Antitumor mechanisms of oligodeoxynucleotides with CpG and polyG motifs in murine prostate cancer cells: decrease of NF-kappaB and AP-1 binding activities and induction of apoptosis

TLR9 Monotherapy in Immune-Competent Mice Suppresses Orthotopic Prostate Tumor Development

Prostate cancer is ranked second in the world for cancer-related deaths in men, highlighting the lack of effective therapies for advanced-stage disease. Toll-like receptors (TLRs) and immunity have a direct role in prostate cancer pathogenesis, but TLR9 has been reported to contribute to both the progression and inhibition of prostate tumorigenesis. To further understand this apparent disparity, we have investigated the effect of TLR9 stimulation on prostate cancer progression in an immune-competent, syngeneic orthotopic mouse model of prostate cancer. Here, we utilized the class B synthetic agonist CPG-1668 to provoke a TLR9-mediated systemic immune response and demonstrate a significant impairment of prostate tumorigenesis. Untreated tumors contained a high abundance of immune-cell infiltrates. However, pharmacological activation of TLR9 resulted in smaller tumors containing significantly fewer M1 macrophages and T cells. TLR9 stimulation of tumor cells in vitro had no effect on cell viability or its downstream transcriptional targets, whereas stimulation in macrophages suppressed cancer cell growth via type I IFN. This suggests that the antitumorigenic effects of CPG-1668 were predominantly mediated by an antitumor immune response. This study demonstrated that systemic TLR9 stimulation negatively regulates prostate cancer tumorigenesis and highlights TLR9 agonists as a useful therapeutic for the treatment of prostate cancer.

Delivery of interleukin-15 to B16 melanoma by electroporation leads to tumor regression and long-term survival

Electroporation (EP) is a method used to physically deliver therapeutic molecules such as plasmid DNA directly to tissues. It has been used safely and successfully in clinical studies and preclinical cancer models to deliver genes to a variety of tissues. In cancer research cytokine therapy is emerging as a promising tool that can be used to boost the host response to tumor antigens. The delivery of cytokines as recombinant proteins can result in toxicity and other adverse effects; however the delivery of cytokine genes using EP has been shown to be safe and effective. Interleukin 15 (IL-15) is a cytokine that promotes the innate as well as the adaptive immune response to cancer cells and bacterial pathogens. In this study we used EP to deliver a human IL-15 plasmid (phIL-15) directly to tumors to examine its anti-cancer effects. B16.F10 melanoma tumors were induced in C57BL/6J mice and phIL-15 was delivered three times over the course of a week. Expression of the transgene, tumor volume, long-term survival and resistance to challenge were monitored in these animals. Delivery of IL-15 plasmid by EP resulted in increased IL-15 expression within the tumor compared to the injection only control. This expression peaked at 12 to 18 hours after the first delivery and was sustained at lower levels after the second and third deliveries. The delivery of the phIL-15 resulted in tumor regression, long-term survival and greater protection against tumor recurrence when cancer cells were reintroduced compared to control plasmid. From these results we can conclude that the delivery of IL-15 plasmid to tumors using EP is a promising avenue to investigate for its anti-tumor effects, however more work needs to be done to increase the stability of the gene once it is delivered and to elucidate the anti-tumor mechanism.

Fully phosphorothioate-modified CpG ODN with PolyG motif inhibits the adhesion of B16 melanoma cells in vitro and tumorigenesis in vivo

Adhesion to the extracellular matrix and endothelial lining of blood vessels is critical for tumor cells to grow at original or metastatic sites. Inhibition of tumor cell adhesion can be an antitumor strategy. Guanosine-rich (G-rich) oligodeoxynucleotides (ODNs) can inhibit the adhesion of certain tumor cells. However, no data exist on how inclusion of the CpG motif in the G-rich sequence influences tumor cell adhesion and subsequent tumorigenesis. In this study, in vitro and in vivo assays were used to evaluate how a panel of ODN-containing contiguous guanosines and the CpG motif influenced adhesion of B16 melanoma cells. The results showed that a self-designed ODN, named BW001, containing the polyG motif and a full phosphorothioate modification backbone could inhibit B16 melanoma cell adhesion on a culture plate or on a plate coated with various substances. In vivo data revealed that B16 melanoma cells co-administered with BW001 and intraperitoneally injected into mice formed fewer tumor colonies in peritoneal cavities. This effect was related to the polyG motif and the full phosphorothioate modification backbone and enhanced by the existence of the CpG motif. Additional in vivo data showed that survival of tumor-bearing mice in the BW001 group was significantly prolonged, subcutaneous melanoma developed much more slowly, and lung dissemination colonies formed much less often than in mice inoculated with B16 melanoma cells only. The effect was CpG motif-dependent. These results suggest that BW001 may exert an integrated antitumor effect.

Dose-effect relationship of CpG oligodeoxyribonucleotide 1826 in murine Lewis lung cancer treated with irradiation

Background

Cytosine-phosphate-guanine (CpG) oligodeoxyribonucleotides (ODNs), which induce signaling via Toll-like receptor 9, have recently been suggested to enhance sensitivity to traditional therapies, including chemotherapy, in certain cancer cell lines. This study aimed to define the dose-effect relationship for CpG ODN 1826 in increasing radiosensitivity and its impact on immune function in a mouse model of Lewis lung cancer.

Methods

The tumor-bearing mouse model was induced by injecting Lewis lung cancer cells into the right anterior leg subcutaneously. Sixty-four C57BL/6 J mice were evenly randomized into eight groups, comprising: a control group; an irradiation group; a CpG ODN 0.15 group; a CpG ODN 0.3 group; a CpG ODN 0.45 group; a CpG 0.15 + irradiation group; a CpG 0.3 + irradiation group; and a CpG 0.45 + irradiation group. Tumor growth, serum tumor necrosis factor-alpha and interleukin-12 concentrations, spleen and thymus exponents, and effect of CpG on the secondary immune response were measured, and apoptosis of tumor cells was investigated using TdT-mediated dUTP nick end labeling (TUNEL) after treatment.

Results

Tumor volumes in the treated groups were smaller than in the control group, with those of the CpG 0.45 + irradiation group being the smallest. TUNEL showed that the apoptosis rate in all the active treatment groups was higher than in the control group. CpG ODN apoptosis rate, serum tumor necrosis factor-alpha and interleukin-12 levels, and the spleen and thymus exponent showed greater improvement in the groups receiving combination therapy of CpG ODN and irradiation than the control group or the group receiving irradiation alone. With the increasing concentration of CpG ODN 1826, its effect became more and more significant, meanwhile, inoculation of Lewis lung cancer cells failed in those CpG ODN-cured mice.

Conclusion

CpG ODNs dramatically increased the radiosensitivity of Lewis lung cancer and enhanced immune function in mice in a dose-related manner.

Toll-like receptor 9 agonists promote IL-8 and TGF-beta1 production via activation of nuclear factor kappaB in PC-3 cells

Chronic infection and resulting inflammation promote tumor development and progression, and Toll-like receptors (TLRs) may play an important role in this process. The aim of this study was to determine whether CpG oligonucleotides (CpG-ODN), which are Toll-like receptor 9 (TLR9) agonists, can promote inflammatory cytokines release from the prostate cancer PC-3 cells through activation of nuclear factor-kappaB (NF-kappaB). Flow cytometry, semiquantitative real-time reverse transcriptase-polymerase chain reaction, enzyme-linked immunosorbent assay, and immunofluorescence analysis were used to detect the transforming growth factor-beta1 (TGF-beta1) and interleukin-8 (IL-8) release and NF-kappaB activation in PC-3 cells after CpG-ODN stimulation. CpG-ODN promoted the expression and secretion of immunosuppressive cytokines TGF-beta1 and IL-8 from PC-3 cells. In addition, after CpG-ODN stimulation, NF-kappaB nuclear translocation was also observed in PC-3 cells, contributing to CpG-induced upregulation of IL-8 and TGF-beta1. Thus, TLR9 agonists may promote IL-8 and TGF-beta1 production in human prostate cancer cells through NF-kappaB activation.

Discovery and development of the G-rich oligonucleotide AS1411 as a novel treatment for cancer

Certain guanine-rich (G-rich) DNA and RNA molecules can associate intermolecularly or intramolecularly to form four stranded or "quadruplex" structures, which have unusual biophysical and biological properties. Several synthetic G-rich quadruplex-forming oligodeoxynucleotides have recently been investigated as therapeutic agents for various human diseases. We refer to these biologically active G-rich oligonucleotides as aptamers because their activities arise from binding to protein targets via shape-specific recognition (analogous to antibody-antigen binding). As therapeutic agents, the G-rich aptamers may have some advantages over monoclonal antibodies and other oligonucleotide-based approaches. For example, quadruplex oligonucleotides are non-immunogenic, heat stable and they have increased resistance to serum nucleases and enhanced cellular uptake compared to unstructured sequences. In this review, we describe the characteristics and activities of G-rich oligonucleotides. We also give a personal perspective on the discovery and development of AS1411, an antiproliferative G-rich phosphodiester oligonucleotide that is currently being tested as an anticancer agent in Phase II clinical trials. This molecule functions as an aptamer to nucleolin, a multifunctional protein that is highly expressed by cancer cells, both intracellularly and on the cell surface. Thus, the serendipitous discovery of the G-rich oligonucleotides also led to the identification of nucleolin as a new molecular target for cancer therapy.

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.

AGRO100 inhibits activation of nuclear factor-kappaB (NF-kappaB) by forming a complex with NF-kappaB essential modulator (NEMO) and nucleolin

AGRO100, also known as AS1411, is an experimental anticancer drug that recently entered human clinical trials. It is a member of a novel class of antiproliferative agents known as G-rich oligonucleotides (GRO), which are non-antisense, guanosine-rich phosphodiester oligodeoxynucleotides that form stable G-quadruplex structures. The biological activity of GROs results from their binding to specific cellular proteins as aptamers. One important target protein of GROs has been previously identified as nucleolin, a multifunctional protein expressed at high levels by cancer cells. Here, we report that AGRO100 also associates with nuclear factor-kappaB (NF-kappaB) essential modulator (NEMO), which is a regulatory subunit of the inhibitor of kappaB (IkappaB) kinase (IKK) complex, and also called IKKgamma. In the classic NF-kappaB pathway, the IKK complex is required for phosphorylation of IkappaBalpha and subsequent activation of the transcription factor NF-kappaB. We found that treatment of cancer cells with AGRO100 inhibits IKK activity and reduces phosphorylation of IkappaBalpha in response to tumor necrosis factor-alpha stimulation. Using a reporter gene assay, we showed that AGRO100 blocks both tumor necrosis factor-alpha-induced and constitutive NF-kappaB activity in human cancer cell lines derived from cervical, prostate, breast, and lung carcinomas. In addition, we showed that, in AGRO100-treated cancer cells, NEMO is coprecipitated by nucleolin, indicating that both proteins are present in the same complex. Our studies suggest that abrogation of NF-kappaB activity may contribute to the anticancer effects of AGRO100 and that nucleolin may play a previously unknown role in regulating the NF-kappaB pathway.

Uptake, cellular distribution and novel cellular binding proteins of immunostimulatory CpG oligodeoxynucleotides in glioblastoma cells

Glioblastomas are the most malignant and most frequent brain tumors and exciting targets of gene and immunotherapy. Despite rapid development of experimental therapy little is known about the cellular behaviour of therapeutic oligodeoxynucleotides (ODNs). Here we designed uptake, cellular distribution and cellular binding proteins of immunostimulatory CpG-ODNs in glioblastoma cells by flow cytometry, fluorescence microscopy and mass spectrometry. Our data show that the phosphorothioate (PS) CpG-ODNs uptake in T98G and C6 cells is dose-, time-, temperature-dependent and independent of the CpG dinucleotides. Uptake can be inhibited by sodium azide, polyanions but not by chloroquine. After internalisation FITC labelled CpG-ODNs showed a spotted distribution in cytoplasm. Dozens of cellular binding proteins were identified using mass spectrometry. The binding of ODNs to proteins is dependent on modification and sequence but independent on CpG motif. ODNs bind to cellular proteins that are important for RNA processing and transport. Furthermore, three novel membrane proteins were identified, which might contribute to uptake of ODNs. ODNs binding to these proteins might interfere with the physiological function and thus might cause unwanted effects. Such binding also might influence the uptake efficiency or cellular distribution of therapeutic ODNs.

Necessity of oligonucleotide aggregation for toll-like receptor 9 activation

Toll-like receptor 9 (TLR9), a member of the interleukin-1 (IL-1) family of pathogen-associated molecular pattern receptors, is activated by unmethylated CpG-containing sequences in bacterial DNA or synthetic oligonucleotides (ODNs) in the endosomal compartment. The stimulation of an IL-1 response is thought to require the aggregation of its receptor. By analogy, we postulated that the potency of a TLR9 ligand should depend first on its ability to enter cells and gain access to TLR9 and second on its capacity to form a multimeric complex capable of cross-linking these receptors. Previously, we selected from a random library a series of phosphodiester ODNs with enhanced ability to permeate cells. Here, we studied the structural requirements for these penetrating ODNs to elicit a functional TLR9 response, as assessed by cytokine production from bone marrow-derived mouse mononuclear cells. The presence of a prototypic murine immunostimulatory DNA hexameric sequence (purine-purine-CG-pyrimidine-pyrimidine) in the ODNs was not sufficient for stimulation. In addition, the TLR9-activating ODNs had to have the ability to form aggregates and often to form secondary structures near the core CpG motifs. Multimerization was promoted by the presence of a guanine-rich 3'-terminus. The phosphodiester ODNs with CpG motifs that did not aggregate antagonized the effects of the multimeric TLR9 activators. These findings suggest that an optimal TLR9 agonist needs to contain a spatially distinct multimerization domain and a receptor binding CpG domain. This concept may prove useful for the design of new TLR9-modulating agents.

Cross-Linked Microparticles as Carriers for the Delivery of Plasmid DNA for Vaccine Development

Plasmid DNA was directly encapsulated into biocompatible polymer microparticles via radical polymerization in an inverse emulsion system. Acrylamide-based microspheres 0.2-1 microm in diameter were prepared using an acid-cleavable difunctional monomer. Retention of the DNA payload at physiological pH with complete release under acidic conditions at lysosomal pH was demonstrated. By trapping the plasmid DNA within the cross-linked microparticle, enzymatic degradation was prevented when exposed to serum nucleases. For vaccine development, these delivery vehicles were also investigated for their ability to generate immune responses when delivered to phagocytic cells of the immune system. Encapsulated plasmid DNA demonstrated immunostimulatory activity in macrophages, leading to cytokine secretion of IL-6 with a response approximately 40-fold higher than that achieved with DNA alone.

Single-stranded DNA induces ataxia telangiectasia mutant (ATM)/p53-dependent DNA damage and apoptotic signals

Single-stranded DNA has been speculated to be the initial signal in the DNA damage signaling pathway. We showed that introduction of single-stranded DNA with diverse sequences into mammalian cells induced DNA damage as well as apoptosis signals. Like DNA damaging agents, single-stranded DNA up-regulated p53 and activated the nuclear kinase ataxia telangiectasia mutant (ATM) as evidenced by phosphorylation of histone 2AX, an endogenous ATM substrate. Single-stranded DNA also triggered apoptosis as evidenced by the formation of caspase-dependent chromosomal DNA strand breaks, cytochrome c release, and increase in reactive oxygen species production. Moreover, single-stranded DNA-induced apoptosis was reduced significantly in p53 null cells and in cells treated with ATM small interfering RNA. These results suggest that single-stranded DNA may act upstream of ATM/p53 in DNA damage signaling.