'Immunomers'--novel 3'-3'-linked CpG oligodeoxyribonucleotides as potent immunomodulatory agents

Fine tuning of CpG spatial distribution with DNA origami for improved cancer vaccination

Multivalent presentation of ligands often enhances receptor activation and downstream signalling. DNA origami offers a precise nanoscale spacing of ligands, a potentially useful feature for therapeutic nanoparticles. Here we use a square-block DNA origami platform to explore the importance of the spacing of CpG oligonucleotides. CpG engages Toll-like receptors and therefore acts to activate dendritic cells. Through in vitro cell culture studies and in vivo tumour treatment models, we demonstrate that square blocks induce Th1 immune polarization when CpG is spaced at 3.5 nm. We observe that this DNA origami vaccine enhances DC activation, antigen cross-presentation, CD8 T-cell activation, Th1-polarized CD4 activation and natural-killer-cell activation. The vaccine also effectively synergizes with anti-PD-L1 for improved cancer immunotherapy in melanoma and lymphoma models and induces long-term T-cell memory. Our results suggest that DNA origami may serve as a platform for controlling adjuvant spacing and co-delivering antigens in vaccines.

Tilsotolimod: an investigational synthetic toll-like receptor 9 (TLR9) agonist for the treatment of refractory solid tumors and melanoma

INTRODUCTION

Cancer immunotherapy has seen tremendous strides in the past 15 years, with the introduction of several novel immunotherapeutic agents. Nevertheless, as clinical practice has shown, significant challenges remain with a considerable number of patients responding sub-optimally to available therapeutic options. Research has demonstrated the important immunoregulatory role of the tumor microenvironment (TME), with the potential to either hinder or promote an effective anti-tumor immune response. As such, scientific efforts have focused on investigating novel candidate immunomodulatory agents with the potential to alter the TME toward a more immunopotentiating composition.

AREAS COVERED

Herein, we discuss the novel investigational toll-like receptor 9 agonist tilsotolimod currently undergoing phase II and III clinical trials for advanced refractory cancer, highlighting its mode of action, efficacy, tolerability, and potential future applications in the treatment of cancer. To this effect, we conducted an exhaustive Web of Science and PubMed search to evaluate available research on tilsotolimod as of August 2021.

EXPERT OPINION

With encouraging early clinical results demonstrating extensive TME immunomodulation and abscopal effects on distant tumor lesions, tilsotolimod has emerged as a potential candidate immunomodulatory agent with the possibility to augment currently available immunotherapy and provide novel avenues of treatment for patients with advanced refectory cancer.

The Evolution of Antisense Oligonucleotide Chemistry-A Personal Journey

Over the last four decades, tremendous progress has been made in use of synthetic oligonucleotides as therapeutics. This has been possible largely by introducing chemical modifications to provide drug like properties to oligonucleotides. In this article I have summarized twists and turns on use of chemical modifications and their road to success and highlight areas of future directions.

Development of CpG oligodeoxynucleotide TLR9 agonists in anti-cancer therapy

INTRODUCTION

Toll-like receptor-9(TLR9) can recognize the foreign unmethylated CpG DNA, and thus intrigue a strong Th1 response which plays a crucial role in the innate and adaptive immune responses. To date, CpG oligodeoxynucleotide (ODN)-based TLR9 agonists have undergone four generations. Each generations' breakthroughs in immune activation, safety profiles and pharmacokinetic properties were confirmed by both preclinical and clinical studies.

AREAS COVERED

We reviewed the development and major clinical trials of TLR9 agonists and summarized the optimization strategies of each generation. The applications, limitations and prospects of TLR9 agonists in cancer immunotherapy are also discussed.

EXPERT OPINION

Clinical trials of CpG ODN TLR9 agonists as a single agent demonstrated insufficient efficacy to reverse the immunosuppressive status of majority of patients with high tumor burden. Therefore, more efforts are now been carried out in combination with chemotherapy, radiotherapy and immunotherapy maintenance therapy as well as vaccine adjuvant. Importantly, the synergistic and complementary effect of TLR9 agonists and tumor immune checkpoint inhibitor therapy is expected to exert greater potential. On the other hand, the double-edged sword effect of TLR9 activation in tumor and toxic effect reported in combination therapies should be noted and further studies required.

Targeting nuclear acid-mediated immunity in cancer immune checkpoint inhibitor therapies

Cancer immunotherapy especially immune checkpoint inhibition has achieved unprecedented successes in cancer treatment. However, there are many patients who failed to benefit from these therapies, highlighting the need for new combinations to increase the clinical efficacy of immune checkpoint inhibitors. In this review, we summarized the latest discoveries on the combination of nucleic acid-sensing immunity and immune checkpoint inhibitors in cancer immunotherapy. Given the critical role of nuclear acid-mediated immunity in maintaining the activation of T cell function, it seems that harnessing the nuclear acid-mediated immunity opens up new strategies to enhance the effect of immune checkpoint inhibitors for tumor control.

Modulation of the tumor microenvironment by intratumoral administration of IMO-2125, a novel TLR9 agonist, for cancer immunotherapy

The objective of cancer immunotherapy is to prime the host's immune system to recognize and attack malignant tumor cells. IMO‑2125, a Toll‑like receptor 9 (TLR9) agonist, exhibited potent antitumor effects in the murine syngeneic A20 lymphoma and the CT26 colon carcinoma models. IMO‑2125 exhibited superior A20 antitumor activity when injected intratumorally (i.t.) compared with equivalent subcutaneous doses. In mice bearing dual CT26 grafts, the i.t. injection of right flank tumors elicited infiltration of cluster of differentiation (CD)3+ T lymphocytes into tumors, resulting in the regression of injected and uninjected left flank tumors. Depletion of CD8+, but not CD4+, T‑cells abrogated the IMO‑2125‑mediated antitumor response, suggesting that CD8+ lymphocytes are required for the antitumor activity. In mice harboring right flank CT26 and left flank β‑galactosidase (β‑gal)‑expressing CT26.CL25 grafts, the i.t. administration of IMO‑2125 to the CT26 graft resulted in potent and dose‑dependent antitumor activity against the two grafts. Splenic T‑cells isolated from these mice responded to AH1 antigen (present in the two tumors) and β‑gal antigen (present only in CT26.CL25) in an interferon γ enzyme‑linked immunospot assay, suggesting the clonal expansion of T‑cells directed against antigens from the two tumors. Mice with ablated CT26 tumors by previous IMO‑2125 treatment rejected re‑implanted CT26 tumor cells, but not A20 tumor cells, demonstrating that the initial IMO‑2125 treatment created a long‑lived tumor‑specific immune memory of CT26 antigens. A quantitative increase in CD3+ T lymphocytes in injected A20 tumors and an upregulation of selected checkpoint genes, including indoleamine 2,3‑dioxygenase (IDO)‑1, IDO‑2, programmed cell death protein-1 (PD-1); programmed cell death protein ligand 1 (PD-L1), carcinoembryonic antigen‑related cell adhesion molecule 1, tumor necrosis factor receptor superfamily member 4 (OX40), OX40 ligand, T‑cell immunoglobulin and mucin‑domain‑containing 3 protein, lymphocyte‑activation gene 3, cytotoxic T‑lymphocyte‑associated protein 4, were observed following IMO‑2125 treatment. IMO‑2125 also increased immune checkpoint gene expression in injected and uninjected contralateral CT26 tumors, suggesting that the co‑administration of anti‑CTLA‑4, anti‑PD‑1 or anti‑PD‑L1 therapies with IMO‑2125 may provide additional therapeutic efficacy.

Immunostimulatory Properties of Lipid Modified CpG Oligonucleotides

Innate immune responses recognizing pathogen associated molecular patterns play important roles in adaptive immunity. As such, ligands which mimic the conserved products of microbial and activate innate immunity are widely used as adjuvants for vaccines. Synthetic single strand oligodeoxynucleotides (ODNs) containing unmethylated cytosine-guanine (CpG) motifs which bind Toll-like receptor 9 (TLR9) are powerful molecular adjuvants, potentiating both humoral and cellular responses. However, CpG ODN's in vitro potency has not been translated to in vivo settings primarily due to issues associated with delivery and toxicity. A major challenge in clinical application of CpG ODN is the efficient delivery to lymph nodes, the anatomic sites where all the immune responses are initiated. Targeting CpG to the key antigen presenting cells (APC) is essential for its application as a vaccine adjuvant, as it not only enhances CpG's efficacy, but also greatly reduces the systemic toxicity. We recently discovered an "albumin-hitchhiking" approach by which CpG ODNs were conjugated to a lipophilic lipid tail and follow subcutaneous injection, accumulated in lymph nodes by binding and transporting with endogenous albumin. This molecular approach targets CpG to antigen presenting cells in the draining lymph nodes via an endogenous albumin-mediated mechanism and simultaneously improves both the efficacy and safety of CpG as a vaccine adjuvant. Since CpG ODNs can be divided into structurally distinct classes, and each class of CpG ODN activates different types of immune cells and triggers different types of immunostimulatory activities, it is important to thoroughly evaluate the efficacy of this "albumin-hitchhiking" strategy in each class of CpG. Here we compare the immunostimulatory activities of three classes of lipid conjugated CpG ODNs in vitro and in vivo. Three representative sequences of lipid modified CpG ODNs were synthesized and their stimulatory effects as a vaccine adjuvant were evaluated. Our results showed that in vitro, lipid modified class A CpG exhibited enhanced stimulatory activities toward TLR transfected reporter cells or bone-marrow derived dendritic cells, whereas lipid-modification of class B or C CpG reduces the activation of TLR9 by 2-3 fold, as compared with unmodified class B and class C CpG, respectively. However, in vivo coadministration of ovalbumin (OVA) protein antigen mixed with lipid-conjugated class B or C CpG ODNs, but not class A CpGs induced dramatically increased OVA-specific humoral and cytotoxic CD8⁺ T cells responses compared with OVA mixed with unmodified CpGs. Further, lipid-modification greatly reduces the toxicity associated with CpG by minimizing the systemic dissemination. Taken together, these results demonstrated that amphiphilic modification of three classes of CpG motifs differentially affected and modulated the immunostimulatory activities in vitro and in vivo. Our study highlights the importance of in vivo lymph node targeting of CpG ODNs in fulfilling their use as vaccine adjuvants, providing implications for the rational design of molecular adjuvant for subunit vaccines.

Immunological and hematological toxicities challenging clinical translation of nucleic acid-based therapeutics

INTRODUCTION

Nucleic acid-based therapeutics (NATs) are proven agents in correcting disorders caused by gene mutations, as treatments against cancer, microbes and viruses, and as vaccine adjuvants. Although many traditional small molecule NATs have been approved for clinical use, commercialization of macromolecular NATs has been considerably slower, and only a few have successfully reached the market. Preclinical and clinical evaluation of macromolecular NATs has revealed many assorted challenges in immunotoxicity, hematotoxicity, pharmacokinetics (PKs), toxicology and formulation. Extensive review has been given to the PK and toxicological concerns of NATs including approaches designed to overcome these issues. Immunological and hematological issues are a commonly reported side effect of NAT treatment; however, literature exploring the mechanistic background of these effects is sparse.

AREAS COVERED

This review focuses on the immunomodulatory properties of various types of therapeutic nucleic acid concepts. The most commonly observed immunological and hematological toxicities are described for various NAT classes, with citations of how to circumvent these toxicities.

EXPERT OPINION

Although some success with overcoming immunological and hematological toxicities of NATs has been achieved in recent years, immunostimulation remains the main dose-limiting factor challenging clinical translation of these promising therapies. Novel delivery vehicles should be considered to overcome this challenge.

Epithelial toll-like receptor 9 signaling in colorectal inflammation and cancer: Clinico-pathogenic aspects

Toll-like receptors (TLRs) recognize specific motifs which are frequently present in bacteria, fungi, prokaryotes and viruses. Amongst TLRs, TLR9 can be activated by such bacterial or viral DNA fragments, immunoglobulin-DNA complexes or synthetic oligonucleotides, which all contain unmethylated cytosine-guanine nucleotide sequences (CpGs). Emerging data indicate that TLR9 signaling has a role in, and may influence, colorectal carcinogenesis and colonic inflammation. CpGs are classified into three groups according to their influence on both the antigen-specific humoral- and cellular immunity, and the production of type 1 interferons and proinflammatory cytokines. TLR9 activation via CpGs may serve as a new therapeutic target for several cancerous and various inflammatory conditions. Due to its probable anti-cancer effects, the application possibilities of TLR9-signaling modulation may be extremely diverse even in colorectal tumors. In this review we aimed to summarize the current knowledge about TLR-signaling in the pathogenesis and therapy of inflammatory bowel diseases and colorectal cancer. Due to the species-specific differences in TLR9 expression, however, one must be careful in translating the animal model data into the human system, because of the differences between CpG-oligodeoxynucleotide-responsive cells. TLR9 agonist DNA-based immunomodulatory sequences could also represent a promising therapeutic alternative in systemic inflammatory conditions and chronic colonic inflammations as their side effects are not significant.

Sequential induction of type I and II interferons mediates a long-lasting gene induction in the liver in response to a novel toll-like receptor 9 agonist

BACKGROUND & AIMS

The toll-like receptor 9 (TLR9) agonist IMO-2125 is currently evaluated in clinical trials for chronic hepatitis C therapy. The aim of this study was to investigate the in vivo mode of action of a closely related compound, referred to as immunomodulatory oligonucleotide (IMO).

METHODS

We analyzed the Jak-STAT pathway activation and induction of interferon-stimulated genes in the liver of wild type, interferon-α/β receptor-deficient and interferon-γ-deficient mice, after administration of IMO.

RESULTS

IMO induced a prolonged activation of the Jak-STAT pathway and upregulation of interferon-stimulated genes in the mouse liver. Contrary to the response observed after interferon-α injection, the signalling induced by IMO was not abrogated following repeated administration. At early time points after IMO injection, STAT1 phosphorylation and interferon-stimulated gene induction required a functional interferon-α/β receptor, whereas at the later time points, the activation was type I interferon-independent. Microarray analysis revealed that IMO induced a broad transcriptional response in the mouse liver. This included upregulation of cytokine and chemokine genes responsible for recruitment of IFN-γ producers, such as T cells and natural killer cells. Interferon-γ-deficient mice showed a transient response to IMO, demonstrating the central role of interferon-γ in sustained activation of Jak-STAT pathway by IMO.

CONCLUSIONS

The bimodal kinetics of response to IMO in the mouse liver are driven by the sequential endogenous production of type I and II interferons. The lack of refractoriness to IMO, combined with the long-lasting induction of interferon-stimulated genes, reveals a favourable pharmacodynamics profile of this novel TLR9 agonist for the treatment of chronic viral hepatitis.

Immune-Stimulatory Dinucleotide at the 5'-End of Oligodeoxynucleotides Is Critical for TLR9-Mediated Immune Responses

Oligodeoxynucleotides (ODNs) containing a CpG or certain synthetic dinucleotides, referred to as immune-stimulatory dinucleotides, induce Toll-like receptor 9 (TLR9)-mediated immune responses. Chemical modifications such as 2'-O-methylribonucleotides incorporated adjacent to the immune-stimulatory dinucleotide on the 5'-side abrogate TLR9-mediated immune responses. In this study, we evaluated the effect of the location of immune-stimulatory dinucleotides in ODNs on TLR9-mediated immune responses. We designed and synthesized ODNs with two immune-stimulatory dinucleotides, one placed toward the 5'-end region and the other toward the 3'-end region, incorporated 2'-O-methylribonucleotides selectively preceding the 5'- or 3'-immune-stimulatory dinucleotide or both, and studied TLR9-mediated immune responses of these compounds in cell-based assays and in vivo in mice. These studies showed that an immune-stimulatory dinucleotide located closer to the 5'-end is critical for and dictates TLR9-mediated immune responses. These studies provide insights for the use of ODNs when employed as TLR9 agonists and antagonists or antisense agents.

Design, synthesis and biological evaluation of novel antagonist compounds of Toll-like receptors 7, 8 and 9

Oligonucleotides containing an immune-stimulatory motif and an immune-regulatory motif act as antagonists of Toll-like receptor (TLR)7 and TLR9. In the present study, we designed and synthesized oligonucleotide-based antagonists of TLR7, 8 and 9 containing a 7-deaza-dG or arabino-G modification in the immune-stimulatory motif and 2′-O-methylribonucleotides as the immune-regulatory motif. We evaluated the biological properties of these novel synthetic oligoribonucleotides as antagonists of TLRs 7, 8 and 9 in murine and human cell-based assays and in vivo in mice and non-human primates. In HEK293, mouse and human cell-based assays, the antagonist compounds inhibited signaling pathways and production of a broad range of cytokines, including tumour necrosis factor alpha (TNF-α), interleukin (IL)-12, IL-6, interferon (IFN)-α, IL-1β and interferon gamma-induced protein (IP)-10, mediated by TLR7, 8 and 9. In vivo in mice, the antagonist compounds inhibited TLR7- and TLR9-mediated cytokine induction in a dose- and time-dependent fashion. Peripheral blood mononuclear cells (PBMCs) obtained from antagonist compound-treated monkeys secreted lower levels of TLR7-, 8- and 9-mediated cytokines than did PBMCs taken before antagonist administration. The antagonist compounds described herein provide novel agents for the potential treatment of autoimmune and inflammatory diseases.

An in situ autologous tumor vaccination with combined radiation therapy and TLR9 agonist therapy

PURPOSE

Recent studies have shown that a new generation of synthetic agonist of Toll-like receptor (TLR) 9 consisting a 3'-3'-attached structure and a dCp7-deaza-dG dinucultodie shows more potent immunostimulatory effects in both mouse and human than conventional CpG oligonucleotides. Radiation therapy (RT) provides a source of tumor antigens that are released from dying, irradiated, tumor cells without causing systemic immunosuppression. We, therefore, examined effect of combining RT with a designer synthetic agonist of TLR9 on anti-tumoral immunity, primary tumor growth retardation and metastases in a murine model of lung cancer.

METHODS

Grouped C57BL/6 and congenic B cell deficient mice (B(-/-)) bearing footpad 3LL tumors were treated with PBS, TLR9 agonist, control oligonucelotide, RT or the combination of RT and TLR9 agonist. Immune phenotype of splenocytes and serum IFN-γ and IL-10 levels were analyzed by FACS and ELISA, 24 h after treatment. Tumor growth, lung metastases and survival rate were monitored and tumor specific antibodies in serum and deposition in tumor tissue were measured by ELISA and immunofluorescence.

RESULTS

TLR9 agonist expanded and activated B cells and plasmacytoid dendritic cells in wild-type mice and natural killer DCs (NKDCs) in B cell-deficient (B(-/-)) mice bearing ectopic Lewis lung adenocarcinoma (3LL). Combined RT with TLR9 agonist treatment inhibited 3LL tumor growth in both wild type and B(-/-) mice. A strong tumor-specific humoral immune response (titer: 1/3200) with deposition of mouse IgG auto-antibodies in tumor tissue were found in wildtype mice, whereas the number of tumor infiltrating NKDCs increased in B(-/-) mice following RT+ TLR9 agonist therapy. Furthermore, mice receiving combination therapy had fewer lung metastases and a higher survival than single treatment cohorts.

CONCLUSIONS

Combination therapy with TLR9 agonist and RT induces systemic anti-tumoral humoral response, augments tumoral infiltration of NKDCs, reduces pulmonary metastases and improves survival in a murine model of 3LL cancer.

TLR9 agonist protects mice from radiation-induced gastrointestinal syndrome

Purpose

Radiation-induced gastrointestinal syndrome (RIGS) is due to the clonogenic loss of crypt cells and villi depopulation, resulting in disruption of mucosal barrier, bacterial invasion, inflammation and sepsis. Intestinal macrophages could recognize invading bacterial DNA via TLR9 receptors and transmit regenerative signals to the neighboring crypt. We therefore investigated whether systemic administration of designer TLR9 agonist could ameliorate RIGS by activating TLR9.

Methods and Materials

Male C57Bl6 mice were distributed in four experimental cohorts, whole body irradiation (WBI) (8.4–10.4 Gy), TLR9 agonist (1 mg/kg s.c.), 1 h pre- or post-WBI and TLR9 agonist+WBI+iMyd88 (pretreatment with inhibitory peptide against Myd88). Animals were observed for survival and intestine was harvested for histological analysis. BALB/c mice with CT26 colon tumors in abdominal wall were irradiated with 14 Gy single dose of whole abdominal irradiation (AIR) for tumor growth study.

Results

Mice receiving pre-WBI TLR9 agonist demonstrated improvement of survival after 10.4 Gy (p<0.03), 9.4 Gy (p<0.008) and 8.4 Gy (p<0.002) of WBI, compared to untreated or iMyd88-treated controls. Post-WBI TLR9 agonist mitigates up to 8.4 Gy WBI (p<0.01). Histological analysis and xylose absorption test demonstrated significant structural and functional restitution of the intestine in WBI+TLR9 agonist cohorts. Although, AIR reduced tumor growth, all animals died within 12 days from RIGS. TLR9 agonist improved the survival of mice beyond 28 days post-AIR (p<0.008) with significant reduction of tumor growth (p<0.0001).

Conclusions

TLR9 agonist treatment could serve both as a prophylactic or mitigating agent against acute radiation syndrome and also as an adjuvant therapy to increase the therapeutic ratio of abdominal Radiation Therapy for Gastro Intestinal malignancies.

Toll-like receptor 9 agonist IMO cooperates with cetuximab in K-ras mutant colorectal and pancreatic cancers

PURPOSE

K-Ras somatic mutations are a strong predictive biomarker for resistance to epidermal growth factor receptor (EGFR) inhibitors in patients with colorectal and pancreatic cancer. We previously showed that the novel Toll-like receptor 9 (TLR9) agonist immunomodulatory oligonucleotide (IMO) has a strong in vivo activity in colorectal cancer models by interfering with EGFR-related signaling and synergizing with the anti-EGFR monoclonal antibody cetuximab.

EXPERIMENTAL DESIGN

In the present study, we investigated, both in vitro and in vivo, the antitumor effect of IMO alone or in combination with cetuximab in subcutaneous colon and orthotopic pancreatic cancer models harboring K-Ras mutations and resistance to EGFR inhibitors.

RESULTS

We showed that IMO was able to significantly restore the sensitivity of K-Ras mutant cancer cells to cetuximab, producing a marked inhibition of cell survival and a complete suppression of mitogen-activated protein kinase phosphorylation, when used in combination with cetuximab. IMO interfered with EGFR-dependent signaling, modulating the functional interaction between TLR9 and EGFR. In vivo, IMO plus cetuximab combination caused a potent and long-lasting cooperative antitumor activity in LS174T colorectal cancer and in orthotopic AsPC1 pancreatic cancer. The capability of IMO to restore cetuximab sensitivity was further confirmed by using K-Ras mutant colorectal cancer cell models obtained through homologous recombination technology.

CONCLUSIONS

We showed that IMO markedly inhibits growth of K-Ras mutant colon and pancreatic cancers in vitro and in nude mice and cooperates with cetuximab via multiple mechanisms of action. Therefore, we propose IMO plus cetuximab as a therapeutic strategy for K-Ras wild-type as well for K-Ras mutant, cetuximab-resistant colorectal and pancreatic cancers.

Novel oligonucleotides containing two 3'-ends complementary to target mRNA show optimal gene-silencing activity

Oligonucleotides are being employed for gene-silencing activity by a variety of mechanisms, including antisense, ribozyme, and siRNA. In the present studies, we designed novel oligonucleotides complementary to targeted mRNAs and studied the effect of 3'-end exposure and oligonucleotide length on gene-silencing activity. We synthesized both oligoribonucleotides (RNAs) and oligodeoxynucleotides (DNAs) with phosphorothioate backbones, consisting of two identical segments complementary to the targeted mRNA attached through their 5'-ends, thereby containing two accessible 3'-ends; these compounds are referred to as gene-silencing oligonucleotides (GSOs). RNA and/or DNA GSOs targeted to MyD88, VEGF, and TLR9 mRNAs had more potent gene-silencing activity than did antisense phosphorothioate oligonucleotides (PS-oligos) in cell-based assays and in vivo. Of the different lengths of GSOs evaluated, 19-mer long RNA and DNA GSOs had the best gene-silencing activity both in vitro and in vivo. These results suggest that GSOs are novel agents for gene silencing that can be delivered systemically with broader applicability.

Toll-like receptor 9 agonists as cancer therapeutics

INTRODUCTION

Toll-like receptor 9 (TLR9) agonists, commonly referred to as CpG oligodeoxynucleotides (ODN), have been added to the arsenal of anti-cancer drugs as monotherapy or in combination with chemotherapy, radiotherapy and other immunotherapeutic approaches as they increase antigen presentation and boost anti-tumor T- and B-cell responses. Several synthetic TLR9 agonists have been developed for clinical grade use and displayed substantial efficacy in the preclinical and clinical models.

AREAS COVERED

This review summarizes TLR9 signaling and the impact of TLR9 agonists on the immune response. The most recent experimental and clinical data are analyzed as well as the development of new TLR9 agonists in current clinical trials.

EXPERT OPINION

Application of TLR9 agonists, in particular, combination strategies with chemo- or radiotherapy seem a promising and efficient immunotherapeutic approach in cancer patients even with refractory disease. Simultaneous application of TLR9 agonists aims at supporting the patient's immune response and overcoming specific immunosuppressant strategies developed by tumors. Combinatory approaches of the future might also seek for synergism of TLR9 agonists with other immunomodulatory strategies such as B-cell activation using the CD40-CD40L system.

Synthesis, purification, and characterization of immune-modulatory oligodeoxynucleotides that act as agonists of Toll-like receptor 9

Methods and protocols for automated synthesis and purification of immune modulatory oligonucleotides (IMOs), a novel class of Toll-like receptor 9 (TLR9) agonists, are described. IMOs containing two short identical sequences of 11-mers with phosphorothioate linkages can be synthesized in parallel synthetic strategy. A C3-linker that mimics the natural inter-nucleotide distance was commonly used for joining the two segments of IMOs. NittoPhase solid support bearing a symmetrical C3-linker (glycerol) and nucleoside-β-cyanoethyl-N,N-diisopropylphosphoramidites were used for IMO synthesis. The parallel synthesis was carried out in a 3'→ 5' direction with removal of the final dimethoxytrityl (DMT) protecting group. After synthesis, the IMO was cleaved and deprotected by treating with aqueous ammonia. The product was purified on anion-exchange HPLC, desalted, lyophilized, and characterized by anion-exchange HPLC, capillary gel electrophoresis, polyacrylamide gel electrophoresis, and MALDI-TOF mass spectral analysis.

Biodegradable CpG DNA hydrogels for sustained delivery of doxorubicin and immunostimulatory signals in tumor-bearing mice

Immunostimulatory CpG DNA was self-assembled to form DNA hydrogels for use as a sustained delivery system for both intercalated doxorubicin (DXR) and immunostimulatory CpG motifs for cancer treatment. X-shaped DNA (X-DNA) was designed as a building unit, and underwent ligation to form DNA hydrogels. Two types of X-DNA were constructed using four oligodeoxynucleotides each, one containing six potent CpG motifs (CpG X-DNA) and the other with none (CpG-free X-DNA). CpG X-DNA was more effective than its components or the CpG-free counterpart in terms of the production of tumor necrosis factor-α from murine macrophage-like RAW264.7 cells, as well as maturation of the murine dendritic DC2.4 cells. The cytotoxic effects of X-DNA, DXR and their complexes were examined in a co-culture system of colon26/Luc cells, a murine adenocarcinoma clone stably expressing firefly luciferase, and RAW264.7 cells. DXR/CpG X-DNA showed the highest ability to inhibit the proliferation of colon26/Luc cells. DXR was slowly released from CpG DNA hydrogels. Injections of DXR/CpG DNA hydrogels into a subcutaneous colon26 tumor effectively inhibited tumor growth. These results show that CpG DNA hydrogels are an effective sustained system for delivery of immunostimulatory signals to TLR9-positive immune cells and DXR to cancer cells.

Impact of nature and length of linker incorporated in agonists on toll-like receptor 9-mediated immune responses

Oligodeoxynucleotides containing unmethylated CpG motifs act as ligands of Toll-like receptor 9 (TLR9). We previously reported a novel class of TLR9 agonists, referred to as immune-modulatory oligonucleotides (IMOs), in which two 11-mers of the same sequence are attached via their 3'-ends through a 1,2,3-propanetriol linker and contain a synthetic immune-stimulatory motif, Cp7-deaza-dG. In the present study, we have examined the impact of length, nature, and stereochemistry of the linker incorporated in agonists for TLR9 activation. The new linkers studied include (S)-(-)-1,2,4-butanetriol, 1,3,5-pentanetriol, cis,cis-1,3,5-cyclohexanetriol, cis,trans-1,3,5-cyclohexanetriol, 1,3,5-tris(2-hydroxyethyl)isocyanurate, tetraethyleneglycol, and hexaethyleneglycol in place of 1,2,3-propanetriol linker. Agonists with various linkers are studied for TLR9-mediated immune responses in HEK293 cells, human cell-based assays, and in vivo in mice. Results of these studies suggest that C3-C5 linkers, 1,2,3-propanetriol, (S)-(-)-1,2,4-butanetriol, or 1,3,5-pentanetriol, are optimal for stimulation of TLR9-mediated immune responses. Rigid C3 linkers with different stereochemistry have little effect on immune stimulation, while linkers longer than C5 reduced TLR9-mediated immune stimulation.

A TLR9 agonist enhances therapeutic effects of telomerase genetic vaccine

The telomerase reverse transcriptase (TERT) is an attractive target for cancer vaccination because its expression is reactivated in most tumors. In this study, we have evaluated the ability of a genetic vaccine targeting murine TERT (mTERT) based on DNA electroporation (DNA-EP) and adenovirus serotype 6 (Ad6) to exert therapeutic effects in combination with a novel TLR9 agonist, referred to as immune modulatory oligonucleotide (IMO), as an adjuvant. IMO was administered to mice at the same time as vaccine. IMO induced dose-dependent cytokine secretion and activation of NK cells. Most importantly, vaccination of mice with IMO in combination with mTERT vaccine conferred therapeutic benefit in tumor bearing animals and this effect was associated with increased NK, DC and T cell tumor infiltration. These data show that appropriate combination of a DNA-EP/Ad6-based cancer vaccine against TERT with IMO induces multiple effects on innate and adaptive immune responses resulting in a significant antitumor efficacy.

Synthesis and immunological activities of novel agonists of toll-like receptor 9

Novel agonists of TLR9 with two 5'-ends and synthetic immune stimulatory motifs, referred to as immune modulatory oligonucleotides (IMOs) are potent agonists of TLR9. In the present study, we have designed and synthesized 15 novel IMOs by incorporating specific chemical modifications and studied their immune response profiles both in vitro and in vivo. Analysis of the immunostimulatory profiles of these IMOs in human and NHP cell-based assays suggest that changes in the number of synthetic immunostimulatory motifs gave only a subtle change in immune stimulation of pDCs as indicated by IFN-alpha production and pDC maturation while the addition of self-complementary sequences produced more dramatic changes in both pDC and B cell stimulation. All IMOs induced cytokine production in vivo immediately after administration in mice. Representative compounds were also compared for the ability to stimulate cytokine production in vivo (IFN-alpha and IP-10) in rhesus macaques after intra-muscular administration.

Emerging oligonucleotide therapies for asthma and chronic obstructive pulmonary disease

Chronic respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD) are disorders of the airways largely related to the presence of persistent inflammation. The approval of inhaled corticosteroids in the early 1970s pioneered a new age of therapy in treating chronic inflammatory airway diseases. This was the first time that an anti-inflammatory product was available to reduce the characteristic lung inflammation in airways and the associated obstruction, inflammation and hyper-responsiveness. Fast forward 40 years: corticosteroids are still an important therapeutic intervention; however, they exhibit limited use in moderate to severe asthma and COPD. Oligonucleotide therapies are an emerging class which include the antisense, the RNAi (siRNA and miRNA), the immunomodulatory, the aptamer and the decoy approaches. As these approaches are rather recent in the respiratory field, most are still early in development. Nevertheless, with limitations of current small molecule therapies and the hurdles faced with biologics, the use of oligonucleotides is relevant and the door is open to the development of this category of therapeutics. This review focuses on the major classes of oligonucleotides that are currently in late stage preclinical or clinical development for the treatment of asthma and COPD, and discusses the implications for their use as therapies for respiratory diseases.

A novel toll-like receptor 9 agonist cooperates with trastuzumab in trastuzumab-resistant breast tumors through multiple mechanisms of action

PURPOSE

Resistance to anti-HER2 monoclonal antibody trastuzumab is a relevant issue in breast cancer patients. Among the mechanisms implicated in trastuzumab resistance, increasing evidence supports a role of tumor microenvironment. We previously found that a novel toll-like receptor 9 agonist, referred to as immune modulatory oligonucleotide (IMO) and currently under clinical investigation, acts through epidermal growth factor receptor (EGFR) and shows direct antiangiogenic effects by cooperating with anti-EGFR or anti-VEGF drugs, thus interfering with cancer cells and microenvironment.

EXPERIMENTAL DESIGN

In this study, we used KPL-4 and JIMT-1 trastuzumab-resistant breast cancer cells to evaluate the combination IMO plus trastuzumab as a therapeutic option for trastuzumab-resistant breast cancers.

RESULTS

IMO inhibits KPL-4 and JIMT-1 xenografts growth and potentiates trastuzumab antitumor effect, with complete suppression of tumor growth, potent enhancement of trastuzumab-mediated antibody-dependent cell-mediated cytotoxicity, and strong inhibition of EGFR/HER2-related signaling. In KPL-4 xenografts, IMO alone interferes with HER signal transduction, whereas trastuzumab is ineffective. IMO induces an HER-dependent signal inhibition also in vitro by modulating a functional interaction between toll-like receptor 9 and HER receptors occurring at membrane level. Finally, IMO plus trastuzumab produces a cooperative antiangiogenic effect related to suppression of endothelial HER-related signaling.

CONCLUSIONS

We showed a cooperative effect of IMO plus trastuzumab in trastuzumab-resistant breast cancers due to IMO direct antitumor and antiangiogenic activity and antibody-dependent cell-mediated cytotoxicity enhancement. Moreover, we provided first evidence of a toll-like receptor 9/HER interaction at membrane level as novel mechanism of action. Altogether, we propose IMO plus trastuzumab as an effective strategy in trastuzumab-resistant breast cancers.

Coadministration of telomerase genetic vaccine and a novel TLR9 agonist in nonhuman primates

The human telomerase reverse transcriptase (hTERT) is an attractive target for human cancer vaccination because its expression is reactivated in most human tumors. We have evaluated the ability of DNA electroporation (DNA-EP) and adenovirus serotype 6 (Ad6) to induce immune responses against hTERT in nonhuman primates (NHPs) (Macaca mulatta). Vaccination was effective in all treated animals, and the adaptive immune response remained detectable and long lasting without side effects. To further enhance the efficacy of the hTERT vaccine, we evaluated the combination of hTERT vaccine and a novel TLR9 agonist, referred to as immunomodulatory oligonucleotide (IMO). Monkeys were dosed weekly with IMO concurrently with the vaccine regimen and showed increases in cytokine secretion and activation of natural killer (NK) cells compared with the group that received vaccine alone. Using a peptide array, a specific profile of B-cell reactive epitopes was identified when hTERT vaccine was combined with IMO. The combination of IMO with hTERT genetic vaccine did not impact vaccine-induced TERT-specific cell-mediated immunity. Our results show that appropriate combination of a DNA-EP/Ad6-based cancer vaccine against hTERT with IMO induces multiple effects on innate and adaptive immune responses in NHPs.

Oligodeoxyribonucleotide-based antagonists for Toll-like receptors 7 and 9

Oligodeoxyribonucleotides containing unmethylated CpG motifs act as TLR9 agonists. In this study, we evaluated oligonucleotides containing an unmethylated CpG motif in which two nucleotides adjacent to the CpG dinucleotide were substituted with 2'-O-methylribonucleotides, resulting in TLR7 and TLR9 antagonists. In mouse and human cell cultures, antagonists did not stimulate immune activation but inhibited TLR7 and TLR9 agonist-induced activity. In mice, antagonists inhibited immune responses induced by TLR9 agonists for up to several days, and the inhibition was dose-dependent. Antagonists also inhibited immune responses induced by an RNA-based TLR7/8 agonist but not TLRs 2, 3, 4, or 5 agonists in mice. Additionally, antagonist inhibited TLR9 agonist-induced IL-6 in lupus-prone MRL/lpr mouse spleen cell cultures. These results indicate that antagonists described herein can suppress immune responses induced by TLR7 and TLR9 agonists. Antagonists may be suitable candidates for treating inflammatory and autoimmune diseases where inappropriate or uncontrolled TLR activation has been implicated.

Impact of secondary structure of toll-like receptor 9 agonists on interferon alpha induction

Oligodeoxynucleotides containing a CpG motif and double- or multistranded structure-forming sequences act as agonists of Toll-like receptor 9 (TLR9) and induce high levels of interferon alpha (IFN-alpha) in addition to other Th1-type cytokines. In the present study, we evaluated three highly effective IFN-alpha-inducing agonists of TLR9 to determine the type of duplex structures formed and the agonist's ability to induce immune responses, including IFN-alpha induction, in human cell-based assays and in vivo in mice and nonhuman primates. Thermal melting studies showed that two of the agonists evaluated had a single melting transition with similar hyperchromicity in both heating and cooling cycles, suggesting the formation of intermolecular duplexes. A third agonist showed a biphasic melting transition in the heating cycle and a monophasic melting transition with lower hyperchromicity during the cooling cycle, suggesting the formation of both intra- and intermolecular duplexes. All three agonists induced the production of Th1-type cytokines and chemokines, including high levels of IFN-alpha, in human peripheral blood mononuclear cell and plasmacytoid dendritic cell cultures. Subcutaneous administration of the two intermolecular duplex-forming agonists, but not the intramolecular duplex-forming agonist, induced cytokine secretion in mice. In nonhuman primates, the two agonists that formed intermolecular duplexes induced IFN-alpha and IP-10 secretion. On the contrary, the agonist that formed an intramolecular duplex induced only low levels of cytokines in nonhuman primates, suggesting that this type of structure formation is less immunostimulatory in vivo than the other structure. Taken together, the present results suggest that oligonucleotide-based agonists of TLR9 that form intermolecular duplexes induce potent immune responses in vivo.

Immunostimulatory CpG oligonucleotides form defined three-dimensional structures: results from an NMR study

The DNA eicosamer 5'-TCCATGACGTTCCTGATGCT-3' is known to stimulate the innate immune system of vertebrae. The immunostimulatory activity is based on the activation of Toll-like receptor 9 (TLR9). While it is known that the CG dinucleotide of the eicosamer has to be unmethylated, the structural basis of the recognition of the DNA through the receptor remains unclear. Oligodeoxynucleotides containing the sequence of the eicosamer, or a portion thereof, ranging in length from hexamer to pentaeicosamer were studied by (1)H NMR spectroscopy. Based on two-dimensional NMR spectra, a number of resonances could be unambiguously assigned. For all oligonucleotides, structural transitions were detected upon heating, as monitored by the line width and chemical shift of low-field resonances. This includes the TC dinucleotide of the 5'-terminal portion, which does not have any clear base-pairing partners. The melting transitions, together with the NOESY cross-peaks, demonstrate that structure formation occurs well beyond the core hexamer 5'-GACGTT-3', a fact that may be important for understanding the molecular recognition by the Toll-like receptors of the innate immune system.

Immunostimulatory DNA as a vaccine adjuvant

Immunostimulatory DNA containing unmethylated CpG motifs is recognized by Toll-like receptor 9, resulting in the activation of innate immune responses that subsequently amplify the adaptive-immune response. Advances in the characterization of Toll-like receptor 9 signaling have identified immunostimulatory sequences (ISS) with distinct biological activities. Numerous animal models have demonstrated that synthetic ISS are effective adjuvants that enhance both humoral and cellular immune responses in diverse indications, ranging from infectious disease to cancer and allergy. An added benefit supporting the use of ISS as a vaccine adjuvant is that the specific activation of a pathway critical to the regulation of the immune response results in minimal toxicity. To date, clinical testing has largely affirmed the potency and safety of ISS-adjuvanted vaccines.

Synthetic agonists of Toll-like receptors 7, 8 and 9

TLRs (Toll-like receptors) are a family of innate immune receptors that induce protective immune responses against infections. Single-stranded viral RNA and bacterial DNA containing unmethylated CpG motifs are the ligands for TLR7 and TLR8 and 9 respectively. We have carried out extensive structure–activity relationship studies of DNA- and RNA-based compounds to elucidate the impact of nucleotide motifs and structures on these TLR-mediated immune responses. These studies have led us to design novel DNA- and RNA-based compounds, which act as potent agonists of TLR9 and TLR7 and 8 respectively. These novel synthetic agonists produce different immune response profiles depending on the structures and nucleotide motifs present in them. The ability to modulate TLR-mediated immune responses with these novel DNA- and RNA-based agonists in a desired fashion may allow targeting a broad range of diseases, including cancers, asthma, allergies and infections, alone or in combination with other therapeutic agents, and their use as adjuvants with vaccines. IMO-2055, our first lead candidate, is a TLR9 agonist that is currently in clinical evaluation in oncology patients. A second candidate, IMO-2125, is also a TLR9 agonist that has been shown to induce high and sustained levels of IFN (interferon) in non-human primates and is being evaluated in HepC-infected human subjects.

Agonists of Toll-like receptor 9 containing synthetic dinucleotide motifs

Oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs activate Toll-like receptor 9 (TLR9). Our previous studies have shown that ODNs containing two 5'-ends are more immunostimulatory than those with one 5'-end. In the present study, to understand the role of functional groups in TLR9 recognition and subsequent immune response, we substituted C or G of a CpG dinucleotide with 5-OH-dC, 5-propyne-dC, furano-dT, 1-(2'-deoxy-beta- d-ribofuranosyl)-2-oxo-7-deaza-8-methyl-purine, dF, 4-thio-dU, N(3)-Me-dC, N (4)-Et-dC, Psi-iso-dC, and arabinoC or 7-deaza-dG, 7-deaza-8-aza-dG, 9-deaza-dG, N(1)-Me-dG, N(2)-Me-dG, 6-Thio-dG, dI, 8-OMe-dG, 8-O-allyl-dG, and arabinoG in ODN containing two 5'-ends. Agonists of TLR9 containing cytosine or guanine modification showed activity in HEK293 cells expressing TLR9, mouse spleen, and human cell-based assays and in vivo in mice. The results presented here provide insight into which specific chemical modifications at C or G of the CpG motif are recognized by TLR9 and the ability to modulate immune responses substituting natural C or G in immune modulatory oligonucleotides.

Structure-efficacy relationships of immunostimulatory activity of CpG-containing oligodeoxynucleotides on mouse spleen cells

AIM

To study the relationship between primary structures of oligodeoxynucleotides (ODN) containing unmethylated deoxycytidyldeoxyguanosine (CpG) dinucleotide motifs and their immunostimulatory activities in mouse spleen cells.

METHODS

A series of CpG ODN with different primary structures were synthesized. Their capabilities to stimulate mouse spleen cell proliferation were determined by [3H]thymidine incorporation assay. Cytokine (interleukin [IL]-6, IL-12, and IFN-alpha) secretion spectra induced by CpG ODN were assessed by ELISA. The ability of CpG ODN to activate natural killer cells was evaluated by standard 4 h (51)Cr-release assay. Flow cytometry was utilized to examine the expressions of various lymphocyte surface molecules on diverse immunocytes. An effective CpG ODN for murine, ODN1826, was set as the template of modification and the positive control.

RESULTS

The immunostimulatory activities of CpG ODN with different sequences and compositions varied markedly, both in character and in extent. It was useless for improving the immunostimulatory activity of ODN1826 by simply increasing the functional hexameric CpG motif number, modifying the site of CpG motifs, or changing the distance between multi-CpG motifs. However, an addition of a self-complementary palindrome structure at the 3'-end, but not the 5'-end of CpG ODN, aroused marked improvement in its activity. Several designed ODN had superior comprehensive immunostimulatory properties compared to ODN1826.

CONCLUSION

The immunostimulatory activity of a CpG ODN was relevant to its primary structure. It was useless for promoting immunostimulatory activity to simply change CpG motif number, space, or distance. The 3'-end palindrome structure of CpG ODN is associated with enhanced immunostimulatory activity.

Stabilized immune modulatory RNA compounds as agonists of Toll-like receptors 7 and 8

Viral and synthetic single-stranded RNAs are the ligands for Toll-like receptor (TLR)7 and TLR8. However, single-stranded RNA is rapidly degraded by ubiquitous RNases, and the studies reported to date have used RNA with lipid carriers. To overcome nuclease susceptibility of RNA, we have synthesized several RNAs incorporating a range of chemical modifications. The present study describes one pool of RNA compounds, referred to as stabilized immune modulatory RNA (SIMRA) compounds, in which two RNA segments are attached through their 3' ends. SIMRA compounds showed greater stability in human serum compared with linear RNA and activated human TLR8, but not TLR7, in HEK293 cells without using lipid carriers. Interestingly, another set of SIMRA compounds containing 7-deazaguanosine substituted for natural guanosine activated human TLR7 and TLR8. Additionally, TLR7- and TLR8-activating compounds, but not the compounds that activated only TLR8, stimulated mouse immune cells in vitro and in vivo and produced dose-dependent T helper 1-type cytokines. Both types of compounds activated human peripheral blood mononuclear cells, but only TLR7- and TLR8-activating compounds activated plasmacytoid dendritic cells and produced high levels of IFN-alpha. In monkeys, s.c. administration of both types of SIMRA compounds induced transient changes in peripheral blood monocytes and neutrophils, and activated T lymphocytes, monocytes, and NK cells. Both types of compounds induced IFN-gamma-inducible protein 10, but only the 7-deazaguanosine-containing compound that activated both TLR7 and TLR8 induced IFN-alpha in monkeys. This is a comprehensive study of RNA-based compounds containing structures and synthetic stimulatory motifs in mouse, monkey, and human systems without using lipid carriers.

TLR9 agonist acts by different mechanisms synergizing with bevacizumab in sensitive and cetuximab-resistant colon cancer xenografts

Synthetic agonists of Toll-like receptor 9 (TLR9), a class of agents that induce specific immune response, exhibit antitumor activity and are currently being investigated in cancer patients. Intriguingly, their mechanisms of action on tumor growth and angiogenesis are still incompletely understood. We recently discovered that a synthetic agonist of TLR9, immune modulatory oligonucleotide (IMO), acts by impairing epidermal growth factor receptor (EGFR) signaling and potently synergizes with anti-EGFR antibody cetuximab in GEO human colon cancer xenografts, whereas it is ineffective in VEGF-overexpressing cetuximab-resistant GEO cetuximab-resistant (GEO-CR) tumors. VEGF is activated by EGFR, and its overexpression causes resistance to EGFR inhibitors. Therefore, we used IMO and the anti-VEGF antibody bevacizumab as tools to study IMO's role on EGFR and angiogenesis and to explore its therapeutic potential in GEO, LS174T, and GEO-CR cancer xenografts. We found that IMO enhances the antibody-dependent cell-mediated cytotoxicity (ADCC) activity of cetuximab, that bevacizumab has no ADCC, and IMO is unable to enhance it. Nevertheless, the IMO-plus-bevacizumab combination synergistically inhibits the growth of GEO and LS174T as well as of GEO-CR tumors, preceded by inhibition of signaling protein expression, microvessel formation, and human, but not murine, VEGF secretion. Moreover, IMO inhibited the growth, adhesion, migration, and capillary formation of VEGF-stimulated endothelial cells. The antitumor activity was irrespective of the TLR9 expression on tumor cells. These studies demonstrate that synthetic agonists of TLR9 interfere with growth and angiogenesis also by EGFR- and ADCC-independent mechanisms affecting endothelial cell functions and provide a strong rationale to combine IMO with bevacizumab and EGFR inhibitory drugs in colon cancer patients.

Oral administration of a synthetic agonist of Toll-like receptor 9 potently modulates peanut-induced allergy in mice

BACKGROUND

Agonists of Toll-like receptor 9 have been shown to induce potent T(H)1-type immune responses and prevent and reverse ovalbumin-induced T(H)2-dominant allergic asthma in mice.

OBJECTIVE

We examined oral administration of a synthetic agonist of Toll-like receptor 9 (immune modulatory oligonucleotide [IMO]) to modulate peanut-induced allergy in mice.

METHODS

In the prevention model mice were sensitized 3 times by means of oral administration of peanut in the presence or absence of IMO. In a treatment protocol mice were sensitized orally with peanut on days 0 and 14 and treated 4 times with oral administration of IMO starting on day 21.

RESULTS

In the prevention study mice that received the combination of IMO/peanut showed decreased IgE and increased IgG2a levels in the serum and intestinal tissue compared with mice sensitized with peanut only. In spleen cell recall experiments, production of IL-5 and IL-13 was inhibited and production of IFN-gamma was increased in mice immunized with the peanut/IMO combination compared with those sensitized with peanut only. In the treatment model IMO-treated mice showed decreased IgE, IL-5, and IL-13 levels and increased IgG2a and IFN-gamma levels in the serum, intestines, and spleen cells compared with PBS-treated mice. A reduction in local inflammation and restoration of normal structure in the intestines was found in the mice that received IMO in both models.

CONCLUSION

These results indicate that IMOs can switch peanut-induced T(H)2 immune responses toward T(H)1 responses accompanied by reduced inflammation in the gastrointestinal tract and anaphylaxis in both the prevention and treatment models.

CLINICAL IMPLICATIONS

IMOs might be suitable candidates for the management of peanut-induced allergy.

Current and future drugs targeting one class of innate immunity receptors: the Toll-like receptors

Innate immunity receptors are germline-encoded receptors that can sense molecular signatures of pathogens and cancer cells. Recent advances in immunology demonstrate the key role of these receptors in inflammation and initiation of subsequent immune responses, including adaptive immunity. Pharmaceutical interest in this field has grown with the retrospective demonstration that some marketed drugs targeting cancer or infectious diseases act via those receptors. In this review, I present an update on the scientific rationale for targeting one class of innate immunity receptor, the Toll-like receptors, and an update on the development status of corresponding drug candidates in infectious diseases, cancer, allergy and vaccines.

Immunomodulatory oligonucleotides as novel therapy for breast cancer: pharmacokinetics, in vitro and in vivo anticancer activity, and potentiation of antibody therapy

Oligonucleotides containing CpG motifs and immunomodulatory oligonucleotides (IMO) containing a synthetic immunostimulatory dinucleotide and a novel DNA structure have been suggested to have potential for the treatment of various human diseases. In the present study, a newly designed IMO was evaluated in several models of human (MCF-7 and BT474 xenograft) and murine (4T1 syngeneic) breast cancer. Pharmacokinetics studies of the IMO administered by s.c., i.v., p.o., or i.p. routes were also accomplished. The IMO was widely distributed to various tissues by all four routes, with s.c. administration yielding the highest concentration in tumor tissue. The IMO inhibited the growth of tumors in all three models of breast cancer, with the lowest dose of the IMO inhibiting MCF-7 xenograft tumor growth by >40%. Combining the IMO with the anticancer antibody, Herceptin, led to potent antitumor effects, resulting in >96% inhibition of tumor growth. The IMO also exerted in vitro antitumor activity, as measured by cell growth, apoptosis, and proliferation assays in the presence of Lipofectin. This is the first report of the pharmacokinetics of this agent in normal and tumor-bearing mice. Based on the present results, we believe that the IMO is a good candidate for clinical development for breast cancer therapy used either alone or in combination with conventional cancer therapeutic agents.

Experimental therapy of prostate cancer with an immunomodulatory oligonucleotide: effects on tumor growth, apoptosis, proliferation, and potentiation of chemotherapy

BACKGROUND

The present study was designed to demonstrate the therapeutic efficacy of a novel immunomodulatory oligonucleotide (IMO) for prostate cancer.

METHODS

We evaluated the effects of the IMO in xenograft (PC-3) and syngeneic (TRAMP C1) models of prostate cancer, and in prostate cancer cells. The IMO was also evaluated in combination with chemotherapy, and the in vitro expression of TLR9 was examined.

RESULTS

The IMO had significant anti-tumor activity in both prostate cancer models and almost complete tumor regression was observed when the IMO was combined with taxotere or gemcitabine. TLR9 mRNA and protein were both expressed in prostate cancer cells. The IMO also induced apoptosis and decreased proliferation and survival of PC-3 cells in vitro in the presence of Lipofectin.

CONCLUSIONS

The IMO inhibits prostate cancer growth in vivo and in vitro, and potentiates the effects of conventional chemotherapeutic agents. This is the first report of TLR9 expression in prostate cancer cells.

Chemotherapy and chemosensitization of non-small cell lung cancer with a novel immunomodulatory oligonucleotide targeting Toll-like receptor 9

Lung cancer is a leading cause of death world-wide and the long-term survival rate for lung cancer patients is one of the lowest for any cancer. New therapies are urgently needed. The present study was designed to evaluate an immunomodulatory oligonucleotide as a novel type of therapy for lung cancer. The in vivo effects of the immunomodulatory oligonucleotides were determined in four tumor models derived from human non-small cell lung cancer (NSCLC) cell lines (A549, H1299, H358, and H520), administered alone or in combination with conventional chemotherapeutic agents used to treat lung cancer. The in vitro effects of the immunomodulatory oligonucleotide on the growth, apoptosis, and proliferation of NSCLC cells were also determined. We also examined NSCLC cells for expression of Toll-like receptor 9 (TLR9), the receptor for the immunomodulatory oligonucleotide. We showed several important findings: (a) treatment with the immunomodulatory oligonucleotide led to potent antitumor effects, inhibiting tumor growth by at least 60% in all four in vivo models; (b) combination with the immunomodulatory oligonucleotide led to enhanced effects following treatment with gemcitabine or Alimta; (c) the immunomodulatory oligonucleotide increased apoptosis, decreased proliferation, and decreased survival in A549 cells in vitro; and (d) both TLR9 mRNA and protein were expressed in NSCLC cells. The immunomodulatory oligonucleotide has potent antitumor effects as monotherapy and in combination with conventional chemotherapeutic agents, and may act directly on NSCLC cells via TLR9. The present study provides a rationale for developing the immunomodulatory oligonucleotide for lung cancer therapy.

CpG oligodeoxynucleotide-induced immunity prevents growth of germinal center-derived B lymphoma cells

Therapeutic efficacy of CpG oligodeoxynucleotide (ODN) ISS 1018 was tested in a murine B cell lymphoma model. Previous studies showed that the B lymphoma cells of SJL mice stimulate vigorous proliferation of host CD4(+) TH cells that is unaccompanied by development of tumor-specific CTL. In the presence of ISS 1018, however, tumor cells stimulated high levels of CTL activity in vitro, and this cytotoxic activity was inhibited when anti-IL-12 mAb was added to the cultures. Tumor cells pre-incubated with ISS 1018 were also able to generate CTL without addition of exogenous ODN, and FACS analysis revealed that following incubation with ISS 1018 for 24 h, tumor cells exhibited upregulation of MHC I, MHC II, and co-stimulatory molecule CD80. Finally, tumor-injected mice treated with ISS 1018 showed significantly less growth of tumor cells in lymph nodes and spleen, and exhibited prolonged survival compared to mice treated with a control ODN. The documented effects of CpG ODNs to stimulate cytokines, such as IL-12, from antigen presenting cells, and to upregulate expression of MHC Class I and Class II, as well as co-stimulatory molecules on tumor cells, are also the likely mechanisms by which CTL are generated by ISS 1018 in the SJL B cell lymphoma model.

Novel oligodeoxynucleotide agonists of TLR9 containing N3-Me-dC or N1-Me-dG modifications

Synthetic oligodeoxynucleotides containing unmethylated CpG motifs activate Toll-Like Receptor 9 (TLR9). Our previous studies have shown the role of hydrogen-bond donor and acceptor groups of cytosine and guanine in the CpG motif and identified synthetic immunostimulatory motifs. In the present study to elucidate the significance of N3-position of cytosine and N1-position of guanine in the CpG motif, we substituted C or G of a CpG dinucleotide with N3-Me-cytosine or N1-Me-guanine, respectively, in immunomodulatory oligodeoxynucleotides (IMOs). IMOs containing N-Me-cytosine or N-Me-guanine in C- or G-position, respectively, of the CpG dinucleotide showed activation of HEK293 cells expressing TLR9, but not TLR3, 7 or 8. IMOs containing N-Me-cytosine or N-Me-guanine modification showed activity in mouse spleen cell cultures, in vivo in mice, and in human cell cultures. In addition, IMOs containing N-Me-substitutions reversed antigen-induced Th2 immune responses towards a Th1-type in OVA-sensitized mouse spleen cell cultures. These studies suggest that TLR9 tolerates a methyl group at N1-position of G and a methyl group at N3-position of C may interfere with TLR9 activation to some extent. These are the first studies elucidating the role of N3-position of cytosine and N1-position of guanine in a CpG motif for TLR9 activation and immune stimulation.

Extended sequence preferences for oligodeoxyribonucleotide activity

Synthetic type B phosphorothioate oligodeoxyribonucleotides (ODN) activate mouse B cells via Toll-like receptor 9 (TLR9). Starting with closely related 15-mer prototype ODN, the sequence requirements for stimulatory (ST-) and inhibitory (IN-) activity were contrasted, by measuring apoptosis protection, G(1) entry and interleukin-6 secretion. ST-ODN and IN-ODN differ in that (1) ST-ODN require a 5' T, (2) the central CG is obligatory, (3) CG must be flanked 3' specifically by TT at the position where IN-ODN have GG, and (4) IN-ODN tolerate truncation of the 3' end better than ST-ODN. Features shared by ST-ODN and IN-ODN include (1) requiring CC adjacent to the 5' end, and (2) avoiding CC immediately 5' to the CG. This pattern is used to create a model of how ST-ODN binding might function to aggregate TLR9 so as to initiate the signal, and how the 5' ends of ST-ODN and IN-ODN compete for binding. Further justification for considering TLR9 to be the ODN receptor was provided by a demonstration that in HEK293 cells transfected with TLR9, the potency of a panel of ODN for activating NF-kappaB roughly parallels that seen in the biological assays in mouse B cells.

Novel toll-like receptor 9 agonist induces epidermal growth factor receptor (EGFR) inhibition and synergistic antitumor activity with EGFR inhibitors

PURPOSE

Immunostimulating Toll-like receptor 9 (TLR9) agonists cause antitumor activity interfering also with cancer proliferation and angiogenesis by mechanisms still incompletely understood. We hypothesized that modified TLR9 agonists could impair epidermal growth factor receptor (EGFR) signaling and, by this means, greatly enhance EGFR inhibitors effect, acting on both the receptor targeting and the immunologic arm.

EXPERIMENTAL DESIGN

We used a novel second-generation, modified, immunomodulatory TLR9 agonist (IMO), alone and in combination with the anti-EGFR monoclonal antibody cetuximab or tyrosine kinase inhibitor gefitinib, on the growth of GEO and cetuximab-resistant derivatives GEO-CR colon cancer xenografts. We have also evaluated the expression of several proteins critical for cell proliferation, apoptosis, and angiogenesis, including EGFR, mitogen-activated protein kinase, Akt, bcl-2, cyclooxygenase-2, vascular endothelial growth factor, and nuclear factor-kappaB.

RESULTS

IMO inhibited GEO growth and signaling by EGFR and the other proteins critical for cell proliferation and angiogenesis. IMO plus the anti-EGFR antibody cetuximab synergistically inhibited tumor growth, signaling proteins, and microvessel formation. EGFR signaling inhibition by IMO is relevant because IMO cooperated also with EGFR tyrosine kinase inhibitor gefitinib in GEO tumors, while it was inactive against GEO-CR xenografts. On the other hand, IMO boosted the non-EGFR-dependent cetuximab activity, causing a cooperative antitumor effect in GEO-CR cells. Finally, combination of IMO, cetuximab and chemotherapeutic irinotecan eradicated the tumors in 90% of mice.

CONCLUSION

IMO interferes with EGFR-related signaling and angiogenesis and has a synergistic antitumor effect with EGFR inhibitors, especially with cetuximab, boosting both the EGFR dependent and independent activity of this agent. Moreover, this therapeutic strategy could be translated in patients affected by colorectal cancer.

CpG immunomer DNA enhances antisense protein kinase A RIalpha inhibition of multidrug-resistant colon carcinoma growth in nude mice: molecular basis for combinatorial therapy

PURPOSE

CpG DNAs induce cytokines, activate natural killer cells, and elicit vigorous T-cell response leading to antitumor effects. Antisense oligodeoxynucleotides targeted against the RIalpha subunit of protein kinase A (antisense PKA RIalpha) induce growth arrest, apoptosis, and differentiation in a variety of cancer cell lines in vitro and in vivo. This study investigated the use of a combinatorial therapy consisting of the RNA-DNA second-generation antisense PKA RIalpha and the CpG immunomer (CpG DNA linked through 3'-3' linkage containing two accessible 5' ends).

EXPERIMENTAL DESIGN

HCT-15 multidrug-resistant colon carcinoma growth in nude mice was used as an experimental model. The inhibitory effect on tumor growth and apoptotic activity of antisense RIalpha and CpG immunomer, singly and in combination, were measured by tumor growth, levels of RIalpha subunit, and antiapoptotic and proapoptotic proteins. Effect on host-immune system was measured by mouse spleen size, interleukin-6 (IL-6) levels in mouse blood, and nuclear factor-kappaB (NF-kappaB) transcription activity in mouse spleen cells.

RESULTS

In combination, CpG immunomer and antisense PKA RIalpha induced additive/supra-additive effect on the inhibition of tumor growth. Antisense RIalpha but not CpG immunomer increased Bax and Bak proapoptotic protein levels and decreased Bcl-2 and RIalpha protein levels in tumor cells. CpG immunomer but not antisense RIalpha induced an enlargement of mouse spleen, increased IL-6 levels in mouse blood, and increased NF-kappaB transcription activity in mouse spleen cells.

CONCLUSIONS

These results show that type I PKA down-regulation and induction of apoptosis in tumor cells by antisense PKA RIalpha, and host-immune stimulation by CpG immunomer are responsible at the molecular level for the supra-additive effects of tumor growth inhibition. Thus, antisense PKA RIalpha and CpG immunomer in combination work cooperatively and as tumor-targeted therapeutics to treat human cancer.

Oligodeoxynucleotides containing synthetic immunostimulatory motifs augment potent Th1 immune responses to HBsAg in mice

Toll-like receptor 9 (TLR9) modulators have potent Th1-adjuvant activity. We recently reported the development of immunomodulatory oligonucleotides (IMOs) containing novel structures (immunomers) and synthetic immunostimulatory CpR (R=2'-deoxy-7-deazguanosine) or R'pG (R'=1-(2'-deoxy-beta-D-ribofuranosyl)-2-oxo-7-deaza-8-methyl-purine) motifs. IMOs activate TLR9 pathways, resulting in cytokine secretion profiles different from those induced by CpG DNA. In the present study we evaluated the adjuvant activity of IMOs containing CpG, CpR, or R'pG motifs in combination with hepatitis B surface antigen (HBsAg) in a mouse model. Mice immunized with HBsAg plus IMO produced higher levels of IgG2a and lower levels of IgG1 than did mice immunized with HBsAg alone or with alum. High IgG2a responses were found at week 4 and remained high until 14 weeks after immunization. Adoptive transfer of splenocytes from HBsAg/IMO-immunized mice to naïve mice resulted in strong IgG2a production in response to antigen boost. Splenocytes of mice immunized with HBsAg/IMO produced high levels of IFN-gamma, but not Th2 cytokines IL-4 and IL-5, in antigen-recall experiments in vitro. The use of IMOs as adjuvants to HBsAg resulted in the production of strong anti-HBsAg antibodies at antigen doses as low as 0.2 microg. These data demonstrate that IMOs enhance the immunogenicity of HBsAg through potent Th1 immune responses, which may allow lower doses of antigen in vaccination.

Oral administration of second-generation immunomodulatory oligonucleotides induces mucosal Th1 immune responses and adjuvant activity

CpG DNA induces potent Th1 immune responses through Toll-like receptor 9. In the present study, we used oligonucleotides consisting of a novel 3'-3'-linked structure and synthetic stimulatory motifs, referred as second-generation immunomodulatory oligonucleotides (IMOs). The stimulatory motifs included: CpR, YpG, or R'pG (R = 2'-deoxy-7-deazaguanosine, Y = 2'-deoxy-5-hydroxy-cytidine, and R' = 1-[2'-deoxy-beta-d-ribofuranosyl]-2-oxo-7-deaza-8-methyl-purine). We evaluated the stability of orally administered IMOs in the gastrointestinal (GI) environment and their ability to induce mucosal immune responses in mice, and compared these characteristics with those of a conventional CpG DNA. The IMOs were significantly more stable than CpG DNA following oral administration, and IMOs induced stronger local and systemic immune responses as determined by MIP-1beta, MCP-1, IP-10, and IL-12 production. Mice orally immunized with ovalbumin (OVA) and IMO had higher levels of IgG2a antibodies in serum and IgA antibodies in intestinal mucosa than did mice immunized with OVA and CpG DNA. These studies demonstrate that IMOs are more stable than CpG DNA in the GI tract and can induce more potent mucosal Th1 adjuvant responses. IMOs may prove to be effective oral adjuvants, able to promote strong systemic and mucosal immune responses to oral vaccines and antigens for therapeutic and prophylactic applications.

Immunomodulatory oligonucleotides containing a cytosine-phosphate-2'-deoxy-7-deazaguanosine motif as potent toll-like receptor 9 agonists

Bacterial DNA and synthetic oligomers containing CpG dinucleotides activate the immune system through Toll-like receptor (TLR) 9. Here, we compare the immunostimulatory activity of three immunomers with different nucleotide sequences containing a synthetic cytosine-phosphate-2'-deoxy-7-deazaguanosine dinucleotide (CpR), called immunomodulatory oligonucleotides (IMOs), in mouse, human, and monkey systems. IMOs induced IL-12 and IFN-gamma secretion more than a control non-CpG IMO in mice. All three IMOs activated HEK293 cells expressing TLR9 but not TLR3, -7, or -8. IMOs induced human B-cell proliferation and enhanced expression of CD86 and CD69 surface markers on B cells. The three IMOs induced CD86 expression on human plasmacytoid dendritic cells, but only IMOs that contained a 5'-terminal TCR nucleotide sequence induced IFN-alpha secretion. A sequence that forms a duplex structure also was required for IFN-alpha induction in human peripheral blood mononuclear cell cultures. IMOs induced chemokine and cytokine gene expression in human peripheral blood mononuclear cells. In monkeys, all three IMOs induced transient changes in peripheral blood leukocytes and lymphocytes and activated B and T lymphocytes. All three IMOs induced IFN-alpha in vivo in monkeys; the IMO sequence that forms a stable secondary structure induced the highest levels of IFN-alpha. These studies are, to our knowledge, the first comprehensive studies to compare the activity of IMOs containing synthetic stimulatory CpR dinucleotides in mouse, monkey, and human systems. These results suggest that IMOs induce strong and rapid immunostimulation and that the CpR dinucleotide is recognized by TLR9, leading to immune-cell activation and cytokine secretion in vitro and in vivo.

Impact of site-specific nucleobase deletions on the arthritogenicity of DNA

Oligodeoxynucleotides (ODN) containing unmethylated CpG motifs (CpG ODN) potently stimulate the innate and acquired immune system. We have compared the in vivo and in vitro inflammatogenic properties of CpG ODNs containing a specific nucleobase deletion either 5'-upstream (ODN-2) or 3'-downstream (ODN-3) of the CpG motif, comparing with a prototype CpG ODN (ODN-1). The frequency of arthritis was similar after intra-articular (i.a.) injections of ODN-1 or ODN-3, but was significantly lower (p < 0.02) after i.a. injections of ODN-2. In vitro production of the pro-inflammatory cytokine TNF-alpha was higher in mouse spleen cell cultures exposed to ODN-2 in comparison to ODN-1. In addition, the level of IL-10 induced by ODN-2 was higher than that induced by ODN-1. On the other hand, TNF-alpha, IL-10, and MCP-1 levels, as well as splenocyte proliferative responses were all significantly lower for ODN-3 than for ODN-1. These results suggest that a 5'-upstream nucleobase deletion reduces arthritogenicity, while maintaining or increasing the production of pro- and anti-inflammatory factors. In contrast, a 3'-downstream nucleobase deletion has no effect on arthritogenicity, despite significantly lower levels of proliferation and pro- and anti-inflammatory cytokines, compared with ODN-1. This study indicates that specific structural elements within the ODN sequence but outside the CpG motif, modulate the immunostimulatory properties of CpG ODNs.