunotherapies. They might provide a promising new target for GC treatment. In the review, we sort out the mechanism of TLRs involved in tumor immunity and summarize the current progress in TLRs-based therapeutic approaches and other immunotherapies in the treatment of GC.

Genetic variants in the regulation region of TLR4 reduce the gastric cancer susceptibility

Gastric cancer (GC) is one of the most common cancers diagnosed in China. It has been suggested that the genetic polymorphisms of Toll-like receptors (TLRs) might be in close relation to tumorigenesis and development of gastric cancer. In this study, we performed a case-control study to investigate the genetic polymorphisms of TLR3, 4, 5, 7 with the genetic susceptibility of gastric cancer. TLRs gene polymorphisms in 471 gastric cancer (GC) patients and 471 healthy controls were analyzed by polymerase chain reaction-restrictive fragment length polymorphism (PCR-RFLP) analysis or TaqMan assays. Odds ratio (OR) and its 95% confidence interval (95%CI) were used to evaluate the association of TLR4 variants with the GC risk via unconditional logistic regression. Our results suggested that variant genotypes of TLR4 rs7869402 (OR = 0.61, 95%CI = 0.40-0.92, P = 0.02) and TLR4 rs7873784 (OR = 0.17, 95%CI = 0.09-0.33, P < 0.01) gene polymorphisms reduced the risk of GC. Stratified analysis showed that rs7869402 T-containing genotype significantly decreased the susceptibility of GC among females (OR = 0.38, 95%CI = 0.16-0.91, P = 0.03), older subjects (OR = 0.48, 95%CI = 0.26-0.87, P = 0.02), non-smokers (OR = 0.41, 95%CI = 0.23-0.71, P < 0.01) and non-drinkers (OR = 0.58, 95%CI = 0.30-0.78, P < 0.01). In case of rs7873784 polymorphism, C-containing genotype reduced the risk of GC among males (OR = 0.08, 95%CI = 0.03-0.21, P < 0.01), but not among females (OR = 0.53, 95%CI = 0.22-1.27, P = 0.15). As to the other four SNPs (TLR3 rs5743303, TLR4 rs1927914, TLR5 rs1640816 and TLR7 rs3853839), no significant correlations were found to be related to the risk of gastric carcinoma. Our research demonstrated the significance of TLRs polymorphisms in decreasing the risk of GC.

A chemical conjugation of JQ-1 and a TLR7 agonist induces tumoricidal effects in a murine model of melanoma via enhanced immunomodulation

In recent years, inhibitors of the BET bromodomain proteins, such as BRD4 inhibitors, have demonstrated robust antitumor activity. JQ-1, a representative small molecular BRD4 inhibitor, is also effective to block PD-1/PD-L1 signaling by significantly decreasing the PD-L1 expression on tumor cells. However, toxicity of BRD4 inhibitors on lymphoid and hematopoietic tissues limits their clinical usage. In this research, we designed and studied an immunogenic BRD4 inhibitor, SZU-119, by coupling JQ-1 with a TLR7 agonist, SZU-101. In vitro, SZU-119 stimulated the production of cytokines in mouse BMDCs and spleen lymphocytes, and inhibited the expression of PD-L1 in mouse B16 tumor cells. In vivo, SZU-119 suppressed the B16 tumor growth at both injected and uninjected sites, and prolonged the survival time of mice. SZU-119 elevated the number of total CD8⁺ and IFN-γ⁺ CD8⁺ T cells in spleens, with greater CTL cytotoxicity to B16 tumor cells. It was also observed that the infiltration of CD8⁺ T cells was increased in tumors at both local and distant sites, and the PD-L1 expression was decreased in tumor cells at the primary site. In conclusion, we have demonstrated that SZU-119 activated the innate immune cells, kept efficacy of PD-L1 blockade and abrogated immune toxicity, showing more potent antitumor effects than the simple mixture of SZU-101 and JQ-1 in a mouse melanoma model. Our work provides new insights for the development of anti-melanoma drugs that concurrently target innate and adaptive immunity.

Immunoadjuvants for cancer immunotherapy: A review of recent developments

Cancer immunotherapy evolved as a new treatment modality to eradicate tumor cells and has gained in popularity after its successful clinical transition. By activating antigen-presenting cells (APCs), and thus, inducing innate or adaptive immune responses, immunoadjuvants have become promising tools for cancer immunotherapy. Different types of immunoadjuvants such as toll-like receptor (TLR) agonists, exosomes, and metallic and plant-derived immunoadjuvants have been studied for their immunological effects. However, the clinical use of immunoadjuvants is limited by short response rates and various side-effects. The rapid progress made in the development of nanoparticle systems as immunoadjuvant carrier vehicles has provided potential carriers for cancer immunotherapy. In this review article, we describe different types of immunoadjuvants, their limitations, modes of action, and the reasons for their clinical adoption. In addition, we review recent progress made in the nanoparticle-based immunoadjuvant field and on the combined use of nanoparticle-based immunoadjuvants and chemotherapy, phototherapy, radiation therapy, and immune checkpoint inhibitor-based therapy. STATEMENT OF SIGNIFICANCE: Cancer immunotherapy emerged as a new hope for treating malignant tumors. Different types of immunoadjuvants serve as an important tool for cancer immunotherapy by activating an innate or adaptive immune response. Limitation of free immunoadjuvant has paved the path for the development of nanoparticle-based immunoadjuvant therapy with the hope of prolonging the therapeutic efficacy. This review highlights the recent advancement made in nanoparticle-based immunoadjuvant therapy in modulating the adaptive and innate immune system. The application of the combinatorial approach of chemotherapy, phototherapy, radiation therapy adds synergy in nanoparticle-based immunoadjuvant therapy. It will broaden the reader's understanding on the recent progress made in immunotherapy with the aid of immunoadjuvant-based nanosystem.

Synthetic MUC1 breast cancer vaccine containing a Toll-like receptor 7 agonist exerts antitumor effects

Adjuvant immunotherapy has recently emerged as a potential treatment strategy for breast cancer. The tumor-associated protein mucin 1 (MUC1) has received increasing attention due to its high expression in numerous types of common tumors, in which MUC1 acts as a cancer antigen. However, the simple mixed composition of an adjuvant and a peptide is not a sufficient rationale for a MUC1 peptide-based vaccine. The present study developed a novel Toll-like receptor 7 (TLR7) agonist-conjugated MUC1 peptide vaccine (T7-MUC1), which elicited an effective immune response and a robust antitumor effect in a mouse breast cancer model. In vitro, T7-MUC1 significantly increased the release of cytokines in mouse bone marrow dendritic cells and spleen lymphocytes, and induced the dendritic cell-cytokine-induced killer response against tumor cells with high MUC1 expression. In vivo, it was observed that the 4T1 tumor weights in mice immunized with the T7-MUC1 conjugate were reduced by ≥70% compared with those in the control group. Furthermore, the therapeutic responses in vivo were attributed to the increase in specific humoral and cellular immunity, including high antibody titers, antibody-dependent cell-mediated cytotoxicity and cytotoxic T-lymphocyte activity. The percentages of CD3⁺/CD8⁺ T-cells were significantly higher in the T7-MUC1 treatment group compared with those in the control group. Therefore, the results of the present study suggested that the T7-MUC1 vaccine inhibited tumor growth in mice and thus may have potential as a therapeutic candidate in clinical trials for breast cancer immunotherapy.

Peptides conjugated to 2-alkoxy-8-oxo-adenine as potential synthetic vaccines triggering TLR7

Covalent linking of immunogenic oligopeptides with synthetic Toll-like receptor ligands is a useful approach to develop self-adjuvanting vaccines. In particular, small-molecule based agonists of Toll-like receptor 7 (TLR7) that are derived from 8-oxo-adenine core are potentially promising because these chemically robust TLR7 ligands can be connected to peptide T-cell epitopes via straightforward solid-phase peptide synthesis. In this contribution we present the synthesis of a Boc-protected 9-benzyl-2-alkoxy-8-oxo-adenine building block and its application in the online solid phase synthesis of three peptide conjugates that differ in the position of the TLR7 ligand within the peptide. The conjugates are able to induce dendritic cell maturation and T cell proliferation while the position of the ligand impacts T cell proliferation potency.

Gastric cancer vaccines synthesized using a TLR7 agonist and their synergistic antitumor effects with 5-fluorouracil

Background

Vaccines play increasingly important roles in cancer treatment due to their advantages of effective targeting and few side effects. Our laboratory has attempted to construct vaccines by conjugating TLR7 agonists with tumor-associated antigens. Furthermore, immunochemotherapy has recently become an appealing approach to cancer therapy. 5-fluorouracil (5-FU), a commonly used chemotherapeutic agent, can reportedly potently and selectively kill tumor-associated MDSCs in vivo.

Methods

Gastric cancer vaccines were synthesized by the covalent attachment of our TLR7 agonist with the gastric cancer antigen MG7-Ag tetra-epitope, leading to T7 − ML (linear tetra-epitope) and T7 − MB (branched tetra-epitope). Cytokines induced by the vaccines in vitro were assessed by ELISA. A tumor challenge model was created by treating BALB/c mice on either a prophylactic or therapeutic vaccination schedule. 5-FU was simultaneously applied to mice in the combination treatment group. CTL and ADCC activities were determined by the LDH method, while CD3⁺/CD8⁺, CD3⁺/CD4⁺ T cells and MDSCs were evaluated by flow cytometry.

Results

In vitro, rapid TNF-α and IL-12 inductions occurred in BMDCs treated with the vaccines. In vivo, among all the vaccines tested, T7 − MB most effectively reduced EAC tumor burdens and induced CTLs, antibodies and ADCC activity in BALB/c mice. Immunization with T7 − MB in combination with 5-FU chemotherapy reduced tumor sizes and extended long-term survival rates, mainly by improving T cell responses, including CTLs, CD3⁺/CD8⁺ and CD3⁺/CD4⁺ T cells. 5-FU also enhanced the T7 − MB efficiency by reversing immunosuppressive factors, i.e., MDSCs, which could not be validly inhibited by the vaccines alone. In addition, T7 − MB repressed tumor growth and immune tolerance when the therapeutic schedule was used, although the effects were weaker than those achieved with either T7 − MB alone or in combination with 5-FU on the prophylactic schedule.

Conclusions

A novel effective gastric cancer vaccine was constructed, and the importance of branched multiple antigen peptides and chemical conjugation to vaccine design were confirmed. The synergistic effects and mechanisms of T7 − MB and 5-FU were also established, observing mainly T cell activation and MDSC inhibition.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1501-z) contains supplementary material, which is available to authorized users.

Anti-tumor Activity of Toll-Like Receptor 7 Agonists

Toll-like receptors (TLRs) are a class of pattern recognition receptors that play a bridging role in innate immunity and adaptive immunity. The activated TLRs not only induce inflammatory responses, but also elicit the development of antigen specific immunity. TLR7, a member of TLR family, is an intracellular receptor expressed on the membrane of endosomes. TLR7 can be triggered not only by ssRNA during viral infections, but also by immune modifiers that share a similar structure to nucleosides. Its powerful immune stimulatory action can be potentially used in the anti-tumor therapy. This article reviewed the anti-tumor activity and mechanism of TLR7 agonists that are frequently applied in preclinical and clinical investigations, and mainly focused on small synthetic molecules, including imiquimod, resiquimod, gardiquimod, and 852A, etc.

Immunomodulatory and Antitumor Effects of a Novel TLR7 Agonist Combined with Lapatinib

As new treatment approaches, both immunotherapy and targeted treatments have been used in the clinical treatment of cancers. These therapies are different from traditional surgery, chemotherapy and radiotherapy. Use of a combination of immunotherapy and targeted treatments may improve tumor clearance. We investigated the feasibility of combining tyrosine kinase inhibitors (TKIs, targeted drugs) and SZU-101 (a novel TLR7 agonist synthesized by our laboratory). Thirteen different TKIs were combined with or without SZU-101 and studied to determine their effects on immunocytes. On the basis of the distinctive results, lapatinib and sunitinib were selected for further tumor-inhibition investigation and determination of the underlying mechanism. Interestingly, we found lapatinib to work better with SZU-101, enhancing tumor clearance in vivo, without affecting the TLR7-NF-κB pathway activated by the TLR7 agonist in mouse spleen lymphocytes and bone marrow dendritic cells (BMDCs).