CpG oligodeoxynucleotide nanomedicines for the prophylaxis or treatment of cancers, infectious diseases, and allergies

Abstract

Unmethylated cytosine-guanine dinucleotide-containing oligodeoxynucleotides (CpG ODNs), which are synthetic agonists of Toll-like receptor 9 (TLR9), activate humoral and cellular immunity and are being developed as vaccine adjuvants to prevent or treat cancers, infectious diseases, and allergies. Free CpG ODNs have been used in many clinical trials implemented to verify their effects. However, recent research has reported that self-assembled CpG ODNs, protein/peptide-CpG ODN conjugates, and nanomaterial-CpG ODN complexes demonstrate higher adjuvant effects than free CpG ODNs, owing to their improved uptake efficiency into cells expressing TLR9. Moreover, protein/peptide-CpG ODN conjugates and nanomaterial-CpG ODN complexes are able to deliver CpG ODNs and antigens (or allergens) to the same types of cells, which enables a higher degree of prophylaxis or therapeutic effect. In this review, the author describes recent trends in the research and development of CpG ODN nanomedicines containing self-assembled CpG ODNs, protein/peptide-CpG ODN conjugates, and nanomaterial-CpG ODN complexes, focusing mainly on the results of preclinical and clinical studies.

Keywords: CpG oligodeoxynucleotides; Toll-like receptor 9; adjuvant; immunostimulation; nanomedicine.

Figure 1

Self-assembled CpG ODN nanomedicines. Notes: (A) Double stem loop immunomodulator MGN1703 with cytosine–guanine (CG) motifs in black. Unmodified from NUCLEIC ACID THERAPEUTICS Vol. 25, Issue 3, 2015, nat.2015.0533, published by Mary Ann Liebert, Inc., New Rochelle, NY. The publisher for this copyrighted material is Mary Ann Liebert, Inc. publishers. (B) X-shaped double-stranded DNA (X-DNA). X_L-DNA forms a ligated complex due to an ACGT sequence at the end of the strand. Adapted from Koo J-E, Shin S-W, Um S-H, Lee J-Y. X-shaped DNA potentiates therapeutic efficacy in colitis-associated colon cancer through dual activation of TLR9 and inflammasomes. Mol Cancer. 2015;14:104. (C) Putative structures of polypodna consisting of three, four, six, or eight ODNs. Adapted with permission from Mohri K, Nishikawa M, Takahashi N, et al. Design and development of nanosized DNA assemblies in polypod-like structures as efficient vehicles for immunostimulatory CpG motifs to immune cells. ACS Nano. 2012;6(7):5931–5940. Copyright © 2012 American Chemical Society. (D) CpG ODN complexed with SPG. Adapted with permission from Kobiyama K, Aoshi T, Narita H, et al. Nonagonistic Dectin-1 ligand transforms CpG into a multitask nanoparticulate TLR9 agonist. Proc Natl Acad Soc U S A. 2014;111(8):3086–3091. Copyright © 2014 National Academy of Sciences. Abbreviations: CpG ODN, cytosine–guanine dinucleotide-containing oligodeoxynucleotide; ds, double strand; ss, single strand; nt, nucleotides; bp, base pairs; t-SPG, triple-stranded schizophyllan; s-SPG, single-stranded SPG.

Figure 2

CpG ODN nanomedicines conjugated with protein or peptide. Notes: (A) Procedure of CpG containing thiolated immunostimulatory DNA sequence (ISS) conjugated with maleimide-modified OVA. Adapted with permission from Macmillan Publishers Ltd: Nature Biotechnology. Cho HJ, Takabayashi K, Cheng P-M, et al. Immunostimulatory DNA-based vaccines induce cytotoxic lymphocyte activation by a T-helper cell-independent mechanism, 2000; 18(5):509–514, copyright 2000. (B) Atomic force microscopic image of CpG-B ODN conjugated with Tat-derived peptide. Nanoring structure of CpG-B (K3) ODN conjugated with Tat-derived peptide (1:16) (a) and three-dimensional topography image of the nanoring (b). (B) From Gungor B, Yagci FC, Tincer G, et al. CpG ODN nanorings induce IFNα from plasmacytoid dendritic cells and demonstrate potent vaccine adjuvant activity. Sci Transl Med. 2014;6:235ra61. Reproduced with permission from AAAS. Copyright © 2014, American Association of Pharmaceutical Scientists. Abbreviations: CpG ODN, cytosine–guanine dinucleotide-containing oligodeoxynucleotide; OVA, ovalbumin.

Figure 3

Nanomaterials-based CpG ODN nanomedicines. Notes: (A) Preparation of virus-like particles (VLPs) with CG motifs (CpGs). VLPs are disassembled, and the RNA is removed. The VLPs are finally reassembled in the presence of CpG G10. Adapted from Kundig TM, Klimek L, Schendzieloz P, Renner WA, Senti G, Bachmann MF. Is the allergen really needed in allergy immunotherapy? Curr Treat Options Allergy. 2015;2(1):72–82. (B) Scanning electron micrograph of chitosan/CpG ODN nanoparticles synthesized by a novel microfluidic method. Adapted from Chen S, Zhang H, Shi X, Wu H, Hanagata N. Microfluidic generation of chitosan/CpG oligodeoxynucleotide nanoparticles with enhanced cellular uptake and immunostimulatory properties. Lab Chip. 2014;14(11):1842–1849 with permission from The Royal Society of Chemistry. Scale bar =1 μm. (C) Scanning electron micrograph of flake-shell SiO₂ nanoparticle; Scale bar =100 nm. Copyright © 2012. Dove Medical Press. Adapted with permission from Manoharan Y, Ji Q, Yamazaki T, et al. Effect of molecular weight of polyethyleneimine on loading of CpG oligodeoxynucleotides onto flake-shell silica nanoparticles for enhanced TLR9-mediated induction of interferon-α. Int J Nanomed. 2012;7:3625–3635. (D) Transmission electron microscopy image of the boron nitride nanosphere. Scale bar =50 nm. Copyright © 2015. Dove Medical Press. Adapted with permission from Zhang H, Feng S, Yan T, Zhi C, Gao X-D, Hanagata N. Polyethyleneimine-functionalized boron nitride nanospheres as efficient carriers for enhancing the immunostimulatory effect of CpG oligodeoxynucleotides. Int J Nanomed. 2015;10:5343–5353. Abbreviations: CpG ODN, cytosine–guanine dinucleotide-containing oligodeoxynucleotide; PLGA, poly(lactic-co-glycolic acid); CG, cytosine–guanine; OVA, ovalbumin.