Structural analysis of polysaccharide/antisense DNA complexes during cytoplasmic target mRNA hybridization

We previously demonstrated antisense oligonucleotides (AS-ODNs) delivery system based on the complex formed with poly (dA) and schizophyllan, a type of β-1,3-glucan. This complex enables efficient intracellular delivery of AS-ODNs. In this communication, we investigated the cytoplasmic translocation of the complex itself and its mechanism of action on mRNA. As a result, we found that the complex moved into the cytoplasm while keeping its structure, and AS-ODN hybridized with the target mRNA. This result encourages pharmaceutical applications of the complex.

Enhanced Therapeutic Efficacy of Immunostimulatory CpG-ODN by Silencing SOCS-1 with Polysaccharide/miR-155 Complexes

For the induction of antigen-specific immune responses, adjuvants as well as antigens are essential. CpG-ODN is a potent agonist of toll-like receptor 9 (TLR9) and is known as an adjuvant to induce cellular immune responses. We previously developed a therapeutic oligonucleotide delivery system based on the formation of a complex between schizophyllan (SPG), a kind of β-1,3-glucan, and poly(dA), which actively delivered CpG-ODN to antigen-presenting cells (APCs) in the draining lymph nodes and induced antigen-specific immune responses. However, unfortunately, the signaling pathway of TLR9 is negatively regulated by an intracellular protein called suppressor of cytokine signaling-1 (SOCS-1), which suppresses the adjuvant effect of CpG-ODN. To solve this, we focused on microRNA-155 (miR-155), which regulates innate and autoimmune processes by targeting SOCS-1. In this study, we proposed a strategy of combining miR-155 and CpG-ODN, each complexed with SPG (denoted as SPG/miR-155 and SPG/CpG, respectively), to induce a more potent immune response. As a result, we showed that the efficient delivery of miR-155 to APCs by a complex form could induce much more potent cellular immune responses than SPG/CpG alone. Furthermore, the mice treated with the combination of SPG/miR-155 and SPG/CpG showed a long delay in tumor growth occurrence and improved survival after tumor inoculation. These results indicate the possibility of therapeutic strategies for cancer.

Binding assay of human Dectin-1 variants for DNA/ β-glucan complex for active-targeting delivery of antisense DNA: Part II

A β-1,3-glucan binding receptor called Dectin-1 is mainly expressed on antigen-presenting immunocytes. Dectin-1 may be a target molecule for receptor-mediated and active-targeting delivery of drugs to regulate or interfere with the immune system. Therapeutic oligonucleotides are one such drug of interest. To this end, we have been studying the complex of schizophyllan (SPG, one of the linear (1,3)-β-ᴅ-glucan family) with oligonucleotide and its delivery mechanism to the Dectin-1 expressing cells. There are at least six types of human Dectin-1 expressed on the cell surface (designated V-1, V-2, etc.), with V-1 having a complete carbohydrate recognition domain (CRD) and stalk, V-2 having a complete CRD but no stalk, and other variants having an incomplete CRD due to exon skipping. Our previous studies have shown that SPG binds only to V-1 and V-2. By contrast, SPG/oligonucleotide complexes bind both V-1 and V-2 more strongly than SPG itself and show a certain affinity, for other variants. As a continuing work, the present paper discusses the structure and nature of all human Dectin-1 variants expressed on the cellular surface. we found that (1) a new N-linked glycosylation site is present in some variants, (2) the glycosylation of Dectin-1 plays an important role in the fate of Dectin-1 and its localization in the cells, and (3) the glycosylation is related to the amount of ingestion of the complex. The present findings suggest that, in addition to V-1 and V-2, two other variants that are highly expressed at the plasma membrane and stabilized by the glycosylation may also be targets of the complex.

Adjuvant Activity Enhanced by Cross-Linked CpG-Oligonucleotides in β-Glucan Nanogel and Its Antitumor Effect

Cancer vaccine has the ability to directly eradicate tumor cells by creating and activating cytotoxic T lymphocytes (CTLs). To achieve efficient CTL activity and to induce Th1 responses, it is essential to administer an appropriate adjuvant as well as an antigen. CpG-ODN is known as a ligand of Toll-like receptor 9 (TLR9) and strongly induces Th1 responses. In our previous study, we developed a CpG-ODN delivery system by use of the formation of complexes between ODN and a β-glucan SPG, denoted as CpG/SPG, and demonstrated that CpG/SPG induces high Th1 responses. In this study, we created a nanogel made from CpG/SPG complexes through DNA-DNA hybridization (cross-linked (CL)-CpG). Immunization with CL-CpG induced much stronger antigen-specific Th1 responses in combination with the antigenic protein ovalbumin (OVA) than that with CpG/SPG. Mice preimmunized with CL-CpG and OVA exhibited a long delay in tumor growth and an improved survival rate after tumor inoculation. These immune inductions can be attributed to the improvement of cellular uptake by the combination of increased size and the cluster effect of the β-glucan recognition site in the nanogel structure. In other words, the particle nature of CL-CpG, instead of the semiflexible rod conformation of CpG/SPG, enhanced the efficacy of a cancer vaccine. The present results indicate that CL-CpG can be used as a potent vaccine adjuvant for the treatment of cancers and infectious diseases.

Enhanced cytokine secretion owing to multiple CpG side chains of DNA duplex

Unmethylated CpG sequences (CpG ODN) stimulate Toll-like receptor 9 (TLR9) to activate innate immunity. We made DNA duplexes from poly(dT)320 and CpG ODN with (dA)40 attached at the 3' end. Circular dichroism and gel electrophoresis indicated that the CpG parts turned outward from the duplex. When we changed the CpG ODN/poly(dT) molar ratio, the amount of IL-12 secreted from J774A.1 cells (murine macrophage-like) reached the maximum at the compositions with two to four CpG portions in one duplex, while the maximum loading was eight CpG ODNs per one poly(dT)320. When the residual free dT parts were hybridized with its control GpC ODN with (dA)40 tail or just (dA)40, the maximum disappeared and the secretion increased with increasing the CpG molar ratio. These results indicated that there is a particular DNA higher-order structure to activate TLR9 more efficiently than single CpG ODN.

Higher order structure of (1,3)-beta-D-glucans and its influence on their biological activities and complexation abilities

(1,3)-beta-D-Glucans form a group of biologically active biopolymers that exist in different structural organizations depending on the environmental conditions. The biological effect of (1,3)-beta-D-glucans is a core issue stimulating large research efforts of the molecular properties and their consequences for action as biological response modifiers. The fascination for these molecules increased further following the finding of their ability to form complexes of defined geometry with a number of structures, ranging from linear architectures as polymers or carbon nanotubes, to globular structures as gold particles or dye molecules. The fascinating information concerning the relationship between sample treatment history and molecular organization has not yet reached out to all the contributors within the field, resulting in unnecessary apparent inconsistencies in the literature. In addition to environmental conditions, the sample history is known to influence on the precise structural organization of these molecules. The present knowledge related to the structure of native as well as denatured, renatured and annealed (1,3)-beta-D-glucans is reviewed. The influence of their structural organization on the biological activity and complexation abilities is discussed, and some factors hindering progress in the understanding of their biological effects or complexation abilities are pointed out.

Complex formation between cationic beta-1,3-glucan and hetero-sequence oligodeoxynucleotide and its delivery into macrophage-like cells to induce cytokine secretion

A cationic polysaccharide bearing a beta-1,3-glucan main-chain structure (CUR-N(+)) forms a complex with a hetero-sequence oligonucleotide, that is, a CpG ODN, and facilitates the transportation of the resultant complex into a murine macrophage-like cell J774.A1, which induces an efficient secretion of a cytokine (IL-12) as compared with that induced by conventional carriers such as poly(ethyleneimine) (PEI) and poly(L-lysine) (PLL).

A Polysaccharide Carrier to Effectively Deliver Native Phosphodiester CpG DNA to Antigen-Presenting Cells

Oligodeoxynucleotides containing unmethylated CpG sequences (CpG DNAs) activate the vertebrate innate immune system via toll-like receptor 9 (TLR-9). Although CpG DNA is a promising immunotherapeutic agent, its short circulation time in biological fluids due to nuclease is the major drawback. This paper proposes that a natural polysaccharide called schizophyllan (SPG) can be used as an effective CpG DNA carrier because SPG can complex with CpG DNA and the resultant complex shows the nuclease resistance of the bound DNA. In order to increase cellular uptake in vitro, we chemically attached spermine, cholesterol, arginine octamer, or RGD peptide to SPG. The complexes made of the chemically modified SPG and CpG DNA having a phosphorothioate (PS) or phosphodiester (PO) backbone led to increased secretion of cytokines of about 4- to 15-fold, compared with the uncomplexed dose. Furthermore, when PO CpG DNA was complexed with unmodified SPG, the IL-12 level increased by almost 3- to 11-fold compared with the naked dose. The PO CpG DNA/unmodified SPG complex data suggested that unmodified SPG might effectively deliver PO in vivo due to the electrically neutral nature of unmodified SPG. When the complexed CpG DNAs were injected intraperitoneally, a large amount of IL-12 production was observed compared with the uncomplexed material. Both in vivo and vitro assays indicated that the SPG complex may be of use for CpG DNA therapy.

Ternary complex consisting of DNA, polycation, and a natural polysaccharide of schizophyllan to induce cellular uptake by antigen presenting cells

A natural polysaccharide called schizophyllan (SPG) can form a complex with polynucleotides, and the complex has been shown to deliver biofunctional short DNAs such as antisense DNAs and CpG-DNAs. Although it is a novel and efficient method, there is a drawback: attachment of homo-polynucleotide tails [for example, poly(dA) or poly(C)] to the end of DNA is necessary to stabilize the complex, because DNA heterosequences cannot bind to SPG. The aim of this paper is to present an alternative method in which SPG/DNA complexes can be made without using the tails. The basic strategy is as follows: since SPG can form hydrophobic domains in aqueous solutions, hydrophobic objects should be encapsulated by this domain. DNA alone is highly hydrophilic; however, once DNA/polycation complexes are made, they should be included by the SPG hydrophobic domain. The aim of this paper is to prove the formation of the polycation/DNA/SPG ternary complex. Gel electrophoresis showed that presence of SPG influenced the migration pattern of polycation+DNA mixtures. With increasing the SPG ratio, the zeta potential (zeta) of the polycation+DNA+SPG mixture decreased drastically to reach almost zeta = 0 and the particle size distributions were altered due to the ternary complex formation. Confocal laser scanning microscopy revealed that the polycation/DNA/SPG ternary complexes showed high uptake efficiency when the complexes were exposed to macrophage-like cells (J774.A1). IL-12 secretion was enhanced when CpG-DNA was added as the ternary complex. These features can be ascribed to the fact that J774.A1 has a SPG recognition site called Dectin-1 on the cellular surface and the ternary complex can be ingested by this pathway.

Synthesis and in Vitro Characterization of Antigen-Conjugated Polysaccharide as a CpG DNA Carrier

Oligodeoxynucleotides containing unmethylated CpG sequences (CpG DNAs) are known as an immune adjuvant. CpG DNAs coupled with a particular antigen enabling both CpG DNA and antigen delivery to the same antigen-presenting cell have been shown to be more effective. Based on our previous finding that beta-(1-->3)-D-glucan schizophyllan (SPG) can be used as a CpG DNA carrier, here we present the synthesis of an antigen-conjugated SPG and the characterization of the conjugate. Ovalbumin (OVA, 43 kDa) was used as a model antigen, and two OVA were conjugated to one SPG molecule (M(w) = 150,000), denoted by OVA-SPG. Circular dichroism and gel electrophoresis showed that OVA-SPG could form a complex with a (dA)(40)-tailed CpG DNA at the 3' end (1,668-(dA)(40)). When OVA-SPG was added to macrophages (J774.A1), the amount of the ingested OVA-SPG was increased compared with that of OVA itself, suggesting that Dectin-1 (proinflammatory nonopsonic receptor for beta-glucans) is involved to ingest OVA-SPG. Furthermore, the complex of the conjugate and DNA was co-localized in the same vesicles, implying that OVA (antigen) and CpG DNA (adjuvant) were ingested into the cell at the same time. This paper shows that OVA-SPG can be used as a CpG DNA carrier to induce antigen-specific immune responses.

CpG DNA/zymosan complex to enhance cytokine secretion owing to the cocktail effect

Zymosan, classified among beta-(1-->3)-d-glucans, is produced from the cell wall of yeast and well known to induce proinflammatory cytokines when ingested by immune cells. We found that zymosan forms a complex with immunostimulatory CpG DNA, where both zymosan and CpG DNA can induce cytokine secretion according to the different mechanisms (i.e., recognized by different receptors). The complex activated macrophages and induced cytokine secretion, more efficiently than separate administration of zymosan or CpG DNA. Microscopic observation showed that this increment of the cytokine secretion can be explained by the fact that zymosan and zymosan/CpG DNA complex are up-taken more than naked CpG DNA. Additionally, existence of two different immunostimulants in the same cells may enhance the immunoresponse. This report presents a new strategy to construct a delivering vehicle for CpG DNA and to enhance its activity with the 'cocktail effect' of the two immunostimulants.

Linear double-stranded DNA that mimics an infective tail of virus genome to enhance transfection

Our previous work showed that a natural beta-(1-->3)-d-glucan schizophyllan (SPG) can form a stable complex with single-stranded oligonucleotides (ssODNs). When protein transduction peptides were attached to SPG and this modified SPG was complexed with ssODNs, the resultant complex could induce cellular transfection of the bound ODNs, without producing serious cytotoxicity. However, no technique was available to transfect double-stranded DNAs (dsDNA) or plasmid DNA using SPG. This paper presents a new approach to transfect dsDNA, showing preparation and transfection efficiency for a minimal-size gene having a loop-shaped poly(dA)(80) on both ends. This poly(dA) loops of dsDNA can form a complex with SPG. An siRNA-coding dsDNA with the poly(dA) loop was complexed with Tat-attached SPG to silence luciferase expression. When LTR-Luc-HeLa cells that can express luciferase under the control of the LTR promoter were exposed to this complex, the expression of luciferase was suppressed (i.e., RNAi effect was enhanced). Cytotoxicity studies showed that the Tat-SPG complex induced much less cell death compared to polyethylenimine, indicating that the proposed method caused less harm than the conventional method. The Tat-SPG/poly(dA) looped dsDNA complex had a structure similar to the viral genome in that the dsDNA ends were able to induce transfection and protection. The present work identifies the SPG and poly(dA) looped minimum-sized gene combination as a candidate for a non-toxic gene delivery system.

PEG-appended beta-(1-->3)-D-glucan schizophyllan to deliver antisense-oligonucleotides with avoiding lysosomal degradation

Schizophyllan is a natural beta-(1-->3)-d-glucan existing as a triple helix in water and as a single chain in dimethylsulfoxide (DMSO). As we already reported, when a homo-polynucleotide [e.g., poly(dA) or poly(C)] is added to the schizophyllan/DMSO solution and subsequently DMSO is exchanged for water, the single chain of schizophyllan forms a complex with the polynucleotide. One of the potential applications for this novel complex is an antisense-oligonucleotide (AS ODN) carrier. The present paper describes a modification technique that enabled us to introduce PEG only to the side chain of schizophyllan. This technique consisted of periodate oxidation of the glucose side chain and subsequent reaction between methoxypolyethylene glycol amine and the formyl terminate, followed by reduction with NaBH4. Subsequently, we made a complex from PEG-appended schizophyllan and an AS ODN sequence, and carried out an in vitro antisense assay, administrating the AS ODN complex to depress A375 c-myb mRNA of A375 melanoma cell lines. The PEG-SPG/AS ODN complex showed more enhanced antisnese effect than naked AS ODN dose, i.e., the same level as that of RGD-appended SPG. Here, the RGD system has been shown one on the most effective AS ODN carrier (Science 261 (1993) 1004-1012). When we added nigericin to the assay system, the antisense effect was not affected in the PEG-SPG system, on the other hand, it was almost eliminated in the RGD system. Nigericin is well known to interrupt transport from endosome to lysosome. Therefore, the difference between the PEG and RGD complexes indicates that, in the PEG system, AS ODN was able to escape from lysosomal degradation. The present work has thus proposed a new strategy to delivery AS ODN using schizophyllan as a new carrier.

Removal of the side-chain glucose groups from schizophyllan improves the thermal stability of the polycytidylic acid complexes under the physiological conditions

Thermal stabilization of the complex between polycytidylic acid [poly(C)] and the modified schizophyllan (SPG) whose hydrophilic side-chain glucose groups are selectively removed utilizing mild Smith-degradation has been investigated. With the decrease in the side-chain glucose groups of schizophyllan, the complex with poly(C) can be considerably stabilized compared with unmodified SPG; for example, the T(m) value after the removal of the side-chain glucose groups from 33.3 (unmodified) to 1.0 is enhanced by 14 degrees C. In addition, the thermal stabilization effect is even operative under the physiological conditions ([NaCl] = 0.15 mol dm(-3)). This effect is exerted owing to the construction of the hydrophobic atmosphere around the complex. Although schizophyllan lost the side-chain glucose groups, it still kept the protection effect of the bound poly(C) chain against RNaseA-mediated hydrolysis as observed for unmodified schizophyllan. The assessment of the cytotoxicity for A375:human malignant melanoma, and HL60:human promyelocytic leukemia revealed that the modified schizophyllan scarcely increases the cytotoxicity. These results indicate that the present modification for schizophyllan is of great significance in a viewpoint to develop the practical gene carriers operative even under the physiological conditions.

A Polysaccharide Carrier for Immunostimulatory CpG DNAs To Enhance Cytokine Secretion‖

A beta-(1 --> 3)-d-glucan schizophyllan (SPG) forms a stoichiometric complex with some polynucleotides. This communication describes our attempt to apply the SPG complex to deliver CpG DNA to endosomes to enhance cytokine secretion. To increase cellular uptake, we introduced spermine, arginine-glycine-aspartic acid tripeptide, octaarginine, or cholesterol to the SPG side chain. The chemically modified SPG showed essentially no cytotoxicity. When CpG DNA complex made therefrom was exposed to macrophages, dramatic enhancement in the cytokine secretion was observed. It increased 5-10 times from the naked dose and 100 times from the background. This performance promises that SPG can be an excellent carrier for CpG DNA.